Mixed Convection Heat Transfer Research Articles

Effect of cavity aspect ratio on mixed convective heat transfer phenomenon inside a lid-driven cavity due to elastic turbulence

This study performs extensive numerical simulations to investigate how the aspect ratio (AR) of a lid-driven cavity influences the onset of elastic instability and elastic turbulence and the subsequent mixed convective heat transfer rate inside it. To this end, we utilize the finite volume method based open source code OpenFOAM along with Rheotool to solve the mass, momentum, energy, and viscoelastic constitutive equations. We find that the dependency of the cavity AR on the heat transfer rate is highly complicated depending upon the values of the Richardson (Ri) and Prandtl numbers (Pr). At low values of Ri, the heat transfer rate continuously decreases with AR irrespective of the value of the Prandtl number and the fluid type, i.e., Newtonian or viscoelastic. The same trend is also observed at high values of Ri and low values of Pr. At these combinations of Ri and Pr, the heat transfer rate is always higher in viscoelastic fluids than in Newtonian fluids due to the presence of elastic turbulence in the former fluids. However, a different trend is observed at high values of both Ri and Pr. At this combination of Ri and Pr, the heat transfer rate increases with AR in Newtonian fluids, whereas it decreases in viscoelastic fluids. Therefore, at high values of AR, Ri, and Pr, the heat transfer rate is higher in Newtonian fluids than that in viscoelastic fluids despite the presence of elastic turbulence in the latter fluids. This is in contrast to the assumption that the elastic turbulence phenomenon always increases the rate of transport processes. A possible explanation for this behavior is provided in this study. Along with the heat transfer aspects, we also provide a detailed discussion on how the cavity aspect ratio influences the corresponding flow dynamics inside the cavity. In particular, we find that the onset of the elastic instability (and the subsequent elastic turbulence) phenomenon is delayed to higher values of the Weissenberg number as the cavity aspect ratio increases. This is in line with prior experimental studies reported in the literature.

Mixed Convection Heat Transfer in a Channel-Open Cavity with Two Heat Sources

Mixed Convection Heat Transfer in a Channel-Open Cavity with Two Heat Sources

Mixed convection heat transfer and entropy generation of MHD hybrid nanofluid in a cubic porous cavity with wavy wall and rotating cylinders

The current simulations are for the three-dimensional (3D) Fe3O4/MWCNT-water hybrid nanofluid flow within a 3D cubic enclosure filled with a porous medium. It was assumed that the flow area contains two rotating cylinders and has an upper wavy wall. Also the magnetic field is also applied to the problem due to magnetic nanoparticles in the base water. The Galerkin finite element method (GFEM) with a triangular element shape was applied to solve the governing equations. The findings were shown for a range of flow parameters such as angular speed of the cylinder (Ω=-500–1000), Hartmann number (Ha = 0–10), Darcy number (Da = 10−5–10−2), and direction of cylinders rotations and their positions in the cavity. The influence of the various parameters on flow, thermal transport, and entropy production is illustrated by the stream function, isotherms, and isentropic contours. Higher values of Ω Da and lower values of Ha enhanced the heat transfer and Nusselt number. Entropy production is mostly due to heat transfer; however, fluid-friction and magneto effects also contribute.

Experimental and numerical study on the heat transfer enhancement over scalene and curved‐side triangular ribs

AbstractThe present study examines the turbulent flow of mixed convection heat transfer enhancement within a rectangular channel considering three different novel shapes of ribs (smooth, scalene, and curved‐side triangular). The investigations were conducted experimentally by developing a new test facility, while the numerical computations were carried out using the finite volume method. The experimental work involves constructing of the channel, ribs, and all equipment and measurement instruments. The numerical work is based on ANSYS FLUENT considering the k–ε turbulent model. The results are presented and compared in terms of Nusselt number, friction factor, and performance factors for Reynolds numbers ranging between 3000 and 12,000. By comparing the average values of the numerically obtained Nusselt number with experimental measurements, the data showed a close agreement with a maximum difference of 5%. It also found that scalene triangular ribs (STRs) provide better performance in terms of heat transfer, although introducing a slight increase in friction losses. STRs showed (20%) increase in Nusselt number compared with smooth channel, and 3%–6% increase in Nusselt number compared with curved‐side triangular ribs (CTRs). In contrast, CTRs have a lower friction factor value of 5% compared with STRs at a low value of a Reynolds number of 3000. Furthermore, the Nusselt number changes significantly (250% increase) by increasing the value of the Reynolds number from 3000 to 12,000. A thermal performance factor of up to 1.28 was achieved for the STRs at the lowest range of Reynolds' number of 3000. The findings from the present study are of practical importance for industries requiring heat transfer enhancement techniques to improve heat transfer equipment performance.

