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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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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23 views

At what point does a cigarette stop burning [closed]

Temperatures of [cigarettes] reach 900°C during a puff and fall to about 400°C between puffs (Guerin 1987). Puffing burns the tobacco on the periphery of the cigarette, and tobacco in the core ...
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65 views

Dissipative forces and reversible processes

A book that I have contains the following lines: For a process to be reversible, the dissipative forces such as viscosity and friction should be absent. My question is why?
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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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62 views

Is it possible to trap hot air at 50 degrees for an year or more [closed]

I have this question that has been running in my mind for days now. Lets say i have some air which i have heated to 50 degrees Celsius. Is there a storage mechanism i can lock this air in and store it ...
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35 views

Highest temperature [duplicate]

The temperature of a body varies with the KE of its particles. The maximum KE can be obtained by making the atoms move about near the speed of light. Let us take the body as a gas so that the body can ...
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2answers
23 views

Finding molar specific heat

For a particular thermodynamic process defined as $P=f(V)$ or $T=g(V)$, where $f$ and $g$ are functions with constants with appropriate units. How to find the molar specific heat of the gas? Given ...
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51 views

As the World Turns [closed]

Does the Earth's axis change with the magnetic reversal as it is taking place?
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36 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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35 views

Gas chamber problem [closed]

Consider a rectangular isolated(non-conducting) chamber as shown below. The chamber is divided into three compartments. The wall separating A and B has negligible mass, no friction and is conducting, ...
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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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22 views

Relation between radius of curvature and heat produced at focus when concave mirror is kept in sunlight [duplicate]

Hi I am newbie here and this is my first question so please do not mind if I don't use the correct language or anything. I want to know the relation between size of a concave mirror ( measured by ...
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1answer
48 views

What is the coefficient of volumetric expansion of water? [closed]

What exactly is coefficient volumetric expansion? Is it $\gamma\,\Delta T$? Since water has maximum density at 4 C, is $\gamma=4\,{\rm C}^\circ$?
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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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1answer
41 views

Heating water- Is it better to heat all of the water at once?

I am curious if it is more efficient to warm a half cup of water and then add an equal amount of room temperature water or warm a full cup together...assuming the water never boils.
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27 views

When you touch a part of a pan that is on a stove [closed]

When you touch a part of a pan that is on a stove
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1answer
49 views

Finding total thermal conductivity (Ksys) for n-number of connected materials

I was playing around with the idea of finding a "total" K value for 2 solid, flush touching pieces of metal. The original problem involved the two touching inline bars with a two different maintained ...
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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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45 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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1answer
31 views

Joule-Kelvin coefficent what does $p$ and $T$ represent?

In the Joule-Kelvin expansion we take a gas at one pressure $p_1$ and throttle it through a valve to another pressure $p_2$ where these two pressures are taken to be constant. The Joule-Kelvin ...
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1answer
60 views

Calculating change in gas volume over time given a constant number of molecules and a changed weight

I was watching a video, and a question came to my mind. Suppose I have a cylindrical piston. I have a rock that rests on a roof, which keeps the gas underneath at a constant pressure & volume. ...
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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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3answers
138 views

General Definition of Steady State

According to many sources (including Wikipedia, Stephani&Kluge, D.J. Acheson) a steady state ist: In systems theory, a system in a steady state has numerous properties that are unchanging in ...
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1answer
82 views

Calculation of Entropy of Debye Solid at High T

I am calculating the kmolar entropy of a Debye solid at low temperature ($T << \theta_D$) and high temperature ($T >> \theta_D$). For the low temperature, I use $U = U_0 + \frac{9 k_B ...
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17 views

Cooldown of a 1 meter wide sphere of water at 10C° in space [closed]

I am wondering how long would it take for such a sphere of water to totally be under 0C°. Let's suppose that the surface tension is enough to keep the topology of the sphere intact an that it will ...
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52 views

The effect of 8 hours 20 degrees C sunshine on the temperature of a stationary car's engine block? [closed]

What temperature of the engine block could be achieved by parking a car (Mazda 3) in full sunlight and facing south all day. Average day temperature 20 degrees Celsius no wind. And then how long to ...
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45 views

Thermodynamics: Deriving inner energy from ideal gas equation of state [closed]

If we know equation of state for ideal gas $ PV = NkT$ where $P$ stands for pressure, $V$ for volume, $N$ for number of particles, $k$ is Boltzmann constant and $T$ is temperature, how can one ...
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49 views

Maxwell Relations - Isentropic Compressibility to Isothermal Compressibility [closed]

I am trying to derive an expression for the isentropic compressibility in terms of thermal expansion coefficient $\alpha_P$, the isothermal compressibility $\kappa _T$ and the constant pressure heat ...
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34 views

Thermodynamic modeling, how is it done? [closed]

How does one in practise experimentally model a system and use the thermodynamic potentials and the laws of thermodynamics? My thoughts so far: Maybe the aim is to arrive at an equation of state. ...
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82 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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125 views

Le Sage's Theory of Gravitation, is “drag” the only reason why this theory fails? [closed]

Le Sage's Theory of Gravitation was originally proposed allready 1690 by Nicolas Fatio, and has ever since been studied by remarkable scientists; Leonhard Eluer once remarked that it was "infinitely ...
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33 views

Turning Heat into Work [closed]

Q) I was told to create a machine which could turn heat into work. The lower its cost, the better it would be(Max around 10 bucks). The higher its efficiency, th.e better it would also be.My attemp is ...
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1answer
55 views

How does air travel after leaving air nozzle?

I am working on a project which involves air nozzles. I am interested in estimating the time it takes for air particles after they leave the nozzle to reach a particular distance away. I have the ...
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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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66 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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101 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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1answer
334 views

Ways to increase efficiency of carnot refrigerator and a four stroke engine? [closed]

What are ways to increase the efficiency of a Carnot refrigerator. I remember something about decreasing the temperature but also about something about the flow rate, and fins? Also, for four stroke ...
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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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1answer
73 views

What is the difference between the Method of Characteristics being formulated in terms of theta & alpha and theta & nu?

So I'm doing an MSc thesis involving the method of characteristics in rocket nozzles. My lecture notes have the MoC formulated such that the positive characteristics are defined as: C+ = Tan ( ...
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2answers
71 views

Flow from higher potential region to lower potential region

In Thermodynamics, it is said that heat transfer takes place from higher temperature to lower temperature. Things having higher temperature have higher potential energy because of more vibratory ...
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2answers
87 views

Does going downhill create cold air in the exhaust of a car?

Consider a car going down a large mountain. Instead of braking continuously, the driver shifts down and the car is able to maintain velocity on just engine braking. No fuel is injected into the ...
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1answer
83 views

Modeling transient heat transfer between two 1-D materials

So I have been working on creating a 1-D model of a material with a layer of heat resistant material stuck to it. For this I have been trying to use the implicit finite-differential method. 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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18 views

Coupled Diff Equation from Bose Einstein distribution [closed]

I am a student doing physics hons and have had very little experience in programming. This semester we are supposed to do a computational project in thermodynamics. I have to solve these two coupled ...