Questions tagged [thermal-conduction]
The thermal-conduction tag has no usage guidance.
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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 ...
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How does hot air rise?
If a balloon is filled with hot air, it is rising due to buoyancy: the mass of the hot air inside the balloon is lower than the mass of the same volume of the cold air outside the balloon cavity.
...
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What does the concept of "Entropy Flow" mean in detail?
Recently a found a paper on the thermoelectric effect:
https://williamsgj.people.cofc.edu/Thermoelectric%20Effect.pdf
When I started with Chapter 5 "Irreversible Thermodynamics" I struggle ...
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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 ...
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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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Doubt in definition of linear thermal expansion
It's stated in my textbook that upon heating a rod , the linear change in its length is directly proportional to its original length and the change in temperature , therefore the equations should look ...
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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 ...
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Derivation of general equation of heat transfer & entropy
In Landau & Lifshtiz Volume 6 on fluid mechanics we derive the general equation of heat transfer by starting with the expression
$$
\partial_t \left( \frac{1}{2} \rho v^2 + \rho \varepsilon \right)...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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Why does water feel cooler than air?
My first assumption was based on "evaporation causes cooling" but I realized that it is not the case as it is cooler even if I am submerged under it. Are all liquids generally cooler than air ?
Just ...
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Cooling down a container in outer space
If I have two containers filled with very hot water(~210°F) 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 ...
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Asymmetric heat conduction?
So I have this side-view drawing.
Now I wonder, will such a multi-layer material have asymmetric heat conduction properties?
Namely, because of radiative conduction, reflective aluminum surface and ...
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What's the true reason behind thermal expansion?
Thermal expansion is a normal concept everyday. There are 2 explanations:
1, thermal expansion result in stress, then result in deformation
2, thermal expansion result in deformation, then result in ...
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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 ...
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Why Onsager's formulation of thermoelectricity is better than Bridgman's?
General comment: despite the longish historical introduction this question is not about the history of physics but rather about a specific conceptual problem in physics.
Following Bridgman in the ...
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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 ...
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Why is a temperature gradient set up in a heated rod? [duplicate]
Suppose a cylindrical rod is maintained at 100 degree Celsius and the other at 0 degree Celsius. My book says that after reaching "Steady State" the rod will have developed a constant temperature ...
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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}$...
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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 $x$:
$$\frac{\partial u(x, t)}{\...
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How do you know you can add thermal resistance but not thermal transmittance?
I followed through the example on this wikipedia page for calculating the thermal resistance of a composite material (a wall) composed of many layers: https://en.wikipedia.org/wiki/...
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Temperature at different points in a metal rod during heat conduction
$$ k = \frac{\frac{Q}{t}}{A(\frac{T_1 - T_2}{L})} $$
where k is thermal conductivity of the solid,
Q is total amount of heat transferred,
t is time taken for the heat transfer,
A is area of the cross ...
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A room with a heater in contact with walls as a heat sink
I have to calculate the increase of my room temperature as a function of the heater's power. The easiest way of doing it is:
$$T_1=\frac{P\Delta t}{C_v V n }+T_0$$
$T_1$ is the final room temperature, ...
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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 ...
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Why does a lot of water vapour come suddenly after the heat source of boiling water is removed? [duplicate]
I have noticed this several times. When I am boiling water, a few seconds before its boiling point, vapours are formed as usual. But if I turn the gas off before boiling, the moment it turns off, I ...
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Why is rock or metal often cold to the touch but wood or plastic is not?
In a room at normal room temperature, certain materials, such as metal, glass, ceramic, or rock, will feel cold to the touch, but others, such as wood or plastic, do not so much.
Which physical ...
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Why does holding a hot object with a cloth make it feel less hot?
Let's say that I held a hot object with a warm cloth. It instantly feels less hot and only warm to the touch. This is because the cloth is an insulator and doesn't allow as large a heat transfer as if ...
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Why doesn't a mercury thermometer follow the rules of volume dilatation?
let's consider a classic mercury thermometer.
I do not understand why it does not behave like a "normal" thermometer which exploits volume dilatation. In a normal thermometer, I'd say that ...
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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, ...
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Why is the ground warm during winter and vice-versa?
I was just looking at the geothermal house heating in Iceland, and came to know that in the winter the water is warm, hence cools the house, but how is it hot, not about us feeling it.. My question is ...
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Why is a sleeping bag so cold when you first get in?
I sometimes put a sweater on when I first get up on a cold morning. The sweater isn't so cold against my skin, but the zipper is. I get this. Even though they are both at the same temperature, the ...
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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 ...
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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 ...
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Confused with stress, strain and linear thermal expansion
Four rods A, B, C, D of same length and material but of different
radii r, 2r , 3r and 4r respectively are held between two rigid
walls. The temperature of all rods is increased by same amount. ...
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Is sun a black body? [duplicate]
My teacher told me that sun is a black body but after reading at various sites whre they say that sun is not a black body but has black body radiations because it cannot absorb all radiations.
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If steam and water, both at 100 °C, were exposed to a person's skin for a small time interval, which would result in a more severe burn?
Imagine that you had two boxes with of steam and water of equal mass, both at $100~^\circ\rm C$, and you decide to expose your left land to the steam and your right to the water for a short period of ...
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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 ...
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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, ...
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Insulated ends of a rod
I'm trying to understand the boundary condition for a rod that's insulated at its ends. The boundary conditions for such a rod is said to be $-k\frac{dT}{dx}=0$. In other words, the temperature ...
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At the atomic level, is heat conduction simply radiation?
Radiation and conduction are two ways that heat is transferred. Convection isn't really a mode of transfer as the actual heat transfer really occurs through radiation/conduction and not by some other ...
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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 ...
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At what speed does heat flow in materials?
When we heat one end of an iron rod on the stove, it takes a considerable time for the other end to be heated to the same temperature as the first end. On the other hand, as we know, the atomic ...
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How to cool a liquid the most efficient way by submerging solids into it?
Consider a certain amount of liquid, and also a solid body of certain mass. The solid is at a lower temperature than the liquid. The goal is to cool the liquid by submerging the solid, and they can't ...
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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 ...
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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 ...
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Why thermal conductivity increases with temperature?
what is the molecular mechanism with which thermal conductivity increases by increasing temperature? at least for metals? I know that heat increases the oscillations of the atoms in the crystal. But ...
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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 ...
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