Thermo-fluidic behaviour of diamond and hourglass microchannels: Investigation from the second law viewpoint

Abstract

The potential of diamond and hourglass microchannels from the second law perspective is explored to amplify the effectiveness of the thermal device for various thermodynamic systems. The chosen design variables cover all relevant physical traits, such as the divergence-convergence effect (divergence-convergence angle, width ratio), geometrical considerations (depth, length), input variables (Reynolds number, supplied heat flux), and conjugate effect (substrate material and thickness). The performance is quantified in terms of thermal and frictional entropy generation, total entropy generation, and augmented entropy generation number. Results reveal that the proposed geometries outperform uniform microchannels for all cases except at higher Reynolds numbers for high divergence-convergence angle, width ratio, length, and low supplied heat flux. The outcome also demonstrates that the diamond microchannel performs slightly better than the hourglass microchannel for all cases except at shorter lengths and higher aspect ratio for Reynolds numbers above 100, owing to flow recirculation zones and the conjugate effect. Additionally, the first and second law attributes of diamond/hourglass microchannels are compared and analyzed. Diamond/hourglass microchannels with superior second law performance at a given design constraint need not exhibit better first law performance simultaneously, and vice versa. Lastly, the current investigation sheds light on design possibilities that enhance the potential of proposed geometries through prudent exploitation of the physical characteristics. The outcomes of this research have the potential to design diamond/hourglass microchannels with the appropriate geometry for a plethora of heat transfer applications.