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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132 views

Does entropy have a physical meaning?

Entropy is incredibly useful as a mathematical tool. But what does it actually mean? I understand that the Boltzmann entropy is defined by: $$S=k\ln{\Omega}$$ With $\Omega$ being the multiplicity ...
28
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4answers
3k views

Why do computers generate heat?

Computers generate heat when they work. Is it a result of information processing or friction (resistance)? Are these just different ways to describe the same thing? Or does some definite part of the ...
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0answers
34 views

Temperature dependence for specific thermal diffusivity in the diffusion formula

I recently found this answer about the diffusion equation (nice one actually), but have one doubt about the temperature dependence of this formula. If the "packet" of energy (terminology suggested ...
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3answers
63 views

Is it possible for heat to flow from body having less heat energy to a body having more heat energy?

Is it possible for heat to flow from a body having less heat energy to a body having more heat energy?
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2answers
111 views

Disequilibrium during infinitesimal steps of a thermodynamic reversible process & cause of maximum work to be achieved during reversible process?

In almost every sites and even in my book,it is written that "Reversible process is the process which is carried out infinitesimally slowly so that in each step thermodynamic equilibrium is maintained ...
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4answers
77 views

Will 5 pizzas in the same Hot Bag stay warmer than 5 pizzas in 5 separate Hot Bags?

For example, say I am delivering 5 pepperoni pizzas to 5 different addresses. In one scenario, I Keep all 5 in the same insulated Hot Bag, I carry that bag to the door, and I quickly remove one of the ...
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2answers
35 views

Does the relation between entropy and temperature depend on the ensemble?

If we change the temperature of a given system, there will be a relation between its entropy and temperature S(T). Is S(T) the same in a canonical ensemble and a grand canonical ensemble? If not, is ...
4
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2answers
43 views

Alternative liquid for Galileo thermometer

So a friend of mine broke my Galileo thermometer recently. The glass tube and the liquid inside were lost, but the bulbs survived. I've cleaned out an old tall glass candle, and tried filling it with ...
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2answers
182 views

Difference between irreversible and entropy?

Cedric Villani recently wrote an article on Landau damping, where at least one topic discussed confused me. Besides discussing the issue of how a process can be microscopically reversible and ...
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3answers
57 views

When the low temperture reservoir with negative temperture (Kelvin), such as Ising model, is the efficiency of ideal heat engine larger than 1?

The ideal Carnot engine works between two heat reservoir with two temperatures $t_h$ and $t_l$. Its efficiency is then $1-\frac{t_l}{t_h}$ . If the low temperture reservoir is the Ising model with ...
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1answer
18 views

Is it possible to cool magnetic dipoles with a magnetic static field?

Suppose you have a bath of magnetic dipoles, with a common mean rotational kinetic energy. Now you apply a very strong magnetic field so that the dipoles align with the field, thus "losing" their ...
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1answer
21 views

Final temperature of an air parcel

How would one find the final temperature of an air parcel ascending adiabatically in the atmosphere? Like which formula would you use? I used the equation of state for dry air to find the initial ...
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1answer
33 views

Dry adiabatic lifting

If an unsaturated air parcel ascends adiabatically in the atmosphere with an initial temperature, would the final temperature of the air parcel, when it reaches it's destination, be the same at the ...
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2answers
93 views

Thermodynamic reversible process

My book says "A process is said to be reversible if it is carried out infinitesimally slowly so that in each step thermodynamic equilibrium of the system remains unchanged & any infinitesimal ...
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1answer
69 views

A puzzle of thermalization in simulating the 3D XY-model

I am learning the classical Monte Carlo simulation. When I simulate the 3D XY-model $$ \beta H = -\beta J \sum_{<i,j>} cos(\theta_i-\theta_j) $$ where $\beta$ is the inverse of the temperature ...
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0answers
14 views

Creating correlated Szilard engines

A demon has a large number of boxes with a single particle in. He / she adiabatically introduces a wall in the box, dividing it in two with a particle in one of the two halves (L, R). The demon does ...
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0answers
24 views

How much energy does a powerlifter need to perform a session of squats?

