Abstract
In this experimental investigation convective heat transfer, friction factor, and thermal enhancement characteristics of straight circular duct fitted with circular ring insert of constant heat flux boundary condition under fully developed laminar flow is presented. Tests have been conducted by using 0.1% volume concentration of Al2O3 nanofluid and water. Inserts of different pitch to diameter ratios of 6.25, 8.33, 12.5, and 16.67 with center core rod were used for this investigation. The circular ring insert shows a superior thermal performance than plain tube. The experimental results demonstrated that the Nusselt number, friction factor, and thermal enhancement factor increases with decrease in pitch to diameter ratio. The circular ring inserts of lower pitch to diameter ratio of 6.25 with nanofluid increases the Nusselt number by 165.38% compared to pure water and the friction factor, found to be 7.89 times higher than that of water. Empirical correlations are develope for Nusselt number and friction factor in terms of Reynolds number, volume concentration, and pitch ratio. The thermal performance factor was found to be greater than unity for all pitch to diameter ratios.
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