Questions tagged [thermal-conductivity]

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55
votes
6answers
50k views

Why does cold metal seem colder than cold air?

(I apologize for this elementary question. I don't know much about physics.) Let's say that I put a metal pot in the refrigerator for several hours. At this point, I guess, the pot and the air (in ...
2
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4answers
7k views

How does the drift velocity of electrons in a conductor depend on the temperature?

How does the drift velocity of electrons in a conductor depend on the temperature? I have two contradicting views for this. First, we can say that increasing the temperature of the conductor will ...
10
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2answers
776 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 ...
20
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8answers
48k views

Are specific heat and thermal conductivity related?

Are there any logical relationship between specific heat capacity and thermal conductivity ? I was wondering about this when I was reading an article on whether to choose cast iron or aluminium ...
1
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1answer
289 views

Heat preserving performance of container relative to content

This question has been addressed in the case of a thermos bottle: Performance of a thermos bottle relative to contents I am asking the question again without the hypothesis that it is a thermos ...
8
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1answer
4k views

How much heating does Earth inner core provide to the surface?

Compared to the energy that the Earth's surface receives from the Sun, how much power comes from the inner melted core? How important is this contribution to the surface temperature?
25
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7answers
99k views

Does an empty refrigerator require more power to stay cold than a full one?

Given that everything else is equal (model of fridge, temperature settings, external temperature, altitude), over a given duration of having the door closed, does it require more electricity to cool ...
11
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3answers
10k views

Cooling down a container in outer space

If I have two containers filled with very hot water(~210F) with one in outer space and one on earth, which one has a higher rate of cooling initially? Imagine the containers are single wall metal ...
6
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3answers
12k views

Why the heat flux vector at a point must be perpendicular to the temperature isothermal surface? Is it a definition or a deduction?

Before the question: I am working on numerical calculation of three dimension parabolic equation that based on Fourier's Law of which I am a little confused. Here comes the law in modern mathematics ...
3
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5answers
3k views

Is perfect thermal insulation possible?

Supposing someone says they have a sample of insulanium with the following properties: If you make a thermos out of insulanium, it will keep a drink hot or cold forever. If you put your hand on a ...
4
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1answer
4k views

When a color LCD/LED display is off it is black, when on it is colored. What color to light is an LCD/LED display

When a modern display using pixels is turned on its colors are different than the black that the screen is actually made up of. When put in light, such as sunlight, does the screen react to the color ...
2
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3answers
1k views

Finite difference formulation of the heat equation with thermal conductivity in 1D

This may seem trivial, but I'm having some trouble deriving the finite difference form of the heat equation with a thermal conductivity function $a(x)$ depending on $x$: $$\frac{\partial u(x, t)}{\...
2
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1answer
402 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 L^3)}{\nu^2}$...
-1
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1answer
32 views

which is more effective chilling for metal casting, thick copper die or water-cooled thin copper mold? [closed]

It is will known that increasing cooling of a metal casting will lead to finer micro-structure which mean higher mechanical properties. If I have 2 molds one is thick copper die ,& second is just ...
14
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4answers
4k views

Which would melt faster on the sidewalk, equal volumes of snow or ice?

Whilst walking back from class, I noticed the piled snow on the sides of the street still hadn't melted after a week despite it being sunny and generally warm $(15°C-18°C)$. "If that snow was ice, ...
0
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1answer
986 views

Ideal gas temperature and pressure gradients?

Consider an ideal gas in a $d\times d\times L$ box with the $L$ dimension in the $x$-direction. Suppose that the opposite $d\times d$ sides of the box are held at temperatures $T_1$ and $T_2$ with $...
7
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6answers
2k views

What's the best strategy to fully fill the fridge with beer bottles and have them all cooled?

I'm having a party. Suppose I'd like to have a fridge full of cold ($6~^\circ\text{C}$ or below) beer bottles, in as short a time frame as possible. The fridge indicates that it is targeting (and ...
5
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1answer
1k views

Why aren't (domestic) kettles insulated?

In my experience of buying and using kettles, I have come across none which are insulated. The obvious reasons as to why it would be beneficial being that heating time would be reduced, similarly, ...
3
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2answers
4k views

How fast is heat transferred by conduction?

How fast is heat transferred by conduction? Is there some simple, but quantitative way that starts from some properties of the material (e.g. its thermal conductivity) and makes rough predictions, for ...
2
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1answer
1k views

Do conventional ovens heat by thermal conduction or radiation?

