Effect of The Surface Pits on The Performance of a Double-Tube Heat Exchanger

Abstract

Heat exchangers are widely used to transfer heat between different fluids in various applications such as cooling systems, heating, and thermal industries. To improve the performance of these exchangers, several methods were used, including adding protrusions or indentations on the surface tube walls to increase fluid turbulence and enhance heat transfer. In this research, the effect of pits on the outer surface of the inner tube, with circular and square shapes arranged in linear and staggered patterns, on the performance of a double-tube heat exchanger with counterflow was studied. The flow of hot water inside the tube was fixed at 3.5 liters/minute at an inlet temperature of 50°C, while the flow of cold water was varied between 4.5 and 7.5 liters/minute at an inlet temperature of 22°C. The results showed that the presence of pits significantly improved thermal performance compared to the smooth tube. The improvement achieved in average Nusselt number is 24% for linear circular pits compared to the smooth tube, while it reached 31% for staggered circular pits. In case of square pits, the improvement achieved in average Nusselt number was 22%for linear arrangement, while it reached 30%for staggered arrangement. These results confirm that the use of pits, especially in a staggered arrangement, is an effective method for improving the performance of heat exchangers.