Heat transfer of impinging air and liquid nitrogen mist jet onto superheated flat surface

This experimental study performs the detailed heat transfer measurements of an impinging air-liquid nitrogen mist jet onto a superheated flat surface at atmospheric pressure with reference to the design of an instant freezing facility. A selection of experimental results illustrates the interacting effects of jet Reynolds number, mass flow ratio of air to liquid nitrogen flows and separation distance on the spatial distributions of heat transfer over the impinging surface. Mechanism associated with phase change of impacting droplets generates an enhanced and uniformly distributed heat transfer region centered on the stagnation point. A narrow oval-ring region encapsulating the enhanced core transits heat transfer from the wetting regime of complete evaporation to the non-wetting rebound regime. Stagnation heat transfer augmentation factor in the range of 1.2-2.8 times of the air-jet level is achieved. An empirical correlation based on the experimental data, which is physically consistent, has been developed to permit the evaluation of stagnation heat transfer. (C) 2003 Elsevier Ltd. All rights reserved.