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Sustainable Environment

2010;():1-5. doi:10.1115/IHTC14-22096.

A large number of split-type air conditioner are widely used in high-rise residential or office buildings in China and the outdoor units of air-conditioner are often installed at the sidewalls or on the roofs in the confined space of a high-rise building. The factors affecting the performance of air-conditioner are the solar radiation, the heat released from the outdoor units, the ventilation of the confined installation space of a building where the outdoor units are installed and so on, which are investigated in this study. The air flow and temperature distribution under steady-state condition near the two outdoor units installed on the same storey in a building are simulated by software FLUENT, in which the porous model and DO radiation model are used. The optimum installation distance from the supporting wall is obtained. The average temperature of the exit surface without wind is 1.18% more than that with wind. The results show that the heat released from the outdoor units and the ventilation of the confined installation space where the outdoor units are installed are the main factors affecting the thermal environment in the confined installation space; The influence of the solar radiation can be neglected.

Commentary by Dr. Valentin Fuster
2010;():7-15. doi:10.1115/IHTC14-22107.

This paper describes a study that starts with an analysis of typical energy demand profiles in a hospital setting followed by a case study of a cogeneration system (CGS) under an energy service company (ESCO) project. The CGS idea is of an autonomous system for the combined generation of electrical, heating, and cooling energy in a hospital. The driving units are two high-efficiency gas engines that produce the electrical and heat energy. A gas engine meets the requirement for high electrical and heating energy demands; a natural gas-fuelled reciprocating engine is used to generate 735 kW of power. In our case, the electrical energy will be used only in the hospital. A deficit in electricity can be covered by purchasing power from the public network. Generated steam drives three steam-fired absorption chillers and is delivered to individual heat consumers. This system can provide simultaneous heating and cooling. No technical obstacles were identified for implementing the CGS. The average ratio between electric and thermal loads in the hospital is suitable for CGS system operation. An analysis performed for a non-optimized CGS system predicted a large potential for energy savings.

Commentary by Dr. Valentin Fuster
2010;():17-25. doi:10.1115/IHTC14-22113.

A gas-turbine cogeneration system with a regenerative air preheater and a single-pressure exhaust gas boiler serves as an example for application of CHP Plant. This CHP plant which can provide 30 MW of electric power and 14kg/s saturated steam at 20 bars. The plant is comprised of a gas turbine, air compressor, combustion chamber, and air pre-heater as well as a heat recovery steam generator (HRSG). The design Parameters of the plant, were chosen as: compressor pressure ratio (re), compressor isentropic efficiency (ηac), gas turbine isentropic efficiency (ηgt), combustion chamber inlet temperature (T3), and turbine inlet temperature (T4). In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function, representing the total cost of the plant in terms of dollar per second, was defined as the sum of the operating cost, related to the fuel consumption. Subsequently, different pars of objective function have been expressed in terms of decision variables. Finally, the optimal values of decision variables were obtained by minimizing the objective function using Evolutionary algorithm such as Genetic Algorithm. The influence of changes in the demanded power on the design parameters has been also studied for 30, 40 MW of net power output.

Commentary by Dr. Valentin Fuster
2010;():27-36. doi:10.1115/IHTC14-22127.

To improve the applicability of water-cooled air-conditioners in the domestic sector, the development of a prediction model for energy performance analysis is needed. This paper addressed the development of an empirical model for predicting the operation performance and the annual energy consumption for the use of water-cooled air-conditioners. An experimental prototype was set up and tested in an environmental chamber in validating the empirical model. The predictions compared well with the experimental results. Furthermore, a high-rise residential building whole-year energy consumption simulation on applications of water-cooled air conditioners in South china was also analyzed. The results show 20.4% energy savings over air-cooled units while the increase in water-side consumption is 31.1%. The overall energy savings were estimated at 16.2% when including the additional water costs.

Commentary by Dr. Valentin Fuster
2010;():37-45. doi:10.1115/IHTC14-22415.

In this paper, a novel heat and mass transfer model was used to simulate the temperature field of both the U-tube heat exchanger and soil around it. Beside two-dimensional N-S equations were solved to consider the seepage of groundwater, an energy equation coupling thermal conduction and groundwater advection was enclosed in the model as well. The energy equation was built according to the real conditions of the U-tube and seepage flow in the soil. Through analyzing the simulation results, the effects of groundwater seepage to the heat transfer process and thermal short-circuiting among U-tube legs are obtained. The influences of soil type, soil physical aspects and backfill on the soil temperature field around the single U-tube of an underground heat exchanger were studied at the same time. The conclusions had great academic significance to the analysis and designing of the underground heat exchanger.

Commentary by Dr. Valentin Fuster
2010;():47-55. doi:10.1115/IHTC14-22470.

We suggest a model of rain scavenging of soluble gaseous pollutants in the atmosphere. It is shown that below-cloud gas scavenging is determined by non-stationary convective diffusion equation with the effective Peclet number. The obtained equation was analyzed numerically in the case of log-normal droplet size distribution. Calculations of scavenging coefficient and the rates of precipitation scavenging are performed for wet removal of ammonia (NH3 ) and sulfur dioxide (SO2 ) from the atmosphere. It is shown that scavenging coefficient is non-stationary and height-dependent. It is found also that the scavenging coefficient strongly depends on initial concentration distribution of soluble gaseous pollutants in the atmosphere. It is shown that in the case of linear distribution of the initial concentration of gaseous pollutants whereby the initial concentration of gaseous pollutants decreases with altitude, the scavenging coefficient increases with height in the beginning of rainfall. At the later stage of the rain scavenging coefficient decreases with height in the upper below-cloud layers of the atmosphere.

Topics: Pollution
Commentary by Dr. Valentin Fuster
2010;():57-65. doi:10.1115/IHTC14-22472.

We analyze non-isothermal absorption of trace gases by the rain droplets with internal circulation which is caused by interfacial shear stresses. It is assumed that the temperature and concentration of soluble trace gases in the atmosphere varies in a vertical direction. The rate of scavenging of soluble trace gases by falling rain droplets is determined by solving heat and mass transfer equations. In the analysis we accounted for the accumulation of the absorbate in the bulk of the falling rain droplet. The problem is solved in the approximation of a thin concentration and temperature boundary layers in the droplet and in the surrounding air. We assumed that the bulk of a droplet, beyond the diffusion boundary layer, is completely mixed and concentration of the absorbate and temperature are homogeneous and time-dependent in the bulk. By combining the generalized similarity transformation method with Duhamel’s theorem, the system of transient conjugate equations of convective diffusion and energy conservation for absorbate transport in liquid and gaseous phases with time-dependent boundary conditions is reduced to a system of linear convolution Volterra integral equations of the second kind which is solved numerically. Calculations are performed using available experimental data on nocturnal temperature profiles in the atmosphere. It is shown than if concentration of a trace gas in the atmosphere is homogeneous and temperature in the atmosphere increases with altitude, droplet absorbs gas during all the period of its fall. Neglecting temperature inhomogenity in the atmosphere described by nocturnal temperature inversion leads to essential underestimation of the trace gas concentration in a droplet on the ground.

Commentary by Dr. Valentin Fuster
2010;():67-76. doi:10.1115/IHTC14-22669.

On the base of modern probability approach closed equation for probability density function of coordinates and velocities of two particles in turbulent flow is obtained. The system of equations for balance of mass, averaged velocities and intensities of turbulent chaotic motion of particles with account of correlated motion of particles are deduced. The closed expressions for intensity of relative chaotic motion between particles are obtained on the base of probability density function of particles displacement with correlation effects. Spectral presentation of second velocity moments of gas phase is used for calculation of intensity of particles relative chaotic motion. Boundary condition taking into account coefficients of new particle formation and momentum restitution during two particles collision is found. Formula for calculation of turbulent coagulation kernel of particles in gravity field is gain. Influence of cloud turbulence and turbulence in a pipe flow on intensity of droplets coagulation is studied. Strong effects of relative turbulent diffusion between droplets, droplets inertia and droplets gravitational settling on intensity of coagulation are found out. Connection between internal structure of turbulence type and coagulation rate is illustrated. The calculation results are compared with data of large eddy simulations. The results of calculation intensity of droplets relative motion in atmospheric conditions are presented.

