1
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0answers
31 views

Radiation heat transfer

I'm looking at the radiosity equations for heat transfer http://en.wikipedia.org/wiki/Radiosity_(heat_transfer)#Radiosity_method Specifically, I'm hesitant to accept the equation: $$ \dot Q_i = ...
0
votes
2answers
34 views

Heating a black body

By definition, Black body has absotivity=emmisstivity=1. This means the black body radiates all energy it accepts. Does this mean the black body cant be heated?
1
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1answer
63 views

Radiation and absorption

Can thermal radiation from a cooler object (B, which emits longer wavelength radiation) ever ADD to the overall thermal energy level of a warmer object (A, which emits shorter wavelength radiation)? ...
0
votes
2answers
808 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, ...
0
votes
1answer
47 views

Radiation pressure thermodynamic paradox

Could the radiation pressure of a black body (theoretically) perform work on the perfectly reflecting apparatus in the figure below? Assume that the block does not hinder the passage of light through ...
0
votes
3answers
71 views

Temperature of thermally isolated space region

If we thermally isolate a region in space, say using a hypothetical material of $0$ conductivity, and measure the region's temperature, will it be 2.7K?
1
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0answers
133 views

Radiative cooling time for a black body

Okay, so this is confusing me a bit. How can I calculate the time it takes to cool a perfect black body from an initial temperature $T$ down to equilibrium temperature (say, 3 K for space)? I know ...
0
votes
0answers
119 views

Does coffee with cream cool slower than black coffee?

At Modernist Cuisine, Nathan Myhrvold states that "Coffee with cream cools about 20% slower than black coffee". He then gives three reasons, two of them related to radiation and the third one to the ...
2
votes
1answer
132 views

How does heat energy travel in space?

How does the heat energy from the Sun reach us on the Earth? Since the kinetic energy of an atom is the amount of heat energy and there is no matter in space, how does heat from the Sun reach us?
0
votes
2answers
759 views

Is there a heat transfer equation that takes conduction, convection, radiation and dT/dt into account?

I see equations that take 2 or 3 of the listed parameters into account but I haven't been able to find one that is that complete. I'm seeking to solve this equation using matlab for a simulation ...
0
votes
0answers
51 views

What state is fire? Solid, Liquid or Gas or Plasma? [duplicate]

What state is fire? Solid, Liquid or Gas or Plasma? I was just roaming around when this question popped out of my mind. In what state is FIRE?
9
votes
6answers
2k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
1
vote
1answer
99 views

What's the relationship between the energy density of a black-body and its radiant exitance?

Through a bit calculation we can derive that in a cavity, the energy density $$u(f,T)=\overline{E(f)}\times G(f)=\frac{8\pi h}{c^3}\frac{f^3}{e^{h\nu /kT}-1}$$ If we take the integral over all ...
1
vote
1answer
130 views

What is the net radiative balance between two blackbodies with different temperature?

Context In trying to understand a crop productivity model, I want to figure out how to derive the equation for the net exchange of longwave radiation between two adjacent blackbodies (soil and ...
1
vote
1answer
158 views

Do bifacial solar panels operate at lower temperature than normal solar panels?

Bifacial solar panels have a glass backplane instead of the usual aluminum and are designed to absorb and convert to electricity light incident on either face. Many manufacturers claim that their ...
6
votes
1answer
176 views

Measuring temperature at a distance

http://www.youtube.com/watch?v=gKYrXHZwtPw In this video it is explained that Land Skin Temperature (LST) are measured by NASA's Aqua and Terra satellites. It seems it works by collecting the ...
1
vote
1answer
169 views

Can't understand a thing about emissivity concept

I can't understand something about emissivity. Emissivity is defined as the ratio of the radiant energy of an object, to radiant energy of blackbody at a temperature $T$. So, The vegetation has ...
3
votes
2answers
226 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
votes
2answers
371 views

Why do moving particles emit thermal radiation?

While answering another question about heat in an atom, the discussion in the comments led to the question of how heat is related to thermal radiation picked up by infrared cameras. The answer is that ...
1
vote
1answer
110 views

What cause scientists to study Black Body Radiation?

After spending hours understanding what exactly Black Body radiation and Ultraviolet catastrophe is, I cannot help myself asking what was the reason that make scientists such as Wilhelm Wien and Max ...
1
vote
2answers
100 views

Extreme heating by Sun on Earth- Can eggs be fried?

Will it be possible to fry eggs in Sahara desert by just keeping them under the sun? If so, then will the radiated eggs be any different? Or will we have to use the solar cooking concept to some ...
-1
votes
1answer
92 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 ...
11
votes
1answer
452 views

Thermodynamically possible to hide a Dyson sphere?

You build a Dyson sphere around a star to capture all its energy. The outer surface of the Dyson sphere still radiates heat at much higher temperature than the cold space background, so you're easy to ...
8
votes
1answer
169 views

radiation thermodynamics paradox

This question is concerned with a thermodynamic paradox for radiating bodies and radiation in a cavity of a specific shape. Consider two nested shells that are axisymmetric ellipsoids with the same ...
2
votes
1answer
138 views

What are the largest thermal gradients achievable in a lab environment?

