Combined Convection Research Articles

Mixed Convection Flow of Magnetized Casson Nanofluid over a Cylindrical Surface

This work aimed to establish a numerical simulation of kerosene oil as a host Casson fluid flowing around a cylindrical shape with an applied magnetic field crossing through it, under constant wall temperature boundary conditions. Nanoparticles of zinc, aluminum, and titanium oxides were included to reinforce its thermal characteristics. The governing model was established based on the Tiwari and Das model. Graphical and numerical results for correlated physical quantities were gained through the Keller Box method, with the assistance of MATLAB software (9.2). The combined convection (λ>0 & λ<0), magnetic parameter (M>0), Casson parameter (β>0), and nanosolid volume fraction (0.1≤χ≤0.2) were the parameter ranges considered in this study. According to the current findings, the growth of mixed convection parameter or volume fraction of ultrafine particles contributes to boosting the rate of energy transport, skin friction, and velocity distribution. Zinc oxide–kerosene oil has the highest velocity and temperature, whatever the parameters influencing it.

Thermal performance in nanofluid and hybrid nanofluid under the influence of mixed convection and viscous dissipation: numerical investigation

The investigation of thermal performance in nanofluids and hybrid nanofluids is of much interest due to their multifarious range of applications in the modern technological world. Therefore, a study is organized to investigate the comparative thermal efficiency of nanofluid and hybrid nanofluid synthesized by Cu, Al2O3 and water. The novel effects of combined convection, viscous dissipation and magnetic field are incorporated in the constitutive model. The flow is considered over a wedge which is capable of stretching and shrinking . The problem is coded in MATHEMATICA 10.0 and then decorated with the effects of pertinent ingrained parameters in the physical ranges. From the results, it is examined that hybrid nanoliquids have high thermal efficiency than conventional nanoliquid due to their high thermal conductance. Particularly, the nanoliquid containing Al2O3 has high thermal performance due to their ultra-high thermal conductivity than the nanoliquid containing Cu particles. The thermal conductivity of Cu is very low than Al2O3, therefore it is examined that the nanoliquid comprising Al2O3 are better for industrial uses due to high thermal enhancement.

Energy, environmental and economic analyses of an indirect cocoa bean solar dryer: A comparison between natural and forced convections

The objective of the research is to present, the numerical simulation modelling of cocoa bean dryer in natural, forced and combined forced and natural convection to predict their effectiveness in a tropical environment. Cost analysis and CO2 mitigation potential of the solar dryer were also presented. The finite difference and fourth-order Runge Kutta method were used to resolve the iterative equations. The drying kinetics, drying rates, CO2 emissions mitigation, thermal efficiency and payback period are estimated in Yaoundé climate in Cameroon. It was difficult to have the moisture content of the product in equilibrium with ambient air using only natural convection. The best mode of functioning is to use forced convection during sunny period and natural convection during not sunny period. With an initial moisture content of 1.2 kg/kg (db), it took 32 h of drying time to obtained final moisture content of 0.15 kg/kg (db) using forced convection during the day and natural convection during the night for each month. The gradients of humidity and temperature are sufficient to have a homogeneous drying in the established product layers. The specific energy consumption range between 5 and 15 kWh per kg of humidity extracted for the combined natural and forced convection. The thermal efficiency of the solar collector is above 30%, while the global thermal efficiency ranges from 5% to 18%. The CO2 emissions mitigation potential per mass of evaporated water ranged between 15 and 25 g of CO2 per kg of water evaporated in a day. The calculated payback period was 2.19 years.

Numerical Study on Mixed Convection Flow and Energy Transfer in an Inclined Channel Cavity: Effect of Baffle Size

The objective of the current numerical study is to explore the combined natural and forced convection and energy transport in a channel with an open cavity. An adiabatic baffle of finite length is attached to the top wall. The sinusoidal heating is implemented on the lower horizontal wall of the open cavity. The other areas of the channel cavity are treated as adiabatic. The governing equations are solved by the control volume technique for various values of relevant factors. The drag force, bulk temperature and average Nusselt number are computed. It is recognised that recirculating eddies beside the baffle become weak or disappear upon increasing the inclination angle of the channel/cavity. The average thermal energy transportation reduces steadily until the Ri = 1 and then it rises for all inclination angles and lengths of the baffle.

