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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Does the density of water ice (any form of water ice) near 0K exceed the density of water at 277.15K?

In a question brought up by my chemistry class, the most we have determined is that the stability of most forms of ice decreases as the temperature decreases. What does this loss of stability do to ...
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95 views

How to calculate electrical and thermal conductivity, enthalpy and density of plasma column in air for a series electric arc?

I am modeling an electric arc according to "Lowke's Simple theory of free burning arc". Its a very interesting theoretical arc model and I want to implement it in Matlab/Simulink. But here, the arc ...
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65 views

How to find specific volume of air beyond normal Psychrometric table

During a calculation of direct-heat dryer, I have ended up with following situation. Inlet temperature of solid TS1 = 35.5 oC Inlet temperature of air TG2 = 615.0 ...
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65 views

Was the impossibility of the second degree perpetuum mobile in the General Relativity ever proven?

Somewhere I've heard, that gravity often likes to work against the entropy. For example, the surprisingly low temperature of the black holes. Or see the gravitational separation of different elements ...
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39 views

Can I measure the volume of a locked room by pumping gas through keyhole and measuring its entropy?

Suppose that I have a locked room and a keyhole in the door and I want to measure the room's volume. Suppose also that I have some "magical" "artificial" inert gas A that doesn't interact with ...
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301 views

Why does specific heat increase with temperature?

Except for monoatomic molecules, specific heat increases with increase in temperature. Why?
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82 views

Is Isochoric compression or expansion possible?

Stirling cycle is made of two isothermal and two isochoric processes. Heat is added isothermally, expansion and compression takes place isochorically, as given by the book. How can a gas be ...
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41 views

Sign convention thermodynamics

Say a system is inside a volume $V$ with surface normal vector $n$ pointing out from the volume. Then there are force vector fields (nonconservative and conservative) depending on parameters external ...
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59 views

Efficiency of an Internal Combustion Engine

This question is about How correct are those comments on efficiecy of internal combustion(IC) engines which calcuate it using 2nd law of thermodynamics.The maximum efficiency of a heat engine can be ...
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26 views

Maxwell relations | U goes down pressure?

Differentiating Helmholtz function $ A = U - TS $ with respect to $V$ we get: $$ (\frac{\partial A}{\partial V})_{\scriptscriptstyle T} = (\frac{\partial U}{\partial V})_{\scriptscriptstyle T} ...
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27 views

When is strain rate constant?

I have started a tricky problem involving strain rates. To simplify it I was wondering if I can assume the strain rate is constant (and therefore that the shear stress is constant with distance above ...
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38 views

Reaction enthalpy-work relationship in a closed piston-cylinder assembly undergoing a chemical reaction

In an closed and insulated piston-cylinder assembly under constant pressure. From first law I should expect $-p(V_f-V_i) = U_f – U_i$ and thus $H_f = H_i$ and $h_f = h_i$. If an exothermic reaction ...
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47 views

Change in internal energy

One definition in my textbook states that total derivative of internal energy $dU$ has the form: $$dU = C_vdT +(\frac{\partial U}{\partial V})_{\scriptscriptstyle T}dV $$ Which I interpret this way: ...
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72 views

How accurate is the Callendar-Van Dusen equation?

... over 0 degC to 100 degC? The equation itself can be found here I can do a very accurate one point calibration of a 1/10 DIN PT100 sensor at 0 degC. If I use the equation to correct for non-linear ...
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64 views

How much sunlight would 'fit' through a fibre optic cable?

Say a parabolic mirror were used to focus the full sunlight spectrum into a single strand of optical fibre. Assuming ideal conditions (perfect reflecting surface, focal point smaller than diameter of ...
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42 views

Must irreversible heat transfer be quasistatic?

Suppose there is an isolated system composed of two subsystems $A$ and $B$ in thermal contact with each other, but mechanically and diffusively insulated from each other. The system starts off with a ...
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48 views

Does mixing violate conservation of energy?

If two fluids in an isolated system mix, the entropy of the system increases. The volume and the number of particles in the system, however, are constant. Thus $$dU=TdS+PdV-\mu dN=TdS>0$$ which ...
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47 views

How does a gas behave if i let it out of a pressurised canister?

So I am working on a problem where I need to know how a gas behaves if it is let out of a canister. My first approach yielded some result, but i can't seem to get all the way, although it seems to me ...
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27 views

debye Specific Heat lattice

my Question is related to a two dimensional quadratic lattice. In our exercise we should find the Debye-Frequency wich is define as integral equal to 3N.In this case i get confused because it is a ...
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59 views

Heat flow through a pipe

I have a pipe, in which a cooling medium flows through it. I would like to know the temperature of the cooling medium at different lengths of the pipe. Is there an equation to relate the length and ...
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34 views

Where do combustibles(gas etc.) fit into the first law?

The first law can be written as $dU=dW + dQ$. As I understand it $W$, work, is mechanical energy from winding up springs, things spinning, flying etc. It's kinetic and potential. As I understand it ...
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39 views

CMB and Gibbs free energy

I was doing my homework and I have a doubt. I proved that if I have the radiation energy density $$u = \frac{U}{V} $$ and $$P = \frac{1}{3}u $$ Then the Gibbs free energy is 0. But, how can I to ...
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49 views

Expansion of solids on heating

I read that when we heat a solid, it expands! Based on circumstances it can expand in area, length and volume! My question is , that do they expand to a certain extent or keep on expanding, if we ...
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33 views

Superconductors in a magnetic field — mixed phase

In my Stat Mech class we're learning about the phase transition between superconducting and non-superconducting metals in the presence of a magnetic field (Chapter 7, Kittel). I understand that the ...
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47 views

Does a fixed amount of gas have slighty more mass when at a higher temperature?

