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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19 views

Why does internal energy remains constant in isothermal system? [on hold]

how to write this answer for 2 marks question simple and straight answer. Please
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2answers
35 views

Ice at zero gravity

I wish to know the behavior of ice at zero gravity, sound at zero gravity. How ice will behave when melted and how sound will break a closed glass at zero gravity vs g on earth? Thanks
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1answer
18 views

Counting the number of microstates that there are for a given configuration. How to prove this result?

I'm doing some statistical physics and I came across a result which I'm not sure how to derive. Any help? The answer turns out to be: Can anyone help with this derivation? Thank you :D
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2answers
42 views

How is the work done by a system turned into internal energy according to the first law of thermodynamics?

I have several questions about the first law of thermodynamics: When we have a force over a piston of a recipient with an ideal gas inside and that piston moves, we have work associated with that. ...
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2answers
74 views

Which one is colder? Zero temperature ice or zero temperature water?

I like to understand that which one of the following items seems colder, when we touch them? zero temperature ice zero temperature water Why? Thank you.
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2answers
44 views

How to calculate temperature of an incandescent bulb filament?

Suppose we have a light bulb, for which we know its power rating, like voltage of $12\mathrm V$, and power consumption of $10\mathrm W$. We also know it's a halogen bulb with a tungsten filament ...
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13 views

Compute the temperature of the reservoirs between which the engine operates [on hold]

An ideal gas for which $c_v$ = 3R/2 is the working substance of a Carnot engine. During the isothermal expansion the volume doubles. The ratio of the final volume to the initial volume in the ...
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32 views

Physical interpretation of legendre transformations in thermodynamics

I have found this question(Physical meaning of Legendre transformation) and I have some questions regarding the transformations in thermodynamics, In thermodynamics we have: $$H= U+PV $$ $$F=U-TS ...
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1answer
27 views

“Definition” of internal energy

Conversation of energy implies that if we have a thermally insulated system which goes from state 1 to state 2: $$\Delta E_{12}=E(2)-E(1)=\Delta W_{12}$$ and the 1st law of thermodynamics ...
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1answer
30 views

How does the second law of thermodynamics affect the efficiency heat-to-work conversion, at the molecular level?

I understand the second law of thermodynamics in terms of the improbability of the high--and-low-velocity particles of a gas to separate themselves so that at one moment they are at different sides of ...
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1answer
37 views

Zero volume at zero Kelvin

Why does the volume of a gas become zero at 0 Kelvin? Can a Bose Einstein condensate be considered as matter? (I mean the volume becomes zero)
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24 views

Gas Pressure in Industrial processes [on hold]

Can anybody please help with the following? Ammonia is produced by the Haber process where nitrogen and hydrogen combine to form ammonia according to the equation: N2 + 3H2 == 2NH3 If 1 mole of N2 is ...
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31 views

Thermodynamics - Gas Laws [on hold]

Can anybody please help with the following problem? The compression ratio of an engine is 16:1. The volume of air in the cylinder is $0.5 \,\mathrm{litres}$ at a temperature of $30 ...
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1answer
30 views

Sufficient conditions for Equipartition Theorem to hold

I was wondering what are the sufficient conditions for the Equipartition Theorem. I know there is another question (For which systems is the equipartition theorem valid?) that somewhats answers this ...
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0answers
11 views

Thermodynamics of a heated enclosure

i have to maintain an aluminum enclosure of size 200x300x400mm at around 80 degrees Celsius, there for i need to calculate the thermodynamics of the system, ie what power of heater i need to achieve ...
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0answers
9 views

Can an intercooler be analysed as any other heat exchanger?

I am doing this project on developing a code for the first and second law analysis of a practical Gas Turbine Cycle. It includes a two-stage compression process and thus, involves an intercooler, ...
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3answers
67 views

At what energy consumption would we get a 1 degree rise in the Earth's temperature?

