Questions tagged [thermal-conductivity]

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67
votes
4answers
12k views

Why don't you get burned by the wood benches in a sauna?

When you go to the sauna you may sit in a room with 90°C+. If it is a "commercial" sauna it will be on for the whole day. How does it come that when you sit on the wood you don't get burned? I ...
55
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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 ...
39
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4answers
6k views

Why are steel thermal mugs much better than plastic ones?

I have several thermal mugs, two of them by the same brand, have the same look, shape and size except that one is in steel (inside and outside) and the other one, plastic. Both have an insulating ...
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 ...
24
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8answers
5k views

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 ...
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 ...
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, ...
13
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3answers
5k views

LED Thermal Modeling (How to solve heat equation with constant heat source)

I have a mechanical design with LEDs that generate heat. I want to estimate the temperature at the LED junction vs. time, but especially at steady state. Knowing the LED voltage drop and current, I ...
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 ...
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 ...
9
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6answers
11k views

What causes contact resistance?

When two components are combined in an electric circuit, there is apart from their own resistances a contact resistance at their junction. This causes a sudden voltage drop of $V_{drop}=R_{contact}I$....
9
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4answers
33k views

What happens when you heat vodka in a microwave?

Since ethanol has a lower dielectric constant than water would the water heat up and boil before the ethanol? Would the water transfer heat to the ethanol and, since ethanol has a lower boiling point, ...
9
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2answers
2k views

When should I take wine out of the fridge - transient heat transfer problem

I am hosting a dinner tonight for which I'll be serving white wine (Riesling to be more specific). Generally white wine is best served chilled (not COLD!) at around ...
9
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4answers
1k views

Phonons and heat conduction

What is the physical picture of heat conduction in a poor conductor? In particular, I'm curious about the role of phonons in conduction in poor conductors. I know that phonons (within the harmonic ...
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?
8
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1answer
8k views

What exactly heats a pool of water on a sunny day

On a sunny day an outdoor swimming pool will heat up fairly quickly. My question is, what is the exact mechanism for this and can we put numerical figures on it? Given that water is clear and ...
8
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1answer
4k views

Are two thin blankets significantly warmer than a single thick blanket?

Almost every source I can find online maintains that two 0.5 cm blankets are significantly warmer than a single 1cm blanket due to air trapped between the thin blankets. However, the thermal ...
7
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2answers
1k views

Does the order in which I layer blankets matter? [closed]

It’s getting cold where I live and I sleep with multiple blankets. I am wondering whether it generally matters how I might use blankets to keep something warm; if I put blanket $A$ on top of blanket $...
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 ...
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 ...
7
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3answers
360 views

Why does an ice stupa not melt for 6 months?

https://www.youtube.com/watch?v=-1s0K_MKAgI&t=303s In this video at 3:55, Mr. Wangchuck explains that the ice stupa doesn't melt because it has less surface area for a given volume compared to ...
7
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2answers
1k views

Is the thermal conductivity of metals affected by magnetic fields?

Especially for a ferromagnet a magnetic field should have a field-induced band shift in the density of states but I wonder if this shift is big enough to be significant and affect the thermal ...
7
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4answers
14k 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 ...
6
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2answers
1k views

Does diamond dust conduct heat as well as diamond?

Diamond is one of the best thermal conductors you can get. If the diamond is crushed into dust and spread out over a flat surface, but still held fairly compact (for instance in a small petri dish), ...
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 ...
6
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3answers
662 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 ...
6
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2answers
157 views

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 ...
5
votes
1answer
853 views

Will heat flow by conduction oscillate until thermodynamic equilibrium is reached in a solid object?

Consider the following thought experiment with $2$ conducting objects $A$ and $B$, where object $A$ is initially at a much higher temperature than object $B$. The objects are now placed in perfect ...
5
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1answer
10k views

How can a material conduct heat but not electricity

Mica is a good conductor of heat but an electrical insulator. According to free electron theory (which applies only to metals) free electrons carry heat and electricity. Therefore, thermal ...
5
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2answers
6k views

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. ...
5
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1answer
635 views

Why do electrically conductive materials tend to be thermally conductive?