Mixed convective heat transfer characteristics and mechanisms in structured packed beds

The structured packed bed is considered a promising reactor owing to its low pressure drop and good heat transfer performance. In the heat transfer process of thermal storage in packed beds, natural convection plays an important role. To obtain the mixed convective heat transfer characteristics and mechanisms in packed beds, numerical simulations and coupling analyses were carried out in this study on the unsteady process of fluid flow and heat transfer. A three-dimensional model of the flow channel in the packed bed was established, and the Navier–Stokes equations and Laminar model were adopted for the computations. The effects of the driving force on fluid flow around a particle were studied in detail. The differences in velocity and density distributions under different flow directions due to effect of the aiding flow or opposing flow were intuitively demonstrated and quantitatively analyzed. It was found that the driving force strengthens the fluid flow near the particle surface when aiding flow occurs and inhibits the fluid flow when opposing flow occurs. The boundary layer structure was changed by the natural convection, which in turn influences the field synergy angle. For the aiding flow, the coordination between the velocity and density fields is higher than that for the opposing flow. By analysis the effects of physical parameters on mixed convective heat transfer, it is indicated that with an increase in the fluid-solid temperature difference or the particle diameter, or a decrease in the fluid temperature, the strengthening or inhibiting effect of natural convection on the heat transfer became more significant.

MHD Mixed Convective Non-Newtonian Stagnation Point Flow Over an Inclined Stretching Sheet: Numerical Simulation

This paper includes numerical simulation upon MHD mixed convective heat transfer properties of stagnation point flow across an angled stretched sheet. Boundary value problem is solved using similarity transformation approach with shooting technique. The impact of different corporeal constraints like mixed convection parameter, thermal radiation parameter, chemical reaction parameter, Brownian motion and thermophoresis, Casson parameter upon velocity and temp profile as well as skin-friction coefficient , Nusselt number, Sherwood number on velocity, temp concentration profile are shown graphically. Casson parameter increases velocity and diminishes temperature profile. Chemical reaction term decreases Sherwood number and increases concentration profile.

Significance of thermo-diffusion and chemical reaction on MHD Casson fluid flows conveying CNTs over a porous stretching sheet

The current work aims to study the magnetic field on mixed convection heat transfer with Casson fluid flow over a porous medium in the presence of the thermo-diffusion mechanisms with CNTs. CNTs have a wide range of industrial, biomedical, energy production, and space cooling applications because they can improve the thermal properties of the base material. A non-linear governing equation is mapped to a set of ordinary differential equations via a similarity transformation. The highlight of the work is the Casson fluid using CNTs over a Darcy porous media through momentum and temperature profile with the support of an analytical process. The various plots are also used to discuss the effects of physical parameters such as Casson fluid; mass transpiration, Darcy number, and Dufour-Soret number on the profiles, which are depicted through graphical representations. Modulating temperature distribution in different industrial applications, including solar collector design, electronic cooling, building ventilation, etc. The study reveals that the thermal radiation, Casson fluid; mass transpiration, Darcy number, Dufour-Soret number, Lewis number, and Prandtl number increase the values of Richardson number, also buoyancy ratio, magnetic parameter, and volume fraction decrease the values of buoyancy ratio, also controls the transfer of heat. Studies are done on boundary effect studies that have an impact on fluid flow. The behavior of physical factors, such as the Lewis, Prandtl, Dufour, and Soret numbers influencing temperature and concentration field, is determined and presented using graphs. Highlights The analytical method is used to executive equations are converted in the highly non-linear ODEs are obtained from PDEs. The importance of SWCNTs and MWCNTs in modifying MHD, Richardson number, Buoyancy ratio Casson nanofluid parameter and Heat source/sink, carbon nanofluid flow is examined. Stretching/shrinking sheet under the impact of Magnetic parameter, Prandtl number, and mass transpiration non-Newtonian heating is considered. Water is a base fluid mixed with SWCNTs and MWCNTs. The impact of magnetic parameter, Casson fluid, Darcy number, Lewis number, Dufour number, Soret number, mass transpiration, and nanoparticle volume fraction parameter studied.