According to relativity, energy and mass are equivalent. Does this mean that the energy added to a fixed amount of gas when it is heated adds slightly to the mass of the gas? The difference would be ...
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100 views

Determine the amount of energy used for baking a cake

Let's suppose we have a room of temperature $T_0$ with an oven of volume $V$, both filled with air of density $\rho$ and specific heat $c$. We need to bake a cake in the temperature $T_1$. Thus we ...
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42 views

Filling an empty box with ambient air

A rigid box has a volume of $V_1$ and is thermally isolated so that it exchanges no heat with its environment. Initially the box is empty, and the air around it has a pressure of $P_0$ and a ...
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59 views

If time somehow went backwards would this violate one of the laws of thermodynamics?

If time somehow went backwards and all the physical events that had occurred in a sequence , would some of the events occurring 'backwards' or in the reverse order violate the principle of entropy or ...
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41 views

What do physicists mean with “classical critical behaviour”?

What do physicists mean with "classical critical behaviour"? As far as I am concerned it should be "power law behaviour" of some quantity close to the critical point but I ask here to be sure.
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119 views

Specific heat capacity for constant volume and constant pressure

I have seen in some exercises that the specific heat capacity for constant volume, $c_{vo}$ and the specific heat capacity for constant pressure, $c_{po}$ , where the $o$ indicates that we are ...
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27 views

What is the heated added and changes in internal energy? thermodynamics

A piston + cylinder initially contains 2 x 10-3 m3 of helium gas at the pressure of 1.01 x 105 Pa and with a temperature of 60'C. The gas is heated allowed to expand at a constant pressure until its ...
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13 views

Chemical potentials of SM particles at high temperatures

Recently I've heard the statement that chemical potentials of SM particles on $T > 1 \text{ GeV}$ are very small, so that Gibbs potential reduces to free energy. How to prove this statement? Does ...
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37 views

Internal energy of a molecule and bonding strength

I had a lecture on thermodynamics. I was told that the bond strength, $\epsilon$, is related to the latent heat of sublimation, $L_s$. $L_s\approx L_f+L_v$ if the melting and boiling points are close, ...
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19 views

Why is the boundary layer thinner on the outside of an outer wall versus the wall inside the house

The convection on the outer suface of the outer wall of a house is larger, because outside a house it's more windy compared to inside. More wind means more turbulence which leads to more transfer of ...
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365 views

Why do some materials have a negative coefficient of thermal expansion in all directions?

Those materials are especially ceramic-glasses. I've found some studies about how does it happens in one dimension (for example a nanocrystalline has a silica helix that works like twisting spring, ...
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71 views

Thermodynamics of a rubber band

I have a streched rubber band and I know that tension f is proportional to the temperature T when the length is constant. How can I proove that internal energy is only a function of temperature? I ...
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42 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
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71 views

Physical interpretation of legendre transformations in thermodynamics

I have found this question(Physical meaning of Legendre transformation) and I have some questions regarding the transformations in thermodynamics, In thermodynamics we have: $$H= U+PV $$ $$F=U-TS ...
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25 views

Can an intercooler be analysed as any other heat exchanger?

I am doing this project on developing a code for the first and second law analysis of a practical Gas Turbine Cycle. It includes a two-stage compression process and thus, involves an intercooler, ...
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12 views

When obtaining the thermodynamic entropy (e.g. by differentiating F) the average entropy is being found. In what sense is this an average?

If I have some expression of the entropy (or another thermodynamic quantity of a system (e.g. pressure) obtained from the Helmholtz free energy, F. Is this the mean (average) or the modal (most ...
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108 views

Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
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22 views

Hot air particles

I have a question- albeit random one!. I recently visited a friends place who used a standard shovel from the shed as a tool for moving hot charcoals around a pizza oven. Unfortunately the shovel was ...
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36 views

Planck Temperature

I have heard of two different things occurring at Planck Temperature: 1. A black hole forms 2. The quantum gravity takes over and the wavelength of light emitted from the object is Planck length ...
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41 views

Heat capacity of a gas in gravitational field

How does one calculate the heat capacity of an infinitely long column (of constant cross-sectional area) of ideal gas in a uniform gravitational field? I tried using the lapse rate $dT/dH$ and putting ...
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47 views

Ratio between thermal conductivity heat transfer coefficient

Consider the Robin boundary condition for the diffusion/heat equation $u_t=a(t)u_{xx}+f(x,t)$: $$\mathrm{-k(t)u_x(0,t)=h(t)u(0,t)}$$ or $$\mathrm{u_x(0,t)+\frac{h(t)}{k(t)}u(0,t)=0}$$ where ...
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13 views

Looking for $\frac{dH}{dT}$ in terms of total latent heat and the change in magnetic moment

As the title states, I'm looking for $\frac{dH}{dT}$ in terms of total latent heat $L$ and the change in magnetic moment $M$. I think I can use the equation $$dU = TdS - MdH$$ where $M$ is the total ...
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41 views

Pressure change in throttling & flow rate reduction in a water circulation

If the pressure in a water pipe line is reduced from 7kgf/cm2 to 4 kgf/cm2, what is the % reduction in flow rate?
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57 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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35 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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136 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 ...