Commentary by Dr. Valentin Fuster
2010;():77-81. doi:10.1115/IHTC14-22704.

Energy efficiency improvement and waste heat utilization in power generation and energy intensive industrial applications are in the main focus of the researchers and engineers nowadays. A great deal of experience was gained by the industrial leaders such as ORMAT, Siemens, Caterpillar, Turboden, and others. However, the commercially and semi-commercially available systems for waste heat utilization have certain restrictions that limit the utilization cycle efficiency to approximately 18%. The paper presents an innovative concept of waste heat utilization system that allows reaching the utilization cycle efficiency up to 28–30% employing low-boiling media such as butane, propane, pentane and others. Applying such a concept to Distributed Generation systems the overall energy efficiency could be boost up to 58–60% and further up to 90% in case of CHP production.

Commentary by Dr. Valentin Fuster
2010;():83-91. doi:10.1115/IHTC14-22849.

This paper presents a parametric study of the indoor climate of a four span greenhouse subjected to natural ventilation. The effect of different heat fluxes through the greenhouse covering on the airflow patterns as well as temperature and velocity distributions were determined. Appropriate effective heat flux boundary conditions were introduced in the CFD model to investigate temperature and velocity distributions at plant level. Initially, three different simulations were done to represent zero wind speed conditions. Secondly, a velocity of 1m/s was specified at the domain inlet boundary. Results indicated that for all cases, the velocity distribution was heterogeneous and quite high for wind still days around midday. Temperature distributions were more homogeneous, decreased with the presence of a wind. Results indicated that a parametric value of 20% of the maximum daily solar radiation approximates previously simulated wall temperatures. It was also concluded that design changes such as additional openings including side and/or more roof ventilators be utilized to enhance ventilation on wind still days, as well as the warmer parts of the day.

Commentary by Dr. Valentin Fuster
2010;():93-100. doi:10.1115/IHTC14-23017.

Double skin facades (DSFs) are building envelopes comprised of two glass facades, a ventilated air cavity and shading devices placed within the cavity. In this paper airflow and heat transfer simulation was conducted for a DSF system equipped with a venetian blind using computational fluid dynamics (CFD) with RNG turbulence model. Simulation was done for a three-level combination of slat tilt angle and blind position. The heat transfer coefficient was directly obtained from CFD simulation. The CFD prediction was validated using experimental data collected for a mechanically ventilated DSF (1.6 m wide and 2.5 m high and 0.15 m wide cavity) equipped with venetian blinds. The present study indicates that the presence of venetian blinds influences the surface heat transfer coefficients (SHTCs), the temperature and the air distribution in the DSF system. Specifically, for the cases considered, the position of the blinds is more important than the slat angles.

Commentary by Dr. Valentin Fuster
2010;():101-109. doi:10.1115/IHTC14-23079.

Transport processes in a sodium alanate hydrogen storage system during desorption are presented. The mathematical model, which considers heat conduction and convection, hydrogen flow governed by Blake-Kozeny law and the chemical kinetics, is solved using the COMSOL Multiphysics® finite element software. The numerical simulation is used to present the time-space evolutions of the temperature, pressure and hydride concentration. The results are discussed for two cases: a finned storage system and a finless one. It is shown that the whole process occurring in the bed is governed and controlled by heat transfer from the heating fluid to the storage media and strengthened by axial heat transfer through the fins. The importance of the hydride bed thermal conductivity has also been evaluated. It was observed that the hydrogen discharge rate in a finless system can be improved if we find ways of increasing the thermal conductivity of the storage media. On the other hand, for a reservoir with fins, heat transfer is good enough that the discharge rate is limited by the kinetics.

Commentary by Dr. Valentin Fuster

Thermodynamic Fundamentals and Systems

2010;():111-116. doi:10.1115/IHTC14-22023.

In 1969, S. G. Brush and C. W. F. Everitt published a historical review, that was reprinted as subchapter 5.5 Maxwell, Osborne Reynolds, and the radiometer, in Stephen G. Brush’s famous book The Kind of Motion We Call Heat. This review covers the history of the explanation of the forces acting on the vanes of Crookes radiometer up to the end of the 19th century. The forces moving the vanes in Crookes radiometer (which are not due to radiation pressure, as initially believed by Crookes and Maxwell) have been recognized as thermal effects of the remaining gas by Reynolds — from his experimental and theoretical work on Thermal Transpiration and Impulsion, in 1879 — and by the development of the differential equations describing Thermal Creeping Flow, induced by tangential stresses due to a temperature gradient on a solid surface by Maxwell, earlier in the same year, 1879. These fundamental physical laws have not yet made their way into the majority of textbooks of heat transfer and fluid mechanics so far. A literature research about the terms of Thermal Transpiration and Thermal Creeping Flow, in connection with the radiometer forces, resulted in a large number of interesting papers; not only the original ones as mentioned in subchapter 5.5 of Brush’s book, but many more in the earlier twentieth century, by Martin Knudsen, Wilhelm Westphal, Albert Einstein, Theodor Sexl, Paul Epstein and others. The forces as calculated from free molecular flow (by Knudsen), increase linearly with pressure, while the forces from Maxwell’s Thermal Creeping Flow decrease with pressure. In an intermediate range of pressures, depending on the characteristic geometrical dimensions of flow channels or radiometer vanes, an appropriate interpolation between these two kinds of forces, as suggested by Wilhelm Westphal and later by G. Hettner, goes through a maximum. Albert Einstein’s approximate solution of the problem happens to give the order of magnitude of the forces in the maximum range. A comprehensive formula and a graph of the these forces versus pressure combines all the relevant theories by Knudsen (1910), Einstein (1924), Maxwell (1879) (and Hettner (1926), Sexl (1928), and Epstein (1929) who found mathematical solutions for Maxwells creeping flow equations for non-isothermal spheres and circular discs, which are important for thermophoresis and for the radiometer). The mechanism of Thermal Creeping Flow will become of increasing interest in micro- and submicro-channels in various new applications, so it ought to be known to every graduate student of heat transfer in the future. That’s one of the reasons why some authors have recently questioned the validity of the classical Navier-Stokes, Fourier, and Fick equations: Dieter Straub (1996) published a book on an Alternative Mathematical Theory of Non-equilibrium Phenomena. Howard Brenner (since 2005) wrote a number of papers, like Navier-Stokes, revisited, and Bi-velocity hydrodynamics, explicitly pointing to the forces acting on the vanes of the lightmill, to thermophoresis and related phenomena. Franz Durst (since 2006) also developed modifications of the classical Navier-Stokes equations. So, Reynolds, Maxwell, and the radiometer may finally have initiated a revision of the fundamental equations of thermofluiddynamics and heat- and mass transfer.

Commentary by Dr. Valentin Fuster
2010;():117-124. doi:10.1115/IHTC14-22027.

Maxwell had advanced the famous velocity distribution law for ideal gas and idea of momentum space. But he had also put the problem about “Maxwell demon” to oppugn that if should the space configuration of momentum exist? This paper defines the pressure resulting from elastic collision based on no-wall space model of ideal gas under the thermodynamic equilibrium. It lets the presupposition about Maxwell velocity space without any actions to be untenable. There are space configurations of momentum for ideal gas whatever in no-wall space or in box with solid wall that is a restriction for order relating space configuration of position of particle. The order and Boltzmann entropy should account for momentum space configuration. This paper proposes a statistic method for local certain region of non-localized particles of ideal gas. The pV and −TS are argued to be two kinds of potential energy. The −TS is the heat potential energy inside of an isolation system which change is equal to the heat exchanging between the system and surrounding.

