Impact of baffle on forced convection heat transfer of CuO/water nanofluid in a micro-scale backward facing step channel

Abstract

Numerical simulations have been carried out to investigate the thermal-hydraulic characteristics using water-based CuO nanofluid with volume f raction (ϕ) = 0 – 5 % and fixed nanoparticle size (dp) = 20 nm at Reynolds numbers (Re) = 100 – 389 in a micro-scale backward facing step channel with and without a baffle using finite volume method. The flow is steady, laminar, and incompressible. The channel has an expansion rat io (ER) = 1.9423with a fixed step height (S) of 490 µm. To study the effect of the baffle, different geometrical configurations have been developed by varying its height and location. Th e height of the baffle is varied as Hb = 160 – 640 µm. The baffle is stationed on the upper wall of the channel at a dimensionless distance (D) = 1, 2, 3 and 4. The upstream, step and upper walls are thermally insulated while the lower wall downstream of the step is under a constant heat flux (qs") = 20000 W/m2. The parameters of interest for analysis are Nusselt number, skin friction coefficient an d ve locity distribution under different flow cond itions. Resu lts indicate that the rise in volume fraction and Reynolds number enhances the Nusselt number, indicating improved heat transfer. However, the skin friction coefficient decreases with the increment in Reynolds number. The increase in baffle hei ght cau ses the Nus selt num ber and skin friction coefficient to rise. As the baffle is moved away from the step, the Nusselt number tends to decrease. In comparison to water, the heat transfer improved by about 164% using CuO nanofluid at Re = 389 with ϕ= 5% in the presence of the baffle with Hb = 640 µm and D = 1. However, the heat transfer enhancement has been achieved at the cost of higher pumping power requirements.