Mixed Convection Flow Research Articles

Computational analysis of entropy generation minimization and heat transfer enhancement in magnetohydrodynamic oscillatory flow of ferrofluids

Improvements in heat transfer rate and entropy generation minimisation are critical issues in many engineering and industrial applications where efficient heat transfer is essential to achieve optimal performance and lower energy consumption. This study investigates the entropy generation of the mixed convection flow of ferrofluids in the presence of viscous and Joule dissipation. The flow is oscillatory and induced by the sinusoidal oscillations of a flat plate in its plane. Two Newtonian fluids, namely, kerosene oil C12H26C15H32 and methanol CH3OH are considered base fluids containing magnetite Fe3O4 nanoparticles. Governing equations are first modelled by employing the fundamental laws of transport phenomena. Then, using scaling analysis, these equations are transformed into a dimensionless system of partial differential equations. Numerical simulations are performed using the Gear-Generalized Differential Quadrature Method (GGDQM), and the model is validated with special cases from the literature. It has been found through numerical analysis that the convergence of GGDQM can be guaranteed by using only a small number of grid points. The thermal boundary layer of methanol-based nanofluid is thicker than that of kerosene. It has been observed that the skin friction coefficient increases for both categories of nanofluids as the values of the Eckert number, solid volume fraction, and Grashof number increase. The Nusselt number increases as the solid volume fraction increases, while the opposite trend is observed when the values of the Hartman, Eckert, and Grashof numbers rise. With increasing values of the Grashof number, the rise in the velocity of methanol-based nanofluids is higher than that of kerosene oil-based nanofluids. The maximum percentage difference between the velocities is identified to be 22.2177% at Gr=4.0. The temperature of methanol-based nanofluids rises more quickly than that of kerosene oil-based nanofluids with increasing values of the Grashof number. It is determined that the largest percentage difference between the temperatures is 20.5968% at Gr=4.0. When Ec=0, the percentage difference between velocities is 29. 1721 %, while the percentage difference between temperatures is 78.7155%. Compared to methanol-based ferrofluid, the volumetric entropy production is more extensive in kerosene-based ferrofluid. On the other hand, in comparison to a kerosene-based nanofluid, thermal irreversibility predominates in a methanol-based nanofluid. The novelty of this study lies in the computational treatment of coupled partial differential equations (momentum and energy) that incorporate buoyancy force, Joule heating and viscous dissipation effects, complementing the underlying physics and mathematical modelling of the research problem.

Irreversibility and spectral analysis for nanofluid with melting and higher order slip effects

This work is intended to examine the impacts of first and second-order velocity slips, viscous dissipation, and melting on mixed convective flow of nickel zinc ferrite + SAE 20W-40 motor oil based nanofluid along a stretching or shrinking sheet for the first time. The multigrade 20W-40 motor oil is categorized by Society of Automotive Engineers (SAE). An irreversibility analysis has also been performed using the second law of thermodynamics. The resulting non-dimensional flow-governing equations are modified into ODEs (Ordinary Differential Equations) and then the numerical estimates are provided by adopting the spectral local linearization method. Next, the efficiency of the above-mentioned spectral procedure is verified through the maximum error norms. Finally, the influence of important parameters included in this evaluation on the flow profiles and physical quantities is systematically represented. Based on the findings, the melting effect enhances the heat transference rate by 24.6% and reduces entropy by 38.4%. The use of higher-order velocity slips and viscous dissipation effects results in a lower friction factor. In the presence and absence of ferrite particles, the streamline visualization is clarified. This type of simulation is extremely useful for the readers in considering the rates of cooling or heating at electromagnetic interfaces, industrial devices, orthopedic joint replacements, aircraft turbines, bone plate surgeries, and so on.

