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 ...
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2answers
114 views
Room temperature and fan orientation
So I'm in a tiny dorm room and I normally point my fan blowing outside the window to cool my room off. I've been in some debates on blowing air out or in is more effective, so I'm hoping to get some ...
2
votes
2answers
197 views
Heat transfer between two surfaces
Suppose I have surface A in contact with surface B, if I apply Fourier's law of heat transfer, which $K$ should I use, $K_a$ or $K_b$?
Essentially asking whether the same block of material heats ...
0
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1answer
58 views
Indicators on how even the heat is distributed?
I'm wondering if there are any good indicators on how even the heat is distributed on an object (for simplicity, a flat object maybe)? What are the possibly reasonable ways to maximize the evenness if ...
1
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2answers
189 views
A hot object exposed to low temperature in a vacuum doesn't lose heat?
I heard somewhere that if the human body were exposed to outer space where the temperature is extremely low, the human won't actually feel cold because in a vacuum, the heat energy doesn't have ...
1
vote
0answers
24 views
Does a flame produce free electrons? [duplicate]
Possible Duplicate:
Does Fire Conduct Electricity? Why?
Is fire plasma?
Does a flame produce free electrons ? Or is the answer sometimes depending on the chemicals ? Does the answer depend ...
0
votes
1answer
125 views
Confused about fire?
Im confused about fire.
The way I see it :
Heat creates (kinetic) energy in mass and this creates stronger vibrations of atoms.
When those vibrations are strong enough the electrons interact ...
3
votes
4answers
364 views
why does a larger thermal conductivity provide a smaller temperature gradient?
I was thinking about Fourier's Law in heat transfer today and for some reason I am just not understanding the relationships it gives us. Fourier's tells us that if the heat transfer rate is kept ...
3
votes
1answer
128 views
Why aren't two systems in thermal equilibrium the same as one system?
I am reading Molecular Driving Forces, 2nd ed., by Dill & Bromberg.
On page 53, example 3.9, we consider why energy exchanges between two systems from the point of view of the 2nd law.
We ...
5
votes
1answer
137 views
Can an induction coil heat two layers of metal?
Imagine we have an induction coil which is strong enough to heat a sheet of metal. We can put a sheet of ferromagnetic metal close to the coil at distance $h_1$, and it gets heated to temperature ...
1
vote
3answers
93 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?
...
8
votes
4answers
731 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, ...
0
votes
1answer
82 views
Is the heat required to alter the Higgs field an 'absolute heat'?
I have read and heard that manipulating the Higgs field would require heating up a local geometry to ridiculous temperature. I am trying to understand if there are stars or places in the universe ...
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votes
1answer
164 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 ...
3
votes
1answer
115 views
How can gas from compressed air can “take” heat from surrounding environment?
I have recently been reading about why a can of compressed air gets cold when the air it contains is discharged. From what I understand the change from a liquid to a gas requires energy and therefore ...
14
votes
1answer
312 views
Is there some way to narrow down the Leidenfrost point for water?
Cooks sometimes use the Leidenfrost effect to estimate the temperature of a frying pan by flicking a few drops of water onto the heated pan. I had no idea, before looking into this, that this could be ...
8
votes
2answers
611 views
Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?
My train of thought was the following:
The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons.
Instead, the temperature ...
2
votes
3answers
120 views
Why is an air conditioner more efficient in a low-thermal-mass house?
Why is an air conditioner more efficient in a low-thermal-mass house?
I recently read
To get these efficiency gains it is important to use the air
conditioner as it is intended: the unit has to ...
1
vote
3answers
191 views
Can one heat up a vacuum?
I've got a question about heating a vacuum. If there were, say, a container in space, at 2.7 degrees kelvin (the typical temperature of space, if I'm not mistaken) and as empty as space (as close to ...
3
votes
0answers
75 views
Thermal imaging camera [closed]
I'm making a tea bag experiment (Make a hollow cylindrical tube from light paper e.g. from an empty tea bag. When the top end of the cylinder is lit, it takes off.) I need to know how hot air is ...
3
votes
1answer
113 views
If layers of insulation are continuously added to a heated object, will it continue to be better insulated?
If you were to keep adding layers of insulation to something, like blankets to a person, would each blanket continue to improve the insulation? Or do you reach some point at which the next blanket ...
3
votes
0answers
41 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 $\ ...
2
votes
0answers
31 views
In a non-degenerate plasma, why are e-e collision negligible compared to e-ion for thermal conduction?
I'm trying to make some order of magnitude estimates of heat transfer in stars - to better understand 1) why conduction is said to be negligible (for non-degenerate matter) and 2) when convection ...
0
votes
2answers
96 views
Stealing heat, or not?
Say I hook a 1KW steam engine to the steam heat in my apartment, and generate 1KW of electricity (the engine is 1KW mechanical, not 1KW thermal) from it, so I don't have to pay ConEd.
That means I ...
1
vote
1answer
91 views
Is $E=mc^2$ reserved to nuclear physics?
I was wondering, while putting a log in my fireplace, how much energy the piece of wood would give. The most famous formula poped into my head: $E=m \cdot c ^ 2$!
Is this formula applicable to a ...
0
votes
0answers
131 views
Constant volume specific heat
A monatomic ideal gas is confined to move in two dimensions. What is the constant volume specific heat for this gas?
