An experimental comparison of SiO₂/water nanofluid heat transfer in square and circular cross-sectional channels

In this paper, with the aim of enhancing the thermal conductivity of the fluid, a nanofluid is prepared based on SiO₂. A series of experimental tests were carried out for both laminar and forced convection regimes in a horizontal tube with two different geometric shapes (circular and square cross section) subjected to constant wall heat flux (4735 W m⁻²). A comparative study has been done to investigate the effect of the geometry on the convective heat transfer. Moreover, the effect of the volume concentration on the behavior of the nanofluid and the base fluid was evaluated by comparing various volume concentrations (0.05, 0.07 and 0.2%). The experiments were done under two different conditions: constant Reynolds number and constant mass flow rate. It was found that the circular-shaped channel could be better for heat transfer purposes at the same flow rate, while the square-shaped channel has a higher heat transfer coefficient at the same Reynolds number. The slope of the lines for the square cross section is more than that for circular cross sections which result in a steeper increase in average heat transfer coefficient versus Reynolds number in the square-shaped channel. The increase of the Reynolds number may decrease the dead zones in the square channel that causes the double enhancement of the average heat transfer coefficient.