Performances of two heat exchangers assisted by ultrasound

In this experimental work, performances of a double-tube heat exchanger are investigated with and without the influence of ultrasonic vibrations. A comparison is made with results obtained previously for an analogous shell-and-tube heat exchanger. The system of interest is made of two concentric straight pipes. An external ultrasonic transducer is connected to the largest one in order to make it vibrate at 35 kHz. A smaller pipe is inserted into the vibrating one in order to build a double-tube heat exchanger, always using water as working fluid. The ratio between the overall heat transfer coefficients with and without ultrasound, named the enhancement factor, was used alongside energy balances as means of comparison between experiments and heat exchangers performances. This enhancement factor was found between 1.5 and 2.3, and slightly more for the shell-and-tube heat exchanger. Nevertheless, whatever the heat exchanger configuration, the use of ultrasonic vibrations appears to be an interesting way for the enhancement of thermal performances.