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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69 views

Free energy a continuous function of temperature but may not be differentiable everywhere?

So according to my understanding, the free energy of the system should be a continuous function of temperature. This is because if the free energy is not continuous at temperature T, then at this ...
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93 views

Effusion of particles from one box to another - pressure calculation

Suppose we have a container divided into equal halves. Right half is fixed at temperature $T$, volume $\frac{V}{2}$. Initially it has pressure $P_0$, a hole of area $A$ is opened between them. I ...
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27 views

Thermodynamics of binary symmetric channels

I am reading this very interesting paper: http://m.iopscience.iop.org/1751-8121/41/40/402002/pdf/1751-8121_41_40_402002.pdf about thermodynamics of channels in information theory. More generally, ...
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291 views

Irreversible heat engines strictly less efficient than reversible ones

I undertand how Canot's theorem implies that irreversible heat engines must be no more efficient than reversible one's, but it isless clear why they need to be less efficient, as I have seen stated in ...
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139 views

Calculating heat capacity from the equation of state

It is known that within thermodynamics alone, given the equation of the state of a system, one cannot explicitly determine the heat capacity. What is the mathematical reason for this? Intuitively, it ...
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309 views

Thermal expansion of two bolts

I have this question asking me about the thermal expansions of two bolts, a steel one, and a brass one. I have the equation: $\ (\delta L/L)/T = \alpha $ I don't understand how I can use this ...
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40 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
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67 views

Given partial derivatives find the state function

I have to find the state function of a gas (which under very low pressures behaves as an ideal gas). So, first I tried writing it as part of an equation $ dV = \dfrac{\partial V}{\partial T}\ dT + ...
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39 views

Snowmaking in the tropics - an estimate of water evaporation

If I set up a snowmaker in the tropics and sprayed water with it how much water would I evaporate? How would I calculate?
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66 views

Radiation heat transfer

I'm looking at the radiosity equations for heat transfer http://en.wikipedia.org/wiki/Radiosity_(heat_transfer)#Radiosity_method Specifically, I'm hesitant to accept the equation: $$ \dot Q_i = ...
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82 views

Restrained expansion of a piston/cylinder

Suppose an ideal gas in a piston cylinder has some initial pressure $p_1$, volume $V_1$, and temperature $T_1$. A pin, which holds the piston in place, is suddenly removed, and the gas quickly ...
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336 views

VdW Gas Entropy/Enthalpy/Gibbs Free Energy of Mixing in 2 Chamber Experiment

What are the equations for $\Delta S_{mix}$, $\Delta G_{mix}$, and $\Delta H_{mix}$ for a real gas? Explanation: In one of the most well known experiments in thermodynamics, two chambers are ...
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74 views

Derivation of cylindrical line heat source problem?

I have a line heat source embedded inside a cylinder and I am trying to find the temperature distribution T(r,t). By using the similarity variable, the solution to the differential equation is ...
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48 views

Vacancy Generation / Annihilation Time (Relaxation Time)

Vacancy Generation/Annihilation Time, Recombination Time and Relaxation Time ($\tau$) are all synonymously used in atomic physics literatures. They're defined as the time that it takes for vacancies ...
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274 views

Partition Function of a three state particle system

I've just finished studying the partition function of a two-state particle system, where particles can have a 0 energy value or E energy value . That is: Where $t_j$ is a variable of value ...
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60 views

How the pressure of a system changes in terms of density?

I am modeling a closed natural circulation loop, filled with water. Some parts of the loop are heated, some are cooled and other are assumed adiabatic. As an effect of heating and cooling the density ...
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37 views

Maximum temperature of an elliptical thermodynamic process

Given a heat engine made from the curve $$V(t)=V_0 +A \cos(\omega t); \qquad P(t)=P_0-B \sin(\omega t).$$ What are the hottest and coldest points of this cycle, and what are the temperatures at those ...
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126 views

Can there be a phase transition without change in entropy and volume?

