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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How is the logarithmic correction to the entropy of a non extremal black hole derived?

I`ve just read, that for non extremal black holes, there exists a logarithmic (and other) correction(s) to the well known term proportional to the area of the horizon such that $S = \frac{A}{4G} + K ...
7
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1answer
341 views

Is a venturi pump feasible at very low pressure?

I need assistance (or experience feedback) in estimating if a Venturi pump would work at low pressure. A boiler under vacuum (10% atmosphere) will produce steam (at a given speed depending on the ...
5
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1answer
173 views

Liquid column “recoils” in a sealed cylinder when hit by a piston — is it possible?

Consider a cylinder filled partially with a liquid (e.g. water). The cylinder is sealed, and is at held at room temperature (e.g 298K). At equilibrium (or when no external disturbance is imparted to ...
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1answer
104 views

Find Solution to the Heat Equation with Bessel Functions and Initial Values

I'm trying to find the time dependent solution to the heat equation in a very long cylinder (the problem only depends on radius, r, and time, t) with the initial value $T(r,0)=T_1$ and the Dirichlet ...
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1answer
354 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic ...
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47 views

If entropy is a state function, then why is all the talk about reversible vs. irreversible processes?

So I'm preparing for my Thermodynamics undergrad exam, and I just can't wrap my head around the significance of reversibility vs. irreversibility of a process in relation to entropy. I mean if entropy ...
3
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1answer
108 views

Why doesn't a Brownian ratchet provide free energy?

A Brownian ratchet is described here at Wikipedia. The "why it fails" section reads: Feynman demonstrated that if the entire device is at the same temperature, the ratchet will not rotate ...
3
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1answer
160 views

Amount of energy to separate Gases - relationship to concentration

I want to understand the efficiencies of separating mixed gases, and for that I want to understand the thermodynamic limit case. Looking at the wikipedia page for entropy of mixing, I find the ...
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1answer
360 views

Does a negative line tension in a 3-fluid immiscible interface make sense?

This question is inspired by this question/answer pair: Is this formula for the energy of a configuration of 3 fluids physically reasonable? Consider three immiscible fluids forming contact surfaces, ...
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1answer
459 views

Coffee cooling in a cup

Will coffee in two differant size styrofoam cups in the same room conditions cool at the same rate? One cup is 8 oz. and the other would be 12 oz.
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169 views

Newton's law of cooling for the heat equation boundary condition

Newton's law of cooling says the temperature of an object satisfies $$ \frac{dT}{dt} = -k(T(t) - T_0),\tag{1} $$ where $T_0$ is the surrounding temperature. See these HTML notes for example. Now if ...
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1answer
37 views

How does the second law of thermodynamics affect the efficiency heat-to-work conversion, at the molecular level?

I understand the second law of thermodynamics in terms of the improbability of the high--and-low-velocity particles of a gas to separate themselves so that at one moment they are at different sides of ...
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116 views

Questions about the second law of thermodynamics

I can not understand the second law of thermodynamics and have trouble explaining the following questions: 1) In the tropics the water near the ocean surface is warmer than the deep water. Does the ...
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48 views

Standard Heat of Combustion

When considering tabulated standard values of heat of combustion (∆H° combustion) or any other similar value, the results are reported for species in their standard states (1 bar pressure, 25°C, etc). ...
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365 views

Caculating thermal stresses in a composite rod

The Question Between two rigid walls separated by a distance $l_1+l_2$, two rods of equal cross-section area $A$, and length, coefficient of linear expansion and Young's modulus $l_1, ...
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25 views

Finding out the temperature difference

If we add 10 spherical bubbles then there will be some change in their area. Is there any way to find out change in temperature of the liquid from the change of its area?
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57 views

When heat is rejected by a system what will be $q$ according to sign convention?

When a system rejects heat it can be assumed that work is done by the system. So as per law the sign convention must be negative. But my physics textbook says the reverse. So is the question.
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24 views

Work of an adiabatic/ compresion: sign?

