Convection - Science topic

The way that the magnetic field affects the flow and thermal gradients determines how the Hartmann number (Ha) affects the creation of entropy in double diffusive convection. This is a broad pattern: The Lorentz force reduces the flow velocity as Ha grows because it raises the strength of the magnetic field. This results in: Less viscous dissipation (less entropy formation from fluid friction) results from reduced velocity gradients. Reduced heat transfer by convection → Greater temperature gradients may cause heat transfer to produce more entropy.

Double-diffusive mixed convection (DDMC) occurs when both thermal and solutal buoyancy forces interact in the presence of forced convection. It has significant applications in various engineering and natural systems where heat and mass transfer play crucial roles. Here are some of the most practical applications:

Hello Mehran Sharifi , thank you so much for answering. I tried to follow what you recommended but I got no luck. Regarding the values for the deactivation part of the function, COMSOL does not accept 0, as it gives an error in the computation.

To try to do some troubleshooting, I made a new file, considering only the first laser and the first layer. I still hade some temperature changes on the point in the middle of the layer that should be deactivated (seen on the Probe Plot in the file below). If you could give it a look, I'd be very grateful.

Double-diffusive forced convection occurs when both temperature and concentration gradients drive convection in a fluid, but the motion is influenced significantly by an external force, such as a pump or fan. This phenomenon has practical applications in various engineering and natural systems, including:

1. Heat Exchangers in Multicomponent Systems

2. Desalination Processes

3. Electrochemical Systems

4. Cooling of Electronics

5. Material Processing

6. Oceanographic and Environmental Engineering

7. Building Systems

8. Biomedical Applications

9. Industrial Drying

Double-diffusive forced convection plays a vital role in optimizing systems that require precise control of both heat and mass transfer in a dynamic and forced flow environment.

Please see my recent article on this matter:

Hubbert's fluid potential concept is indeed foundational in hydrogeology and reservoir engineering, particularly for describing groundwater flow and single-phase fluid flow in porous media. However, its application to variable-density, multiphase flow systems, such as oil reservoirs, introduces complexities that deserve careful consideration.

In single-phase, constant-density flow, the governing equations reduce to Laplace's or Poisson's equations, ensuring that flow lines strictly follow the gradient of a scalar potential function (hydraulic head or pressure). However, in a variable-density system—such as oil-water or gas-oil systems—density variations make the flow field nonlinear and dependent on:

For variable-density flow, we can define an equivalent potential field, but it is no longer scalar in the classical sense. Instead:

In multiphase systems, a rotational component can emerge due to:

This implies the flow is no longer purely irrotational, and vorticity (rotational flow) may exist locally. The rotational component does not invalidate the potential field concept but rather suggests it must be augmented with additional vector terms to describe convective and capillary-driven flows.

Yes, rotational components arising from density-driven flow or capillary effects can be superimposed onto the primary potential field, especially in transition zones like the water-oil contact (WOC) and gas-oil contact (GOC). These regions often exhibit capillary equilibrium, where gradients in capillary pressure balance gravitational forces, creating complex flow patterns.

Such flows are governed by coupled Darcy and continuity equations, including terms for relative permeabilities, saturation gradients, and multiphase interaction forces.

While Hubbert's potential field remains a useful approximation, the introduction of variable density, capillary forces, and multiphase flow challenges its direct application. Instead, augmented potential fields and hybrid formulations incorporating rotational effects provide a more comprehensive framework for reservoir engineering. This approach allows capturing both irrotational flow components (potential gradients) and rotational or convective movements (vorticity effects) in variable-density systems.

Let's try to troubleshoot further. Can you please provide more details about your simulation setup: 1. What type of analysis are you running (e.g., steady-state, transient, thermal)? 2. What are your boundary conditions (e.g., temperature, heat flux, convection)? 3. What materials are you using, and have you checked their thermal properties? 4. Have you applied any mesh controls or refinements? 5. Are there any other warnings or errors in the ANSYS output? Additionally, you can try: 1. Checking the ANSYS documentation for specific guidance on temperature limits. 2. Searching online forums or communities for similar issues. 3. Reaching out to ANSYS support or consulting with an expert. Let's work together to resolve this issue!

