Backward-facing Step Channel Research Articles

Numerical Analysis of Heat Transfer Enhancement Using Water / FMWCNT Nanofluid Passed in a 2D Backward Facing Step Channel

Numerical Analysis of Heat Transfer Enhancement Using Water / FMWCNT Nanofluid Passed in a 2D Backward Facing Step Channel

Multi-objective optimisation of a 2D backward-sfacing step channel with porous baffles

Porous baffles can be used to enhance heat transfer in various engineering applications, including electronic cooling, gas turbine blades, and chemical reactors. Also, the backward-facing step is a widely used configuration in fluid dynamics studies due to its simplicity and relevance to real-world geometries. This study examines heat transfer and flow characteristics in a backward-facing step channel featuring a heated bottom wall and two porous baffles. A computational fluid dynamics model, validated against prior research, is used to investigate flow and temperature fields. The innovation of this work lies in the application of multi-objective optimisation to search for a set of solutions that establish a trade-off between the average Nusselt number and the pressure drop. The optimisation specifically considers various parameters of the porous baffles, including height, width, distance from the step, and Darcy number, to identify optimal design configurations. Results show that porous baffles significantly improve heat transfer compared to a backward-facing step channel without them, despite an increase in pressure drop due to their presence. This work offers valuable insights into the trade-off between heat transfer performance and pressure drop, crucial for designing efficient heat transfer systems. By exploring the Pareto-Frontier, which represents various optimal design solutions, the study provides practical guidance when seeking to optimise heat transfer in backward-facing step channels with porous baffles. The findings contribute to advancing the understanding of heat transfer enhancement, highlighting the potential of porous baffles as a viable solution for improving thermal management in engineering systems.

Turbulent forced convection flow of water-based nanofluids with temperature-dependent properties over backward-facing step channel with upwardly deflected downstream wall

The heat transfer performances of various water-based nanofluids (NFs) relative to the base fluid in turbulent forced convection flow within a 2-D backward-facing step (BFS) channel with an upwardly deflected downstream wall with a uniform heat flux are analyzed using the package OpenFOAM. The k-ω shear stress transport (SST) model based on the Euler-Euler single-phase framework is used. The performance evaluation criterion (PEC) is defined to assess the relative importance of the enhanced heat transfer and intensified resistance (pressure drop) caused by Cu/water NFs and MWCNT-Fe3O4/water hybrid NFs (low concentration NFs), Fe3O4/water NFs, and Cu-MWCNT/water hybrid NFs (high concentration NFs). At Re = 30215, the maximum enhancement of the average Nusselt number (ANN) is 7% when the copper NPs are added to the water. In addition, the increment of the deflection angle from 0.0 to 1.27 enhances the ANN values by 44 ∼ 45% concerning low-concentration NFs. At Re = 7940, the friction factor increases by 24.3% and 32.1% when copper and MWCNT-Fe3O4 hybrid NPs are dispersed in the base fluid, respectively. The highest PEC value (1.07) is achieved when the copper NPs with ϕ = 0.003 are used in configuration BFS1 at Re = 7940. Using MWCNT-Fe3O4 hybrid NPs is only proposed at lower Re numbers when the downstream wall is deflected and ϕ = 0.001. At Re = 30215, due to the addition of magnetic NPs, the ANN value abates by 28.5% and 30.7%, respectively, in the canonical case and configuration BFS2. Among the high-concentration NFs, the highest PEC (1.05) is obtained using Cu-MWCNT hybrid NPs with ϕ = 0.01 at Re = 30215 when the downstream wall is deflected upwardly. As Mouromtseff (Mo) number-based figure-of-merit (FOM) verifies, the worst scenario (PEC < 1.0) is substituting the base fluid with Fe3O4/water NFs. Cu-MWCNT/water hybrid NFs with ϕ = 0.02 become an effective coolant (PEC > 1.0) when the deflection angle and Re number increase simultaneously.

