Numerical investigation on dimpled target average heat transfer in free-surface water jet impingement and its enhancement effect versus flat plate target

Abstract

Jet impingement serves as an effective method to enhance heat transfer in diverse industrial applications, utilizing either a separate fluid from the ambient (free-surface jet) or identical fluids (submerged jet). The target surface undergoes distinct thermal processes, featuring zones like the stagnation zone, boundary layer formation, and the transition from laminar to turbulent wall flow. However, heat transfer efficiency diminishes significantly due to pressure gradient changes beyond the stagnation zone, impeding flow and boundary layer development. Addressing this decline through surface modification techniques, such as incorporating spherical dimples, emerges as an innovative approach. This study develops a numerical model via Computational Fluid Dynamics (CFD) simulations utilizing Volume of Fluid (VOF) modeling for water jet impingement on a flat plate target. The model’s validity is established by comparing hydrodynamic and thermal aspects in both laminar and turbulent scenarios against established experimental data in literature. Nine dimpled target surfaces, featuring diverse dimensional properties and positioning configurations, are examined using this model to explore potential enhancements in heat transfer intensity. The findings indicate a notable increase in the overall surface average Nusselt number, potentially reaching up to 50% by implementing dimples in the current context. Moreover, the study highlights that the radial distribution of dimples and the non-uniform flow path ahead of the incoming fluid, which differs from parallel flat flow, result in varying effects based on dimensional properties. For instance, it has been found that modifying dimensions such as deepening dimples or altering their proximity could yield contrary effects, emphasizing the need for an optimization methodology to determine the most efficient dimpled surface setup within a given geometry.