Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

learn more… | top users | synonyms (3)

1
vote
2answers
1k views

Adiabatic filling of a container

Suppose a thermally insulated container is filled with atmospheric air until the pressure reaches 5000 psi. This could represent the filling of a diving cylinder, before thermal dissipation becomes ...
1
vote
1answer
261 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
2answers
179 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
vote
3answers
3k views

Office Air Conditioning and Open Windows

Today is nice and sunny and the air con is on in the office. It's a fairly large office seating 20 people, 30x30x15ft with 20 small windows and a single large AC unit on the back wall where there are ...
1
vote
1answer
435 views

Can we make a Maxwell's Demon using Quantum Computers?

Although I'm reasonably sure that quantum computing advances will not lead to the ability to construct a machine that globally violates the 2nd law of thermodynamics, it feels like a difficult ...
1
vote
1answer
16k views

How much work is needed to compress a certain volume of gas?

I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
1
vote
2answers
2k views

design of the heat exchanger…in chimney

I want to design a heat exchanger in a chimney in order to utilize heat from chimney. I have done several experiments, but I could not determine the exact length of tube (carrying water), such that ...
1
vote
2answers
7k views

Why does Joule-Thomson expansion of a gas do no (external) work?

I understand one of the benefits of the Hampson-Linde cycle is that there are no cold-side moving parts, but isn't one losing an awful lot of energy in the throttling process? There must be something ...
1
vote
3answers
274 views

If humans were able to catch all sun energy reaching the earth for their use, will the climate change?

I guess that energy will be used up and, at the end, will contribute to heat the earth, so I see no big differences... please explain your point of view.
1
vote
2answers
289 views

If I put 3 bottles of water next to each other in the fridge, which one is cold first?

I was wondering: If I put three bottles of water next to each other in the fridge, which one is cold first? Does it matter? Is it the one in the middle because it gets refrigerated by the other two? ...
1
vote
1answer
72 views

Why does time always flow forward?

According to the BBC Earth " Physics says that any event in our day-to-day lives could happen in reverse, at any time".Then why can't we just turn time backwards?
1
vote
2answers
100 views

Doesn't the success of statistical physics seem somewhat unreasonable?

It seems to me a rather big coincidence that statistical physics works so well. I can see how consistent macroscopic observations can occur just because the microstates that give rise to that ...
1
vote
1answer
57 views

Heat loss by gas compression - reversible vs. irreversible

I just solved a problem involving the following scenario: A gas following the van der Waals equation of state (not an ideal gas) is placed in a cylinder and undergoes isothermal compression. The ...
1
vote
2answers
93 views

Why can't the entropy of an isolated system decrease? [duplicate]

I read that heat cannot flow from cooler body to hotter because for that entropy of the system becomes negative. Why is that so? Why we cannot have negative entropy?
1
vote
2answers
48 views

Does extra carbon in air help ice melt faster? [closed]

If you increased the carbon (perhaps more specifically carbon dioxide), in a controlled environment around ice, does it increase the rate that the ice melted?
1
vote
1answer
35 views

Water + RF + Spark = Continuous Fire

Can anyone explain the physics of what is happening in the following video? https://youtu.be/p8xYUDiSGDk?t=37 Is this process Radiolysis? At what radio frequency & power level is h20 ...
1
vote
2answers
53 views

Heat Losses from water pan due to vaporisation before boiling

I'm studying heat transfer from an electric heater to a cooking pan (Stainless steel) filled with water; specifically, my problem is related to water vaporisation, as I've already found good models to ...
1
vote
2answers
71 views

Why is such huge mount of heat released by brute-force GPG cipher?

Please see GnuPG FAQ. I'm really interested in how to derive to "boil the ocean" by using the Landauer bound and the Margolus–Levitin limit. Any suggestion is welcome.
1
vote
2answers
178 views

The NERVA had to use liquid H2… But why?