It's hard finding substances that are good insulators of one and conductive of the other. Why the correlation? And why do some materials not have this correlation?
5
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2answers
2k views

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 ...
5
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1answer
4k views

What is the temperature of water at the end of the pipe?

I need to solve the following problem for a practical application. Water, initially at temperature $T_0$, flows with a constant speed $v$ through a PVC tube of length $l$ and diameter $D$. The ...
5
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3answers
7k views

Why is oil a poor conductor of heat?

Why is oil a poor conductor of heat as compared to metals? It is used in transformers to conduct heat to external fins. But is it ever used for heat insulation?
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, ...
5
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1answer
1k views

How does temperature in a solid sphere change with time when moving through a gas?

I'm interested in the following problem: There is a solid sphere with radius $r$ and mass $m$ at temperature $T_{s0}$. It is moving at velocity $v_s$ through a gas of temperature $T_g$. How does the ...
5
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1answer
3k views

Why do some metal containers not conduct heat, while some do?

Some metal containers such as the Nissan Thermos ones, even if 100 C water is filled inside, the container is still cold to the touch on the outside. It won't be even warm: At the same time, some ...
5
votes
1answer
476 views

How do I calculate how long water will take to warm from 22°C to 35°C?

I'm a microbiologist and my physics is not up to par for figuring this out. I've requested our engineering department to perform a temperature mapping of the vessel, but they can't do it for me. I ...
5
votes
1answer
736 views

How do I measure the temperature of a tiny water droplet?

How do I accurately (+/- 0.1 degrees Celsius or better) measure the temperature of a small (5 to 50 microliter) water droplet without noticeably affecting its temperature? The mass of a thermistor or ...
5
votes
2answers
658 views

Wiedemann-Franz law

The Wiedemann-Franz law states that the ratio of thermal conductivity $\kappa$ and electrical conductivity $\sigma$ for metals fairly accurately obeys $\kappa/\sigma = LT$, where $T$ is the ...
5
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4answers
655 views

Temperature distribution in a current carrying conductor

A rod of uniform cross section and composition is connected across a battery. Let the middle part of the rod(when divided into three equal parts) is heated uniformly. A book says that the temperature ...
4
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3answers
2k views

Thermal Conductivity of Metals

My textbook says on conduction: These 'free' electrons can rapidly carry energy from the hotter to the cooler regions of the metal, so metals are generally good conductors of heat. A metal rod at ...
4
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2answers
6k views

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.
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 ...
4
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6answers
3k views

Why engines don't melt?

The temperatures of internal combustion engines are well above the melting points of the component materials. For example, temperatures can reach 2200° C whereas the melting point of aluminium is 659°...
4
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6answers
3k views

What does thermal conductivity actually measure?

Forgive my layman, non-physicist terminology used here. Hopefully I'm not too much of a caveman to express myself properly. What does thermal conductivity actually express? Is it measuring the amount ...
4
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2answers
94 views

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 ...
4
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4answers
10k views

Heat transfer by conduction is not possible for gases?

Today one of my instructor told me that gases cannot have heat transfer thru conduction because molecules are far apart and so it cannot transfer heat,infact the diffusion process of gases transfers ...
4
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1answer
1k views

What is the time correlation function in the Green-Kubo formulation of ionic current?

I am reading a paper, and I came across the Green-Kubo formulation, where the conductivity $\sigma$ of charged particles is related to the time correlation function of the $z$-component of the ...
4
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1answer
120 views

If we can compare thermal currents to electric currents, can we use electric current laws for thermal currrents?

I mean, me I take the Kirchoff's laws or other similar laws. Can we find analogous laws for the same in thermal physics?

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