Enhancing heat transfer in double tube heat exchanger by nail rod inserts: numerical and experimental study

Abstract

Double-tube heat exchanger (DTHX) is extensively utilized in many applications because of their small size, easy maintenance, and suitability for high-pressure applications. In this study, the heat transfer enhancement in a DTHX is studied experimentally and numerically by adding a nail rod insert (NRI). The study is performed with a steel nails rod insert 1000 mm long and a turbulence flow with a Reynolds number ranging from 3200 to 5700. Three different pitches of NRI such as 100 mm, 50 mm, and 25 mm are investigated. The attained results reveal that inserting nail rods raises the Nu number, and additional improvement can be attained by reducing pitch length. Nu number enhancement ratios for 25 mm pitch NRI are 1.81–1.9 times higher than the plain tube. Pressure drop rises in all configurations with NRI due to turbulence and obstructive NRI area. Among various pitch lengths, 25 mm exhibits the highest values of pressure drop where these values are overlooked concerning potential heat transfer improvements. Exergy efficiency rises across all cases with NRI, correlating with increased heat transfer, resulting in a 128% improvement in exergy efficiency for 25 mm pitch length. The numerical findings elucidate that the novel insert augments flow turbulence with secondary flows, thereby improving heat transfer in DTHX. A comprehensive analysis is presented with temperature, velocity, and pressure drop distributions from the numerical results.