Numerical study on heat and mass transfer characteristics in the spray zone for an improved closed-type heat source tower

Abstract

It is of great scientific significance to strengthen the heat transfer process in the closed-type heat source tower by improving its structure and operation mode. In this study, an improved closed-type heat source tower was proposed, which uses spray zone instead of finned tube heat exchanger to solve the disadvantages of traditional heat exchanger such as high air flow resistance and local frost formation. On this basis, an improved transient numerical model of spray zone in the closed-type heat source tower was established, and the effects of mass flow rate, initial temperature of the spray solution, velocity and spray angle on heat and mass transfer characteristics were studied. The results show that the effect of velocity on the transfer rate of sensible and latent heat is different. When the velocity of humid air exceeds 1.2 m/s, it will cause the sensible heat transfer rate to decrease slightly; however, it promotes the transfer rate of latent heat significantly, resulting in greater dilution of the spray solution. When the spray angle is between 100° and 120°, the total heat transfer rate increases by about 6 % for every 10° increase in spray angle. However, excessive spray angle will cause the droplets to adhere to the wall, thus increasing latent heat transfer and weakening sensible heat transfer rates. Additionally, the mass flow rate of the spray solution has a significant impact on both sensible heat and latent heat transfer, but the initial temperature only has a remarkable influence on sensible heat transfer. Finally, the optimal combination of axial relative velocity, spray angle, mass flow rate and initial temperature of spray solution is given based on response surface analysis, which are 3.7 m/s, 102.9°, 1.5 kg/s and −7.4 °C, respectively.