TY - JOUR
TI - Heat transfer characteristics of Al2O3/water nanofluid in laminar flow conditions with circular ring insert
AU - Mala Dharmalingam
AU - Sechassalom Sendhilnathan
AU - Sivan Suresh
JN - Thermal Science
PY - 2016
VL - 20
IS - 14
SP - 1159
EP - 1168
PT - Article
AB - 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.