Convective and boiling heat transfer from a heated surface to an impinging, planar jet of water
Abstract
Cooling of hot rolled steel strip is often accomplished with planar, impinging jets of water. Liquid jet cooling is also well suited for dissipating the heat generated by microelectronic circuits. Although thorough studies of transport processes in impinging gas jets have been performed, the data base and predictive methods for impinging liquid jets are relatively undeveloped. The important heat transfer mechanisms for liquid jet cooling have not been identified. Boiling studies have been limited to the region directly beneath the jet. Methods and equipment have been developed for measuring the heat transfer to an impinging liquid jet. The rationale for each approach has been carefully documented. Alternative methods and designs are also described. Surface temperature distributions were measured for heat fluxes of 0.25 to 2.5 MW/m$\sp2$, jet velocities of 1.8 to 4.5 m/s and water temperatures of 30 to 60$\sp\circ$C. These measurements are unique in that heat fluxes sufficient to induce steady convective boiling were delivered to an area large enough to accommodate local measurements both in the impingement and parallel flow regions. The results of this study include local heat transfer coefficients for single phase convection, partial boiling and fully developed nucleate boiling. Heat transfer in the laminar boundary layer was shown to be sensitive to free stream turbulence. The response of boiling and non-boiling heat transfer processes to changes in the heat flux, flow rate and fluid temperature were described on the basis of surface temperature data and the results of a photographic study. Boiling lowered the critical Reynolds number for the onset of boundary layer turbulence. Subsequent mixing in the boundary layer reduced surface temperatures, thereby reducing the number density of active nucleation sites. Surface temperatures approached a uniform value when the heat flux was sufficiently high to support vigorous nucleate boiling.
Degree
Ph.D.
Advisors
Viskanta, Purdue University.
Subject Area
Mechanical engineering
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