The NERVA engine, developed at the late 60ies, was a nuclear thermal rocket developed for vacuum use in space craft. It was supposed to use Liquid Hydrogen, a cryogenic fuel with quite a few issues ...
1
vote
2answers
126 views

Why is Gibbs Free Energy not equal to 0? Its definition itself makes it 0

Gibbs Free Energy is defined as $$G = H - TS$$ and the change in $G,$ $$\Delta G = \Delta H - T\Delta S,$$ (isothermal and isobaric) Now at constant pressure, $q = \Delta H$ and Entropy is ...
1
vote
2answers
129 views

How does the second law of thermodynamics forbid the possibility of perpetual machine of the second kind?

Fermi in his lecture asserts: The second law of thermodynamics rules out the possibility of constructing a perpetuum mobile of the second kind. So, this means there can be no machine which just ...
1
vote
3answers
75 views

why do coiled wire create so much heat?

I am wondering how coiled wire creates so much heat when a current is passed through it. Is it just a larger surface area of heated substance is available or are interacting forces at work eg ...
1
vote
1answer
40 views

How is isobaric process compatible with change of volume of gas?

We have an ideal gas enclosed in cylinder whose top is covered by a piston of certain weight $mg$. At this stage, the piston is at rest which means the force by which the gas acts on the piston ...
1
vote
3answers
75 views

Is there a dynamic prelude to the state equation?

If I'm not mistaken, the state equation $$PV=nRT$$ also known as the 'ideal gas law' serves as a mathematical model relating pressure-volume-mass-temperature states of an assumed ideal gas. In other ...
1
vote
1answer
87 views

Why do people wear black in the Middle East?

I have read various dubious explanations as to why people often wear black in the heat, from cultural to somehow encouraging the evaporation of sweat (unconvincing). So, does anyone know what, if any ...
1
vote
1answer
151 views

What ice pack formula can hold the largest energy difference?

I recently bought some Freez Pak brand ice packs. The label advertises: "Colder Than Ice". I realize now that it's just a stupid marketing claim, but at first, it got me wondering if they had some ...
1
vote
3answers
123 views

How much effect does painting a domestic radiator have?

Yes, I know it should be called a convector :-) The obvious effect is that a coat of paint, which is generally a thermal insulator, can limit the rate of heat transfer from the metal to the air. But ...
1
vote
2answers
123 views

Why can't liquid nitrogen be sealed in gas cylinders?

By observing the phase diagram of nitrogen, hydrogen and carbon dioxide, I discovered the supercritical region. I can easily buy a gas tank of carbon dioxide at 250 Bars. However I never saw any ...
1
vote
5answers
141 views

What happens to the kinetic energy of a dropped ball when it comes to rest on the ground?

If we want to drop a ball from a height, we calculated that potential energy at bottom is zero and we say it is converted into kinetic energy. At that movement, if it is a kind of sand, we find it ...
1
vote
2answers
74 views

unchanged temperature of balloon inside freezer

I'd tried to put a balloon in the freezer and after enough time (several hours), I took it out and noticed that as I touch it that it's temperature did not drop down . I took an empty balloon ( not ...
1
vote
1answer
240 views

Entropy change in mixing two gases

The entropy change of an ideal gas is calculated as \begin{equation} \Delta S = C_V n\ln(\frac{T}{T_0}) + nR\ln{\frac{V}{V_0}} \end{equation} derived by integrating $dU = TdS - pdV$. It is only true ...
1
vote
1answer
91 views

Classifying regions of Van der Waal like gas

Given the equation of state $$p+a\left(\frac{N}{V}\right)=\frac{Nk_BT}{V-bN} \tag 1$$ Taking into account of the fact that a realistic model requires $p \geq 0, V \geq Nb, N>0$ classify the ...
1
vote
2answers
59 views

what is the supercritical state?

is the supercritical state of matter a separate state of matter or is it a combination of a liquid and a gas? could someone give me an overview of this state and its properties. i have seen some ...
1
vote
2answers
323 views

Why is heat transfer better from within circular tubes versus ex. square tubes?

