EFFECT OF AIR BUBBLE INJECTION ON THE PERFORMANCE OF A DOUBLE PIPE HEAT EXCHANGER USING CFD
Prof. Pushparaj Singh, Jeewan Prakash Chauhan
Heat exchanger, double pipe, Air bubble injection, Heat transfer, ANSYS 14.5, Overall heat transfer coefficient, Nusselt number.
Upgrade the thermal performance of heat exchangers, increasing the heat transfer coefficient is largely based on, and it is referred to as the technologies of the enhanced heat transfer. Because of the energy crisis occurred in the 70s last century, the technology of enhanced heat transfer achieved rapid development and the number of published papers in this field grew fast every year. In recent years, researchers have tried to reduce the size and weight of heat exchangers without reduction of heat transfer rate. Numerous methods have been presented to increase the heat transfer rate and performance of heat exchangers in the past decades. Generally, these techniques can be categorized into two principal types: (1) passive techniques which require no direct application of external power, such as using of nanofluids, coarsening heat exchanger surfaces and inserting fluid turbulators (2) active techniques which require external power, for instance surface vibration and electrostatic fields.
Air bubble injection is one such technique but passive one to enhance the heat transfer rate. Air bubbles are induced to any flowing fluid channels to maximize the heat transfer characteristics of the fluid. As per the different studies, the bubble dynamics creates much impact on the wall skin friction drag. Injecting bubbles in the flowing fluid reduces the density of the liquid that leads to the generation of baroclinic vorticity on larger scale.
In present work attempts are made to enhance the heat transfer rate in double pipe heat exchangers by injecting air bubbles. For this a double pipe heat exchanger were used in which a tube is inserted with 12 no. of holes by which air bubbles are injected. Modelling is done using ANSYS. The CFD simulated results achieved from double pipe heat exchanger are compared with with and without air bubble injection. Based on the results, From the CFD analysis it has been observed that using air bubble the Nusselt number and overall heat transfer coefficient increased. As compared the overall heat transfer coefficient using air bubble increase by 1.27 times as compared to without air bubble injection. Nusselt number using air bubble increase by 1.23 times as compared to without air bubble