Numerical Investigation of Heat Transfer Enhancement of Turbulent Flow in Dimpled Tubes

Abstract

The importance of heat transfer enhancement has gained greater significance in many engineering applications, and a great amount of effort has been devoted to the use different techniques to improve the thermal performance of flowing fluids in pipes.  Dimpled tubes were used for this purpose in this study.  In this investigation, the heat transfer-flow characteristics of turbulent flow in dimpled tubes subjected to uniform heat flux are numerically investigated. The rate of heat transfer, friction factor, and performance evaluation criterion were determined for various designs of dimpled tubes and compared with smooth tubes. The considered cases are conducted in the Reynolds number range of 3000 to 12,000. The ANSYS Fluent R19 is used for this purpose. The Reynolds-averaged Navier-Stokes equations (RANS) are used to model the governing flow equations. The realizable k-ε turbulence model is used with enhanced wall conditions to simulate turbulent flow adjacent to the inner wall surface. The results revealed that the rate of heat exchange in dimpled tubes higher than that of smooth ones. but with additional pressure loss.  Moreover, the heat transfer performance of the staggered arrangement is higher than the inline arrangement by 17 %.   Also, the performance evaluation criteria (PEC) increases with the increasing in dimples diameter, and decreases with increasing in relative pitch spacing, the maximum  enhancement  reaches 31% for d = 5 mm, and  relative pitch spacing        S/D = 2 at  Re = 4000.