No abstract

The single phase heat transfer characteristics of square arrays of impinging water sprays were investigated experimentally. A total of 230 experimental points, covering a wide range of flow rates and different spray array geometries were obtained with three different models of commercially available full cone spray nozzles. Results were compared to an available correlation for the area average heat transfer coefficient of impinging arrays of submerged jets. It is shown that spray impingement techniques may provide the same heat transfer coefficient obtained with impinging jets under much smaller coolant flow rates per unit heated area. Coolant pumping power required by both techniques was also compared. It is shown that spray arrays require, for the establishment of a given area average heat transfer coefficient, more pumping power than submerged jet arrays.

The nucleate boiling of subcooled water, under 100 cm 2 square arrays of impinging sprays, was experimentally investigated. Three types of commercially available full cone pressure nozzles, of distinct flow capacities, allowed for runs where the average impinging coolant mass flux spanned the 0.3-7.2 kg/m 2 -s range. Array geometry was varied adjusting nozzleto-nozzle and nozzle-to-impingement surface distances. Experimental construction allowed for good drainage of spent coolant and unrestricted air entrainment to spray cones. The average heat flux through the heated, upward-facing, copper impingement surface was found to be equal to the sum of single-phase and nucleate boiling heat flux components. The phase-change component was experimentally observed to depend upon wall excess temperature only. The proposed heat transfer correlation reproduces original experimental data with a mean absolute error of 10.6%. Non-critical-heat-flux (non-CHF) cooling capacity and efficiencies of up to, respectively, 2000 kJ/kg and 83% were observed.