Numerical Investigation of Hydrothermal Performance and Entropy Generation Through Backward Facing Step Channel with Oval Rib

Numerical Investigation of Hydrothermal Performance and Entropy Generation Through Backward Facing Step Channel with Oval Rib

Hydrothermal performance for forced convective flow of viscoplastic fluid through a backward facing step channel

The hydrothermal performance for steady, laminar forced convective flow of viscoplastic fluid through a backward facing step channel is studied. The effect of Bingham number (0 ≤ Bn ≤ 1), Reynolds number (50 ≤ Re ≤ 300), and power law index (0.2 ≤ n ≤ 1) on the thermal and flow characteristics are analyzed. A recirculatory zone is generated at the step corner and the findings depict a decrement in the length of reattachment as n and Bn increases. The temperature drop in the vicinity of the step increases as Bn increases. Also, it is found that the local Nusselt number (Nu) attains a peak in the vicinity of the step and the maximum Nu in this region increases with the increase in Bn. Moreover, for any particular value of Bn, Nu decreases with the increase in n. Also, the average Nusselt number increases significantly for viscoplastic fluids in comparison to shear-thinning and Newtonian fluids, and the heat transfer rate increases as Bn increases. Furthermore, there exists a critical value of Bn that alters the variation of average Nusselt number with the power-law index in case of separated flows.

HYDROTHERMAL PERFORMANCE IMPROVEMENT OF MICROSCALE BACKWARD-FACING STEP CHANNEL BY EMPLOYING VORTEX GENERATORS AND NANOFLUIDS

HYDROTHERMAL PERFORMANCE IMPROVEMENT OF MICROSCALE BACKWARD-FACING STEP CHANNEL BY EMPLOYING VORTEX GENERATORS AND NANOFLUIDS

Experimental Investigation of Nanofluid Turbulent Flow Over Microscale Backward-Facing Step

Experimental research was presented in this paper to illustrate the heat transmission and flow characteristics of nanofluid on a microscale backward-facing step channel. Except for the downstream wall, which was applied with uniform heat flow, the channel side walls were deemed adiabatic. Water was used as the base fluid and mixed with 30 nm diameter CuO nanoparticles with a volume fraction in the range of 0-0.04. The experiment was conducted at a Reynolds number range of 5,000–10,000. The results showed that the Nusselt number increases as the volume fraction increases. However, the increase in the nanoparticle volume fraction leads to an increment in the friction factor. Furthermore, the results indicated that increasing the Reynolds number lead to the volume fraction decreasing. It was found that there is an improvement of heat transfer by applying the CuO/water nanofluid with a 0.03 volume fraction of CuO nanoparticles with a significant performance evaluation criterion (PEC&gt;1).

Cooling of hot cylinder placed in a flexible backward-facing step channel

This paper copes with the mixed convection heat transfer and fluid–structure interaction (FSI) of a hot cylinder placed in a backward-step channel. The step is set to be flexible and deforms according to the force imparted by fluid. To attain the best cooling, different configurations of the flexible step were assessed. Equations governing the problem are solved using the finite element technique with the Arbitrary Lagrangian–Eulerian (ALE) approach to go along the moving domain. The influential parameters of such a problem are the Reynolds number Re, Richardson number Ri and the configuration of the flexible back step. Results demonstrated an improvement in the Nusselt number where at Ri = 100, a step of horizontal flexible wall augments the Nusselt number by 7.3% and 1.4% when Re = 100 and 500, respectively. Including the pressure drop in a performance criterion, it is shown that making the vertical wall of the step flexible (VFW) improves the aspects of heat transfer and the hydrodynamic of low Reynolds number, while at high Reynolds number, all suggested configurations of flexible step do not improve the performance criterion. It is found also that Reynolds number greatly improves the performance criterion while Richardson number does not.

Comparison of single-phase Newtonian and non-Newtonian nanofluid and two-phase models for convective heat transfer of nanofluid flow in backward-facing step

The aim is to investigate the application of nanofluids for improving the heat transfer in a backward-facing step channel. Numerical simulations are performed using single-phase models for both Newtonian and non-Newtonian fluids in the Reynolds number range 280–470. Constant and temperature-dependent thermo-physical properties of different volume fractions (0–4%) of nanoparticles are considered. The thermal enhancement of the nanofluids within the channel is analyzed and compared with the experimental data. A detailed comparison of different CFD models is established. Numerical results are obtained with two types of single-phase models (Newtonian and non-Newtonian) and three types of two-phase models (mixture, volume of fluid (VOF), Eulerian) and compared with experimental results obtained for the Nusselt number. The finite volume method is used to solve the system of governing partial differential equations describing the steady-state, two-dimensional, laminar, mixed convective flow in a micro backward facing step channel with uniform heat flux. The single-phase and two-phase models predict practically equivalent hydrodynamic fields, but significantly different thermal fields are observed in our results. The performance efficiency coefficient (PEC) is determined using single-phase and two-phase methods for Al2O3-water nanofluids at different Reynolds numbers to investigate their thermal performance.

