An experimental investigation on thermo-physical properties and overall performance of MWCNT/heat transfer oil nanofluid flow inside vertical helically coiled tubes

This study deals with an experimental investigation on the thermo-physical properties and overall performance of MWCNT/heat transfer oil nanofluids flow inside vertical helically coiled tubes. Data were acquired for the laminar flow in the thermal entrance region, while the temperature of the tube wall was constant at around 95 °C leading to isothermal boundary condition. Pure heat transfer oil and nanofluids with particle weight concentrations of 0.1%, 0.2% and 0.4% were utilized as the working fluids. It was observed that most conventional models fail to predict the thermo-physical properties of the applied nanofluids accurately, especially in case of the specific heat capacity. Therefore, rough empirical correlations were developed to estimate such properties for the working fluids. In addition, the overall performance of the tested helically coiled tubes was assessed based on the performance index and optimum work conditions were determined. High overall performance index of up to 6.4 was obtained for the simultaneous utilization of both heat transfer enhancement techniques considered in this paper. Hence, applying the methods studied here could be considered as a good choice in practical applications.