Showing papers on "Combined forced and natural convection published in 2021"

Physics-Informed Neural Networks for Heat Transfer Problems

Abstract: Physics-informed neural networks (PINNs) have gained popularity across different engineering fields due to their effectiveness in solving realistic problems with noisy data and often partially missing physics. In PINNs, automatic differentiation is leveraged to evaluate differential operators without discretization errors, and a multitask learning problem is defined in order to simultaneously fit observed data while respecting the underlying governing laws of physics. Here, we present applications of PINNs to various prototype heat transfer problems, targeting in particular realistic conditions not readily tackled with traditional computational methods. To this end, we first consider forced and mixed convection with unknown thermal boundary conditions on the heated surfaces and aim to obtain the temperature and velocity fields everywhere in the domain, including the boundaries, given some sparse temperature measurements. We also consider the prototype Stefan problem for two-phase flow, aiming to infer the moving interface, the velocity and temperature fields everywhere as well as the different conductivities of a solid and a liquid phase, given a few temperature measurements inside the domain. Finally, we present some realistic industrial applications related to power electronics to highlight the practicality of PINNs as well as the effective use of neural networks in solving general heat transfer problems of industrial complexity. Taken together, the results presented herein demonstrate that PINNs not only can solve ill-posed problems, which are beyond the reach of traditional computational methods, but they can also bridge the gap between computational and experimental heat transfer.

Thermally radioactive bioconvection flow of Carreau nanofluid with modified Cattaneo-Christov expressions and exponential space-based heat source

Abstract: The nanoparticles proved a motivating research area in the fourth generation of the world due to their extensive use in science and infrastructure, such as vehicle cooling, higher heat transfer rates in microchips, food manufacturing, biotechnology, biochemistry, transportation, metrology and nuclear reactors. Dispersing the nanoparticles within base fluid is a newly approach for implementations of heat transfer and biomedicine/bioengineering. The current determination is committed to explore the features of bioconvection in Carreau nanofluid flow under the influence of various thermal consequences. The flow is originated by a stretched cylinder. The characteristics of Cattaneo-Christov heat and mass flux are applied to examine the heat/mass transportation of nanofluid. The effects of thermal radiation and activation energy are also considered. The consequences of Brownian movement and thermophoresis features are analyzed by incorporating Buongiorno’s nanofluid model. The governing partial differential equations are transmuted into the structure of nonlinear ordinary differential equations by introducing suitable transformation. The shooting technique is used to achieve the numerical simulations of nonlinear system. The physical impacts of prominent parameters on velocity, temperature distribution, concentration field and microorganisms profile are examined and captured graphically. The numerical outcomes against various flow quantities are also presented in tabular form. The results convey that a higher temperature profile is observed with larger values of thermal Biot number, exponential base sink parameter and thermal relaxation parameter while a decrement in temperature is noticed with increasing mixed convection parameter. The concentration profile shows an increasing trend with mass concentration parameter and concentration relaxation parameter. Moreover, the microorganism field decline with Peclet number and bioconvection Lewis number.

Cattaneo–Christov heat flux model for stagnation point flow of micropolar nanofluid toward a nonlinear stretching surface with slip effects

Abstract: Cattaneo–Christov with variable thermal relaxation time and entropy generation is the main concern of this study. The micropolar fluid with absorption of heat in the existence of mixed convection and partial slip is scrutinized. Two distinct nanoparticles, i.e., single-wall carbon nanotube and multi-wall carbon nanotube, are immerged in micropolar fluid to interrogate the feature of heat and mass transfer. The non-dimensional similarity transformation is utilized to transform the partial differential equations into nonlinear ordinary differential equations, and resulting coupled equations are solved numerically using bvp4c from MATLAB. The present results show the fabulous agreement with previous published results. The temperature field diminishes with larger thermal relaxation time parameter. Entropy generation profile is an increasing function of Brinkmann number, while Bejan number is a diminishing function. Further the solid volume fraction diminishes the velocity profile and enhances the temperature distribution and entropy generation.

