Numerical Simulation of Exhaust Gas Cooling in Channels with Periodic Elbows for Application in Compact Heat Recovery Systems

Miniature and Micro devices represent the new frontier for advanced heat and mass transfer technology. Due to the small length scales, the use of CFD is very useful for designing and optimizing microfluidic devices since experimentation and visualization at these scales can be difficult. In this work a high temperature air microfluidic cooling strategy for applications such as compact waste heat recovery, exhaust gas recirculation and fuel cell thermal management is proposed. Initially, the application of a simple straight microchannel is considered. In an effort to partially compensate for the poor thermal properties of air, right-angle bends are introduced in order to induce Dean vortices which periodically restart the thermal boundary layer development, thus improving the heat transfer and fluid mixing. Numerical simulations in the range of 100 ≤ ReDh ≤ 1000 have been carried out for channels of square cross-section. Channel wall lengths of 1.0 mm are investigated for elbow spacings of 5 mm, 10 mm and 15 mm. High temperature air (300°C) at atmospheric inlet pressure is the working fluid. The results indicate that the elbows substantially improve the local and average heat transfer in the channels while increasing the pressure drop. Design considerations are discussed which take into account the heat transfer and pressure drop characteristics of the channels.