Commentary by Dr. Valentin Fuster
2010;():125-127. doi:10.1115/IHTC14-22252.

In the present work, an extremum principle of entransy dissipation is developed by taking into account the contribution of fluid friction. It is found that this extremum principle of entransy dissipation leads to the same balance equations as given in continuum mechanics for the steady heat conduction and shear flow in an incompressible fluid.

Commentary by Dr. Valentin Fuster
2010;():129-134. doi:10.1115/IHTC14-22317.

In previous researches, we have been focusing on the performance of the each element heat transfer and hydraulic performance of refrigeration cycle. Experimental investigations have been repeated several times and, finally, we have substantial data base including the effect of lubricant oil. Moreover, the mal-distribution of two-phase in an evaporator can be also predicted from the experimental data base. Under these circumstances, this study is intended to effectively put the construction of an automotive CO2 air conditioning system into practical design use through the simulation using the above-mentioned data base. This paper describes the refrigeration cycle performance prediction of each element (e.g. an evaporator, a gas-cooler, and so on) by a simulation using substantial data base and various available correlations proposed by us and several other researchers. In the performance prediction model of heat exchangers, local heat transfer and flow characteristics are considered and in addition, the effects of lubricant oil on heat transfer and pressure drop are duly considered. The comparison is also made between simulation results and bench test results using a real automotive air conditioning system. Finally, the developed simulation method can predict the cooling ability successfully within ±5%. By incorporating the lubricant oil effect, the simulation results are improved to ±5% and ±15% for the cooling ability and pressure drop respectively.

Commentary by Dr. Valentin Fuster
2010;():135-140. doi:10.1115/IHTC14-22356.

In this study, we aim at developing the heat driven type water cooler using metal hydride (abbr., MH) alloy. Heat driven type MH water cooler is one of the chemical heat pumps, and the endothermic reaction on the cooling part MH (to put it simply, MH2) is used for the cooling. Because MH is too expensive (200∼300 $ per 1kg) and has an unfavorable activation characteristic, this cooler has not been used generally yet. In order to increase the system performance, we use a new TiFe alloy, which has been developed by co-researcher, to the heat source part MH (to put it simply, MH1). Moreover, to improve the cooling load per MH mass, we mix the brush type carbon fiber, 2 mass% into MH beds. By this method, the cooling load per MH mass is been increased to 0.078 kW/kg (MH2).

Topics: Heat , Metals , Water
Commentary by Dr. Valentin Fuster
2010;():141-150. doi:10.1115/IHTC14-22413.

Using the analogy between heat and mass transfer processes, the recently developed entransy theory is extended in this paper to tackle the coupled heat and mass transfer processes so as to analyze and optimize the performance of evaporative cooling systems. We first introduce a few new concepts including the moisture entransy, moisture entransy dissipation, and the thermal resistance in terms of the moisture entransy dissipation. Thereinafter, the moisture entransy is employed to describe the endothermic ability of a moist air. The moisture entransy dissipation on the other hand is used to measure the loss of the endothermic ability, i.e. the irreversibility, in the coupled heat and mass transfer processes, which consists of three parts: (1) the sensible heat entransy dissipation, (2) the latent heat entransy dissipation, and (3) the entransy dissipation induced by a temperature potential. And then the new thermal resistance, defined as the moisture entransy dissipation rate divided by the squared refrigerating effect output rate, is recommended as an index to effectively reflect the performance of the evaporative cooling system. Meanwhile, a minimum thermal resistance law for optimizing the evaporative cooling systems is developed. In the end, several direct and indirect evaporative cooling processes are analyzed to illustrate the applications of the proposed concepts.

Commentary by Dr. Valentin Fuster
2010;():151-158. doi:10.1115/IHTC14-22838.

Charging and discharging operations of on-board hydrogen adsorption storage systems involve exothermic and endothermic processes. Temperature elevations caused by the released heat of adsorption, compression work and thermal mass introduced from the inlet gas result with a reduction of the storage capacity. The main objective of this work was the investigation of the impact of temperature elevations on the decrease of adsorption storage capacity during high-pressure charging of a hydrogen cryo-adsorption storage tank. The experimental operating conditions were compatible with practical applications for hydrogen adsorption on-board storage systems. The analysis was conducted with two adsorbent classes: activated carbon (NORIT R0.8) and metal-organic-frameworks (Cu-BTC-1,3,5). Adsorption isotherms for hydrogen uptake for both adsorbents are measured by a gravimetric method and fitted in accordance to the Langmuir equation. The experimental study was carried out in a cylindrical tank with granular adsorbents in which the bed temperature was measured at various positions. A typical average temperature increase in the core of the storage column during hydrogen charging experiments with the CuBTC and NORIT R0.8 was 16.2 K and 20.4 K at 2 MPa respectively. Such temperature elevation results in a loss in the adsorption storage capacity of 14.75% for the system packed with the CuBTC adsorbent. Solutions for increased efficiency of the hydrogen cryo-adsorption storage tanks are proposed.

Commentary by Dr. Valentin Fuster
2010;():159-168. doi:10.1115/IHTC14-23135.

Pyroelectric energy conversion offers a novel approach for directly converting waste heat into electricity. This paper reports numerical simulations of a prototypical pyroelectric energy converter. The two-dimensional mass, momentum, and energy equations were solved to predict the local and time-dependent pressure, velocity, and temperature. Then, the heat input, pump power, and electrical power generated were estimated, along with the thermodynamic energy efficiency of the device. It was established that reducing the length of the device and the viscosity of the working fluid improved the energy efficiency and power density by increasing the optimum operating frequency of the device. Results show that a maximum efficiency of 5.2% at 0.5 Hz corresponding to 55.4% of the Carnot efficiency between 145 and 185°C can be achieved when using commercial 1.5 cst silicone oil. The maximum power density was found to be 38.4 W/l of pyroelectric material.

Commentary by Dr. Valentin Fuster
2010;():169-177. doi:10.1115/IHTC14-23185.

The performance of an air dehumidification system with lithium chloride solution used as a desiccant was studied experimentally. First, the mass-transfer coefficients were measured for a structured packed dehumidifier/regenerator. It was shown that the overall mass-transfer coefficients varied from 2.5 to 7.8 g/(m2 ·s) when the air velocity was increased from 0.5 to 1.5 m/s in the dehumidifier and varied from 1.2 to 2.7 g/(m2 ·s) in the regenerator. Second, experiments on the air dehumidification system were conducted. The experimental results showed that higher humidity in summer and lower humidity in winter resulted in decreased dehumidifying (humidifying) efficiency.

Commentary by Dr. Valentin Fuster
2010;():179-182. doi:10.1115/IHTC14-23362.

Drawing on relevant theories, a quantitative study on model and basic concepts for thermodynamic system has been conducted. It Includes following concepts: thermodynamic system (system interior, system border and system outside), the border (border wall and border gate), the open degree (not only the function of space and time, but also related to energy, quality and information), the exchange rate (including quality, energy and information exchange rate; and it is a composite function, correlated to the opening degree of border, the state inside the system, time and space and so on). Accordingly, the relationship between the opening degree and the exchange rate of system has been analyzed, and the system stability (opening degree) criterion is derived.

Topics: Thermal systems
Commentary by Dr. Valentin Fuster
2010;():183-192. doi:10.1115/IHTC14-23412.