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

Numerical simulations have been carried out to investigate the thermal-hydraulic characteristics using water-based CuO nanofluid with volume fraction (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 ratio (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. The 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 and velocity distribution under different flow conditions. Results 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 height causes the Nusselt number 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.

Heat transfer enhancement for nanofluid flows over a microscale backward-facing step

In this paper, we provide a numerical study of laminar flow in a micro-sized backward-facing step channel for water-based nanofluids containing Al2O3 and TiO2 nanoparticles and investigate the impact of the temperature differences between the inlet and the downward wall temperatures. The present work is the first study to introduce a temperature-dependent separation flow model. The velocity increases with increasing concentration of nanoparticles. However, when comparing Al2O3 and TiO2 nanofluids, Al2O3 has a velocity and shear stress higher than TiO2 for 0.04 volume fraction. Increasing the volume fraction of nanofluid led to an increase in the rate of heat transfer from the wall to the fluid, as the thermal properties improved as the volume ratio increased. The performance efficiency index (PEI) decreases as the volume fraction of the particle increases after a certain amount of nanoparticles. The simulation results of the nanofluid separation flow in the recirculation and reattachment shows that the velocity increases as the temperature difference increases, the size of the primary and secondary recirculation regions behind the step is significantly influenced with the temperature difference, a larger temperature difference means a larger recirculation zone.

Comparative Study of Thermal Performance of Different Nanofluids in a Double Backward-Facing Step Channel: A Numerical Approach

Two-dimensional numerical simulations are conducted to study forced convection flow of different water-based nanofluids (ZnO, Al2O3, and SiO2) with volume fractions ( ϕ ) = 0–5% and fixed nanoparticle size (dp) = 20 nm for Reynolds numbers (Re) = 50–225 over a double backward-facing step with an expansion ratio (ER) = 2 under constant heat flux (q″ = 3000 W/m2) condition using the finite volume method. Results indicate that the local Nusselt number increases with volume fraction and Reynolds number for all working fluids. In comparison to water, the maximum heat transfer augmentation of about 21.22% was achieved by using water-SiO2 nanofluid at Re = 225 with ϕ = 5% and dp = 20 nm. Under similar conditions, the Al2O3 and ZnO nanofluids demonstrated 14.23% and 11.86% augmentation in heat transfer in comparison to water. The skin friction coefficient decreases with the increase in Re for all working fluids. No significant differences are observed in the values of skin friction coefficient among all working fluids at a particular Re. These results indicate that the heat transfer enhancement has been achieved with no increased energy requirements. In addition, the velocity increases with the rise in Re, with SiO2 nanofluid exhibiting the highest velocity as compared to other working fluids.

Turbulent finite element model applied for blood flow calculation in arterial bifurcation

Background and objectiveDue to the relatively low fluid velocities in major arteries and veins, blood flow is by default laminar, however, turbulence can occur as a result of stenosis or other obstacles. Hemodynamic parameters like Wall Shear Stress or Oscillatory Shear Index can be used for plaque formation prediction, and these parameters are depended on the nature of the flow. Implementation of the k-ω turbulent flow in the Finite Element solver aims to improve numerical analysis of cardio-vascular condition development and progression. Calculation of turbulent fluid flow in this paper is performed using a two-equation turbulent finite element model that can calculate values in the viscous sublayer. MethodsImplicit integration of the equations is used for determining the fluid velocity, turbulent kinetic energy and dissipation of turbulent kinetic energy. These values are calculated in the finite element nodes for each step of the incremental-iterative procedure. Developed turbulent finite element model with the customized generation of finite element meshes is used for calculating complex blood flow problems. ResultsTurbulent model is verified on an example of fluid flow in the backward-facing step channel and analysis results correspond well with the experimental ones from the literature. Further, a turbulent model is applied for the simulation of blood flow through artery bifurcation. Verification of numerical examples obtained using different commercial software packages (Ansys, COMSOL Multiphysics) ensuring usage and accuracy of PAK in-house solver. ConclusionsAnalysis results show that turbulence cannot be neglected in the modelling of cardio-vascular conditions and that cardiologists can use the proposed tools and methods for investigating the hemodynamic conditions inside the bifurcation of arteries. Appropriate agreement between experimental results, and results obtained using commercial solutions and the k-ω turbulent flow in the Finite Element solver PAK, validate methodology presented in this paper. However, small deviations between the results underline the importance of the proper boundary condition prescription and mesh size and node distribution, which is also discussed in this paper. Due to the implicit integration implemented in PAK solver, time step size has an insignificant influence on the analysis results, assuming the initial time increments are sufficiently small to ensure proper discretization of velocity and pressure pulsatile functions.