I am looking for a system capable of creating a gradient of $100\, \mathrm{K}/\mathrm{\mu \textrm{m}}$ on a $30\, \mathrm{\mu}\textrm{m}$ spacing of a system mounted on a Si-N membrane. My so-called ...
0
votes
1answer
58 views

heat spread from hot coil: diffusion, radiation?

When modeling the heat spread from a hot object through a vacuum (or a gas), what is the dominant physical process for heat energy transportation? Thermal diffusion, thermal radiation, a mix of the ...
2
votes
2answers
175 views

Does the black body emit more than any other type of body?

I found this on Wikipedia article on black bodies: A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The ...
4
votes
1answer
223 views

How is the index of refraction dependence in Planck's law compatible with thermodynamics?

In various formulae for black-body radiation where $c$ appears, there is an implicit index of refraction dependence, since $c=c_0/n$, where $c$ is the speed of light, $c_0$ is the speed of light in ...
15
votes
6answers
1k views

What are the various physical mechanisms for energy transfer to the photon during blackbody emission?

By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
0
votes
1answer
89 views

Landauer's principle vs Wien's displacement law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of kTln2? If it is so, can we also argue ...
0
votes
0answers
79 views

Landauer's principle vs Rayleigh–Jeans law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of $kTln2$? If it is so, can we also ...
5
votes
1answer
922 views

Historic derivation of Wien's law

Every book I've read, including a lot of websites, Wikipedia, etc, say that Wien derived this: $$\rho_\nu(T)=\rho(\nu,T)=\nu^3f\left(\frac{\nu}{T}\right)$$ Being $\rho_v(T)$ the spectral enegy ...
17
votes
2answers
417 views

Why aren't gas planets and stars fuzzy? [duplicate]

The edge of Jupiter looks very sharp. Even more bothersome, the edge of the sun looks sharp, aside from kind of a soup of particles floating above it. The sun's surface has an incredibly low ...
1
vote
3answers
663 views

What's the physical difference between a convective heater and an infrared heater?

Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air? ...
-1
votes
2answers
438 views

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 ...
0
votes
1answer
219 views

What is the relation between surface area and radiation, if any?

Basically I wonder what happens to emitted radiation by douubling a light e.g. twice the surface area of the sun will emit how much more radiation? 4 times more? Is there a formula?
3
votes
0answers
67 views

Photon pumping in Laser

Let's consider a ring laser where the laser must pass through the gain material before it is sent toward a partially reflective surface $\ R=1-T $. The other mirrors are perfect reflectors with $\ ...
3
votes
2answers
471 views

How to interpret Stefan-Boltzmann's law?

The Stefan-Boltzmann equation states $e=\sigma T^4$, but how do we interpret this? Is this completely wrong: A body of size $s^2$ generates the radiation/temperature $T^4$ for a given size and a ...
2
votes
2answers
887 views

Possible colors of fire?

I have learnt that depending on the various gases those are involved in the reaction that produces fire, different colors (yellow, red or blue) of flames become visible. I have a question .. what are ...
5
votes
4answers
258 views

what is the basic form of the 'fire'? [duplicate]

Possible Duplicate: Is fire matter or energy? What is the basic form of fire? physics defines every entity by a basic form either solid or liquid or as a gas, example: water is liquid, ice ...
1
vote
1answer
842 views

Do materials cool down in the vacuum of space?

Do materials cool down in the vacuum of space? If yes, how does it really work?
33
votes
5answers
6k views

Is fire plasma?

Is Fire a Plasma? If not, what is it then? If yes why, don't we teach kids this basic example? UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify ...
-1
votes
1answer
240 views

Black body balloon in vacuum [closed]

The problem statement, all variables and given/known data There is a perfectly spherical balloon with surface painted black. It is placed in a perfect vacuum. It is gently inflated with an ideal ...
1
vote
1answer
195 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 ...
2
votes
4answers
2k 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 ...
4
votes
2answers
163 views

Optical element is heated by laser: is it possible to get oscillating heat distribution?

Imagine that we have thin optical element, which is irradiated by laser. Laser heats element, so there is some heat distribution in element. There is a heat sink through upper and lower element faces ...
13
votes
4answers
1k views

Entropy of radiation emitted into space

In several papers I see something equivalent to the following expression for the entropy of radiation given by an astronomical object such as the Sun (assuming the object can be approximated as a ...
3
votes
2answers
300 views

How might a resonant antenna and black body radiation interact?

How does an antenna behave when it is cooled so that its black-body radiation is emitting energy at its resonant frequency? Edit: To clarify, its not how they're related in general, but how might ...
8
votes
1answer
831 views

What temperature can you attain with a solar furnace?

A solar furnace is a device that concentrates the sun's light on a small point to heat it up to high temperature. One can imagine that in the limit of being completely surrounded by mirrors, your ...
6
votes
3answers
7k views

Why do lightbulbs continue to glow after the light is turned off?

I've noticed that whenever I turn the lamp off in my room at night, the lightbulb seems to continue to glow for a minute or so after that. It's not bright though; the only way I even notice it is if ...