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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Is thermodynamic free energy and potential energy the same thing?

The equation for free energy $F$ and potential energy $E_{pot}$ are: $$ F=U-TS \\ E_{pot} = E_{tot} -E_{kin} $$ But the temperature $T$ is proportional to the average kinetic energy of a system. So ...
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70 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 ...
2
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1answer
111 views

Relativity of simultaneity and the second law of thermodynamics? [closed]

Has the connection been noted between these two? I have been studying special relativity and in learning Minkowski diagrams I have noticed that as v approaches c, the relativity of simultaneity is so ...
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51 views

What to do when you are living in very cold environment? [closed]

I am on my way to a shimla, and as it is one of the coldest places of India. Previously I lived in a warm environment of southern india. What would be the correct way to live in a cold environment? I ...
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2answers
100 views

How to understand the indeterminate process in thermodynamics?

Consider a closed composite system with an internal movable adiabatic wall. If we release the piston, thermodynamics cannot determine the final equilibrium state (the temperature cannot be ...
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55 views

Building free energy directly from Lagrangian

Energy can be built from Lagrangian when considering the symmetry of time $(\frac{\partial L}{\partial t}=0)$. Free energy is a generalization of energy when the system exchanges heat with the ...
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2answers
127 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
62 views

Would it really require 44 car batteries to heat my pool? [closed]

After doing some research and math, I 'discovered' that it would take 44 (give or take 20%) car batteries to heat 1,000 gallon pool by 10 degrees. Is this right or am I missing something? It seems a ...
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100 views

Is there a relation between (non-) existence of magnetic monopoles and thermodynamics?

This question follows on previous work on connections between (other) areas of physics and thermodynamics as in here, here and even here. P. Dirac (an electrical engineer initially) was one of the ...
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31 views

Cooling - in vs out? [closed]

Suppose I have a 20x20x20 c"m plastic box where the top cover is open. On the top cover there is a fan ( 20x20 cm) which suppose to cool a cpu which is in the box . At the bottom there is a CPU ...
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1answer
31 views

Director field fluctuations in a liquid crystal in a magnetic field

If we consider the Frank elastic free energy in the equal constants limit (for more details, see here Chapter 4.1.) with an external magnetic field, we have $$ F = \frac{1}{2}\int \text{d}^3 r\left ( ...
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1answer
83 views

How to use specific heats and temperature change in a system to calculate mass?

In a system where multiple liquids and solids are mixed together with different specific heats at different initial temperatures, reaching an equilibrium temperature, how do all of these things relate ...
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1answer
115 views

Thermodynamics, chaperones : How to model polymer fragmentation

Living polymers are well described by equilibrium statistical physics. Now I would like to consider a case were living polymers undergo fragmentation due to chaperones. I can think of a kinetic ...
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0answers
72 views

Could CP violation be exploited to violate the second law?

I don't understand well CP-violation, but since it introduces a microscopic irreversible process, couldn't it be somehow exploited to decrease entropy? For instance, if we could somehow use it to bias ...
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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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56 views

What's the connection between being homogeneous in energy and having a proper time scale?

Towards the end of page 8 of this scientific paper, I have found the following sentence: ...given the fact that the system is homogeneous in energy, or equivalently, that it has no proper time ...
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3answers
189 views

work equals heat in isothermal process only for ideal gas?

Is it only for an ideal gas that the work equals negative the heat in an isothermal process or is this general for all kinds of systems? Or put differently, how do I know that for an ideal gas the ...
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47 views

Medical/Physics Question - Cut Off Finger Preservation

This question might require some knowledge of medical/tissue, but physicists seem to know everything, so figured I've give it a shot here ;) When people put cut off fingers they are told to put the ...
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100 views

Finding internal energy using equation of state

I have an equation of state as a function of $p$ (pressure), $T$ (temperature) and $V$ (volume) for a real gas and need to find an expression for the internal energy $U$. I know this is given by the ...
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88 views

Thermodynamics - convection current

please could someone help explain the mechanism of a convection current as I keep finding conflicting explanations. Is a convection current caused by differences in density or differences in pressure? ...
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493 views

Basic Thermodynamics: Quasistatic Adiabatic Process

I'm going through the exercises in a Thermodynamics book, just to revise and build my intuition. Right now, I'm working on: Show that for a quasistatic adiabatic process in a perfect gas, with ...
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49 views

What is the difference between thermodynamical equilibrium and statistical equilibrium?

I am trying to understand what is the different between thermodynamical equilibrium and statistical equilibrium, for example, between photons and electrons at the early universe. (I read through paper ...
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3answers
1k views

Improving our homemade hot tub design?

My brother and I built a wood burning, convection based, thermal circulating hot-tub. (With and oxyacetylene torch, lots of 1.5" pipe, a brake drum, and a thirty year old jacuzzi). Our design is ...
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50 views

What mechanisms require the use of different polarities in DC welding?

