Temperature-Controlled Transition Boiling at the Stagnation Zone during Submerged Jet Impingement of a Dielectric Fluid

Two-phase jet impingement offers high heat transfer coefficients suitable for thermal management in applications ranging from metals processing to electronics cooling. Most prior fundamental studies focus on heat-flux-controlled nucleate boiling up to the critical heat flux (CHF). There has been comparatively little investigation of two-phase jet impingement under surface-temperature-controlled conditions, despite applications that impose heating conditions that lie between the extremes of prescribed flux versus temperature. Exploring boiling regimes that occur during temperature-controlled conditions is important to understand the design space. In particular, two-phase jet impingement differs from pool boiling in the transition boiling regime. Impingement of subcooled liquid rewets the surface, thereby delaying the start of complete film boiling in the stagnation zone. As the surface temperature increases, the heat flux dissipated is relatively constant, forming a so-called “shoulder” on the boiling curve. Prior studies of this shoulder effect exclusively use water as the working fluid. In this study, temperature-controlled submerged jet impingement is experimentally characterized using the dielectric liquid HFE-7100. A single 3 mm-diameter jet orifice impinges on a 9.8 mm-diameter circular copper heater surface covered by the jet stagnation zone. The shoulder effect is observed by incrementing the surface superheat in the transition regime using a PID controller. The boiling data are supplemented by high-speed imaging to relate the flow phenomena observed in the confinement gap to the temperature-controlled boiling curve performance.