Experimental study on turbulent flow and heat transfer in an air to water heat exchanger using perforated circular-ring

In this study, heat transfer and pressure loss in an air to water double pipe heat exchanger are experimentally investigated. Typical circular-ring (TCR) and perforated circular-ring (PCR) turbulators are placed in annular pipe. The working fluids are air, flowing in the annular pipe, and water through the inner circular tube. The experiments are conducted for different governing parameters namely; air flow Reynolds number (6000-12,000), pitch ratio (1.83, 2.92 and 5.83) and number of perforated hole (0, 2, 4 and 8). Correlations for friction factor, Nusselt number and thermal performance are presented according to experimental data. Results indicated that using PCRs leads to obtain lower heat transfer enhancement than the CRs because of reduction of intersection angle between the velocity and the temperature field. Thermal performance increases with increase of N but it decreases with increase of Reynolds number and pitch ratio.