Investigations of leakage mechanisms and its influences on a micro swing engine considering rarefaction effects

Considering rarefaction effects, this paper investigated mechanisms of the clearance leakage and its influences on a micro swing engine for the micro power generation by employing three different flow models named as discrete velocity direction (DVD1) model, Navier-Stokes equations with slip boundary conditions (NS-slip(2)) and no-slip boundary conditions (NS-no slip(3)). Using the DVD model, this paper firstly studied leakage mechanisms of a micro Couette-Poisueille flow. Factors which control the leakage in different regimes were obtained. Furthermore, the system-level predictions of the clearance leakage in the micro swing engine have been conducted by solving the Navier-Stokes equations. The leakage flow regime, patterns and characteristics were presented. Results by NS-slip and NS-no slip were compared to study the rarefaction effects. Finally, investigations of the engine size and the gap height on the engine performance have been conducted. The significance of the leakage in different engine size regimes was presented, and the results show that rarefaction effects affect the indicated thermal efficiency greatly with the decrease of the engine size scale. (C) 2016 Elsevier Ltd. All rights reserved.