Modeling laser-induced convective flows in COMSOL involves simulating the interaction of laser heating with a fluid medium, resulting in temperature gradients that drive convective flows. This type of simulation typically couples thermal, fluid, and, in some cases, electromagnetic physics. Below are the steps to create such a model:

1. Set up the Geometry:

2. Select the Physics Interfaces:

3. Define Material Properties:

4. Set up Laser Heating:

5. Set up the Fluid Flow:

6. Couple Heat Transfer and Fluid Flow:

7. Define Boundary and Initial Conditions:

8. Mesh the Geometry:

9. Set Up the Study:

10. Run the Simulation:

11. Post-Processing and Visualization:

Additional Considerations:

By following these steps and adjusting for specific laser parameters and fluid properties, you can effectively model laser-induced convective flows in COMSOL.

Sure, Benelhaoues Mohamed

The role of advection of fluxes in modelling dispersion in convective boundary layers

Babatunde J. Abiodun, Leif Enger

First published: July 2002 Part A

Citations: 3

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Abstract A Eulerian three-dimensional higher-order closure dispersion model is presented. The model uses mean wind and turbulence quantities from a second-order atmospheric boundary-layer model. The dispersion model is validated against results from tank and field experiments and compared to results from Lagrangian dispersion models. The results show quite good agreement with experiment and Lagrangian modelling results for point source dispersion in a convective boundary layer (CBL). Sensitivity studies with the model help to identify the role played by advection and horizontal transport terms in the equations for the fluxes in simulating the essential features of pollutant dispersion.Results from the sensitivity tests show that the characteristic features of dispersion from point sources in the CBL—with an ascending plume during ground-level release and a descending plume from a lifted point source—are caused by an imbalance between the advection and diffusion terms in the equation for the vertical flux. Furthermore, it is shown that there is also a tendency for the plume to split horizontally, which is similarly caused by an imbalance between the advection and diffusion terms in horizontal fluxes. The simulated lateral standard deviations of distance x from a point source, for the vertically integrated concentration, are proportional to x close to the source and to x1/2 far away from the source, if and only if the advection and diffusion terms are included in the equations for the turbulent fluxes of concentration. Copyright © 2002 Royal Meteorological Society.

These are surfaces that are directly exposed to the furnace temperature and radiation. In the case of a column (H-Section), all surfaces are exposed to the furnace temperature, so all surfaces should be considered exposed. These are surfaces that are not directly exposed to the furnace temperature and radiation. In the case of a column, there are no unexposed surfaces since all surfaces are exposed to the furnace temperature. For accurate heat transfer simulations, radiation and convection interactions should be assigned to the exposed surfaces. This is because these surfaces are directly interacting with the furnace temperature and radiation.

Thank you for your answer,

I mean here (concept of local temperature difference, is difference between the surface and fluid temperature(or bulk fluid temperature)) the difference between the max temperature (wall) and the min temperature in the fluid at the same isosurface or plane (cross section 3D pipe).

Kind regards,

Ammar Laichi

Thank you for your answer,

If I use a PRESTO and second order to solve pressure , Momentum and energy equation with simple algorithm for velocity-pressure copling. How i can set up the underrelaxation factor?

Hey there Ammar Laichi,

When it comes to mixed convection in water flowing through a circular pipe, considering the Boussinesq hypothesis can provide valuable insights into temperature distribution.

In this scenario, the temperature range within each cross-section of the pipe is influenced by the balance between buoyancy-driven flow and forced convection. The Boussinesq approximation assumes that the density variation due to temperature differences is negligible, except for the buoyancy force term in the momentum equation.

Typically, in mixed convection, the temperature gradient across the pipe's cross-section varies, with warmer fluid accumulating near the center and cooler fluid closer to the pipe walls. This temperature profile is influenced by factors such as the Reynolds number, Grashof number, and Prandtl number, along with the imposed heat flux.

The precise range of temperatures within each cross-section depends on various parameters such as flow rate, pipe diameter, fluid properties, and boundary conditions. However, generally speaking, in mixed convection, the temperature difference between the center and the wall of the pipe may vary within a certain range, often with the central region being warmer than the outer regions.