Context: I'm studying basic thermodynamics. My lecture notes pose a question, whether there can be a phase transition without a change in entropy or volume ? Do you have any hints on where to start ...
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95 views

Conduction– conservation of energy

So I know that conduction is transfer of thermal energy by direct contact via molecular collisions. For conduction, $Q/t$ is the rate of heat flow and is heat current ($I$). My textbook says that ...
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84 views

How to calculate the van der Waals force from the van der Walls equation?

Given the van der Waals equation $$\left(p+\frac{n^2a}{V^2}\right)\left(V-nb\right)=nRT$$ and the van der Waals constants $a$ and $b$, how can I find the van der Walls force between two atoms at ...
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326 views

Does coffee with cream cool slower than black coffee?

At Modernist Cuisine, Nathan Myhrvold states that "Coffee with cream cools about 20% slower than black coffee". He then gives three reasons, two of them related to radiation and the third one to the ...
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67 views

Transitions in a magnetic refrigeration

The graph below (see attached) shows the measured magnetization against temperature at room pressure for the material Gd and for another material for use in a magnetic refrigerator at room ...
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178 views

Average number of spin up particles

In a paramagnetic system, where $N = N_\uparrow + N_\downarrow$ is fixed, how does one calculate the average number of spin-up particles $\langle N_\uparrow \rangle$? You can assume we have the ...
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32 views

Cycle with unspecified irreversbile transformation. Find $P,V$ in the various states.

I've been thinking to this for the last two hours and haven't been able to come with a solution. Problem. A mole of gas initially at pressure $P_A = 2 \text { atm}$ and occupying a volume ...
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64 views

What is the origin of the kinetic theory of temperature?

Count Rumford's experiments with canon barrels are often cited here, but the kinetic theory certainly precedes them. Another candidate is Daniel Bernoulli, who, in his 1738 book Hydrodynamica showed ...
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237 views

Density distribution of gas in a centrifugal field

The problem asks me to find the density of gas in a cylinder of radius $R$ and length $l$ rotating about its axis with angular velocity $ω$, there being a total of $N$ molecules in the cylinder. What ...
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613 views

Calculate water use and design parameters for closed loop wet cooling tower

I am looking to estimate water use at a power plant with a closed loop wet cooling tower system. I have done some reading on cooling towers, but am struggling to connect the equations to a final ...
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283 views

Thermodynamic quantities of thin soap film on wire frame

Here is a question I am trying to solve. Sorry for the highlighting, it is not relevant. Here are my answers. For a), I would write $dE = dQ + dW$, following the first principle of thermodynamics. ...
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1k views

Definitions in thermodynamics: temperature, thermal equilibrium, heat

I'm currently reading Fermi's "Thermodynamics" and I'm trying to grasp the (possibly different) right definitions for temperature, thermal equilibrium, heat. To clarify, I'm looking for definitions ...
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449 views

Making an equal amount of positive and negative energy?

I was wondering if it would be possible to create an amount of positive energy out of a vacuum, in addition to an equal amount of negative energy, thus not violating the first law of thermodynamics, ...
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77 views

Where does the relation $u=h_f-RT+(c_p-R)(T-T_0)$ come from?

I'm working on a college project for a subject called Motorcycle Engineering, and in this project I'm supposed to do some reverse engineering on a MATLAB program to model the engine of the motorcycle. ...
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99 views

Compressibility and specific heat: interconnectedness and independence?

Consider a Mott insulator (insulator arising from strong correlations). This is an incompressible phase i.e. it costs energy to add a single particle to it; the ease of compression (compressibility) ...
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94 views

Biological Themodynamics - What does an endpoint saturated signal mean. How does it relate to equillibrium constant

I have had a question that has been bugging me for a couple of years in my graduate school career, and I was wondering if perhaps some physicist could help explain it to me. Given an endpoint assay ...
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64 views

Can I run a pulse tube cooler in reverse to generate pressure oscillations?