This study is concerned with pyroelectric energy conversion to directly convert waste heat into electricity. The pyroelectric effect refers to the flow of charges to or from the surface of a material upon heating or cooling. A prototypical pyroelectric energy converter was designed, built, and tested. It performed the Olsen cycle consisting of two isothermal and two isovoltage processes in the charge-voltage diagram. Co-polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films sandwiched between metallic electrodes were used as the pyroelectric elements. Their temperature oscillation, charge, and voltage along with the overall heat input and output were measured experimentally. Then, the electrical power generated and the energy efficiency of the device were computed. The effects of channel width, frequency, and stroke length on temperature swing, heat input, and energy and power densities were investigated. Reducing the channel width and increasing the stroke length had the largest effect on device performance. A maximum energy density of 130 J/L of P(VDF-TrFE) was achieved at 0.061 Hz frequency with temperature oscillating between 69.3 and 87.6°C. Furthermore, a maximum power density of 10.7 W/L of P(VDF-TrFE) was obtained at 0.12 Hz between 70.5 and 85.3°C. In both cases, the voltages in the Olsen cycle were 923 and 1732 V imposed on a 45.7 microns thick 60/40 P(VDF-TrFE) films. To the best of our knowledge, this is the largest energy density achieved by any pyroelectric energy converter using P(VDF-TrFE). It also matches performances reported in the literature for more expensive lead zirconate stannum titanate ceramic films operated at higher temperatures between 110 and 185°C.

Commentary by Dr. Valentin Fuster

Keynotes

2010;():193-207. doi:10.1115/IHTC14-22384.

Engineers are faced with two major challenges when carrying out the thermal-fluid design of a complex system consisting of many interacting components such as the PBMR power plant. The first challenge is to predict the performance of all the individual thermal-fluid components. The second challenge is to predict the performance of the integrated plant consisting of all its sub-systems. The complexity associated with the thermal-fluid design of complex systems requires the use of a variety of analysis techniques and simulation tools. These range from simple one-dimensional models that do not capture all the significant physical phenomena, to large-scale three-dimensional CFD codes that, for practical reasons, can not simulate the entire plant as a single integrated model. In the systems CFD approach a network code serves as the framework to link the models of the various components together and to control the solution. The models of the components can be of varying degrees of complexity. These can range from simple lumped models to complex fully three-dimensional CFD models. This paper gives a brief overview of the systems CFD (SCFD) approach and an overview of the SCFD model of the pebble bed nuclear reactor that was developed.

Commentary by Dr. Valentin Fuster
2010;():209-228. doi:10.1115/IHTC14-22570.

In recent years considerable attention has been paid to the study of microscale flow and heat transfer with phase change and chemical reactions. This article reviews the patterns of the microscale two-phase gas-liquid flow, the statistical parameters of slug flow and capillary phenomena in annular flow for a rectangular microchannel. The evaporative and condensing heat transfer model for the curved liquid microfilm in microchannel and near contact line is developed and discussed. The influence of forced convection, nucleate boiling and thin film evaporation on microscale flow boiling heat transfer is reviewed and analyzed. The model of forced boiling heat transfer in microchannel is developed and compared with the existing experimental data. The mechanism and patterns of microscale explosive evaporation in the MEMS system is determined at high external heat flux density and the acousto-thermal model of the explosive evaporation is considered. The results of calculations are compared with the experimental data. The peculiarities of heat and mass transfer in a micro channel with surface catalytic reactions producing the hydrogen are presented. The kinetics of sequence of chemical reactions at nanoscale catalyst under conditions of significant nonuniformity of temperature and species concentration fields is considered.

Commentary by Dr. Valentin Fuster
2010;():229-249. doi:10.1115/IHTC14-22959.

Films are ubiquitous in nature and play an important role in our daily life. The paper focuses on the recent progress that has been achieved in the interfacial thermal fluid phenomena in thin liquid films and rivulets through conducting experiments and theory. Phase shift schlieren technique, fluorescence method and infrared thermography have been used. A spanwise regular structures formation was discovered for films falling down an inclined plate with a built-in local rectangular heater. If the heating is low enough, a stable 2D flow with a bump at the front edge of the heater is observed. For lager heat flux this primary flow becomes unstable, and the instability leads to another steady 3D flow, which looks like a regular structure with a periodically bent leading bump and an array of longitudinal rolls or rivulets descending from it downstream. The heat flux needed for the onset of instability grows almost linearly with the increase of Re number. Strong surface temperature gradients up to 10–15 K/mm, both in the streamwise and spanwise directions have been measured. For a wavy film it was found that heating may increase the wave amplitude because thermocapillary forces are directed from the valley to the crest of the wave. Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel are a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. Experiments with water and FC-72 in flat channels (height 0.2–2 mm) have been conducted. Maps of flow regimes were plotted. It was found that stratified flow exists and stable in the channels with 0.2 mm height and 40 mm width. The critical heat flux for a shear driven film may be up to 10 times higher than that for a falling liquid film, and reaches 400 W/cm2 in experiments with water at atmospheric pressure. Some experiments have been done during parabolic flight campaigns of the European Space Agency under microgravity conditions. It was found that decreasing of gravity leads to a flow destabilization.

Commentary by Dr. Valentin Fuster
2010;():251-270. doi:10.1115/IHTC14-23339.

Theoretical analysis and experimental investigations have shown that the mean heat fluxes in turbulent gaseous flows are influenced not only by the mean scalar fields (temperature and molar fraction of the species), but also by the scalar fluctuations. It is widely recognized that the increase of radiative fluxes in comparison with laminar flows may exceed 100%. This interaction between turbulence and radiation is mainly due to the non-linearity between radiative emission and temperature. It is particularly important in reactive flows, since temperature fluctuations are typically higher in these flows than in non-reactive ones. In this article, a survey of the theory concerning turbulence-radiation interaction (TRI) is presented, along with applications in numerical simulations. We firstly present experimental and theoretical fundamentals on TRI. Then, direct numerical simulation and stochastic methods are addressed. Although they provide reliable information on TRI, they are too computationally demanding for practical applications. We will then focus on methods based on the solution of the time-averaged form of the conservation equations. Although many different approaches are available, we will concentrate on two methods. One is based on the solution of the time-averaged form of the radiative transfer equation using the optically thin fluctuation approximation, and a combustion model based on a prescribed probability density function (pdf) approach. The second one is based on the photon Monte Carlo method for radiative transfer calculations in media represented by discrete particle fields, and a combustion model based on the Monte Carlo solution of the transport equation for the joint pdf of scalars. Finally, the role of TRI in large eddy simulation is discussed, and the main consequences of TRI in combustion systems are summarized.

Commentary by Dr. Valentin Fuster
2010;():271-286. doi:10.1115/IHTC14-23340.

The human thermal regulatory system is remarkable. It allows humans to live under environmental temperatures that range from −45 °C in Arctic regions to + 50 °C in the Saharan desert, while maintaining the temperature of critical organs within ± 1 °C of 37 °C, without employing heating and cooling systems that we now take for granted. Of course, that requires building suitable shelters and wearing appropriate clothing, but it is still quite remarkable.

Commentary by Dr. Valentin Fuster
2010;():287-308. doi:10.1115/IHTC14-23341.

Hydrogen can be produced from water splitting with relatively high efficiency using high-temperature electrolysis. This technology makes use of solid-oxide cells, running in the electrolysis mode to produce hydrogen from steam, while consuming electricity and high-temperature process heat. When coupled to an advanced high temperature nuclear reactor, the overall thermal-to-hydrogen efficiency for high-temperature electrolysis can be as high as 50%, which is about double the overall efficiency of conventional low-temperature electrolysis. Current large-scale hydrogen production is based almost exclusively on steam reforming of methane, a method that consumes a precious fossil fuel while emitting carbon dioxide to the atmosphere. Demand for hydrogen is increasing rapidly for refining of increasingly low-grade petroleum resources, such as the Athabasca oil sands and for ammonia-based fertilizer production. Large quantities of hydrogen are also required for carbon-efficient conversion of biomass to liquid fuels. With supplemental nuclear hydrogen, almost all of the carbon in the biomass can be converted to liquid fuels in a nearly carbon-neutral fashion. Ultimately, hydrogen may be employed as a direct transportation fuel in a “hydrogen economy.” The large quantity of hydrogen that would be required for this concept should be produced without consuming fossil fuels or emitting greenhouse gases. An overview of the high-temperature electrolysis technology will be presented, including basic theory, modeling, and experimental activities. Modeling activities include both computational fluid dynamics and large-scale systems analysis. We have also demonstrated high-temperature electrolysis in our laboratory at the 15 kW scale, achieving a hydrogen production rate in excess of 5500 L/hr.