As far as I am concerned the adiabatic work it is given by: $$ W_{adi}=\frac{P_{f}V_{f}-P_{i}V_{i}}{\gamma -1}$$ While I have seen in other examples that it is used with $1-\gamma$ in the ...
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63 views

What creates black streams in fountain-type fireworks?

For the New Year celebration of 2014, my nephews set off a series of fountain-type fireworks (as shown below). When one looks carefully into the shower of light, one notices that a fair number of ...
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106 views

NPT simulations: what is the inertia of volume fluctuations (using periodic boundary conditions)?

NPT molecular dynamics (MD) are most often implemented by adding some kind of piston that regulates the pressure. The inertia of this piston determines the dynamics of volume fluctuations in the ...
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92 views

How does this Stirling engine work?

I'm looking at this Stirling engine, which I believe is a variation of an alpha type. It was developed by Nasa back in the 1980's. The thing is, I can't figure out how the hydrogen cycles through the ...
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75 views

Would a cone shaped Stirling engine work?

A Stirling engine evidently functions by heating and cooling air, thus making the piston move up and down. What if the heated side of the cylinder were shaped as a sort of cone with a gentle slope, ...
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81 views

Expression of $\kappa_S$ in photon gas

I'm calculating some properties of the photon gas. That gas is defined by $$U=aVT^4$$ $$P=\dfrac{1}{3}aT^4$$ I calculated photon gas entropy: $$S = \dfrac{4}{3}aT^3V $$ I could calculate $c_V$. ...
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893 views

What is the difference between heat and work

If 700 J of work is applied onto a gas, and therefore the gas contracted 0.005 m^3 (from 0.01m^3), and the temperature stayed at a constant rate of 300 kelvin, then how come when pressure is added to ...
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140 views

What's the typical material used as a low-k ILD in semiconductors?

Semiconductor companies (namely IBM, Intel, TSMC and etc.) may use different low-k materials as inter-layer dielectric (ILD) in their fabrication process. I'm wondering what is the most typical one. ...
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206 views

Definition and Measurment of Energy and Heat in Thermodynamics

The concept of work is clear from mechanics, where $dW=F\cdot dx$, leading to $dW=PdV$. Also different forms of energy are defined in mechanics, e.g., $E=\frac{1}{2}m v^2$, etc. How are the energy and ...
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74 views

Experimental heat equation for a bottle of water

I'm not sure if this question belongs here, because I'm asking a question about experimental data rather than theoretic formula. Anyway, I'm trying to figure out the time-temperature relation of the ...
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141 views

diesel steam engine

Let's imagine a diesel engine's cylinder head would be heated by external means, to some hundred degree celsius, and the fuel would be replaced by water. We've made modifications so that water ...
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170 views

Food kept in a container in my pressure cooker cooks slower

The pressure cooker is heated at the base to cook the food. The pressure cooker releases steam when the force exerted by pressure exceeds the counterweight, at which point the weight rises up allowing ...
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62 views

Which pressure to use in the $T~ds$ equation?

Let's say I have an adiabatic, rigid, open container that has an amount of air at some pressure, $P_\text{cv}$, and some temperature, $T_\text{cv}$. I have heated pressurized air coming into the ...
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91 views

Best material for heat transfer between ice and water

What is the best container material for heat transfer between ice and water? this is a difficult question to ask without displaying a picture of what I'm meaning.
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31 views

Is there a thermodynamic law or theorem that expresses how systems “break” or “change” when enough energy is added?

I have a simple question about thermodynamic laws, and I am hoping you can help me. Let's say that I have a sphere container with some pressurized gas in it. I can slowly increase the pressure over ...
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133 views

Rotary Steam Engine

Leon Crux invented the concept of interlocking archimedes spirals that eventually led to the scroll compressor but intended it to be used as a rotary steam engine. However technological limitations of ...
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66 views

What is the relationship between strain and electric current?

