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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General relation between power density of any engine and dissiapation rate and temperature

Many years ago ( before my university studies ) I read that renewable resources are fundamentally limited by laws of thermodynamics to produce energy very slowly (low specific power or power density) ...
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45 views

Violently shaking object

Would violently shaking something cause a temperature change? For example, if a container of water was shook violently enough; would it be possible to make it boil?
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1k views

What happens to a body, initially at 300K, kept in isolated space? Will it's temperature drop to 0k?

With regards to Thermal Radiation, given a stable body initially at 300 Kelvin placed in isolation, after continuous Thermal Radiation will it's temperature gradually reduce to 0 kelvin ...
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18 views

What will be the final temperature of water when heating at a a rate 10J/s?

If I supply heat of rate 10W to water of mass 250g and initial temperature of water is 29 degC then what will be the final temperature of water when steady state is reached. **Water is heating in open ...
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18 views

COP of Stirling engine

If we consider the theoretical maximum of COP for a heat pump, we will see that it is possible to make it infinite by approaching the temperatures of each source to each other. Yet, in a real engine ...
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2answers
55 views

Using Maxwell's demon alongside quantum mechanics to contradict 2nd law of thermodynamics

Suppose we have a steady state universe with a gas chamber resembling that of Maxwell's demon that is used to power this hypothetical heat engine as molecules transfer to their respectable sides based ...
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22 views

Water as heat source in a heat pump

Consider we have water flowing in a pipe, which is working as a hot source for a heat pump. We are able to know the temperature of the water in both ends of the pipe, yet we don't have information ...
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29 views

In the Leidenfrost effect why dropplets of water can travel uphill?

The Leidenfrost effect is a phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer keeping that liquid from ...
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25 views

The potential profile of two batteries in series

I would like to know the potential profile in two batteries in series, like the battery in the attached image.
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1answer
37 views

Can sound frequency create more ideal conditions for fire?

You may have seen the recent story of a device that engineers claim can extinguish flames using sound frequency. An older article loosely explains the theory behind how this works: Sound travels ...
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44 views

Thermodynamics and Axioms and the like

Can thermodynamics and any important related information be expressed as a set of axioms with various 'rules of manipulation'?
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82 views

Why is $\int_{s} \mathbf{h}\cdot \mathbf{n} da = - \dfrac{dQ}{dt}$ & not $\int_{s} \mathbf{h} \cdot\mathbf{n} da = - \dfrac{dQ}{dt} .{dt}$?

I was reading the Lectures of Feynman about surface integral where a situation in which heat is conserved has been dealt. Let there be $Q$ heat energy present inside a body. Now, if there is net heat ...
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24 views

If it is sunny and 25 degrees [on hold]

If it is sunny and 25 degrees outside, What is the temperature inside a van? Will food stay cold?
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27 views

why the direction opposite to the heat energy of sound energy? [on hold]

The experimental studies of thermoacoustic cooler, shin-ichi sakamoto, the direction opposite to the heat energy of sound energy.
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46 views

Why temperature of liquid drops after spraying thru a nozzle?

We have tested in our lab as mentioned in the picture. We connected hot water at 130degree F at 40Psig to a nozzle(bottle sprayer).we measured the temperature differences inside tank and after ...
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1answer
29 views

Heat diffusion equation with time dependent specific heat capacity

What is the correct form of the heat diffusion equation in 1D if we take into account the temperature dependency of specific heat capacity? $$ \rho\frac{d(cT)}{dt} = ...
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13 views

Heat Engines and Thermal Pumps [on hold]

A steam engine is to have its thermal efficiency improved from 8.00% to 10.0% while continuing to produce 4500J of useful work each cycle. a) Does the ratio if the heat increase, remain the same, or ...
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11 views

Model for temperature and pressure inside a heated vessel with liquid being pumped into it

I am working on a problem where a pressure vessel is pressurized by heating the vessel to a high temperature and then injecting a liquid into the vessel that boils and hence increases the pressure in ...
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19 views

Timescales for isothermal processes

My understanding is that processes in ideal gases need to take place over relatively long timescales to be idealised as "isothermal" such that the gas temperature can be assumed not to change. For ...
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30 views

Landau theory of phase transation

In his article http://www.ujp.bitp.kiev.ua/files/journals/53/si/53SI08p.pdf, Landau defines probability distribution $\rho$ which is related to symmetry of crystal. If crystal has certain symmetry ...
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28 views

How to calculate liquid pressure regardless of the gravity?

Assume we have a balloon in a tank filled with a liquid , without any gravitational forces: We just know the Temperature, V0 and V1 I want to calculate the pressure exerted from the liquid on the ...
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1answer
23 views

Turning ice into water in a calorimeter with steam? [on hold]

So there's this question I've been having trouble with here it is: A 0.050-kg copper calorimeter contains 0.050-kg of ice at -10°C. What mass of steam at 100.0°C is required to convert the ice to ...
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1k views

What would it be like “inside” a star?

This question was triggered by a discussion regarding the computer game Elite: Dangerous, where spaceships routinely operate in close proximity to stars (two or three light seconds away), at which ...
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26 views

Pressure change with adiabatic compression problem [closed]

So, I have to solve this problem: 2 moles of a perfect gas are compressed from $p_1=10$kPa to an unknown pressure, $p_2$. Throughout the process the temperature changes from $T_1=273.15K$ to ...
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21 views

How does antarctica stay frozen? [migrated]

Antarctica is receiving heat from the Sun everyday, so how does it stay frozen? I have made some thoughts about the answer but unsure of whether it is correct I hope people here can clarify. The ...
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1answer
38 views

Why is the Specific Heat of Helium 36 times greater than Xenon?

