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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108 views

What controls the heating ability of steamers?

Pictured below is a standalone steamer used for foaming and heating milk for milk-based coffee drinks like cappuccinos and lattes. They can be filled with water up to the pressure relief incorporated ...
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170 views

Dynamic structure factor

Dynamic structure factor is the spatial and temporal Fourier transform of Van Hoves time dependent pair correlation function. It is written as $$ S(k,\omega)= \frac{1}{2\pi}\int F(k,t)\exp(i\omega ...
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5k views

Calculation of number density from material density

Material density is given by $ \rho =m/V$, where $m$ is mass and $V$ is volume. Again number density given by $n=N/V$, where $N$ is the total number of particle. How can I calculate number density $n$ ...
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365 views

relation between first law of thermodynamics and statistical mechanics definition of entropy

From the definition of entropy as $S= - Tr (\rho\, ln \rho)$ one obtains that $S = \frac{\langle E \rangle}{T} + \log Z.$ The first law of thermodynamics has $dS = {dE \over T}$. Why is there no ...
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108 views

Thermodynamics of a bar, specific heat

I have a problem and I don't understand how the book solves it. It says I have a bar such that $$F=aT^2(L-L_0)$$ where $F$ is the force or tension of the bar, $T$ is the temperature, and $L$ the ...
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2k views

Constant pressure and temperature mixing of 2 different ideal gases - possible work and heat?

A simple question I hope... Initially, have two separate containers of 2 different ideal gases, 1.) N1, P, T, V1 and 2.) N2, P, T, V2. After mixing, the pressure and temperature are still P and T, ...
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329 views

Order of phase transition: Which free energy to use?

I am unclear about the adjective "first" or "second" used in phase transitions. Take the liquid-gas transition for example. If we vary the volume of the system at constant T, at some point we will ...
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233 views

Calculating the $\frac{dp}{dT}$ slope using Clausis-Clapeyron

I've produced experimental data over how the boiling point of water varies with pressure and temperature and plotted this in a PT graph. I would like to verify my results using theory. The ...
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126 views

Parameter determining argon phase

Currently I am working a molecular simulation to determine phases of an argon NPT ensemble using Lennard Jones potential. Mainly I use the radial distribution function to determine solid, liquid, or ...
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372 views

How much energy Maxwell's demon will earn?

Suppose we have one mole of one-atom ideal gas at temperature $T$. Suppose Maxwell's daemon has separated molecules into two sections, one with speed below mean and another with speed above mean. ...
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98 views

Problem evaluating moles in a an isochor transformation

I have a problem with an isochor transformation. Me and my group of study made an experiment that want to check Gay-Lussac’s law. We registered the equilibrium states and fitted the $P = nRT / V$, ...
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205 views

Thermodynamic process when nebula is heated

The basic thermodynamics problem is stated as follows. The nebula contains a very tenuous gas of a given number density (atoms per volume) that is being heated to a given temperature. What is the ...
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217 views

Can I estimate the long-term surface heat transfer coefficient based on a temperature difference between the air surface and ground surface?

I want to estimate the long-term or annual heat transfer coefficient for the earth's surface in a particular area where the mean annual air surface temperature is about 13$^\circ$C, and the mean ...
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1k views

What arrangement of sound waves would be needed to heat air in a typical sized room?

From what I understand, sound is simply the jostling of the molecules that make up the air in a specific pattern, widely known as waves. I also know that these are longitudinal waves. If we were to ...
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223 views

Calibrating an electronic temperature sensor based on power consumption

I'm working with an electronic temperature logger that is being affected by heat generated internally. How does one come up with a calibration equation to calculate a more accurate reading of ambient ...
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703 views

ratio between work and heat [closed]

I am really stuck on a problem in my textbook: Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. ...
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283 views

Why does an ice rink use a primary and secondary coolant?

A normal refrigeration cycle uses one coolant, so why does vapor compression cycle of an ice rink you a primary coolant and a secondary coolant?
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501 views

State-dependent diffusions: Fick's law vs. Fokker-Planck's, which and why?

Consider a "state-dependent diffusion": a diffusion process for which the diffusion coefficient $D(x)$ depends on the (stochastic) state $x$ of the system. (An example is provided by the diffusion of ...
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422 views

Multi-component mixture phase equilibrium criteria

For a pure species, the equlibrium between liquid phase and vapour phase is given by the equality of molar Gibbs energy in both phase: $$\underline{G}^l=\underline{G}^v$$ Where $\underline{G}$ with ...
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243 views

Temperature and latent heat

Building a bronze stature we make a mold and pour in the liquid bronze when the bronze hardens we remove the mold. The mold is made of 3 Kg of steel and the statue has a mas of 1 Kg. The specific ...
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182 views

Determine the flow and amplitude equation for thermal energy (with Del operator)

It is a question vector calculus and Maxwell's laws. I put it this way. Let's say, we are working in a $3$-Dimensional space ( e.g $x\cdot y\cdot z = 4\cdot3\cdot2$, a certain room/class of that size ...
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1k views

Ideal gas with two kinds of particles, Grand canonical partition function

Consider an ideal gas contained in a volume V at temperature T. If all particles are identical the Grand canonical partition function can be calculated using $$Z_g(V,T,z) := \sum_{N=0}^\infty z^N ...
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845 views

Thermodynamics, bullet fired into ice

I'm beginning to study basic thermodynamics and I want to solve this exercise: It fires a lead bullet from $3g$ to $30^oC$ with a speed of $240\frac{m}{s}$ to a block of ice at $0^0C$. How much ice ...
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312 views

Entropy of a black hole can be zero?

