The dependence of the efficiency of liquid usage (eta) at CHF on spray parameters was experimentally investigated for subcooled water spray cooling. A spray can be characterized by three independent parameters (droplet Sauter-mean diameter, d(32), droplet velocity, V, and droplet flux, N). In this study, each of these parameters was varied with the other two kept constant by using a combination of spray nozzles, operating pressures, and distance between the nozzle exit and the heater surface. It was found that eta varies with N-2/3, d(32)(-14/5) and V-1/4, respectively, when two of the three spray parameters are kept nearly constant. It was also found that CHF varies with N-1/16 and V-1/4 and is relatively independent of d(32). It is concluded that to achieve the maximum possible CHF while using the minimum quantity of water, it is desirable to select nozzles that produce as small a droplet diameter with as high a velocity as possible. (C) 2004 Elsevier Ltd. All rights reserved.