Improving hydrothermal performance of double-tube heat exchanger with modified twisted tape inserts using hybrid nanofluid

The experimental studies on Al2O3 + TiO2 hybrid nanofluid flowing under the turbulent condition in a double-tube heat exchanger with various modified V-cuts twisted tape inserts are performed to study the hydrothermal characteristics. The hybrid nanofluid is prepared with a volume concentration of 0.1% by dispersing Al2O3 and TiO2 nanoparticles by equal volume ratio in distilled water. The effect of using twisted tape turbulator (with and without V-cuts) and hybrid nanofluid on the heat transfer and pressure drop characteristics are evaluated for different twist ratios, V-cut depth ratios, V-cut width ratios and hybrid nanofluid inlet temperatures. Results show that Nusselt number as well as friction factor increases with the decrease in twisting ratio, increase in depth ratio, decrease in width ratio and decrease in nanofluid inlet temperature. Maximum improvements in 132% for Nusselt number and 55% for friction factor are obtained as compared to that for the water in the tube without twisted tape. The values of thermal performance factor and entropy generation ratio are greater than unity for hybrid nanofluid for all modified twisted tape inserts.