Mixed convection heat transfer of nanofluids over backward facing step having a slotted baffle

Mixed convection heat transfer over a 2-D backward facing step with an inclined slotted baffle by using nanofluids is numerically investigated. Continuity, momentum and energy equations were solved by using Finite Volume Method with SIMPLE algorithm to link the pressure and velocity fields. Different Reynolds numbers from 50 to 400 were applied. In addition, the downstream wall of the step from 10 ⩽ X ⩽ 15 was subjected to a uniform heat flux of 10,000 W/m2 while the upper wall and the baffle are kept insulated. Five different geometries (without baffle, with a vertical solid baffle, with a solid inclined baffle, with two inclined slotted baffle) were compared to find the best for heat transfer enhancement. Different nanoparticles such as Al2O3, CuO, ZnO and SiO2 with different volume fractions from 0% to 4% and different nanoparticle diameter from 20 to 50 nm were considered with water as a base fluid to explore the best nanofluid for heat transfer enhancement. It is clearly shown that nanofluids with more nanofluid volume fraction and small nanoparticle diameter affect the heat transfer considerably. Results clearly illustrated that SiO2 with 4% volume fraction and 20 nm nanoparticle diameter shows the best performance for heat transfer enhancement in compared with other nanoparticles. It is also found that the inclined baffle has the maximum average Nusselt number along the heated wall with high pressure drop and skin friction coefficient. However, by increasing Reynolds number, the inclined slotted baffle at D = 0.5 had an appropriate average Nusselt number and minimal changes of pressure drop and skin friction which can be considered as the appropriate geometry.