Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

learn more… | top users | synonyms (3)

1
vote
2answers
37 views

estimating deviations from ideal gas behaviour

How can one estimate the pressure at which argon atoms show deviations from ideal gas behaviour due to the finite size of the atoms? I have tried Taylor expanding the hard sphere gas equation: $$P'(...
1
vote
1answer
29 views

Example of a Carnot machine made of a different physical system than a ideal gas?

Anybody knows an example of a Carnot machine made with any different thing than a gas? For example wire or a magnet. I was wondering that since I read the Kardar's book on Statistical Mechanics. He ...
2
votes
1answer
97 views

Cooling of a hot metal object in air

We have this experiment where a metal bar is heated and then we have to make a model for the cooling that occurs. We get numbers for how long it takes the metal bar to cool from 200 to 100 degrees ...
0
votes
1answer
106 views

Finite Difference Method (FDM) solution to heat equation in material having two different conductivity

I am not from a mechanical engineering background and I have not taken any courses in PDE so this may seem trivial for many. and I am writing a Matlab code with the objective to solve for the ...
0
votes
1answer
16 views

Relate conductor current with temperature

I'm working with heating wires and I wan't to probe that for a wire with a constant radio it's only needed to know the current to estimate the temperature. Can I just say that if for a given current ...
2
votes
0answers
17 views

Fermi-Pasta-Ulam for the beam equation

The Fermi-Pasta-Ulam numerical experiment is based upon the discrete wave equation, with a small non-linearity added to the forcing term. Does anybody know of similar research performed on the beam ...
0
votes
0answers
25 views

Time to recover to ambient temperature from a cold condition

How to find the time taken by an object ( Made of say Aluminium) weighing about 1 Kg initially at a low temperature ( say -40 degree C) to regain temperature to ambient levels ( say + 30 Degree C) ...
-1
votes
1answer
35 views

Adiabatic compression for an ideal gas

I´m trying to solve the exercise 7.4-11 of Callen Thermodynamics 2nd edition. Where a 2-mole ideal gas of pressure $10^5$ Pa and temperature of $273.15$ K (0° C) is adiabatically compressed to $573.15$...
1
vote
2answers
70 views

Why does the sign of Delta H indicate whether the reaction is exothermic or endothermic?

If $\Delta H = Q + W$ (assuming constant conditions), then there are two terms involved in calculating $\Delta H$, only one of which measures heat gained/released. It is possible then for $\Delta H$ ...
0
votes
1answer
75 views

Poincare recurrence time of the Universe

I've read around a bit, and it seems to be universal that the notion of a Poincare recurrence time for the universe exists. And it seems to be debated that the universe can be given an entropy, as it ...
0
votes
1answer
30 views

Can the air be cooled by blowing it around an earthern pot

It is clear that water gets cooled in an earthern pot thru evaporation etc. If we blow (fast) warm/hot air around such an enclosed pot (pot is further lying in say another bigger pot) so that the air ...
1
vote
4answers
110 views

Is it possible for a system to become irreversible?

Imagine a ball bouncing in a box for a long time. We know, there is a certain path it can go to bounce off infinitely (see the image). If it gets to this state, it will never be able to get back again....
1
vote
0answers
46 views

Estimate heating wires temperature

Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption. I've tried to measure the ...
0
votes
0answers
42 views

Inversion and Isenthalpic Curves for van der Waals EOS

When I plot the isenthalpic curves in P-T plane, I see Joule-Thomson coefficient is positive in the lower inversion curve but it must be negative. Some authors consider the minimum inversion ...
1
vote
3answers
99 views

Evaporation of water

Consider a cylinder that there is water inside it. The volume (and so the pressure) of the cylinder is adjustable by a piston. The thickness of the cylinder and piston is very negligible. The cylinder ...
0
votes
1answer
26 views

Statiscal treatment of multiparticle system (Thermodynamics) [closed]

If a system of two energy levels with energies $\epsilon_1$ and $\epsilon_2$ is populated N particles at temperature T. The degeneracy of both levels is one. The particles populate the microstates to ...
2
votes
1answer
55 views

Can a High Enough Temperature Create a Black Hole?