To get a more specific understanding of the temperature distribution in your particular setup, it's essential to conduct detailed simulations or experiments considering the specific geometrical and flow conditions.

Hope this sheds some light on your query! If you Ammar Laichi need further clarification or have more questions, feel free to ask.

To me your results make perfect sense. Firstly, the thickness of the velocity boundary layer is dictated by the thermal boundary layer (buoyancy depends on density differences caused by the varying temperature). Increasing Pr, e.g. by decreasing the thermal diffusivity will lead to a thinner thermal boundary layer, hence also a thinner velocity boundary layer. Given that the buoyancy forces are the same (temp.difference is constant), the thinner velocity boundary layer yields higher shear stresses and as a consequence a lower maximum velocity. Increasing Pr by increasing viscosity would also reduce the max fluid velocity simply because of the increased viscosity.

Thank you for the clarification Jan.

In that case I agree with you that the subject is both interesting and in need of further investigation. The calculation of the EEI is performed in a climatic sense over decade-long scales. So, in the approach you propose, I think that it is necessary to do a similar averaging and compare the anomaly of the intensity of all the metrics/mechanisms that you mention against anomalies in EEI.

Nevertheless, I would argue that the situation you examine in your test case, is a rearrangement of heat through advection within the system itself, and of course it is being examined on the scale of synoptic meteorology and not the climatic one. Even after all the statistics and averaging, you will still have to explain the mechanism of how an anomaly in, say, 850hPa southerly winds in the Arctic, translates to an increase in emitted ToA longwave radiation.

My original argument about complexity remains, as the EEI has to do with the surface of the whole Earth (or top of the atmosphere), meaning that one of the mechanisms you propose could be counteracting an other, in a complex system with so many degrees of freedom; thus, I would definitely anticipate to find some non-linearities involved.

Don't get me wrong, I still find this a highly relevant and interesting research topic. I am probably not as optimistic in finding straightforward one-to-one relations.

All the best

Stamatis

Sorry. I never used Comsol.

Convection with an elastic wall, often referred to as convective heat transfer with a deformable or elastic boundary, has several practical applications across various fields:

### Biomedical Engineering:

1. **Tissue Heating and Cooling**: In hyperthermia treatment, where tumors are heated for therapeutic purposes, or in cryotherapy where tissues are cooled, understanding convective heat transfer with an elastic boundary is crucial. This helps in modeling the temperature changes in biological tissues during such treatments.

### Aerospace Engineering:

2. **Aeroelasticity and Thermal Protection Systems**: In designing aerospace structures, especially those experiencing high temperatures during re-entry, understanding convective heat transfer with an elastic boundary is important for thermal protection systems. Materials may deform due to heating, and this interaction between heat transfer and structural deformation is vital for ensuring the integrity of the spacecraft or aircraft.

### Material Science and Manufacturing:

3. **Molding and Forming Processes**: Processes like blow molding or thermoforming involve heating materials and then deforming them into specific shapes. Understanding convective heat transfer with an elastic wall helps in optimizing heating and deformation processes to achieve desired shapes and properties.

### Microfluidics and Nanotechnology:

4. **Microfluidic Devices**: In microfluidics, where tiny amounts of fluid are manipulated, convective heat transfer with elastic walls is significant. Understanding how heat interacts with deformable microchannels or membranes is crucial for designing efficient microfluidic devices for various applications such as lab-on-a-chip systems, drug delivery, or bio-sensing.

### Energy Systems:

5. **Thermal Management in Energy Devices**: In batteries, fuel cells, or other energy devices, managing heat is critical. Understanding convective heat transfer with elastic boundaries helps in designing efficient thermal management systems to maintain optimal operating temperatures, prevent overheating, and ensure longer device lifespan.

### Robotics and Soft Materials:

6. **Soft Robotics**: Deformable or elastic boundaries are common in soft robotics. Understanding convective heat transfer with such boundaries aids in designing soft robotic systems where thermal effects influence the mechanical behavior or deformation of the materials used.

