Experimental Studies of f-CNT Nanofluids in a Helical Coil Heat Exchanger

Abstract

Hydrodynamic and heat transfer characteristics of long-term stable nanofluids are very crucial for their industrial applications. Also utilization of coils is beneficial for industries as it provides a high rate of heat transfer and is compact in size too. So, the main focus of this study is to investigate the hydrodynamic and heat transfer characteristics of long-term stable f-CNT nanofluids when flowing inside a coil-based heat exchanger. f-CNT nanofluids were prepared by utilizing modified two-step method. To analyze the effect of different parameters on hydrodynamic and convective heat transfer characteristics, f-CNT concentration, $$ {\varvec{D}}_{{\mathbf{c}}}$$ , and Re were varied from 0 to 0.048 vol%, 95 to 175 mm, and 2300 to 9500, respectively. According to results, f-CNT concentration, $$ {\varvec{D}}_{{\mathbf{c}}}$$ , and Re substantially influenced the hydrodynamic and heat transfer characteristics of f-CNT nanofluids. It was found that improvement in h (152%) was much higher than the enhancement in friction factor (49%) when f-CNT nanofluid at 0.048 vol% was flowing through the coil of 95 mm diameter. Based on the heat transfer and hydrodynamic data, performance index was evaluated. The maximum performance index was calculated ⁓ 2.5, suggesting that the utilization of helical coils and f-CNT nanofluids is an excellent choice in industrial applications. Based on the experimental data, empirical correlations have been proposed to calculate the friction factor and Nusselt number for f-CNT nanofluids when flowing inside coils of different diameters and at different f-CNT concentrations. The proposed correlations explain the present experimental data within ± 15% and ± 20%, for friction factor and Nu, respectively.