Forced Convection Phase-Change Heat Transfer with StreamwiseCurvature and Two-Phase Approach Flow

This project is predominantly an experimental study of forced convection boiling heat transfer from small regions to a channel flow. Application of the results lie in the design of equipment where small, high-heat-flux regions must be cooled: x-ray sources for lithography and medicine, microwave klystrons, lasers, microelectronic and optical devices, gas turbines, fusion reactor instrumentation and first walls, high-speed aircraft leading surfaces and quenching in materials processing. Theoretical or scientific value lies in the description of the boiling behavior in situations where the thermal boundary layer and bubble boundary layer thicknesses are small relative to the channel size. Effects to be documented are: heating length, bulk velocity, subcooling, pressure, fluid type, streamwise curvature of the heated wall and the void fraction of the flow approaching the heated surface. The program begins by completing an ongoing study on the effect of wall concave curvature on subcooled flow boiling characteristics. In this study, all the voids are constrained to very near the heated surface. The next phase and the main portion of the study is one where the flow approaching the heated region is a two-phase mixture of vapor and liquid in thermodynamic equilibrium. In this study, the effect of approach flow void fraction and two-phase flow regime will be investigated in flow within straight channels and within concave-curved channels. With concave curvature, voids are rapidly transported away from the heated wall by the cross-stream pressure gradient established in the curved flow. This effect is presently being investigated for a situation where the approaching flow is a subcooled liquid. The continuation project will characterize the stronger benefit that will be seen when the entry flow is a two-phase mixture in that there will be a substantial increase, between straight flow and curved flow, of the heat flux at the point of departure from nucleate boiling (DNB). Once characterized and described, this can be capitalized upon in the design of cooling schemes for the above engineering systems.