Non-Similar Solutions of Dissipative Buoyancy Flow and Heat Transfer Induced by Water-Based Graphene Oxide Nanofluid through a Yawed Cylinder

The fluid flow through blunt bodies that are yawed and un-yawed frequently happens in many engineering applications. The practical significance of deep-water applications such as propagation control, splitting the boundary layer over submerged blocks, and preventing recirculation bubbles is explained by the fluid flow across a yawed cylinder. The current work examined the mixed convective flow and convective heat transfer by incorporating water-based graphene oxide nanofluid around a yawed cylinder with viscous dissipation and irregular heat source/sink. To investigate the heat diffusion across the system of buoyancy effects, the mathematical formulation of the problem was modeled in terms of coupled, nonlinear partial differential equations. The boundary value problem of the fourth-order (bvp4c) solver was operated to find the non-similarity solution. The outcomes indicated that the velocity in both directions enlarged owing to the higher impacts of yaw angle for the phenomenon of assisting flow but decreased for the instance of opposing flow, while the temperature of nanofluid increased because of heightened estimations of yaw angle for both assisting and opposing flows. In addition, with larger impacts of nanoparticle volume fraction, the shear stresses were enhanced by about 0.76% and 0.93% for the case of assisting flow, while for the case of opposing flow, they improved by almost 0.65% and 1.38%, respectively.

Darcy-Forchheimer Flow of a Nanofluid Over a Porous Plate with Thermal Radiation and Brownian Motion

This research looked at the effects of thermal radiation and Brownian motion on the mixed convection heat and mass transfer of nanofluid over a porous plate in a Darcy-Forchheimer flow. The controlling partial differential equations are converted to ordinary differential equations and numerically solved by using Runge-Kutta fourth-order alongside shooting approach. Different physical parameters’ effects on temperature, velocity, and concentration distribution are studied. In addition, the results are also graphically represented. The reduced local Nusselt number and Sherwood number are shown and compared to previous investigations; the comparisons are extremely close. According to the results, the rate of heat transfer is lowered by 63.83% when the Brownian parameter is increased from 0.2 to 1 (in case of suction) and by 83.31% when the Brownian parameter is increased from 0.2 to 1 (in the case of injection). Also, in the case of suction, thermophoresis parameters lowered it by 50.48%, and in the case of injection, it was reduced by 65.08%.

Mixed convection heat transfer and transient flow of high-pressure gas in a large-scale cavity with rotating blade

Mixed convection heat transfer phenomenon, incorporating natural and forced convection process, occurs widely in natural and industrial fields. Nevertheless, few works have investigated numerically the turbulent mixed convection heat transfer within the large-scale structure under high-pressure condition. In this study, a three-dimensional numerical model of a large-scale closed cavity with two rotating blades and reactor has been built on account of the finite volume method, aiming to explore the mixed convection heat transfer and turbulent flow of internal high-pressure gas. Compressible gas with varying thermophysical properties was chosen as the heat transfer medium and the numerical model was solved by Unsteady Reynolds-Averaged Navier-Stokes (URANS). Turbulent flow and heat transfer, inside the enclosure and reactor, were compared through the variation of the Reynolds number (Re), gas pressure (P) and heating surface temperature (Th). The results signify that for given P and Th, varying Re has a consistent impact on the transient flow and heat transfer process inside the enclosure and reactor. The turbulent flow and thermal transport are enhanced as increasing the Re. When the Re = 900,000, an enhanced forced convection effect is found inside the reactor. Dissimilar impacts on the flow field and thermal transport inside the enclosure and reactor are found with changing gas pressure owing to the interaction of natural and forced convection. The flow field attenuates gradually as the increment in P, and thereby larger high-temperature zone is achieved at a smaller pressure inside the enclosure, whilst inside the reactor, faster heat conduction is attained at a bigger pressure. Changing heating surface temperature has a more significant influence on the flow field and heat transfer inside the reactor compared to the enclosure. Additionally, increasing the Re and Th has a smaller effect on the average Nusselt number (Nuavg) while a positive correlation between the Nuavg and P is obtained.

