Experimental investigation on the characteristics of film thickness and temperature on the heated surface during spray cooling

The heat dissipation problem has become a new challenge for improving the comfort of the built environment. Spray cooling, as an efficient heat exchange technique, attracts more attention. In the present study, an experimental work was performed to investigate the influence of the liquid film produced by a pressure-swirl nozzle on the heat transfer in spray cooling. The film thickness and heated surface temperature at different water flow rates (100–160 ml/min), spray heights (2–10 mm) and temperature of heaters (0–140 °C) were studied. The experimental results indicated that the water film was not flat, and a raised zone was formed under the pressure-swirl nozzle. The time-average film thickness of the raised zone first increased and then decreased with the increase of spray heights. Besides, the amplitude of the water film became larger with the temperature of heaters, and the maximum thickness was 3.82 mm. The heat transfer under experimental conditions was located in the non-boiling region. The non-uniformity of the temperature distribution became more significant with the temperature of heaters, and the maximum standard deviation was 4.66 °C. Besides, the main heat transfer mechanism inside the raised zone was the droplet impingement instead of the raised zone's collapse when spray heights were more than 6 mm, and the heat outside of the raised zone was mainly removed by the film convection. The experimental findings are conducive to further study on the heat transfer under spray cooling.