I am curious which energy transfer mechanism dominates in a conventional oven, thermal conduction or thermal radiation? A naive guess would be that early on, when the food is still cold, the heat ...
2
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3answers
1k views

Why does room temperature water and metal feel almost as cool as each other?

From what I've read about heat, temperature and conductivity, I understand that the reason water at room temperature feels colder than most other things at the same temperature (like wood, air, cotton)...
0
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1answer
659 views

Conduction problem?

I came across the following problem in my textbook today: A container of negligible heat capacity contains $1~\rm{kg}$ of water. It is connected by a steel rod of length $10~\rm m$ and area of cross-...
7
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3answers
891 views

Of all the electrical energy used in a home, is there any portion that won't eventually become thermal energy in the home?

Considering all of the appliances that the average home uses--microwaves, light bulbs, dishwashers, refrigerators--is it safe to say that all of the electrical energy in a home will be converted to ...
6
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3answers
663 views

Is a radioactive-powered hand warmer possible? Can it be made to work safely?

So my knowledge of radioactive isotopes is limited to a series of youtube videos. I assume this idea is very dangerous and should never be attempted, but my curiosity still thrives. I own a tritium ...
4
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5answers
18k views

Why water inside a vessel placed in a body of boiling water does not boil?

Imagine a plastic sac filled with water placed in a pan of boiling water. I wonder why the water inside the sac does not boil. The temperature of the water inside the sac should be the same as that of ...
3
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1answer
4k views

Why is the lid of the cookware kept on induction cooker not hot?

Induction cookware cooks food by inducing an electro magnetic field in the ferro-magnetic cookware. Since iron offers a lot of resistance to the current, the current is converted into heat in the ...
3
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3answers
633 views

Measurements for thermal diffusivity of graphene?

We have known for a long time that graphene has in-plane thermal conductivity ranging between 2000 and 4000 $W m^{-1} K^{-1}$. But in order to model heat transport on a sheet of graphene, we need more ...
3
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2answers
4k views

Performance of a thermos bottle relative to contents

I'm not a physicist but I majored it at high school (a long time ago) and I study university math. Me and my roommate discussed whether the performance of a Thermos bottle is influenced by how full ...
2
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3answers
722 views

Conceptual difficulty in understanding Fourier's Law of heat conduction

I am having a bit of difficulty understanding the statement of Fourier's law of heat conduction. As mentioned in Georg Joos, Theoretical Physics The quantity of heat passing per second through unit ...
1
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1answer
5k views

On a molecular level, how does heat transfer take place?

When an ice molecule hits a water molecule, the water molecule adds kinetic energy to the ice molecule. Why do the water molecules lose kinetic energy? In other words, why does heat like to go where ...
1
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4answers
3k views

Maximum efficiency for a counter-current heat exchanger (double flux controlled motorized ventilation)

I am not sure if I can explain the question correctly because I don't know the name of this mechanism in English. This is my explanation attempt: In a house, a tube is expelling the air from the ...
1
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0answers
1k views

Thermal expansion of two bolts

I have this question asking me about the thermal expansions of two bolts, a steel one, and a brass one. I have the equation: $\ (\delta L/L)/T = \alpha $ I don't understand how I can use this ...
1
vote
1answer
470 views

Thermal conduction through 1D rod with changing thermal diffusivity?

I've been working with solving partial differential equations in 1D numerically using the finite difference scheme. My case is for example this: I've got a rod that's insulated around the sides such ...
0
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1answer
40 views

Heat absorbed from a reservoir by a moving object [closed]

Imagine two bodies, say a body A with an infinite heat capacity(reservoir) and the another body B with some finite heat capacity($C = \alpha \ T_{B}(t) $). They come into direct contact with each ...
0
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4answers
6k views

Why are compressed air tanks cold? [duplicate]

Why is a compressed air tank cold to the touch when it’s in a compressed state before use?
0
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2answers
37 views

Why can't information be conducted out of a black hole? [closed]

Why can't information be conducted out of a black hole? Does gravity affect conduction? What is the temperature profile in equilibrium of a metal pole half in, half out of a very large BH such that ...
0
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1answer
159 views

Cup of water and cup of water with oil on top [closed]

the teacher gave me this problem to solve. So i hope you can help me with it. Here is the problem: John poured 150ml ob boiling water in 2 cups made out of polystyrene. Cups are open on the top so ...
-1
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3answers
287 views

Bird on electric wire: theoretical distance between the two bird legs [closed]

Hey guys, please someone help me with this exercise :) For our exercise, assume that the bird’s body resistance (from leg to leg) is 50kΩ. Given is a high voltage power line with a current of 100A ...