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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114 views

Doesn't this LED created by MIT violate the second law of thermodynamics?

Here is the article I am referring to: http://www.wired.co.uk/news/archive/2012-03/09/230-percent-efficient-leds In their own words (or at least the article writer's), "it appears to draw in heat ...
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72 views

Mathematical definition of reversible processes

If I label an initial thermodynamic state as $\psi$ and the final thermodynamic state as $\xi$ then can I say that under a reversible process the two states are related to each other by a continuous ...
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27 views

Energy contribution due to matter transfer

I have a very important question that lingers in my mind for a long time: In the fundamental relations of Gibbsian Thermodynamics, I simply don't understand how the last term appears. I have ...
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70 views

Good thermodynamics/statistical mechanics books that treat the apparent paradoxes in the theory

I am working on a small project mainly concerning the Gibbs and mixing paradoxes arising in thermodynamics/statistical mechanics. Still cannot find good literature on the topic. Any suggestions (I ...
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44 views

Why dynamic equilibrium exists?

We know that at equilibrium Gibbs energy is minimum. We also know that at equilibrium both forward and reverse reactions occur simultaneously, and also we know that for a reaction to be spontaneous ...
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42 views

Derivation of a equation in closed, phases coexisting system

I'm trying to show that for a closed system consisting of two phases coexisting in equilibrium at a temperature $T$ and under a pressure $P$. $$(\frac{\partial P}{\partial ...
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64 views

Reverse-engineering an equation of state

Suppose we have a fluid of some kind with a (let's keep it simple) barotropic equation of state: $p = p(\rho)$. Typically, I see that one starts with a function $p$ and $\textit{then}$ solves the ...
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35 views

How to derive an expression for entropy generation in a diffusive, reacting continuum

I'm trying to understand a derivation from "The Thermodynamics of Linear Fluids and Fluid Mixtures," by Miloslav Pekař and Ivan Samohýl (2014). The derivation produces an expression for the entropy ...
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24 views

How can one induce rapid temperature changes in a controlled environment?

What kind of processes are there using which it is possible to change the temperature of a material as fast as possible. You are allowed to use any material you want. Constraints - It should ...
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43 views

Gauss-Bonnet correction to Carnot's efficiency

Could any one tell explicitly, how did the author get $Tc$ Vs $\alpha$ Plot given in Figure 3 in Gauss-Bonnet Black Holes and Holographic Heat Engines Beyond Large N
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56 views

In an equilibrium of two systems, why is not true that $\frac{\delta S_{1}}{\delta N_{1}} = \frac{\delta S_{2}}{\delta N_{2}}$?

Why is not true that $\frac{\delta S_{1}}{\delta N_{1}} = \frac{\delta S_{2}}{\delta N_{2}}$ across two systems that exchange particles? It is true, instead, that $\frac{\delta F_{1}}{\delta N_{1}} = ...
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44 views

Substantial uneasiness as to the Joule free expansion (unresolved in spite of many readings)

Ok so, to do things well, let me present the set-up: we have an insulated container that is partitioned into two equal halves, one of which contains an ideal gas with parameters P1, V1 and T1, the ...
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11 views

What happens to carbon deposits in car engines when heated?

I am trying to determine the characteristics of carbon deposits in a gasoline automobile engine. Will the carbon deposits in and around the cylinders of an automobile engine soften, harden, or ...
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45 views

Is there any relation between the entropy of a system and the kinetic energy of molecules in the system?

The kinetic energy of the molecules in the system increases when we provide heat to the system,thereby increasing its temperature under certain conditions. Similarly providing heat to a liquid ...
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58 views

First law of thermodynamics with additional term

I read in a paper that a "known expression for the heat received by a body" is $$dQ=dU+pdV-\mathbf{v}\cdot d\mathbf{P}$$ where $\mathbf{P}$ is the linear momentum of the body, $p$ is the pressure, ...
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81 views

entropy and dispersion

If I know the positions and the speeds of each particle in a box over the time, how can I compute the entropy ? (I`m making a simulation where I want to show that the disperion of the particles over ...
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28 views

In a heat pump, why is $Q_{h} - Q_{c} = W_{on}$?