### Environmental Engineering:

7. **Geothermal Applications**: In geothermal systems, understanding convective heat transfer in deformable geological formations is important for harnessing and utilizing geothermal energy efficiently.

These applications highlight the significance of comprehending convective heat transfer with elastic boundaries across various fields, influencing areas from medical treatments to space exploration and from energy systems to materials engineering.

explain your idea

Mixed double-diffusive convection, characterized by the simultaneous presence of temperature and concentration gradients in a fluid, offers several advantages in various applications. Here are some key advantages, along with explanations:

It's important to note that the advantages of mixed double-diffusive convection are context-dependent, and the specific benefits may vary based on the characteristics of the system and the application. In many cases, understanding and controlling mixed double-diffusive convection can lead to improved efficiency and performance in a wide range of engineering and natural systems.

Thanks Professor Filippo Maria Denaro

All materials have elasticity, do you mean wall that deforms under the pressure of the fluid?

Anywhere the cylinder is hot and rotating may be an application.

Respected Amjed A. Kadhim

Thank you so much for your explanation.

Double-diffusive convection flow with Soret and Dufour effects in an irregular geometry in the presence of thermal radiation

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https://doi.org/10.1016/j.icheatmasstransfer.2022.106026Get rights and content

Abstract

In this study, the effect of radiation on double-diffusive natural convection is investigated by considering the phenomena of Soret and Dufour in complex geometry, for the first time. The multi-time relaxation lattice Boltzmann method has been adopted to calculate the momentum, energy, and species equations. The radiative transfer equation has been solved using the finite volume method. Complex boundaries have been simulated by the sharp interface-immersed boundary method. The influences of effective parameters including the optical thickness (τ = 1 to 100), Rayleigh number (Ra = 104 and 105), Planck number (Pl = 0.01 to 1), Buoyancy ratio (Br = − 5 to 5), Soret number (Sr = − 1 to 1), and Dufour number (Df = − 1 to 1) have been analyzed on the flow field, heat, and mass transfer in a square cavity with an internal circular cylinder. Moreover, temporal variations of velocity and phase space trajectory have been used to study the effects of radiation on unsteady flow behavior. Results indicate that, the increment in optical thickness significantly reduces radiation, while a sweep behavior occurs in mass and heat transfer. Increasing the Dufour (Soret) parameter depending on the value of the Soret (Dufour) parameter can increase or decrease the mass (heat) transfer.