Entropy generation analysis on zero mass flux effects of nonlinear mixed convective Williamson nanofluid flow with christov-Cattaneo heat flux

Entropy generation analysis on zero mass flux effects of nonlinear mixed convective Williamson nanofluid flow with christov-Cattaneo heat flux

Numerical investigation of corrugated wall configuration on hydrothermal performance and irreversibility characteristics

Improving thermal performance while minimizing pressure differences and irreversibility characteristics remains a persistent challenge in thermo-mechanical systems. This study investigates a corrugated channel with different profiles (triangular, square, and elliptical) for steady, laminar, incompressible, and mixed convective flow through a backward-facing step. The impact of corrugated wall geometrical characteristics, such as height, width, and angle, on hydrothermal performance is explored. Additionally, the study investigates the influence of inline and staggered arrangements for various channel configurations. The finite element method is employed for numerical investigation of thermohydraulic and irreversibility characteristics. Results, presented through streamlines, contours, and line plots, reveal a significant modulation of reattachment length based on corrugate architecture. Notably, the local Nusselt number is highest at the initial interaction with the corrugated channel, regardless of the channel configuration. Hydrothermal measurements highlight elliptical configurations as optimal, exhibiting a 60% improvement in thermal performance compared to a non-corrugated channel. Moreover, increasing corrugate height results in higher Nusselt numbers, pressure drops, and irreversibility. Reduced corrugate width leads to a higher Nusselt number due to the formation of a secondary recirculation zone. An elliptical corrugate with a 0° angle inclination yields the highest Nusselt number by facilitating a stronger recirculation zone. Thus, optimal corrugated wall configuration involves higher height, lower width, and no angle inclination, emphasizing the significant impact of these parameters on hydrothermal performance and their importance as design characteristics.

Influences of blowing and internal heating processes on steady MHD mixed convective boundary layer flows of radiating titanium dioxide‐ethylene glycol nanofluids

AbstractThe present analysis intends predominantly to explore the multiple behaviors of radiating ethylene glycol‐based titanium dioxide nanofluids during their steady boundary layer flows near a vertical permeable surface under the prominent impacts of uniform blowing and nonuniform internal heating processes. By incorporating the dynamical contribution of Lorentz and buoyancy forces in the momentum equation and adopting the single‐phase nanofluid approach along with the constitutive equations of the second‐grade rheological model and Corcione's correlations, the governing partial differential equations and their appropriate boundary conditions are derived mathematically based on the boundary layer theory and other admissible physical approximations. After several simplifications, the aforesaid differential formulation is converted into a set of ordinary differential equations and realistic boundary conditions, which are solved thereafter numerically using GDQ's‐NT method. Moreover, it is demonstrated that the strengthening in the blowing and internal heating processes has a boosting effect on the velocity and temperature profiles. However, the other influencing parameters show dissimilar dynamical and thermal trends. Furthermore, it is witnessed that the mixed convective heat transfer, the viscoelasticity trend of the nanofluidic medium, and the nanoparticles’ loading exhibit an enhancing impression on the surface heat transfer rate.

MHD mixed convective Maxwell liquid flow passing an unsteady stretched sheet

This study is aimed to investigate the unsteady two-dimensional combined forced and natural convective motion of MHD Maxwell liquid passing a stretched surface. Non-Newtonian feature of the liquid is portrayed with the ‘upper convected Maxwell fluid’ model. A prearranged surface ‘temperature’ at the boundary is considered. ‘Similarity transformations’ are applied to find the self-similar solutions and then the altered ‘equations’ are numerically solved with the help of ‘Runge-Kutta method with shooting technique’. The behaviours of ‘flow’ and ‘heat’ transportation characters for diverse foremost ‘parameters’ are examined and discussed in detail for clear understanding about the non-Newtonian flow features and related thermal field. The interesting behaviours of flow and heat transfer characters warrant further studies of this problem for other type of situations. Due to unsteadiness, ‘velocity and temperature’ are seen to reduce for ‘buoyancy aided and opposed’ flows. Also, it is noted that for ‘buoyancy aided and opposed flows’, liquid velocity diminishes for rising ‘Hartmann number’. The influences of mounting ‘Maxwell parameter’ are to delay fluid velocity for either value of mixed convection parameter. However, for this case temperature is improved. Owing to mixed convection, liquid velocity increases but the temperature reduces within the ‘boundary layer’ area. Here lies the significance of the present study as this result is very much helpful for industrial applications for cooling purpose of different devices.

