This paper presents the results of heat transfer measurement and analysis for two 5×5×1 cm porous channels. The channels were made of sintered bronze beads with two different mean diameters, dp=0.72 and 1.59 mm. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 0.8, 1.6, 2.4, and 3.2 W/cm2 with air velocity ranging from 0.16 to 5 m/s and inlet air pressure of 1~3 atm. The measurement covers the data in both thermal entrance and thermally fully developed regions. The local Nusselt numbers were correlated in the fully developed region. The fully developed Nusselt numbers were analyzed theoretically by using a non-Darcy, two-equation flow model. Heat transfer between the solid and fluid phases was modeled by a relation of the form hloc=ARen. A wall function was introduced to model the transverse thermal dispersion process for the wall effect on the lateral mixing of fluid. The predicted fully developed Nusselt numbers are in good agreement with the measured values.

A study of non-Darcian forced convection in an asymmetric heating sintered porous channel is carried out to investigate the feasibility of using this channel as a heat sink for high-performance forced air cooling in microelectronics. A volume-averaging technique is applied to obtain the macroscopic equations with the non-Darcian effects of no-slip boundary, flow inertia, and thermal dispersion. Local non-thermal-equilibrium is assumed between the solid and the fluid phases. The analysis reveals that the particle Reynolds number significantly affects the solid-to-fluid heat transfer coefficients. A wall function is introduced to model the transverse thermal dispersion process for the wall effect on the lateral mixing of fluid. The local heat transfer coefficient at the inlet is modeled by a modified impinging jet result, and the noninsulated thermal condition is considered at exit. The numerical results are found to be in good agreement with the experimental results in the ranges of 32 ≤ Red ≤ 428 and q = 0.8 ~ 3.2 W/cm2 for Pr = 0.71.

This work presents visualization and measurement of the evaporation resistance for operating flat-plate heat pipes with sintered multi-layer copper-mesh wick. A glass plate was adopted as the top wall for visualization. The multi-layer copper-mesh wick was sintered on the copper bottom plate. With different combinations of 100 and 200 mesh screens, the wick thickness ranged from 0.26 mm to 0.8 mm. Uniform heating was applied to the base plate near one end with a heated surface of 1.1×1.1 cm2. At the other end was a cooling water jacket. At various water charges, the evaporation resistances were measured with evaporation behavior visualized for heat fluxes of 16–160 W/cm2. Quiescent surface evaporation without nucleate boiling was observed for all test conditions. With heat flux increased, the water film receded and the evaporation resistance reduced. The minimum evaporation resistances were found when a thin water film was sustained in the bottom mesh layer. With heat flux further increased, partial dry-out appeared with dry patches in the bottom mesh holes, first at the upstream end of the heated area and then expanded across the evaporator. The evaporation resistance rose in response to the appearance and expansion of partial dry-out. When the fine 200 mesh screen was used as the bottom layer, its thinner thickness and stronger capillarity led to smaller minimum evaporation resistances.

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This paper investigates the effects of peripheral wall conduction and Darcy number on laminar mixed convection in the fully developed region of a horizontal square porous channel with a uniform heat input. Because of the combined effects on nonaxisymmetric channel configuration, buoyancy-induced secondary flow, and noninfinite wall conduction parameter, the flow and heat transfer characteristics are greatly affected by the peripherally nonuniform wall temperature distribution. A modified Darcy-Forchheimer-Ergun flow model in the porous medium and a finite-difference method are applied. Secondary flow patterns, isotherms, wall temperature distributions, the friction factor, and the Nusselt number are presented for a flow in the Darcian porous medium (Da→0) to a pure fluid flow (Da → ∞) with Kp = 10−4 − 104, Gr = 0 − 1010, and Pr = 0.1, 0.73, 7.2, and 100. Wall temperature distributions and the Nusselt numbers are compared with existing experimental data.