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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Dry Ice Sublimation time, practical calculations

I would like to send a parcel to a family abroad with frozen (to the temperature of -18 ° C.) products.The products are small balls having a diameter of 4 cm. Balls are made from pizza dough. I'm ...
48
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3answers
5k views

Is it possible to start fire using moonlight?

You can start fire by focusing the sunlight using the magnifying glass. I searched the web whether you can do the same using moonlight. And found this and this - the first two in Google search ...
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1answer
30 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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2answers
154 views

What's the efficiency of real heat engines?

Real heat engines always have lower efficiency than the Carnot efficiency. I wonder how efficient real engines can be? Can their efficiency get anywhere near the Carnot-limit?
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1answer
22 views

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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0answers
13 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
11 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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1answer
290 views

How does Landauer's Principle apply in quantum (and generally reversible) computing

I understand that a reversible computer does not dissipate heat through the Landauer's principle whilst running - the memory state at all times is a bijective function of the state at any other time. ...
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1answer
864 views

Adiabatic expansion in van der Waals gas

Given a Van der Waals gas with state equation: $$\left( P+\frac{N^2 a}{V^2}\right)\left( V-Nb \right)=NkT,$$ show that the equation of an adiabatic process is: $$\left( ...
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1answer
61 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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4answers
1k views

Crash course in classical thermodynamics

I've been working on some projects lately where it would be very handy to know more about thermodynamics than I do, but sadly I never had a chance to take a proper thermodynamics course in college. ...
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16 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
28 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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2answers
721 views

What causes a Phase-Transition?

A phase transition occurs when for example, heat is applied continuously to a liquid and after a certain time it converts into a gas. How does this process work in detail? Is their a chain reaction ...
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0answers
29 views

Here is a question I am trying to solve. Sorry for the highlighting, it is not relevant [on hold]

Thermodynamics initial pression,= 5 bar final pression= 2 bar The steam expand adiabatically PV^(1.120)=C providen initial volume= 3.64x10^(-4metres cubes) diameter piston= 50 mm= 0.05 m a) ...
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0answers
16 views

Calculating entropy (heat exchange) [on hold]

This is a homework question. Suppose 30 gram of metal gallium melts at 36°C. The melting temperature is 29.9 °C and specific heat of fusion is 80.3 kJ/kg. Is the total change of entropy simply ΔS = ...
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1answer
37 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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3answers
1k views

How would you store heat?

Um .. naive question perhaps but if somebody wanted to store heat, how would they go about it? Can heat be stored? I'm told that decomposing kitchen waste in a closed vessel results in a rise in ...
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2answers
79 views

Contradiction on Entropy of the “universe” decreasing

I have hit what seems to be a contradiction concerning entropy. In my class, we measured the entropy change of photosynthesis which is obviously a non-spontaneous process. We used the formula, ...
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0answers
9 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
75 views

Which thermoelectric effect is better?

I am doing an experiment which requires the thermoelectric effect. I know about the Seebeck and the Peltier effects. Well, from what I have found till now on these topics is that they both can produce ...
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1answer
35 views

can I tune a magnetic field to conduct heat from a rotating object?

Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?
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2answers
125 views

Will a water-cooled system heat up a room less than an air-cooled system?

Recently - motivated by the recent heat where we live - an acquaintance argued that a water cooled computer will not heat up the room as much as an air cooled computer will. His reasoning was that the ...
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1answer
79 views

How to prove R value for insulation?

I ran some tests on different types of insulation. I heated water, and placed it into an insulated box. The temperature was recorded every minute, for the water, as well as the air. The insulation ...
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1answer
17 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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0answers
16 views

Work done by a turbine in a reversible adiabatic process

Why is the change in enthalpy equal to work done in this case. I believe the change in internal energy should be the answer.
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2answers
768 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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3answers
231 views

Distinguishable, Indistinguishable Paramagnetic Ideal Gas

In the canonical ensemble, the partition function for an ideal gas is given by: $$\frac{Z}{N!}$$ The factor $N!$ accounts for the indistinguishability of the particles of the ideal gas. What ...
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2answers
163 views

How much electricity can be produced by my thermoelectric generator?

