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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Entropy change at varying volumes

I have two questions both related to each other: 1.What is the effect of change in volume (whether increasing or decreasing), of a system, under isothermal conditions? How does this change in ...
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2answers
35 views

Clausius statement of 2nd Law

I'm slightly messed up with Clausius statement of 2nd Law. I've seen at least two versions, which seem to be conceptually different. a) It is impossible to transfer heat from a colder body to a ...
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32 views

Robin boundary conditions for the heat equation

Consider a 3D channel with fluid or gas with walls $\Gamma_1$, inflow part $\Gamma_2$ and outflow part $\Gamma_3$. The temperature is described by the heat equation: $$ \frac{\partial T}{\partial t} ...
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1answer
33 views

Problem Boltzmann distribution [closed]

I am trying to solve a problem about boltzmann distribution. If(A)=0.74 Uf(V)=0.037 Ia(A)=0.130 I have to find ...
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22 views

Boltzmann Distribution [duplicate]

I am trying to solve a problem about boltzmann distribution. If(A)=0.74 Uf(V)=0.037 Ia(A)=0.130 I have to find ...
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2answers
49 views

Only differences in chemical potential have physical meaning?

Is the statement in the title true? Does the chemical potential of a single pure substance that does not undergo any chemical reactions or phase changes have any physical meaning?
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23 views

maximun work in a reversible process

I often read maximum work done is by a reversible process. Shouldnt the more appropriate sensence should be maximum work done per unit of heat is maximum in a reversible process. ?
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36 views

Johnson-Nyquist noise for resistive element with temperature gradient

In Nyquist's 1928 paper, Thermal agitation of electric charge in conductors, the voltage noise for a resistor is derived assuming a circuit in thermal equilibrium and one temperature. How does the ...
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1answer
53 views

Energy without temperature

If you know the entropy $S$ of your system. Is there a general way to calculate the internal energy $U$ of your system? So the entropy $S$ is the only thing I know of my system. I have no information ...
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2answers
3k views

Why would the lack of air in a mine in an asteroid prevent you from flooding it?

In Isaac Asimov's I, Robot novel, two scientists stationed in an asteroid where mining activities are performed say "We could flood the mines, if this weren't an airless asteroid" when considering ...
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1answer
35 views

What is the overall rate of heat conduction through two pipes of different dimensions if the thermal conductivity is not constant?

I am trying to work out how I would find the rate of heat transfer through two pipes made of the same material that are joined at their ends but which have different cross-sectional areas and lengths. ...
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32 views

What does negative absolute temperature mean? [duplicate]

I always understood that the concept of absolute temperature stems from the third law of thermodynamics and that the lowest theoretical possible temperature is zero degrees Kelvin. However, ...
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40 views

Why can thermal shocks damage/break materials?

When an object is heated a lot and then brutally cooled down or vice-versa, it can crack or even break spectacularly. What happens inside that makes it do that? Is it only because the hot core swells ...
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34 views

Answer to: Is a suit that hides a soldier's heat signature fundamentally possible? [closed]

I'm new so I'm unable to post an answer to this question: Is a suit that hides a soldier's heat signature fundamentally possible? But I am a Physicist. And yes it is. The simplest answer that I ...
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1answer
65 views

Why doesn't a Brownian ratchet provide free energy?

A Brownian ratchet is described here at Wikipedia. The "why it fails" section reads: Feynman demonstrated that if the entire device is at the same temperature, the ratchet will not rotate ...
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14 views

final state when Saturated liquid-vapour mixture contained in a rigid tank is heated

I have this question: Determine the final state when a 2 kg of Saturated liquid-vapour mixture at 50 °C contained in a rigid tank is heated so that the it reaches a single phase for each of the case ...
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1answer
32 views

Make a circuit so that it heats water as rapidly as possible

To do this I understand that we need to create the greatest power. What I don't understand is why would we need to use a parallel circuit instead of a series circuit to create the greater power?
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1answer
32 views

Does Nucleation Occur during Phase Equilibrium?

