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Questions tagged [thermodynamics]

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

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$\dot{W}_{lost}$ due to irreversible processes in a refrigeration unit

The condenser of a refrigeration system steadily admits $\dot{m} = 50 g/s$ of saturated R134a with a pressure $P_1 = 650kPa$ and a quality $x_1 = 0.9$. The condenser rejects $\dot{Q} = 7kW$ of heat to ...
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How does the door itself play into heat conducted from one door handle to the other?

I imagine have the door plays somewhat of a role and was curious what the terminology would be. I imagine be a bit too complex to simplify into a math formula.
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Confusion with entropy change associated with thermal reservoirs in an isobaric process

On chapter 8, Entropy, Zemansky and Dittman's book Heat and Thermodynamics has a problem with following details: A body of constant heat capacity $C_p$ and at a temperature $T_i$ is put in contact ...
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Fluctuating Thermodynamic Properties in an ensemble

I am trying to determine what the fluctuating thermodynamic properties are in the (µ,P,S) ensemble. However I'm really not sure how to determine that. I do know that the corresponding thermodynamic ...
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How to calculate the time to uniformly heat an object by natural convection?

I want to heat a piece of steel in a muffle until I bring it to a uniform temperature. The idea is to preheat the muffle to a certain temperature and then place the piece in it and wait for it to get ...
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2answers
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Can anyone explain equivalence of statistical entropy and thermodynamic entropy?

I read on wikipedia how Clausius came to define entropy after studying the Carnot cycle (He found a relation between heat transfer and temperature which was a state function,and named it entropy) but ...
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1answer
31 views

Does bag size and volume affect heat loss rate? [on hold]

Same size of ice cream been placed in small insulation and big insulation bag respectively. Whixh bags of ice cream melts first? How can we explain about the correlation of bag size and melting rate?
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1answer
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Can indistinguishable microstates evolve into different macroscopic states?

I guess this question is more about definition than about any physical principle. Can a given physical system (or can there be a physical system) admit microstates that have identical macroscopic ...
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53 views

Can the universe build itself back together after the Heat Death?

We all know that due to the 2nd Law of Thermodynamics the universe after a certain long period of time will eventually have all its energy spread out homogeneously and reach a Heat Death where nothing ...
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1answer
42 views

How to quantify the mixing of two hard-spheres gases?

Suppose that there are two types of hard-spheres gases ($a$ and $b$) in a box. Suppose that their radius is much smaller than the box's characteristic size. These two gases tend to repel each other. ...
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1answer
33 views

Is the specific heat capacity the same between real and ideal gases?

From Section 2.4.1 of this link where the change in the specific internal energy of a gas is given as $d u = \frac{\partial u}{\partial T} dT + \frac{\partial u}{\partial v} dv $ They define ideal ...
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Given two substances of different specific heats, how do you find the final temperature and these phase related things

Given two substances of different specific heats, how do you find the final temperature of them both, phase of either substance if there was a phase change, and how much either substance has changed ...
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1answer
32 views

How can a reversible path be substituted by a reversible zigzag path?

Say I have a thermodynamic process with parameters P,T,V [Pressure, temperature and volume], path starting from an initial state to a final state, to go back to the initial state we have to stay in ...
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Why do we have to dump the extra entropy created in a heat engine?

In his introduction to thermophysics, Daniel Schroeder writes the following about the process in a heat engine: Only part of the energy absorbed as heat can be converted to work. The reason is, ...
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Thermal Efficiency

For a thermally efficient house, is it better for the windows to be framed with something like aluminium, or steel? I am considering the thermal conductivities, aluminium has a value of 200, while ...
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1answer
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I reasoned that if $T_2 > T_1$ then $E_1>E_2$. Obviously this can't be right, what is the flaw in my logic?

