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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Derivation of thermodynamic temperature

In deriving thermodynamic temperature scale, it uses the concept that heat transfer between two reservoirs is the function of the reservoirs' temperatures. i.e. Q1/Q2=$Φ(T_1,T_2)$. And then further ...
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31 views

difference between Heat and temperature [duplicate]

Temperature is often said to be average kinetic energy of the atoms and heat the sum of kinetic energy of all atoms. I dont agree with this definition of Heat as Heat is NOT energy. It is mode of ...
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2answers
169 views

Understanding mechanical equilibrium

In this site, mechanical equilibrium is defined as when there is no net force between the system and the boundary, it is in mechanical equilibrium. Now, what does it mean by net force? What would ...
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32 views

Does this violate Stefan's law

Radiation energy per unit time is given Stefan-Boltzmann law as being proportional to temperature to the 4th power, and to surface area of the body. (For black bodies) This was told to me in our ...
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68 views

thermodynamics poisson's ratio of mixtures

air consists of 79% nitrogen and 21% diatomic gas(say) . to perform calculations on ΔH on adiabatic expansions, instead of taking as parts , can i take it as a uniform gas with some γ(poission's ...
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121 views

Simplest way to analytically determine whether a claimed heat transfer process obeys the second law of thermodynamics?

I want to find the simplest method to determine whether a proposed heat transfer process violates the second law of thermodynamics. Specifically I am looking for a method that meets the following ...
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37 views

Lindblad equation derivation

I'm reading A simple derivation of the Lindblad equation. It introduces a Hamiltonian for a system consisting of a principal system $S$, a heat bath $B$ and an interaction term: ...
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17 views

Superfluid across a temperature gradient

As I understand it, superfluids cannot sustain temperature gradients; specifically, if a gradient is introduced somewhere on the boundary of the superfluid, a "second sound" thermal wave propagates ...
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51 views

Simple thermodynamic proof that light from a source cannot be focused to heat an object above the source's temperature

I was thinking about the question in the title. I found the following thread, and some of the answers are making my head spin! Is it possible to focus the radiation from a black body to make ...
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51 views

How to find Entropy of system in terms of Magnetic Field and Temperature

I'm studying for final exams and I have a question about how to find the entropy of a particular system. The system is a lattice of paramagnetic atoms fixed to the lattice sites, with an external ...
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1answer
25 views

Acceleration of a container in thermodynamics

How will accelerating a container with an ideal gas in it affect the conditions? My initial thoughts are that the ideal gas will collect at the opposite end of acceleration, which means that the ...
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1answer
49 views

What is the relationship between liquid-gas expansion pressure and surface area to volume ratio?

If a set volume of liquid is heated above its boiling point, how does the pressure that that volume of gas generates relate to the surface area of the medium in which it is enclosed in. For ...
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25 views

Does the orientation matter by a heat mirror?

I have a roller blind, which has a heat mirror, so one side seems to be covered with some sort of metal. In summer the metallic side faces outwards, so it can reflect the sunlight. Now in the winter ...
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45 views

What is a heat source and heat sink in relation to thermodynamics? [closed]

Honestly, I have exams in two weeks and this is something I missed. What is a heat source and heat sink and how do they interact? I get that a heat sink is for dissipating heat, and it's obvious that ...
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18 views

temperature and velocity exchange

So there is a relation between total temperature and velocity of a fluid. In an adiabatic flow what determines how much one property (velocity or temperature will change)? I know the equation. But ...
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62 views

Schottky Anomaly - Heat Capacity

I'm having a little bit of a difficulty understanding the origins of the schottky anomaly at low temperatures in the heat capacity of certain materials with restricted energy levels. As I understand, ...
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60 views

Work done by heating a balloon with $H_2$ ideal gas

I have a difficulty treating this problem. Could you help me to understand the questions, please (I did my attempt)? Problem Consider a spherical balloon filled with $H_2$ gas. Due to a ...
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110 views

Isentropic efficiency of gas expansion process

let a compressed gas expand. If the process is isentropic, the relationship between its temperature before expansion, and its temperature after expansion is related to its heat capacity ratio. The ...
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1answer
31 views

How constant volume gas thermomether keeps the volume constant?