Given that these are single atoms, why should the specific heat difference be so great? And more specifically, why does it take 36 times as much energy to raise the temperature of a given mass of ...
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11 views

first law of thermodynamics ATMOSPHERIC HEAT' [closed]

my system directly draws heat from the atmosphere and produces energy. my system according to the theory would provide energy continuosly. can anyone give me assisstance in solving my problem
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34 views

Which one will come to the room temp. faster? [closed]

Suppose there is a bottle of water at 10 degrees C and ice at -10 degrees C both in a room, where temperature is 0 degrees C. Which one will come faster near the room temperature?
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32 views

Which is a more effective cooling method?

Assume I have a refrigerator at 0C and I put a can of soda at the center of the refrigerator. The temperature inside the refrigerator will be increased to 5C after I put the soda in, but will go back ...
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1answer
37 views

When to use h = Cp∆T or u = Cv∆T

I'm getting myself confused on when to use h = cp∆T or u = cv∆T where cp is the specific ...
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8 views

Comparing work required at compressing gas & pumping liquid

In one of online lectures comparing Vapour compression cycles (conventional refrigerators) with Thermal compression cycles (absorption chillers) it was said that former required more 'high quality' ...
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33 views

Maxwell Relations in Thermodynamics - Specific Heat [closed]

I am not able to solve that question: Using Maxwell relations and the fact that $C_p = T \dfrac{\partial S}{\partial T}\Big|_p$ $C_V = T \dfrac{\partial S}{\partial T}\Big|_V$ Show that I can ...
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8 views

How do I calculate temperature diffusion in a gas contained in a heatsink?

To simplify the problem, consider a sphere with a diameter of $25\mathrm{mm}$ inside an infinite heatsink at $300\mathrm{K}$. At $t=0$ I instantaneously raise the temperature of the gas in the ...
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24 views

Is the diffusion coefficient time-dependent?

It is known that in the partial differential equation: $$u_t=au_{xx} $$ within the limits $0<x<1$ and $a>0$, the diffusion coefficient, arises in the mathematical modelling of a process of ...
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37 views

Is it possible to efficiently extract phonons from a lattice?

The population inversion generated in lasers occurs in multi-level atomic systems. As an example, the Nd:YAG energy diagram is shown below. The pump pushes the Nd ions up to the upper levels, and ...
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28 views

Convection and radiation heat transfer

It's been some years since my last physics exam and I really need a refreshment in this. I'm stuck in getting a rough estimation of heat exchange between 2 objects separeted by air: let's say object 1 ...
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2answers
33 views

Entropy change in an irreversible process between 2 equilibrium state

Calculating entropy change in an irreversible process between 2 states requires computing the change in entropy for any reversible process between the 2 same states, but why? If someone could provide ...
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1answer
152 views

Do some of the laws of Thermodynamics break down in Quantum Mechanics?

I do not know if this is a stupid question as i am not an expert in thermodynamics and certainly no expert in QM. So,we know that the laws of thermodynamics are laws based on statistics.thus require ...
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24 views

Can inefficitiencies of electrolysis be overcome using batteries charged by alternators? [closed]

We know that you cannot create a perpetual motion motor. But, what if you could produce a two stage motor. A battery that begin the electrolysis of water providing a combustion engine with burnable ...
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1answer
28 views

Spin correlation function identity

The correlation function G between two spins is usually defined as $$ G=\langle \sigma_a \sigma_b\rangle - \langle \sigma_a\rangle \langle\sigma_b\rangle $$ The $\sigma$ are the value of the spins ...
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43 views

How fast do I have to dry myself for a hot shower to heat my body?

I am not a physicist. I would like to know how fast do I have to dry myself after taking a hot shower to get more heat from the shower, than lost because the water on my skin increasing heat exchange ...
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17 views

Does the heat flow vector depend on the proximity of isotherms?

Suppose, there be two isotherms at varying temperatures. Heat energy will flow from higher temperature isotherm to the lower; thus we can assign vector to each point & it will tell about the rate ...
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32 views

Are there laws/equations regarding how a specific material heats up above ambient?

I'll preface this question by saying that I have limited knowledge of physics, especially in thermodynamics, so please bear with me. The goal I have an electrical resistor, like the one below (nice ...
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22 views

How is the Joule normalised?

Apologies if this question is a duplicate, I tried searching for this question both on Google and here, but was unable to find an answer. A Joule is defined in various ways, some of them being: ...
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Fuel Saved through different routes

Can you save fuel and if so how much in a diesel engine traveling from point A to point B? Mountaineous Terrain. Shorter dist. or longer one? please answer.
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1answer
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Rough/ballpark thermodynamics and black body temperature question

This is probobly pretty basic but I got into a debate with someone and the temperature of Titan came up, and I did some quick and dirty calculations - as follows. Titan is about 9.5 times as far from ...
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39 views

Can bulk modulus ever be negative? Can somebody illustrate with an example!

I was particularly confused when my teacher proved that $C_p > C_v$ for substances other than ideal gas for which the difference between the two is R . However the proof involved assuming that the ...
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20 views

What does these $\Delta \Delta G$ numbers signify? [migrated]

I was reading a paper and came across this table showing $ \Delta \Delta G$ numbers of different nucleotide sequences in DNA/RNA. I know that $\Delta G$ is free energy and $ \Delta \Delta G$ is ...
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38 views

Are reversible and irreversible processes frame dependent?

since it is all about time. If I have a look at an irreversible process from a frame where time runs really slow. is there a possibility of considering that process reversible from that frame?
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218 views

Why does the system move until equal temperatures are obtained?

In my college level thermodynamics class, the teacher gave us the example of a closed system which consisted of a box thermally insulated. A piston fully divides the box in two parts, and each is ...