Boundary-layer treatment of film condensation in the presence of a solid matrix
Boundary-layer treatment of film condensation in the presence of a solid matrix
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DOI：
10.1016/0017-9310(86)90191-2
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发表时间：
1986-06
影响因子：
5.2
通讯作者：
M. Kaviany
中科院分区：
文献类型：
--
作者：
M. Kaviany
LAMINAR, steady-state film condensation and boiling, along a plane surface submerged in a porous medium, have been studied analytically [l, 23 assuming that capillarity and non-Darcian effects are not significant. The results, based on these assumptions, give the Nusselt number, condensate flow rate, and film thickness as a function of the subcooling (or superheating) parameter. The Prandtl number, which is introduced through thecomparison between the thermal and momentum boundary-layer thickness, is not present because of the uniform film velocity distribution resulting from the application of Darcy’s law. The capillary pressure, which is proportional to cr (K/~)-“~ and depends on the saturation, can become significant at low permeabilities. As the permeability increases, the inertia and boundary effects become important and for very high permeabilities the results based on no rigid matrix present [3, 43 must hold. However, since the film thickness decreases with an increase in permeability, then for the boundary-layer treatment to be valid, the small length scale associated with the microstructure of the rigid matrix must be much smaller than the film thickness. If this condition is satisfied, then the non-Darcy regime can be examined and, also, the parameters indicative of transition to the Darcian regime can be determined. In this study the boundary layer and similarity treatment of film condensation in the absence of any solid matrix [3, 4] are extended to include the first-order resistance resulting from the presence of a solid matrix. This is done by applying an expansion method [5](up to a third order) which has previously been used for treating natural convection in porous media [6]. The findings are then compared to those based on application of Darcy’s law [1, 2].
