Experimental Study On Heat Transfer And System Simulation Of Spray Cooling

Spray cooling is a promising candidate to provide cooling for microelectronic and high-power devices. Compared with the traditional cooling methods, with the advantages of high heat flux capacity, small amounts of work fluid demand, low temperature difference between surface and working-fluid, compact structure, spray cooling will have a broad application prospect in high-flux removal.However, heat transfer mechanism of spray cooling is complicated, and the study on it is still in its infancy so far. The main objection of this work is to investigate the effects of parameters on heat transfer in spray cooling under experiments, to understand its heat transfer mechanism and to establish a system simulation model by LabVIEW.Spray characteristics have an important influence on spray cooling. Therefore, a Doppler anemometry was used to study the spray characteristics for two nozzles, Results show that droplets parameters distribute non-uniformly. At the horizontal plane which with a certain distances to nozzle orifice; spray region is divided into entrainment region, mainstream region and exterior spray region along the radial direction. Axial velocities, axial velocities, Sauter mean diameters (SMD) and droplet numbers are numerous in mainstream region, and rare at the two other regions.In order to be convenient to adjust the parameters, observe the experimental phenomenon, and analyze the effects of parameters on spray characteristics, an opened experimental platform was established in this thesis. A digital camera and IR were used to investigate the heating surface and temperature distribution on it visually. The effects of spray height, volumetric flux, spray angle, inlet temperature and incident angle to heat transfer of spray cooling was studied. Generally, the optimal heat transfer was considered to achieve at the spray height of the heating surface inscribed perfectly. However, this study finds that heat transfer come to its best at a smaller spray height, which is different from the traditional concept of formers.Based on the former experimental system, a closed experimental loop was established. To use it can be more practical to simulate the real conditions of heat transfer characteristics of spray cooling. According to the experimental results, lowering the inlet pressure can significantly enhance heat transfer in spray cooling. When the system pressure was in 7.5 ~ 8.1kPa, compared with in the open environment (1atm), heat transfer was found to be decreased by 70%. When the system pressure increased from 2.5kPa to 100kPa, the heat transfer decreased exponentially. Sodium sulfate solution additives can enhance the spray cooling heat transfer accordingly.Basing on the analysis of the experimental data and heat transfer mechanism, a simulation model of closed spray cooling system was established by LabVIEW. Simulation results show that with the increasing of the heating power, the spray chamber temperature, wall temperature, heat transfer coefficient, and the volume of evaporation increase in the two-phase region. When nuclear boiling occurs, heat flux increases and heat transfer enhanced dramatically. Improving the volumetric flux of condenser cooling water can reduce the saturation temperature, and simultaneously, enhance heat transfer.