Parametric optimization of heat transfer characteristics for helical coils

Abstract

In this study, helically coiled tubes are used in a shell, and the effects of tube diameter, coil diameter, Reynolds number, Dean number and flow rate on heat transfer and pressure drop during laminar single-phase flows of pure and nanofluid are investigated. Performance evaluation criteria and effectiveness analyses are performed considering tube and coil diameters in a standard catalogue, and the most suitable heat exchanger's size and optimum flow rate are determined as a novel study including the largest number of tested tubes. The outcomes showed that the helically coiled tube gives not only higher heat transfer, but also higher pressure drop compared to straight one. The heat transfer coefficient in helically coiled tube increases with the increase in Reynolds number, Dean number, tube diameter and flow rate and decreases with the increase in coil diameter. On the other side, the pressure drop in helically coiled tube increases with the increase in Reynolds number, Dean number and flow rate and decreases with the increase in tube and coil diameter. As a result, performance evaluation criteria are found to be more reliable compared to effectiveness because it includes both friction factor and Nusselt number. Besides, the optimal nanoparticle type and nanofluid volume concentration for helically coiled tube heat exchangers are obtained taking in consideration the heat transfer and pressure drop results. The results showed that the use of nanofluid in helically coiled tube increases both heat transfer and pressure drop, and the performance evaluation criteria value of nanofluids is determined higher than that for the water. Also, heat transfer and pressure drop increase with the increase in volume concentration of the nanofluid. The highest efficiency in the helically coiled tube heat exchanger under laminar flow regime and constant heat flux boundary condition is achieved by using Fe/water nanofluid with 0.5% volumetric concentration at 0.05 kg s(-1) flow rate in the helically coiled tube with 0.018 m tube diameter and 0.1 m coil diameter. Finally, the necessity of the optimization study on this issue has been understood in the light of obtained findings. This study can be considered as a model for defining the optimal heat exchanger sizes and operating conditions for different working fluid applications or requirements.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 3 Given name: [Ahmet Selim] Last name [Dalkilic]. Also, kindly confirm the details in the metadata are correct.We confirm that the author names are presented accurately and in the correct sequence.