Numerical study on combined convection heat transfer flow problem in a porous corrugated enclosure

AbstractIn this study, we numerically analyzed the unsteady two‐dimensional combined convection flow problem in a porous‐corrugated enclosure whose upper wall is moving with uniform velocity associated with sinusoidal temperature distribution. The vertical sidewalls of the porous‐corrugated enclosure are kept at constant cold temperature while square‐shaped undulations at the bottom wall are discretely heated. Five different cases are considered depending on the discrete isothermal heating. In this paper, we have used the vorticity‐stream‐function formulation of the Brinkmann‐extended Darcy model to numerically simulate the momentum transfer in a porous‐corrugated enclosure. A transformation‐free higher‐order compact (HOC) scheme is used to discretize the nonlinear coupled transport equations, and an advanced iterative solver, like the hybrid‐bi‐conjugate‐gradient stabilized technique, is used to solve the system of algebraic equations generated from the numerical discretization. The present higher‐order compact scheme is fourth‐order accurate in space coordinates and second‐order accurate in the time variable. The numerically simulated results are analyzed over a range of key parameters, like Darcy number , Reynolds Number , Prandtl number , and with fixed high Grashof number , to study the effects of these leading parameters on the characteristics of heat transfer, fluid flow and isothermal distributions in the porous‐corrugated enclosure. These numerically computed results are presented in the form of streamlines, isotherms, Nusselt number plots, and so forth. Our computed results show numerous flow features which have not been studied previously.

Flow Reversal of Fully Developed Combined Convection in a Vertical Channel with Boundary Condition of a Third Kind

The heat transfer process of combined convection and its flow pattern in a vertical channel is important, especially in environmental, industrial and engineering applications. There has been some concern regarding the heat transfer process in which it is difficult, expensive and time consuming. There are three main objectives to satisfy the purpose of this study which are to determine the impact on flow and heat transfer of the Robin temperature boundary condition, to verify whether the viscous dissipation plays a classical role in fluid flow and heat transfer and lastly to compare the degree of heat transfer facilitated by the boundary conditions of Dirichlet, Neumann and Robin. In this study, the effects of different dimensional parameters were tested and the flow reversal phenomenon was discussed. The Boundary Value Problem (BVP) was solved numerically using Maple using a built-in routine, dsolve. Validation study to the previously published problem was carried out to verify the accuracy of the present computation. The transformation of partial differential equation to ordinary differential equation involved similarity technique. The numerical results of the flow and temperature variables were presented graphically. The flow reversal occurred when the value of internal heat generation (G) and combined convection parameter (λ) were large. There was no occurrence of flow reversal when the values of local heating exponent (p) and the Biot Numbers (Bi) increase. However, the value of mass transfer coefficient (N) was different, gave no significant impact.

Analysis of combined radiation and convection heat transfer inside a porous medium with heat source electronic devices

In this study, a numerical study is performed on the cooling phenomenon of three heat source electronic devices. The electronic devices are cooled in the form of natural heat transfer by the airflow in a porous medium. Electronic devices are installed on the boundary walls of a square environment. Cooling simulations are performed by drawing flow lines and constant temperature lines. Our main goal is to find the highest cooling rate in different Darcy numbers and different Rayleigh numbers in our investigation. The range of Darcy numbers and Rayleigh numbers is between 0.0001 to 0.01 and 1000 to 100,000, respectively. Our investigation showed the maximum cooling is obtained at the Darcy number of about 0.01. And also, by decreasing the value of Darcy number, a higher cooling rate for the hot boundary walls is achieved.

