Study on Spray Mist Cooling Between Two Adjacent Parallel Boards

Experiments of dielectric liquid spray mist cooling of a row of 9, 38 mm square heaters located along one side of a 400 mm channel formed by two adjacent parallel boards were carried out. The objective was to determine the heat removal capability of the approach as a function of heater downstream distance from a single atomizer for channel height (board pitch) and orientation effects. Fundamental characteristics of the spray field and heat transfer were sought and no attempt was made to optimize the system for high heat transfer rate. The fluid used was FC-72 which as delivered into the gap between the boards by a full-cone TG0.3 atomizer oriented parallel to the row of heaters. The results indicate that heat transfer in the upstream region is dominated by droplet impingement which depends on the board pitch. The heat removal at the leading heater is up to 4 W/cm² at 60°C uniform heater temperature. The heat transfer rate in the downstream region is determined by the flow pattern of the liquid film on the boards, which in turn depends on droplet behavior between the boards. For the horizontal orientation, gravitational forces cause the droplets to fall onto the heated board and improve heat transfer in the middle region along the heaters. This effect was enhanced and heat transfer coefficient was improved with the increase of liquid temperature which is consistent with the phenomena observed in the experiments. For the vertical orientation, gravitational effects do not appear to have an effect on heat transfer. Flow pattern of liquid film in the downstream region is heavily affected by the liquid distribution in the upstream region in the vertical orientation. In this case, the liquid film pattern was preserved and shifted downstream when the power to the upstream heaters was turned off. The heat removal at the “leading” heater at a specific uniform heater temperature is shown to depend on the subcooling of liquid for both orientations.