Thermal-hydraulic performances and synergy effect between heat and flow distribution in a truncated doubled-layered heat sink with Y-shaped fractal network

In this paper, a novel truncated double-layered (TDL) heat sink with Y-shaped fractal network are proposed. First, thermal and hydraulic performances of double-layered (DL) bionic heat sink are investigated, it's found that though DL heat sink presents lower peak temperature, there is still a large temperature gradient around the inlet. Therefore, the DL heat sink is improved to a TDL one, where the top layer of heat sink is partially truncated. Results show that TDL heat sink improves temperature uniformity around the inlet by 24-30% and requires less pumping power. It's interesting to notice that heat exchange in two layers aren't equal under the same flow rate in each layer. Heat exchange ratio (Q(eff1)/O-eff2) in DL heat sink rises from 1.26 to 1.33 with increasing flow rate, while in the TDL one, it rises from 1.31 to 1.39. To make the best of heat transfer advantage of the bottom layer, a MATLAB function based on flow ratio and thermal resistance are developed and an optimal flow ratio lambda = 2 with the minimum thermal resistance is obtained. It's found that there is a waste of cooling potential when lambda not equal 2, while the cooling potentials of fluids are fully utilized in two layers at lambda = 2, where the outlet temperatures in two layers are the same. In the end, the relationship between heat and flow distribution is discussed and it's revealed that only when heat distribution is accordant with flow distribution Q(eff1)/Q(eff2) = lambda, can the TDL heat sink achieve the best cooling performance. (C) 2019 Elsevier Ltd. All rights reserved.