Mixed convective and radiative heat transfer of LiF-BeF2-ThF4-UF4 in a vertical circular tube

Molten salts are promising fluids for applications involving heat transfer and thermal energy storage. The buoyancy effect and radiative heat transfer effect are frequently ignored in previous studies that concentrate on forced convective heat transfer of molten salts. However, these effects might not be negligible, particularly for laminar flows of optically semi-transparent fluids, such as molten salts. Therefore, this study tries to understand the heat transfer characteristics of molten salts, including mixed (forced and natural) convective heat transfer and radiative heat transfer. A two-dimensional axisymmetric model is created in STAR-CCM+ for assisting (buoyancy-assisted) laminar flows of LiF-BeF2-ThF4-UF4 (67.5–20.0–12.0–0.5 mol%) in a 5-m long, 15-mm-inner-diameter vertical circular tube. The effects of several non-dimensional parameters on the velocity, temperature, and Nusselt number are examined, including the Reynolds number (Re¯=2.0×102to1.8×103), Grashof number (Gr¯=3.1×103to5.4×104), optical thickness (τ=0.1τ0to10τ0, τ0 = 0.27, 2.11, and 446.47 for the three bands λI = 0.10 to 3.36 µm, λII = 3.36 to 5.42 µm, and λIII = 5.42 to 100.00 µm, respectively), and emissivity (ε=0.0to1.0). A flow regime map is also suggested to assess the radiative heat transfer effect in molten salts. Our analysis demonstrates that: (1) the predicted results in this study deviate from published experimental data by 14.5 to 45.1 % without taking the buoyancy effect and radiative heat transfer effect into account, however, these differences are dramatically decreased to 10.1 to 17.4 % while considering the buoyancy effect or 7.5 to 14.7 % while considering the buoyancy effect and radiative heat transfer effect; (2) the radiative heat transfer effect tends to mitigate the buoyancy effect, but their net effect enhances heat transfer; (3) the buoyancy effect factor fbuoy and thermal radiation effect factor frad are, respectively, up to 38.5 % and 19.5 % under the conditions investigated, illustrating the need to evaluate the two effects for molten salts; (4)fbuoy becomes larger for smaller values of Re¯, τ, and ε, and larger values of Gr¯ and non-dimensional axial location x/Di. frad becomes larger for smaller values of Re¯ and larger values of Gr¯, τ, ε, and x/Di; and (5) the flow regime map provided in this study aids in determining whether the radiative heat transfer effect in molten salts is negligible.

Numerical investigation of turbulent mixed convection flow and heat transfer characteristics of 2 × 2 subchannels with spacer grids

AbstractIn turbulent mixed convection conditions, flow and heat transfer can deteriorate under specific conditions, thus affecting the performance of the safety of the system, which could imperil the safety of the nuclear reactor. In this paper, by analyzing the velocity, temperature distributions, and other thermal‐hydraulic parameters, the steady‐state computational fluid dynamics approach with the SST k–ω turbulence model used in this study was verified. Then, flow and heat transfer characteristics in turbulent mixed convection inside 2 × 2 subchannels with and without spacer grids were investigated. The results showed that the velocity profiles were distorted and the heat transfer capacity was impaired due to the influence of buoyancy. The Nusselt number ratio (Nu/Nuf) between turbulent mixed convection and forced convection increased with the increase of Reynolds number (Re) until unity but decreased with the increases of Grashof number (Gr) and Buoyancy parameter (Bo*).