Consider a system of N independent harmonic oscillators moving in two dimensions. ...
1
vote
0answers
44 views
Can I estimate the long-term surface heat transfer coefficient based on a temperature difference between the air surface and ground surface?
I want to estimate the long-term or annual heat transfer coefficient for the earth's surface in a particular area where the mean annual air surface temperature is about 13$^\circ$C, and the mean ...
-2
votes
1answer
220 views
Why do phonons cause excellent heat conduction in diamonds?
Phonons are the quantum of lattice vibrations in crystals and are not to be confused with photons, the gauge bosons of the electromagnetic force. Apparently, they contribute to heat conduction, but I ...
5
votes
0answers
179 views
Where to place a fan in order to cool a room the fastest [closed]
Imagine I have room that is very hot and it is colder outside. I want to cool it down using a fan.
Scenario 1
There is only one door. I have one fan.
Where should I put it and which way should it ...
0
votes
1answer
69 views
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas?
I think that you need work to preserve this process and you bring thermal ...
3
votes
1answer
144 views
Rayleigh-Benard Convection
I found this nice paper about RB convection. However I am confused by what is going on page 6. In particular why we are suddenly using Helmholtz equation to find spatially periodic solutions. Aren't ...
-2
votes
1answer
198 views
Where is the candle hottest?
Where is the hottest spot above a lit candle? In the flame or just above the flame tip or some cm above the flame or other?
Update
My question more precisely concerns the heat energy I can get from ...
3
votes
2answers
539 views
How air humidity affects how much time is needed for heating the air?
In cold weathers it is suggested to put a humidifier since the air gets too dry. I wonder how the humidity affects how much time is needed to get the air at a temperature of 20 Celsius degrees? I mean ...
0
votes
3answers
641 views
Does closing curtains 'make your home warmer'?
I mean, in the sense that the act of closing curtains would somehow reduce the amount of heat loss of the house to the outside, thus making it warmer for a given supply of heating.
4
votes
0answers
121 views
Thermodynamic relations from Gibbs-Duhem
Given the Gibbs-Duhem relation
$V dp = S dT - N d \mu$, I am having trouble deriving the following identity:
$\ (\frac{\partial N}{\partial \mu})_{V,T} = N (\frac{\partial \rho}{\partial p})_T$
...
3
votes
1answer
300 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 ...
2
votes
2answers
267 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
197 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 ...
4
votes
3answers
319 views
Can I take heat from the air and convert it to electricity?
Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house.
...
0
votes
0answers
79 views
How can I measure the calories consumed in daily activity? [closed]
From a nice question here:
How are the calories in food calculated?
I can roughly understand how people provide the data of calories in certain food.
However, I am still confused about 2 things.
1) ...
0
votes
2answers
2k views
What is the characteristic length of a cylinder
I have a cold cylinder that is submerged in hot water and I need to find the convective heat transfer coefficient. I can do the whole process but I am stuck finding the characteristic length. I found ...
1
vote
2answers
119 views
How cold should it be outside for a hot coffee mug to break?
So I like to go outside for a morning coffee with a cigarette. In winter here it's usually between -5C to -25C, and sometimes it gets down to -30C and colder. Assuming that my coffee is about 75-80C, ...
5
votes
4answers
1k views
After what speed air friction starts to heat up an object?
I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster.
But ...
7
votes
4answers
667 views
Why does pizza cheese seem hotter than the crust?
When I eat hot pizza or a melted cheese sandwich, the cheese feels a lot hotter than the crust or bread: in particular, the cheese might scald the roof of my mouth. but the crust will not. Is this
...
5
votes
1answer
101 views
Which came first, movement or heat?
According to my measly understanding of the universe, when particles hit one another, some of their kinetic energy is transformed into heat. But when we heat particles (for instance, putting a bucket ...
0
votes
1answer
460 views
Heat Exchanger Calculation
I have a tank of oil at 55 degrees c. I plan to run a copper pipe 8mm in diameter (1mm thickness) into a coil 15m long inside the tank. For all purposes of assumption, the copper pipe is perfectly ...
0
votes
1answer
121 views
What is the ion drag mechanism in dielectric heating?
While reading about dielectric heating on Wikipedia, I read about the ion drag mechanism but there wasn't enough information about.
I know there is another Phys.SE question talking about the ion drag ...
3
votes
1answer
189 views
Why do non-stick frying pans work?
Modern non-stick frying pans use a mixture of titanium and ceramic that is sandblasted onto the pan surface, and then fired to 2,000 °C (according to Wikipedia).
Can anyone explain (at the molecular ...
1
vote
1answer
139 views
What arrangement of sound waves would be needed to heat air in a typical sized room?
From what I understand, sound is simply the jostling of the molecules that make up the air in a specific pattern, widely known as waves. I also know that these are longitudinal waves. If we were to ...
-1
votes
1answer
96 views
I need help with this question on Heat Capacity
A calorimeter has a Heat Capacity of $70 J/K$. There is $150g$ water with a temperature of $20^oC$ in this calorimeter. In this, you put a metal cube of $60g$ with a temperature of $100^oC$. The ...
4
votes
1answer
125 views
What would jumping into a pool and feeling cold be called? Conduction, or convection?
This was another question from my son's workbook. It said:
...
