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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21 views

Emulating changes in building temperature

I need to emulate what happens to the temperature in a building when turning the heating on and off, for a kind of computer simulation. I don't even know where to start, so I hope you can help me out. ...
-3
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1answer
80 views

Can someone explain about M-theory? [on hold]

Can someone explain about M-theory? I am very new to M-theory and string theory. I am very through with classical physics and little bits of quantum mechanics. Will you be able to explain why ...
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1answer
152 views

What causes a heat generating source to stabilize at a certain temperature? (Answered by myself, I think)

For example, we out a heat sink on a microprocessor to keep it cooler. I understand that if we run 100 watts of electricity through the microprocessor, it will generate 100 watts of heat, or 100 ...
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4answers
46 views

Does work done require interaction between system and surrounding?

There's no work done for a person climbing upstairs because the energy is converted to PE within system only. The person is the system. How true is the above statement?
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1answer
48 views

Is the MaxEnt “interpretation” of statistical mechanics the current mainstream approach?

I've only recently started studying statistical mechanics and I'm quite confused with the MaxEnt and anti-MaxEnt ideas. I'm looking for a concise answer, if it is possible, not really a description ...
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0answers
25 views

What is the pressure of a charged gas?

I have $N$ ${\rm H}^+$ gas molecules in a sealed, electrically insulated container. What equation can I use to accurately calculate the pressure of the gas? It seems to me that $PV = nRT$ will not ...
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4answers
131 views

Does it matter which blanket I take below and which one above when I cover myself with the two? [closed]

If I take two blankets together, one is more insulating and the other less insulating, to cover myself, does it matter which one I take below and which one above? Will there be the same amount of heat ...
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1answer
28 views

Why the air is more compressed near to the ground

I'm studying the adiabatic effect of the air on the atmosphere but i can't understand why the compression near to the ground is higher, is something relate to the higher pressure caused by the earth ...
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0answers
8 views

Range of thermocouples

Why do thermocouples have a restricted range of temperature that can measure, say for example some go from –200 °C to +268 °C, what makes them to be useless below or above?, I know above may become ...
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1answer
2k 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: $\alpha_s = 0.83$ ...
2
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0answers
47 views

Flow between two infinite plates [on hold]

I recently got set this problem and I was wondering if anyone would be able to give me some hints/intuition on how to solve it. Thanks. An incompressible thermal conducting fluid is contained between ...
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1answer
2k views

Carnot efficiency, coefficient of performance for a refrigerator

I was reading that a new type of refrigerator might reach a coefficient of performance (COP) of 10. This seems quite the achievement and the authors state that their approach might achieve a Carnot ...
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1answer
74 views
+50

What causes a eutectic point?

What causes the melting point depression known as a eutectic point? The temperature depression of a eutectic point can be calculated from the enthaplies and entropies of fusion of the two ...
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1answer
26 views

How to reduce cooling time of hot aluminum casting / block?

I am doing project on "reduction of cooling time of hot Aluminium casting/block". Aluminum casting / block temperature is 250degree C (532 K), size diameter 600mm x 150mm and weight 25kg. In order ...
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2answers
89 views

first law of thermodynamics change in internal energy

Change in state {for example from liquid to gas} is an isothermal process but the change in internal energy is not zero in this process isn't this contradictory?
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0answers
24 views

entropy balance equation in thermodynamics [on hold]

can any body help me to prove the following entropy balance equation. \begin{equation} T \frac{ds}{dt}=- div \mathbf{q} \end{equation} where $T$ is absolute temperature and $s$ is entropy $\mathbf{q}$ ...
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3answers
97 views

How does pressurized gas constantly push?

If a gas, such as hydrogen, is pressurized into an air tight container, a force in terms of pascals (or whatever unit you want to use) is exerted, correct? That is what pushes against every surface ...
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1answer
68 views
+50

Non-extensivity in a few body system

Thermodynamics finds application in many areas of physics, many of them sharing the feature of fluid-like or many-body like behavior. However, small systems or few body systems have been studied too ...
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1answer
38 views

Entropy reversal in magnets

Entropy is an irreversible phenomenon without any energy supplied to reverse it. I was reading about paramagnetic substances and how dipoles align inside them on application of magnetic field. My ...
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1answer
40 views

Fermi Level: chemical potential vs. electrochemical potential

In solid-state physics it is understood that the Fermi-Level is the electrochemical potential. The Fermi-Level is defined to: However, in thermodynamics this formula is referred to as the ...
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1answer
310 views

Does a thermally expanding torus experience internal stress?

I'm trying to learn continuum mechanics and thermo-mechanics. As we know, heating an object increases the mean atomic distance $a_0$ of the atoms in a rigid body. Let's assume it is a linear elastic ...
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1answer
25 views

Thermal expansion of metal spring

I am attempting to figure out why a laser layout tool I have is drifting over time. It was designed with a small adjustment mechanism that relies on a spring to apply pressure to a fulcrum that ...
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3answers
178 views

Heat flow in a hollow cylinder

Consider a hollow cylinder of different outer radius and inner radius and two different temperatures are maintained at the outer and inner surfaces such that inner temperature is higher. Because of ...
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1answer
51 views

What ice pack formula can hold the largest energy difference?

I recently bought some Freez Pak brand ice packs. The label advertises: "Colder Than Ice". I realize now that it's just a stupid marketing claim, but at first, it got me wondering if they had some ...
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0answers
30 views

change in free energy at natural state

I am styding a book on thermoelasticity, here free energy $f(e_{ij},T)$ is expended into taylor series in the vicinity of the natural state (when $e_{ij}=0$,$T=T_0$) and entropy s such that ...
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2answers
82 views

Can kinetic energy in atoms result in emission of all types of EM radiation?