We have an entropy function and I've shown that for this function $T_1(E_1)=T_2(E_2)$. Further, the fact that the entropy function is concave is stated. There are two systems in contact and only ...
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1answer
28 views

Random walk with Ammonia molecule [on hold]

This question is from Keith Stowe's Introduction to Thermodynamics book under Random walk. The question is something like this: I am aware that I am not supposed to post homework questions like this ...
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3answers
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Conceptual question in thermodynamics about isothermal processes

If a process is isothermal then Δ U is zero. So ΔQ is non zero. But isn't ΔQ=nCΔT. Implying that ΔQ is zero. Where am I wrong? (Considering ideal nature)
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On isentropic compression of ideal gases, work and internal energy

I'm trying to understand something about isentropic compression of Hydrogen. If you are assuming constant specific heats, the work done during an isentropic compression is $$W = \frac{k}{k-1}\cdot ...
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1answer
41 views

Is the work done by friction considered as heat?

In the first law of thermodynamics, We write the change in internal energy in terms of heat exchanged and work done. The answer to the above question doesn't matter if our final aim is to find the ...
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1answer
44 views

On Joule's free expansion experiment

While reading through an introductory textbook in Thermodynamics, I've come across a series of arguments that seem somewhat arbitrary/vague, on which I'd like some clarification. To begin with, the ...
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What is the topology of a phase diagram?

Looking at various two-variable phase diagrams I was struck by that on every one I have seen so far all the phases formed simple connected regions; see, for example the phase diagrams of $H_2O$ or of $...
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Why is the number of excited vibrational modes $g(\nu)d\nu$ proportional to $x^2e^{-x}$ in Debye's theory?

I come across a problem in Terrell Hill's "Introduction to statistical thermodynamics" saying that: In the Debye theory, the number of excited vibrational modes in the frequency range $\nu$ to $\nu+...
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Periodicity trick for Kerr Black Holes

I am slightly confused concerning the euclidean section of a Kerr black hole. In page 5 of the following paper https://arxiv.org/abs/hep-th/9908022 it is said that in order to get the euclidean ...
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1answer
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What's the difference between static and stagnation properties? [on hold]

Difference between static and stagnation properties.
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1answer
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Derivation of Proportionality of Phase Space Volume log(Γ)∝N

In the derivation of extensivity of entropy for the micro-canonical ensemble, we assume an ensemble of two systems with the energies $E_1$ and $E_2$. The total energy is given as $E<E_1+E_2<E+\...
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What was the informational content of the universe at the Planck time?

If the energy of $1 \, \mathrm{bit}$ of information is $k_{\small{\text{B}}}T \ln{2}$, then the energy of that bit increases with the temperature of the system. When I try to calculate how much energy ...
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5answers
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Why does the energy of a thermodynamic system depend on the volume?

In thermodynamics one assumes that the energy (or other observables) of the system only depend on a few parameters like the temperature, the particle number and also the volume: $dE = \left(\frac{\...
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33 views

Interpertation of Motron Number

The Reynolds number is interpreted as the ratio of inertial to viscous forces in a flow. Are there similar interpertations for The Motron Number?
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1answer
52 views

Are waterfalls heating the planet?

This might seem like a really obnoxious question, but hear me out. During the last physics class, we determined that water that bursts down a 50m high waterfall undergoes $0.117K$ of temperature ...
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2answers
65 views

Question on convective heat transfer

Why is the following formula used when we define heat transfer due to convection on a flat plate?: $$ q=h(T_s-T_\infty)$$ Where $T_s$ is the temperature of surface at a particular location and $T_\...
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Thermodynamics and classroom [on hold]

The temperature of a classroom with dimentions of 10*8*3 m ia to be maintained at 23 degree. there are 30 students and a teacher in the room. the metabolic rates of a student and a teacher are 320 kj/...
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Potential Energy of Particles

I read the following statement in my textbook While a liquid is boiling, the energy supplied to the liquid goes to breaking the bonds between neighbouring molecules. Can anyone explain the process ...
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2answers
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Pressure correction and volume correction in van der Waals' equation of state

I have a problem in understanding the van der Waals real gas equation and it goes like this. $$ nRT=\left(P+a\frac{n^2}{V^2}\right)(V-nb) $$ Do the variables $P$ and $V$ on the RHS have the same ...
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What is meant by finite harmonic oscillator?

