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The purpose of this research is to study the forced convection heat transfer and flow characteristics of water base fly ash-Cu (80:20% by volume) hybrid nanofluid (HNF) flow through a copper tube under a constant heat flux (CHF) of 7962W/m2 experimentally and numerically. The present work presents results for the concentrations of 0.5–2.0 vol% at a fluid inlet temperature of 30 °C in the flow rate range of 5–16 LPM. HNF stability, thermal conductivity, and viscosity were experimentally analyzed and compared with the established correlations. The maximum augmentation in Nusselt number (Nu) was 57.1% and 8.95% at a concentration of 2.0% relative to water for HNF and fly ash nanofluid (FANF), respectively. The total entropy generation varies inversely with the Reynolds number (Re). The pressure drop (Δp) of HNF is greater than the FANF and water. The development of correlations with experimental data is for determining Nu and friction factors of HNF. Bejan number (Be) of HNF and FANF varies inversely with concentration and Re improvement. The values of thermal performance factor (TPF) enhance with concentration, and a maximum TPF value observed is 1.52 at 2% concentration. The performance of the computational analyses is with ANSYS software gives a reasonable agreement between them.

This article presents experimental studies for the determination of heat transfer coefficient (HTC) and friction factor for the flow of a fly ash nanofluid in a copper tube under constant heat flux boundary condition. Fly ash/water nanofluid in the concentration range of 0.5–2.0 vol % is used. Stability, viscosity, and thermal conductivity have been found experimentally and validated with previously reported literature. Experimentation was performed at various flow rates and bulk fluid temperature of 30 °C . The highest thermal conductivity ratio and viscosity ratio of 1.21 and 1.18 were observed for a concentration of 2 vol% at 30 °C. The augmentation in Nusselt number (Nu) and friction factor was 46.9% and 9.89%, respectively at 2.0 vol%, when compared to the base fluid. With an increase in Reynolds number, the total entropy generation reduces, whereas the friction entropy generation increased. The maximum PEC value of 1.42 was observed at 2 vol% for fly ash nanofluid. The experimental findings are compared with CFD results, with good agreement between them. ANSYS Fluent software is used for computational validation.

Nanofluids have gained extensive attention due to their role in improving the efficiency of thermal systems. The present study reports a further enhancement in heat transfer coefficients in combination with structural modifications of flow systems namely, the addition of tape inserts. Experiments are undertaken to determine heat transfer coefficients and friction factor of TiO2/water nanofluid up to 3.0% volume concentration at an average temperature of 30 °C. The investigations are undertaken in the Reynolds number range of 8000–30,000 for flow in tubes and with tapes of different twist ratios. A significant enhancement of 23.2% in the heat transfer coefficients is observed at 1.0% concentration for flow in a tube. With the use of twisted tapes, the heat transfer coefficient increased with decrease in twist ratio for water and nanofluid. The heat transfer coefficient and friction factor are respectively 81.1% and 1.5 times greater at Re = 23,558 with 1.0% concentration and twist ratio of 5, compared to values with flow of water in a tube. An increase in the nanofluid concentration to 3.0% decreased heat transfer coefficients to values lower than water for flow in a tube and with tape inserts. A thermal system with tape insert of twist ratio 15 and 1.0% TiO2 concentration gives maximum advantage ratio, if pressure drop is considered along with enhancement in heat transfer coefficient.

Nucleate boiling heat transfer from horizontal tubes has been analyzed using dimensional analysis and the postulations of different investigators. Inclusion of certain non-dimensional parameters in the analysis has resulted in closer approximation with the experimental data when compared with the regression equations of earlier investigators. The present correlation has been further tested with experimental data of Borishansky et al. [V.M. Borishansky, B.I. Bodrovich, F.P. Minchenko, Heat transfer during nucleate boiling of water and ethyl alcohol, in a volume of collection of articles, in: S.S. Kutateladze (Ed.), Aspects of Heat Transfer and Hydraulics of Two-Phase Mixtures, Govt. Energy Publishing House, Moscow, 1961, pp. 75–93] for water and ethyl alcohol obtained at different pressures on tubes with diameter varying between 5 to 7 mm. It is found that the correlation can predict the experimental values with a maximum deviation of ± 16 % .