My very basic understanding of GR leads me to think that if a substance has a high enough temperature, it can transform into a black hole without a mass required to create a black hole. The equation ...
1
vote
4answers
51 views

How can removing energy from a system do work? (ice)

Water freezing into ice expands, damaging roads, breaking rocks, etc. To my understanding, this is doing work (in a physics sense) by removing energy from the system. How is this possible?
0
votes
0answers
36 views

how to calculate enthalpy and internal energy in relation to heat capacities?

I remember that $\mathrm du=c\mathrm dT$ and $\mathrm dh=c\mathrm dT$ with $c$ being two different heat capacities, but I can't find anything about it, any help?
-1
votes
1answer
39 views

Thermodynamics: efficiency of a heat engine [closed]

How can we calculate efficiency of a real heat engine? Do we have to consider volume of an object while calculating efficiency? Like in this question If so, how we have to proceed? Thanks in ...
0
votes
3answers
34 views

specific volume in a saturated steam mixture

In saturation temperature, we have both gas and liquid. In the steam tables, I don't know if the liquid is in form of droplets inside the steam or in the form of normal liquid water at the bottom of ...
0
votes
0answers
11 views

Acoustic energy

Let's Assume that I'm sitting in a hypothetical container(room) whose 6 walls are PERFECTLY AND IDEALLY rigid and also are PERFECTLY reflective. Now if I start speaking anything in this room and so ...
4
votes
3answers
135 views

Does entropy always increase with temperature? [duplicate]

For any system can we always say that entropy increases with temperature. In other words: $$\left(\frac{\partial S}{\partial T} \right)_{\{\alpha\}}\ge0$$ where $\{\alpha\}$ is the set of parameters ...
5
votes
1answer
133 views

Obtaining the temperature from Bose-Einstein and Fermi-Dirac distribution

Lets say you are given a distribution function $f(p)$ and you want to define a temperature, $T_f$, for this distribution. (I assume $\mu = 0$.) It is then natural to define a temperature the ...
0
votes
3answers
61 views

Clausius Inequality with three reservoirs

Deriving Clausius inequality in the case of two reservoirs is quite simple. We assume that there is a thermal machine operating between two reservoirs, the first at temperature $T_1$ and the second at ...
3
votes
1answer
64 views

2 times the velocity, 4 times the energy, 8 times the heat

In SpaceX's webcast today they talked about the first stage getting back to Earth with twice the velocity as usual. I quote: "So 4 times as much energy means harder on the stage, and 8 times as much ...
2
votes
2answers
130 views

How do ceiling fans cool or heat?

Why does a ceiling fan blowing air downward cool in the summertime: whereas a ceiling fan sucking air upwards heats in the wintertime: ? Why isn't it the other way around?
0
votes
1answer
38 views

How do I find the temperature of an object being heated on one side and cooled on the other [closed]

Ok so i'm trying to figure out what temperature a beam would be when one end is put into the ground and the other side is in the open air above. Assuming the beam is perfectly insulated besides the ...
6
votes
1answer
84 views

Intuition about the cosmological significance of the chemical potential

A definition of the chemical potential that has always served me well is $$\mu_i = \Big(\frac{\partial U}{\partial N_i}\Big)_{S,V},$$ that is, the amount of energy one would have to add to a system ...
1
vote
0answers
22 views

Liquid Temperature Profile

Suppose I have a one meter cubed box of liquid and I know that it is in a $-4^\circ~\rm C$ room for some amount of time, but was at a uniform $25^\circ ~\rm C$ when it was placed inside. I know I can ...
0
votes
1answer
43 views

Why does increasing heat conductivity decrease Nusselt number?

Normally we expect that when heat conductivity(k) increases heat transfer is also increases. But for fluids increasing k decreases Nusselt number. My senses tell that using high conductive fluid cause ...
0
votes
1answer
35 views

Can condensation occur in a unsaturated vapor?

Consider that a gas mixture of vapor$+$inert gas is unsaturated with concentration (or molar fraction) $x_\infty$ far from a clear, cooled substrate of temperature $T_\text{w}$, i.e. $T_\text{w}<T_\...
0
votes
1answer
24 views

How can excite a semiconductor to make a photon just by heat in room temperature?

I want to know if a semiconductor in room temperature can excite by heat, producing photon, without any other source of energy?
17
votes
6answers
535 views

Do gases have phonons?

