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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47 views
What is the coefficient $\mu_\text{air}$?
I am answering some exercises in thermodynamics, and I am still in trouble with some values and constants.
In the exercise, it is given: $\mu_\text{air}=1.8\cdot10^{-5}~\text{kg/m s}$. What for is ...
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0answers
31 views
How does the volume change affect an adiabatic process?
A gas consisting of rigid diatomic molecules was initially under standard conditions. Then the gas was compressed adiabatically, 5 times the original volume. Find the mean KE of rotating molecules ...
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2answers
40 views
Dividing values with units
I'm reading about the subject of heat in a basic physics book. If I am not mistaken the formula to work out how much energy is required to increase the temperature of water is
...
2
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3answers
75 views
Question about the proof that heat capacity goes to zero if temperature approaches $0K$
I don't completely understand the proof that is given for the claim that the heat capacity goes to zero, if the temperature approaches $0K$.
They do it as follows, if $C_x$ is the heat capacity where ...
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1answer
454 views
Finding electric power generated using heat transfer
I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$.
Given:
$\alpha_s = 0.83$
...
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2answers
34 views
Isothermal Gas Expansion, a Reversible or Irreversible process?
Consider the following situation. A certain quantity of ideal monatomic gas (say one mole) is confined in a cylinder by a piston and is maintained at constant temperature (say $T_0$) by thermal ...
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1answer
25 views
A Calorimetry Problem
I have a question in calorimetry from an old competitive exam. The question is:
The temperature of $100$ grams of water is to be raised from $24 ^\circ$C to $90 ^\circ$C by adding steam to it. ...
3
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0answers
46 views
Lattice model completely constrained by boundary data
I am dealing with a lattice model that has the peculiar property that if I specify all the spins on the boundary, by local conservation laws, the whole lattice configuration (throughout the whole ...
2
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1answer
25 views
Does increasing the pressure of the gas in a container by pumping gas into it increase temperature?
Basis is the ideal gas law: http://en.wikipedia.org/wiki/Ideal_gas_law
This law only states a mathematical relationship between many variables. It does not state what happens if one of the variables ...
2
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2answers
69 views
Why is it faster (as in proportion to volume) to boil 4 cups of water than to boil 2 cups?
I did an experiment where I boiled two cups (500ml) of water in a kettle, and it took 1:30 minutes to reach around 98 C, average. However, when I boiled 4 cups of water, (1L) it only took me 2:30 ...
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1answer
199 views
Does a negative line tension in a 3-fluid immiscible interface make sense?
This question is inspired by this question/answer pair: Is this formula for the energy of a configuration of 3 fluids physically reasonable?
Consider three immiscible fluids forming contact surfaces, ...
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3answers
69 views
How does an earthen pot keep water cool?
I understand that evaporative cooling takes place thanks to small pores contained in the pot and that allow some water to go through and evaporate. However I couldn't understand clearly whether water ...
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2answers
854 views
Thermodynamics - Sign convention
I use the sign convention:
Heat absorbed by the system = $q+$ (positive)
Heat evolved by the system = $q-$ (negative)
Work done on the system = $w +$ (positive)
Work done by the system = $w -$ ...
3
votes
3answers
796 views
Could life survive a pole shift caused by an asteroid collision?
Could life on earth survive a large pole shift caused by an asteroid collision?
I became aware that there are people who believe that the earth's pole suddenly shifts. That is, its rotational ...
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1answer
62 views
Maximizing Multiplicity of Einstein Solid == (Temperature = $\infty$)?
If I have a system consisting of 2 Einstein solids (A and B) is it equivalent to say that maximizing the multiplicity of the ...
5
votes
1answer
180 views
Thermo homework (HW) problem
I do not believe this question can be solved with the thermodynamics knowledge that I have learned thus far, but someone correct me if I am wrong:
A 0.2-m³ tank containing helium at 15 bar and ...
1
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1answer
73 views
Does brown but transparent swimming pool water heat significantly faster than western style highly chlorinated pools?
Eastern European swimming pools are often brown tinted water. i was told it was the color of the chemical to keep the pools clean, but who knows. These pools did not smell unsanitary and may have even ...
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1answer
69 views
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas?
I think that you need work to preserve this process and you bring thermal ...
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3answers
169 views
Definition of entropy
In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is ...
6
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1answer
1k views
LED Thermal Modeling (How to solve heat equation with constant heat source)
I have a mechanical design with LEDs that generate heat. I want to estimate the temperature at the LED junction vs. time, but especially at steady state.
Knowing the LED voltage drop and current, I ...
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1answer
217 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.
...
1
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1answer
37 views
What's the criteria for black hole thermodynamically stability? (And dynamical?)
It looks like usual criteria (positivity of Hessian; what geometrically means a cancave of entropy) is no useful, becouse entropy is not additive and not extensive for black hole. Then what is the ...
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0answers
46 views
Air pressure in balloon
I have to calculate the air pressure inside of an hot air balloon. After some searching I found out that I can use the ideal gas law: PV = nRT (from Wikipedia)
So to get the pressure in the balloon I ...
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1answer
81 views
Is it possible (theoretically) to divide Black Hole into two parts? [duplicate]
I have read that it's not possible.
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0answers
39 views
What is the physical meaning of fact, that Reissner-Nordstrom black hole is thermodynamically unstable?
It is known, that Reissner-Nordstrom black hole is thermodynamically unstable [1].
Does it mean, that there is no Reissner-Nordstrom black hole in physical world?
Does it mean, that there may be ...
2
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3answers
418 views
Does high entropy means low symmetry?
According to Bogolubov postulate (various texts name it differently) in Non-equilibrium thermodynamics, the number of needed parameters to describe our system is decreasing with time, and finally at ...