Introduction

Double-diffusive convection is a common phenomenon in natural and industrial applications such as crystal growth, oceanography [1], pollutant movement [2], drying technologies [3], metal manufacturing processes [4], chemical reactors [5], plastic and metal extrusion industries [6]. This phenomenon is created by buoyancy forces due to the simultaneous gradients of temperature and concentration [7]. The heat transfer produced by the concentration gradient is called the Dufour effect, and the mass transfer created by the temperature gradient is called the Soret effect. These effects play an important role in the natural convection flow when the temperature and concentration gradients are large. Nithyadevi and Yang [8] performed a numerical analysis on the natural convection flow of water with mass transfer by taking the effects of Soret and Dufour. Their studied geometry was a partially heated square cavity. They considered two modes, in their study. In the first case, they assumed that the concentration of the right wall was higher than the left wall, and in the second case, the left wall had been considered at a higher concentration than the right wall. One of the obtained results was that, as the number of thermal Rayleigh numbers increases, the heat and mass transfer rates increase too. In addition, it was observed that high values of the Dufour parameters cause the fluid particle to move with higher velocity and heat transfer rate. In the first case, they found that increasing the Soret parameter causes a reduction in the velocity and increases the mass transfer rate. In contrast, in the second case, the opposite behavior occurs. Bég et al. [9] investigated the heat and mass transfer processes of natural convection from a spherical body enclosed in a micropolar fluid by considering the effects of Soret and Dufour. It was found that increasing the Soret number causes an enhancement in the rates of heat transfer. Wang et al. [10,11] investigated the oscillation of a convection flow caused by the simultaneous effect of temperature and concentration gradients by taking the effects of Soret and Dufour in a horizontal cavity. It was found that with increasing buoyancy ratio, the flow structure has variation in a way that the flow changes from a steady state to a chaotic flow and finally to a periodic oscillation. Also, as the Soret and Dufour ascend, the oscillating convection changes from chaotic flow to periodic oscillation. Kefayati [12] analyzed the convection flow of a non-Newtonian fluid by considering the effects of Soret and Dufour in a square enclosure. They found that the Dufour parameter affects heat and mass transfer. In contrast, the Soret number only has a significant effect on mass transfer. Ren and Chan [13] proposed a new numerical method based on the lattice Boltzmann method (LBM), assuming the simultaneous heat and mass transfer with the effects of the Soret and Dufour in a square cavity. Kefayati [14,15] presented a finite-difference LB model to study natural convection flow caused by mass and temperature gradients in the presence of the Soret and Dufour effects. The geometry was an inclined porous cavity filled with a non-Newtonian fluid. It was clear that, for different Rayleigh numbers, by increasing the Dufour number, the heat transfer will increase, and on the other hand, the mass transfer rate has been increased by enhancing the Soret number. Liu et al. [16] proposed a non-equilibrium multiple-relaxation-time lattice Boltzmann (MRT-LB) model to investigate the heat and mass transfer problems resulting from concentration and temperature gradients with the effects of Soret and Dufour. In this study, they used a rectangular cavity to show the capability of their method and showed that their method is more stable than other LB models. Xu et al. [17] investigated the double-diffusive natural convection (DDNC) phenomenon in the presence of the Soret and Dufour effects around a cylinder with a circular geometry within a square cavity. It has been observed that the simultaneous increase in the Soret and Dufour numbers stabilized the flow in the unsteady state and reduced heat and mass transfer. In a numerical study, Qiu et al. [18] investigated the effects of the Rayleigh number, buoyancy ratio, and aspect ratio on natural convection flow with the effects of Soret and Dufour in a horizontal enclosure filled with low Prandtl number fluids. One of their results point was found that the role of convection heat transfer becomes more significant as buoyancy ratio enhances under different Prandtl numbers. Kefayati [19] investigates the effects of Lewis number, Bingham number, Rayleigh number, Eckert number, inclined angle, Dufour number, Soret number, and buoyancy ratio on the flow characteristics, the heat and mass transfer, as well as the entropy generations in a square enclosure. It was found that with the increase in the Soret and Dufour numbers, the entropy generations increase due to fluid friction and heat transfer. Kaladhar et al. [20] investigated the effects of chemical reaction, slip, and Soret and Dufour parameters on the flow characteristics and the heat and mass transfer of mixed convection flow within an annulus. By considering the results, it was understood that raising the Soret parameter amplifies the concentration profile while the fluid flow velocity and temperature profile decreases. In numerical research work, Sardar et al. [21] studied the effects of Soret and Dufour numbers, magnetic parameter, Prandtl number, wedge angle, Schmidt number, Brownian motion parameter, variable wall temperature and concentration, and thermophoresis parameter on heat and mass transfer rates during the mixed convection flow of a Nano-fluid on a wedge. One of the presented results was that if the Dufour number takes higher values, the thickness of the thermal boundary layer increases. With increasing the Soret number and the thermophoresis parameter, the boundary layer thickness of the nanoparticle volume fraction increases. By using Buongirno's nanofluid model, Salleh et al. [22], investigated the effect of Soret and Dufour on flow behavior along with mass and heat transfer characteristics of forced convection flow around a long, narrow needle. It has been found that in a particular region, the heat and mass transfer rates were inversely related to the Dufour and directly related to the Soret, and increasing the needle thickness will cause a reduction in heat and mass transfer. Wang et al. [23] investigated the effects of Soret, Dufour, buoyancy ratio, Lewis, and Rayleigh number on the flow characteristics and the heat and mass transfer for the convection flow within an open square cavity. The results indicated that when the buoyancy