Spraying liquid on a hot surface is an effective method for dissipating high heat fluxes from integrated circuit chips. In this study, HAGO nozzle was used to create the spray and a closed system with water as a test liquid was used. The effect of presence of non-condensibles in the closed system on the heat transfer coefficient in both single phase and boiling modes were investigated. Maintaining an air partial pressure of 3.1 kPa, while varying the vapor partial pressure from 7.3 kPa to 97.9 kPa, the total system pressure was varied from 10.4 kPa to 101 kPa. Experiments were also conducted by keeping the system pressure constant at 101 kPa and varying the air partial pressure inside the chamber from 2.75kPa to 93.7kPa. In each case, liquid temperature corresponded to the saturation temperature corresponding to partial pressure of vapor and this was also approximately the ambient temperature of vapor and air mixture in the chamber. It was found that in the single phase regime, overall heat transfer coefficient for lower concentration of non-condensibles in the system is much higher than that for the case with more non-condensibles. In boiling, heat transfer coefficient depends on the total system pressure in the system. For the same system pressure, data for different partial pressures of air overlap. For a water mass flux of 17.5ml/min/cm(2) at room temperature, critical heat flux as high as 230W/cm(2) was obtained at a surface temperature of 127degreesC. (C) 2004 Elsevier Ltd. All rights reserved.