I already know the fact that when solid objects heat up, they emit thermal energy which is also known as infrared radiation. However, if the atoms in that solid were to begin gaining more or less ...
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1answer
42 views

Is the $\mu VE$ ensemble possible to formulate?

I have recently learned about ensembles in statistical mechanics, and I've seen multiple applications and interpretations of the EVN (microcanonical), TVN (canonical), $\mu$VT (grand canonical) and ...
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0answers
20 views

Adiabatic Surfaces in thermodynamics

In some lecture notes on thermodynamics there is a discussion as to whether by assuming the first law of thermodynamics alone we can prove the existence of a adiabatic surface in three dimensions. To ...
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0answers
13 views

What is the relation between scattering amplitudes, fluctuations, response functions and correlations in macroscopic equilibrium systems?

In Kardar's book Statistical Physics of Fields, he mentions that that correlations at different length scales can be measured by scattering. If its electric correlations, you would scatter light and ...
2
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1answer
122 views

Does a cooler, submerged in water, keep beer colder, longer?

Looking around the web, I see some submerged bucket-like things, without insulation, and some floating coolers, where the actual cooler is not submerged. Given that your water temperature is lower ...
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0answers
44 views

How to make two equations dimensionless? [on hold]

I recently got set this problem and am having trouble scaling the resulting equations. Any help would be appreciated. An incompressible thermal conducting fluid is contained between two infinite ...
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0answers
16 views

Application of surface tension in thermodynamics [on hold]

I'm writing a paper about surface tension, and have problems with finding literature about application of surface tension in measuring some thermodynamics quantities. Can you help me? Thank you
0
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1answer
30 views

Why is Cv used in the adiabatic expansion of Carnot Cycle to calculate internal energy

When I took this class years ago, I simply accepted it as fact. However, now that I'm teaching it, the following bugs me....a lot. Why do they use Cv to describe the change of internal energy during ...
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1answer
37 views

Open systems (Conservation of Energy): is a temperature change possible if a tube is thermally isolated?

Full question: consider an perfectly thermally isolated cylinder. Water is flowing through this cylinder from the entry to the exit. Is it possible for the water flowing through the exit to have a ...
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2answers
42 views

Removal of heat from a closed system using electricity

I was thinking this morning about how heat could be removed from a system in such a way that it is stored for future use. My ideas are a form of thermo-electric system that converts heat into ...
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2answers
424 views

Definition of stress at the microscale

Take, for simplicity, a Lennard-Jones fluid below the critical temperature, which is to say that there is a phase separation into fluid and gas and thus an interface is formed. The macroscale picture ...
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2answers
55 views

If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
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3answers
190 views

Thermo - Plotting constant pressure and temperature on a Pv and Ts diagram

I was just curious what the saturation curve for water (plotting pressure versus specific volume) would look like if you drew both a line of constant pressure as well as constant temperature. I am ...
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3answers
6k views

How much energy in form of heat does a human body emit?

How much energy in form of heat does a human body emit at rest level?
3
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1answer
111 views

Do magnetic fields cause ionisation of gases?

I am doing my final year engineering project on Magnetic Field Assisted Combustion and was curious to see what people thought about it. Companies sell rare earth magnetic arrangements to be attached ...
6
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0answers
189 views

Does the radius of the Universe correspond to its total entropy?

I heard a claim that due to holographic principle, the surface area of the cosmic horizon corresponds to the universe's total entropy. As such the initial state had zero surface area and later ...
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3answers
73 views

What is the relationship between entropy and work? [on hold]

Can someone explain the relationship between entropy and work? I've been reading my textbook and looking online but I feel like I'm missing something. Can someone explain it in layman's terms :)
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1answer
93 views
+50

Pressure and Temperature in a few-body system

This question is very much related to this other one, and the introduction is the same. If we want to define intensive properties for few-body systems it is not straightforward. I am referring ...
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1answer
99 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. ...
2
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3answers
64 views

Questions on Carnot's theorem

This article on Carnot's theorem states that All heat engines between two heat reservoirs are less efficient than a Carnot heat engine operating between the same reservoirs. However, it only ...
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1answer
92 views

What is the relationship between liquid-gas expansion pressure and surface area to volume ratio?

If a set volume of liquid is heated above its boiling point, how does the pressure that that volume of gas generates relate to the surface area of the medium in which it is enclosed in. For ...
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3answers
379 views

How do greenhouse gases trap heat?

I am looking for a molecular-level understanding of the greenhouse effect. What is it about the carbon-dioxide molecule (and methane, and water, etc) that is different from other gasses ...
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1answer
1k views

Comparison between isobaric, isothermal and adiabatic expansion

Please check if my understandings of these terms are right because they are a bit confusing to me. For all three types of expansions, a change in volume means work is done by the system to the ...
0
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1answer
19 views

Adiabatic cooling in a closed system

Please forgive me ahead of time if something I say isn't correct, I've just started to read about thermodynamics ever since I developed a fascination for the anti-griddle (by the way does anyone know ...
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2answers
52 views

Is heat supposed to bounce on an insulator or slowly go through it?

I have a simple flat electric heater at home, fixed on a wall. 50% of the energy is absorbed by the wall !! What would happen if I put some isolation material between the heater and the wall ? Would ...