Dynamics of multiple solutions of Darcy–Forchheimer saturated flow of Cross nanofluid by a vertical thin needle point

Abstract: Nanofluids have exposed a significant promise in the thermal development of several industrial systems, and at the same time, the flow via needle has major applications in modern construction systems including microstructure electric gadgets and microscale cooling gadgets for thermal migration applications. According to these applications, the current investigation concentrates to deliberate on 2D steady, laminar and incompressible flow of magneto-Cross nanofluid towards the region of moving thin needle in the occurrence of Darcy–Forchheimer porous medium, Ohmic and viscous dissipation with chemical reaction and mixed convection. The new dimensionless similarity variables are introduced to convert the nonlinear expressions governing the flow and transfer of heat. The change in velocity, thermal and concentration profiles for various non-dimensional parameters is deliberated briefly and illustrated with the help of suitable plots. Further, analysis of skin friction and rate of heat transfer is done through graphs. The results obtained are validated by existing works and are found to have a good agreement. The result outcome reveals that advanced values of magnetic parameter and Weissenberg number slowdown the fluid velocity motion. Also, upshot in Brownian motion and thermophoresis parameters improves the thermal profile.

MHD mixed convection of localized heat source/sink in an Al2O3-Cu/water hybrid nanofluid in L-shaped cavity

Abstract: The effect of source/sink heat location and size on Magneto-hydrodynamic mixed convection in hybrid nanofluid of Al2O3-Cu/Water within the L-shaped cavity is studied in this paper Two uniform heat sources are put at the corners of the bottom walls of enclosure and the beginning and the end of L-shape enclosure set to be at the cold temperature The other parts of enclosure’s walls are supposed to be insulated The finite difference method and Boussinesq approximation is utilized to discrete the governing equations The fundamental flow physics and thermal behavior are explored in terms of pertinent parameters such as the effects of sink/source heat generation, magnetic field and angle, Hartmann number, cavity length ratio, and hybrid volume fraction on average and surface Nusselt number, streamlines, isotherms, and entropy generation are studied The results demonstrate that maximum amount of the sink power causes the best heat transfer performance

Analysis of unsteady mixed convection of Cu–water nanofluid in an oscillatory, lid-driven enclosure using lattice Boltzmann method

Abstract: The unsteady physics of laminar mixed convection in a lid-driven enclosure filled with Cu–water nanofluid is numerically investigated. The top wall moves with constant velocity or with a temporally sinusoidal function, while the other walls are fixed. The horizontal top and bottom walls are, respectively, held at the low and high temperatures, and the vertical walls are assumed to be adiabatic. The governing equations along with the boundary conditions are solved through D2Q9 fluid flow and D2Q5 thermal lattice Boltzmann network. The effects of Richardson number and volume fractions of nanoparticles on the fluid flow and heat transfer are investigated. For the first time in the literature, the current study considers the mechanical power required for moving the top wall of the enclosure under various conditions. This reveals that the power demand increases if the enclosure is filled with a nanofluid in comparison with that with a pure fluid. Keeping a constant heat transfer rate, the required power diminishes by implementing a temporally sinusoidal velocity on the top wall rather than a constant velocity. Reducing frequency of the wall oscillation leads to heat transfer enhancement. Similarly, dropping Richardson number and raising the volume fraction of the nanoparticles enhance the heat transfer rate. Through these analyses, the present study provides a physical insight into the less investigated problem of unsteady mixed convection in enclosures with oscillatory walls.

Mixed convective slip flow of hybrid nanofluid (MWCNTs + Cu + Water), nanofluid (MWCNTs + Water) and base fluid (Water): a comparative investigation

Abstract: Here, we addressed comparative investigation of hybrid nanofluid (MWCNTs + Cu + Water), nanofluid (MWCNTs + Water) and base fluid (Water). Flow is due to curved sheet. Flow via slip boundary condition is examined. Heat transport analysis is carried out in the presence of viscous dissipation, mixed convection and convective boundary condition. Transformation procedure is adopted for converting PDEs (continuity eq., momentum eq., energy eq. and boundary conditions) into ODEs. These nonlinear coupled ODEs are solved via shooting method with RK-4 algorithms (bvp4c). Behaviors of involved parameters on flow, Nusselt number (heat transfer rate), temperature and skin friction coefficient are analyzed graphically. Velocity of fluid enhances with increment in nanoparticles volume fraction for multi-walled CNTs, nanoparticle volume fraction for Cu and mixed convection parameter, while it can be reduced via higher estimations of velocity slip parameter. Temperature of the fluid varies directly with an increase in nanoparticles volume fraction for multi-walled CNTs, nanoparticle volume fraction for Cu, Eckert number and thermal Biot number. Skin friction coefficient is reduced via higher mixed convection as well as velocity slip parameters. Nusselt number intensifies with increment in nanoparticles volume fraction for multi-walled CNTs, nanoparticle volume fraction for Cu, Eckert and thermal Biot numbers. During comparative study amongst hybrid nanomaterial, nanomaterial and base fluid, efficient behavior is noted for hybrid nanomaterial.