Darcy–Forchheimer flow of Carreau fluid over a curved stretching surface with slip condition and variable thermal conductivity

The aim of this study is to perform analysis of nonlinear mixed convection flow of Carreau fluid due to curved stretched surface with slip condition. Furthermore, the effect of Darcy–Forchheimer and MHD is taken into consideration. The energy equation is modified by considering the variable thermal conductivity with Joule heating effect. The governing equations of the problem are highly nonlinear partial differential equations subjected to boundary conditions. Similarity transformations are used to transform nonlinear PDEs into ODEs. The numerical technique is used to solve this problem via bvp4c. The main outcomes of this research are that the impact of Forchheimer and porosity parameter tends to decrease the fluid velocity for shear thickening case. The velocity slip condition increases the fluid velocity only near the surface but the fluid velocity away from the surface does not get affected. The changing thermal conductivity raises the temperature of the fluid near the boundary. Furthermore, the impacts of various parameters on the velocity and temperature profiles are demonstrated. The values of local Nusselt number and skin friction for a different parameter are provided.

Effect of Hall current, Soret number, and inclined magnetic field on entropy generation of mixed convection Jeffrey fluid flow through sloping channel under Navier‐slip condition

AbstractIn this research article, the irreversibility of Jeffery fluid in mixed convective flow with inclined channel under the influence of Navier‐slip condition is analyzed. The effects of Hall current, Soret number, and an inclined magnetic field are taken into account. The spectral quasi‐linearization method (SQLM) is used to solve the governing equations after transforming them into a dimensionless form. The impacts of various parameters on velocity, temperature, and concentration are examined graphically. With the use of tabular data, variations in skin friction, the Nusselt number, and the Sherwood number are also discussed. Our findings indicate that entropy production increases with higher values of the magnetic parameter, Hall current, and inclination angle. Conversely, we have observed an opposing trend with an increased value of slip condition at the left plate and the Jeffrey fluid parameter.

Mixed convection flow of radiated Sutterby nanofluid by stretchable cylinder with irreversibility and heat generation

Entropy generation has gained consideration of researchers due to its applications. Applications of entropy occur in chillers, desert collars, refrigerators, and all type of heat transfer devices. Due to vast range of applications of entropy, in this study irreversibility in Sutterby nanofluid flow by stretchable cylinder is discussed. While reporting momentum equation magnetic field and mixed convection effects are considered. Influences of radiation, Joule heating, and heat source are deliberated in the expression for thermal energy. Chemical reaction impact is taken in the modeling of concentration equation. Irreversibility for the considered flow is obtained by utilizing thermodynamics second law. Dimensional partial differential equations (PDEs) representing the flow are transformed to dimensionless ordinary differential equations(ODEs) through similarity transformations. Solution of ODEs is obtained via NDSolve code of Mathematica. Impact of flow parameters on velocity, entropy, temperature, Bejan number, and concentration are studied graphically. Engineering quantities are analyzed numerically. It is noticed through achieved results that velocity drops for higher magnetic variable while upsurges for higher curvature variable. Thermal field boosts for higher magnetic and heat source parameter. For rising diffusion and radiation variables entropy improves.

