Couette-Poiseuille flow over a backward-facing step: Investigating hydrothermal performance and irreversibility analysis

The present study investigates the hydrothermal performance of Couette -Poiseuille flow over a backward-facing step. With a focus on the irreversibility analyses, the study sheds light on the flow behavior and explores the impact of key parameters, including Reynolds number, and wall terminal velocities. The study investigates a range of laminar Reynolds numbers between 100 and 800, as well as wall terminal velocities, Ut between -3 and 3. Notably, the results reveal a unique flow structure appears at negative Ut, where multiple separation zones (bounces) form downstream of the step. The number of bounces depends on both Re and Ut. An enhancement in the Nusselt number can be observed as the value of -Ut increases, which can be directly correlated to the increase in the number of bounces and the decrease in the reattachment length. On the contrary, the increase in the +Ut results in a decrease in heat transfer, driven by the increase in the reattachment length. The thermal performance factor, TPF shows an improvement for Re of 200 and 400 at Ut of -0.5, while TPF worsens as the value of -Ut increases due to the pressure drop induced by separation bubbles. Thermal entropy generation was identified as the main source of irreversibility processes for all cases.