transport mechanism involving bulk motion of a medium

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15 views

Why does increasing heat conductivity decrease Nusselt number?

Normally we expect that when heat conductivity(k) increases heat transfer is also increases. But for fluids increasing k decreases Nusselt number. My senses tell that using high conductive fluid cause ...
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0answers
21 views

Calculate Temperature change in a solid due to resistive heating

Trying to calculate temperature increase in a solid due to resistive heating by a current flow, is this along the right lines? First I have calculated resistance due to resistivity, then calculated ...
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0answers
17 views

Inductance heating, Temp Change [duplicate]

I am trying to find the temperature increase of a solid(copper) in a gas (air) due to an electric current passing through the solid (inductance). I need to encompass any temperature losses from the ...
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0answers
49 views

Maximum temperature possible on earth

What is maximum temperature that can we have on earth on a single day? Lets say an air mass is static over an area and there is no way for air mass to move, sun warming it up would increase ...
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2answers
36 views

Thermodynamics : Heat transfer : Conduction or convection?

I have an hot object, that is place in a room of 20°C. My goal is to be able to estimate how warm the object will be in T seconds. To be able to do that, I must first understand what is really ...
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0answers
23 views

Water in pot with a heat source beneath it to boil it, does the water move?

I mean if there is there heat transfer by convection in the water? since convection requires motion. if it moves, then how can i determine the velocity of the water?
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1answer
12k views

What is Convective acceleration of flow velocity?

I know that $\frac {dv}{dt}=a$ is acceleration, but: What is convective acceleration of a flow velocity? What is difference between $(v\cdot \nabla) v$ and $v\cdot (\nabla v)$?
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4answers
62k views

What exactly is the difference between radiation, conduction, and convection?

Okay, so everywhere I've read, I hear the main difference is the requirement of a medium. But for example, if you take the case of heat 'radiating' from a red-hot iron, isn't that actually convection ...
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1answer
3k views

Finding electric power generated using heat transfer

I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$. Given: $\alpha_s = 0.83$ ...
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2answers
125 views

Heat loss via convection

Suppose I have a glass container (trough) and I want to heat the water inside. I put it on a hot plate. Now, even though the hot plate is at $110\,^{\circ}C$, the liquid only reaches $50\,^{\circ}C$. ...
3
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1answer
95 views

What causes the differential rotation of the Sun?

I have read the explanation in Wikipedia, but the problem is that because I'm a beginner in physics, I don't quite understand what more than half of the words mean! Here is the explanation from ...
0
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1answer
76 views

flat plate isoflux convection - how to calculate temperature

I am an engineer trying to design a simple 1D program for evaluating the temperatures of a multi-layer heatsink that includes convection and radiation heat transfer from the external surface. For a ...
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1answer
13 views

Which are the best books I can refer for turbulent heat transfer and its computation?

I am a graduate student. I wanted to do computation on heat transfer problem mainly heat convection. I am working on turbulent regime. Can you kindly suggest some good books so that I can get ...
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0answers
19 views

How much power is being actually delivered by an electric heater to a cooking pan?

I've been doing experiments on an electric heater heating a cooking pan filled with 2 litres of water, from 20°C to 70°C; now I'm trying to draw a theoretical heat transfer model thath should match ...
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0answers
35 views

What is the use of thermal boundary layer and velocity boundary layer?

In heat transfer by convection, why must we show the thermal boundary layer and the velocity boundary layer. What do they signify? Also how are these terms related to the Prandtl number? And what is ...
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1answer
59 views

Is there a difference between solid-to-fluid convection and fluid-to-fluid convection?

I found an online calculator relating to convective heat transfer, but the calculator's description says it's for heat transfer between a solid surface and a moving fluid. However, the definitions ...
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3answers
79 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 ...
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0answers
23 views

Extension of the advection diffusion equation with diffusion perpendicular to the flow

Assume you model particle flow in fluid in a cylinder by an advection-diffusion equation, thus taking into account both diffusion and bulk flow. What would happen to the model if you would, at some ...
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1answer
29 views

When does heat conduction become convection?

Okay, I have a hard time wrapping my head around something, I think, pretty basic. For a little hobby project of mine I was making a fermentation-box for beer brewing allowing me to accurately ...
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4answers
253 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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4answers
10k 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?
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2answers
40 views

Hot Object In a Cooler Space [closed]

How would you calculate the heat given by an object that is hotter than its surroundings? I know there's Newton's Cooling Law, but what about any heat given off by radiation? Are these additive ...
19
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2answers
45k 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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1answer
51 views

Time dependent heating of a conductor

I have a conductor that's being heated with current. I want to know the temperature of the conductor Steady state soultion is: ...
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0answers
89 views

Heat transfer through convection in human body

How does the heat transfer takes place in human body through convection in these two situations. 1) when environment temperature is less than body core temperature($37^0C)$, say it is around $25^0C$. ...
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3answers
17k 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 ...
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1answer
89 views

Convective heat transfer

At y = 0 It is said that the heat is transferred by conduction because the fluid has a velocity equal to 0 (no-slip conditions). But the temperature of the fluid for y=0 is equal to Ts(temperature ...
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0answers
41 views

How can I get the boundary and initial conditions of the convection–diffusion equation consistant?

I want to solve the 1D convection–diffusion equation. The boundary conditions are a flux in from the bottom and a flux out on the top. Furthermore I want no concentration inside at the beginning. I ...
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1answer
552 views

Convective boundary condition

Consider a fluid over a sheet which is placed horizontally along the x-axis. The lower face of the sheet is in contact with another fluid at temperature $T_f$ ( it is heating the sheet). The sheet is ...
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0answers
170 views

Numerical Solution of the Propagation-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 ...
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1answer
2k 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 ...
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2answers
46 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 ...
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0answers
39 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
87 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 ...
4
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4answers
6k 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 ...
21
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1answer
2k 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 ...
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0answers
20 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
13 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 ...
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0answers
45 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 ...
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2answers
415 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 ...
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3answers
3k 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
90 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 ...
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1answer
122 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 ...
6
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2answers
14k views

Convective and Diffusive terms in Navier Stokes Equations

My question has 2 parts: I just followed the derivation of Navier Stokes (for Control Volume CFD analysis) and was able to understand most parts. However, the book I use (by Versteeg) does not ...
2
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1answer
56 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 ...
76
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12answers
25k 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 ...
1
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1answer
634 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 ...
2
votes
3answers
7k 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, ...
1
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1answer
480 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 ...