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The purpose of this study is to determine the optimum design parameters of the heat exchanger with circular ring inserts and Al2O3/water nanofluid using Taguchi experimental design method. The basic principle of using nanofluid and circular ring inserts is to enhance the heat transfer characteristics of a heat exchanger, thus reducing the size and cost of it. The effects of the three design parameters, such as Reynolds number (Re), pitch to diameter ratio (p/d) of circular ring inserts, and volume concentration (ϕ) of nanofluid on heat transfer characteristics are investigated. In the Taguchi experimental design method, Nusselt number and friction factor are considered as performance parameters. An L9 orthogonal array is chosen as an experimental plan for the design parameters. The results are then analyzed by using ANOVA statistical tools. The optimum configurations of control factors for Nusselt number and friction factor are A3B3C3 and A3B1C2, respectively. The results also proved that the Taguchi experimental design method has been successfully applied in the study. Numerical and experimental results are in very good agreement with each other. [ABSTRACT FROM AUTHOR]

An experimental work had been carried out to investigate the heat transfer and friction factor characteristics of Al2O3 /water nanofluid with circular ring inserts of various pitch to diameter ratios at constant heat flux condition. Al2O3 /water nanofluids with two different volume concentrations were used as the working fluid. The experiments were performed in the turbulent flow regime of 5000 to 25 000 Reynolds number. The results showed that the heat transfer characteristics of Al2O3 /water nanofluids were intensified compared to water and it increases when utilised with circular ring insert. The Nusselt number enhancement of 0.3% volume concentration of nanofluid in the tube without insert was 8.61% and with insert was 38.71% compared to water. Based on the investigation, two correlations among various parameters namely, Nusselt number (Nu), friction factor(f), Prandtl number (Pr), pitch to diameter ratio (p/d), Reynolds number (Re) and particle volume fraction (f) were presented. Over the range investigated, the maximum thermal performance factor of 1.26 is found with the simultaneous employment of the insert and Al2O3/water nanofluid at 0.3% volume concentration. [ABSTRACT FROM AUTHOR]