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Questions tagged [thermodynamics]

Covers the study of (primarily homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using the tag: [statistical-mechanics].

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Reciprocating compressor [closed]

A reciprocating compressor is to be designed for a domestic refrigerator of 100 W cooling capacity. The refrigerator operates at an evaporator temperature of -23.3 C and a condensing temperature of 54....
DARA GARAGE  's user avatar
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Clarification on definitions in statistical mechanics [closed]

I've spent a good while searching for thorough explanations of some basic statistical mechanics concepts and despite how significant of a field it is, I find it is extremely difficult to find ...
user62783's user avatar
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Thermodynamic work and potential functions

I was reading about the maximum thermodynamic work of a system (Z) that is going to equilibrium. \begin{equation} dZ = dU + p_0 + T_0dS \end{equation} I then came across the thermodynamic potential ...
Skaeler's user avatar
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Is the 2nd law a reason for the irreversibility of natural processes or a consequence of it?

I have been introduced to chemical engineering thermodynamics due to my academic background. I had learnt about internal energy, entropy etc and applied the equations to various scenarios of practical ...
Explorer's user avatar
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2 answers
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Entropy change of an isolated system consisting of two thermally conductive blocks of equal isochoric heat capacity at different temperatures

A classic example considered in most introductory treatments of elementary thermodynamics consists of two thermally conductive (e.g., metal) blocks placed in thermal contact. In particular, I find ...
user104761's user avatar
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Relating specific heat capacity with the rate of cooling

By Newton’s law of cooling, the rate of heat loss (cooling) is directly proportional to the difference in the temperatures between the body and its environment. On the other hand, Specific heat ...
Emmanuel_III's user avatar
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Measurability of the energy difference of two states with different mole numbers

In H.B. Callen's thermodynamics (2nd ed. p. 18), after expaining why "the methods of mechanics permit us to measure the energy difference of any two states with equal mole numbers", the ...
Yao Wang's user avatar
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1 answer
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If I'm inside water, is the amount of heat energy I can receive capped because water can't go above 100°C?

I just learned about double-boiling, where instead of putting a pot directly on the flame stove (where it can get too hot), you put a big tub of water on the flame, and put the pot in the tub of water....
chausies's user avatar
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What do we mean when we say the CMB has a temperature and how do we measure it?

I have read this: An object without any internal degrees of freedom, like a single photon, can't really have a temperature. But an ensemble of photons can have a temperature. If you put an ensemble ...
Árpád Szendrei's user avatar
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Does the expansion of the universe cause the universe reach maximum entropy faster than a non expanding universe?

I've seen Does an expanding universe cool down? So I understand an expanding universe cools down, my question is, does an expanding universe reach maximum entropy faster than a non-expanding universe? ...
scm's user avatar
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Thermodynamic diagrams in Hamiltonian mechanics

If we compare the fundamental thermodynamic relation $(1)$ and the Hamilton's principal function $(2)$, than we have two practically identical equations: $$dU=TdS-pdV \tag1$$ $$dS=pdq-Hdt\tag 2$$ In ...
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Should I hold a baby formula bottle to cool it down faster?

The formula is prepared at 60 C and must cooled to 37 C before serving. The ambient temperature is 20 C. My overlord doesn't like to wait - should I hold the bottle in my hand to cool it down faster? ...
daniel.sedlacek's user avatar
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What are good introductory books for contact geometry in non-equilibrium thermo?

As far as I can understand, Mrugala's paper on the geometry of thermodynamic processes covers introductory prerequisites for the contact formalism applied to thermodynamics, however, I know there's a ...
3 votes
1 answer
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Landau and Lifshitz Principles of Statistical Mechanics

I've been reading Landau and Lifshitz book on Statistical Mechanicals and some aspects about how they lay out the principles has me a little confused. Let us now consider a macroscopic body or system ...
user62783's user avatar
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Unitary Evolution and the Second Law of Thermodynamics [duplicate]

Apologies for the long question. This problem has been mentioned multiple times on this platform, with no real resolution, in my opinion. So I'd like to gather all my thoughts below with hopes of ...
Sahand Tabatabaei's user avatar
2 votes
1 answer
31 views

Estimating Heat transfering by measuring [closed]

Consider the setup with closed chamber with two flat metal objects with know dimensions. The first object can be heated or cooled by peltier module and the second one is placed on top of the first one....
elektro_vujke's user avatar
1 vote
2 answers
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Contribution of rotational mode in ideal gas law

The ideal gas law is very accurate for an $N_2$ gas when the temperature is around 300K and the pressure is around 1atm. At these conditions, $N_2$'s compressibility factor is 0.997, which means that ...
Plemath's user avatar
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Why can photon be treated like gas?

