Active heat transfer enhancement in air cooled heat sinks using integrated centrifugal fans

Abstract

The enhancement of convective heat transfer in an air-cooled heat sink using integrated, interdigitated impellers was investigated. The experimentally investigated heat sink is representative of a subcomponent of an unconventional heat exchanger with a loop heat pipe, multiple parallel flat-plate condensers, and integrated, interdigitated centrifugal fans, designed to meet the challenges of thermal management in compact electronic systems. The close integration of impeller blades with heat transfer surfaces results in a decreased thermal resistance per unit pumping power compared to conventional forced convection heat sinks.The fan performance (i.e.fan curve and power consumption) and heat transfer of a single integrated fan heat sink were experimentally characterized for 12 impeller designs and modeled in terms of dimensionless correlations. Correlations were developed to give estimates of the dimensionless fan curve and the dimensionless power curve based on the fan geometry. Additionally, a two-parameter correlation was developed to estimate the dimensionless heat flux based on the fan’s operating point. The heat transfer in the integrated fans was observed to be a function of the operating point (i.e. the rotational speed of the impeller and the flow rate of air), with only a weak direct dependence on the fan geometry. The insensitivity of the heat transfer performance to the impeller geometry greatly simplifies the design process of integrated fan heat sinks because the fan design can be optimized independently of the heat transfer performance. Finally, the heat transfer enhancement (compared to pressure-driven flow at the same flow rate) appears to be due to turbulent flow structures induced by the impeller.