Experimental and numerical study on heat transfer enhancement using ultrasonic vibration in a double-pipe heat exchanger

•Experimental and numerical study of heat transfer in a double-pipe under ultrasound.•The effect of fluid flow and acoustic power are investigated on heat transfer.•Enhancement factor is considered as a criterion for evaluating thermal performance.•Using ultrasonic waves is more effective in low streaming Reynolds numbers.•Overall heat transfer coefficient enhances up to 60% in the presence of ultrasound. Heat transfer enhancement of double-pipe heat exchanger in the presence of ultrasonic vibrations is experimentally and numerically studied. A novel experimental setup made of two concentric pipes is constructed and a bolted Langevin ultrasonic transducer is used for applying the ultrasonic vibrations to the inner pipe with a frequency of 26.7 kHz. The numerical simulation is carried out by OpenFOAM software to clarify the reason for heat transfer enhancement. The effects of hot and cold fluid flow rates and acoustic power on heat transfer and pressure drop are studied in this work. The performance of heat exchanger is investigated by comparing the overall heat transfer coefficient and pressure drop with and without the influence of ultrasonic vibrations. Results show that using ultrasonic vibration is more effective at low fluid flow rates. As a result, heat transfer enhances about 60% for both cold and hot fluid flow rates of 0.5 L/min, while heat transfer enhancement is equal to 20% for cold and hot fluid flow rates of 1 and 1.5 L/min, respectively, at the transmitted acoustic power of 120 W. Numerical results demonstrate that the cross-stream flows generated by propagation of ultrasonic waves into the cold fluid are responsible for heat transfer enhancement.