Heat is energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objects and systems, but its origin and properties can be understood in terms of their microscopic ...
3
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2answers
417 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 ...
1
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1answer
362 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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1answer
190 views
For how long can we make an air balloon stay flying via remotely controlled heat system?
I wonder how a function $$f=f(h, m_{\mathrm empty}, V_{max}, T_{h}), $$ with the top height $h$, the empty mass $m$, the maximum volume $V_{max}$, and the temperature of the heater $T_{h}$ would look ...
4
votes
1answer
98 views
Intuitive picture for spin-fluctuations contribution to specific heat of He3
Usually when discussing Fermi liquid theory, it is stated that due to the quasiparticles effectively behaving like a free electron gas with effective mass, the specific heat is linear in $T$ at small ...
3
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2answers
564 views
Why is oil a poor conductor of heat?
Why is oil a poor conductor of heat? Does it help in insulation?
3
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1answer
829 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 ...
1
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1answer
212 views
Per unit area, is there more heat transfer through the open top of a mug or the side walls?
I had a mug of hot coffee cool too rapidly for my liking the other day, which made me wonder what was the greater contributor to heat loss for a typical open-top ceramic mug: the open top, the walls, ...
6
votes
1answer
351 views
Microwave oven + water: dielectric heating or ion drag?
When you place a water or food in a microwave oven, it heats.
Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating?
AFAIK, in distilled water (which is a ...
2
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1answer
156 views
How to express the heat capacity in terms of heat?
The first law of thermodynamics divides the internal energy change into contributions of heat and work.
$$\text dU=\omega_Q-\omega_W,$$
Here I chose the notation to emphasise that the two parts are ...
1
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1answer
472 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:
$\alpha_s = 0.83$
...
1
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1answer
713 views
How much disolved oxygen is removed by boiling water?
Apologies if this is a chemistry question
I've read that drinking water contains dissolved oxygen to the tune of $10\:\rm{ppm}$.
I've also read that raising the temperature of water will remove some ...
3
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1answer
359 views
Can we explain physical similarities between Black Scholes PDE and the Mass Balance PDE (e.g. Advection-Diffusion equation)?
Both the Black-Scholes PDE{*} and the Mass/Material Balance PDE have a similar mathematical form of the PDE which is evident from the fact that on change of variables from Black-Scholes PDE we derive ...
5
votes
4answers
662 views
Sauna thermodynamics
Why does it get hotter (feel hotter) in a sauna when one pours water over the hot stones?
Wikipedia says that the water condenses onto the skin, but the actual air humidity is so low that I doubt ...
2
votes
2answers
1k views
Will the hole on a metal disc expand or contract upon heating? [duplicate]
Possible Duplicate:
Will a hole cut into a metal disk expand or shrink when the disc is heated?
The metal disc of diameter D1 has a hole in it and the diameter of the hole is D2 (D2
Now, ...
2
votes
1answer
64 views
Is there an abstract notion of heat within a microscopical system?
The microstates of a system are said to be unobservable. I can introduce the entropy as a measure of the number of microstates, which lead to the same macroscopic variables. So in this detailed ...
3
votes
1answer
57 views
Good references for specific heats
Does anyone know of a good reference for specific heats? It seems that it is no longer popular to publish values. I am especially interested in the specific heats of polymers.
1
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1answer
334 views
Heat absorbed by a room
How can one calculate the amount of heat absorbed inside a room in a single day using the temperature readings of the day?
If the temperature has to be reduced from 30C to 20C how much heat should be ...
1
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2answers
1k views
Microwaves vs Gas or Electric Coil heating of a water boiler in a typical household
Wouldn't it be more energy efficient and or safe to use microwaves to heat our home's water boiler instead of using dangerous gas or hot electric coils that could catch other things on fire? I'm kinda ...
1
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1answer
137 views
2d or 1d conduction in this scenario?
There is a rectangular fin attached to a heat exchanger with a base temperature of 350K. The fin has uniform properties and experiencesa uniform heat generation. It also experiences heat transfer with ...
4
votes
3answers
1k views
Why does hot oil explode when pouring water on it?
I am puzzled to know, What is the reason of hot oil make sound and explode when we pouring water on it?
3
votes
1answer
130 views
In a Sterling Engine, does heat from the hot side transfer to the cold side?
A Sterling Engine is a closed system. The "hot" side oscillates between higher temperature with higher pressure and lower temperature with lower pressure. Does Nature switch back and forth between ...
0
votes
1answer
166 views
At what point can we assume the tip of a fin is adiabatic?
Let's say there is a fin that is 1mm thick, extends 8mm from the surface, and is 10 mm wide. The fin is exposed to a moving fluid. Can we assume the adiabatic tip condition and use the characteristic, ...
1
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1answer
487 views
In what situations do I use the characteristic length of a fin to find the surface area?
So I'm learning about fins in heat transfer and it seems that there are two separate formulas for the surface area of a rectangular fin of length L, width w and thickness t. The fin is attached to a ...
2
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4answers
978 views
Which is more efficient, heating water in microwave or electric stove?
So our propane tank in the kitchen ran out again today.
Which is more energy efficient, boiling water in a microwave on an electric stove? All things being equal i.e. starting temperature and mass ...
0
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1answer
541 views
What's the temperature distribution of a plane wall insulated on one side with no internal heat gen.?
Let's say we have a plane wall that is insulated on one side, exposed to a fluid on the other side, and has no internal heat generation. Would the shape of the temperature distribution be a constant? ...
2
votes
1answer
680 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 ...