Strain or stress can be caused by different sources. I categorized theses sources as mechanical, thermal and electrical loads and formulated the total stress as follows: $$ \epsilon_{total} = ...
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32 views

Decompression cooler

How would I figure the needed pressure differential to freeze water inside a cooler using ambient air? I am assuming that the combined gas law would apply here and that the formula P1•V1/T1=P2•V2/T2 ...
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128 views

Please correct my understanding of Clausius-Clapeyron and latent heat

As I work a problem set, I'm being asked to calculate the latent heat associated with a particular phase transition of $NH_3$ (solid -> liquid, liquid -> gas, solid -> gas). I'm being told to perform ...
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36 views

How to compute the change in entropy of s system when the temperature is decreasing?

How to compute the change in entropy of s system when the temperature is decreasing? Such a question may be too general,then we may ask a special case:How to compute the change in entropy of Annealing ...
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271 views

Constant Pressure lines in evaporation diagram

Assume that there is the following $T-H$ phase diagram with the constant pressure lines. Which is greater preasure? The preasure drops as we move to lower temperatures (i.e. from top to bottom)? ...
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376 views

How does the volume change affect an adiabatic process?

A gas consisting of rigid diatomic molecules was initially under standard conditions. Then the gas was compressed adiabatically, 5 times the original volume. Find the mean KE of rotating molecules ...
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47 views

How connected thermodynamical stability and dynamical stability for black holes?

Criteria for thermodynamical stability is the convex of entropy. But for black hole entropy is non-additive.
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63 views

Lambda transition data points of $\require{mhchem}\ce{^4He}$

I'm looking to get some data on the lambda transition of $\require{mhchem}\ce{^4He}$. I need the data points of the specific heat vs. temperature graph, if that makes sense.
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49 views

Heat of adsorption from fugacity data

I have a set of data relating the fugacity ($\approx$ pressure) to the loading for a given set of temperatures. There are three temperature sets each having five fugacity vs. loading points. The ...
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64 views

Increase in number of micro states explanation or restatement of second law?

Is the boltzmann's expression of entropy as log of micro states leading to the formulation that system is more likely to be in a macrostate with more no. Of micro states really is an explanation or ...
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89 views

Landauer's principle vs Rayleigh–Jeans law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of $kTln2$? If it is so, can we also ...
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651 views

Entalpy and entropy role in freezing-point depression phenomena

There's this "atomic" explanation of the freezing-point phenomena on Wikipedia that leaves me really intrigued. Consider the problem in which the solvent freezes to a very nearly pure crystal, ...
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101 views

Using thermodynamics and Kinematics together to solve a parachuter problem?

I need to find a parachutist's displacement after a given height (nearly 37000m) and at a given latitude. I have his mass, area, parachute area, drop height, parachute deployment height, data about ...
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236 views

Constant volume specific heat

A monatomic ideal gas is confined to move in two dimensions. What is the constant volume specific heat for this gas? Consider a system of N independent harmonic oscillators moving in two dimensions. ...
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571 views

Carnot Engine for Finite Reservoirs

Two solid, finite thermal reservoirs have temperatures of $T_1$ and $T_2$ respectively and an engine operates between the two. Assume $T_1 > T_2$ and that each reservoir has constant heat capacity ...
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157 views

direct conversion of heat to electric potential / current - are there theories that contradict the 'Kelvin Statement'?

In particular, William Thomson (Kelvin) appeared to be wrong about key things in physics (initially X-rays, aether, even aviation feasibility). ...
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164 views

2 streams going into an engine and 2 come out. Find the enthalpy?

Problem: Steam supply to an engine is made of two streams that mix before entering the engine. Stream 1 flows at a $.01\frac{kg}{s}$ with an enthalpy of $2952\frac{kJ}{kg}$ and a velocity of ...