Numerical investigation on double pipe heat exchanger for augmentation of heat transfer having twisted inner pipe with conical ring turbulator

Abstract

Double pipe heat exchanger is made of two concentric pipe where one carries hot fluid and another one carries cold fluid inside the pipe. The walls of the pipes allow heat to pass between the fluids. Enhancing the transfer of heat is crucial for effective heat exchangers. This study focuses on evaluating the impact of a fully twisted inner pipe along with conical ring turbulator by conducting a numerical analysis of the double-pipe heat exchanger (DPHE). The analysis considered both parallel and counterflow configurations for fluid-to fluid heat transfer. Additionally a straight elliptical pipe, two other pipes with three twists and full twists along their lengths are investigated to compare heat transfer rate, pressure drop, and turbulence. The realizable k-turbulence model is used, and a grid independency study has conducted using a 3-dimensional structured and unstructured mesh approach. The fully twisted effect generates a swirling motion, and conical rings are inserted inside the outer pipe as a passive turbulator to guide the flow towards the inner pipe, where the hot fluid passes. The regime of turbulent flow is studied within the range of Reynolds numbers from 5000 to 26,000 with water is simulated as the model fluid. Comparing the results, the inner twisted pipe with the conical ring exhibits a significant improvement in the Nusselt number, reaching 445 in the counterflow direction with the six rings. The Performance Evaluation Factor (PEF) is also greater than 1 for both parallel and counterflow flow, indicating that enhancement of the rate of heat transfer, outweighs the decrease in pressure drop. Particularly in counterflow directions the PEF is 2.3 which is impressive. Overall, full twist along the pipe lengths enhances the heat exchanger's performance and full twist with six conical ring fortify most in both flow directions