Experimental examination of thermohydraulic characteristics of a new vibrating rubber tube turbulator with multiple air bubble outlets inserted inside a double-pipe heat exchanger

Abstract

This experimental study explores a new method for improving heat transfer in heat exchangers by utilizing bubble injection alongside electromagnetic vibration techniques. Instead of conventional bubble injection, a vibrating rubber tube with multiple air outlets is employed to introduce bubbles into the working fluid. This configuration ensures uniform bubble distribution along both axial and radial directions, while the rubber tube's continuous vibration disrupts the thermal boundary layer, promoting turbulence and further enhancing heat transfer. The effects of various parameters are investigated, including Reynolds numbers spanning from 1050 to 7370, bubble injection flow rates between 0.5 and 2 l/min, rubber tube diameters of 3-5 mm, and air outlet numbers ranging from 30 to 90. Results show that increasing the bubble flow rate and tube diameter enhances both heat transfer and the friction coefficient. In contrast, increasing the number of air outlets improves heat transfer while reducing the friction coefficient. A maximum TEF of 4.42 is achieved at a bubble flow rate of 1.5 l/ min, a tube diameter of 5 mm, and 90 air outlets. Under these conditions, the Nusselt number and friction coefficient are up to 10.43 and 13.1 times higher, respectively, compared to those of a plain tube.