Water-cooled micro/minichannel heat sinks are an important component in managing the temperature of electronic components, particularly where high density of heat rejection is required. This study examines the potential to decrease the thermal resistance and enhance convective heat transfer of a serpentine heat exchanger, by introducing chevron fins which create secondary flow paths. This novel design is found to significantly reduce both the pressure drop across the heat exchanger and the total thermal resistance by up to 60% and 10%, respectively, and enhance the average Nusselt number by 15%. A three-dimensional conjugate heat transfer model is developed and validated against experimental measurements, before being used to carry out a parametric study involving the chevron oblique angle, secondary channel width and heat flux. The design of the serpentine minichannel with chevron fins is then optimised in terms of the minichannel width, minichannel number and chevron oblique angle. A 50 point Optimal Latin Hypercubes (OLHC) Design of Experiment (DoE) is constructed within the design variable space, using a permutation genetic algorithm, and accurate metamodels built using a Radial Basis Function (RBF) approach. A Pareto front is constructed which enables designers to explore appropriate compromises between designs with low pressure drop and those with low thermal resistance.
An experimental and numerical investigation of water-cooled serpentine rectangular minichannel heat sinks (MCHS) has been performed to assess their suitability for the thermal management of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) devices. A Finite Element-based conjugate heat transfer model is developed, validated experimentally and used to determine the optimal minichannel width and number of minichannels for a case with a uniform heat flux of 100 W/cm 2. The optimisation process uses a 30 point Optimal Latin Hypercubes Design of Experiments, generated from a permutation genetic algorithm, and accurate metamodels built using a Moving Least Square approach. A Pareto front is then constructed to enable the compromises available between designs with a low pressure drop and those with low thermal resistance to be explored and an appropriate minichannel width and number of minichannels to be chosen. These parameters are then used within conjugate heat transfer models of a serpentine MCHS with silicon, silicon carbide, diamond and graphene heat spreaders placed above a GaN HEMT heating source of area 4.8 × 0.8 mm 2 , generating 1823 W/cm 2. A nanocrystalline diamond (NCD) layer with thickness of 2 µm is mounted on the top surface of the GaN HEMT to function as a heat spreader to mitigate the hot spots. The effect of volumetric flow rate and heat spreader thickness on the chip temperature has been investigated numerically and each of these has been shown to be influential. For example, at a volumetric flow rate of 0.10 l/min, the maximum chip temperature can be reduced from 124.7 o C to 96.7 o C by employing a 25 µm thick graphene heat spreader attached to the serpentine MCHS together with a NCD layer compared with a serpentine MCHS without these heat spreaders.
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