Identification of the Dominant Heat Transfer Mechanisms during Confined Two-phase Jet Impingement

Two-phase jet impingement is a compact cooling technology capable of dissipating the large heat fluxes required for thermal management of high-power electronics devices. It is important to understand the primary heat transfer mechanisms that occur during regimes of jet impingement for which boiling occurs, specifically in the confined impingement geometries common to electronics cooling applications. In this study, heat transfer from a surface is experimentally characterized in both confined jet impingement and pool boiling configurations. The dielectric liquid HFE-7100 is used as the working fluid. For the impingement configuration, the jet issues through a single orifice with a diameter of 2 mm, at exit velocities of 1 m/s and 3.33 m/s, into a confinement gap with an orifice-to-target spacing ratio of 3. Additional orifice-to-target spacings of 0.5 and 5 times the jet diameter are tested at the lower jet velocity. The heat flux applied at the surface was increased in steps to characterize the single-phase and two-phase heat transfer performance; all experiments were carried through to critical heat flux conditions. Over the range of velocities and orifice-to-target spacings tested, the jet impingement data in the fully boiling regime coincide with the pool boiling data. This result indicates, for the range of parameters considered in this study, that nucleate boiling is the dominant heat transfer mechanism in the fully boiling regime in confined jet impingement. The impinging jet velocity and orifice-to-target spacing only influence the single-phase heat transfer and critical heat flux.