I understand that during phase transition nucleation must occur. I'm wondering, once phase equilibrium is established, does nucleation still occur? For instance, in liquid-vapour equilibrium, does ...
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1answer
38 views

Confusion about the Definition of Boiling Point

From the description of boiling here: Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the ...
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0answers
29 views

How does Brake specific fuel consumption vary with Brake mean effective pressure?

I'm aware that there is a certain relationship between brake specific fuel consumption (BSFC) and brake mean effective pressure (BMEP), but I am wondering if someone could explain how each varies with ...
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6answers
3k views

Is a suit that hides a soldier's heat signature fundamentally possible?

I recently played "Crysis", a game where the protagonist wears a suit that allows the player to hide both himself and his heat signature. Then I watched Iron Man 3, where a kid suggests that Tony ...
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0answers
22 views

Trying to calculate the length of a tube to heat Ar gas

If one were trying to heat Argon gas from ambient (~20C) through a mild steel tube of some diameter 'd' how long would it need to be? Additional unknown includes flow rate of Ar gas so some general ...
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1answer
88 views

Why do vapour cones form around jet fighters?

Apparently this phenomenon has nothing to do with jets breaking the sound barrier and has something to do with the Prandtl-Glauert singularity as described on Wikipedia. But, the Wikipedia article ...
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19 views

How do we compute the volumetric efficiency of an engine which is based on forced induction?

The volumetric efficiency of a naturally aspirated engine is computed by: $$n= \frac{V_1}{V_2}$$ With n: volumetric efficiency $V_1$: actual volume of air drawn $V_2$: volume swept by piston ...
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30 views

Two Limits in Thermodynamics - Reducing Driving Force and Increasing Resistance

I just wanted to clarify what is probably a very obvious idea. Suppose I'm holding a a piston separating two containers at different pressures. If I release the piston, it will naturally move, ...
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1answer
20 views

Latent heat of solidification

What is the heat release mechanism involved in solidification from liquid phase? Is the energy transferred to nucleation centres?
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1answer
34 views

Evaporation of water at room temperature

Could anybody refer me to some literature (textbooks or research, although preferably textbooks!) dedicated to explaining quantitatively the phenomenon of evaporation of fluids? I understand that it's ...
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1answer
31 views

Schwabl states that a change in external parameters cannot increase entropy. If so, how can an adiabatic process be irreversible?

I am working my way through trying to understand statistical physics, and this particular, apparent inconsistency has had me stuck for days. Any help or advice would be hugely appreciated. I was ...
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2answers
63 views

Explanation for negative specific heat capacities in stars?

I've just found out that a negative specific heat capacity is possible. But I have been trying to find an explanation for this with no success. Negative heat capacity would mean that when a system ...
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0answers
51 views

Does entropy increases due to gravity? [closed]

Imagine travelling to the surface of a neutron star where the very intense gravity would make you weigh 140 trillion times more than we do on earth. It's enough to significantly raise the entropy of ...
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4answers
152 views

What is the actual energy content of the Sun?

Beside the energy released by nuclear fusion in the core, the Sun is a hot plasma of hydrogen and helium ranging from thousands to million of degrees. So how does that translate into energy ? I have ...
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2answers
133 views

Why can we say that $\bar{d}Q=TdS$?

When we introduce entropy we do this by saying that: $$\bar{d}Q=TdS.$$ Now I was wondering why this should be true? I know that by looking at a Carnot cycle, we do get this relation for reversible ...
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1answer
35 views

Compute convective heat transfer coefficient for a condensing steam

I have a question about convective heat transfer coefficients. I am trying to figure out how much steam I can condense in this specific heat exchanger. Steam at 9 MPa is condensed in a 1 shell pass, ...
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2answers
39 views

How can we tell if a molecule is in thermodynamic equilibrium from scattering data?

