Dropwise evaporative cooling of hot water: A novel methodology to enhance heat transfer rate at very high surface temperatures

Abstract

Newly developed cooling techniques including spray cooling and air-atomized cooling are oriented on one basic phenomenon, i.e., dropwise evaporative cooling. The dropwise evaporative cooling is mainly controlled by the physical and thermal properties of the coolant and the droplet dynamics during evaporation. Different researchers have tried to enhance dropwise evaporation process by enhancing any one of the aforesaid characteristics and as consequence the achieved heat transfer rate is lower than the quenching rate required for the fast cooling operation. In addition to the above, the open literature does not disclose any methodologies, which consider simultaneously all the above-mentioned properties in the enhancement of heat transfer. Therefore, in the current research, an attempt has been made to augment the heat transfer rate in case of dropwise evaporative cooling process by altering simultaneously the thermal properties, physical properties and the flow dynamics of the droplet. The current proposed methodology to obtain fast evaporation is by altering thermal, physical and flow properties and this is achieved by increasing the water temperature. The experimental investigation considers water temperature and the substrate temperature as the independent variables. The heat transfer analysis depicts that the increment in initial plate temperature and water temperature have significant effects on evaporation time. On increasing water temperature from 10 to 60 °C, the evaporation time is reduced by ∼200% due to the chances of reduction of recoiling characteristics after impingement, creation of high heat transfer area and decrement of sensible heat extraction period. With the increasing substrate temperature, the evaporation time decreases due to the increment of the thermal conductivity of the coolant. In addition to the above, the mechanism for the aforesaid enhancement process is tried to reveal by developing the mathematical models. In addition to the above, the enhancement capability of the hot water is compared with different potential coolants. From the comparison, it is concluded that the heat removal capacity of hot water is significant and it can also replace the considered coolants without depicting the disadvantages of the considered coolants in the literature. For the verification, experimental results are compared with the numerical results. The comparison discloses that the developed model is quite accurate and shows insignificant variation from the experimental results. A suitable model and vapour film thickness are also determined from the numerical investigations.