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

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Joule thompson effect temperature change question?

Please can someone tell me what is the greatest amount of temperature change one can get from the Joule-Thompson throttling process? Is there a formula witch relates the temperatures and pressure's ...
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22 views

Question about fluid expansion

Hy, When a hot and dense fluid suddenly expands, how much can it cool down. Lets take for example an expansion valve from an AC, does the fluid do work when passing through the valve or does it not ...
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1answer
47 views

Joule Thomson effect

I have difficulties to understand the Joule Thomson coefficient given on the wikipedia page. It says that $(\partial_p T) = \frac{V}{C_p}( T \alpha -1)$. Now my problem is that I don't know about ...
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1answer
68 views

Thermodynamics and Internal Energy

I've been working on this problem for quite some time trying to figure out the most efficient way of answering it, So here goes the problem: There is a container, containing a monoatomic gas with ...
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0answers
25 views

Heat sink simulation with a fan

I am trying to solve this problem using advection-diffusion model and finite element method for solving it due to the complex geometry. Basically the problem i'm trying to solve using OpenFOAM is see ...
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0answers
20 views

Which factors are most important for choosing the optimal working fluid in a Stirling engine?

The theoretical factors I can think of are heat capacity, thermal conductivity, and viscosity. It seems to me that helium should be the better than hydrogen since it has lower heat capacity but also ...
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241 views

Definition of stress at the microscale

Take, for simplicity, a Lennard-Jones fluid below the critical temperature, which is to say that there is a phase separation into fluid and gas and thus an interface is formed. The macroscale picture ...
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2answers
117 views

Symplectic geometry in thermodynamics

There seems to be analogues between Hamiltonian dynamics and thermodynamics given the Legendre transforms between Lagrangian and Hamiltonian functions and all of Maxwell's relations. Poincarè tried to ...
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1answer
57 views

Why are heat-shields on re-entry vehicles smooth and not textured to increase drag?

Meteorites naturally texture themselves via the formation of regmaglypts, 'thumbprint-shaped' indentations caused by ablation of their surface, during entry into the atmosphere. This appears to ...
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1answer
848 views

Why is black the best emitter?

Why are emitters colored black better emitters than other colors? Why is white a worse emitter?
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1answer
82 views

Calculate mass of ice needed to cool water $\Delta$T degrees

I have a question about a thermodynamics formula I'd like to apply in my solution to a problem. The problem is "Determine how much ice one needs to toss into boiling water of mass $m_{w}$ such that ...
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4answers
201 views

Can a single molecule have a state?

I was studying a book about thermodynamics of nanosystems and I got stuck with this question in my mind which I couldn't find an answer for. For instance, does a single water molecule have a state, ...
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1answer
29 views

Can a Fermi gas and a Bose gas be both at the same pressure and temperature?

The title says it all: can a Fermi gas and a Bose gas be both at the same pressure and temperature? It comes from a quiz about statistical mechanics
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2answers
36 views

transfer of heat from lower to higher temperature [duplicate]

Can heat be transfer from low temperature body to high temperature body? Because according to second law of thermodynamics it can be transfered. But how?
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1answer
71 views

Meaning of chemical equilibrium between two phases

Suppose two phases 1 and 2 of water, say ice and water, are kept in a closed container, at a fixed temperature $T$ and fixed pressure $P$? Then I have the following question: Is phase 1 in ...
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2answers
64 views

Free Expansion - Paradox?

Let's say I have an isolated, adiabatic chamber which is divided into two parts with a massless, frictionless piston. One part has vacuum, while the other has a gas. In the beginning, they are at ...
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1answer
83 views

Does tin foil keep heat out?

For example, if i were mailing a box of chocolates and lined the inside of the box with foil, then wrapped the chocolate in bubble wrap and placed it inside the foil lined box, would the box heat up ...
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0answers
25 views

What is the minimum temperature of a metal surface to ignite a cigarette touching it perpendicularly?