If energy consumption continues to rise at (say) 4% per year, how long before the heat dissipation seriously impacts climate?
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21 views

a physical model for pde [on hold]

Consider the initial boundary value problem $$u_t=a(t)u_{xx},\,\,\,0<x<1,\,\,\,t>0$$ $$-ku_x(0,t)=hu(0,t),\,\,\,t>0$$ $$u(1,t)=u_0,\,\,\,t>0$$ $$u(x,0)=f(x),\,\,\,t>0$$ where ...
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0answers
7 views

When obtaining the thermodynamic entropy (e.g. by differentiating F) the average entropy is being found. In what sense is this an average?

If I have some expression of the entropy (or another thermodynamic quantity of a system (e.g. pressure) obtained from the Helmholtz free energy, F. Is this the mean (average) or the modal (most ...
4
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1answer
65 views

Historical Survey of Statistical Mechanics

Statistical mechanics is a subject with a particularly rich history. I think of the early debates of Boltzmann and Loschmidt, the rather confusing differences between the approaches of Gibbs and ...
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15 views

How to design a radiator to dissipate heat? [on hold]

I am making heat radiator that dissipates the heat from water coolant lines coming off of another project of mine. The coolant lines will flow into a barrel, radiate as much heat off as possible, and ...
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1answer
32 views

Writing an equation for the INTERNAL energy for a BRAYTON cycle

I am trying to understand the equation for the change in internal energy in the Brayton Cycle. Both the websites below gave me this formula :Change in U=q1+q2−w=0 ...
0
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1answer
31 views

What are the state variables like temperature after the system has done an adiabatic irreversible process? [on hold]

Consider a system containing ideal gas which is initially at a volume $V_{1}$ and then suddenly its volume is increased to a volume $V_{2}$. What is the final temperature of the system if the initial ...
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32 views

Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
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0answers
21 views

Is $\mathrm{d}H = C_P \mathrm{d}T$ and $\mathrm{d}U = C_V \mathrm{d}T$ always true?

Is $\mathrm{d}H = C_P \mathrm{d}T$ and $\mathrm{d}U = C_V \mathrm{d}T$ always true for ideal gases?
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1answer
16 views

Why is work done by an otto cycle along the 2 adiabatic curve negative?

I define the work done by the system as +dw and work done on the system as -dw. Looking through my notes on Otto cycle, I observed that the for the two adiabatic curves in a clockwise cycle such that ...
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2answers
77 views

How long does it take for water to boil when subjected to intense heat?

I have a rather odd question that may just boil (sorry) down to a fairly simple problem I can't solve. The scenario is this: A person is testing the intensity of a super-focused beam of sunlight in a ...
0
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0answers
20 views

Hot air particles

I have a question- albeit random one!. I recently visited a friends place who used a standard shovel from the shed as a tool for moving hot charcoals around a pizza oven. Unfortunately the shovel was ...
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0answers
32 views

Square of velocity = 2 times temperature times specific heat capacity ; seems too tidy [on hold]

So I did some algebra and came up with the following $v^2 = 2Tc$ where $ v = $ average velocity of the particles $ T = $ tempreture $ c = $ specific heat capacity but this seems too tidy
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13 views

How to find heat transfer and released heat? [on hold]

Given the sterling cycle with the following processes 1-2 isothermal expansion - heat addition from external source 2-3 constant volume heat transfer - internal heat transfer from the gas to the ...
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0answers
13 views

Finding the temperature needed to have speed of gas atom equal to Ve [on hold]

We are given n moles of a monatomic gas Argon Molar mass 6.4*10^-26. Pressure equal to 101300 pascals. Temperature = 300 K Need to find the average speed of one of the atom of the gas. Secondly I ...
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1answer
40 views

To find average speed of gas molecule when the temperature is incresed

We are given moles of gas let say $n$. Temperature is increased from $T_1$ to $T_2$. Volume is held constant at $V_0$. We need to find the average speed of gas molecule when the temperature $T_2$ is ...
0
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0answers
11 views

How to calculate how much energy is needed to fuse makro particles such as a certain type of plastic? [on hold]

As the title suggests, how do I calculate that? I would like to fuse plastic particles of the size around 0.1 millimeter using ultrasound. What equations do I need?
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30 views

Legendre transformation: non-convex/non-convave functions

The Legendre transformation is used to derive the Hamiltonian from the Lagrangian, and it finds many applications in thermodynamics to convert between the different potentials. $ f(x) \rightarrow ...
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1answer
22 views

showing that polytropic exponent n = 5/3 corresponds to an isentropic process for a monoatomic ideal gas [on hold]

Given an ideal monoatomic gas with $pV = NT$ and $E = \frac{3}{2}NT$ what are the types of processes described by $n = 0, 1, \frac{5}{3}$, where n is the polytropic exponent ($p V ^ n = const.$)? ...
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33 views

Why does transfer of $^3$He from the rich to sparse phases in a dilution refrigerator cause cooling?

