transport mechanism involving bulk motion of a medium

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52 views

Numerical Solution of the Convection Dispersion equation

I have asked this question on Computational Science and also on Mathoverflow, but no satisfactory answers so far. I thought maybe the physics community could shed some insight on the issue. I am ...
1
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2answers
19 views

Is air infiltration a type of convective heat transfer (convection)

I have a building / physics question... A major source of heat loss in homes and buildings is infiltration through cracks (warm air from inside seeping out). Wondering if this falls in the category ...
1
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0answers
29 views

Forced convection: temperature gradient in conical pipe

My situation involves a conical pipe of known dimensions and material composition. Warmer-than-ambient air is added to the small end at a steady, known flow rate. I'm hoping for a way to estimate ...
0
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0answers
29 views

Heat flow through a pipe

I have a pipe, in which a cooling medium flows through it. I would like to know the temperature of the cooling medium at different lengths of the pipe. Is there an equation to relate the length and ...
20
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1answer
1k views

Why does a match go out if you hold it so the flame is up?

I have noticed something which may have been noticed already: take a match, and light it, then hold it so that the flame is directly above your hand. The flame will eventually go out. My guess as to ...
0
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0answers
18 views

Why is the boundary layer thinner on the outside of an outer wall versus the wall inside the house

The convection on the outer suface of the outer wall of a house is larger, because outside a house it's more windy compared to inside. More wind means more turbulence which leads to more transfer of ...
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0answers
6 views

Vertical wall at 3 different temperatures - do the same natural convection coefficient correlations apply?

I have an vertical enclosure that consists of 3 shelves, each with its own temperature and are thermally isolated from each other. We will call the shelves A, B, and C with A being the base shelf. The ...
0
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0answers
31 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
9
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2answers
276 views

How does the sun's surface conduct thermal energy from the convective zone to the corona?

How does the surface of the photosphere conduct thermal energy from the convective zone to the corona, while remaining at such a relatively low temperature itself? It seems odd to me that the ...
0
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3answers
156 views

Is heat from a stovetop, transfered through convection, radiation or conduction?

It doesn't appear to be convection, as there are no moving objects (or are there); probably not radiation (?), so it is conduction? I really don't know much about heat transfer and thermodynamics, ...
0
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1answer
46 views

Series of parallel thermal resistance connection for this enclosure?

Let's say that I have an 2D enclosure in the shape of a pyramid with unequal areas for the faces and I am looking to determine in the inside air temperature. The parameters I know are the outer and ...
1
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1answer
61 views

Why Benard cells are usually hexagonal?

Solution of equations of convection (hydrodynamics equations in Boussinesq approximation) involves existence of convective cells, so-called Benard cells. They are represented by superposition of ...
4
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3answers
1k views

What is the exact difference between diffusion, convection and advection?

I have tried to explore the information but still not very clear on the exact difference between diffusion, convection and advection. Can anyone help me out to clear my concept?
2
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1answer
45 views

When I'm in a warm room how much of the warmth I feel is due to radiation from surfaces?

Say I'm in a room heated to 23C, once the temperature is in balance all the objects will also be 23C and radiating heat towards me. How much of the warmth I feel is due to this radiation, and how much ...
0
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0answers
41 views

Heat sink simulation with a fan

I am trying to solve this problem using advection-diffusion model and finite element method for solving it due to the complex geometry. Basically the problem i'm trying to solve using OpenFOAM is see ...
0
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2answers
53 views

Photon walk in stars with convection

I'm having trouble figuring this out. I've read, that when photons are created via nuclear processes inside a star, it can take about 1 million years for photons to actually reach the surface of a ...
1
vote
1answer
292 views

Heat transfer between the bulk of the fluid inside the pipe and the pipe external surface

In an article from Wikipedia about heat transfer coefficients in the section Combining heat transfer coefficients there is an equation which describes the rate of heat transfer between the bulk of the ...
1
vote
1answer
240 views

Rate of Temperature Change due to Heat addition

I might be wrong but I will give a little background leading to my question. I am trying to calculate the heat generation in the advection-diffusion equation for heat generation due to friction by ...
2
votes
2answers
95 views

How stable are Benard Cells when the thermal gradient begins decreasing?