Commentary by Dr. Valentin Fuster
2010;():309-324. doi:10.1115/IHTC14-23344.

Because of the importance of fundamental knowledge on turbulent heat transfer for further decreasing entropy production and improving efficiency in various thermo-fluid systems, we revisit a classical issue whether enhancing heat transfer is possible with skin friction reduced or at least not increased as much as heat transfer. The answer that numerous previous studies suggest is quite pessimistic because the analogy concept of momentum and heat transport holds well in a wide range of flows. Nevertheless, the recent progress in analyzing turbulence mechanics and designing turbulence control offers a chance to develop a scheme for dissimilar momentum and heat transport. By reexamining the governing equations and boundary conditions for convective heat transfer, the basic strategies for achieving dissimilar control in turbulent flow is generally classified into two groups, i.e., one for the averaged quantities and the other for the turbulent fluctuating components. As a result, two different approaches are discussed presently. First, under three typical heating conditions, the contribution of turbulent transport to wall friction and heat transfer is mathematically formulated, and it is shown that the difference in how the local turbulent transport of momentum and that of heat contribute to the friction and heat transfer coefficients is a key to answer whether the dissimilar control is feasible. Such control is likely to be achieved when the weight distributions for the stress and flux in the derived relationships are different. Secondly, we introduce a more general methodology, i.e., the optimal control theory. The Fréchet differentials obtained clearly show that the responses of velocity and scalar fields to a given control input are quite different due to the fact that the velocity is a divergence-free vector while the temperature is a conservative scalar. By exploiting this inherent difference, the dissimilar control can be achieved even in flows where the averaged momentum and heat transport equations have the same form.

Commentary by Dr. Valentin Fuster
2010;():325-341. doi:10.1115/IHTC14-23345.

Metal hydrides are formed when certain metals or alloys are exposed to hydrogen at favorable temperatures and pressures. In order to sustain the sorption of hydrogen during this exothermic process, the generated heat has to be removed effectively. Release of hydrogen is an endothermic process needing supply of heat to the metal hydride matrix. Depending on the application, the heat transfer medium can be either a liquid or a gas. Reduction of the total weight of hydrogen storage devices is essential towards utilization of hydrogen for mobile and portable applications. While a variety of new storage materials with desirable sorption characteristics are being suggested, optimal thermal design of the storage device remains a major challenge. Lack of thermodynamic, transport and thermophysical property data of the material particles and of the bed is another drawback which needs to be addressed.

Commentary by Dr. Valentin Fuster
2010;():343-362. doi:10.1115/IHTC14-23346.

This paper reports some important results obtained from a series of microgravity experiments on the Marangoni convection that takes place in liquid bridges. This project, called Marangoni Experiment in Space (MEIS), started from August 22, 2008 as the first science experiment on the Japanese Experimental Module “KIBO” at the ISS. Two series of experiments, MEIS-1 and 2, were conducted in 2008 and 2009, respectively. The experimental methods used are explained in some detail. The maximum size of the liquid bridge that could be realized during these experiments was 30 mm in diameter and 60 mm in length, giving an aspect ratio of 2.0. The results are obtained for a wide range of aspect ratios of the liquid bridges, including the values that cannot be reached in 1g experiments, and therefore, they provide indispensable amount of data for the study of instability mechanisms of the Marangoni convection.

Commentary by Dr. Valentin Fuster
2010;():363-377. doi:10.1115/IHTC14-23348.

Entropy generation in a velocity and temperature field is shown to be very significant in momentum and heat transfer problems. After the determination of this post-processing quantity many details about the physics of a problem are available. This second law analysis (SLA) is a tool for conceptual considerations, for the determination of losses, both in the velocity and the temperature field, and it helps to assess complex convective heat transfer processes. These three aspects in conjunction with entropy generation are discussed in detail and illustrated by several examples.

Commentary by Dr. Valentin Fuster
2010;():379-398. doi:10.1115/IHTC14-23349.

Systematic methods for the solution of inverse problems have developed significantly during the last twenty years and have become a powerful tool for analysis and design in engineering. Inverse analysis is nowadays a common practice in which the groups involved with experiments and numerical simulation synergistically collaborate throughout the research work, in order to obtain the maximum of information regarding the physical problem under study. Inverse problems are mathematically classified as ill-posed, that is, their solutions do not satisfy either one of the requirements of existence, uniqueness or stability. The solution approaches generally consist of the reformulation of the inverse problem in terms of an approximate well-posed problem. In this paper we briefly review various approaches for the solution of inverse problems, including those based on classical regularization techniques and those based on the Bayesian statistics. Applications of inverse problems are then presented for cases of practical interest, such as the characterization of non-homogeneous materials and the prediction of the temperature field in oil pipelines.

Commentary by Dr. Valentin Fuster
2010;():399-409. doi:10.1115/IHTC14-23350.

Carbon nanotubes and graphene are extra-ordinal material with remarkable electrical, optical, mechanical and thermal properties. Films of vertically aligned (VA-) SWNTs and horizontally aligned (HA-) SWNTs are synthesized on quartz and crystal quartz substrates, respectively. These aligned film should inherit the remarkable properties of SWNTs. The recent progress in growth control and characterization techniques will be discussed. The CVD growth mechanism of VA-SWNTs is discussed based on the in-situ growth monitoring by laser absorption during CVD. For the precisely patterned growth of SWNTs, we recently propose a surface-energy-difference driven selective deposition of catalyst for localized growth of SWNTs. For a self assembled monolayer (SAM) patterned Si surface, catalyst particles deposit and SWNTs grow only on the hydrophilic regions. The proposed all-liquid-based approach possesses significant advantages in scalability and resolution over state-to-the-art techniques, which we believe can greatly advance the fabrication of nano-devices using high-quality as-grown SWNTs. The optical characterization of the VA-SWNT film using polarized absorption, polarized Raman, and photoluminescence spectroscopy will be discussed. The extremely high and peculiar thermal conductivity of single-walled carbon nanotubes has been explored by non-equilibrium molecular dynamics simulation approaches. The thermal properties of the vertically aligned film and composite materials are studied by several experimental techniques and Monte Carlo simulations based on molecular dynamics inputs of thermal conductivity and thermal boundary resistance. Current understanding of thermal properties of the film is discussed.

Commentary by Dr. Valentin Fuster
2010;():411-428. doi:10.1115/IHTC14-23351.

Energy simulation (ES) computer programs have been and still are widely used in the design and analysis of building energy systems. However, most ES programs assume that the air in the indoor building space is well mixed. As a result such programs cannot accurately predict building energy consumption for buildings with non-uniform air temperature distributions in the indoor space. They also cannot predict variations in thermal comfort levels in different parts of the building. Computational Fluid Dynamics (CFD), as a result, has become quite widely used in the design and evaluation of buildings energy systems in recent years. CFD can be used, for example, to predict the thermal comfort, natural lighting, natural ventilation, spread of smoke and contaminants in the building, and indoor air quality in a building. As a result it is proving to be an extremely valuable tool in the design of buildings and building systems. This, together with the fact that today’s commercial CFD software packages are relatively easy to use, has led to this quite widespread adoption of CFD methods in building energy analysis. Energy usage in buildings can be decreased by, for example, the use of daylighting (use of solar illumination in place of artificial lighting), by the use of natural ventilation, and by solar heating. CFD analysis provides a means of relatively accurately studying the effect of building design on the effectiveness of daylighting, natural ventilation, and solar heating. Another example of the use of CFD is in the study of the effect of various window blind arrangements on the building performance. In order for a CFD package to be used effectively in building energy analysis it should allow the use of a wide range of turbulence models, it should allow the incident solar radiation on the building to be found and used in the calculation of the indoor flow and temperature fields, it should allow the radiant heat exchange in the building to be incorporated into the calculation, and it should allow the effects of the thermal masses of the walls, floors, etc. to be easily incorporated into the calculation when they are deemed to be important. In this paper, the use of CFD methods in building energy analysis will be discussed as will some applications of CFD in building design. The use of CFD methods in developing design guidelines for particular types of buildings will also be briefly discussed.

