Heat transfer and entropy generation in air jet impingement on a model rough surface

Air jet impingement is an effective enhanced heat transfer technique which has been widely applied in cooling of electronic components and drying of continuous sheets of materials, etc. Although steady and unsteady impingement systems have led to many studies on jet impingement flow and heat transfer, the vast majority of them focus on smooth surfaces. As the flow and thermal physics of jet impingement on a rough surface are significantly different from that on a smooth surface, a numerical study was performed on the two-dimensional air jet impingement with a model rough surface by computational fluid dynamics method. A sinusoidal wave was employed to model the rough impinging target surface subjected to a slot jet nozzle. A dimensionless heat transfer enhancement factor was introduced to quantify the effect of jet flow Reynolds number, jet impingement dimension, and surface roughness as well as temperature difference between jet flow and impinging target on the heat transfer of jet impingement. It is observed that the roughness effect is minimal in the impingement zone while it is prominent in the wall jet region, and the surface roughness plays a dominant role on the enhancement factor of heat transfer rate compared with jet geometrical dimension, Reynolds number of jet flow as well as temperature difference. Furthermore, entropy generation analysis was also performed on the heat and mass transfer in air jet impingement, and optimal designs were found with entropy generation minimization principle accordingly.