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A Minichannel Heat Exchanger System for Heating, Boiling, and Superheating Water by Radiant Combustion

[+] Author Affiliations
Mikel L. Sawyer, Aly H. Shaaban

Applied Research Associates, Tyndall AFB, FL

Reza Salavani

Air Force Research Laboratory, Tyndall AFB, FL

Paper No. HT-FED2004-56582, pp. 511-519; 9 pages
doi:10.1115/HT-FED2004-56582
From:
  • ASME 2004 Heat Transfer/Fluids Engineering Summer Conference
  • Volume 4
  • Charlotte, North Carolina, USA, July 11–15, 2004
  • Conference Sponsors: Heat Transfer Division and Fluids Engineering Division
  • ISBN: 0-7918-4693-8 | eISBN: 0-7918-3740-8
  • Copyright © 2004 by ASME

abstract

A minichannel steam generator is being developed for a fuel reformer. The reformer will convert jet fuel to a hydrogen-rich stream for a 10 kW fuel cell. A first model has been built and tested. It was a once-through design with of two sequential heat exchangers. Exhaust gases produced saturated liquid in the first unit. The second surrounded a radiant propane burner. The system heated 1.2 to 2.6 gm/s of de-ionized water to more than 650 °C at exit pressures from 106 to 240 kPa. These flows and temperatures meet the requirements for the 10 kW fuel reformer. The minichannel system operated across three regimes: liquid heating, boiling, and superheating. It used multiple channels in parallel. At certain locations, the number of the parallel channels was changed to restrain the total pressure drop. The channel hydraulic diameter was 0.14 cm. The Reynolds number for the water ranged from 620 to 1,260 in the boiling section and from 1,260 to 3,140 in the superheating section, based on averaged fluid properties. The total pressure drop in the heat exchanger pair ranged from 470 to 870 kPa. The water absorbed heat fluxes ranging from 0.3 to 1.2 W/cm2 in the single-phase regions and 4.7 to 9.8 W/cm2 in the boiling region. These values were based on the wetted wall area. The boiling data falls in the range of published results for similar mass flux. An increased capacity for absorbing heat flux was demonstrated as coolant mass flux or Reynolds number increased. This paper also discusses the reasons for calculating heat flux based on heated area and based on wetted channel area. The need to identify clearly the basis of heat flux is addressed.

Copyright © 2004 by ASME

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