Commentary by Dr. Valentin Fuster
2010;():429-440. doi:10.1115/IHTC14-23352.

Chip microscale liquid-cooling reduces conductive and convective resistance thereby improving the efficiency of datacenters by allowing coolant temperatures above the free cooling limit in all climates. This eliminates the need for chillers and allows the thermal energy to be re-used in cold climates. Replacing the combustion processes for secondary users with recycled heat from the datacenter effectively eliminates carbon dioxide emission during the winter season and reduces operating cost throughout the year. The energy balance of emission-reduced datacenters is compared with a classical air cooled datacenter, a datacenter with free cooling in a cold climate zone, and a datacenter with chiller-mediated energy re-use. Hot water cooled datacenters reduce the effective energy cost by almost a factor of two compared to a current datacenter and reduce the carbon footprint by an even larger factor. Our energy re-use concept has been demonstrated in terms of cost and energy savings in a 60°C liquid cooled supercomputer. Additional alternative energy re-use schemes in hot climates for desalination and adsorption cooling allow close to full use of datacenter heat in all climates and all seasons. Output temperatures for these applications compared to space heating need to be 10–20°C higher which becomes possible through hotspot adapted cooling that eliminates mixing of fluids with different temperatures. In addition, interlayer cooled chip stacks allow double sided hotspot optimized cooling even closer to the heat source with low flow rates and low pumping power. This improves the large efficiency gain that becomes possible through 3D chip stacking.

Commentary by Dr. Valentin Fuster
2010;():441-460. doi:10.1115/IHTC14-23353.

As the scale of devices becomes small, thermal control and heat dissipation from these devices can be effectively accomplished through the implementation of microchannel passages. The small passages provide a high surface area to volume ratio that enables higher heat transfer rates. High performance microchannel heat exchangers are also attractive in applications where space and/or weight constraints dictate the size of a heat exchanger or where performance enhancement is desired. This survey article provides a historical perspective of the progress made in understanding the underlying mechanisms in single-phase liquid flow and two-phase flow boiling processes and their use in high heat flux removal applications. Future research directions for (i) further enhancing the single-phase heat transfer performance, and (ii) enabling practical implementation of flow boiling in microchannel heat exchangers, are outlined.

Commentary by Dr. Valentin Fuster
2010;():461-480. doi:10.1115/IHTC14-23354.

This lecture is dedicated to the memory of Professor Eddie Leonardi, formerly International Heat Transfer Conference (IHTC-13) Secretary, who tragically died at an early age on December 14, 2008. Eddie Leonardi had a large range of research interests: he worked in both computational fluid dynamics/heat transfer and refrigeration and air-conditioning for over 25 years. However starting from his PhD ‘A numerical Study of the effects of fluid properties on Natural Convection’ awarded in 1984, one of his main passions has been natural convection and therefore the focus of this lecture will be on what Eddie Leonardi has achieved in numerical and experimental investigations of laminar natural convective flows. A number of examples will be presented which illustrate important difficulties of numerical calculations and experimental comparisons. Eddie Leonardi demonstrated that variable properties have important effects and significant differences occur when different fluids are used, so that non-dimensionalisation is not an appropriate tool when dealing with fluids in thermally driven flows in which there are significant changes in transport properties. Difficulties in comparing numerical solutions with either numerically generated data or experimental results will be discussed with reference to two-dimensional natural convection and three-dimensional Rayleigh-Bénard convection in bounded domains with conducting boundaries. For a number of years Eddie Leonardi was involved in a joint US-French-Australian research program — the MEPHISTO experiment on crystal growth — and studied the effects of convection on solidification and melting under microgravity conditions. The results of this research will be described. Finally, results of experimental and numerical studies of natural convection for Building Integrated Photovoltaic (BIPV) applications in which Eddie Leonardi had been working in the last few years will also be presented.

Commentary by Dr. Valentin Fuster
2010;():481-500. doi:10.1115/IHTC14-23363.

Complex macroscale and microscale heat and mass transfer phenomena encountered in several thermal energy storage and transport systems are discussed. Thermal storage and transport systems involving ice slurries and nanoemulsions of phase change materials can be used for either cooling or heating applications or both, which can contribute to the reduced usage of electricity during peak hours. But heat and mass transfer and stability issues are encountered in the production, transport and storage of the heat storage media. Both the heat transfer enhancement effect and detrimental effects such as Ostwald ripening and supercooling will be discussed. Another interesting microscale phenomenon recently encountered in energy transport devices such as heat pipes is the enhancement of heat transport with the use of self-rewetting fluids. Critical heat fluxes in boiling can be enhanced by up to 300% and this helps prevent liquid dryout at high heat fluxes in different types of heat pipes. Both the nature of the enhancement effect and possible mechanisms will be discussed.

Commentary by Dr. Valentin Fuster
2010;():501-517. doi:10.1115/IHTC14-23367.

During the few decades, computational techniques for simulating heat transfer in complex industrial systems have reached maturity. Combined with increasingly sophisticated modeling of turbulence, chemistry, radiation, phase change and other physics, powerful computational fluid dynamics (CFD) and computational heat transfer (CHT) solvers have been developed which are beginning to enter the industrial design cycle. In this paper, an overview of emerging simulation needs is first given, and currently-available CFD techniques are evaluated in light of these needs. Emerging computational methods which address some of the failings of current techniques are then reviewed. New research opportunities for computational heat transfer, such as in sub-micron and multiscale heat transport, are reviewed. As computational techniques and physical models become mature, there is increasing demand for predictive simulation, that is, simulation which is not only verified and validated, but whose uncertainty is also quantified. Current work in the area of sensitivity computation and uncertainty propagation is described.

Commentary by Dr. Valentin Fuster
2010;():519-536. doi:10.1115/IHTC14-23373.

Thermal systems often involve multiple spatial and temporal scales, where transport information from one scale is relevant at others. Optimized thermal design of such systems and their control require approaches for their rapid simulation. These activities are of increasing significance due to the need for energy efficiency in the operation of these systems. Traditional full-field simulation methodologies are typically unable to resolve these scales in a computationally efficient manner. We handle the simulations of conjugate transport processes over selected length scales of interest via reduced order modeling through approaches such as compact finite elements, and proper orthogonal decomposition. In order to incorporate the influence of length scales beyond these, lumped models are invoked, with appropriate handshaking between the two frameworks. We illustrate the methodology through selected examples, with a focus on information technology systems.

Commentary by Dr. Valentin Fuster
2010;():537-547. doi:10.1115/IHTC14-23375.

In this paper, the finite element method for modelling of microchannel flow and heat transfer is discussed. The situations that need unstructured mesh technology are highlighted in addition to the flexible nature of the finite element method for problems with the need for adaptive refinement. Many of these aspects are demonstrated by solving flow and heat transfer through microchannels. Both mechanically driven and electrokinetically driven single phase flows in microchannels are considered. A brief discussion is provided on enhancement methods in which the finite element modelling can help. Only a selection of results are presented in this paper. More results will be presented during the conference.

Commentary by Dr. Valentin Fuster
2010;():549-557. doi:10.1115/IHTC14-23378.

