Experimental studies on thermal and flow resistance behaviors of turbulent flow through a heat exchanger tube with conical-diffuser inserts

Abstract

In this research, an experimental investigation of the thermal and flow friction characteristics of tubular heat exchanger (HE) for single-phase forced convective flow with conical-diffuser inserted in the inner tube was performed. The aim of using the conical-diffuser is to create vortex flows having a significant influence on the flow turbulence intensity leading to higher heat transfer enhancement in the tested tube. The air flow and heat transfer characteristics are presented for turbulent flow, Reynolds numbers (Re) ranged from 4190 to 25,800. Three different pitch ratios (PR) of conical-diffuser arrangements in the test tube are introduced with PR = 1, 3, 5, 7 and 9 in each run. The heat transfer and energy loss due to friction for propelling air through the tube are presented in terms of Nusselt number (Nu) and friction factor (f), respectively. It was found that each application of the conical diffuser can help to increase considerably the heat transfer rate over that of the plain/smooth tube by about 247%. The thermal enhancement factor (TEF) of the conical-diffuser is in the range of 1.28–1.35 where its maximum, regarded as the optimum point, is at PR = 1 and Re = 4190.

Keywords

• conical-diffuser
• heat exchanger
• vortex flow
• flow resistance
• thermal performance