Second law efficiency analysis of air injection into inner tube of double tube heat exchanger

At present study, thermal performance of a double tube heat exchanger due to stream of air/water two phase flow through inner tube is experimentally studied. Air and hot water were mixed in a T-junction outside heat exchanger and then were followed into inner tube of heat exchanger. Told water flow rate was kept constant and was equal to 2 lit/min. For hot water flow rate, four different flow rates of 3, 4, 5 and 6 lit/min was considered. Also inlet temperature of cold and hot water streams were almost constant and were within range of 17–19 °C and 48–50 °C. Also, for air flow rate five different flow rates of 1, 2, 3, 4 and 5 lit/min were considered. Volume fraction was within the range of 0.14 and 0.62. Obtained results were analyzed based on several energetic and exergitic parameters including pressure drop, effectiveness, Number of Transfer Units, heat transfer coefficient, dimensionless exergy loss and Witte-Shamsundar efficiency factor. Results presented an increment of 33% and 38% in heat transfer coefficient and Number of Transfer Units, respectively. Maximum value of Witte-Shamsundar efficiency factor was found to be 0.973 and was related to Volume fraction of 0.57 and has occurred at counter flow.