So the level of mercury on the left is being kept down by the pressure of the gas, correct? When the temperature rises, shouldn't the mercury level on the left go down? And when the mercury level go ...
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47 views

Why does NASA use gold to hold heat in even though its conductive? [duplicate]

I heard that NASA uses gold to prevent heat loss even though gold is conductive. How does NASA prevent heat loss with a conductive material?
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38 views

Johnson Noise: Source of thermal fluctuations

I've read a lot online about Johnson noise being caused by thermal fluctuations, and the Wikipedia page of thermal fluctuations attributes this to the fact that particles don't all have the same ...
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1answer
50 views

Difference between solid and gases thermal expansion

The coefficient of linear expansion is $$\Delta L = L \,\alpha \Delta T,$$ where $\Delta t$ can be the difference of any two temperatures. However, in volume expansion of gases, $$\Delta V = V ...
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42 views

Deriving an Expression for Helmoltz free energy

Given the equations of states for an isolated system: $$E=\frac32 pV$$ $$p=aVT^4$$ I was asked to find the Helmoltz free energy per particle, $F=E-TS$, as a function of $T$ and $V$. I began with the ...
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1answer
23 views

Location of heat conversion in heat engines

If I put a large glass dome on a heap of coal, and burn it, I would expect the air to heat up certain amount. But if I put a coal power plant to that dome, and use it to burn the same amount of coal, ...
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121 views

How can q=mcp(deltaT) be made dimensionless?

Specifically, how can I make $m C_p$ dimensionless? I've tried using the Reynolds number and Peclet number definitions to plug into there but the closest I've gotten to was: $q=\pi D Re Pe ...
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23 views

Max thickness that can be cooled in a certain time

A frozen-food company freezes its spinach by first compressing it into large slabs and then exposing the slab of spinach to a low-temperature cooling medium. The large slab of compressed spinach is ...
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27 views

Non-steady state gas expansion

Please look at the following link for the sketch of the problem: Adiabatic Expansion with expanding control volume I have a certain amount of gas at a certain pressure and temperature at the start. ...
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18 views

why a engine convert all of its heat into work? [duplicate]

Why does heat is released to sink at lower temperature why all of the heat that is taken by a engine from heat reservior cannot be converted into work? I know that it has something to do with the ...
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103 views

In thermodynamic identity, dU=TdS-PdV. Are dS and dV orthogonal or is (T,P) defined in a conjugated space from (dS,dV)?

In thermodynamic identity, we say dU=TdS-pdV, and only Maxwell's relation is required for U to be a proper behaved thermodynamics variable. But from multivariable calculus, that result requires dS ...
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26 views

Adiabatic Relation in Plasma Invariant and Thermodynamics

In the problem above, I know how to do the 1D part. Basically, you just plug $V_{l\,l} = \frac{J}{L}$ into $\langle \frac{1}{2} m v^2\rangle = \frac{1}{2} k T$. After you get $T$ in terms of $L$, ...
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83 views

Is this Process Possible?

An inventor has devised a complicated non-flow process in which 1 mol of air is the working fluid. The net effects of the process are claimed to be: A change in state of air from 250$^{\circ}$C and ...
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1answer
53 views

Will the heat increases with the resistance?

I have studied that the nichrome, which has high resistance, is used in heat coils to increase the heat released. But according to this equation, $$H=\frac{V^2}{R} t,$$ heat is inversely proportional ...
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1answer
44 views

Are there materials with an adiabatic compressibility higher than that of common gases?

