Summary
The rapid improvements in electronic devices have led to a high demand for effective cooling techniques. The purpose of this study was to investigate the heat transfer characteristics and performance of different aluminum heat sinks filled with aluminum foam for an Intel core i7 processor. The aluminum foam heat sinks were subjected to water flow covering the non‐Darcy flow regime (300‐600 Reynolds numbers). The bottom side of the heat sinks was heated with a heat flux between 8.5 and 13.8 W/cm2. Three different heat sinks were examined in this study. Models A, B, and C contained two, three and four channels, respectively. Each channel gap was filled with ERG aluminum foam. The distributions of the local surface temperature and the local Nusselt number were measured for each heat sink design. The experimental data were compared with the numerical results. The average Nusselt number was obtained for the range of Reynolds numbers, and an empirical correlation of the average Nusselt number as a function of the Reynolds number was derived for each heat sink. The pressure drop across the characteristics of each heat sink design was measured. The thermal performance of each aluminum foam heat sink was evaluated based on the average Nusselt number and the required pumping power. The experimental results revealed that model B achieved the highest average Nusselt number compared with models A and C. However, model C had the highest surface to volume ratio; the thermal boundary layers, which are formed on adjacent fin surfaces inside the aluminum foam, interface with each other causing a reduction in the overall heat transfer. The numerical results were in good agreement with experimental data of local Nusselt number and local temperature with maximum relative errors of 2% and 1%, respectively.
Ground source heat pumps (GSHP) have been used in various types of residential and commercial buildings due to their high efficiency. Numerical models are useful to predict the overall performance and ground temperature response of these systems. This paper presents a hybrid model that contains a modified finite element model and an analytical solution for a single conventional vertical borehole system. In this modified finite element model, turbulent heat transfer equations were solved for the ground heat exchanger and the actual building load variation and heat pump performance variation were considered. The present model was then used to explore an emerging geo-exchange technology, which involves the use of a bentonite slurry enhanced with graphite flakes in the vicinity of a borehole heat exchanger. The results revealed slight increases in the mean average ground temperature in the vicinity of the borehole by 1.1 C over 4 years. Furthermore, the analytical solution of the ground temperature response was in good agreement with the results obtained using the finite element model within a maximum relative error of 3% (0.5 C). The results revealed that the 40 m depth bentonite-based borehole achieved better performance than the conventional design by 5% to 13% in the monthly average COP.
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