Transient characteristics of coupled thermal radiation and natural convection in a three-dimensional cylindrical cavity containing a heated plate

In this study, a numerical study of transient combined natural convection and surface radiation in a cylindrical cavity with a heated plate placed inside is carried out using the open-source platform OpenFOAM. The effects of the Rayleigh number (105 ? Ra ? 107), inclination angle (0? ? ? ? 90?), and surface emissivity (0 ? ? ? 1) on the velocity components, temperature field, and Nusselt number are investigated in detail. Results show that the Rayleigh number has a greater effect on the radiative heat transfer than on natural convection. Radiative heat transfer increases monotonously with the increase of surface emissivity, and its contribution could be over 50% of the total heat transfer rate. The inclination angle of the plate affects the flow structure, but the difference in total Nusselt number is less than 10% for various inclination angles. Results in this study provide insights into the transient characteristics of coupled thermal radiation and natural convection in a three-dimensional cavity and will guide the optimal design of related devices.

Nanofluids modeling and energy transformation under the influence of mixed convection: Role of aluminum and γ-aluminum nanoparticles.

The analysis of nanofluids under various physical scenarios convinced the researchers and scientists because of their broad range of applications in potential area of the current time like chemical engineering, biomedical engineering and applied thermal engineering etc. To give the final shape of many industrial and engineering processes, enhanced heat transfer desired, therefore, the study of Al2O3-H2O, γAl2O3-H2O, Al2O3-C2H6O2, and γAl2O3- C2H6O2 nanofluids is reported. The model successfully achieved after mathematical operations and by appealing similarity transforms. To examine the behavior of heat transfer, numerical tools utilized and performed the results. It is observed that enhanced heat transfer in Al2O3-H2O, γAl2O3-H2O, Al2O3-C2H6O2, and γAl2O3-C2H6O2 could be attained by setting nanoparticles concentration up to 20%. For Al2O3-H2O, γAl2O3-H2O, optimum heat transfer trends noticed due to their prominent thermophysical values. Also, fewer effects of combined convection on examined.

Combined Convective Transport of Brinkman-viscoelastic Fluid Across Horizontal Circular Cylinder with Convective Boundary Condition

Traditional heat transfer fluids frequently encounter several limitations in the heat transfer process, due to the lower thermal conductivity in heat transfer process industries, and also has an impact on the performance of heat transfer in industrial sectors. In order to overcome the problem, researchers have currently considered an alternative development of heat transfer of fluids. Hence, this study will concentrate on the problem of steady combined convective transport. In particular, the flow of Brinkman-viscoelastic fluid over a horizontal circular cylinder with the influence of convective boundary condition (CBC) was investigated. Using the necessary similarity transformation, the governing equations were converted into a less complicated form and numerically solved by using Runge-Kutta-Fehlberg-method, which was programmed in Maple software. The influence of Biot number, combined convection, Brinkman and viscoelastic parameters are analyzed and demonstrated in graphs and tables. Numerical result showed that the fluid velocity increased with improving conjugate and combined convection parameter, but decreased with increasing Brinkman and viscoelastic parameter. It is also discovered the reverse trend on temperature profiles.

Numerical study for energy performance optimization of hollow concrete blocks for roofing in a hot climate of Morocco

• A numerical approach is performed for calculating the thermal inertia parameters. • The traditional roofs had the most significant total thermal load over 24-hours. • Integrate passive techniques into hollow blocks enhances their energy performance. • The inside heat transfer coefficient strongly impacts the roof's thermal inertia. • The outside heat transfer coefficient has no effect on the roof's thermal inertia. The roof is the component of the envelope more subjected to climatic excitations, and it contributes to a significant part of the total building's cooling load in hot climates. Therefore, the thermal optimization of hollow concrete blocks for roofing can considerably reduce the enormous energy consumption used for cooling buildings. For this purpose, the thermal inertia of different configurations of roofs built with traditional concrete blocks used in Morocco with three and six cavities was studied numerically. First, a two-dimensional coupled heat transfer by conduction, convection, and radiation was investigated in the steady-state using the Galerkin finite element method to generate an equivalent homogeneous monolayer block with similar thermal behaviour to the original hollow-block roof. After that, the transient heat conduction equation under real thermal solicitations is solved using a numerical inversion of the Laplace domain solution by utilizing the De Hoog algorithm to evaluate the dynamic thermal characteristics of the roofs. The results report that the emissivity and inside combined convection and radiation heat transfer coefficients significantly impact the roof's thermal inertia. In addition, it is shown that the configuration based on using a low emissivity coating and inserting an insulating material between the outer surface of the block and the slab could reduce the total thermal load over 24-hours by about 93.1% compared to the traditional configuration, which is beneficial to minimize the energy consumption used for cooling buildings.