I need help patching up the current holes in my understanding of a heat pump's process. I've explained my understanding and questions that accompany it. The standard explanation as to why $Q_{h} - ...
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36 views

Heat Capacities ratio equal to 1

In which situations can be found the ratio between $C_{P}$ and $C_{V}$ to be equal to the unity? I have read in other places that it happens for liquids and solids because they can be assumed to be ...
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65 views

Is Gibbs free energy really a true energy that can be used to do work?

Gibbs energy came from the relation $$\Delta S_\text{universe}= \Delta S_\text{surroundings}+\Delta S_\text{system}\ge 0.$$ By little algebra, we can arrive at $$\Delta S_\text{universe}= ...
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64 views

Why doesn't entropy get decreased in adiabatic expansion process?

I was reading the second step of Carnot cycle in which the system undergoes adiabatic expansion doing work & thus decreasing the internal energy of itself. The entropy didn't change as no further ...
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99 views

Why does hot water and cold water makes different sounds while filling a bucket from a tap

When I fill hot water in a bucket while bathing, there is a difference in the noise it makes compared to cold water. Is there any Relation between temperature of water and sound it makes during ...
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51 views

Dependence of the magneto-rotational instability (MRI) on thermal relaxation?

The MRI is the most efficient driver of turbulence in accretion discs (as measured by the effective scalar stress). The magnetic field, being properly coupled to the gas (weak coupling), connects the ...
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39 views

Best introduction to the link between information and thermodynamics

I have a solid understanding of classical thermodynamics, as well as a reasonable understanding of statistical mechanics and some of the philosophical issues regarding entropy. However, I've never ...
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44 views

Analog to the Gay-Lussac free expansion experiment for a gas of photons?

Can the experiment of Gay-Lussac and Joule on the free expansion of (ideal) gas be repeated for 'light' (gas of photons)?
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24 views

LED characteristics to use in heating a material sample?

I am looking to be able to heat a sample of material, typically less than 500mg and sitting in a fused silica sample holder about 10mm diameter. Wondering about using (say) a 5W LED with narrow ...
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78 views

Deriving the adiabatic relation for an ideal gas from a differential geometry point of view

Recall $Q = dU + W$ (First Thermodynamic law, energy conservation). If $Q=0$ (for adiabatic process, either adiabatic expansion or contraction), and supposing $W = pdV$, then $0 = dU + pdV$. Either ...
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46 views

WIll aluminium foil get hot in microoven if I wrap it with paper?

A aluminium foil doesn't get hot easily because of it's heat conductivity. Will it get hot in microwave oven if I wrap it with paper?
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42 views

Average distance between molecules

What is the average distance betweeen the gas molecules in a classroom? I want to use that $$l= \frac{kT}{p \pi d^2 \sqrt{2}} $$ where $k$ is Boltzmann's constant and d the diameter of the molecule. ...
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30 views

Problem in deriving the inner energy of a photon gas

We know that photons, as bosonic particles, obey Bose-Einstein statistics with $$ \langle n_{\mathbf{k} \sigma} \rangle = \frac{1}{\exp(\hbar \omega_k/k_B T) - 1} $$ the average number of photons in a ...
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33 views

Adiabatic Surfaces in thermodynamics

In some lecture notes on thermodynamics there is a discussion as to whether by assuming the first law of thermodynamics alone we can prove the existence of a adiabatic surface in three dimensions. To ...
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38 views

What is the relation between scattering amplitudes, fluctuations, response functions and correlations in macroscopic equilibrium systems?

In Kardar's book Statistical Physics of Fields, he mentions that that correlations at different length scales can be measured by scattering. If its electric correlations, you would scatter light and ...
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56 views

Is there a local canonical ensemble partition function for a Bose-Einstein gas?

