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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112 views

Thermodynamics: Caclulate final temperature with hot metal in gas [closed]

I've been working on this problem for a couple of hours now, and I think that I simply don't understand the basic principles that tie into the problem: (note that I attempted this problem and it was ...
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1answer
45 views

Is every imaginable quasi-static locus (with non-decreasing entropy) physically realisable?

If I have an isolated composite system which is dependent on several extensive properties (say $U_i, V_i$ and $N_i$ for each subsystem $i$) then a quasi-static locus is just a continuous curve through ...
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121 views

What is the best way to heat air? [closed]

I want to know which way we could create hot air most efficient, how can we convert all energy input into air temperature and decrease air density as much as possible? Is the plasma (such as fire) is ...
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170 views

gibbs free energy and maximum work

I'm getting confused between two important results.... Gibbs free energy G = H-TS where h is the enthalpy and S is the entropy. This relation indicates only when the temperature and pressure are ...
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353 views

Isentropic and Isothermal Compressibility

Why isentropic compressibility is greater than isothermal compressibility ? While deriving $C_p$ and $C_v$ relation, I got $\frac{Cp}{Cv}$ as $\frac{ke}{Kt}$. Which tells us that $Ke > Kt$. But ...
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1answer
44 views

Classical limit of non-interacting, relativistic quantum gas (Kapusta/Gale p.8)

I want to understand two equations in "Finite temperature field theory" by Kapusta and Gale on page 8. The partition function is $$ \ln Z = V\int \frac{d^3 p}{(2\pi)^3}\;\ln\left(1\pm ...
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94 views

fugacity of gases and gaseous mixtures

Is fugacity defined only for gases and gaseous solution.? In many books it is given that fugacity is "effective pressure", what does it mean? If it is applicable to liquids and liquid solutions then ...
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1answer
37 views

How to calculate heat generated from cosmic dust in space? [duplicate]

Say I have a spaceship, and I'm flying it through space at a constant high velocity V. The spaceship is pretty large (big surface area). In space however, there is cosmic dust scattered throughout ...
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57 views

How do I set up the tridiagonal matrix for a heat diffusion with layers of different thermal diffusivity?

I have Scala code that recreates the Crank-Nicolson solutions for the diffusion equations, and matches 'Excel for Scientists and Engineers' (Joe Billo, Wiley). However, I would like to be able to ...
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1answer
44 views

Does no variables change in an adiabatic + isothermal system?

Adiabatic + isothermal = no heat and temperature change. Does that mean the system will remain as it is? If it is adiabatic + isovolumetric or adiabatic + isobaric , is it as well no change in any ...
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1k views

Comparison between isobaric, isothermal and adiabatic expansion

Please check if my understandings of these terms are right because they are a bit confusing to me. For all three types of expansions, a change in volume means work is done by the system to the ...
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3answers
120 views

When the low temperture reservoir with negative temperture (Kelvin), such as Ising model, is the efficiency of ideal heat engine larger than 1?

The ideal Carnot engine works between two heat reservoir with two temperatures $t_h$ and $t_l$. Its efficiency is then $1-\frac{t_l}{t_h}$ . If the low temperture reservoir is the Ising model with ...
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59 views

Cooling 8 L of frying oil using ice [closed]

I have 8L of frying oil (canola) - if I put it in a metal canister after frying and put that canister in ice water, what is the minimum amount of ice water that I need to bring the oil to a ...
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1answer
51 views

Can you choose the variables of a state function?

I'm confused. I was first introduced to entropy as a state function of internal energy and volume $$S(U,V) \Rightarrow dS = C_v\frac{\mathrm{d}T}{T} - p\frac{\mathrm{d}V}{T} $$ wich is the ...
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62 views

Are Maxwell Relations valid only out of saturation?

My thermodynamics book suggests that the Maxwell Relations must be used when dealing with a single-phase system. The equations come right after the section Mathematical Relations for the Homogeneous ...
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104 views

Woodstove coppertubing heat exchanger [closed]

I am trying to use the excess temperature of my wood stove's stack to heat a copper tube heat exchanger with water running through it. The water is piped through my concrete floor for radiant floor ...
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1answer
105 views

Spontaneity / Free Energy of Non-Isothermal Process

I'm trying to determine a lower bound for the work input necessary to make an entropy-reducing process "spontaneous" in the sense that the 2nd law is not violated. For a constant temperature and ...
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3answers
160 views

Ice and liquid water interacting across a boundary

Imagine we have two thermodynamic systems, one a mass of ice and the other an equal mass of liquid water, with both at 273.16K. Each system is isolated, except that they can interact with each other ...
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53 views

What are the thermal properties of a “perfectly rigid” container?

can a "perfectly rigid" container be a diathermal boundary? I checked the wikipedia article for heat and read: Kinetic theory explains transfers of energy as heat as macroscopic manifestations of ...
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1answer
164 views

Calculate heat transfer out of a basement [closed]

I am thinking it should be possible to calculate heat loss out of basement based on the temperature of the walls, but am not sure how to do it (what the equations are). For example, lets say the ...
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3answers
1k views