Development of a non-stationary thermal environment analysis method for combined convection and radiation air conditioning

Advanced thermal environment simulation technology has been developing rapidly in recent years. The thermal environment simulation tools used in thermal engineering can be broadly classified into energy simulations and computational fluid dynamics programs. The combination of these approaches allows the high-accuracy prediction of a non-stationary thermal environment in a continuous space. The main feature of the coupled analysis method is that the radiation is calculated using energy simulation, which reduces the analysis load and makes transient analysis possible. Here, a method was devised for predicting the thermal environment of air conditioners and radiant panels, and its accuracy was verified. By coupling the convective heat transfer coefficient, the maximum mean absolute error of the proposed method was calculated to be 0.674 [-], which is acceptable considering the variable environmental conditions. Although in the acceptable range, this error is attributable to computational fluid dynamics, which is a steady-state analysis and does not fully track the non-stationarity of the radiant panel because of its stop–start nature. The results of this analysis are comprehensive, with the convective heat transfer coefficient calculated using the input conditions for each wall. Regarding the energy simulation, when temperature stratification occurred near a surface, such as the ceiling, a small error was induced because the reference temperature was set to the bulk temperature. However, as the overall trend was captured by the analysis method, these minor errors were deemed acceptable. These results show that the proposed method can be applied to a range of applications, including office spaces.

Analytical solutions of advection-dispersion-reaction equation with first decay under constant and time-dependent boundary conditions: Mass transfer shape factor effects

To describe the combined dispersion and convection mechanisms of solute transport through porous media, one may typically refer to the advection-dispersion equation (ADE). In this study, a generalized analytical solution to the ADE combined with first order decay term is derived for the problem of solute transport through porous media in one-dimensional finite region considering transient boundary conditions. First, the addressed convection-dispersion-reaction equation is simplified into a diffusion equation. Subsequently, an analytical solution is generated for a general fractured porous medium for a case where a fracture is viewed as the transient boundary condition. To verify the proposed analytical solution, experimental data acquired from literature as well as numerical techniques of finite difference and element are utilized. Previous studies have utilized fixed values for mass transfer shaper factor which is deployed in dual porosity modeling approach of fractured reservoirs, while in reality this parameter changes over time. In this regard, an attempt is made to attain mass transfer shape factor while considering the impacts of important parameters such as Péclet number, and decay coefficient during both pseudo steady state (PSS) and transient periods. Moreover, for two circumstances of linearly ascending and constant concentration boundary conditions, a correlation is developed to compute PSS mass transfer shape factor as a function of Péclet number, dimensionless time, and decay coefficient. The results illustrated the dependency of PSS shape factor on the decay coefficient, Péclet number, and time while transient shape factor solely depended on time. In addition, the findings showed that the larger the Péclet number, the larger the PSS matrix-fracture mass transfer shape factor. The obtained analytical solution is helpful when validating the numerical simulation results and for performing fast sensitivity analysis. The developed mass transfer shape factor can be applied in the dual porosity modeling part of the commercial reservoir simulation software packages for more accurately modeling the solute transport in the fractured reservoirs.

