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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16 views

Zero vol. at zero Kelvin

Why the volume of a gas become zero at 0 kelvin?Can Bose einstein condensate be considered as a matter? (I mean the vol. becomes zero)
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22 views

Gas Pressure in Industrial processes

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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25 views

Thermodynamics - Gas Laws

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
22 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
9 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
64 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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0answers
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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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 ...
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1answer
44 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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14 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
28 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 ...
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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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29 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 ...
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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 ...
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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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27 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
21 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
57 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
68 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
37 views

To find the temperature at equilibrium [on hold]

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 ...
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2answers
39 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
43 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
46 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 ...
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2answers
64 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 ...
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1answer
34 views

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

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 [on hold]

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 ...
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1answer
70 views

A possible way to initiate a nuclear fusion reaction without a nuclear fission trigger [on hold]

A few years back I read in either Popular Science or Popular Mechanics about a new kind of high explosive that had an energy density many times higher than the most potent ones previously developed, ...
2
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1answer
160 views

Increasing the efficiency of solar cell systems

As far as I know, there are currently two main approaches to utilising solar radiation for maximum energy conversion to electricity. These are either direct conversion to electricity, using ...
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0answers
23 views

Derivation of adiabatic T-V realtion [closed]

This is giving me hard time to the point of extreme annoyance with the algebraic manipulation. I have $$P^{-R} T^{C_v+R}$$. How do I get to $$\text{TP}^{\frac{(1-\gamma )}{\gamma }}$$ Appreciate any ...
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0answers
11 views

Solving a Non-Isentropic rankine Cycle [closed]

So I have been using a computer program to determine the various state parameters of a Rankine cycle for homework and I've hit a bit of snag. I can't seem to fully solve for the system with the knowns ...
0
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1answer
48 views

How much work can we extract from a black hole?

Recently, I've read an article on scientific regarding the possibility of a stairwell into a blackhole (unsurprisingly, it isn't possible). I've found the following question more interesting: ...
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3answers
162 views
+50

Causality principle and Entropy (Second Law)

I was reading about the light cone in relativity and I got to the point where in order to avoid paradoxes one can introduce the causality principle: Causality Principle: For every inertial ...
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Determine the pressure on the low-pressure side of a gas flowing through an orifice [closed]

A gas flows through a small orifice in a pipe as shown above. On the higher pressure side, the gas is at 1Mpa and temperature of 300K. The pressure reduces to 1kPa after it flows through the ...
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0answers
42 views

Heat equation with with time varying boundary condition [on hold]

I am trying to solve the heat equation: $$\frac{\partial U}{\partial t}=k \frac{\partial^2 U}{\partial x^2}$$ with the following boundary conditions: \begin{align} U(x,0)&=0 \qquad t<0\\ ...
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2answers
53 views

Practical understanding of energies in LHC collisions

Is visible light emitted at the point of collision in the LHC? If so, how bright? How much water could be heated up by 10 degrees celsius (this is the energy from collision only, not the energy to ...
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26 views

Thermodynamics helppp [closed]

Steam flows steadily through an adiabatic turbine At the inlet the condition of the steam is 10MPa, 450 C and a velocity of 80 m/s, and the exit condition of the steam is 10 kPa, 92% quality and 50 ...