I've found lots of information on the formation of Benard Cells and convection currents but very little information about what happens to the self-organized structures when the energy gradient being ...
0
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0answers
202 views

What is the minimum volume in which, for a given temperature difference $\Delta T$, natural convection would occur?

I'm trying to figure out if convection will occur in a plastic bottle slice and what length of slice would be optimal to achieve high R value transparent insulation on the cheap. The bottle slice is ...
1
vote
1answer
599 views

Will a liquid boil quicker if it is stirred versus if it is not stirred

Will the whole liquid boil quicker on a stove-top if it stirred versus if not stirred? What should be the frequency of stirring to get to boiling point quickly? please explain your hypotheses with ...
2
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0answers
29 views

Vanishing viscosity in eqn. of heat transfer for free convection: on what argument?

In Landau's and Lifshitz' Fluid Mechanics on the derivation of the equation of heat transfer for free convection p. 218, they write In the thermal conduction equation (50.2), the viscosity term ...
0
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1answer
86 views

At what gap width between two plates does convection not occur?

Does the Grashof number lead to the answer? The Wikipedia article (https://en.wikipedia.org/wiki/Grashof_number) yields an equation for vertical plates $$Gr_L = \frac{g\beta(T_s-T_\infty ...
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3answers
172 views

Convective heat transfer coeficient equation

I am attempting to model a situation, in which a sphere of some material of identifiable thermal properties is receiving heat at a constant rate. And that material is coming into equilibrium with the ...
6
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1answer
376 views

How does the windchill factor exist above 98.6 degrees?

As I understand it, the explanation of the windchill factor goes like this: Your body is warmer than the air around it, therefore it loses a certain amount of heat to the air. This warms up the ...
0
votes
1answer
276 views

How hot does the upstairs need to be before it will heat the basement through convection?

During the winter we keep the basement door closed so that the cold air from upstairs won't flow into the basement. Then we heat the basement and the upstairs gets heated partially by conduction ...
2
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2answers
226 views

Which temperature to evaluate fluid properties in pipe?

I am always confused about which temperature to evaluate fluid properties at. Let's say I have a helical pipe and I know the inlet temperature, outlet temperature, and surface temperature and the ...
0
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0answers
262 views

Determine pipe outlet temperature without length?

Let's say I am flowing a fluid through a pipe that has a constant surface temperature. Is it possible to determine the heat flux on the inner surface without knowing the pipe's length when the only ...
4
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4answers
4k views

Improving our homemade hot tub design? [closed]

My brother and I built a wood burning, convection based, thermal circulating hot-tub. (With and oxyacetylene torch, lots of 1.5" pipe, a brake drum, and a thirty year old jacuzzi). Our design is ...
2
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4answers
564 views

Boiling Order (Thermodynamics) [closed]

Three pots made of the same material are placed one inside the other and all pots are filled with water to the same level. If heat is applied to the bottom of the outermost pot what will be the ...
2
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3answers
4k views

Realistic calculation of heat loss for pipe

Good day everyone, I am new on this site and I hope to find here help, since I am not going anywhere with the literature I have found. I try to calculate realistically the heat loss of a hot, ...
68
votes
12answers
17k views

Why are radiators always placed under windows?

I don't know if anyone else has noticed this but in most buildings and most rooms, radiators are predominantly placed under a window. Now, in my eyes, that is the worst place to put them; hot air ...
0
votes
0answers
101 views

Fluid mechanics Grashoff number

When I derived the Grashof number (for natural convection at a vertical plate) starting with the ratio of buoyancy forces to viscous forces, I realized that I had set the Reynolds number to 1 (ie I ...
2
votes
1answer
126 views

How can I predict the convective updraft speed above a stove element?