Numerical assessment of mixed convection flow of Walters-B nanofluid over a stretching surface with Newtonian heating and mass transfer

Abstract: The existing research investigates the numerical solution of a mixed convection flow of Walters-B nanofluid over a stretching sheet with Newtonian heating and mass transfer subject to the availability of magnetic field and mass suction. The impact of thermal radiation and chemical reaction with the Newtonian heat and mass transfer is conducted in detail. Also, the effects of nanoparticles are analyzed via considering the Brownian and thermophoresis motion. By utilizing similarity transformations, the relevant nonlinear governing equations with corresponding boundary conditions are modified to coupled nonlinear ordinary differential equations. These transformed coupled nonlinear ordinary differential equations are then solved numerically by providing the numerical approach bvp4c in MATLAB. The influence of multiple values of emerging parameters is studied by providing some graphs and tables with the consideration of both assisting and opposing flow regions. It is observed that the buoyancy parameter decays the velocity boundary layer thickness for assisting flow and the reverse trend is observed for opposing flow, as well as the viscoelasticity of nanofluid and Hartman number gradually reduces the boundary layer thickness. Further, the viscoelasticity parameter results in boosting the skin friction coefficient for both assisting and opposing flows whereas the Brownian and the thermophoresis motion have a reducing effect on the Nusselt number and Sherwood number enhances with the improvement of radiation parameter.

Entropy generation of tangent hyperbolic nanofluid flow over a circular cylinder in the presence of nonlinear Boussinesq approximation: a non-similar solution

Abstract: The analysis of entropy generation has received notable attention in the study of nanofluids because the prime objective of nanofluids is to admit high heat fluxes. The entropy production can be utilized to generate the entropy in any irreversible heat transfer process which is important in thermal machines. This work presents to explore the fluid transport characteristics and entropy generation of a tangent hyperbolic nanofluid over a horizontal circular cylinder with the influence of nonlinear Boussinesq approximation. The dimensionless nonlinear partial differential equations have been solved by using an implicit finite difference Keller box scheme. The impacts of active parameters on the flow field like Weissenberg number, power-law index, magnetic field, mixed convection, Brownian motion, thermal convention, thermophoresis and radiation are illustrated with graphs and tables. The current results exposed that the nanofluid velocity enhances for enhancing the mixed convection parameter. Isotherms thickness is escalated with increasing values of radiation parameter. Total entropy generation rises for higher values of dimensionless temperature ratio parameter.

Dynamics of Activation Energy and Nonlinear Mixed Convection in Darcy-Forchheimer Radiated Flow of Carreau Nanofluid Near Stagnation Point Region

Abstract: In this research work, heat and mass transport and radiated, two-dimensional, steady, incompressible nanofluid flow of non-Newtonian material (Carreau fluid) over a stretchable moving surface of sheet is examined. The flow is saturated through Darcy-Forchheimer porous medium and generated by stretching phenomenon. Furthermore, magnetodydrodynamics (MHD), mixed convection, heat generation/absorption, nonlinear thermal radiation, thermophoresis diffusion, activation energy, Brownian motion, and chemical reaction effects are accounted to develop the governing expressions, i.e., momentum, energy, and concentration for the considered flow problem. The governing equations are first altered into nonlinear ordinary differential equations with the help of appropriate similarity variables and then computational results are computed by Built-in-Shooting technique via mathematica. The salient aspects of sundry variables are discussed graphically on the velocity field, skin friction coefficient, temperature profile, Nusselt number, concentration field, and Sherwood number. Outcomes illustrate that the velocity field and temperature profile have contrast behavior against higher values of magnetic parameter. Also, the engineering quantities are discussed numerically with the help of important flow variables and the results are demonstrated through tables.

Mixed convection flow of hybrid nanoparticle along a Riga surface with Thomson and Troian slip condition

Abstract: The target of current research is to discuss the induced magnetic field stagnation point flow of carbon nanoliquids influenced by Riga surface with Thomson and Troian slip condition. The heat transfer phenomenon is manipulated over Cattaneo–Christov heat flux model with thermal stratification and heat generation or absorption. The flow model is transferred into nondimensionless form via convenient transformation. The numerical outcome of nonlinear complex equations is made by using bvp4c technique. The effects of emerging parameters on the velocity, temperature and concentration distribution are deliberated graphically. The velocity profile enhances with velocity ratio parameter and modified Hartman number. Further, the solid volume fraction enhances the temperature distribution and Sherwood number.

