Experimental Study On A Spray And Falling-Film Cooling System

After spraying, the cooling medium retains potential cooling capability and, consequently, can form a falling film to further cool the downward area. In this paper, the flow patterns and the heat transfer coefficients are correlated respectively in the spray zone and the falling film zone on a vertical semi-cylindrical heating surface. The incident angle of spray (0 degrees-45 degrees), the spray distance (2 mm similar to 6 mm) and the spray pressure (1 bar similar to 5 bar) are varied in the experiments. In the spray cone, as the recirculation region which varies with different parameters shrinks, the heat transfer coefficient tends to increase. For the falling film zone, if the loss rate of the liquid is low, the flow speeds in the falling films can be compared directly by examining the film thickness. As the film thickness is reduced, the flow speed in the film is increased, resulting in the higher heat transfer coefficient. The angle of 30 degrees is the most effective to exploit the cooling capability of the two zones. In most cases, the cooling medium after spraying can still cool the surface by the equivalent of at least 40% cooling capability of the spray zone, which indicates significant potential cooling capability which could be developed in whole spray cooling systems. An empirical correlation is presented to estimate the cooling capacity ratio on spray and falling film zone. These results may be helpful when undertaking innovative design of a spray and falling film cooling facility.