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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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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59 views

(Iso-baric / iso-choric) Thermodynamic cycle question

A very simply question: Is something that even somewhat resemble a thermodynamic cycle consisting of two iso-baric and two iso-choric cycles possible (such that you get a simple rectangle representing ...
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18 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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112 views

Is the thermal time constant simply the heat capacity divided by thermal conductivity?

My professor gave me this temperature decay data to make an exponential fit and told me that the time constant tau should be heat capacity over thermal conductivity. I'm looking at the wikipedia page ...
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48 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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48 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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74 views

Can I make a cold air trap (thermal equilibrium)

Thermodynamic buoyancy. I have an air intake for combustion air entering into a basement furnace room. During cold weather, the air enters unchecked (no damper on pipe is allowed). I have this 5 ...
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51 views

Equilibrium Condition

In classical thermodynamics, equilibrium conditions means maximum entropy for a closed state. However, people always talk about equilibrium for open systems as well. How can one say that an open ...
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73 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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81 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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59 views

Radiant barrier effect on inside of a hot water tank

I am trying to determine if a radiant barrier on the inside of a hot water tank would increase its insulating value. Normally radiant barriers are used in house construction to reduce heat loss by ...
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63 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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64 views

Rijke tube: Why Sound is maximum when heated 1/4th length from bottom of tube

Why is it that the maximum sound coming from a Rijke tube happens only when heated wire gauze is placed at 1/4th the length of the tube from the bottom. According to Rayleigh: If heat be ...
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17 views

What coefficients may be used for evaluation the heat keeping?

The final goal is to compare two objects (similar to boxes) from the standpoint of keeping the heat inside? May be there is numerical coefficient or any approaches?
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42 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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502 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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197 views

Does coffee with cream cool slower than black coffee?

At Modernist Cuisine, Nathan Myhrvold states that "Coffee with cream cools about 20% slower than black coffee". He then gives three reasons, two of them related to radiation and the third one to the ...
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63 views

Legendre transformation of Entropy as a natural function of T, V, n

I have come across a question asking to get a Legendre transformation of entropy which is a natural function of 1/T, V, n starting from entropy being a natural function of T, V and n. However, I have ...
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87 views

Calculate thermal conductance of thick walls of a cuboid, given material conductivity and cube size

Note 1: This is probably as much a maths question as physics. Note 2: I am not sure if my use of the the term conductance is correct. I want to make a kiln. The walls will be thick. I can come to ...
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55 views

Linearity of the critical isochore?

When looking at the pressure-temperature diagram along the critical isochore (up to quite high reduced temperatures) a very linear trend can be observed. From a theoretical point of view, is the ...
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112 views

Characteristic length of differential element of cylinder surface?

I am trying to find the Nusselt number for a small element of the outside of a cylinder that has a height of $Delta z$. I found the average Grashof number of a surface as $$Gr_{L}=\frac{\beta \rho ...
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72 views

How to relate compression ratio to work input for a compressor in a heat pump

So I need to calculate the COP (Coefficient of Performance) for a 6-ton air conditioner system in terms of the compression ratio. I understand that: $$COP=\frac{Q_L}{W_{net,in}}$$ I cannot find out ...
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56 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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131 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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37 views

Properties of material affecting magnetic refrigeration

I am reading about magnetic refrigeration at the moment - I see that two factors affecting the applicability of the material for use in magnetic refrigeration is that they must react strongly (i.e the ...
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50 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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101 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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114 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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80 views

thermoelectric effect

The Absolute Seebeck effect states that an electric potential (voltage) is produced to any isolated conducting when subject to a temperature gradient.But why? My view of this is that when you apply ...
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60 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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85 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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101 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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52 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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30 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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102 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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34 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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209 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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257 views

Triple point temperature and freezing point

Why does the triple point temperature have very similar values to the freezing point, in most substances?
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243 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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42 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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56 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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46 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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61 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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86 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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472 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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97 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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203 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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421 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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147 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). ...