Experimental study of single and doublet liquid jet impingement on the liquid film of a horizontal heated plate

This study used infrared thermography to experimentally investigate heat transfer from liquid jet impingement on a horizontal heated plate. The effects of the jet-to-surface height ratio (18.75–75), impingement angle (60°- 120°), and jet Reynolds number (793–3178) were examined to assess their influence on surface liquid film behavior and cooling performance. When the liquid jet hits the heated surface, it creates a hydraulic jump region and a stable flow liquid film. At lower Reynolds numbers, heat transfer approaches evaporation conditions, confining the hydraulic jump near the stagnation region and eliminating surface wave patterns. Doublet jets impingement causes atomization and enhances local disturbances in the liquid film on the surface, leading to improved heat transfer in the hydraulic jump region. Increasing the impingement height led to the noticeable formation of a liquid column from the impinging jets, with optimal heat transfer observed at a jet-to-nozzle height ratio of 50. However, further height increments disrupt the liquid ligaments, inducing excessive droplet formation, thereby reducing jet momentum and heat transfer. A jet impingement angle of 90° consistently results in superior heat transfer improvement, regardless of the jet-to-surface height ratios. Doublet jets increase Nusselt numbers by 18–233% compared to single jets across the range of jet Reynolds numbers studied. The findings show that impinging jet collision and jet impingement-driven liquid film effects impact heat transfer distribution. Doublet jets are more effective than single jets at a fixed cooling flow rate, suggesting that converting traditional liquid impingement jets to a doublet configuration can enhance cooling performance in confined spaces.