A two‐stage reliable computational scheme for stochastic unsteady mixed convection flow of Casson nanofluid

AbstractResearchers can incorporate uncertainties in computational fluid dynamics (CFD) that go beyond the inaccuracies caused by numerical discretization thanks to stochastic simulations. This study confirms the validity of current stochastic modeling tools by providing examples of stochastic simulations in conjunction with numerical solutions for incompressible flows. A numerical technique for solving deterministic and stochastic models is developed in this work. Our approach employs the Euler‐Maruyama method for stochastic modeling, representing a stochastic version of the third‐order explicit‐implicit scheme. For the deterministic model, the scheme is third‐order accurate. The consistency and stability of the constructed scheme are provided in the mean square sense. The scheme is the predictor–corrector type that is built on two time levels. Moreover, a mathematical model of the Casson nanofluid flow with variable thermal conductivity is given with the effect of the chemical reaction. The appropriate transformations are used to condense the set of partial differential equations (PDEs) down to one that is dimensionless. The scheme is applied for the deterministic and stochastic models of dimensionless flow problems. The velocity profile's deterministic and stochastic behavior are shown using contour plots. Results show that growing values of the thermal mixed convection parameter enhance the velocity profile. This article presents the progress made in stochastic computational fluid dynamics (SCFD) and highlights the energy‐related aspects of our discoveries. Our computational approach and stochastic modeling techniques provide new insights into the energy properties of Casson nanofluid flow, specifically regarding the variability of thermal conductivity and chemical processes. Our objective is to clarify the complex interaction of these factors on energy dynamics. This article presents a contemporary summary of the latest SCFD advancements. Additionally, it highlights potential directions for future research and unresolved issues that require attention from the members of the field of computational mathematics.

Magneto-Hydro-Dynamic Generator with Joule Heating and Viscous Dissipation: An Analytic Investigation of Mixed Convection Flow

Magneto-Hydro-Dynamic Generator with Joule Heating and Viscous Dissipation: An Analytic Investigation of Mixed Convection Flow

Insight of mixed convectional heat transport in molybdenum disulfide-water nanofluid flow on moving vertical permeable plate with homogeneous-heterogeneous reactions

This analysis is framed to take care of the high heat transfer demand from various application prospects and in this context nanofluid may be in consideration because nanofluids are well-known liquids with higher heat transfer capabilities. Here, a mixed convection flow of Molybdenum disulfide-water (MoS2-H2O) nanofluid on a moving vertical plate is examined when there are chemical reactions. Nanofluid problem is investigated using Tiwari and Das model, and numerically solved by “bvp4c” method. For the considered effects in the study, overshoots in temperature profile of nanofluid are observed. Momentum and thermal layer thicknesses become thinner with suction and thicker with blowing. Temperature overshoot is higher for blowing cases. Enhanced homogeneous–heterogeneous reactions lead to rise of the concentration boundary layer’s thickness. Also, magnitude of surface-drag force decays and cooling rate enhances with MoS2-H2O nanofluid mixed convection. For weaker suction and for blowing, cooling of nanofluid is faster with larger volume fraction of nanoparticles, but contrast results are obtained for greater suction. Importantly, compared to the homogeneous reaction, the heterogeneous reaction exhibits more impactful influences on flow and heat-mass transport characters.

Impact of five obstacles with constant temperatures on the mixed convection flow of water/copper nanofluid in a rectangular cavity with a magnetic field

In this research, we conduct a computational investigation into the mixed convection flow of copper/water nanofluids (NFs) within a rectangular cavity, utilizing the Lattice Boltzmann Method (LBM). The cavity is uniquely configured with five high-temperature obstructions (HOBs), and we vary their dimensions and positions to evaluate Nusselt numbers (Nu) across a range of Richardson numbers (Ri). The three walls of the cavity, excluding the moveable top wall, are thermally insulated, while the latter is maintained at a lower temperature. A constant magnetic field (MCF) exerts influence within the cavity, with Ri spanning from 0.01 to 100, HOBs ranging from 0.1 to 0.5, and HOBs at the bottom wall spanning from 0.25 to 0.4. This numerical investigation is executed using a customized in-house code, focusing on examining heat transfer (HTR) dynamics within the cavity. Our findings reveal that augmenting the height of the HOBs and positioning them closer to the cold wall significantly enhances the average Nusselt number (Nuav). Conversely, an increase in Ri leads to a reduction in Nuav on the cold wall. Specifically, the most notable enhancement, with a 66.7 % increase in Nuav, occurs at Ri = 0.01 when HOBs are elevated from 0.1 to 0.5. On the other hand, an increment in Ri from 0.01 to 100 results in a 79.4 % reduction in Nuav. Furthermore, elevating the HOBs from 0.25 to 0.4 produces a substantial 44.3 % increase in Nuav.