Explanations of the dilution cooling process seem to state without explanation that moving a $^3$He atom across the boundary from the $^3$He rich to the $^3$He sparse phases takes up heat from the ...
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18 views

Planck Temperature

I have heard of two different things occurring at Planck Temperature: 1. A black hole forms 2. The quantum gravity takes over and the wavelength of light emitted from the object is Planck length ...
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0answers
17 views

Heat capacity of a gas in gravitational field

How does one calculate the heat capacity of an infinitely long column (of constant cross-sectional area) of ideal gas in a uniform gravitational field? I tried using the lapse rate $dT/dH$ and putting ...
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1answer
58 views

How can i turn home gas from liquid to gas [on hold]

I hope i am not too off topic, couldn't find a more suitable stack-exchange forum for this, if there is a better one, please point me to it, Well my question is the following, I am working on a ...
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2answers
69 views

Why do we feel hot because of sunlight? [on hold]

sunlight , light generally , is an electromagnetic wave which turns into heat when it contacts a matter (solid,liquid,etc..) is that right ?
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0answers
47 views

To find the temperature at equilibrium [closed]

A 4.4-kg block of ice originally at 263 K is placed in thermal contact with a 14.8-kg block of silver (cAg = 233 J/kg-K) which is initially at 1021 K. The H2O - silver system is insulated so no heat ...
2
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2answers
41 views

Any general method of determining changes in speed of sound with pressure?

I need to correct speed of sound measurements in various gases for changes in ambient pressure, typically 700-1100 mBar. Is there any general theoretical model available for this? Especially something ...
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1answer
44 views

Boltzmann Distribution - why maximum number of microstates?

I've recently started to learn statistical mechanics and I've run into Boltzmann Distribution. I wanted to see how it is derived and found some articles on web, but no one of them explain why the idea ...
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0answers
48 views

How do I model this Quantum Cascade Laser (QCL) using COMSOL? [on hold]

I'm trying to model this: GaAs on-top of a heat-sink made of Copper. It's trying to simulate a type of Quantum Cascade Laser, I'm looking at the effect the temperature has by running a 10V voltage ...
2
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2answers
65 views

Does the second law of thermodynamics take into consideration interactions between particles?

If one searches Google or textbooks on 2nd Law of Thermodnamics, one usually finds a statement that is either equivalent or implies the following. The entropy of the universe always increases. But ...
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1answer
12 views

Full ionization meaning

I'm confused as to what full ionization mean? I have the mean molecular weight of electrons and ions and I have to calculate the ideal gas pressure for a star. Do I have to add them up as usual or do ...
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1answer
23 views

Series of parallel thermal resistance connection for this enclosure?

Let's say that I have an 2D enclosure in the shape of a pyramid with unequal areas for the faces and I am looking to determine in the inside air temperature. The parameters I know are the outer and ...
1
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1answer
34 views

Equation involving; elastic modulus, poisson ratio, radius and pressure of a sphere [closed]

I am trying to determine the expansion of a spherical pressure vessel. I am certain that an equation exist that will define the change of radius of the sphere as the pressure increases. The vessel ...
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0answers
26 views

Specific heat and latent heat of fusion [closed]

A thermally isolated vessel contains 100g of water at 0 degree c. When air above the water is pumped out, some of the water freezes and some evaporates at 0 degree c itself. Calculate the mass of the ...
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2answers
73 views

If you heat a closed tube, does its mass change?

This is a result of a debate with friends. We were more concerned with the nano- and smaller-scale effects than the larger effects. Let's assume that we have a closed tube filled with air. We weigh ...