Entropy Generation of CuO-Water Nanofluid in a Cavity with an Intruded Rectangular Fin

Entropy generation and heat transfer in cavities have received significant interest due to the ever-increasing demand for enhancing thermal performances in many scientific and engineering fields. In particular, nanofluids are being used increasingly in engineering applications and real-life problems, as they exhibit significantly better thermal properties than basic heat transfer fluids, for example, water, oil, or ethylene glycol. This study investigates the entropy generation and heat transfer of a nanofluid in a confined cavity with a moving top wall and a rectangular fin at the bottom. Here, a macro-homogeneous model based on a previously developed model is employed for investigating the mixed convective flow and heat transfer of CuO-water nanofluid. Various fin geometries, Rayleigh numbers, Reynolds numbers, and nanofluid concentrations have been employed. Present results indicate that the heat transfer rate can be improved, while entropy generation can be minimized using nanofluids instead of conventional heat transfer fluids.

Mixed Convection Heat Transfer From Swirling Open Spherical Cavity

Abstract This work reports a numerical study on mixed convection flows around a swirling spherical shaped open vessel in air within the laminar regime. This investigation is quite important and relevant in various industrial operations like centrifugal casting, formation of shield surfaces, thermal processing of different food stuffs, etc. This study aims to characterize the fluid flow and heat transfer behavior from both inner and outer surfaces of the open cavity. Governing differential equations, such as continuity, momentum, and energy are solved by using finite volume technique to describe the effect of relevant pertinent parameters over wide range: Rayleigh number (103≤Ra≤107), height to diameter ratio (0.15≤h/D≤0.95), and Reynolds number (0≤ReD≤300). It is observed that the plume is deformed greatly by swirling effect at higher ReD and lower Ra for a fixed h/D. The percentage of increase of heat transfer rate from ReD=0 to ReD≠ 0 is significantly higher at lower Ra for all cases of h/D. Lastly, a suitable correlation for average Nusselt number is proposed as a function of Ra, h/D, and ReD, which shows a satisfactory agreement with numerical data. This correlation is expected to be helpful for academic and industrial purposes.

Impact of size and location of outflow opening vent on mixed convective heat transfer induced by two aligned heated cylinders immersed in a partially open channel

AbstractThe current work deals with the numerical investigation of mixed convection occurring from two hot cylinders placed inside vented ducts under different sizes of inflow and locations of outflow opening vents. The mathematical formulation is solved based on the finite volume approach. The location of the outflow section is changed to left, center, and right of enclosure. Impacts of inflow section sizes (1 = 0.125 and 1 = 0.25), locations of outflow section ( = ), space between cylinders (), Reynolds number (), and Richardson number () are implemented. Findings display that the average Nusselt number (Nu) is exceeded by 20% for low due to the effect of nonsymmetrical inflow and outflow sections as compared with the case of equal opening vents. For large Ri, a higher Nu is obtained for nonequal opening vents in comparison with the case of equal opening vents by 10%. The difference in the average Nu between left and right cylinders is about 11%. Findings display that the enhancement in Nu due to the large spacing size between cylinders as compared with those of low spacing size is about 35%. The variations of Nu display the opening vents ratio, Re, , and have an extreme action on the characteristics of flow and temperature fields.

Numerical study of mixed and free convection heat transfer under ocean conditions

The mixed and free convection heat transfer of vertical upward flow under ocean conditions is studied numerically. The turbulent heat transfer in a smooth circular tube at low flow rates and the effects of ocean conditions are validated by experimental data. A CFD method based on the v2-f turbulence model and additional inertial force is established. The analysis indicates that the effects of ocean conditions on heat transfer depend on the Buoyancy parameter. In particular, for the mixed convection regime, the overall heat transfer increases, and the local heat transfer deterioration is aggravated. The mixed and free convection heat transfer under ocean conditions is dominated by the Coriolis force and gravity, so the influence of rolling radius is weak. As the rolling period increases, the heat transfer variation increases due to the inclination effects. However, as the rolling amplitude increases, the heat transfer behavior is non-monotonic and difficult to predict due to the combined action of Coriolis effects and buoyancy effects. The introduction of pulsating flow breaks the symmetry of heat transfer, and the hot spot only appears on one side. The overall heat transfer increases, but the local heat transfer deterioration is further aggravated.

