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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Maximum Principle vs. Minimum Principle in Non-equilibrium Thermodynamics
Prigogine's Min. principle states that in steady-state non-equilibrium systems the entropy generation rate is at a minimum, i.e., a system will seek a steady-state that has min entropy generation. ...
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203 views
Why is temperature constant during melting?
This is an elementary question but I do not know the answer to it. During a phase transition such as melting a solid to a liquid the temperature remains constant. At any lower temperature the heat ...
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4answers
158 views
Is energy extensivity necessary in thermodynamics?
Given a partition of a system into two smaller systems, the energy $U$ is devided into $U_1$ and $U_2$, with
$$U=\mathcal{P}(U_1,U_2):=U_1+U_2,$$
so that $U_2$ is given by $U-U_1$. Here the ...
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5answers
999 views
Recommendations for Statistical Mechanics book
I saw Book recommendations
No reference to Statistical Mechanics there.
I learned thermodynamics and the basics of statistical mechanics but I'd like to
sit through a good advanced book/books.
Mainly ...
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4answers
2k views
Why does maximal entropy imply equilibrium?
From a purely thermodynamical point of view, why does that entropy have to be a maximum at equilibrium? Say there is equilibrium, i.e. no net heat flow, why can the entropy not be sitting at a ...
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5k views
How does a maple syrup evaporator work?
Some background info on what an evaporator is:
It is a system of metal pans set over a heat source. Sap constantly enters the first pan controlled by a float valve to keep a constant depth. The pans ...
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1answer
352 views
Microwave oven + water: dielectric heating or ion drag?
When you place a water or food in a microwave oven, it heats.
Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating?
AFAIK, in distilled water (which is a ...
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87 views
Is there a relativity-compatible thermodynamics?
I am just wondering that laws in thermodynamics are not Lorentz invariant, it only involves the $T^{00}$ component. Tolman gave a formalism in his book. For example, the first law is replaced by the ...
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2answers
169 views
When should I take wine out of the fridge - transient heat transfer problem
I am hosting a dinner tonight for which I'll be serving white wine (Riesling to be more specific). Generally white wine is best served chilled (not COLD!) at around ...
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2answers
152 views
relativistic spaceship, CMB radiation and thermodynamics
Scenario: a spaceship is travelling at a high fraction of $c$. The interstellar gas and CMB radiation has blueshifted significantly and we are facing a possible melting of the front radiation shield!
...
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1answer
376 views
Wick rotation and the arrow of time
It is well known that we can switch from a statistical system to a quantum mechanical system by a Wick rotation. Has this rotation some implication on the way the time flow? namely, this is an ...
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1answer
197 views
Melting point, is it determined only experimentally?
I am interested in the underlying physics of the concept of a melting point, a temperature at which an object tends to gain enough energy to break the bonds that hold it together and be in a liquid ...
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2answers
76 views
Is it possible to have annealing without creep?
Annealing can repair a material by allowing atoms to find the minimum energy state; since solids have a surface tension this process will allow cracks to fuse and reverse fatigue. However, annealing ...
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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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4answers
990 views
Should I heat my room when I'm not here, energy-efficiently speaking?
I was wondering as it's getting cold : is it better for my electricity bill to shut down completely my (electric) heater during day, and to turn it on again when I come home (then it will have to heat ...
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7answers
834 views
Is it theoretically possible to reach 0 kelvin?
I'm having a discussion with someone.
I said that it is -even theoretically- impossible to reach 0K, because that would imply that all molecules in the substance would stand perfectly still.
He said ...
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4answers
1k views
After what speed air friction starts to heat up an object?
I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster.
But ...
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3answers
902 views
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213 views
experimental technique for measuring temperature of an ant
I am taking a course on thermodynamics. I have a question from my text(halliday & resnick,physics-1). They asked me to measure temperature of an ant or an insect or a small body,like a small ...
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592 views
Is energy the ability to do work?
Here was my argument against this, the second law of thermodynamics, in effect says that, there is no heat engine that can take all of some energy that was transferred to it by heat and do work on ...
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4answers
2k views
What causes hot things to glow, and at what temperature?
I have an electric stove, and when I turn it on and turn off the lights, I notice the stove glowing.
However, as I turn down the temperature, it eventually goes away completely. Is there a cut-off ...
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2answers
110 views
Solidification by the application of heat
When you add heat to a liquid (or a fluid), can it be solidified? If not, why in the world does an egg's stuffs become solid (or at least no more a liquid) when you 'boil' it in water?
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4answers
664 views
Sauna thermodynamics
Why does it get hotter (feel hotter) in a sauna when one pours water over the hot stones?
Wikipedia says that the water condenses onto the skin, but the actual air humidity is so low that I doubt ...
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3answers
446 views
Can temperature be defined as propensity to transmit thermal energy?
I was recently surprised to learn that defining temperature isn't easy. For a long time, it was defined operationally: how much does a thermometer expand. Also surprising, temperature isn't a ...
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3answers
386 views
Are negative temperatures typically associated with negative absolute pressures?
Negative temperatures and negative absolute pressures are both possible in physical systems. Negative temperatures arise in (for example) populations of two-state systems, which have a maximum amount ...
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2answers
464 views
What happens if you connect a hot resistor to a cold resistor?
