Heat transfer and fluid flow over microscale backward and forward facing step: A review

Research on convective heat transfer in the microscale backward-facing step (MBFS) and microscale forward-facing step (MFFS) has been extensively conducted in the past decade. This review summarizes numerous researches on the three topics; the first section focuses on studying the effect of the geometry on the fluid flow and heat transfer behavior. The second and the third sections concentrate on the effect of the inclination angle and the flow regime on the fluid flow and heat transfer enhancement. The purpose of this article is to get a clear view and detailed summary of the influence of several parameters such as the geometrical specifications, type of fluids and boundary conditions. The enhancement in the Nusselt number is the main target of such research where correlation equations were developed in numerical and experimental studies are reported

Numerical study of assisting and opposing mixed convective nanofluid flows in an inclined circular pipe

A numerical investigation of mixed convection is carried out to study the heat transfer and fluid flow characteristics in an inclined circular pipe using the finite volume method. The pipe has L/D of 500 and it was subjected to a uniform heat flux boundary condition. Four types of nanofluids (Al2O3, CuO, SiO2, and TiO2 with H2O) with nanoparticles concentration in the range of 0 ≤ φ ≤ 5% and nanoparticles diameter in the range of 20 ≤ dp ≤ 60 nm were used. The pipe inclination angle was in the range of 30∘ ≤ θ ≤ 75∘ using assisting and opposing flow. The influences of Reynolds number in the range of 100 ≤ Re ≤ 2000, and Grashof numbers in the range of 6.3 × 102 ≤ Gr ≤ 8.37 × 103 were examined. It is found that the velocity and wall shear stress are increased as Re number increases, while the surface temperature decreases. There is no significant effect of increasing Gr number on thermal and flow fields. The velocity and wall shear stress are increased and the surface temperature is decreased as φ and dp are decreased. It is concluded that the surface temperature is increased as the pipe inclination angle increases from the horizontal position (θ = 0°) to the inclined position (θ = 75°). In addition, it is inferred that the heat transfer is enhanced using SiO2 nanofluid compared with other nanofluids types. Furtheremore, it is enhanced using assisting flow compared to opposing flow

Mixed Convection Over a Backward-Facing Step in a Vertical Duct Using Nanofluids-Buoyancy Opposing Case

Predictions are reported for buoyancy-opposing laminar mixed convection using nanofluids over a backward-facing step in a vertical duct, in which the upstream wall and the step simulated are 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 was maintained at constant temperature equivalent to the inlet fluid temperature. The conservation equations are solved using the finite volume method. Eight different types of nanoparticles, Au, Ag, Al2O3, Cu, CuO, diamond, SiO2, and TiO2, with 5% volume fraction are used. 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 33.3 ≤ Re ≤ 100. The downstream wall was fixed at uniform wall temperature in the range of 0 ≤ ΔT ≤ 30 °C which is higher than the inlet flow temperature. Results reveal that the recirculation region that develops behind the backward-facing step in the case of forced convection and low buoyancy-opposing level disappears when the buoyancy-opposing increases. An upward opposing flow is developed at the heated downstream wall from the exit to the step wall at high Reynolds number and high temperature difference, while at low Reynolds number and high temperature difference; the upward opposing flow is passed over the step wall and a shallow recirculation region is formed on the adiabatic upstream wall. It is found that SiO2 nanofluid has the highest Nusselt number at the highest buoyancy level. The skin friction coefficient decreases as Reynolds number and Prandtl number increase

Buoyancy-assisted mixed convective flow over backward-facing step in a vertical duct using nanofluids

Laminar mixed convective buoyancy assisting flow through a two-dimensional vertical duct with a backward-facing step using nanofluids as a medium is numerically simulated using finite volume technique. Different types of nanoparticles such as Au, Ag, Al2O3, Cu, CuO, diamond, SiO2 and TiO2 with 5 % volume fraction are used. The wall downstream of the step was maintained at a uniform wall temperature, while the straight wall that forms the other side of the duct was maintained at constant temperature equivalent to the inlet fluid temperature. The walls upstream of the step and the backward-facing step were considered as adiabatic surfaces. The duct has 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 downstream wall was fixed at uniform wall temperature 0 = ?T= 30 °C, which was higher than the inlet flow temperature. The Reynolds number in the range of 75 = Re = 225 was considered. It is found that a recirculation region was developed straight behind the backward-facing step which appeared between the edge of the step and few millimeters before the corner which connect the step and the downstream wall. In the few millimeters gap between the recirculation region and the downstream wall, a U-turn flow was developed opposite to the recirculation flow which mixed with the unrecirculated flow and traveled along the channel. Two maximum and one minimum peaks in Nusselt number were developed along the heated downstream wall. It is inferred that Au nanofluid has the highest maximum peaks while diamond nanofluid has the highest minimum peak. Nanofluids with a higher Prandtl number have a higher peak of Nusselt numbers after the separation and the recirculation flow disappeared

A multinational cross-sectional study on the awareness and concerns of healthcare providers toward monkeypox and the promotion of the monkeypox vaccination

BackgroundThe aim of this study was to explore potential healthcare workers' (HCWs) concerns about the monkeypox virus in order to create practical solutions to manage this disease.MethodsOnline cross-sectional research was conducted in 11 Arabic countries (Egypt, Saudi Arabia, Yemen, Syria, Libya, Algeria, Tunisia, Iraq, Palestine, Jordan, and Sudan) from 2 August 2022 to 28 December 2022.ResultsApproximately 82% of respondents felt the need to acquire further information. The acceptability of the vaccine against monkeypox has been indicated by more than half of the participants (54.5%). Furthermore, we state that 45% of the participants are knowledgeable about the monkeypox virus, and 53.1% of the participants have never been affected with COVID-19 before are more worried about COVID-19 than about monkeypox. Participants diagnosed with COVID-19 were 0.63 times less likely to worry about monkeypox than those who were not diagnosed with COVID-19. A greater willingness to get the monkeypox vaccination was seen among the age group 21–30 years (42.4%) compared to the other age groups.ConclusionMost healthcare professionals have a moderate knowledge of the monkeypox virus. Furthermore, they demonstrated a low willingness to get the vaccination against the monkeypox virus