ratio is −1, the lowest rate of heat and mass transfer occurs. They also found that heat and mass transfer rates enhance as the Soret and Dufour numbers increase. In contrast, the Soret and Dufour impact on the heat and mass transfer rate is not obvious when Lewis number equal to 1. Hussain et al. [24] investigated the mixed convection flow with heat and mass transfer in the presence of a magnetic field in a cavity with a porous medium. In that study, they analyze the effects of buoyancy ratio, Soret and Dufour numbers, Darcy number, the inclination of the magnetic field, Lewis number, Hartmann number, and power low index on flow, temperature, and concentration patterns, as well as heat and mass transfer rates along with entropy generation. By considering their result, we can find that an increase in the Dufour number, Darcy number, and power low index leads to an increase in the heat and mass transfer rates. The mass transfer has an upward relationship with the Soret and Lewis number. In all of the above studies, researchers have concluded that two important physical phenomena, the effect of Soret and Dufour, play a significant role in fluid flow behavior, heat, and mass transfer of DDNC. On the other hand, it has been shown that DDNC has numerous practical applications inside closed spaces at low temperatures that can ignore the effects of radiative heat transfer. However, in high-temperature situations, radiation, due to its proportionality to the fourth power of absolute temperature, has an important effect on DDNC in the processes such as nuclear reactors, crystal growth, combustion chambers, etc. [25]. Hence, this issue has received a lot of attention in recent decades. Laouar-Meftah et al. [25] studied the DDNC phenomenon in the presence of radiation heat transfer in a two-dimensional enclosure with a non-gray medium. It was indicated from their result that at any given value of the buoyancy ratio and in all flow regimes, radiation reduces the total heat transfer. The unsteady and two-dimensional natural convection flow in the presence of radiation around a semi-infinitely moving vertical cylinder has been studied by Ganesan and Loganathan [26] and considering the mass transfer. It was seen that the radiation parameter has a significant effect on temperature and velocity distributions. Ibrahimi and Lemonnier [27] investigated the transient convection flow combined with radiation in a square enclosure under the presence of thermal and solutal buoyancy forces. They obtained that in aiding situation, the radiation accelerates the transition to a steady state. At the same time, while in the opposing, it takes longer for the flow to reach the steady-state, from the oscillating state. Abidi et al. [28] presented a numerical study on the effect of radiation on three-dimensional DDNC in a cubic enclosure. They investigated the conduction-radiation parameter and the optical thickness on flow behavior. They observed that in thermally dominated flow, increasing the conduction-radiation parameter causes a change from a multicellular inner core to a unicellular one. In a solutally dominated flow, the opposite behavior occurs. In addition, they found that at all values of the buoyancy ratio, the radiation will cause an increase in the transverse velocity. Moufekkir et al. [29,30] presented a numerical analysis in which the effects of various physical parameters on DDNC in a square cavity filled with a gray fluid have been studied. They concluded that volumetric radiation modifies the flow structure and temperature distributions. Serrano-Arllano and Gijón-Rivera [31] analyzed the DDNC phenomenon coupled with radiation in a two-dimensional enclosure. They concluded that radiative heat transfer, especially at high Rayleigh number values, reduces convection heat transfer while it will increase the total heat transfer. In a numerical study, Laouar-Meftah et al. [32] studied the effect of radiation on natural convection flow along with heat and mass transfer within a two-dimensional enclosure filled with a non-gray gas. They considered two modes. In the first case, they assumed that the thermal and solutal buoyancy forces were cooperating, and in the second case, they were opposing. It has been found from their result that in the first case, radiation has a significant effect on temperature and concentration characteristics and also reduces the total heat transfer while having little effect on mass transfer. But in the second case, radiation has a greater effect, which depends on the nature of the flow regime. Cherifi et al. [33] analyzed the effect of thermal radiation on DDNC in a cubic cavity filled with a non-gray gas. It was found that radiation creates oblique stratification in the structure of constant temperature and concentration lines, and also, the total heat transfer on the vertical walls is reduced. At the same time, there is little change in mass transfer. In a numerical study, Nee [34] investigated the DDNC phenomenon of a participant fluid in a rectangular enclosure. One of the results was that increasing the radiation parameter reduces the transfer heat rate while having little effect on the mass transfer rate. The effect of thermal radiation on the flow, heat, and mass transfer characteristics of double diffusion convection has been investigated many times by considering the effects of Soret and Dufour in simple one-dimensional geometries [[35], [36], [37], [38], [39]]. Reza-E-Rabbi et al. [35] have performed numerical work to indicate the effect of radiation on the magnetic multiphase nanofluid flow over a stretching sheet. They also considered the presence of a nonlinear chemical reaction in this modeling. The results revealed that increasing the radiation, magnetic, and heat source parameters along with the Dufour number causes a reduction in the heat transfer coefficient profiles. Ijaz Khan et al. [36] investigated the effects of different flow controlling parameters on nonlinear mixed convection MHD flow in the presence of radiative heat transfer. Our outcomes illustrated that the rate of heat transfer decreases under the influence of the Prandtl number and the intensity of the magnetic field, and the rate of mass transfer increases against large values of the Schmidt number and the activation energy parameter. Ijaz Khan et al. [37] investigated the entropy generation and fluid transport properties of tangent hyperbolic nanofluid over a sheet in mixed convection flow by considering a binary chemical reaction and thermal radiation. In all of the mentioned research, the volumetric radiation has been simulated by the Rosseland approximation. While obtaining the radiation source term in the energy equation is simplified using the Rosseland appr

