Influence of transverse vibrations on convective heat transfer in parallel flow tube-in-tube heat exchanger

Tube-in-tube heat exchangers are widely used in food processing industries and wastewater treatment for both heating and cooling. Enhancement techniques namely active, passive, and compound are developed to reduce the thermal resistance in heat exchangers by improving convective heat transfer with or without increase in surface area. The present experimental study is aimed at analyzing the influence of vibrations on the convective heat transfer of a parallel flow tube-in-tube heat exchanger. The heat exchanger is placed in horizontal position and is subjected to transverse vibrations under turbulent fluid flow conditions. Experiments were performed at four frequencies (20, 40, 60, and 100 Hz), three amplitudes (1, 2, and 3 m/s(2)), and three vibration generator positions along its length, in the Reynolds number range of 10 710 to 21 420. An enhancement in Nusselt number is found with vibration than without vibration throughout the entire range of Reynolds numbers. A maximum enhancement of 33% at 40 Hz frequency, 3 m/s(2)amplitude, and vibration generator position at three-fourth of the tube length was observed. Empirical correlations are developed for Nusselt number to determine the heat transfer coefficient with vibration with an error of +/- 10%.