Batteries are considered to be a critical component for making future transportation more energy-efficient and less dependent on petroleum through hybrid, plug-in hybrid, electric, and fuel cell vehicles. In this paper, the current status of batteries for electric drive vehicle applications will be discussed. Special attention will be given to the thermal issues associated with batteries in vehicle environment. We will also discuss future needs of batteries for further development.

Commentary by Dr. Valentin Fuster
2010;():559-573. doi:10.1115/IHTC14-23379.

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material’s surface texture is of substantial importance. Several micro and nanostructures designs have been proposed to enhance a material’s emissivity and its radiative coherence, as control of thermal emission is of crucial concern in the design of infrared sources, in electronic chip coolants, in high-efficiency photovoltaic cells, and in solar energy conversion.

Commentary by Dr. Valentin Fuster
2010;():575-589. doi:10.1115/IHTC14-23383.

Adsorption refrigeration and heat pump systems have been considered as very important means for the efficient use of low grade thermal energy in the temperature range of 60–150°C. Sorption systems are merely heat exchanger based thermodynamic systems, and therefore a good design to optimize heat and mass transfer with reaction or sorption processes is very important for high performance of the systems. Studies on heat and mass transfer enhancement in adsorption beds have been done extensively. Notable techniques is whereby the adsorbent bed is fitted with finned heat exchanger embedded with adsorbent particles, or the adsorbent particles may be compressed and solidified and then coupled with finned tube or plate heat exchangers. The use of expanded graphite seems to be an effective method to improve both heat and mass transfer in the reaction bed. Studies have also shows the need to enhance the heat transfer in adsorption bed to match with the heat transfer of thermal fluids. Use of heat pipes and good thermal loop design could yield higher thermal performances of a sorption system, when coupled with adsorption beds to provide heating and cooling to the beds. A novel design with passive evaporation, known as rising film evaporation coupled with a gravity heat pipe was introduced for high cooling output. It has also been shown that heat and mass recovery in the internal sorption systems is critical, and novel arrangement of thermal fluid and refrigerant may result in high performance sorption systems. Based upon the above researches, various sorption systems have been developed, and high efficient performances have been reached. Typical sorption systems include (1) A silica gel-water adsorption water chillier with a COP about 0.55 when powered with 80°C hot water, (2) A CaCl2 -ammonia adsorption refrigerator with a COP over 0.3 at −20 °C when powered with 120 °C water vapor, which has a specific cooling power about 600 W/kg-adsorbent. The above mentioned systems have shown that solid sorption systems have become market potential products, and low grade thermal energy, which is usually considered as waste heat, could be utilized to provide high grade cooling. This paper gives details of high efficient solid sorption systems recently developed, their heat transfer design, thermodynamic system coupling, and performance test results. Some examples of low grade thermal powered cooling systems are also presented.

Commentary by Dr. Valentin Fuster
2010;():591-599. doi:10.1115/IHTC14-23396.

Fuel cells are electrochemical energy conversion devices that convert chemical energy in fuels directly into electrical energy, without the process of combustion. As a result, they are not constrained by the thermodynamic limitations of heat engines and therefore have the potential to achieve higher efficiencies. Various fuel cell types exist, operating from room temperature to over 1000 °C. This paper focuses on two of the leading fuel cell types, namely the lower temperature (80–120 °C) polymer electrolyte membrane fuel cell (PEMFC) and the higher temperature (500–1000 °C) solid oxide fuel cell (SOFC), with particular attention paid to the importance of thermal management and heat transfer in these systems, as it is thermal transients, and the appropriate design of the thermal management sub-system, that frequently limit fuel cell system performance and durability. Two examples of research from the authors’ laboratories are given; the first relates to the measurement and modelling of heat transfer in PEMFCs; the second to the thermal management of SOFCs.

Commentary by Dr. Valentin Fuster
2010;():601-619. doi:10.1115/IHTC14-23404.

Heat due to lattice vibration (phonons) is traditionally regarded as harmful for information processing. In this paper, we will demonstrate via numerical simulation, theoretical analysis and experiments that, phonons, can be manipulated like electrons. They can be used to carry and process information. Basic phononic devices such as thermal diode, thermal transistor, thermal logic gate and thermal memory will be discussed via nonlinear lattice model. Moreover, we will also discuss how to manipulate and tune thermal conductivity of nanostructure so that to control heat flow. Both theoretical and experimental works will be shown.

Commentary by Dr. Valentin Fuster
2010;():621-637. doi:10.1115/IHTC14-23405.

In many industrial processes or natural phenomena coupled heat and mass transfer and fluid flow take place in configurations combining a clear fluid and a porous medium. Since the pioneering work by Beavers and Joseph (1967), the modelling of such systems has been a controversial issue, essentially due to the description of the interface between the fluid and the porous domains. The validity of the so-called one-domain approach — more intuitive and numerically simpler to implement — compared to a two-domain description where the interface is explicitly accounted for, is now clearly assessed. This paper reports recent developments and the current state of the art on this topic, concerning the numerical simulation of such flows as well as the stability studies. The continuity of the conservation equations between a fluid and a porous medium are examined and the conditions for a correct handling of the discontinuity of the macroscopic properties are analyzed. A particular class of problems dealing with thermal and double diffusive natural convection mechanisms in partially porous enclosures is presented, and it is shown that this configuration exhibits specific features in terms of the heat and mass transfer characteristics, depending on the properties of the porous domain. From the viewpoint of the stability of convection in a horizontal layer where a fluid layer lies on top of a porous medium, the analysis shows that the onset of convection is strongly influenced by the presence of the porous medium. The case of thermal convection is fully detailed and many open problems arise in the field of double diffusive convection.

Commentary by Dr. Valentin Fuster
2010;():639-651. doi:10.1115/IHTC14-23406.

The heat transfer coefficient of convection from the wall to the flow depends on flow type, on surface temperature distribution in a stream-wise direction, and in transient cases also on time. In so-called conjugated problems, the surface temperature distribution of the wall and flow are coupled together. Thus, the simultaneous solution of convection between the flow and wall, and conduction in the wall is required because heat transfer coefficients are not known. For external and internal flows very accurate approximate analytical expressions have been derived for heat transfer in different kinds of boundary conditions which change in flow direction. Due to the linearity of the energy equation the superposition principle can be adopted to couple with these expressions the surface temperature and heat flux distributions in conjugated problems. In the paper this type of approach is adopted and applied to a number of industrial applications ranging from flat plates of electroluminecence displays to the optimization of heat transfer in fins, fin arrays and mobile phones.

Commentary by Dr. Valentin Fuster
2010;():653-669. doi:10.1115/IHTC14-23407.

The phenomena of direct contact condensation (DCC) of steam jet submerged into a water pool occurs due to the actuation of steam discharging devices in many industrial processes and there are practically two kinds of technical concerns to consider. The one is a concern on the thermal mixing in water pool. The other concern is on thermo-hydraulically induced mechanical loads on the structures of relevant systems. Both concerns may be inter-related with each other in terms of thermally-induced hydrodynamic loads on the relevant system. There are two kinds of viewpoints in terms of DCC-induced thermal mixing in a pool: the local hot spot, which may affect the stability of condensation phenomena, and the thermal stratification, which usually exists over the whole pool region. Both aspects can be well described only if the local behaviour of condensing steam jet and the resultant turbulent jet in a pool are well understood. In this paper, the DCC-related thermo-fluid dynamic features are discussed, based mainly on our experiences of developing the relevant engineering systems over the past years. Fundamental characteristics of condensing steam jets are discussed, including the local behaviour of condensing jets and the resultant turbulent jet to importantly affect the macroscopic circulation in a pool. Then the local analysis of condensing jet behaviour and the global analysis of thermal mixing in a pool are discussed with practical application to engineering in mind.

Topics: Condensation , Steam
Commentary by Dr. Valentin Fuster
2010;():671-689. doi:10.1115/IHTC14-23408.

