Effect of air bubble injection on the performance of a horizontal helical shell and coiled tube heat exchanger: An experimental study

This paper aims to study experimentally the effects of air bubble injection on the performance of a horizontal helical shell and coiled tube heat exchanger. The variations of number of thermal units (NTU), exergy loss and effectiveness due to the air bubbles injection with different air flow rates are evaluated. A new procedure for injecting the air bubbles into the shell side flow of the heat exchanger is proposed. The results exhibited a significant increase in the effectiveness and NTU of the heat exchanger as the air bubbles were injected. It is suggested that the disturbance and perhaps the turbulence intensity of the shell side flow are increased due to the motion of air bubbles resulting in an increment in the value of NTU and exergy loss. In addition, the mixing effect of the bubbles and the interaction with the thermal boundary layer can increase the velocity (hence the Reynolds number) of the shell side flow.