Dual Solutions in Mixed Convection Flow Along Non-Isothermal Inclined Cylinder Containing Gyrotactic Microorganism

The purpose of this research is to present dual solution for combined free and forced convection flow towards a non-isothermal permeable inclined cylinder containing gyrotactic microorganism. Though several researches were done on dual solutions for mixed convection and also along the vertical cylinder for the numerous engineering applications but very few works have done on dual solutions for mixed convection with gyrotactic microorganisms. Two steps are performed here to carry out numerical calculations. Firstly, the governing partial differential equations are simplified into set of coupled non-linear ordinary differential equations using similarity transformations and then solved numerically using bvp4c function from MATLAB. Dual solutions are observed for heat, mass and density of motile microorganism transfer rate and also for velocity, temperature, concentration, and microorganism profile beyond a critical point. The research is reached to excellent argument by comparison in few cases between the results obtained from MATLAB and Maple algorithm. The heat, mass and motile microorganism transfer rate decreases from free to mixed convection regime and then increases to forced convection regime with the influence of different flow control parameters. The results also indicate that dual solutions for different flow profiles exist only in free convection dominated regime.

A computational study of the triple-diffusive nonlinear convective nanoliquid flow over a wedge under convective boundary constraints

The present study is concerned with a triple-diffusive nonlinear (quadratic) combined convective nanoliquid flow at a wedge under the influence of convective boundary constraints and viscous dissipation. There would be many potential applications of this study of which a thermal system, geothermal power plants, aerodynamics, manufacturing of gate disk valves, nuclear power plants are just to name a few. In the wake of these potential applications, the study of fluid flow over the wedge has been found to be innovative and very interesting in the analysis of the influence of combined quadratic convection, viscous dissipation, diffusion of nanoparticles and hydrogen and oxygen in liquid state. A set of nonlinear coupled partial differential equations with boundary constraints constitute the modelled flow problem. Further, these equations are converted into non-dimensional form by employing the non-similar transformations. The equations thus obtained are then solved by utilizing the Quasilinearization technique and implicit finite difference approximation. The findings of the study reveals that the higher values Schmidt number reduce mass diffusivity of liquid oxygen as against liquid hydrogen. As a result, the fluid species' concentration profile varies inversely as increase corresponding surface gradient increases. Enhancing Biot number values enhances the magnitude of energy transfer rate.

Experimental and numerical study of mixed convection with surface radiation heat transfer in an air-filled ventilated cavity

The present study deals with the experimental and numerical investigation of steady combined laminar mixed convection and surface radiation heat transfer in the air-filled enclosure subjected to a constant heat flux supplied to the vent side of the cavity. Experimental results are presented for heat inputs, Q = 3.19 W–16.71 W, Reynolds number, Re = 4814–166385, and Richardson number, Ri = 0.1–25. In the present study, the numerical simulation is also performed in the two–dimensional vented cavity to enrich the experimental work for aspect ratio, A = 1–5, and surface emissivity, ε = 0.05–0.85. The momentum and energy equations under Boussinesq approximations are solved using a well-known finite-volume method, and numerical code is developed in Fortan 90 for getting all numerical results. Based on the experimental data, correlations are developed for the Nusselt number and maximum temperature of the heated surface.

Transient nanofluid flow and energy dissipation from wavy surface using magnetic field and two rotating cylinders

The problem of transient Magnetohydrodynamic (MHD) combined convection within a wavy-heated rectangular cavity having two inner cylinders is investigated using the non-homogeneous nanofluid scheme. The lower wavy surface of the cavity is kept at a constant hot temperature (Th) while the upper flat surface is kept at a constant cold temperature (Tc). The remaining surfaces (vertical surfaces) are maintained adiabatic. An Al2O3/water nanofluid is filled inside the cavity and a non-homogeneous approach is adopted to solve governing equations by using the Galerkin method. The effect of some parameters such as the angular rotational speed, the volume fraction of nanoparticles, Hartmann number on the flow and heat transfer characteristics are examined. The results indicate that the waving of the hot base of the cavity enhances the Nusselt number. The maximal Nusselt numbers are obtained when the number of undulations N is 2, where the Nusselt number augments by 18% when N is boosted from 0 to 2 and by 16% from 0 to and 5. Also, the outcomes reveal that the enhancement of the Nusselt number as a result of raising the rotational speed of the two cylinders from 0 to ± 500 is about 315%.