Kind of an extension to this question:
If you heat up an object, and put it in contact with a colder object, in an ideal insulated box, the heat from one will transfer to the other through thermal ...
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4answers
182 views
Can a single molecule have a temperature?
A show on the weather channel said that as a water molecule ascends in the atmosphere it cools. Does it make sense to talk about the temperature of a single molecule?
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1answer
176 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? ...
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2answers
2k views
Minimal temperature achievable by vanilla Peltier element?
I wonder, are there any fundamental issues leading to reduced performance of Peltier elements at cryogenic temperatures (-100C and lower)?
What is theoretical/practical minimum temperature ...
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4answers
1k views
Is there an equation for convective heat transfer?
Is there an equation I can use to calculate the temperature (as a function of time) of an object which is gaining or losing heat by convection? Or equivalently, the rate of energy transfer from the ...
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1answer
154 views
Can an induction coil heat two layers of metal?
Imagine we have an induction coil which is strong enough to heat a sheet of metal. We can put a sheet of ferromagnetic metal close to the coil at distance $h_1$, and it gets heated to temperature ...
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2answers
96 views
Why is the gas halo of the Milky Way so hot?
I have read on the webpage of NASA that there is a massive hot gas halo around our galaxy. Its temperature is between 100,000 and 1 million Kelvins or more. I do not understand why is it so hot. The ...
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5answers
2k views
Why was the universe in a extraordinarily low-entropy state right after the big bang?
Let me start by saying that I have no scientific background whatsoever. I am very interested in science though and I'm currently enjoying Brian Greene's The Fabric of the Cosmos. I'm at chapter 7 and ...
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1answer
497 views
Meaning of what C. P. Snow said about the laws of thermodynamics [closed]
My native language is not English and I am having hard time understanding the meaning of the following statements which are to explain the laws of thermodynamics.
The 1st law: you cannot win ...
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2k views
Are specific heat and thermal conductivity related?
Are there any logical relationship between specific heat capacity and thermal conductivity ?
I was wondering about this when I was reading an article on whether to choose cast iron or aluminium ...
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2answers
375 views
Temperature below absolute zero?
I saw this Nature article today, which cites e.g. arXiv:1211.0545.
And it makes no sense to me. The temperature of a collection of particles is the average kinetic energy of those particles. Kinetic ...
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1answer
174 views
Is a black hole's surface area invariant for distant intertial observers?
Let's imagine I'm very far from any massive objects, so my local space-time is Minkowskian. Off in the distance is a black hole, far enough away that it doesn't noticeably curve space-time near me, ...
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2answers
284 views
Proof that Statistical Mechanics is a model of Themodynamics
The laws of thermodynamics are essentially four axioms of a mathematical theory.
The expectation values of a statistical ensemble are supposed to satisfy the axioms of thermodynamics (under the ...
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170 views
Evaporating water in -30ºC
I don't really know anything about physics even though I pretended studying it for years.
How is this explained?: ...
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1answer
396 views
Estimating hydrogen loss by Jeans escape
I'm looking at Jeans (thermal) escape of hydrogen from the early Earth's atmosphere. I understand how to calculate the rate in (g cm^-2 s^-1) using the number density, average particle velocity, and ...
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1answer
130 views
Dropping condition
Imagine opening a water tap in order to have a smooth and cylindrical outflow and then slowly decrease the flow by adjusting the knob. At a certain moment, the side profile of the flow will become ...
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1answer
88 views
What exactly heats a pool of water on a sunny day
On a sunny day an outdoor swimming pool will heat up fairly quickly. My question is, what is the exact mechanism for this and can we put numerical figures on it?
Given that water is clear and ...
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1answer
96 views
What happens at the interface between two universes with opposite thermodynamic arrows of time? [closed]
I was trying to think but cannot figure it out. For instance, if the interaction is small, for instance limited to a windows, the observers in each universe will see that the other goes in reverse. ...
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1answer
256 views
What is the importance of Joule's experiment?
I was reading about the experiment of Joule (Italian wiki page). I'm not sure how it's called in English, since there is only an Italian and French version. In any case, in the page it is stated that ...
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3answers
1k views
Pressure drop in a pipe due to cooling
I’m trying to better my understanding of the thermodynamics and momentum balance of pipe flows. The following situation, however, is making me scratch my head and I’ve found no help in my books.
...
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2answers
328 views
Can the work done between two non-equilibrium states be calculated?
The work done during a process between two equilibrium states can be described by thermodynamics. Even when process itself is out of equilibrium, the thermodynamic laws can still be used, though ...
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1answer
572 views
What temperature can you attain with a solar furnace?
A solar furnace is a device that concentrates the sun's light on a small point to heat it up to high temperature. One can imagine that in the limit of being completely surrounded by mirrors, your ...
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2answers
447 views
Experiments that measure the time a gas takes to reach equilibrium
If you take two ideal gases at different temperatures, and allow them to share energy through heat, they'll eventually reach a thermodynamic equilibrium state that has higher entropy than the ...
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1answer
183 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 ...
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1answer
105 views
Which came first, movement or heat?
According to my measly understanding of the universe, when particles hit one another, some of their kinetic energy is transformed into heat. But when we heat particles (for instance, putting a bucket ...