So I started the math myself and I'm hoping someone can look this over and improve on my idea. Let's say that a powerlifter performs the following sets of squats: % 1RM = lifted weight in percent ...
2
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1answer
53 views

How to calculate Gibbs free energy of diamond?

How the effect of crystal structure on Gibbs free energy is calculated? For example, how the Gibbs free energy of diamond is 2.9 kJ/mol, while that of graphite is 0?
33
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4answers
5k views

How close can you get to lava before burning?

As the title asks: How close can you get to lava before burning? I know that it depends on an number of factors; speed of lava flow, wind direction/strength, type(?) of lava flow (related to speed, ...
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3answers
147 views

Asymmetric heat conduction?

So I have this side-view drawing. Now I wonder, will such a multi-layer material have asymmetric heat conduction properties? Namely, because of radiative conduction, reflective aluminum surface ...
3
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3answers
83 views

Definition of Entropy in thermodynamics

In most textbooks, the definition of entropy in reversible processes on a system $S$ is given simply as $$d S=\delta Q/T.$$ It seems to me this definition is insufficient since it does not specify ...
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1answer
24 views

Simple modelling of seasonal variation of temperature?

I'm really curious about this: What is the simplest (or most simplified) differential equation that accounts for the variations of temperature throughout the year at some point on the northern ...
1
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1answer
27 views

Modeling a wine cooler heat loss to ambient

I'm trying to model the steady state heat loss to ambient, in W, for a wine cooler similar to the following: For the modeling, I will need the following variables/constants: $T_a$ [K]: Ambient ...
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1answer
31 views

Thermal emission cathode electron velocity distribution

I can't find any experimental data (or theoretical expression) on what is the velocity (or energy) distribution of thermal emission cathode electrons emmited from the cathode at approximately 2000 K ...
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1answer
277 views

What happens to the temperature when an ideal gas is compressed?

I am rather confused about this. I know from Charles' law that under constant pressure, the volume of a gas is directly proportional to its absolute temperature i.e. $$\frac{V_1}{T_1} = ...
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0answers
23 views

Is the rapid compression of a non-insulated/insulated cylinder “practically” the same process?

I recently had an exercise which had us examine the following 4 situations: A quasi-static isothermic compression of a mono-atomic ideal gas. A rapid compression of a mono-atomic ideal gas, where ...
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2answers
39 views

Why is it that in a warm shower water feels hotter near the head?

When the water first hits your body, it feels warmer than when it streams down towards your feet. I realize that part of this is due to the water cooling down by dissipation to the surrounding as it ...
3
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2answers
96 views

Will a microwave heat sand?

I want to cook Turkish coffee on heated sand at school. I have difficulty accessing some easier method of heating, so I was going to try to heat sand in a microwave. It was then pointed out to me that ...
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6answers
100 views

Thermodynamics only deals with homogenous systems?

In Thermodynamics quantities like pressure, temperature and entropy are associated with overall states of a macroscopic system. In that case, we do not talk about "the quantity $Q$ at the point $p$ of ...
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1answer
52 views

Does air conduct heat better than saturated steam?

This engineering toolbox table shows thermal conductivity of steam at 0.016. I understand that water is better in conducting heat than air, but if I read this correctly, steam is worse in conducting ...
5
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1answer
67 views

Thermodynamics: heat transfer

I hope this question isn't too simplistic but I've been in a discussion with someone who claims that no energy is transferred between a cool object and a warm one (either by radiation or conduction) ...
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2answers
59 views

Relationship between two viewpoints on Thermodynamics

I've always seem the standard viewpoint on Thermodynamics that it is all about studying phenomena related to a property of systems called temperature. Then we have the zeroth law which allows us to ...
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2answers
53 views

How does the temperature in a bucket of water with ice change over time?

I'm curious what happens to the temperature of the water in a bucket of water with ice in it. Let's start with a bucket with just ice in it, and we add water, in a room which is room temperature. It ...
5
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1answer
104 views

Can quantum vacuum carry entropy?

