A numerical investigation of heat transfer enhancements with the effects of nanofluid and inserts in a circular tube

This work presents a numerical study to investigate the heat transfer enhancement in a horizontal circular tube using two metal oxide nanofluids (γAl2O3-distilled water and CuO-distilled water) with a twisted tape. Typical and clockwise-counter clockwise twisted tapes were used with a twist ratio 4. The studied concentrations of nanofluids are 0, 1, 2, and 3% by volume under fully developed turbulent flow in the Reynolds number range of 5000 to 20000 with uniform heat flux 2000 W/m2. Throughout the whole numerical analysis procedure, it is made by using of the commercial software package ANSYS FLUENT. The effect of Reynolds number, concentration of nanofluid and nanofluid types on the heat transfer enhancement, average Nusselt number, velocity profile and frictional loss were studied. The maximum enhancement in the heat transfer under the model flow conditions is found when Nusselt number ratio is equal to 1.859, which occurs in the clockwise-counter clockwise twisted tape model without nanofluid for Reynolds number of around 5000. The maximum of heat transfer enhancement in terms of Nusselt number ratio are 3.6 for CuO-water nanofluid and 3.2 for Al2O3-water nanofluid. These values occur at 3 % concentration and the low Reynolds number (nearly 5000) for the clockwise-counter clockwise twisted tape. The increase in the friction factor ratio is generally more pronounced at low Reynolds number than high Reynolds number. The maximum increase in the friction factor ratio for CuO-water nanofluid is 6.4 and for Al2O3-water nanofluid, is 6.1. These values occur at the maximum heat transfer enhancement condition for the clockwise-counter clockwise twisted tape. Keywords: nanofluid, heat transfer, enhancement, twisted tapes, Reynolds number, Nusselt number, friction factor.