In Cosmology, especially when studying Cosmic Dynamic, sometime we will treat photons as gas to calculate its pressure, but according to my understanding, photon and gas are nothing alike. Why can ...
Polaris5744's user avatar
5 votes
1 answer
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Net particle number density for relativistic particles at finite chemical potential (tricky integral)

Question: How does one show that the chemical potential of relativistic fermions is negligible at high energies? In particular, I would like to show that the difference between the particle density $n$...
Henry Deith's user avatar
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Why is the First Law of Thermodynamic related to Fluid Equation?

In Cosmology, there is a equation called Fluid Equation: $$\dot{{\varepsilon}}+3\frac{\dot{a}}{a}(\varepsilon+P)=0.$$ It is derived by taking time derivative of the First Law of Thermodynamic: $\dot{E}...
Polaris5744's user avatar
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What book should I read to learn about the magnetocaloric effect

I am trying to study the magnetocaloric effect for a project but I can't find any good resources that deeply talk about it. Could you make any good recommandation to learn the basics about this effect ...
-2 votes
4 answers
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In a universe with no photons, will everything necessarily be at absolute zero temperature?

Imagine a universe governed by the same physical laws as ours, i.e., the same fundamental forces, with the only caveat that there are no photons, hence no electromagnetic radiation in this universe. ...
N Unnikrishnan's user avatar
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Is it physically possible for an ordered system to endure forever? [duplicate]

I am seeking to understand whether my theological views align with the current understanding of the second law of thermodynamics. As a physicalist, I believe that all ontological existents consist of ...
Mohammad Abu-Zidan's user avatar
2 votes
0 answers
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Modified Joule-Thomson expansion

I was trying to solve a thermodynamics problem about the Joule-Thomson (Joule-Kelvin) expansion and I can't reach the answer. The book has the solution, but there's a term which I don't get where it ...
Facundo's user avatar
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Why different references express mass densities as $\mathrm{MeV}/\mathrm{fm}^3$ or $1/\mathrm{fm}^3$?

I was reading some papers about equations of state and have found that some of them express the mass density in terms of $\mathrm{MeV}/\mathrm{fm}^3$ and others in terms of $1/\mathrm{fm}^3$. Why is ...
johan's user avatar
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Is there an analogous Unruh effect for observers on a rigidly rotating ring?

I read up on the Unruh effect recently and what I got from it is that its basically a result of transforming to Rindler coordinates and using a Bogoliubov transformation to change the creation and ...
Aravind Karthigeyan's user avatar
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Can we derive friction from collisions with environment?

I would like to know if friction, that is, the term $-\alpha \dot{x}$ in the equation of a conservative system $\ddot{x} = -\nabla U(x) -\alpha \dot{x}$ can be derived in some way, by assuming elastic ...
Plop's user avatar
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Gibbs phase rule argument about battery voltage dependency on state of charge

I'm studying battery physics, particularly the dynamics of full discharge, and I am having trouble understanding an argument that is based on the Gibb's phase rule $$F=C-P+2$$ I understand the phase ...
mike1994's user avatar
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Meixner and the Impossibility of Non-equilibirum Entropy [closed]

Meixner in a series of publications, see a short list below, starting from 1959 criticized and ultimately denied the possibility of defining the entropy concept in an irreversible process. His ...
hyportnex's user avatar
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Entropy in irreversible adiabtic process

We know that, $$dS=\dfrac{\delta Q_{rev}}{T}$$ If you have an irreversible adiabatic process between two thermodynamic equilibrium end states of a system, there exists no possible reversible adiabatic ...
Shivansh Jain's user avatar
5 votes
5 answers
526 views

Use of Clausius theorem to prove entropy inequality in Fermi's Thermodynamics

At the beginning of Section 13 (at the bottom half of page 54 through the top half of page 55) of Enrico Fermi's classic Thermodynamics, he sets out to prove the relation (using his notation) $$S(B) - ...
user104761's user avatar
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Why is warming food in the microwave work and not heat? [duplicate]

In Schroeder's An Introduction to Thermal Physics, heat is defined as the "spontaneous flow of energy from one object to another" and work is defined thermodynamically as any other transfer ...
PineappleThursday's user avatar
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Microscopic derivation of Newtons law of viscosity?