Suppose you have a cigarette tip touching a metal surface at a 90 degree angle, exposed to air at 25C / 1atm, no wind, normal oxygen concentration. Cigarette is a regular brand, tobacco with paper ...
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41 views

Decreasing Temperature and Pressure of a closed system

I have a closed system that contains a pocket of gas. What happens to the volume of the gas when the ambient pressure acting on the system decreases, and the internal energy of the system decreases. ...
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2answers
76 views

Why doesn't a glass french press shatter when boiling water is poured in?

When I was little, I accidentally shattered a glass cooking instrument due to applying far too drastic a temperature change to it. Since then, I've been a bit afraid of doing it again. Of late, I've ...
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1answer
64 views

Difference between collisional and collisionless Boltzmann equations?

Reading an excellent answer, I've read about there are different Boltzmann statistics for a collision-less system (f.e. stars in a galaxy) and in a system with collisions (f.e. gas in a closed box). ...
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1answer
33 views

Thermodynamics - mass of gas expelled

Question: An open vessel contains 200 mg of air at 17 degrees Celsius. What percentage of weight of air would be expelled if the vessel is heated to 117 degrees Celsius if the pressure is to ...
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1answer
64 views

Is there a “high temperature” variant of 0 degrees Kelvin? [duplicate]

I know that -273.15 degrees celsius, also known as Absolute Zero or 0K is the low temperature limit for objects, but is it possible that there is a 'highest temperature?' I would have to guess that ...
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1answer
75 views

If an object falls - regarding air resistance - does the Potential or Kinetic energy get converted into thermal energy as it is falling?

I read a paragraph on the transfer of potential energy to kinetic energy and heat from this website: Even if air resistance slows down the ball, the potential energy is the same (Mb x g x H). ...
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0answers
64 views

Diffusion in a chemical potential gradient

I am having troubles to understand to connection between equilibrium and non equilibrium thermodynamics. I am studying a mixture of molecules $A,B,C$ and solvent $S$. The free energy $F$ is given by ...
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1answer
121 views

Blackbody radiation in thermally inhomogeneous environment

The power radiated by the backbody is according to Stefan-Boltzmann law $$ P = \sigma \varepsilon A (T^4-T_{env}^{4} ).$$ Is the parameter $T_{env}$ supposed to be only the temperature in the near ...
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2answers
102 views

Does radiating heat to outer space through the atmospheric transparency window have any impact on heat loss?

I was reading this article: Passive radiative cooling below ambient air temperature under direct sunlight The authors are improving upon the age-old idea of reflecting incoming sunlight while ...
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1answer
102 views

Do the stars in a galaxy have a thermal kinetic energy distribution?

I think, there is practically everything given to that: many point-like masses, able to exchange energy pseudo-randomly, and far long enough time to reach a thermodynamical equilibrium. Of course, ...
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1answer
90 views

Is temperature affected by gravitational potential?

Ok, I feel a bit silly asking this. I'm asking in relation to this question here on the molecular basis of hydrostatic pressure in a gas. There's been quite a bit of discussion and one of the ...
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0answers
80 views

Negative temperature thermodynamics

I asked this question about thermodynamics. I considered $$T=\frac{\partial U}{\partial S}$$ at constant $V$ and $N$ (number of particles), but now I can't figure out the change of $U$ with respect ...
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2answers
536 views

Where does the joules come from (ideal gas constant)?

I have not done any physics in ages and have recently started studying it. The first chapter in my book deals with the ideal gas constant: $$pV=nRT$$ It is rewritten as: $$R=\frac{pV}{nT}$$ When I ...
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1answer
33 views

Is the equilibrium state in thermodynamics a consequence of the second law of thermodynamics?

Is the thermal equilibrium state the state of maximum entropy? Is it a consequence of the second law of thermodynamics?
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1answer
55 views

Human body emits Radiation [closed]

Human being emits which type of waves and how to find that waves any possibility to detect this waves by Using sensors
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0answers
35 views

I need to remove water from a system [closed]

I work in an industry and I need to remove water from a system. The scenario: There is a washer and a blower on a conveyor belt. The item being washed is plastic (not sure what type) and can't be ...
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0answers
34 views

How can we describe or model the spread of ice during the freezing of the surface of a still lake?

