Modeling and Optimization of Multilayer Minichannel Heat Sinks in Single-Phase Flow

Liquid-cooled small channel heat sinks are a promising heat dissipation method for high power electronic devices. Traditional mini and microchannel heat sinks consist of a single layer of high aspect ratio rectangular channels. An alternative approach investigated in this paper is to stack multiple layers of low aspect ratio (circular or square cross-section) channels together to create multiple layer minichannel heat sinks. These multilayer heat sinks can achieve high heat flux due to the high heat transfer coefficients from small channels coupled with the large surface areas from the multilayer structure. In this research, multilayer copper and silicon carbide (SiC) minichannel heat sinks were experimentally and computationally characterized in single-phase flow over various flow rates. The experimental data indicated that in many cases, multilayer heat sinks have significant advantages over single-layer equivalents with reductions in thermal resistance and pressure drop. In order to investigate the optimal design of such structures, a detailed 3-D resistance network model was developed and used to predict the heat sink surface temperature and fluid pressure drop. The model uses an uncoupled approach and was validated by compared with conjugate CFD simulations and the experimental data. An extensive parametric study was performed on copper and SiC heat sinks with respect to channel geometry, number of layers, and thermal conductivity. The simulations indicated that for a fixed overall heat sink flow rate, an optimum number of channel layers exists for copper and SiC because of the competing trends of increasing surface area and decreasing per channel flow rate as the number of layers increases. In addition, the heat sink “effectiveness” decreases with increasing number of layers as the thermal resistance from the top surface, where heat is applied, to the lower layers of the heat sink becomes excessive. In the simulation the optimized number of layers is highly dependent on material, channel width, channel aspect ratio, and wall thickness. If the pumping power is an important issue for the optimization, the heat sink with medium channel width is a wise choice, which achieves small thermal resistance with reasonable pressure drop.