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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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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78 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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286 views

Radiative cooling time for a black body

Okay, so this is confusing me a bit. How can I calculate the time it takes to cool a perfect black body from an initial temperature $T$ down to equilibrium temperature (say, 3 K for space)? I know ...
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307 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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64 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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175 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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62 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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225 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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532 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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275 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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428 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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76 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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89 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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87 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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60 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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58 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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115 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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279 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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88 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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383 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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665 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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134 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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451 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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135 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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185 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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94 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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48 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?
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137 views

“This is not a perpetual motion machine, because reservoir temperatures are changing.” Is it a valid argument?

I've already faced this situation several times: given a statement (in area of thermodynamics) I used it to provide an example of some perpetual motion machine (of first or second kind). Therefore, I ...
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60 views

Temperature measurement, precision

I am having problems with one of the problems I have done (a) which is basically $\theta = 273.16K (19/15) = 346.00K$ For (b) I am given that the length is 15.00cm when the thermometer is incontact ...
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47 views

What is the fluid approximation for BCS action?

For a system with free fermion gas at finite density (i.e. free Dirac action), we have an ideal fluid description with rho, p, n. What is the fluid description for BCS action? Suppose we have a box ...
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450 views

Is the $mL_c$ value for triangular and rectangular fins the same value?

I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong. ...
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475 views

How equivalent are heat energy and work energy in connection with a spinning flywheel?

Let's say we have two identical spinning flywheels, that have arbitrary geometry, and are made of copper. Now we apply some heat energy at the center point of flywheel A, causing it to slow down a ...
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64 views

How many times brighter could the stars shine without raising the temperature of space?

If my understanding is correct, the temperature of space (as defined by the temperature that a black-body will reach) has been decreasing since the big bang. It has never increased. Additionally, ...
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742 views

Do the properties of two streams flowing into an engine add together when they mix?

Let's say I have two stream supplys that have separate mass flow rates, enthalpies, and velocities that flow into an engine. Upstream of the engine's inlet, the two streams mix to form one stream that ...
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98 views

How to compute the heat flow for a specific material for some given boundary temperature?

Assume I have a bounded material with heat sources inside. The material is known (i.e. I know heat capacity and all relevant data) and the temperature of the boundary is fixed. I solved the (steady ...
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11 views

Is it impossible to find the exact analytic form of the molar volume of liquid and gas in phase transition from the van der Waal equations?

I want to find the molar volume $v_g , v_l$ of gas and liquid respectively in the coexistence curve of phase diagram with given temperature when ideal van der Waal gas $$ P = ...
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28 views

What do physicists mean with “classical critical behaviour”?

What do physicists mean with "classical critical behaviour"? As far as I am concerned it should be "power law behaviour" of some quantity close to the critical point but I ask here to be sure.
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12 views

Specific heat capacity for constant volume and constant pressure

I have seen in some exercises that the specific heat capacity for constant volume, $c_{vo}$ and the specific heat capacity for constant pressure, $c_{po}$ , where the $o$ indicates that we are ...
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9 views

What is the heated added and changes in internal energy? thermodynamics

A piston + cylinder initially contains 2 x 10-3 m3 of helium gas at the pressure of 1.01 x 105 Pa and with a temperature of 60'C. The gas is heated allowed to expand at a constant pressure until its ...
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13 views

Chemical potentials of SM particles at high temperatures

Recently I've heard the statement that chemical potentials of SM particles on $T > 1 \text{ GeV}$ are very small, so that Gibbs potential reduces to free energy. How to prove this statement? Does ...
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18 views

Superficial velocity as a function of position along flow path

I am wanting to estimate the superficial velocity of a fluid as a function of position. The system I'm trying to evaluate is as shown below: A cylinder of porous media with the source acting on ...
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20 views

Internal energy of a molecule and bonding strength

I had a lecture on thermodynamics. I was told that the bond strength, $\epsilon$, is related to the latent heat of sublimation, $L_s$. $L_s\approx L_f+L_v$ if the melting and boiling points are close, ...
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37 views

Entropy of a system of gravitationally interacting particles

Lets suppose there is a container in space where there are some particles moving very fast. But due to gravitational attractions between the particles they would just come to a corner of the box. ...
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14 views

Why is the boundary layer thinner on the outside of an outer wall versus the wall inside the house

The convection on the outer suface of the outer wall of a house is larger, because outside a house it's more windy compared to inside. More wind means more turbulence which leads to more transfer of ...
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36 views

Why is there steam in a hot shower even though the water is not boiling?

When I take a hot shower, there is normally a fair amount of steam. However, I don't think the water coming out of the shower-head is actually boiling (unless I am mistaken). Why is there water ...