Book Description

Advances in electronics fabrication, coupled with the demand for increased computing power, have driven the demand for innovative cooling solutions to dissipate waste heat generated by these devices. To meet future demands, research and development has focused on robust and stable two-phase heat transfer devices. A confined impinging jet is explored as means of utilizing two-phase heat transfer while minimizing flow instabilities observed in microchannel devices. The test configuration consists of a 4 mm diameter jet of water that impinges on a 38 mm diameter heated aluminum surface. Experimental parameters include inlet mass flow rates from 150 to 600 g/min, nozzle-to-surface spacing from 1 to 8 mm, and input heat fluxes from 0 to 90 W/cm2. Results were used to assess the influence of the testing parameters on the heat transfer performance and stability characteristics of a two-phase confined impinging jet. Stability characteristics were explored using power spectral densities (PSDs) of the inlet pressure time series data. Confined impinging jets, over the range of conditions tested, were found to be stable and an efficient means of removing large amounts of waste heat. The radial geometry of the confined jet allows the fluid to expand as it flows radially away from the nozzle, which suppresses instabilities found in microchannel array geometries. Conditions of the heater surface were found to strongly influence two-phase performance. Analysis of PSDs, for stable operation, showed dominate frequencies in the range of 1-4 Hz, which were attributed to generated vapor expanding in the outlet plenum and the subsequent collapse as it condensed. A stability indicator was developed by inducing artificial instabilities into the system by varying the amount of cross sectional area available for outlet vapor removal and compared to the results for stable operation.