2
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0answers
19 views
Can one get clear ice crystals from a dirty suspension?
Euteictic freeze crystallization is a method where an electrolytic solution is cooled and separated into a stream of (relativly) clean, pure ice and a salty brine. I know anectdotally of wine ...
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0answers
74 views
Mechanical Equivalent of Heat
Recently I have been looking up James Joule's experiment regarding the mechanical equivalent of heat. After viewing some drawings of the apparatus, I assumed that the lines holding the weights would ...
5
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2answers
159 views
First law of thermodynamics?
The first law says that the change in internal energy is equal to the work done on the system (W) minus the work done by the system (Q). However, can $Q$ be any kind of work, such as mechanical work? ...
2
votes
1answer
50 views
Thermodynamics, PV diagrams?
My teacher told me that the total amount of work done on or by a gas can be represented by the area enclosed in the process in a PV diagram. This is only valid for non isothermic processes, right?
7
votes
1answer
617 views
Why is compressible flow near the choke point so efficient?
Imagine a steady state, one-dimensional, compressible flow in a horizontal pipe of constant cross sectional area. This flow can be isothermal, adiabatic (Fanno), or diabatic (Rayleigh). As an ...
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2answers
94 views
Computer cooling with dry ice, ideas and question; thermodynamics
I am designing a cooling system for my computer and had a few questions.
So I have a computer water cooling radiator and I want to cool it as much as I can.
My first two ideas were an old window A/C ...
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0answers
49 views
Is there axiom of entropy's additivity in thermodynamics? [closed]
I would be glad for some links on books.
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0answers
24 views
Total massflow through heat exchanger
I am working on a project and I stumbled on a problem. The project is to design a heat pump to replace the old system (actual problem, not some homework problem). There are 100 or so induction units ...
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0answers
30 views
How connected thermodynamical stability and dynamical stability for black holes?
Criteria for thermodynamical stability is the convex of entropy. But for black hole entropy is non-additive.
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3answers
221 views
How can I determine the coefficient $k$ in $ \dfrac{dT}{dt} = -k(T - 100 \mathrm{^\circ C}) $?
I recently spend some time on cooking and I'm curious about the time evolution of the temperature of the water. I did some experiment and the temperature is of the form
$$ T = 100 \mathrm{^\circ C} + ...
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vote
1answer
94 views
Joule-Thomson effect of Van der Waals gas
I'm supposed to calculate the inversion pressure $p_i$ of a Van der Waals gas. The state equation of the Van der Waals gas is: $$(p + \frac{a}{V^2})(V-b) = RT.$$ To get a hold of the inversion ...
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4answers
85 views
The Preference for Low Energy States
The idea that systems will achieve the lowest energy state they can because they are more "stable" is clear enough. My question is, what causes this tendency? I've researched the question and been ...
2
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2answers
31 views
Gas Circulation Using Pressure Difference
Dear all, see attached picture
Please, is it possible to have the gas recirculated from the gas phase to the liquid as described in the diagram assuming the gas is not soluble in the water.
These ...
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2answers
66 views
Is it possible to “add cold” or to “add heat” to systems?
Amanda just poured herself a cup of hot coffee to get her day started.
She took her first sip and nearly burned her tongue. Since she didn't
have much time to sit and wait for it to cool down, ...
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votes
3answers
74 views
How do you determine the heat transfer from a P-V diagram?
I doubt this question has been addressed properly before, but if there are similar answers, do direct them to me.
I am currently studying the First Law of Thermodynamics, which includes the p-V ...
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3answers
274 views
Has anyone theorized a connection between entropy and quantum uncertainty?
I apologize if this kind of idle theorizing is frowned upon here, but I was wondering if it is possible that the Second Law of Thermodynamics is a consequence of quantum uncertainty.
I've heard ...
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0answers
51 views
Explain to me how this water cooler works?
Goodday all,
I was recently reading up on a few projects that might be of interest to me when I found "CPU Bong water coolers", there isn't much online on them so I figure I would ask y'all.
If you ...
3
votes
1answer
71 views
Error in Sear's and Zemansky's University Physics with Modern Physics 13th Edition (Young and Freeman)?
I was reading up on the Ideal Gas Equation in University Physics with Modern Physics by Young and Freeman when I chanced upon a seemingly illogical mathematical equation.
Can anyone rectify this ...
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1answer
54 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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0answers
14 views
What is the effect of an increase in pressure on latent heat of vaporization?
What is latent heat of vaporization ($L_v$) in the first place? Wikipedia seems to indicate that it is the energy used in overcoming intermolecular interactions, without taking into account at all any ...
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5answers
437 views
Why isn't temperature measured in units of energy?
Temperature is the average of the kinetic energies of all molecules of a body. Then, why do we consider it a different fundamental physical quantity altogether [K], and not an alternate form of ...
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1answer
210 views
Expressions for canonical partition function and probabilities $p(E_i)$
Given an atom with 4 allowed states corresponding to the energy levels
$E_1 = 0$, $E_2 = E$, and $E_3 = 2E$ with degeneracies 1, 1, and 2 respectively.
How do I find the expressions for the ...
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0answers
19 views
Heat transfer in fluid between two horizontal plates vs unconfined case
I often see the correlation for turbulent heat transfer between liquid cells published by Globe and Dropkin (1959). In the original paper the fluid was confined between two horizontal plates and ...
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1answer
679 views
Beginner Thermal Dynamics Question [closed]
A syringe is set up filled with air (mainly N2 and O2) as shown in the diagram below. The surface area of the syringe is 15.3 cm2. The initial pressure inside the syringe is Pi = 114 kPa and the ...