Numerical investigation of double-diffusive mixed convection of Fe3O4/Cu/Al2O3-water nanofluid flow through a backward-facing-step channel subjected to magnetic field

PurposeThis study aims to investigate the buoyancy-induced heat and mass transfer phenomena in a backward-facing-step (BFS) channel subjected to applied magnetic field using different types of nanofluid.Design/methodology/approachConservation equations of mass, momentum, energy and concentration are used through velocity-vorticity form of Navier–Stokes equations and solved using Galerkin’s weighted residual finite element method. The density variation is handled by Boussinesq approximation caused by thermo-solutal buoyancy forces evolved at the channel bottom wall having high heat and concentration. Simulations were carried out for the variation of Hartmann number (0 to 100), buoyancy ratio (−10 to +10), three types of water-based nanofluid i.e. Fe3O4, Cu, Al2O3 at χ = 6%, Re = 200 and Ri = 0.1.FindingsThe mutual interaction of magnetic force, inertial force and nature of thermal-solutal buoyancy forces play a significant role in the heat and mass transport phenomena. Results show that the size of the recirculation zone increases at N = 1 for aiding thermo-solutal buoyancy force, whereas the applied magnetic field dampened the fluid-convection process. With an increase in buoyancy ratio, Al2O3 nanoparticle shows a maximum 54% and 67% increase in convective heat and mass transfer, respectively at Ha = 20 followed by Fe3O4 and Cu. However, with increase in Ha the Nuavg and Shavg diminish by maximum 62.33% and 74.56%, respectively, for Fe3O4 nanoparticles at N = 5 followed by Al2O3 and Cu.Originality/valueThis research study numerically examines the sensitivity of Fe3O4, Cu and Al2O3 nanoparticles in a magnetic field for buoyancy-induced mixed convective heat and mass transfer phenomena in a BFS channel, which was not analyzed earlier.

Fluid flow and heat transfer over corrugated backward facing step channel

The convective heat transfer and flow field characteristics through a backward-facing step (BFS) channel combined with a corrugated wall is investigated numerically and experimentally. Uniform heat flux is applied on 200 mm of the downstream wall, while the rest of the walls are considered isolated surfaces. The range of Reynolds number (Re) of the flow was between 5000 and 20,000. The governing equations were solved using the RNG k−ε turbulent model. The effects of wavelength and amplitude height of the corrugated wall on the friction factor and Nusselt number are studied. The results indicated that the fluid flow in the BFS channel combined with the corrugated wall significantly enhanced the heat transfer with increased friction. The average increase in the heat transfer rate and friction factor in the experiment is 40.7% and 46.2% respectively. The simulation results are comparable to the experimental ones. According to the simulations, the channel with an amplitude height of 4 mm and a wavelength of 20 mm has the highest heat transfer enhancement, reaching a performance evaluation criterion factor of 1.33 at 5000 Re.

Effects of inlet velocity profiles of hybrid nanofluid flow on mixed convection through a backward facing step channel under partial magnetic field

In this paper, mixed convection flow of a hybrid nanofluid is numerically studied in a backward facing step channel in the presence of a uniform partial magnetic field. Four different inlet velocity profiles are also taken into account. Stream function-vorticity formulation of governing dimensionless equations is adopted. The radial basis function pseudo spectral method for spatial derivatives and the backward-Euler method for time derivatives are implemented on nonuniform grids for numerical simulation of the problem. The influence of Hartmann number (between 0 and 50), Richardson number (between 0.01 and 100), the center of partial magnetic field (between 1 and 3) and the solid nanoparticle concentrations (between 0.01 and 0.04) are numerically examined. The results reveal that the smallest convective heat transfer is achieved in the step-centered partial magnetic field. The increase in magnetite nanoparticles has a significant influence on convective heat transfer, particularly, in case of sinusoidal velocity profile.