Multiscale simulation is a rapidly evolving area of research that will have a great impact on computational mathematics and numerical modeling in engineering. In this keynote lecture following parts are included. First, what is multiscale problem. In the thermal and fluid science multiscale problems may be classified into two categories: multiscale process and multiscale system. By multiscale process we mean that the overall behavior is governed by processes occur at different length scales. By multiscale system we refer to a system that is characterized by a large variation in length scales. The cooling of an electronic system is such a typical multiscale system. Existing numerical methods for three geometric scales (macro, meso and micro) are briefly mentioned. In the second part the necessity of multiscale simulation is discussed. Examples are provided for multiscale process and multiscale system. In this lecture focus is put on the simulation of multiscale process. In the third section numerical approaches developed for the simulation of multiscale processes are presented. There are two types of simulation approaches. One is the usage of a general governing equation and solving the entire flow field involving a variation of several orders in characteristic geometric scale. The other is the so-called “solving regionally and coupling at the interfaces”. In this approach the processes at different length level is simulated by different numerical methods and then information is exchanged at the interfaces between different regions. The exchange of information should be conducted in a way that is physically meaningful, mathematically stable, and computationally efficient. The key point is the establishment of the reconstruction operator, which transforms the data of few variables of macroscopic computation to large amount of variables of microscale or mesoscale simulation. For different coupling cases the existing methods for such operators are briefly reviewed. In the fourth part, four numerical examples of multiscale simulation are presented: liquid flow in nanochannels with roughness by using MDS and FVM, flow and heat transfer in a micro nozzle by using DSMC in fluid and FVM in solid, flow past a cylinder and natural convection heat transfer in a square cavity by using coupled FVM and LBM. Finally, it is pointed out that we have a long way to go in order to have a successful full multiscale simulation for the complicated engineering problems as transport process in PEMFC and refrigerant condensation process on a enhanced surface. Further researches are highly required to establish robust and quick-convergent numerical solution approaches. Some further research needs are proposed.

Commentary by Dr. Valentin Fuster
2010;():691-708. doi:10.1115/IHTC14-23409.

Recent experimentation of boiling in different environments, namely in reduced or enhanced gravity and/or in the presence of electric fields, have shed new light on the comprehension of boiling phenomena and have focused the objectives of future investigation. The recent results achieved by the author and other research groups around the world are reported and discussed in the paper. After a short introduction on some fundamental phenomena and their dependence on force fields, pool and flow boiling are dealt with. In particular, it is stressed that due to increased coalescence peculiar flow regimes take place in reduced gravity, influencing the heat transfer performance. The application of an electric field may, in some instances, delay or avoid these regime transitions. In boiling at high flowrate, the phenomena are dominated by inertia and thus gravity-independent; however the threshold at which this occurs has still to be determined.

Commentary by Dr. Valentin Fuster
2010;():709-722. doi:10.1115/IHTC14-23411.

On October 30th 2009, a major industrial consortium initiated the so-called DESERTEC project which aims at providing by 2050 15% of the European electricity from renewable energy sources in North Africa, while at the same time securing energy, water, income and employment for this region. In the heart of this concept are solar thermal power plants which can provide affordable, reliable and dispatchable electricity. While this technology has been known for about 100 years, new developments and market introduction programs have recently triggered world-wide activities leading to the present project pipeline of 8.5 GW and 42 billion Euro. To become competitive with mid-load electricity from conventional power plants within the next 10–15 years, mass production of components, increased plant size and planning/operating experience will be accompanied by technological innovations which are presently in the development or even demonstration stage. The scale of construction, the high temperatures and the naturally transient operation provide formidable challenges for academic and industrial R&D. Experimental and theoretical research involving all mechanisms of heat transfer and fluid flow is required together with large-scale demonstration to resolve the combined challenges of performance and cost.

Commentary by Dr. Valentin Fuster
2010;():723-733. doi:10.1115/IHTC14-23414.

The performance goal of modern gas turbine engines, both land-base and air-breathing engines, can be achieved by increasing the turbine inlet temperature (TIT). The level of TIT in the near future can reach as high as 1700°C for utility turbines and over 1900°C for advanced military engines. To ensure the turbine airfoil component integrity operated under such a condition, advanced cooling capacity by both external and internal means is necessary to remove the excessive heat load from the turbine airfoil. This paper discusses state-of-the-art airfoil cooling technologies along with the associated thermal transport issues. Discussion is given based on five key regions on and around an airfoil: leading edge, main body, trailing edge, endwall and near tip. Potential implications and challenges of near-term developments in coal-gas based turbines on the cooling technologies are identified. A literature survey focusing primarily on the past four to five years since the last International Heat Transfer Conference has also been performed.

Commentary by Dr. Valentin Fuster
2010;():735-752. doi:10.1115/IHTC14-23420.

Heat transfer in foods is a commonplace operation in the home and restaurant, but is also the basis for a very large industry. Foods are complex non-Newtonian soft solids or structured liquids whose thermal behaviour is difficult to model; but engineering understanding is needed to develop processes that are safe and products that are attractive to the consumer. The increasing incidence of obesity in the developed world, and of food shortage elsewhere, demands that the industry adopts processes that give nutritious products in environmentally acceptable ways. This paper reviews the heat transfer problems that are found in food processing, with particular reference to the modelling of heating operations to ensure safety, problems that are found in the fouling and cleaning and process plant, and how heating and cooling are used to generate structure. Research challenges for the future are outlined.

Commentary by Dr. Valentin Fuster
2010;():753-773. doi:10.1115/IHTC14-23421.

Optimization of heat exchangers (HE), compact heat exchangers (CHE) and micro-heat exchangers by design of their basic structure is the focus of this work. Consistant models are developed to describe transport phenomena in a porous medium that take into account the scales and other characteristics of the medium morphology. Equation sets allowing for turbulence and two-temperature or two-concentration diffusion are obtained for non-isotropic porous media with interface exchange. The equations differ from known equations and were developed using a rigorous averaging technique, hierarchical modeling methodology, and fully turbulent models with Reynolds stresses and fluxes in the space of every pore. The transport equations are shown to have additional integral and differential terms. The description of the structural morphology determines the importance of these terms and the range of application of the closure schemes. A natural way to transfer from transport equations in a porous media with integral terms to differential equations with coefficients that could be experimentally or numerically evaluated and determined is described. The relationship between CFD, experiment and closure needed for the volume averaged equations is discussed. Mathematical models for modeling momentum and heat transport based on well established averaging theorems are developed. Use of a ‘porous media’ length scale is shown to be very beneficial in collapsing complex data onto a single curve yielding simple heat transfer and friction factor correlations. The general transport equations developed for a single phase fluid in a heat exchange medium have many more integral and differential terms than the homogenized or classical continuum mechanics equations. Once these terms are dealt with by closure, the resulting equation set is relatively simple and their solution is obtained using simple numerical methods quickly enough for multiple parameter optimization using Design of Experiment (DOE) or Genetic Algorithms (GA). Current efforts to significantly improve the performance of a HE for electronic cooling, a two temperature problem, and of a finned tube heat exchanger, a three temperature problem, are described.

Topics: Heat transfer
Commentary by Dr. Valentin Fuster
2010;():775-793. doi:10.1115/IHTC14-23422.

Recent advances in diagnostic methods are providing new capacity for detailed measurement of turbulent, reacting flows in which heat transfer is dominant. Radiation typically becomes dominant in flames containing soot and/or with sufficient physical size, so is important in many flames of practical significance. The presence of particles, including soot, increases the coupling between the turbulence, chemistry and radiative heat transfer processes. Particles also increase the difficulties of laser-based measurements by increasing the interferences to the signal and the attenuation of the beam. The paper reviews recent advances in techniques to measure temperature, mixture fraction, soot volume fraction, velocity, particle number density and the scattered, absorbed and transmitted components of radiation propagation through particle laden systems.

Commentary by Dr. Valentin Fuster

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