Abstract
•Experimental study has been conducted to estimate the convective heat transfer, friction factor and effectiveness of Fe3O4/water nanofluids flow in an inner tube of double-pipe heat exchanger and with longitudinal strip inserts.•The Nusselt number is increased to 14.7% and it further increased to 41.29% at 0.06% vol. of nanofluid flow in an inner tube with longitudinal strip inserts, AR=1 at a Re=28954 compared to water data.•The friction factor penalty is 1.092-times and it further increased to 1.267-times at 0.06% vol. nanofluid flow in a tube with the longitudinal strip insert, AR=1 at a Re=28954 compared to water data.•The overall performance of double pipe heat exchanger for nanofluid with longitudinal strip inserts are expressed in terms of effectiveness and number of transfer units (NTU).•New correlations for Nusselt number and friction factor have been developed based on the experimental data.
Heat transfer, friction factor, effectiveness and number of transfer units (NTU) were determined experimentally for a Fe3O4 nanofluid flowing through the inner tube with longitudinal strip inserts of a double pipe U-bend heat exchanger. Different concentrations of the Fe3O4 nanofluid, which is the hot fluid, were used in the present study and cold water circulates in the annulus region of the double pipe heat exchanger. The heat transfer and friction factor experiments were conducted for the Reynolds number range from 15,000 to 30,000 with the Fe3O4 nanofluid volume concentrations of 0.005%, 0.01%, 0.03% and 0.06%. The effect on heat transfer and friction factor of longitudinal strip inserts in the inner tube is studied for three different strip aspect ratios (AR) with the values of 1, 2 and 4, respectively. The results indicate the Nusselt number on the nanofluid side increases with increasing Reynolds number and particle concentration, and with decreasing aspect ratio of the longitudinal strip inserts. The Nusselt number enhancement, compared to the water data, for the 0.06% volume concentration of the nanofluid is 14.7% and it further increases to 41.29% for the same 0.06% concentration with the longitudinal strip insert with AR equal to 1 for the Reynolds number of 28,954. Compared to water data, the friction factor for the 0.06% volume concentration of the nanofluid increases by 1.092-times and it further increases to 1.267-times for the same concentration with the longitudinal strip insert with AR equal to 1 for the Reynolds number of 28,954. The overall performance of the double pipe heat exchanger with longitudinal strip inserts in the nanofluid side is expressed in terms of effectiveness and number of transfer units (NTU). New correlations for the Nusselt number and friction factor are reported and they are based on the obtained experimental data.