It is claimed that heat exchange, through the tube-suface, is best from within circular tubes versus either (not sure which is correct): from outside of the tube itself other shapes like for example ...
1
vote
3answers
3k views

How does temperature relate to the kinetic energy of molecules?

In ideal gas model, temperature is the measure of average kinetic energy of the gas molecules. If by some means the gas particles are accelerated to a very high speed in one direction, KE certainly ...
1
vote
2answers
2k views

How to calculate temperature of an incandescent bulb filament?

Suppose we have a light bulb, for which we know its power rating, like voltage of $12\mathrm V$, and power consumption of $10\mathrm W$. We also know it's a halogen bulb with a tungsten filament ...
1
vote
3answers
103 views

At what energy consumption would we get a 1 degree rise in the Earth's temperature?

If energy consumption continues to rise at (say) 4% per year, how long before the heat dissipation seriously impacts climate?
1
vote
1answer
92 views

Chemical reaction A+B$\leftrightarrow$C. Equilibrium VS Non Equilibrium

Could you please confirm or say why I am wrong? Let us consider the steady state of the chemical reaction $A+B \leftrightarrow^{k_+}_{k_-} C$, with $k_+$ and $k_-$ the forward and backward rates. ...
1
vote
1answer
63 views

How can heaters using the same type of fuel be more or less efficient than each other? [duplicate]

I can understand there being a cost difference if you used gas vs electricity to heat your home. But for heaters using the same energy source, how can they be more or less efficient than each other? ...
1
vote
1answer
62 views

Does $\delta W=pdV$ hold for non-ideal gases

I have that for quasistatic processes, $$ \delta W= \textbf{f}\cdot d\textbf{x} $$ so for a gas $\delta W=pdV$. Does this only hold ideal gases or will it hold for van der waal's gas?
1
vote
2answers
415 views

Extensive variables in thermodynamics

Extensive variables in thermodynamics are those which scale linearly with the system size. It is known that a ratio of two extensive variables is an intensive variable. Now, the number of particles ...
1
vote
1answer
2k views
1
vote
2answers
112 views

Does a room aerate faster when it's cold outside?

When we open the window and it's cold outside, we feel that the cold air spreads quickly. But at the end, does the cold air propagate faster than if the outside air temperature were warm? In other ...
1
vote
4answers
7k views

Relation between temperature and pressure?

I was just working on a special question but I ignored the effect of temperature on it and now it becomes very important to me. What is the relation between Pressure and Temperature? Suppose we ...
1
vote
1answer
567 views

Emissivity of vacuum for radiation heat

What is the heat radiation emissivity of vacuum? For air as well? What is the difference? I understand that the vacuum has reflectivity of 0, So what is the other two values are in $$ reflectivity + ...
1
vote
1answer
2k views

Can a liquid boil in a closed container?

The title says it all. When one fills a container (with water for example) and closes it so no air can escape from it, then heats the container continuously, can the liquid boil or completely ...
1
vote
2answers
377 views

Is thermodynamic equilibrium static or dynamic?

Suppose, two parts of a system $A$ & $B$. They were at varying temperatures and hadn't achieved mechanical equilibrium. After the relaxation time, $A$ & $B$ were at thermal and mechanical ...
1
vote
2answers
6k views

Change in entropy adiabatic expansion

I think that an adiabatic expansion of a gas should cause the entropy to increase. On the other hand we have for adiabatic processes that $dQ = 0$ and therefore $dS= 0$, which is why I thought that ...
1
vote
2answers
449 views

Why does room temperature water and metal feel almost as cool as each other?

From what I've read about heat, temperature and conductivity, I understand that the reason water at room temperature feels colder than most other things at the same temperature (like wood, air, ...
1
vote
2answers
331 views

second law of thermodynamics

I'm a high school rookie learning thermodynamics right now by myself. I got really confused that the second law of thermodynamics states that the entropy of the universe is always increasing. If the ...