Design And Optimization For The Double-layered Microchannel Heat Sink With Truncated Top Channels

Double-layered microchannel heat sink (DL-MCHS) owns many outstanding advantages such as compact size, high heat dissipation per heat load, low coolant requirement, and low operation cost; hence, it has attracted many attentions since it has been proposed. Up to now, many works involving theoretical analysis, experimental researches, and numerical simulations had been carried out to study the cooling performance of DL-MCHS. Although the DL-MCHS has been developed more than ten years, the heating effect that top coolant heats bottom coolant is still existed, which can significantly inhibit the further improvement of DL-MCHS. Hence, an improved design of double-layered microchannel heat sink with truncated top channels (TDL-MCHS) was proposed and the multi-parameter optimization by simplified conjugate-gradient method was adopted to optimize the TDL-MCHS.Firstly, single-parameter research was adopted to analyze the effects of the number of channels, channel width, channel height, and bottom coolant velocity on the cooling performance of DL-MCHS. The results show that there exists a strongly coupling relationship among the above parameters which means that the single-parameter research cannot obtain the optimal cooling performacne. Therefore, multi-parameter optimization should be carried out. In the multi-parameter optimization, number of channels, channel width, bottom channel height, and bottom coolant inlet velocity were selected as search variables to achieve the optimal heat sink performance. Then, two single-objective multi-parameter optimizations based on different objective functions (one is maximum temperature change on the bottom wall, the other is thermal resistance) were performed at a constant pumping power. The results indicated that the maximum temperature change on the bottom wall and the thermal resistance cannot achieve their optimal values simultaneously by the two single-objective optimizations. Thus a multi-objective optimization was carried out.After optimizations, the heating effect is still existed. In order to weak the heating effect, the TDL-MCHS was proposed. The simulations show that, there exists an optimal truncation position in the TDL-MCHS. The optimal truncation position exists at where top coolant has the same temperature with bottom coolant. In addition, the optimal truncation position is determined by the trade-off between the cooling effect and heating effect of top coolant. Furthermore, effects of the bottom channel length, number of channels, channel-to-pitch width ratio, and total pumping power on the performance of TDL-MCHS were investigated. It is found that for the original DL-MCHS with a long bottom channel, a large number of channels, a small channel-to-pitch width ratio or the heat sink is required to operate at a small pumping power, the heating effect of top coolant is found to be more obvious. Thus, the truncated design is strongly recommended.Finally, to further improve the cooling performance of the TDL-MCHS and look for the optimal truncation position, a multi-parameter optimization for the TDL-MCHS has been carried out. In the multi-parameter optimization, the number of channels, channel width, channel height, and truncation length of top channels are employed as search variables, pumping power, and coolant volumetric flow rates are chosen as constraint conditions, and thermal resistance is regarded as objective function. The optimization begins with three different initial guesses. The results show that the optimal thermal resistance is 0.102 K/W for a constant pumping power of 0.05 W, which is respectively reduced by 60.3%,49.3%, and 56.2% compared with the three initial designs; while, for a constant coolant volumetric flow of 200 ml/min, the optimal thermal resistance is 0.093 K/W which is reduced by 31.1%,32.6%, and 36.3% respectively.