I am using a thermoelectric cooler from a pc's heatsink to produce electricity. Its size is 30mm by 30mm. I will cool it on one side at -10 degree Celsius and the other at 24 degree Celsius. Can ...
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1answer
84 views

Conservation of energy when focusing black body radiation on another black body

This question about whether or not it is possible to focus black-body radiation to make something hotter than the radiation's source was answered mostly negative: the second law of thermodynamics ...
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0answers
9 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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5answers
2k views

Is it possible to focus the radiation from a black body to make something hotter than that black body?

My previous question wasn't specific enough. I'll try to be more specific. Let's imagine we have a hot body let's say 6000K hot that emits lots of thermal radiation. Let's assume 1kW of radiative ...
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3answers
54 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
33 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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40 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. ...
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1answer
39 views

Thermodynamics phase change question

why is specific volume of Saturated water greater at 1 MPA than at 0.1 MPA during the phase change process check out the T-V diagram here in the link. ...
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3answers
3k views

How does water help extinguish fire?

How does water extinguish fire? Heat energy from the fire is transferred to the water, isn't that how it works? How does water deprive oxygen and stop combustion? How is the specific heat of water ...
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0answers
12 views

SI Units for Isothermal Incompressibility and Specific heat capacity at constant volume

I am looking for the SI units of Isothermal Incompressibility and Specific heat capacity at constant volume. What I found was that Isothermal compression was measured in $\frac{m^2}{N}$ so I'm ...
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1answer
18 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 ...
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2answers
143 views

Self Stirring Boiling Liquid

A couple of weeks ago, a friend and I were brewing a new batch of beer. We boil our wort in a turkey fryer. Pretty standard setup for beginners. Anyway, our wort was getting pretty close to boiling ...
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1answer
46 views

'Mechanical equilibrium does not necessarily mean that the pressure is same at all points of the system' - why?

If there are variations in pressure or elastic stress within the system,parts of the system may move, or expand or contract. Eventually these motions,expansions or contractions will cease, and when ...
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1answer
41 views

Why does Air Pressure not Matter in Phase Equilibrium?

So long as we are in the ideal gas range, the presence of air does not affect the liquid/solid-vapour equilibrium in any way (such as equilibrium vapour pressure, melting point etc.). Is there a ...
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3answers
8k views

Why is air a poor conductor of heat?

Today, I was reading an article How Thermoses Work It goes on to explain all three processes of heat transfer: Conduction Radiation Convection In Convection, It states, If it weren't for ...
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1answer
59 views

Why wouldn't a room temperature superconductor violate the laws of physics?

I understand that the laws of physics (as we know them) cannot be violated, but what I would like to know is what I'm missing, because I know there is some explanation that I'm not accounting for. ...
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1answer
81 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
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0answers
35 views

Why are electric charge and magnetization extensive properties? [closed]

While reading about extensive properties examples I came across electric charge and magnetization. But I couldn't understand why are they extensive properties?
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0answers
94 views

Lennard-Jones induced pseudo-molecules

It can be shown that the Lennard-Jones potential - which describes the interaction between particles in non-ideal gases - gives rise to pseudo-molecules: after a triple "collision" of three ...
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0answers
18 views

relation between heat capacity at constant magnetic field and the heat capacity at constant magnetization [closed]

One of the exercises in Pathria, statistical mechanics asks us to prove, for any magnetizable material, $$C_H-C_M=-T\left(\frac{\partial H}{\partial T}\right)_M\left(\frac{\partial M}{\partial ...
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11 views

dynamic structure factor for nucleation

I know that using the peak position/moment of structure factor or may be by first zero or minimum of pair correlation function we can estimate the characteristic length scale in a phase separating ...
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0answers
13 views

Calculating entropy [duplicate]

Suppose 30 gram of metal Gallium melts at 36 °C. The specific heat of fusion is 80.3 kJ/kg and the melting temperature is 29.9 °C. Explain if the melting of the Gallium in this process is ...