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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An interesting question on the mass of a droplet of liquid experiencing the Leidenfrost Effect

Background and Inspiration: I have seen numerous demonstrations of the leidenfrost effect, both on the internet and in my mother's kitchen. But I started wondering about a general case after having a ...
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26 views

Is using molar terms with maxwells relations misguided?

My professor wants me to do a lot of derivations using maxwells relations. One of the things he wants me to prove is that from the Van der Waals equation of state one can say: $\Big(\frac{\partial ...
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15 views

Kettle barbecue thermodynamics question

I have an old kettle barbecue which lost its legs to rust. I then placed the dome on top of a truck's brake drum and throttled the airflow by mounting the brake drum on a plate with holes drilled in ...
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27 views

Melting icicles

If I break off the bottom half of an icicle, will the top half melt faster?     ...
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21 views

Equation of State of PVT system

Find the Equation of State of a fluid with Volume expansivity $\alpha_P$ and an isothermal compresibility $\kappa_T$ are given by $$\alpha_P=\alpha_0 \Big(1-\frac{P}{P_0}\Big) \\ \: \: \: \: ...
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26 views

Isothermal Expansion in Real Gases

I understand that for a ideal gas in the case of reversible isothermal expansion, $\Delta U=0$ and $-Q=W$ but in case of a real or van der Waal gases, how can I find $Q$, $\Delta U$ and $\Delta S$?
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45 views

Can energy be extracted indefinitely from a mass dipole/mass negative mass pair in perpetual motion?

Some days ago I have read this short piece of article by Hammond which caused me to revisit the theoretical properties of negative mass. It is known that a pair consists of ordinary mass and negative ...
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47 views

Calculating the heat transfer into CO$_2$ gas at a constant pressure

I am having trouble with a homework question and I am just not sure how to attack it. We have not covered how to deal with non-ideal gases yet, and we are expected to answer this question without that ...
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28 views

reflecting foil on window

Assumptions: A house window acts as a cavity resonator, and so can be treated as a blackbody. If the room temperature is 20 C then the outgoing radiation is 418 W/m2 If the outside temperature is ...
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32 views

What are the Fermi and Debye temperature constants?

What are the Fermi temperature and Debye temperature constants? We were discussing these in class and I don't fully understand what these constants are or why we have them. Can anyone explain?
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47 views

Ising Model with All Spins Interacting with All Other Spins

I am studying the Ising model with all spins interacting with all other spins and have formulated $Z$. I am trying to understand what it means to study at large N but not infinite N. I know that at ...
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16 views

How numbers of being stretched effects on the internal pressure of a balloon

When you blow a balloon, the shell would become thinner. By according to mulins effect, when a rubber material is stretched, its stress-strain diagram changes and of course also its internal pressure. ...
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Temperatures reached in arc flashes

Good morning, I have a question regarding the arc flashes. Some papers mention that temperatures of nearly 20000 K can be reached during an arc flash. Could anyone explain how to come up with those ...
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14 views

Trying to determine transient response of air conditioned room

I have an air conditioned room which intakes airflow at temperature $T_{in}$ at a mass flow rate $\dot m$. The air leaks out of the room at mass flow rate $\dot m$ and temperature $T_{room}$. The room ...
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74 views

Partial derivative of Helmholtz free energy from entropy and internal energy

I want to know how to derive pressure $p$ from a partial differential of Helmholtz free energy $F$. I want to start from $F(T, V, N) = U(S(T,V,N),V, N) - TS(T, V, N)$, where $U$ and $V$ are ...
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42 views

How can energy be partitioned equally when energy is relative?

According to the Equipartition theorem in a system at equilibrium the energy should be on average be divided equally between the available degrees of freedom. The most common examples are the three ...
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41 views

Constant volume gas thermometer

Well, in the notes I took in thermodynamics' class I have a graph that plots Pressure of boiling point $P_b$ over Pressure of freezing point $P_f$ at constant volume in terms of Pressure of boiling ...
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37 views

Calculating saturation mixing ratio for water in air

If I have air pressure (in, say, Pa) and air temperature (in, say, K) - how do I calculate the saturation mixing ratio for water? I can't seem to find it anywhere and it's a fairly useful quantity to ...
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39 views

General boundary condition for 1D heat equation

I'm studying from Numerical Solution of Partial Differential Equations by K.W.Morton and D.F.Mayers (Amazon link). I'm confused with general boundary conditions. Could someone give me a clue? For ...
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28 views

heat transfer between objects

when we touch a very hot object, the edges of our skin interact with the object's high energy and velocity particles and molecules. why is it physically that we get "burned" by extremely cold objects ...
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24 views

Chemical potential and origin of pressure in a solid

Pressure of a gas is related to the rate of change of momentum of the particles; the temperature is the mean kinetic energy of the particles. Can the chemical potential be given a similar physical ...
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38 views

Partition function for a two state system

We have a system of two energy states and we treat classical distinguishable and indistinguishable particles respectively. For the distinguishable case I thought that all in the left one one left ...
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18 views

When does exergy destruction occur?

I am doing a project on developing a code for the first and second law analysis of the Brayton Simple and Modified cycles. The first law part is simple. But I have run into a roadblock when I started ...
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14 views

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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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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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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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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35 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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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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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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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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40 views

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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30 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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50 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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33 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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15 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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49 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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40 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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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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17 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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39 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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54 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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81 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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35 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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40 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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108 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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26 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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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 ...