The effects of coil spring turbulators inserted to the concentric heat exchangers on the heat transfer and pressure losses

Heat exchangers have a wide range of usage in industry applications, especially in thermal power plants, heating, ventilation and air-conditioning systems. The thermal performance of heat exchangers are defined as efficiency. One of the most widely preferred way for heat transfer augmentation in heat exchangers is the use of some inserts called turbulators. In this study, heat transfer characteristics and pressure drop of a double pipe heat exchanger with inserted coil springs, are investigated. Design parameters for the coil spring turbulators are pitch of the coil spring, thickness of the coil wire and the length of the coil spring. The working fluid in the experiments is air and the Reynolds number ranged from 30,000 to 80,000 to provide fully developed turbulence flow conditions. Also, to determine the effects of the parameters used in the experiments on Nusselt number and friction factor the ANOVA (Analysis of Varience) method is used. Optimum parameter levels for the heat transfer and fricton factor are determined by Taguchi Experimental Design Method. The values such as Nusselt number, friction factor, efficiency-NTU, dimensionless exergy loss are obtained for both tabulated and untabulated pipe flow, and some new experimental correlations are developed. Keywords: heat exchanger, coil spring turbulators, heat transfer, exergy, ANOVA, Taguchi