The Thermal Characteristics Of Multilayer Minichannel Heat Sinks In Single-Phase And Two-Phase Flow

摘要

Liquid cooled small channel heat sinks have become a promising heat dissipation method for future high power electrical devices. Traditional mini and microchannel heat sinks consist of a single layer of low-aspect ratio rectangular channels. The alternative new heat sinks are fabricated by stacking many channels together to create multiple layer channels. These multilayer heat sinks can achieve high heat flux due to high heat transfer coefficients from small channels and large surface area from multilayer structure. In this research, multilayer copper and silicon carbide (SIC) minichannel heat sinks were tested in single-phase flow. It was shown that multilayer heat sinks have significant advantages over single-layer equivalents with reductions both in thermal resistance and pressure drop. A 3-D resistance network model for single and multilayered heat sinks was developed and validated. Parametric study and optimization on copper and SiC heat sinks with respect to channel geometries, number of layers, and heat sink conductivity were conducted by using the model.Both copper and SiC heat sinks were also tested in two-phase flow. In experiments, the multilayer copper heat sinks achieved smaller average surface temperature than their single-layer counterpart at low heat flux. However the multilayer copper heat sinks gradually lost stability at high heat flux, which lead to increased surface temperature. The redistribution of flow in different layers caused by pressure discrepancy in different layers was believed to be the cause. A three-zone model, which dividing the flow in small channels into three distinguishing parts: single-phase flow, subcooled boiling flow, and saturated boiling flow, was proposed to describe the different two-phase flow regimes. In each zone, the local heat transfer coefficient was computed by corresponding correlation. Several boiling correlations combined with the resistance network model were used to compute the heat sink surface temperature distributions, which were compared with experimental results. It was found the classical boiling correlations for macro channels are not suitable for the minichannels, frequently overestimating the boiling heat transfer coefficient. Boiling correlations for small channels are more consistent with experimental data and the predictions of Yu's correlation match the experimental results best.