Heat exchanger improvement via curved, angular and wavy microfluidic channels: A comparison of numerical and experimental results

In order to improve upon a conventional straight microchannel heat sink, a range of curved, angular and wavy microchannels were designed in order to increase fluid mixing via the occurrence of secondary flow interactions, in particular Dean vortices, hence augmenting heat transport. Both numerical models conducted in FLUENT and laboratory experiments were employed to investigate the heat transfer enhancement of a range of geometries (single curved, wavy, sawtooth, U-turn and square-wave). In both studies, every channel demonstrated significantly higher Nusselt Numbers and Thermal Performance Factors (TPF) than an equivalent straight channel, despite an increase in pressure drop. The relative order of the channels in terms of TPF was the same for both experiments and numerical simulations, with the exception of the U-turn channel which performed better in the former. However, experimental TPF results were found to be 15–20% of those from the simulation — these differences are associated with the relative simplicity of the numerical model and additional non-linear impacts in the experiments. Overall, wavy channels were found to have superior performance, especially over angular channels with sharp turns, thus it is suggested that wavy microchannels are the most advantageous designs for the development of heat sinks, especially in terms of minimising pressure drop whilst still making use of the enhanced heat transfer properties of Dean vortices. Finally, for a given wavy channel, an optimal input flow rate condition is also determined.