Taimoor Ali This makes sense, as it is combined heat and mass transfer. I do not get the radiation part though. Bird, Stewart and Lightfoot's excellent book covers combined heat and mass transfer quite well.

Thanks for your quick response and suggestion.

I suggest the book by Tennekes, H., & Lumley, J. L. (1972). A first course in turbulence. MIT Press. Available on: https://www.academia.edu/download/54563360/Henk_Tennekes__John_L._Lumley_A_First_Course_in_Turbulence.pdf (more than 12 000 citations) is essential for a fundamental understanding of the physical mechanisms of turbulence.

At a boundary surface you can either specify the temperature or heat flux, not both, as the one determines the other. So if you have nodes on the the boundary line which separates these two regions, then, I think you can specify one of these two conditions alternately on every consecutive node.

Regards

Dr Kumar Eswaran

Professor

That all depends on what the air is doing in relation to the surfaces of interest. Is the air flowing? Is the air stagnant? Is the air free to flow should the opportunity for natural convection arise? Please provide more information.

explain your idea

explain your idea

explain your idea

Forced convection is a process where fluid flow is artificially induced, typically by mechanical means such as fans, blowers, or pumps, to enhance heat transfer between a surface and the fluid. It is widely used in various practical applications across different industries. Some of the most practical applications of forced convection are:

These are just a few examples of the practical applications of forced convection. In general, forced convection is employed whenever there is a need to enhance heat transfer between a solid surface and a fluid, whether it is for cooling, heating, or drying purposes in various industrial, commercial, and residential settings.

Well, there are several applications in microfluidics,

1 "Mixed convection in a vertical parallel-plate channel with opposing buoyancy forces" by S. Tardu and A. E. Akay (International Journal of Heat and Mass Transfer, Volume 49, Issues 3–4, February 2006, Pages 760-768). This paper presents experimental and numerical data on mixed convection in a vertical parallel-plate channel with opposing buoyancy forces.

2. "Mixed convection in a vertical parallel-plate channel with uniform heat flux" by S. M. Sohel Murshed and C. A. Nieto de Castro (International Journal of Heat and Mass Transfer, Volume 49, Issues 9–10, April 2006, Pages 1592-1602). This paper presents experimental and numerical data on mixed convection in a vertical parallel-plate channel with uniform heat flux.

Double diffusive forced convection, also known as thermosolutal convection, has a wide range of practical applications across different fields, including engineering, geophysics, and materials science. Some of the most practical applications of double diffusive forced convection include:

Overall, the practical applications of double diffusive forced convection are diverse and wide-ranging. Its use in different fields helps to improve our understanding of fluid mechanics, energy transfer, and material science.

I think from the answers that the topic requires some details.

If you write a scalar equation in the normal direction to the outflow, you can write approximately something like (d/dt +vn*d/dn) f= d/dn(alpha*df/dn).