In gas metal arc welding, an electric arc forms between the work piece and a consumable wire, heating the work piece and also melting the tip of this consumable wire, which is continually fed into the ...
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66 views

Time needed to heat water in a pot [closed]

I have a pot with water of mass $m$ and it is heated by a stove element of temperature $T_E$ and with a surface area of $A$. The water starts at temperature $T_W > 0^\circ\, C$. How ...
2
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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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47 views

What are the physics challenges of rain farming [closed]

Rain farming is an engineering concept, employing the technology of industrial cooling towers, to deliver vast amounts of water to the lower levels of the troposphere as warm moist air. This question ...
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128 views

Second derivative of vapor pressure from a cubic equation of state

It is quite easy to compute the first derivative of vapor pressure with respect to temperature from a cubic equation of state at least at the critical point since there is a continuity with the ...
2
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1answer
112 views

Entropy with infinite baths

I'm struggling with the following problem: (Stephen J. Blundell, Concepts in Thermal Physics S. 154 Problem 14.5): A block of lead of heat capacity 1kJ/K is cooled from 200K to 100K in two ...
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126 views

Trace of the number operator in second quantization

I would like to find the helmholtz free energy of a system $F=-T ln(Tr[e^{\frac{-H}{T}}])$ namely a bcs superconductor (using Annett's notation) $H=\sum E_k (b_{k\uparrow}^\dagger ...
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26 views

Can I usefully interpret a non-unital completely positive (CP) map as a cooling process?

Non-unital completely positive (CP) maps take a maximally mixed quantum state (aka a normalized identity matrix aka an infinite temperature state) and map it to something else. This necessarily ...
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269 views

Theoretical or experimental violations of the 2nd Law of Thermodynamics? [closed]

Theoretical challenges to the 2nd Law? What are some the theoretical challenges to the 2nd Law? (cf. Čápek, Vladislav, and Daniel P. Sheehan. Challenges to the Second Law of Thermodynamics: Theory ...
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206 views

What limits the mass transfer from a boiler to a condenser in a sealed vessel?

If we set up an evacuated vessel where we keep one end at a higher temperature than the other, and then introduce a liquid at the warm end, it will evaporate and condense at the cooler end. If we trap ...
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76 views

commutator to entropy in an uncertainty relationship?

Question: Does there exist a commutator to entropy in an uncertainty relationship? Similar Energy and time for instance.
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112 views

Heat equation with Neumann boundary conditions

I would like to explore some ideas with different geometries exchanging energy mainly by radiation. This means solving Laplace equation for the steady state. However the boundary conditions are always ...
2
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63 views

Is there a source that provides data for the temperature coefficient of resistivity at different temperatures?

I'm looking for a source where I can find the temperature coefficient of resistivity at different temperatures for pure metals. Tables are everywhere for 20$\,^{\circ}$C, but I'm having difficulties ...
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51 views

What's the domain of usability of these two expressions for entropy

$$dS=\frac{dQ}{T}$$ $$S=k\ln \Omega$$ What assumptions are being made about the system/process that allow for using those expressions?
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88 views

Why does the water diffuse at right angles in my coffee? [closed]

I purchase an espresso shot each morning at my local coffee shop, and I usually water it down slightly to take the edge off as well as to cool it. Recently, I have noticed that when I pour the cold ...
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108 views

How long would it take for a container in vacuum to leak half of its air? [closed]

Let's say I know the size of the container, size of the hole the air leaks through, pressure the air is under and temperature of the air if that helps anything. Is it possible to calculate this only ...
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87 views

Can one get clear ice crystals from a dirty suspension?

Euteictic freeze crystallization is a method where an electrolytic solution is cooled and separated into a stream of (relativly) clean, pure ice and a salty brine. I know anectdotally of wine ...
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2answers
3k views

What is the effect of an increase in pressure on latent heat of vaporization?

What is latent heat of vaporization ($L_v$) in the first place? Wikipedia seems to indicate that it is the energy used in overcoming intermolecular interactions, without taking into account at all any ...
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114 views

Calculate how hot PLA will become

I am trying to attach the shaft of a brass heating tip to a PLA component. My problem is that the tip will have to reach a temperature of about 200°C and the PLA can only handle a temperature of about ...
2
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1answer
353 views

What defines the adiabatic flame temperature?

What defines the adiabatic flame temperature? In a case I have to solve, I need to describe the combustion of natural gas (Groningen natural gas, to be specific). However, I am having some problems ...
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2answers
212 views

Does the black body emit more than any other type of body?

I found this on Wikipedia article on black bodies: A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The ...
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46 views

Interface condition for heat exchange

I would like to compute the heat distribution of a piece of metal with some surrounding material. The heat is assumed to propagate by diffusion, so inside the metal piece and also on the outside, the ...
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120 views

Will humid air mitigate airborn dust due to neutralization of static electricity?

I have came to understand that humid air will help prevent electrostatic forces that can propel dust and cause it to cling to surfaces. My first question: is this above statement true? If the answer ...
2
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1answer
261 views

The definition of entropy

As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only ...
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65 views

In a non-degenerate plasma, why are e-e collision negligible compared to e-ion for thermal conduction?

I'm trying to make some order of magnitude estimates of heat transfer in stars - to better understand 1) why conduction is said to be negligible (for non-degenerate matter) and 2) when convection ...
2
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1answer
601 views

Physics-based derivation of the formula for entropy [duplicate]

Possible Duplicate: Proof of $S=-\sum p\ln p$? I am looking for a derivation of the formula $$S~=~-\Sigma_ip_i \log (p_i).$$ for entropy, from first principles. I only wish to assume the ...
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2answers
320 views

Convergance of a system to Boltzmann distribution

Consider a system with finite-dimension state X and energy E(X), with dynamics which follow the Langevin equation $\frac{dX}{dt}=-\nabla_X{E(X)}+\eta(t)$ where $\eta$ is white noise ...