Numerical investigation of combined heat transfer (mixed convection-radiation) in 2D channel using the LBM

In this paper, the problem of combined convection (forced and natural) and radiation heat transfer between two parallel plates (channel) with isothermal walls has been numerically studied. For this purpose, the equations of momentum, energy and radiation transfer must be solved. In this study, lattice Boltzmann method is used to solve all of the equations simultaneously, that, to increase the stability for solving the energy equation by lattice Boltzmann method, a modern approach called the two relaxation time model was used. The medium inside the channel was considered as a participating medium to solve the radiation transfer equation. Finally, after the formulation of governing equations and boundary conditions for the present problem in the lattice Boltzmann method, validating the results and simultaneously solving the equations, the effects of some parameters such as optical thickness, Planck number and Richardson number with changing the angle of the channel are studied on heat transfer, flow and temperature distribution.The results showed that the radiation parameters have a significant effect on the problem and can change the velocity and temperature distribution of the channel. In between these parameters, the Planck number has the most effect on the temperature and velocity of the fluid flow. Increasing the angle of the channel relative to the horizon increases the effect of buoyancy force, fluid velocity variations and fluid temperature values.

Impact of inhomogeneous unsteady participating media in a coupled convection–radiation system using finite element based methods

Combined convection–radiation is a common phenomenon in many engineering problems. A differentially–heated rectangular enclosure is a widely–used benchmark for testing numerical techniques developed for solving the coupled momentum and energy equations related to combined convection–radiation. Previous studies have tended to describe the phenomenon in cases using simplified characteristics for the participating media including the assumptions of: (i) uniform distribution, (ii) homogeneous cross section, (iii) grey gas radiation and (iv) under steady state conditions. The effects of an inhomogeneous unsteady participating media, e.g. composed of a mixture of gases, are arguably understudied. In this work the effect of an inhomogeneous unsteady participating media on combined convection–radiation inside a rectangular enclosure is considered, under both grey and non-grey gas modelling approaches involving a mixture of gases. A key novelty in this work is the inclusion of the ability to handle inhomogeneous participating media which change in space, time and absorption cross section values as a result of the convection–radiation coupling, allowing us to assess different gas modelling approaches. A global gas radiation model is used and a new non–uniform discretisation method for the absorption distribution function is introduced; this method allows a better handling of those energy groups in which the Planck absorption coefficient is low, improving the performance of the spherical harmonics method and mitigating ray–effects on finite elements in angle discretisation. The momentum and energy equations are solved numerically using finite element based discretisation methods. The radiative transfer equation is solved numerically using both spherical harmonics and finite elements for the angular discretisation, with their relative performance compared. The results highlight the importance that the characteristics of the participating media can have on the convection phenomenon and therefore on the resulting temperature field.

Assisting and Opposing Stagnation Point Pseudoplastic Nano Liquid Flow towards a Flexible Riga Sheet: A Computational Approach

Nanofluids are used as coolants in heat transport devices like heat exchangers, radiators, and electronic cooling systems (like a flat plate) because of their improved thermal properties. The preeminent perspective of this study is to highlight the influence of combined convection on heat transfer and pseudoplastic non-Newtonian nanofluid flow towards an extendable Riga surface. Buongiorno model is incorporated in the present study to tackle a diverse range of Reynolds numbers and to analyze the behavior of the pseudoplastic nanofluid flow. Nanofluid features are scrutinized through Brownian motion and thermophoresis diffusion. By the use of the boundary layer principle, the compact form of flow equations is transformed into component forms. The modeled system is numerically simulated. The effects of various physical parameters on skin friction, mass transfer, and thermal energy are numerically computed. Fluctuations of velocity increased when modified Hartmann number and mixed convection parameter are boosted, where it collapses for Weissenberg number and width parameter. It can be revealed that the temperature curve gets down if modified Hartmann number, mixed convection, and buoyancy ratio parameters upgrade. Concentration patterns diminish when there is an incline in width parameter and Lewis number; on the other hand, it went upward for Brownian motion parameter, modified Hartmann, and Prandtl number.