Experimental study of nanofluids flow and heat transfer over a backward-facing step channel

The forced convective heat transfer and friction factor of nanofluids flow over a backward-facing step (BFS) in a channel with the base wall dissipating a uniform heat flux are experimentally investigated in this paper. Nanoparticles such as CuO and MgO dispersed in pure ethylene glycol (EG) with average diameters of 40 nm, and volume concentrations of 0, 1, 3, and 5% are considered as the working nanofluids. The results indicate that the heat transfer rate increases as the volume concentration of nanoparticles increased. The Nusselt number is enhanced up to 11% at 0.05 volume concentration compared to pure EG. The friction factor increases up to approximately 15% at Reynolds number (Re) of 5000 and volume concentrations of 0.01 and 0.03. The maximum value of the PEC in a BFS channel is 1.5 for the CuO-EG and 1.2 for the MgO-EG at a volume concentrations of 0.03 and Re = 20,000.

Thermo-Solutal Buoyancy Effect on Heat and Mass Transfer in a Backward-Facing Step Channel Under the Influence of Different Shapes of Nanoparticles

Abstract Double-diffusive mixed convection in a backward-facing step (BFS) channel for different shapes of nanoparticles is analyzed using velocity–vorticity equations. The effect of four shapes of alumina nanoparticles at volume fractions χ of 1–5% on heat and mass transfer are studied for buoyancy ratios, N from −3 to 3 at Re = 200, Ri = 0.1, and Pr = 6.2. As χ increases, the Nuav decreases for all shapes at N = −3; however, it increases with an increase in N from 1 to 3. At N = 3, the Nu increases by 29% for blades shape, whereas a 28% decrease was noticed for platelets shape. An increase in χ of nanoparticles results in a decrease of Shav for N = 1–3, with a maximum decrease of 57% being observed at N = −3 for cylinders shape. The τav at the bottom wall continues to increase up to a maximum of 400% for platelets shape for N = 3.

Optimization of double diffusive mixed convection in a BFS channel filled with Alumina nanoparticle using Taguchi method and utility concept

This research work focuses on the implementation of Taguchi method and utility concept for optimization of flow, geometrical and thermo-physical parameters for mixed convective heat and mass transfer in a backward facing step (BFS) channel filled with Alumina nanoparticle doped in water-ethylene glycol mixture. Mass, momentum, energy and solutal conservation equations for the flow field are cast in velocity-vorticity form of Navier-Stokes equations, which are solved using Galerkin’s weighted residual finite element method through isoparametric formulation. The following six parameters, expansion ratio of the BFS channel (H/h), Reynolds number (Re), buoyancy ratio (N), nanoparticle volume fraction (χ), shape of nanoparticles and thermal Grashof number (GrT) at three levels are considered as controlling parameters for optimization using Taguchi method. An L27 orthogonal array has been chosen to get the levels of the six parameters for the 27 trial runs. Simulation results were obtained for 27 trial runs from which three different sets of optimum levels of the control parameters were obtained for maximum Nu and Sh and minimum wall shear stress during double diffusive mixed convection in the channel. Then, in order to obtain a single set of optimum levels of the control parameters to achieve maximum heat and mass transfer and minimum wall shear stress concurrently, utility concept has been implemented. Taguchi results indicate that expansion ratio and volume fraction of nanoparticles are the significant contributing parameters to achieve maximum heat and mass transfer and minimum wall shear stress. Utility concept predicts the average Nusselt number less by 2% and Sherwood number less by 3% compared to the Taguchi method with equal weightage of 40% assumed for Nusselt and Sherwood numbers and 20% for wall shear stress.

Effect of corrugated wall combined with backward-facing step channel on fluid flow and heat transfer

The turbulent fluid flow and heat transfer were numerically studied through backward-facing step combined with various corrugated walls. The governing equation was solved using Finite Volume Method (FVM) and the SIMPLE algorithm was applied to investigate the effect of backward-facing step with corrugated downstream on heat transfer characteristics. A constant heat flux was applied on the downstream wall, while the other walls were considered as adiabatic surfaces. Parameters such as corrugated design, amplitude height (1, 2, 3, 4 and 5 mm) and Reynolds number (Re) in the range of 5000 to 20,000 were used. The performance evaluation criteria (PEC) were estimated to show the heat transfer augmentation. The results indicated that using a corrugated wall with a backward-facing step increased significantly the heat transfer accompanied by a slight increase in the skin friction coefficient simultaneously. The best heat transfer augmentation was observed for the trapezoidal corrugation at 4 mm amplitude height and 20 mm pitch diameter. Combining the corrugated wall with backward-facing step enhanced the Nusselt number (Nu) up to 62% at Re = 5000. The performance evaluation criteria increased with the increase of amplitude height until it reached 4 mm and then decreased steeply.