We have a molecule that is emitting/absorbing photons. We know the Hamiltonian and that there are several levels. We count the emitted photons at different angles and frequencies. We can also do ...
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1answer
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Why charge is an extensive property [duplicate]

While reading examples of extensive properties, I cam across electric charge. Can someone please explain to me why electric charge is considered to be an extensive property? We know that extensive ...
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25 views

joule-thomson effect and linde process

According to the j-t effect the decrease in the temperature is a result of the work done by molecule to expand thus increasing their PE and decreasing their KE, but in the linde process the next step ...
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0answers
16 views

Can the effectiveness of a heat sink be increased with surface texturing?

Some supercapacitors use chemical etching to increase their surface area by several orders of magnitude. Could a similar process be used on a heat sink to increase its surface area and thus its ...
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0answers
17 views

Recommend books on thermodynamics [duplicate]

I want to take on thermo I will be analysing boilers, gas cycles ,ic engines etc. I want to Analyse all of these by using the basic laws gof thermo on my own (if i could) .I have cengel boles book and ...
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2answers
47 views

How much entropy is produced in evaporating water due to irreversible evaporation towards equilibrium (humidity=100%)?

$dS=dH/T_{boil}$ for the increase in entropy by changing a phase at saturation ($T=373\text K$ for $p=1\text {atm}$ for water). However, water also obviously evaporates below boiling point when ...
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1answer
74 views

Calculating Boltzmann constant using semiconductor

My task from the latest laboratory exercise in physics is to calculate Boltzmann constant from known temperature, current and voltage. We were given this circuit: By changing the resistor value, I ...
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18 views

Thermal resistance of an aluminium plate to ambient?

I have heaters mounted on an aluminium plate inside an enclosure, and I would like to know what the temperature of the plate will be at thermal equilibrium for a given heating power. For this I need ...
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1answer
23 views

Work done in adiabatic reversible process

I was solving a problem on turbine.the steam works on turbine adiabatic reversibly .Is change in enthalpy or is it change in internal energy which equal this work?
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799 views

Is a black body sphere inside a black body shell hotter than the shell?

I am missing something very basic here. Let us assume the shell is at a fixed temperature T by a power generator. The sphere inside will radiate the same power it absorbs. The power radiated by the ...
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2answers
76 views

How stable are Benard Cells when the thermal gradient begins decreasing?

I've found lots of information on the formation of Benard Cells and convection currents but very little information about what happens to the self-organized structures when the energy gradient being ...
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3answers
70 views

Can Thermal Energy be converted into usable energy?

I'm going to go out on a limb and ask a question that will probably be a bit humiliating: Can Thermal Energy be converted into usable energy? I've been reading about conservation of energy, and I know ...
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1answer
39 views

Freezing or melting Brine

In the freezing of brine, is it possible to do it at a rater or in such a way that the water only freezes or the ice is somehow isolated? Or conversely is this possible in the melting of brine-ice?
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0answers
46 views

Euler Equation Arbitrary Quantities

I have a question about the Euler equation. For some state I can write down: $$ U = TS - pV + \mu N$$ In this equation $T$, $p$, $V$, and $N$ are directly measurable so they have fixed values. ...
3
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1answer
78 views

How do door-less refrigerators keep cool air inside?

I got curious when I saw a door-less refrigerator for the first time. It was in a shop and I couldn't control myself so I began to look around to see how they work but I couldn't figure it out. They ...
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1answer
45 views

Question Regarding Nucleation in Phase Change

When liquid turns into solid a nucleus is required. Is the same requirement present for solid-liquid (melting)? Do condensation also require nucleation sites like in freezing? When I look at ...
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1answer
23 views

How can I compute heat retention of a heated ceramic floor?

The U.S. department of energy suggests electric radiant floor heat can be cost effective if the floor is preheated during off peak electricity hours if installed within an appropriately massive ...