Chebyshev polynomials for generalized Couette flow of fractional Jeffrey nanofluid subjected to several thermochemical effects

Abstract: The generalized Couette flow of Jeffrey nanofluid through porous medium, subjected to the oscillating pressure gradient and mixed convection, is numerically simulated using variable-order fractional calculus. The effect of several involving parameters such as chemical reactions, heat generation, thermophoresis, radiation, channel inclination, and Soret effect is also considered. To the best of the authors’ knowledge, the described general form of the Couette flow problem is not tackled by the researchers yet. The non-dimensional form of heat, mass, and momentum equations is solved as a coupled set. The effect of several parameters such as Grashof, Hartmann, Prandtl, Soret, and Schmidt numbers in addition to oscillation frequency, retardation time, radiation, heat absorption, and reaction rate are determined and presented graphically. An operational matrix method based on the second kind shifted Chebyshev polynomials is proposed to investigate the behavior of the interested problem. In fact, regarding the established method, the unknown solutions are expanded by the mentioned basis polynomials. Then, the operational matrix of the variable-order fractional derivative is utilized to transfer the problem into solving an algebraic system of equations. According to the obtained results, the growth of fractional order from 0 to 1 changes the skin friction coefficient, Nu and flow rate by $$-18.1$$ , 35.5, and $$10\%$$ , respectively.

Numerical Simulation of Hybrid Nanofluid Mixed Convection in a Lid-Driven Square Cavity with Magnetic Field Using High-Order Compact Scheme.

Abstract: In this study, the energy transference of a hybrid Al2O3-Cu-H2O nanosuspension within a lid-driven heated square chamber is simulated. The domain is affected by a horizontal magnetic field. The vertical sidewalls are insulated and the horizontal borders of the chamber are held at different fixed temperatures. A fourth-order accuracy compact method is applied to work out the vorticity-stream function view of incompressible Oberbeck-Boussinesq equations. The method used is validated against previous numerical and experimental works and good agreement is shown. The flow patterns, Nusselt numbers, and velocity profiles are studied for different Richardson numbers, Hartmann numbers, and the solid volume fraction of hybrid nanoparticles. Flow field and heat convection are highly affected by the magnetic field and volume fraction of each type of nanoparticles in a hybrid nanofluid. The results show an improvement of heat transfer using nanoparticles. To achieve a higher heat transmission rate by using the hybrid nanofluid, flow parameters like Richardson number and Hartmann number should be considered.

Comparative Study of Mixed Convective MHD Cu-Water Nanofluid Flow over a Cone and Wedge using Modified Buongiorno’s Model in Presence of Thermal Radiation and Chemical Reaction via Cattaneo-Christov Double Diffusion Model

Abstract: The steady Cu-water nanofluid flow in presence of magnetic field is investigated numerically under the effects of mixed convection, thermal radiation and chemical reaction. For investigating the nanofluid flow, the flow over two different geometries, cone and wedge have been considered. The Tiwari and Das nanofluid model is implemented together with Buongiorno nanofluid model. Thermal and concentration diffusion are studied using the Cattaneo-Christov double diffusion model. At the boundary of the surface, no slip and zero mass flux condition are implemented to control the nanoparticle volume fraction at surface. Constitutive laws of flow are obtained in form of ordinary differential equations by the use of similarity transformation. The modeled flow problem is solved numerically by the Runge-Kutta-Fehlberg method and shooting scheme. Variation in flow properties due to parameters involved is presented graphically and through tabular values. The effect of thermal radiation and thermal relaxation parameter is to increase heat transfer. The temperature of nanofluid and drag force at surface increases due to enhanced magnetic field. The nanoparticles are found to be concentrated near the surface of cone and wedge but concentration decreases with chemical reaction parameter and Schmidt number as fluid moves towards far field.

