Effects of Thin Film Heat Spreader on Hot Spots Mitigation in Heat Sinks

The effects of graphene platelets and diamond based thin film heat spreaders on maximum temperature of integrated electronic circuits were investigated. A fully three-dimensional conjugate heat transfer analysis was performed to investigate the effects of thin film material and thickness on the temperature of a hot spot and temperature uniformity on the heated surface of the integrated circuit when subjected to forced convective cooling. Two different materials, diamond and graphene were simulated as materials for thin films. The thin film heat spreaders were applied to the top wall of an array of micro pin-fins having circular cross sections. The integrated circuit with a 4 × 3 mm footprint featured a 0.5 × 0.5 mm hot spot located on the top wall which was also exposed to a uniform background heat flux of 500 W cm−1. A hot spot uniform heat flux of magnitude 2000 W cm−2 was centrally situated on the top surface over a small area of 0.5 × 0.5 mm. Both isotropic and anisotropic properties of the thin film heat spreaders made of graphene platelets and diamond were computationally analyzed. The conjugate heat transfer analysis incorporated thermal contact resistance between the thin film and the silicon substrate. The isotropic thin film heat spreaders significantly reduced the hot spot temperature and increased temperature uniformity, allowing for increased thermal loads. Furthermore, it was found that thickness of the thin film heat spreader need not be greater than a few tens of microns

Heat exchanger based on paraffin/expanded graphite composites for breathing air cooling in fire

The enormous amount of heat in fires can push inhalation temperature to ~500 K, which is fatal to the civilians. However, conventional rescue respirators are unable to control the breathing air temperature. In this work, we utilized paraffin/expanded graphite (EG) composites to construct a heat exchanger for breathing air cooling. The material itself can be used as the mechanical support, the heat spreader and the heat absorber at the same time. The composites of 0~35 wt% EG were prepared and characterized. The results showed the paraffin was uniformly absorbed in the porous structures of EG. And the paraffin/EG composite with 25 wt% EG has better performance both in simulation and experiment. The heat exchanger constructed by this composite shows good cooling efficiency by cooling the inlet air from 500 K to a breathable 313 K and sustaining for more than 20 minutes.