The Effect of Confinement on the Development of an Axisymmetric Wall Jet in Confined Jet Impingement

Impinging jets have been widely used in the industry for cooling, heating, drying and many other purposes due to their excellent level of mass and heat transfer capacities. When issued into a confinement gap fully filled with working liquid, which is a typical configuration for the compact cooling devices designed to handle the extremely high heat fluxes generated by continuously working electronic components, they are classified as submerged confined impingement jets. Though the complicated flow field induced by the jet has attracted enormous amount of research efforts from heat transfer as well as fluid dynamics points of view, many key questions still remain unanswered. The present work reports a detailed experimental study of the flow field surrounding an axisymmetric, confined, impingement jet using stereo particle image velocimetry (SPIV). The experiments are conducted at three different orifice-to-plate spacings (2, 4 and 8 jet diameters) across Reynolds number ranging from 1000 to 9000. A maximum spatial resolution of 25 μm is achieved and the temporal resolution of the measurement remains 750 Hz. Special attention has been paid to the development of the triple-layered wall-jet with incomplete self-similarity. The jet core length and expansion angle for the vertical impingement jet has been calculated and presented. At small confinement height, the recirculating vortical structure has been found to strongly affect the wall-jet development. These flow field measurements and analysis will serve to inform a variety of practical applications in which impinging jets are used.