Thermal Performance Comparison for Five Liquid Heat Sink Designs

Five high-flow liquid-cooled heat sink designs are compared for the cooling of a single chip CPU. Five distinctive design configurations are considered with regard to the introduction, passage, and extraction of cooling fluid. The typical water flow rate is about 3.8 liters per minute (lpm) with flow passages in the primary heat transfer area ranging from 2 to 0.1mm. The design configurations are summarized and compared, considering: the primary convective heat transfer area, flow passage streamlining, acceleration mechanisms, and nominal fluid velocity in the primary heat transfer area. Overall pressure drop and thermal resistance are compared for varying flow rates of water. At the nominal flow, the pressure drops ranged from 1 kPa to 20 kPa. In the restrictive designs, such as nozzles, flow acceleration accounts for the largest source of pressure drop. In some designs, a large fraction of the overall pressure drop is due to circuitous flow associated with the introduction and/or extraction of flow which contributes little to heat removal. At the nominal flow, the overall thermal resistance varied from 0.14 to 0.18 C/W. As flow rate increases the overall thermal resistance decreases. Results indicated that 80 to 85% of the total thermal resistance is due to conduction and about 15 to 20% attributed to convection at the nominal flow rate. There is minimal thermal benefit for flow rates beyond twice the nominal while this substantially increases fluid pumping requirements. This study highlights design features which yield above average heat transfer performance with minimal pressure drop for high-flow liquid-cooled heat sinks.