So, we know that the state of quantum vacuum does carry energy, as it was measured in the Casimir effect. This energy comes from particles almost instantaneous creation and annihilation. Even if they ...
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0answers
12 views

Which constant is required to calculate the energy in a thermal analysis?

I want to calculate the energy in a thermal analysis. I want to do it in analogy to the electrostatic field, because I'm interested calculating the $H_1$ error in a Finite Element analysis. For ...
3
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2answers
110 views

“Violation” of the Second Law

I can't reconcile some facts about entropy and irreversibility. This depresses me, because I feel I can't quite grasp the importance of entropy. I will illustrate my problems with an example given by ...
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1answer
62 views

Thermal equilibrium

If two objects close together in a vacuum are in thermal equilibrium with their surroundings, but are of different sizes so they are actually emitting radically different amounts of energy, is it ...
0
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1answer
35 views

compressibility of cold atoms in optical lattices

The compressibility of cold bosons in an optical lattice is defined as $\kappa = \frac{\partial \langle n\rangle}{\partial \mu}$, where $\langle n\rangle$ is the density and $\mu$ is the chemical ...
2
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3answers
163 views

How to combat the black-body temperature of an object?

I'm trying to model the temperature of a large spacecraft for a space colony simulation game I'm working on. In another question, I checked my calculations for the steady-state black-body temperature ...
2
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1answer
38 views

What's wrong with this temperature-in-space calculation?

I'm trying to calculate the steady-state temperature of a body in space, but my numbers are coming up much too small. For example, for a 1-meter cube, I'm getting a temperature of 194 K (or -81 C). ...
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0answers
22 views

Is it true that 3 different types of sound produces at different stages while boiling a water? [duplicate]

I have heard this from someone that 3 different types of sound occurs when we boil the water . is it really true ?
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4answers
138 views

What happens when I place an ice cube into boiling water

My friend tried this experiment at home: She put an ice cube into boiling water. The water in the container stops boiling while the ice melts to water. My question: Why does the water stop boiling ...
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0answers
39 views

Cooling 8 L of frying oil using ice [closed]

I have 8L of frying oil (canola) - if I put it in a metal canister after frying and put that canister in ice water, what is the minimum amount of ice water that I need to bring the oil to a ...
1
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1answer
47 views

MIcrocanonical and Canonical - The thermodynamic limit

Considering a two level system with energies $ 0 $ and $ \epsilon$, we write out the single particle partition function with ease to be, also N-particle partition function for non-interacting ...
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1answer
52 views

How to prove this equation $W_b= {P_2V_2 - P_1V_1 \over 1-n}$

$W_b = \int$Pdv $PV^{n}$=C $P=CV^{-n}$ W=$\int cv^{-n} $dv =c$\int_{v1}^{v2}V^{-n}$ dv =c[${v^{-n+1} \over 1-n}]_{v1}^{v2}$ How to get rid of the (-n+1)? to prove $W_b= {P_2V_2 - P_1V_1 \over ...
3
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1answer
103 views

How does statistical mechanics predict that hot air rises?

Does hot air rise -- from a statistical-mechanical viewpoint Question #6329 asks whether and why hot air rises. The consensus answer is straightforward: - hot air is less dense than cold air - ...
2
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1answer
53 views

What's the point with equilibrium in Thermodynamics?

All the Thermodynamics books I saw until now state that in Thermodynamics we are mainly concearned with equilibrium states (I know there's "non-equilibrium Thermodynamics", but I'm interested on the ...
2
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4answers
103 views

Why work $W$ and heat $Q$ are different concepts?

I understand heat as the flow of energy (through radiation, convection or conduction) from one body to another. When I think about conduction (for example) I visualize particles that jiggle a lot ...
6
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1answer
125 views

Why do phase transitions even exist? Why not smooth density change curves?

Why do phase transitions even exist? Why not smooth density change curves? What properties of matter, quantum or otherwise, predicts that matter will undergo phases at different pressures and ...
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1answer
39 views

Thermodynamics phase change question

why is specific volume of Saturated water greater at 1 MPA than at 0.1 MPA during the phase change process check out the T-V diagram here in the link. ...