Investigation On Heat Transfer Performance Of Spray Cooling System

With the development of industrial technology, the heat dissipation problem has drastically restricted the development of microelectronic technology, aerospace industry, laser equipment, metal process and other fields. The spray cooling method is considered as an effective way to strengthen the heat dissipation. In this paper, a closed spray cooling system has established to investigate the influence factors of spray cooling, the influence of lubricant oil on spray cooling performance, and an open spray cooling system has established to investigate the influence of Al₂O₃-water nanofluid on spray cooling performance.In the closed spray cooling system with R134 a, as the heat flux and the subcooled temperature are constant, the mass flow rate exists a critical value. As the mass flow rate is smaller than the critical value, the heat surface temperature decreases with the mass flow rate increasing, but when the mass flow rate exceeds the critical value, the heat surface temperature increases with the mass flow rate increasing. When the mass flow rate and the subcooled temperature keep constant, there also exists a critical value of heat flux, which makes the evaporation capacity equal to the supplement of droplet; therefore, the heat transfer coefficient can reach the maximum value. As the heat flux and the mass flow rate are fixed, the variation of subcooled temperature doesn’t have significantly influence on the heat surface temperature and the heat transfer coefficient.Lubricant oil has a great impact on the spray cooling system performance, when the heat flux and the mass flow rate are fixed at 29.8 W/cm2 and 2.0 kg/h, respectively, and the inlet temperature is constant, the heat transfer coefficient decreases from 18400 W/（m2×°C） to 7200 W/（m2×°C） with the oil concentration rising from 0.00% to 5.99%. Furthermore, when the oil concentration is fixed at a relative high percentage 3.26%, and the heat flux and inlet temperature keep constant, during the mass flow rate increasing, the variation of heat transfer coefficient goes through three stages: firstly it increases to the maximum value, then it decreases to the minimum value, and lastly it rebounds up with the mass flow rate increasing continuously. Moreover, heat transfer coefficient increases with the heat flux rising when the mass flow rate and the oil concentration keep constant.In order to study the influence of nanomaterial on the performance of spray cooling system, an open spray cooling system with Al₂O₃-water nanofluid was established. When the heat flux is 17.3 W/cm2, the volumetric flow rate is 80 ml/min and the inlet temperature is 19 °C, the heat surface temperature is 37.2 °C with water as the working fluid; at the same conditions, the heat surface temperature are 30.3 °C and 38.8 °C with Al₂O₃-water nanofluid as the coolant, which mass fraction are 0.02% and 0.1% respectively. The results showed that lower mass fraction of Al₂O₃ can significantly enhance heat transfer, but higher fraction restrains heat transfer.