Experimental investigation of turbulent heat transfer performance in internal flow using a star shape cross sectioned twisted rod inserts

Abstract

In the present investigation, the heat transfer and pressure drop characteristics of a circular tube fitted with a new 5 point star shape cross sectioned twisted rod inserts are experimentally reported for fully developed turbulent flow regime. Test runs were conducted in a concentric double pipe heat exchanger in the Reynolds number (Re) range of 8000–32,000 with water as a working fluid. For different investigated geometries of insert, the average Nusselt number ratio (${\text{Nu}}_{\text{a}} /{\text{Nu}}_{\text{p}}$) and average friction factor ratio (${\text{f}}_{\text{a}} /{\text{f}}_{\text{p}}$) with and without inserts are reported to be in the range of 1.79–2.79 and 2.44–4.17 respectively. The Nusselt number ratio (${\text{Nu}}_{\text{a}} /{\text{Nu}}_{\text{c}}$) based on equal pumping power is also reported and found to be in the range of 0.94–1.24. The effects of varying pitch to length of insert ratio (p/l) and diameter of insert to the inner diameter of tube ratio (d/Di) on heat transfer and pressure drop are reported and empirical correlation is given for Nusselt number in terms of Reynolds number (Re), pitch to length of insert ratio (p/l), insert diameter to inner diameter of tube ratio (d/Di) and Prandtl number (Pr).