I want to know the rate at which air will ascend above a stove element. Is there some relationship between ambient air temperature, element temperature, and speed of the resulting updraft? If ...
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vote
1answer
767 views

Is the convective heat coefficient always dependent on heat flux and delta T?

I'm having a difficult discussion with a colleague because I'm running heat flow simulations for a small heater (5 mm^2 area), and I insist that if we're going to run more electrical power through the ...
0
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2answers
779 views

Why do we feel a sudden chill?

When we are in a room, especially in some old houses, we feel this sudden rush of cold air. How does a strong air current arise and pass away so quickly?(lasts for about a second) I know air-currents ...
-1
votes
1answer
174 views

Heat Sink Design-Choice of Material [closed]

I am currently designing a heat sink for OPA 549. Among the many considerations, for example, the choice of material, the geometry of heat sink, the design of fins and all the parameters that come ...
3
votes
2answers
543 views

Why do some air-conditioned stores blast you with jets of air as you enter?

I went to a grocery store on a hot day that was very well air-conditioned, and I noticed as I went through the open entrance that there seemed to be a very powerful downward air current right at the ...
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1answer
1k views

Do metals generally lose more heat by convection than non-metals?

I've been experimenting with radiative cooling lately and in my mind convection is always an enemy (especially forced convection since the modules are outdoors). Looking at Newton's law of cooling, ...
3
votes
1answer
103 views

Can convection cells evolve in stably stratified fluid?

Assume stably stratified fluid but not in equilibrium, e.g. with non-constant temperature gradient for example. Can convection cells be present? Typical example of convection cells is Rayleigh–Bénard ...
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1answer
427 views

What happens to pipe outlet temperature here?

I have a fluid flowing through a pipe in the ocean and there is heat transfer from the ocean to the fluid in the pipe. I prepared a simulation and the results show that if I increase the mass flow ...
6
votes
2answers
418 views

Is it cheaper to boil water on high gas heat or low gas heat?

Assume my time value is \$0. High gas heat adds more energy per second to the water but the pot may absorb the heat less efficiently, or maybe the shape of the flame is less good, or for other reasons ...
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3answers
2k views

What's the physical difference between a convective heater and an infrared heater?

Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air? ...
3
votes
1answer
347 views

Rayleigh-Benard Convection

I found this nice paper about RB convection. However I am confused by what is going on page 6. In particular why we are suddenly using Helmholtz equation to find spatially periodic solutions. Aren't ...
0
votes
2answers
12k views

What is the characteristic length of a cylinder

I have a cold cylinder that is submerged in hot water and I need to find the convective heat transfer coefficient. I can do the whole process but I am stuck finding the characteristic length. I found ...
2
votes
1answer
5k views

Boussinesq approximation for the Navier Stokes' equation - discrepancy

In the Navier Stokes' equation: $\rho_0 \left( \frac{\partial v}{\partial t} + v \cdot \nabla v\right) = -\nabla p + \mu \nabla^2 v + \hat{f}$ I included the temperature variation of density as ...
8
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3answers
429 views

What is the microscopic picture for warm air rising?

The usual explanation for warm fluids rising past cooler ones is that the warmer fluid has a lower density. I'm trying to understand what this looks like at a molecular scale. The density seems to ...
14
votes
2answers
30k views

What exactly is the difference between advection and convection?

After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms. Sometimes, the term convection seems to ...
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vote
1answer
627 views

How would I calculate the convection coefficient in transient convection?

So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I ...
2
votes
2answers
249 views

How would I go about solving this transient convection problem if the mean fluid temperature is constantly changing?

Let's say I have a ceramic slab on a conveyor belt that is initially at $450\,^{\circ}\mathrm{C}$ and there is air being blown over it at a speed of $35 \frac{m}{s}$ with an ambient temperature of ...