Experimental evaluation of heat transfer performance of double vertical coils and shell heat exchanger with altered inlet configuration under low-frequency ultrasound

Abstract

The heat transfer and pressure drop of the water flow were investigated inside double vertical coils and a shell heat exchanger by altering the configuration of the inlet flow channel using two or four inlet ports under 28 kHz ultrasound. The inlet flow on the shell side was set at Reynolds numbers of 200, 400, or 600. The effects were examined of the altered position of activated ultrasonic transducers at P1–P9. The results showed that the Nusselt number on the shell side was enhanced by 11.6 % by modifying the inlet flow configuration from two to four channels. In addition, the heat transfer capability was boosted by approximately 9 % when the ultrasonic waves were irradiated into the heat exchanger. The relationship between effectiveness and the number of transfer units under ultrasound irradiation was also presented and discussed to simplify heat exchanger analysis. It showed that the waves enhanced the heat transfer capacity of the heat exchanger by up to 5.7 %. By altering the inlet configuration, the pressure drop on the shell side was reduced by 36.8–39.1 %, while ultrasonic waves only affected the pressure drop by less than 1 %. Using a performance evaluation criterion indicator, the performance of the ultrasonic heat exchangers could be improved by a maximum of 1.065 and 1.089 for two and four inlet ports, respectively. Additionally, the thermal efficiency of using ultrasound was evaluated, indicating that the ultrasonic effects resulted in a higher heat exchange performance than the supplied wave energy.