A phonon is a quantized unit of sound; they are encountered when quantizing lattice vibrations in solids. Now, even an ideal gas supports sound waves, but in such a case, interactions between atoms ...
0
votes
1answer
33 views

Two rising bubbles of differing temperatures

Consider two bubbles rising through some medium (water, for example). Given that the two bubbles have the same initial size, pressure, and temperature but differing velocities, which bubble will be ...
3
votes
1answer
68 views

If Black holes are maximal entropy how can they evaporate?

According to Hawking/Bekenstein a black hole represents the highest amount of entropy for a given volume, (actually the entropy is related to the surface area of the black hole but the fact that they ...
0
votes
0answers
30 views

Calculate Temperature change in a solid due to resistive heating

Trying to calculate temperature increase in a solid due to resistive heating by a current flow, is this along the right lines? First I have calculated resistance due to resistivity, then calculated ...
0
votes
0answers
18 views

Inductance heating, Temp Change [duplicate]

I am trying to find the temperature increase of a solid(copper) in a gas (air) due to an electric current passing through the solid (inductance). I need to encompass any temperature losses from the ...
-2
votes
2answers
99 views

Entropy always increases in a closed system - what if the universe is open?

An interesting question I was asked: Entropy always increases in a closed system - what if the universe is open? Does that mean that entropy can decrease in such a system? Of course, I think there is ...
0
votes
1answer
25 views

Effect of wall friction on stagnation pressure and temperature

We have incompressible air flowing through a cylindrical pipe, from section A to section B. The process is considered to be stationary. My theory book says that, because of the frictional losses on ...
0
votes
1answer
15 views

Does frequency of mechanical vibration of material affect its blackbody radiation spectrum

Can we see the difference in emissivity for instance between the same object vibrating in two different frequencies ?
0
votes
1answer
36 views

Confusion about Isobaric processes

Suppose in a ballon of gas is given an extra bit of heat, so as to getting the ballon's internal energy slightly up and this will work out to achieve a little bulk for the ballon. Though the whole way ...
0
votes
0answers
16 views

Rugged Energy Landcapes (Free Energy vs Potential Energy Questions)

A spin glass has what is called a "rugged energy landscape." That is, when you cool down below a certain temperature, the system divides into many wells, all corresponding to slightly different ...
1
vote
1answer
30 views

Why do $C_p$, $\alpha$ and $\kappa_T$ all approach to infinity when two phases coexist at the mean time?

My textbook (writed by Chinese) says that when two phases of a system coexist at the same time, this system's isobaric thermal capacity $C_p=T(\frac{\partial S}{\partial T})_p$, coefficient of ...
0
votes
2answers
52 views

Maxwell's area construction, why?

In the standard derivation of Maxwell's area construction (which can be found on page 4 of this pdf) the following equation is often written: $$G(p_1,T)=G(p_0,T)+\int^{p_1}_{p_0}Vdp $$ When the two ...
0
votes
0answers
23 views

Project Orion pusher plate computer modeling

Linked from the space.stackexchange forum: http://space.stackexchange.com/questions/15051/orion-project-npp-pusher-plate-computer-models-and-survivability Project Orion is discussed as if it is a ...
0
votes
0answers
55 views

Would it be correct to state that all the forms of everyday matter (mountains, tables, buildings, people, etc.) are in a metastable state?

We had a fire going in the backyard of a friends house this weekend, and after thinking about the chemical reactions occurring in the wood (and anything else we threw into the pit), I started to ...
1
vote
1answer
64 views

Why are glass beads used in a fractionating column?

Most sources do not go beyond saying that glass beads help increase the surface area for condensation of the liquid of the higher boiling point while using the method of Fractional Distillation to ...
0
votes
0answers
35 views

How can I get the exit temperature of water entered 100 degree in a pipe surrounded by 30 degree water?

Assume any value for: Length of the pipe The material of the pipe Velocity Heat transfer coefficient. I tried considering it as parallel flow heat exchanger but the water in this example isn't ...
1
vote
1answer
64 views

Confusion about inverse square law and temperature increase of an object

I know the inverse square law means that radiation intensity decreases in proportion to the radial distance from the source (I is proportional to 1/r^2). Does this apply to the temperature increase ...