Slip velocity and temperature jump effects on molybdenum disulfide MoS2 and silicon oxide SiO2 hybrid nanofluid near irregular 3D surface

Abstract: Various techniques have been employed by researchers with the aim to enhance the thermal performance of regular fluids such as water, kerosene oil etc. Nowadays the focus is on the hybrid nano materials as they are more effective in order to enhance the thermal conductivity of the fluids and liquid alloys as compared to nanofluids. This study is also performed with the objective of analyzing steady mixed convection flow near a 3D non-uniform vertical surface together with slips effects embedded in a porous medium with hybrid nano particles. The suspension under consideration is prepared in water to form MoS2–SiO2/water hybrid nanofluid by dissolving an inorganic compound Molybdenum disulfide (MoS2) and silicon dioxide (SiO2). The mathematical model describing the fluid flow has been formulated and similarity equations have been derived with the help of similarity transformations. The simulations of the obtained flow have been determined by employing bvp4c solver in MATLAB. The simulations for various physical parameters in the model demonstrate that incorporation of the hybrid nano particles in the fluid mixture result in higher heat transfer compared to the heat transfer produced by simple nanofluids. It is found that in order to obtain an efficient thermal system, the hybrid nano-particles should be considered in place of single type of nano particles. Moreover, the velocities of both the hybrid nano-fluids and simple nanofluids are enhanced by the mixed convection parameter however it is reduced by the porosity in both cases. It is also realized that an increment in the volume fraction of nano particles φ1 corresponds to increase in heat transfer rate. Additionally, the temperature measurements are at its lowest for τ2 while the maximum temperature is observed in case of solid volume fraction of nanoparticles φ1. The heat transfer rate in MoS2–SiO2/H20 is better than that of MoS2-H20. On the other hand, we can witness that the fluid velocity slows down by increasing the velocity power index parameter n. It is evident from investigation that hybrid nanofluids play a vital role in fluid transmission and higher temperature distribution is attained for nanofluid.

Mixed convection heat transfer of AL2O3 nanofluid in a horizontal channel subjected with two heat sources

Abstract: Mixed convection flow is investigated numerically for nanofluid flow and heat transfer in a horizontal channel considering two localized heat sources compared with pure fluid. The channel’s walls are insulated and the heat sources are at the center of the channel. Al2O3 nanoparticles are employed to modify the thermal conductivity of the base fluid. The effect of different parameters including Richardson number, Reynolds number, thermal conductivity, sources separation distance and the length-to-height ratio of heat sources is investigated. The results indicate that by enhancing the Richardson number from 1 to 10, the heat transfer from the source surfaces slightly increases; however, no significant effect is observed on thermal behavior. Increasing Reynolds number modifies heat transfer from sources and has a large effect on the streamlines and isotherms. In Richardson number of 5, for Reynolds number of 5, 50, 100, 150, the Nusselt number is 1.01, 4.50, 14.11 and 22.13, respectively. Furthermore, for a higher sources thermal conductivity, heat transfer increases due to the lower thermal resistance. The increase in average Nusselt number with changing the dimensionless thermal conductivity in the range of $$1 \le \bar{k} \le 100$$ is 314%. By examining the length-to-height ratio of heat sources, the results show that heat transfer decreases initially and then increases for higher values of length-to-height ratios. Furthermore, the heat sources separation distance shows a pronounce influence on heat transfer and thermal distribution. Besides, the results show that the effect of nanofluid concentration on average Nusselt number is more significant at low Reynolds number. The increase of average Nusselt number for Reynolds numbers of 5, 80 and 150 is 25%, 15% and 6.5%, respectively.

Three dimensional mixed convection flow of hybrid casson nanofluid past a non-linear stretching surface: A modified Buongiorno’s model aspects

Abstract: The purpose of this study is to determine the role of mixed convection, Brownian motion, and thermophoresis in the dynamics of Casson hybrid nanofluid in a bidirectional nonlinear stretching sheet. For the flow model, a combination of Tiwari and Das models, as well as Buongiornos model, is considered. The thermophysical characteristics of G r , T i O 2 , and blood are employed. With the assistance of relevant similarity transformation, the describing flow equations of a Casson hybrid nanofluid model are reformed in the form of a system with a single independent variable. The solution for these equations is obtained using the RKF-45 approach. The velocity, temperature, and concentration fields are visually developed for both linear and non-linear stretching sheets, and the implications of the major parameters are presented in detail. It is clear from the current investigation that heat and mass transfer characteristics of fluid are better in the case of linear stretching than non-linear stretching. Furthermore, the mixed convection parameter is found to enhance the fluid flow velocity. However, the trend is quite opposite in the thermal and concentration fields. Meanwhile, the increase in the yield stress caused due to the rise in the Casson parameter decreases the flow velocity.