Influence of nanofluids on mixed convective heat transfer over a horizontal backward‐facing step

Abstract

Predictions are reported for laminar mixed convection using various types of nanofluids over a horizontal backward-facing step in a duct, in which the upstream wall and the step are considered adiabatic surfaces, while the downstream wall from the step is heated to a uniform temperature that is higher than the inlet fluid temperature. The straight wall that forms the other side of the duct is maintained at constant temperature equivalent to the inlet fluid temperature. Eight different types of nanoparticles, Au, Ag, Al 2 O 3 , Cu, CuO, diamond, SiO 2 , and TiO 2 , with 5% volume fraction are used. The conservation equations along with the boundary conditions are solved using the finite volume method. Results presented in this paper are for a step height of 4.9 mm and an expansion ratio of 1.942, while the total length in the downstream of the step is 0.5 m. The Reynolds number is in the range of 75 ≤ Re ≤ 225. The downstream wall was fixed at a uniform wall temperature in the range of 0 ≤ ∆T ≤ 30°C which is higher than the inlet flow temperature. Results reveal that there is a primary recirculation region for all nanofluids behind the step. It is noticed that nanofluids without secondary recirculation region have a higher Nusselt number and it increases with Prandtl number decrement. On the other hand, nanofluids with secondary recirculation regions are found to have a lower Nusselt number. Diamond nanofluid has the highest Nusselt number in the primary recirculation region, while SiO 2 nanofluid has the highest Nusselt number downstream of the primary recirculation region. The skin friction coefficient increases as the temperature difference increases and the Reynolds number decreases.

The effect of nanofluids flow on mixed convection heat transfer over microscale backward-facing step

“…In many circumstances the flow separation is undesirable and leads to unwanted pressure drop and energy losses. While, in another instances the flow separation may be encouraged and leading to enhance mixing or heat and mass transfer rates due to the mixing of high and low energy fluids which occurs in the separation and reattachment flow region [1].…”

“…This complex flow structure presents in many applications for instance cooling of electronic equipments, cooling of nuclear energy system equipment, flow in valves, combustion champers, cooling turbine blades and heat exchangers [1].…”

“…The step flow is the phenomena of separation and subsequent reattachment due to the sudden expansion in flow passage which occurs in many engineering applications where cooling or heating is required [1]. In many circumstances the flow separation is undesirable and leads to unwanted pressure drop and energy losses.…”

Experimental study of nanofluid flow and heat transfer over microscale backward- and forward-facing steps

“…These nanoparticles can be for instance Al 2 O 3 , SiO 2 , Cu, CuO, ZnO and TiO 2 [18]. Many researchers have investigated the effects of nanofluids in the enhancement of heat transfer and the fluid flow [19][20][21][22][23][24][25][26][27][28][29][30][31].…”

Simulation of heat transfer to separation Air flow in a concentric pipe

“…Futher research were extended to various kind of working fluids (i.e. nanofluids), boundary conditions and geometries [6][7][8]. In the advent of numerical codes and sophisticated instrumentations, the complex flow in and around the recirculation can be investigated.…”