Book excerpt: This study expands upon the current knowledge of the relationship between the heat transfer and fluid flow characteristics of air-assisted water impingement jets. Fluid flow and heat transfer characteristics of air-assisted water jet impingement were experimentally investigated under a fixed water flow rate condition with varying relative height (H/d). The test fluids were water and air. The effects of nozzle-to-plate spacing at volumetric qualities [beta]=0.3, 0.5, 0.7, and 0.8 where [beta] is the ratio of the volume of air to the total volume of the two-phase mixture on the hydraulic jump diameter, stagnation pressure, and stagnation Nusselt number were considered. The results showed that stagnation Nusselt number, hydraulic jump diameter, and stagnation pressure increased as the relative height decreased and the volumetric quality increased with the maximum values occurring at H/d of 0.02 and a volumetric quality of 0.8. This research is most applicable in the use of cooling of industrial applications such as cooling of electronics and processing of materials.