1
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0answers
175 views
Is the $mL_c$ value for triangular and rectangular fins the same value?
I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong.
...
2
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1answer
278 views
How do I find average temperature given a temperature distribution?
I was told to find the temperature distribution of a wire with a current going through it. So I found $$T(x)=T_{\infty}-\frac{\dot{q}}{km^{2}}[\frac{cosh(mx)}{cosh(mL)}-1]$$
I need to find the ...
1
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1answer
82 views
Terminology question about energy
I'm looking for the appropriate term to use for what gets "used up" as potential energy is converted to heat and work. For example, some of the the energy in solar radiation is converted by ...
5
votes
4answers
989 views
Should I heat my room when I'm not here, energy-efficiently speaking?
I was wondering as it's getting cold : is it better for my electricity bill to shut down completely my (electric) heater during day, and to turn it on again when I come home (then it will have to heat ...
0
votes
1answer
193 views
When to use Heat Diffusivity eqn and when to use Fourier's law to find temperature distribution?
Let's say that there is a circular conical section that has diameter $D=.25x$ without any heat generation and I need to find the temperature distribution.
Originially I thought I could use the heat ...
0
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2answers
120 views
Does it make sense to have a theory of thermodynamics about coldness?
When someone comes in from the cold to a heated room, it sometimes feels like there is coldness radiating away from that person. Is there a sense in which we can say that coldness radiates similarly ...
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1answer
498 views
How does heat transfer between two atoms in solid material?
Been looking at heat equation and it's derivation, according to Wikipedia it uses 2 mathematical assumptions. My problem is that although it all seems OK, what is the physics of heat transfer in ...
2
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1answer
872 views
Heat Flux and Spatial Temperature Gradients
The derivation for Heat Equation I am reading starts by stating
Net change of heat inside $[x,x+\Delta x]$ = Net flux of heat across boundaries + Total heat generated inside $[x,x+\Delta x]$ and ...
2
votes
0answers
423 views
When do I know if energy stored in an object is 0 or nonzero? (Heat transfer)
There is uniform internal heat generation at $\dot{q}=5\times10^{7} \frac{W}{m^{3}}$ is occurring in a cylindrical nuclear reactor fuel rod of 50 mm diameter and under steady state conditions the ...
0
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1answer
303 views
Temperature change effected by electric heater [closed]
A 40-gallon electric water heater has a 10kW heating element. What will the water temperature be after 15 min of heating if the start temp is 50F degrees.
There must be an equation. I can't find it ...
5
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3answers
342 views
What made the keys in my pocket so hot?
Not sure where to ask this question - thought you guys would probably have the best idea!
Today a single key on my keychain in my pocket heated up so that it was too hot to handle and scalded my leg. ...
1
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1answer
274 views
Given two boiling temperatures and pressures, how can I find the latent heat?
I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat ...
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votes
3answers
476 views
Can heat be extracted and concentrated? [closed]
If one could devise an answer to this question, electricity would be free for everyones disposal. (seems like a good dream but in reality free energy will be this worlds downfall)
7
votes
2answers
406 views
How much more energy does it take for a human body to heat 0C ice vs 0C water?
I'm trying to determine if going through the trouble of ingesting ice is worth the hassle versus ingesting ice-cold water, but my physics skills are rusty.
If I drink a gram of ice water at ~0C, my ...
0
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1answer
139 views
Is this a simple system in which no heat transfer is possible?
Let's say that a hot gas is trapped in a metal box. This metal box is magnetically suspended in another structure with a low temperature. The inner box does not touch anything. And there is a void in ...
0
votes
1answer
112 views
Heat transfer speed - affected by difference in relative heat?
If I put something at room temperature in an environment that is at roughly half room temperature, does it get colder less quickly than if it were placed into an environment with 1/4 room temperature, ...
7
votes
4answers
246 views
How to guess the content of a christmas present?
Let us assume that the present does not make any recognizable sounds when shaken (meow splat - the present now contains a dead kitten). Let us furthermore assume ...
5
votes
3answers
2k views
Could a sleeping bag be warmer if you are naked inside?
I have heard conflicting theories about the best way to keep warm in a sleeping bag in the winter. Some people say you should bundle up in your sleeping bag and another theory says that you should be ...
1
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1answer
261 views
Heat transfer, Cold vs. Hot
If you boil water inside a pot the outer rim bubbles first, I imagine because its hotter. Does that same concept apply for the inside of a refrigerator for example. Is the outer rim always more ...
0
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0answers
1k views
How to determine size of a Heat Exchanger?
I am designing a Tube heat-exchanger, similar to this:
My process requires water (at room temperature, 18C ~ 22C) that is being pumped out of a small tank (300 Liters) to be heated in a ...
1
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2answers
114 views
How does cooling scale with volume?
What equation would give me the answer to the question, "If i have a cup of water at a tempature of say boiling, how long would that cup of water take to cool off compared to say half that size of a ...
4
votes
3answers
3k views
Why is air a poor conductor of heat?
Today, I was reading an article How Thermoses Work
It goes on to explain all three processes of heat transfer:
Conduction
Radiation
Convection
In Convection, It states,
If it weren't for ...
1
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1answer
390 views
Understanding the Seebeck effect
Thermoelectricity is, as I understand it, the difference in voltage between the hot and cold ends of two dissimilar materials. If two materials are connected at two different junctions, the hot ...
2
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3answers
954 views
Does stirring water in a bucket in whirlpool keeps it warm?
I did an experiment when I was a teenager. I want to prove/see what really went on in that experiment.
When taking a bath, take a warm water in bucket and start taking a bath. You will notice that ...