The grand canonical partition function for a Bose-Einstein gas is $$ Z_{\text{grand bos}} = \exp \left( \sum_{j=0}^{\infty} -\ln \left( 1-e^{\beta(\mu-\epsilon_j)} \right)g_j \right) $$ where $\beta$ ...
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56 views

Calculating stable orbital resonance and other factors into orbits

Firstly here is a brief summary of what I trying to accomplish. From a predetermined total solar system mass , star count in that system, per-star classification and mass I am building a system of ...
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73 views

Is thermal and electrical conductivity correlated for all phases of matter?

After reading this interesting post about why copper is a great heat conductor, I wondered if a plasma would conduct heat better than a gas. Or, are some properties like density more important for ...
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86 views

When can we assume a body to behave like a black body?

In an experiment I estimated the temperature of a Tungsten bulb filament measuring the resistance of it, and tried to verify whether the power of the filament is proportional to the fourth power of ...
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51 views

Expression of heat by the Brownian motion

folks. I was reading a paper from PRE and I'm not sure what's going on about the following equation. So for the system composed of two heat baths governed by Brownian motion, the entropy change of the ...
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36 views

Making Pudding; A complicated non-equilibrium statistical process?

There are a lot of non-equilibrium processes examples given in physics literature. But some processes that are present in everyday life are not treated. As an example, the formation of pudding can be ...
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64 views

Thermodynamics with explicit math

Nathaniel adeptly answers a question on thermodynamics by making the variable dependencies explicit: Determine the Dependence of S (Entropy) on V and T Is there a thermodynamics text that is written ...
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107 views

How does fluid velocity affect the dissolution of some solute in the fluid?

Suppose we have a perfect sphere of some solute such as sugar and we place it in a fluid such as water, at a certain temperature, that is not moving. It will dissolve and diffuse into the water due to ...
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69 views

Why can't the energy gained due to entropy be used for doing work?

Gibbs energy is defined as the energy 'available' to do work at constant temperature & pressure.The energy required to make the system from none under constant pressure is the enthalpy, that must ...
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34 views

Dependence of latent heat on pressure

It is known that the latent heat of vaporization increases as external pressure decreases. What is the cause of this phenomenon?
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70 views

Measuring variation of saturated vapour pressure with temperature

Is it possible to measure variation of saturated vapour pressure of water with time.I just hesitate about it.My suggested procedure which is incomplete is given below Procedure that I would like to ...
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33 views

Internal heating effects of a circuit element?

The heat-up of a solid circuit component in an electric circuit (for which no chemical reactions, phase changes reactions or other stuctural changes take place) may include: Joule heating $\dot ...
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33 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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19 views

Increased pressure of Liquid Pitch and Limestone (Bitumen/Asphalt) @ approximately 300 degrees Fahrenheit

If liquid pitch and limestone (20/80 mostly limestone) is pumped (appx. 5 gpm) out of a nozzle that restricts the flow compared to the flow that would be achieved straight out of the pump ( no ...
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44 views

Specific heat at constant volume

Me and my friend came across this derivation is some lecture notes of our thermal physics module. We have been trying to calculate the partial differential of the internal energy but cannot get the ...
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41 views

Thermal Equilibrium of two thin sheets

While reading Gibbs' Elementary Principles in Statistical Mechanics I came across this footnote: The most simple test of the equality of temperature of two bodies is that they remain in ...
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140 views

Temperature change in adiabatic free expansion

Consider a gas with fixed number of particles $N$ undergoing adiabatic free expansion from $V_1$ to $V_2$. Apparently we have the following relation $$\Delta ...
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13 views

Vertical wall at 3 different temperatures - do the same natural convection coefficient correlations apply?

I have an vertical enclosure that consists of 3 shelves, each with its own temperature and are thermally isolated from each other. We will call the shelves A, B, and C with A being the base shelf. The ...
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42 views

Heat transfer coefficients

I am trying to make a model of non-stationary heating on a plate and I have questions considering coefficients. I am using explicit method to solve it (have to use it). I am not sure if I am using the ...