A modification of explicit time integrator scheme for unsteady power-law nanofluid flow over the moving sheets

This paper introduces an exponential time integrator scheme for solving partial differential equations in time, specifically addressing the scalar time-dependent convection-diffusion equation. The proposed second-order accurate scheme is demonstrated to be stable. It is applied to analyze the heat and mass transfer mixed convective flow of power-law nanofluid over flat and oscillatory sheets. The governing equations are transformed into a dimensionless set of partial differential equations, with the continuity equation discretized using a first-order scheme. The proposed time integrator scheme is employed in the time direction, complemented by second-order central discretization in the space direction for the momentum, energy, and nanoparticle volume fraction equations. Quantitative results indicate intriguing trends, indicating that an increase in the Prandtl number and thermophoresis parameter leads to a decrease in the local Nusselt number. This modified time integrator is a valuable tool for exploring the dynamics of unsteady power-law nanofluid flow over moving sheets across various scenarios. Its versatility extends to the examination of unstable fluid flows. This work improves engineering and technological design and operation in nanofluid dynamics. Improving numerical simulations’ precision and computational efficiency deepens our comprehension of fundamental physics, yielding helpful information for enhancing systems that rely on nanofluids.

A finite difference explicit-implicit scheme for fractal heat and mass transportation of Williamson nanofluid flow in quantum calculus

This study introduces a novel and versatile fractal finite difference scheme designed to address unsteady flow challenges in quantum calculus over flat and oscillatory sheets. Motivated by the need to advance our understanding of nanofluid dynamics, particularly in heat and mass transportation, this research aims to bridge existing gaps and contribute to improving computational methodologies. Our approach involves a two-stage scheme incorporating explicit and implicit methods, focusing on q-derivatives for spatial terms within the mathematical model. The system encompasses the Navier-Stokes equation, energy equation, and concentration equation, offering a comprehensive framework for analyzing mixed convective Williamson nanofluid flow under the influence of chemical reactions. The convergence condition for the time-dependent partial differential equations system, particularly the scalar convection-diffusion equation, is presented. Stability requirements for our proposed fractal scheme are also delineated. Notably, our study explores the implications of the Weisenberg parameter on the velocity profile, revealing a decline that underscores its influence on nanofluid behavior. Our fractal finite difference scheme demonstrates a substantially faster convergence rate than the fractal Crank-Nicolson scheme. This outcome emphasizes the computational efficiency and efficacy of our proposed technique. In a broader context, our work contributes to the field by leveraging fractal geometry and quantum calculus to enhance our understanding of nanofluid dynamics. These tools present exciting opportunities for groundbreaking applications and technological advancements across various industries. As we delve into these research areas, our work sets the stage for exploration, providing a framework with great potential for transformative progress in nanofluid dynamics.

Effects of heater positions on magneto-hydrodynamic convection of CuO-water nanofluid flow in a grooved channel

