| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 90 === A series of experimental and theoretical investigations on the fluid flow and heat transfer behavior in porous aluminum foam channels have been successfully performed. The parametric studies on the local and average heat transfer characteristics have been explored. The influencing parameters include steady-state air preheating temperature ratio at channel inlet (), Reynolds number (Re) and porosity/pore density of test specimen (/PPI). The ranges of the above-mentioned parameters are: = 1.8-3.0, Re = 2219-7595 and /PPI = 07-0.93/5-40PPI. In hydrodynamic aspect, the porous flow characteristics such as the Darcy number (Da), inertia coefficient (CF) and Darcy friction factor (f) have been investigated. In heat transfer aspect, from the study, it manifests that the erroneous deviation of the results evaluated by the transient liquid crystal method from the measured data become more significant for the cases with lower porosities. The main reasons to cause this discrepancy may be due to the following two effects: (1) the transient energy storage due to the matrix capacity and (2) the conductive heat transfer due to the direct contact between the solid matrix and channel wall. In order to overcome the deficiency of using the transient liquid crystal method to the study in porous channels with low porosities, a new semi-empirical model with an improved single blow method for exploring the heat transfer behavior in aluminum foam channels has been successfully developed. The heat transfer paths and mechanisms in porous channels have also been explored. The relationships among the fluid-solid, fluid-wall, effective solid-wall heat transfer coefficients and solid matrix capacity for porous channels have been presented. In addition, the influencing parameters on local and average heat transfer behavior have also been studied. The heat transfer enhancement of porous channels to hollow channels are, , much greater than unity and generally decrease with increasing Re. Two new correlations of and in terms of , Re, Da, and are proposed. Furthermore, a concept of the amount of enhanced heat transfer is also introduced. A new empirical correlation of j/f in terms of , Da and is presented.
As compared with the results evaluated by the transient liquid crystal method, the channel wall temperatures predicted by the semi-empirical model have a more satisfactory agreement with the experimental data, especially for the cases with smaller porosities. The limitations with relevant error maps of using the transient liquid crystal method in porous aluminum foam channels are finally postulated.
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