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Heat Transfer at an Evaporating Front in Porous Media

[+] Author Affiliations
V. K. Chaitanya Pakala, O. A. Plumb

University of Wyoming, Laramie, WY

Paper No. HT2009-88240, pp. 317-326; 10 pages
doi:10.1115/HT2009-88240
From:
  • ASME 2009 Heat Transfer Summer Conference collocated with the InterPACK09 and 3rd Energy Sustainability Conferences
  • Volume 3: Combustion, Fire and Reacting Flow; Heat Transfer in Multiphase Systems; Heat Transfer in Transport Phenomena in Manufacturing and Materials Processing; Heat and Mass Transfer in Biotechnology; Low Temperature Heat Transfer; Environmental Heat Transfer; Heat Transfer Education; Visualization of Heat Transfer
  • San Francisco, California, USA, July 19–23, 2009
  • Conference Sponsors: Heat Transfer Division
  • ISBN: 978-0-7918-4358-1 | eISBN: 978-0-7918-3851-8
  • Copyright © 2009 by ASME

abstract

Evaporating fronts propagate through porous media during drying processes, underground coal gasification, geothermal energy production from hot dry rock, and around nuclear waste repositories. Present work will focus on the one-dimensional heat transfer at the interface between vapor saturated porous matrix and water saturated porous region and evaluate the conditions for which various approximations yield an accurate representation of front velocity. An implicit finite difference scheme is utilized to simulate the propagation of an evaporating front in a porous medium saturated with water and undergoing the phase change process. The assumption of local thermal equilibrium (LTE) which results in a one-equation model and a simple two-equation model that does not assume LTE are examined by comparison with a quasi-analytic numerical model. We consider the case for low Reynolds number, hence Nusselt number is assumed constant. Results illustrate that the one-equation model does not yield accurate results even if the length scale for diffusion in the solid phase is relatively small. The one-equation model predicts faster front propagation than the two-equation model. It is illustrated that the one-equation model yields satisfactory results only when thermophysical properties characterized by the volume weighted ratio of thermal diffusivities is reduced to an order of magnitude less than those for the applications of interest. In addition, consistent with the established “rule of thumb”, for Biot < 0.1, the traditional two-equation model which makes the lumped capacitance assumption for the solid phase compares well with a two-equation model that more accurately predicts the time dependent diffusion in the solid phase using Duhamel’s theorem.

Copyright © 2009 by ASME

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