Effect of twisted tape inserts on heat transfer, friction factor of Fe3O4 nanofluids flow in a double pipe U-bend heat exchanger

The convective heat transfer, friction factor, effectiveness and number of transfer units (NTU) of Fe3O4/water nanofluids flow in a double pipe U-bend heat exchanger and with twisted tape inserts were estimated experimentally. The experiments were conducted in the Reynolds number range from 16,000 to 32,000, particle volume concentrations range from 0.005% to 0.06% and twisted tape inserts of H/D = 10, 15 and 20 were used. The Nusselt number of nanofluids increases with increase of particle volume concentrations and Reynolds number and it further increases with decrease of twist ratio of twisted tape inserts. The Nusselt number is enhanced to 14.76% (no insert) and it is further increased to 38.75% (with twisted tape inserts of H/D = 10) at 0.06% volume concentration and at Reynolds number of 30,000 compare to water data. Similarly, the friction factor penalty of 1.092-times (no insert) and further friction penalty of 1.251-times (with twisted tape inserts of H/D = 10) at Reynolds number of 30,000 compared to water data. New Nusselt number and friction factor correlations have been proposed based on the experimental data. Finally the effectiveness and NTU of heat exchanger is enhanced for nanofluids flow in a double pipe heat exchanger with twisted tape inserts.