The utilization of novel jet extension designs in multi-jet impingement for crossflow mitigation and thermal efficiency enhancement

The aim of this study is to mitigate the distorting effect of crossflow on jet flow and to enhance heat transfer performance in multi-jet impingement heat transfer. To accomplish this objective, novel jet extension designs are proposed: a design with uniform jet extension, a design with linear jet extension in the streamwise direction, a design featuring an initial increase followed by a decrease, a design featuring an initial decrease followed by an increase, and a design where the last five jets exhibit a uniform extension inside the region mostly influenced by crossflow. The effects of various novel jet extension designs on flow and heat transfer are analyzed numerically in this study, focusing on the following: velocity contours, streamlines and velocity vectors, Local Nusselt number variations, variations of the average Nusselt number, friction coefficient, and thermal enhancement factor with Reynolds number. The study findings indicate that the investigated nozzle extension designs yield a notable enhancement of 13.26% in heat transfer. However, it is important to note that these designs may also lead to a substantial rise of 39% in the friction coefficient. In relation to thermohydraulic performance, it is found that all extension designs exhibit better results when compared to the reference state. Notably, the uniform extension design with dimensionless nozzle length of 2 demonstrates a higher degree of thermohydraulic performance.