Heat Exchanger Improvement Via Curved Microfluidic Channels: Impacts of Cross-Sectional Geometry and Dean Vortex Strength

Abstract

The efficiency of conventional heat exchangers is restricted by many factors, such as effectiveness of convective heat transfer and the cost of their operation. The current research deals with these issues by developing a novel method for building a lower-cost yet more efficient heat sink. This method involves using a specially designed curved microchannel to utilize the enhanced fluid mixing characteristics of Dean vortices and thus transferring heat efficiently. Numerical models have been employed to investigate the heat transfer enhancement of curved channels over straight equivalents, with the aim of optimizing the heat exchanger design based on the parameters of maximizing heat transfer while minimizing pressure drop and unit cost. A range of cross-sectional geometries for the curved channels was compared, showing significantly higher Nusselt numbers than equivalent straight channels throughout and finding superior performance factors for square, circular, and symmetrical trapezoidal profiles. Due to the difficulty and expense in manufacturing circular microchannels, the relatively simple to fabricate square and symmetrical trapezoidal channels are put forward as the most advantageous designs. The variation of Nusselt number over the length of the channel for a range of different curvatures (and hence Dean numbers) is also examined, showing significantly higher heat transfer occurring in strongly curved channels, especially in areas where the generated Dean vortices are strongest. The variation in Nusselt number was found to form the shape of an “arc.” In this way, a relationship between the Dean number and the Nusselt number is characterized and discussed, leading to suggestions regarding optimal microfluidic heat transfer design.