RETRACTED: Mixed convective heat transfer in a power-law fluid in a square enclosure: Higher order finite element solutions

Incorporation of momentum gradients produced due to inertial motion of the lid along with the presence of temperature differences in the configuration make the physical problem more significant. The joint variation of momentum and thermal diffusion in diversified natural liquids is recognized as mixed convection. Valuable attention has been received by such a phenomenon in different areas of science and technology such as in wind current–based solar receivers, electronic instruments, control of emergency shutdown in reactors, thermal exchangers, oceanic currents, control of atmospheric pollution, and so on. So, the main focus is to contemplate hydrothermal characteristics of a power-law fluid contained in a square cavity with the movement of the upper lid and being thermally adiabatic. The other extremities are considered to be at rest, and the base wall is prescribed with uniform/non-uniform temperature distributions. The governing formulation of the problem is handled by executing a finite element approach. Hybrid meshing is performed for domain discretization, and weak variational formulation is utilized for formulation discretization. Second-degree polynomials are employed as the interpolation function, providing information about velocity and temperature distributions at boundary and intermediate nodes. The system of finalized non-linear equations is resolved by using the Paradiso software. The results for velocity and temperature distributions are attained comparatively for uniformly and non-uniformly heated profiles. The kinetic energy and average Nusselt number are also computed against flow concerning variables. From the attained graphical and tabular data, it is deduced that by increasing the Reynolds number, inertial forces dominate over buoyancy forces and the effect of lid movement is prominent on flow characteristics. It is also inferred that for the shear thickening case and for all values of the Reynolds number, the average Nusselt number shows a constant behavior.

Influence of nanoparticles on the electromagnetic hydrodynamic mixed convection flow and heat transfer of a polymeric FENE-P fluid past a Riga plate in the presence of Arrhenius chemical reaction

This article discusses the mixed convection flow of a non-Newtonian FENE-P polymeric fluid past a Riga plate and examines how the Lorentz force responds to temperature and nanoparticle concentration fluxes. The mathematical model considers the Grinberg-term for the wall parallel Lorentz force induced by the Riga plate as well as the Brownian motion and thermophoresis effects caused by chemically reactive nanofluid. The governing boundary layer equations are transformed by applying the strong suction condition. We numerically solve the problem using MATLAB package bvp4c based on finite-difference scheme to investigate physical parameters of interest like skin friction coefficient, Nusselt number, and Sherwood number. Polymers are explored as a potential agent for controlling velocity. The flow-aiding and flow-opposing Lorentz forces can be used to regulate the magnitude of skin friction, Nusselt, and Sherwood numbers, respectively which is significant in engineering and industrial applications. There is also a thorough explanation of nanoparticle concentration and polymers' role as drag coefficient, heat, and mass transfer rates control. Drag reduction is observed in the case of opposing flow mechanism and polymers inclusion.

Enhancement of mixed convection heat transfer in a square cavity via a freely moving elastic ring

Enhancement of mixed convection heat transfer in a square cavity via a freely moving elastic ring

MHD mixed convection non-isothermal flow and heat transfer analysis of non-Newtonian fluid saturated in I-shaped cavity

The current numerical study comprises the MHD lid-driven flow of bi-viscosity fluid inside the I-shaped cavity with variable heated short side walls, uniformly heated bottom and the rest of the walls are supposed to be adiabatic. Physical problems are formulated mathematically by exhausting the Navier-stokes and energy balance equation with the help of bi-viscosity model. In governing equations, pressure terms are eliminated by using the Penalty method, and then Galerkin weighted-residual procedure with finite element technique is used to solve them. The obtained results establish that the fluid flow velocity and heat transfer rate have been increased by increasing the bi-viscosity parameter and Reynolds number respectively. The intensity of streamlines and circulation cells increases with an increasing Grashof number, due to enhanced convective flow. Furthermore, the magnitude of Nusselt number along the bottom lid decreases by with an increase in the value of from to The applications of the under-considered problem can be found in numerous heat transfer phenomena, such as in heat exchangers, solar collectors, polymer suspensions, cooling processes of devices, production of food, manufacturing float glass, chemical catalytic reactors, and high-performance boilers.