Setting to zero the diffusive flux in the RHS is equivalent to prescribe a homogeneous Neumann BC and produces a convective-like BC.

This approach is largely used, for example in Fluent.

Average heat transfer coefficient on the interface of solid-liquid can be obtained from the Fluent->Reports->Surface integrals -> Facet average -> select the interface plane -> heat transfer coefficient and calculate or save the parameter as output variable.

I don't know about harmonic analysis, but in water there can be internal waves. The phenomenon is called seiche, and is explained here: https://en.wikipedia.org/wiki/Seiche This can cause the temperature at one point to fluctuate in line with the water. Especially around the thermocline.

Dear Dr. Ahmed,

Double diffusion convection plays a significant role in upwelling of nutrients and vertical transport of heat and salt in oceans. Salt fingering contributes to vertical mixing in the oceans. Such mixing helps regulate the gradual overturning circulation of the ocean, which control the climate of the earth.

Just to be clear, if i define heat flux using heat flux boundary condition to be zero then it would make heat transfer due to convection as well as conduction to be zero however i only wanted to have conduction from top surface of battery cell.

Using convective boundary condition , defining h to be zero at top surface will it cause only heat transfer due to convection to be zero ?

Umat to script load and interaction film conditions

Is a tropical cyclone formed randomly from a convective cell? Look at the satellite image. We see a mirror picture relative to the equator. Is the probability of such a coincidence zero? Drawing from open Internet resources.

Do not pay too much attention on the shape of the regions, that can be misleading since of the 1D spatial problem.

The best way to start understanding the hyperbolic character is to use the simple linear problem dphi/dt+u dphi/dx=0. Then, consider the exact solution phi(x,t)=phi(x-u*t,0) that is phi is constant along the characteristic line dx/dt=u. Compare that to the CFL=u*dt/h to see what happens in case of upwind. You will see when you get an interpolation or an extrapolation of the values.

For a deeper understand of such problems, have a look at the tectbook of Leveque.

Hello Sir

Your question is not clear.

Please give a clear problem to understand your question.

look for Ion Boldea Books, You may find a solution there.

I reasoned by analogy of heat transfer in a plane air layer (e.g in double pane windows). At ambient temperature, convection starts at 2 cm (see attached file)

At higher temperatures however, this may change.

Following...

It sounds like you're using some canned software package. This problem can easily be solved without any special software. You could do such a calculation in an Excel spreadsheet Q=UA(Tp-Ta)+εσ(Tp^4-Ta^4).

assign the mesh geometry for heat transfer and not for 3D Stress

I quite agree, which is why students need experienced faculty to warn and coach them on such details. Even if the professor's experience is in a somewhat different area, there are still similar challenges in any experimental study. Another example of this problem: I know a professor who has published a dozen papers on nuclear reactor design yet has never set foot inside a nuclear plant. This is like giving a seminar on horseback riding yet having never actually touched a horse, let alone ridden one.

Double-diffusive convection is a mixing process that occurs when two fluid components diffuse at different rates interact. Upwelling of nutrients and vertical heat and salt transport in oceans, for example.

Source:

Animasaun I. L. (2016). Double diffusive unsteady convective micropolar flow past a vertical porous plate moving through binary mixture using modified Boussinesq approximation. Ain Shams Engineering Journal 7(2), 755 – 765. http://dx.doi.org/10.1016/j.asej.2015.06.010

Heloi Tanoue

U can use these codes if u work on ANSYS APDL

/SOL

DELTIM,60,0,0

OUTRES,ERASE

OUTRES,ALL,ALL

KBC,0

TIME,7200

/SOLU

SOLVE

This looks like a transient heat transfer problem being modelled as steady state one. The main debate issue on such problems is always the boundary conditions assumed to make the mathematics feasible: traditionally either constant temperature or constant heat flux were used, while neither is the real case.

Transient conduction into a semi-infinite solid is covered in Carslaw and Jaegers old, but excellent, book.

Shiron Thalagala Hi, did you find the solution manual. I urgently needed it and search the internet throughout.

Thanks