What does it mean to take finite harmonic oscillator, In research article "http://iopscience.iop.org/article/10.1088/1367-2630/17/11/113015 ", we were finding effective number of cobosons in ...
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3answers
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Atmospheric pressure, density and temperature variation with altitude

I'm trying to understand how one can calculate pressure, density and temperature of the atmosphere as a function of altitude. My assumptions are mostly sourced from https://en.wikipedia.org/wiki/...
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2answers
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Degrees of freedom for diatomic molecules [duplicate]

I have a doubt in understanding about the degrees of freedom (dof) ......as I have learned dof is nothing but the necessary parameters to specify the location and configuration of a system.....if that'...
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1answer
34 views

Maximum information stored in nested black holes

The question goes along the lines of understanding how does the entropy-information additivity works when black holes are inside other black holes, including the special case where the inner black ...
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1answer
40 views

Why can we not use the specific heat to determine the work done on steam in a Rankine cycle?

Okay, I am trying to work backwards from an exam which I messed up and I am trying to figure out what the lecturer did based on his answers posted online. Looking back, I realise one mistake I made ...
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54 views

Enthalpy Partial Derivative [on hold]

I am trying to derive and prove that $$\frac {dH}{dT}_\text{const. volume} = C_p- (\alpha^2) \cdot V\cdot \frac T{\beta} + \alpha\cdot \frac V{\beta}$$ I keep getting stuck around $C_p-C_v = (\...
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1answer
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Question about carnot two phase power cycle

The figure below is based on material presented in an MIT OpenCoursware program on thermodynamics on the web. They were comparing a Carnot two-phase power cycle to a Rankine cycle with superheating (...
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Brayton Cycle PV diagram when regeneration is not possible

https://www.ecourses.ou.edu/ebook/thermodynamics/ch09/sec092/media/th090203p.gif Above is the case of ideal Brayton cycle when the temperature at exit of turbine ( state 4 ) is greater than the ...
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Show that having a thermodynamic potential in terms of its natural variables will give complete information about the system

I have only have one textbook on thermodynamics and this proof isn't featured (Fermi, only 140 or so pages) and my lecture notes say 'this proof is beyond the scope of the course...', but I'm curious. ...
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Free stress boundary condition and Laplace Law

Assume an aggregate for which free-stress boundary condition is imposed and in which there is considered as a fluid, so that the pressure is uniform inside. Does it mean that at the boundary: $P-P_{...
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1answer
48 views

Melting ice inside water by increasing pressure

An ice cube is floating in water inside a container and the system is in thermal equilibrium. And let say we somehow immerse the ice cube slowly into deeper region inside the container (we may pull a ...
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37 views

Does hot water turns to ice quicker than cold water? [duplicate]

I kept hot water by mistake in freezer and noticed that it turned to ice pretty quickly and then I simultaneously put hot and cold water in freezer, still the results were the same. How so?
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Champagne bubbles and gravity

One of the influences on bubble size is the speed with which a bubble rises in a glass - this, I believe, is due to the force of gravity which acts on the liquid around the CO2. The greater the ...
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How do you find the propagated uncertainty for the thermal expansion coefficient?

I am currently working on a lab report involving thermal expansion coefficients. The main idea of the lab was to identify materials based on their thermal expansion coefficient. Each material was a ...
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What is the most energy efficient way to heat and maintain the temperature in a tank (vertical column) of water with 4 heating elements? [closed]

1) Given the following tank of water with four heating elements in two groups, A and B, where the elements in each group are switched on and off together, what is the optimal way to heat the tank of ...
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1answer
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Integrating Carnahan-Starling Pressure

Given the Carnahan-Starling equation of state for a solution of hard-spheres, $$ Z = \frac{P}{\rho k_BT} = \frac{1 + \eta + \eta^2 - \eta^3}{(1-\eta)^3}$$ where $\rho = N/V$ is the number density and ...