PurposeThis study aims to delve into the coupled mixed convective heat transport process within a grooved channel cavity using CuO-water nanofluid and an inclined magnetic field. The cavity undergoes isothermal heating from the bottom, with variations in the positions of heated walls across the grooved channel. The aim is to assess the impact of heater positions on thermal performance and identify the most effective configuration.Design/methodology/approachNumerical solutions to the evolved transport equations are obtained using a finite volume method-based indigenous solver. The dimensionless parameters of Reynolds number (1 ≤ Re ≤ 500), Richardson number (0.1 ≤ Ri ≤ 100), Hartmann number (0 ≤ Ha ≤ 70) and magnetic field inclination angle (0° ≤ γ ≤ 180°) are considered. The solved variables generate both local and global variables after discretization using the semi-implicit method for pressure linked equations algorithm on nonuniform grids.FindingsThe study reveals that optimal heat transfer occurs when the heater is positioned at the right corner of the grooved cavity. Heat transfer augmentation ranges from 0.5% to 168.53% for Re = 50 to 300 compared to the bottom-heated case. The magnetic field’s orientation significantly influences the average heat transfer, initially rising and then declining with increasing inclination angle. Overall, this analysis underscores the effectiveness of heater positions in achieving superior thermal performance in a grooved channel cavity.Research limitations/implicationsThis concept can be extended to explore enhanced thermal performance under various thermal boundary conditions, considering wall curvature effects, different geometry orientations and the presence of porous structures, either numerically or experimentally.Practical implicationsThe findings are applicable across diverse fields, including biomedical systems, heat exchanging devices, electronic cooling systems, food processing, drying processes, crystallization, mixing processes and beyond.Originality/valueThis work provides a novel exploration of CuO-water nanofluid flow in mixed convection within a grooved channel cavity under the influence of an inclined magnetic field. The influence of different heater positions on thermomagnetic convection in such a cavity has not been extensively investigated before, contributing to the originality and value of this research.

Efficient passive GDQLL scrutinization of an advanced steady EMHD mixed convective nanofluid flow problem via Wakif–Buongiorno approach and generalized transport laws

Owing to the practical importance of nanofluids and their adjustable thermal capabilities, this study intends to develop a robust generalized differential quadrature local linearization (GDQLL) algorithm for examining realistically the heat and mass aspects of electrically conducting nanofluids during their non-Darcian laminar motion nearby a convectively heating vertical surface of an active electromagnetic actuator (i.e., Riga plate). By invoking Wakif–Buongiorno model and Oberbeck–Boussinesq approximations along with other generalized transport laws (i.e., Cattaneo–Christov and non-Fick’s laws) and Grinberg’s concept, a set of gigantic partial differential equations is stated appropriately in the sense of the boundary layer approximations for describing exhaustively the present EMHD mixed convective nonhomogeneous flow under the passive control strategy of nanoparticles within the nanofluidic medium. Operationally, the dimensionless differential forms of the governing boundary equations are derived properly by introducing reasonable mathematical adjustments into the preliminary formulation. In this case, the differential complexity of the leading differential structure is reduced to a nonlinear coupled system of ordinary differential equations, whose discrete numerical solutions are computed perfectly via a well-structured GDQLL algorithm. As foremost outcomes, it is demonstrated that the nanofluid motion and its surface thermal enhancement rate can be reinforced significantly through the thermal strengthening in the convective heating and mixed convective process as well as via the electromagnetic improvement in the driven aspect of Lorentz’s forces.

Mixed convection hybrid nanofluid flow over a stationary permeable vertical cone with thermal radiation and convective boundary condition

AbstractMany real‐world devices, such as heat exchangers, geothermal reservoirs, and cooling systems, utilize the concept of boundary layer flow across a cone geometry. The current study presents and analyses the mathematical formulation for the mixed convection flow of a hybrid nanofluid over a permeable stationary cone. The heat transfer analysis considers the effects of thermal radiation and convective boundary condition. Numerical and statistical analyses of this flow problem yield new, physically significant results. The numerical analysis is carried out using the bvp4c solver in Matlab. Similarity transformations are performed to obtain a system of nonlinear ordinary differential equations from the governing partial differential equations and boundary conditions. In both assisting and opposing flows, spherical‐ and platelet‐shaped nanoparticles are observed to produce the lowest and highest local skin friction coefficient, respectively. The spherical‐ and blade‐shaped nanoparticles also offer the highest and lowest local Nusselt number, respectively, with a difference of 6.4% (assisting) and 6.03% (opposing). Meanwhile, the increase in the mixed convection parameter raised the velocity profile but diminished the temperature profile of the hybrid nanofluid. Then, the relationship of the Biot number , suction , and thermal radiation ) parameters with the local Nusselt number is investigated through the response surface methodology (RSM). The local Nusselt number for the current flow problem is estimated to be maximized at 0.814323 (assisting) and 0.814629 (opposing) when these parameters are at the highest range of , , and . Several researchers had presented experimental studies conducted at different temperatures (15, 25, 35°C), mass flow rates (ranging from 0.00076 to 0.041 kg/s), and nanoparticle concentrations (0.387, 0.992, 3.12, 4.71 mass%).

