David T. Vader

Electronics package with improved thermal management by thermoacoustic heat pumping

Electronic chips are cooled to an efficient operating temperature by engaging their exposed planar surfaces with a heat sink assembly. The heat sink assembly is a part of the cold end heat sink of a thermoacoustic heat pump that utilizes either traveling wave or standing wave heat pumping to transport heat from the cold end heat exchanger to the warm end heat exchanger, utilizing a coaxial pulse tube refrigerator to pump or transport the heat from the electronic chips and the cold end heat exchanger.

Convective Nucleate Boiling on a Heated Surface Cooled by an Impinging, Planar Jet of Water

Convective nucleate boiling has been studied on a flat, upward facing, constant heat flux surface cooled by a planar, impinging water jet. Surface temperature distributions are presented for jet velocities between 1.8 and 4.5 m/s, fluid temperatures of 30, 40, and 50°C, and heat fluxes between 0.25 and 2.5 MW/m2 . Although the critical Reynolds number, Rex*,c , is independent of heat flux for q” < q”ONB , boiling incipience strongly affects the transition to a turbulent boundary layer. As the heat flux increases, vapor bubbles of 1 mm diameter first appear at the point of maximum surface temperature, which also marks the onset of boundary layer turbulence. The leading edge of these bubbles moves toward the stagnation line and Rex*,c decreases with further increases in heat flux. Acceleration in the stagnation region stabilizes the flow, however, so that boundary layer turbulence is restricted to x/wj ≳ 1.6. With increasing heat flux, vigorous nucleate boiling covers more of the heater and surface temperature variations decrease.

A method for measuring steady local heat transfer to an impinging liquid jet

Abstract A new apparatus has been developed to measure local convection coefficients for heat transfer to an impinging liquid jet. The heater and measurement systems and the data reduction procedure are described. Heat fluxes of 0.25–2.5 MW/m 2 were delivered to a 119 × 35.7 mm surface by passing an electric current through a thin metal plate. The temperature and heat flux distributions at the jet-surface interface were computed from temperatures measured at 5.1 mm intervals on the opposite side of the heater. The apparatus is unique in that heat fluxes sufficient to induce steady convective boiling were delivered to an area large enough to accomodate local measurements in both the jet impingement and parallel flow regions. This paper emphasizes the experimental method, including a discussion of uncertainties, and selected results are presented to show that the methodology is viable.