Radial parallel plate flow with mechanical agitation

Abstract

Computer processors have significant and rising cooling requirements, with electronics cooling estimated to consume 1% of global energy consumption. An integrated fan heat sink was designed to help alleviate this issue, and is designed to simultaneously improve heat transfer and efficiency. Current designs chiefly focus on improving heat transfer without concern for overall energy efficiency. The novel heat sink integrates fans directly into a heat pipe loop, with impellers located in between series of parallel condensers, with a single evaporator located on the interface of the heated chip. The proximity of the fans to the hot surfaces improves overall heat transfer while maintaining a high efficiency. The impellers push air radially outward through parallel heated plates, with an air intake from the center. Little research has been done on the fluid mechanic properties of this physical situation, particularly with an impeller agitating the air stream. For the design of the integrated heat sink, it is desirable to understand the thermal properties of the channel in terms of various parameters such as impeller geometry and speed, gap thickness, and mass flow rates. Experiments were performed to determine the local heat transfer coefficient between two heated plates with the presence of an impeller with different parameters. The results from these tests were used to infer the properties of the flow. These experiments are designed to replicate the flow in one distinct channel in the integrated fan heat sink, and can be expanded to observe the convective heat transfer characteristics of the entire device. It was found that the impellers enhance heat transfer significantly beyond that of inducing flow, by up to five times. It was then shown that the presence of impeller blades have a direct effect on the heat transfer by comparing different size impellers. Both mass flow rate (radial Reynolds number) and rotational velocity of the impeller were found to have significant, independent, effects on heat transfer. The cause of the increase in heat transfer from the blades is from an increase in turbulent mixing.