Black holes are one of highest density objects in the universe. Because of this high density(m/v) more matter is highly compressed in a very small volume( i am guessing that molecules cant freely move ...
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495 views

Efficiency of parallel and sequential heat pumps

Consider two identical heat pumps, for example, split-system air conditioners. There're two ways to make them work - in parallel or sequential. Parallel means that "hot" radiators of the machines are ...
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628 views

How would I calculate the convection coefficient in transient convection?

So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I ...
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374 views

What is lambda R in Richardson's Law?

I've got to calculate the thermionic emission through a diode, so I need to use Richardson's Law. However, one thing's got me confused - according to the Wikipedia page: $$J = A_GT^2e^\frac{-W}{kt}$$ ...
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412 views

Boltzmann Brain Immortality

This is a somewhat philosophical question. Given that even after person A's death, there's a non-zero chance that a brain fluctuates into existence with exactly the same structure and memories as A's ...
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3k views

How much disolved oxygen is removed by boiling water?

Apologies if this is a chemistry question I've read that drinking water contains dissolved oxygen to the tune of $10\:\rm{ppm}$. I've also read that raising the temperature of water will remove some ...
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285 views

2d or 1d conduction in this scenario?

There is a rectangular fin attached to a heat exchanger with a base temperature of 350K. The fin has uniform properties and experiencesa uniform heat generation. It also experiences heat transfer with ...
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2k views

In what situations do I use the characteristic length of a fin to find the surface area?

So I'm learning about fins in heat transfer and it seems that there are two separate formulas for the surface area of a rectangular fin of length L, width w and thickness t. The fin is attached to a ...
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1answer
96 views

Terminology question about energy

I'm looking for the appropriate term to use for what gets "used up" as potential energy is converted to heat and work. For example, some of the the energy in solar radiation is converted by ...
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2answers
224 views

How does cooling scale with volume?

What equation would give me the answer to the question, "If i have a cup of water at a tempature of say boiling, how long would that cup of water take to cool off compared to say half that size of a ...
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210 views

What is the molecular model of heat of mixing?

Heat can be evolved or absorbed when two dissimilar liquids are mixed together at constant temperature and pressure. This is called the heat of mixing of the mixture. I'm trying to understand the ...
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225 views

Depalma Free Energy fields

Few years ago I read some papers about Free Energy, written by Bruce de Palma, a physicist who is said to be the inventor of the N-Machine, which is an device that works with free energy latent in the ...
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2answers
415 views

simulations at constant pressure-volume and constant volume-temperature

I have read some papers where the authors perform simulations at constant pressure and constant volumen or sometimes constant volume constant temperature. My question is when is it better to use one ...
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1answer
150 views

SDE for particle, PDE for the density

Given a particle on the plane we can assume that it follows 2D Brownian motion. On the other hand if there is a lot of such a Brownian particles one can be interested in the evolution of the density ...
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162 views

thermal energy while calculating Langevin Forces

I have a quick question from thermodynamics. I remember that we take kT/2 as the kinetic energy per degree of freedom in kinetic theory of gases. But when we do langevin forces (for example in ...
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654 views

free adiabatic expansion

My question is mainly an engineering question. Assume I have a turbine in which I adiabatically expand compressed air. The air cools down and does work to its surroundings, which is captured by the ...
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3answers
7k views

Derivation of polytropic process equation

I know that a polytropic process equation is often the result of an empirical fit of a P-V curve that allows one to derive some nice analytical equations for the process. Is there actually a ...
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1answer
277 views

How to vizualize a heat pump microscopically?

Hey guys, while learning thermodynamics i wondered how a the principle of a heat pump would look at a microscopic level, not on a quantum mechanical level. I learned that when a hot and a less hot ...
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55 views

Zeroth law of thermodynamics and related discrepancy?

Consider the case: Assume molecules to sphere and their |velocity| as an indication of their temperature. Now for head on elastic collision (i.e transfer of heat), assume the momentum is conserved ...
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28 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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33 views

Why do particles in a medium have different speeds?

If thermal conduction occurs because of particles colliding with each other and imparting kinetic energy to each other, won’t the particles of an isolated medium collide with each other until the ...
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43 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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26 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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1answer
38 views

Single story, hotter outside, some shade from porch, enough to cool house with/without air flowing?

So, I know this question, without shade or one-story, has been answered many times on the 'net, so I have some actual physics for the one-story. I am fairly certain my roommate mixed up thermal ...
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1answer
21 views

Nature of system taken in thermodynamics

Why is thermodynamic system always taken as macroscopic ? What will be the changes if one considers the same as microscopic ?
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28 views

Internal energy in phase transition

As I understand, in the process of state transition (fusion or vaporization) the temperature remains constant for the duration the process is happening. The internal energy is a function of only ...
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41 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 ...