Since a pulse tube cooler is basically a Stirling engine without moving parts running "in reverse", does that imply that when I keep the cold end at ambient temperature and apply heat to the hot end, ...
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59 views

commutators in an uncertainty relationship derived from a partition function?

The maximum information principle for the discrete case gives rise to a partition function (>>> see details here) $$Z(\lambda_1,\ldots, \lambda_m) = \sum_{i=1}^n \exp\left[\lambda_1 f_1(x_i) + \cdots ...
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119 views

Traditional Transfer Matrix on the Potts model — how it grows for strip lattices?

What is the transfer matrix size for a strip lattice of width $n$ vertices, with arbitrary $q$?? I am not sure if it is $q^n$ x $q^n$ or something else. Any reference is also welcome.
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132 views

Please correct my understanding of Clausius-Clapeyron and latent heat

As I work a problem set, I'm being asked to calculate the latent heat associated with a particular phase transition of $NH_3$ (solid -> liquid, liquid -> gas, solid -> gas). I'm being told to perform ...
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304 views

ideal gas law modelization in a vacuum chamber

I am trying to model a pressure sensor in COMSOL. The basic work is that there is current flowing inside it, if the pressure of the gas around it drops down, the temperature goes down as well (ideal ...
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89 views

Calculate heat loss of aquifer with unknown shape

I am trying to calculate the heat loss of an aquifer. An aquifer is basically a hot-cold storage $80\: \mathrm{meters}$ under the ground. It is an open system and utilizes groundwater. By pumping for ...
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423 views

Explain to me how this water cooler works?

Goodday all, I was recently reading up on a few projects that might be of interest to me when I found "CPU Bong water coolers", there isn't much online on them so I figure I would ask y'all. If you ...
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729 views

what's the difference between linear n-atom molecule and nonlinear n-atom molecule?

I am reading a material about the degree of freedom for linear n-atom molecule and nonlinear n-atom molecule. Here is my analysis for a diatomic molecule, if there are two atoms, we have to use 3 ...
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39 views

Henry's Law in metals

For fixed temperature the concentration of a gas dissolved in a solution is directly proportional to the gas pressure $p$, i.e. $c_s (T,p) = f(T)p$. Since $H_2$ only dissolves in metals as single ...
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144 views

What temperatures can be reached in an air-to-air thermocompressor nozzle and why?

People are generally of the opinion that the boiler injector cannot be redesigned to run on air. In other words, an air-to-air thermocompressor that puts fresh air into a tank without a mechanical ...
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2k views

Joule-Thomson effect of Van der Waals gas

I'm supposed to calculate the inversion pressure $p_i$ of a Van der Waals gas. The state equation of the Van der Waals gas is: $$(p + \frac{a}{V^2})(V-b) = RT.$$ To get a hold of the inversion ...
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476 views

Rotational Constant and Moment of Inertia of Fluorine gas

I have come across some homework question on thermodynamics which needs me to calculate $B$ of $F_2$ My attempt: $B= \frac{h}{8\pi^2cI}$ where $I=\mu r^2=\frac{m_1m_2}{m_1+m_2} r^2$ Atomic mass of ...
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143 views

How to solve state parameters using these givens for an ideal gas?

In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
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193 views

How much money does an unused but plugged-in cellphone-charger waste in a year, if its not getting warm?

Is it right as xkcd states: You can use heat flow to come up with simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day. Or, more ...
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53 views

Height of a piston in a heated cylinder containing H2O

I'm a first time user and I hope I won't be too enigmatic asking the following question: I have a cylinder (radius= $6$ $\text{cm}$) with a frictionless piston on top of it and inside $30$ $g$ of ...
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102 views

Several questions about spring chiller and LMTD

I'm designing a simple copper coil wort chiller. Digging formulas I'm having hard time to figure some things out, perhaps some simple guides may help me to go the right direction: LMTD need inlet ...
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50 views

Free Energy and quantum measurement

Free Energy must be expended to reset the state of an measurement apparatus. Is this statement valid in all situations? Is there a Definitive mathematical exposition?