Premise: I live in a place where it is unquestionably wintertime in every aspect of the phrase. I was driving down the street and I drove by a lake. There was a recent and sudden temperature drop ...
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2answers
61 views

Can kinetic energy in atoms result in emission of all types of EM radiation?

I already know the fact that when solid objects heat up, they emit thermal energy which is also known as infrared radiation. However, if the atoms in that solid were to begin gaining more or less ...
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16 views

Are all partial molar properties defined as a derivative at constant T,P?

Are all partial molar properties defined as a derivative at constant T,P? Are molar derivatives at constant T,V or S,P or S,P of any use? Is there a reason for that or mere convention?
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1answer
69 views

What makes a thermodynamic canonical variable canonical?

The last paragraph of page 1352 of IUPAC Technical Report Use of Legendre transforms in chemical thermodynamics" (Alberty, R.A., Pure Appl. Chem., Vol. 73, No. 8, pp. 1349–1380, 2001) says that ...
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1answer
75 views

Thermodynamics - internal energy

What would the curve that describes the change of internal energy ($U$) with the volume ($V$) be like if the change in the temperature is negative? My try: For a ideal monoatomic gas, we have ...
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1answer
54 views

How is heat and temperature related? How will a thermometer react in the following conditions? [closed]

Consider the cooking stove and LPG fuel for example, all my questions will be related to it. Assume I have a frying pan made of steel which is kept on the the stove with the knob set to moderate. ...
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1answer
37 views

Closed system, gas change in time

I'm trying to find out how to determine how a pressure of gas changes in time, but I can't find a way. I have a system with constant volume $V$ (closed system, exchanges heat with environment through ...
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17 views

Heating water with low and high gas heat

Similar type question is asked before but i'm looking for other aspect of it. I observed that if water is heated with low gas heat, it takes long time but it retains it high temperature for long time ...
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4answers
174 views

More detail on why pressure increases at the bottom of a column of gas

The question Why does the air pressure at the surface of the earth exactly equal the weight of the entire air column above it asks why the air pressure at any elevation is equal to the weight of the ...
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1answer
57 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, ...
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81 views

What's the physical meaning of the integral of the squared temperature in a one-dimensional rod, used to prove uniqueness of soln. in heat eqn.?

Before getting to the question, some background. Let $u(x,t)$ be the temperature in a laterally insulated rod of length $L$, at position $x$ and time $t$. The temperature satisfies the heat equation ...
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2answers
139 views

What is the difference between classical thermodynamics and statistical mechanics? [duplicate]

What is the difference between classical thermodynamics and statistical mechanics? To me, they are greatly different but are different approaches for explaining same thing. But I do prefer ...
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1answer
41 views

Equivalence of different definitions for chemical potential

In some books, the chemical potential is defined in term of the Gibbs energy as $$ \mu_i \equiv \left( \frac{\partial G}{\partial n_i} \right)_{P,T,n_j} $$ where $n_j$ indicates all mole numbers ...
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2answers
75 views

What is the solution for the apparent contradiction of Second law due to energy fluctuation?

A system has maximum entropy when it has reached thermal equilibrium. But as statistical mechanics say, there is always an otherwise infinitesimal probability of particles to confine at a corner of ...
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0answers
37 views

Effects of pressure rate of change on the temperature of a fixed amount of gas

In Vol I,Chap 1-2 of the Feynman lectures on Physics,Feynman talks about how a change in pressure of a fixed amount of gas enclosed in a piston can cause its temperature to increase/decrease. He ...
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2answers
91 views

How can there be any probability of finding the molecules clustered in half of the box,the other being empty?

Suppose,there are six molecules(indistinguishable) constantly jostling around in a box. The central configuration is when there are $3$ molecules in either halves of the box and having probability ...