Are there materials with an adiabatic compressibility, measured at atmospheric pressure, higher than that of common gases? Is there any fundamental upper limit to the differential compressibility of ...
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20 views

Pressure components in a film

I am performing molecular-dynamics simulations of a polymer near a crystalline substrate (polymer film). I am comparing the mechanical properties in the film with the properties in the bulk polymer. ...
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90 views

Calculating The Change in Thermodynamic Potentials for Reversible Adiabatic Expansion of Real Gas

The question asks to find which quantities have a change of zero for the reversible adiabatic expansion of a real gas: Entropy, Enthalpy, Internal Energy, Helmholtz Energy, and Gibbs Energy. Change ...
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1answer
113 views

Is the physics of $j = \rho v$ questionable? What are the consequences? [closed]

In electrodynamics you have the quantity $\mathbf{j}$, which represents density of current per surface area. It is often said that $\mathbf{j} = \rho\mathbf{v}$, for geometric reasons. When I make ...
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30 views

Where did the energy of the universe come from? [duplicate]

Last week my Physics teacher asked the class this question: If the internal energy of the universe is constant, then where did all the energy come from originally?
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12 views

Calculating vapor quality in a two-phase region

I'm currently trying to find the vapour quality of a refrigerant in a two-phase region of cycle. I know $v_l$ and $v_g$, the specific volumes of the liquid and gas. I also know the temperature and ...
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72 views

Solution to a kinetic temperature problem

I have a particular equation that needs to be solved for the kinetic temperature of a stream of gas particles. If we let the kinetic temperature be designated by the letter x, the equation becomes, ...
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32 views

Callen's Second Postulate - Composite or Closed+Composite systems?

In section 1.9 of Callen's Thermodynamics he says: The single, all-encompassing problem of thermodynamics is the determination of the equilibrium state that eventually results after the removal of ...
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1answer
62 views

Boundary value problem

Consider the boundary value problem \begin{align} \frac{du}{dt}&= \frac{d^2u}{dx^2} , \\ u(0,t)&=0 \\ u(L,t)&=0 \\ u(x,0)&=f(x) \end{align} I know how to solve it using ...
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1answer
46 views

Entropy change at varying volumes

I have two questions both related to each other: 1.What is the effect of change in volume (whether increasing or decreasing), of a system, under isothermal conditions? How does this change in ...
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51 views

Robin boundary conditions for the heat equation

Consider a 3D channel with fluid or gas with walls $\Gamma_1$, inflow part $\Gamma_2$ and outflow part $\Gamma_3$. The temperature is described by the heat equation: $$ \frac{\partial T}{\partial t} ...
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28 views

Boltzmann Distribution [duplicate]

I am trying to solve a problem about boltzmann distribution. If(A)=0.74 Uf(V)=0.037 Ia(A)=0.130 I have to find ...
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2answers
120 views

Only differences in chemical potential have physical meaning?

Is the statement in the title true? Does the chemical potential of a single pure substance that does not undergo any chemical reactions or phase changes have any physical meaning?
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28 views

maximun work in a reversible process

I often read maximum work done is by a reversible process. Shouldnt the more appropriate sensence should be maximum work done per unit of heat is maximum in a reversible process. ?
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72 views

What is the overall rate of heat conduction through two pipes of different dimensions if the thermal conductivity is not constant?

I am trying to work out how I would find the rate of heat transfer through two pipes made of the same material that are joined at their ends but which have different cross-sectional areas and lengths. ...
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36 views

What does negative absolute temperature mean? [duplicate]

I always understood that the concept of absolute temperature stems from the third law of thermodynamics and that the lowest theoretical possible temperature is zero degrees Kelvin. However, ...
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45 views

Why can thermal shocks damage/break materials?

When an object is heated a lot and then brutally cooled down or vice-versa, it can crack or even break spectacularly. What happens inside that makes it do that? Is it only because the hot core swells ...
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27 views

final state when Saturated liquid-vapour mixture contained in a rigid tank is heated

I have this question: Determine the final state when a 2 kg of Saturated liquid-vapour mixture at 50 °C contained in a rigid tank is heated so that the it reaches a single phase for each of the case ...