Newtons viscosity law says that viscous stress is proportional to spatial velocity gradient. When used in hydrodynamic problems it results in the Laplacian of the velocity field appearing in the ...
YoussefMabrouk's user avatar
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2 answers
41 views

Experiment to determine friction coefficient

I've come up with an experiment to determine the dynamic friction coefficient of two bodies made up of arbitrary materials, and I'd like to know whether it is good enough or if it needs polishing (...
Lagrangiano's user avatar
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Definition of convection heat transfer not unambiguous? [duplicate]

What is actually the definition of convection in the context of heat transfer, if there is one? Wikipedia states: Convection (or convective heat transfer) is the transfer of heat from one place to ...
feliszingiber's user avatar
1 vote
1 answer
62 views

Heat equation two stage process - Additivity? some other approach?

I'm struggling a bit how to apply a standard solution to the heat equation to my own practical problem. I have some intuition, but do not know whether this intuition is justified. I don't understand ...
W_vH's user avatar
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Meaning of $n$-critical point

My lecture notes about field theory refer to a tricritical point as a point in which a continuous phase transition line meets a discontinuous phase transition line. In the following it refers to a ...
Dirac's delta's user avatar
2 votes
0 answers
61 views

How to obtain the first law of BH mechanics from the Smarr formula

In general relativity coupled to electromagnetism in $d$ dimensions, the Smarr formula relates the thermodynamical variables present in a rotating, electrically charged black hole. More specifically, ...
user728261's user avatar
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0 answers
42 views

How can red LEDs still give a faint glow at a voltage of only 1.4V? [duplicate]

How can a red LED work at a voltage of only $1.4{\rm V}$? Red photons have an energy of $1.77{\rm V}$ if we use $\lambda = 0.7\mu\text{m}$ in the relation: $$ E = \hbar \omega = \frac{2\pi\hbar c}{\...
Jos Bergervoet's user avatar
5 votes
3 answers
434 views

What causes the latent heat of solidification?

Every explanation that I read says: "When a crystal (solid state) forms from a liquid, heat is being produced." This seems rather weird, why would the production of something as ordered as ...
User198's user avatar
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0 answers
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Is it possible to arrange two or more lenses and mirrors so that I can focus both sun’s rays at a single point

I know similar questions have been asked but I’m still not convinced. I understand it would violate 2nd law of thermodynamics to generate a temperature hotter than the sun using one lens. I’m asking ...
MrElliptical's user avatar
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1 answer
43 views

How does doppler cooling work?

I have trouble understanding how doppler cooling works. I understand that an atom moving towards laser sees the laser light blue-shifted and if the laser frequency is slightly below the atom's ...
python3 programmer's user avatar
3 votes
1 answer
56 views

Why does fat get stuck to ice after solidification?

Suppose we put ice cubes into soup, which consists of saturated fat in liquid form and water in liquid form. When we put ice cube inside of it, fat gets solidified and when we remove ice cube, fat is ...
NikoMolecule's user avatar
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2 answers
103 views

Are calories an appropriate measurement of energy for biological systems? [closed]

According to this source, a calorie is an inappropriate unit to quantify the energy contained in food because a "calorie is heat energy" and "humans don't absorb photons" but ...
Jon Behnken's user avatar
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1 answer
39 views

Friedmann fluid equation in the non-relativistic case

The Friedmann fluid equation I am referring to is: $$ a\frac{d\rho}{da} = -3(\rho+P) .$$ In the non-relativistic (low temperature) case for an ideal gas universe (representing matter), I know that the ...
Andreas Christophilopoulos's user avatar
1 vote
0 answers
75 views

Do neutrons have a higher entropy than protons?

Since free neutrons want to undergo beta decay into a proton while protons are relatively stable does that mean that neutrons have higher entropy than protons?
Oreoluwa Matilukuro's user avatar
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$q$-potential in grand canonical ensemble

I was recently going through R.K. Pathria's Grand canonical ensemble chapter and found the following section confusing under physical significance of statistical quantities. The author mentions; To ...
Apoorv Mishra's user avatar
1 vote
1 answer
94 views

What is the relationship between Clausius Inequality and 2nd Law?

I am confused about the application of the 2nd Law for reversible and irreversible processes and cycles. I want to know how the Clausius principle, the Kelvin-Planck statement, and the Clausius ...
Skaeler's user avatar
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1 answer
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Origin of ideal gas fluid dynamics equations including the adiabatic index

I was given a system of equations that supposedly describes the fluid dynamics of an ideal gas. The equations are: $$ \begin{align} &\frac{\rho}{m} = \frac{p}{T} &\text{(ideal gas law)} \\\\ &...
Nico G.'s user avatar
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1 answer
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$P-v$ diagrams and isotherms with two inflection points

I have a very simple naive question concerning the interpretation of the following situation. Let there be an isotherm in a $P-v$ diagram which has two inflection points (different specific volumes, ...
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