Analysis of mixed convective stagnation point flow of hybrid nanofluid over sheet with variable thermal conductivity and slip Conditions: A Model-Based study

This research looks at the stagnation point flow of MHD Al2O3-Cu/H2O hybrid nanofluid against a permeable, vertically extending surface that uses thermal radiation and how different models of thermal conductivity affect it. This study is unique because it looks at how changes in thermal conductivity, mixed convection, and the slip velocity of hybrid nanofluids affect the stretching surface. It also looks at how changes in temperature, skin-friction coefficient, Nusselt number, and velocity affect convective thermal boundary conditions. With the use of boundary layer approximations, the complicated system of PDEs is simplified. The dimensionality of these PDEs and the boundary conditions they include are eliminated by applying certain modifications. Combining a local non-similarity approach up to the second truncation level with MATLAB's built-in finite difference code (bvp4c), one can obtain the results of the updated model. The research demonstrates and analyzes the impact of different factors on fluid flow and heat transfer characteristics in the studied flow situations. This is done by comparing the computed data with available literature and presenting the findings in graphical form. Tables are generated to present the numerical fluctuations of the drag coefficient and Nusselt number. This study shows how important thermal conductivity is in the mixed convection of hybrid nanofluids and looks into what happens when the thermal conductivity parameter is changed. Significantly, an augmentation in this parameter results in an elevation in the temperature distribution of the hybrid nanofluid while simultaneously reducing the rate of heat transfer across various models. Furthermore, increasing the nanoparticle volume fraction parameter leads to higher temperature and Nusselt number profiles while reducing skin friction. The mixed convection parameter has a notable impact on increasing the friction coefficient on the stretched vertical surface. However, because these elements function as regulating variables, it decreases when the magnetic, mass suction, and velocity slip parameters are present. The results also demonstrate notable discrepancies in the mean Nusselt values generated by various thermal conductivity models. According to the analysis, the Hamilton-Crosser model has the lowest average Nusselt numbers, followed by the Yamada-Ota model and the Xue model, in that order.

Opposing Mixed Convection Heat Transfer for Turbulent Single-Phase Flows

Convection, wherein forced and natural convections are prominent, is known as mixed convection. Specifically, when a forced convection flow is downward, this flow is called opposing flow. The objectives of this study are to gain a comprehensive understanding of opposing flow mixed convection heat transfer and to establish the prediction methodology by evaluating existing correlations and models. Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Because the definition of nondimensional parameters and their validated range confirmed by experiments differ for each correlation reported in previous studies, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing flow mixed convection and the single-phase heat transfer correlations implemented in the thermal–hydraulic system codes. Furthermore, the authors evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations can accurately predict all the experimental data. The effect of the difference in the thermal boundary conditions, i.e., uniform heat flux and uniform wall temperature, on the turbulent mixed convection heat transfer coefficient is not substantial. The authors confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids. The authors investigated the extrapolation performance of the mixed convection heat transfer correlations for a wide range of nondimensional parameters and observed that the Jackson and Fewster, Churchill, and Aicher and Martin correlations exhibit excellent extrapolation performance with respect to natural and forced convection flows, indicating that they can be applied beyond the parameter range validated experimentally.