Zeroth Law of Thermodynamics, temperature, and ordering

In my thermodynamics course (and in other places on the internet) it is asserted that the Zeroth Law of Thermodynamics can be used to define the concept of temperature. One statement of the Zeroth ...
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54 views

Is there an efficiency-optimizing layout of items in a refrigerator? [closed]

Is there some optimal layout of items, or types of items (characterized by size, shape, density, solid/liquid, etc) that will allow a common household refrigerator to function with optimal energy ...
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141 views

Milk-First School

I have always been struck by the huge amount of different arguments about the issue: When you make a cup of tea, the milk should be poured first or added to the cup after the tea? Wikipedia, ...
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1answer
58 views

minimum possible absolute temperature in the universe? [duplicate]

Sorry guys i went wrong in my previous question , actually my question is what is the minimum possible absolute temperature in the universe of what ever substance...?
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47 views

White bread toasted seems hotter than brown bread?

Ok this is a bit of a random question but I 99% of the time use white bread for toast and I always toast my bread the same amount and every time I take it out it's too hot to handle and the butter ...
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1answer
370 views

Does the energy required to increase a volume of water's temperature increase as that temperature increases?

Obviously in a simple, classroom style experiment the energy required to increase water temperature is a constant and thus wouldn't change, but what if we made the experiment just slightly more real ...
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161 views

What algorithms can be used to compute the binodal in a ternary Flory-Huggins theory?

What are the most popular algorithms used to obtain a binodal curve for the ternary mixture (starting from Flory-Huggins theory)? I would like to obtain a plot similar to the one calculated here ...
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1answer
76 views

Chemical potentials for multicomponent solids

I have a problem understanding how to deal with the chemical potential when two thermodynamic systems are in contact. For simplicity, let us consider $T=0\ K$. We have a system that is composed of two ...
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67 views

Confusion on entropy in the universe [closed]

I was researching about the heat-death of the universe, and I was wondering if my understanding of it so far is factual to the theory? However, the 3rd Law of Thermodynamics prevents the universe’s ...
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34 views

Gibbs equation and reversibility [duplicate]

The equation $$TdS=dU+PdV$$ is a combination of $$dQ=dU+PdV$$ and $$TdS=dQ.$$ But in some process that is very irreversible, $TdS>dQ$, should we write $$TdS>dU+PdV$$ instead of the first ...
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54 views

Supercritical Steam Expansion [closed]

Ten kg of steam at 500 bar is expanded at constant pressure until its volume increases to seven times its initial value of 0.01 $m^3 $. (a) Calculate the initial and final temperature of the steam ...
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100 views

Specific Internal Energy Decreases with Increasing Pressure?

I was looking at "Properties of Compressed Liquid Water" (Table A-5) in Fundamentals of Engineering Thermodynamics by Moran. Table A-5 shows that the specific internal energy $u$ of compressed liquid ...
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1answer
57 views

Spherical Shaped Electrical Leads for Thermal Conductivity Mitigation?

I am designing a thermionic converter and one of the biggest inefficiencies is the thermal conductivity and limited electrical conductivity of the leads. I'm trying to mitigate the loss of heat ...
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1answer
61 views

Vapor-compression refrigeration

In a vapor-compression refrigeration system I would like to understand the following : Why is there a need for the compressor ? Can't the saturated vapor from the evaporator be cooled directly in ...
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1answer
290 views

Can you extract energy from “hot” things without a temperature differential?

I've been reading about extracting energy from heat, particularly Sterling engines. There's always a temperature gradient. Heat flows from the hot side to the cold side through the working fluid. As ...
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69 views

Free energy a continuous function of temperature but may not be differentiable everywhere?

So according to my understanding, the free energy of the system should be a continuous function of temperature. This is because if the free energy is not continuous at temperature T, then at this ...
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52 views

Cost vs. purity producing liquid oxygen [closed]

We are a group of rocket amatures who build rockets using LOX and ethanol as propellent. We normally buy the LOX from supplier. But lately we have been discussing if there is an easy way to produce it ...
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93 views

Effusion of particles from one box to another - pressure calculation

Suppose we have a container divided into equal halves. Right half is fixed at temperature $T$, volume $\frac{V}{2}$. Initially it has pressure $P_0$, a hole of area $A$ is opened between them. I ...
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27 views

Thermodynamics of binary symmetric channels

I am reading this very interesting paper: http://m.iopscience.iop.org/1751-8121/41/40/402002/pdf/1751-8121_41_40_402002.pdf about thermodynamics of channels in information theory. More generally, ...
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300 views

Irreversible heat engines strictly less efficient than reversible ones

I undertand how Canot's theorem implies that irreversible heat engines must be no more efficient than reversible one's, but it isless clear why they need to be less efficient, as I have seen stated in ...
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139 views

Calculating heat capacity from the equation of state

It is known that within thermodynamics alone, given the equation of the state of a system, one cannot explicitly determine the heat capacity. What is the mathematical reason for this? Intuitively, it ...
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309 views

Thermal expansion of two bolts

I have this question asking me about the thermal expansions of two bolts, a steel one, and a brass one. I have the equation: $\ (\delta L/L)/T = \alpha $ I don't understand how I can use this ...
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1answer
299 views

Chemical Potential with Pressure at Constant Temperature

The above picture shows how the Gibbs free energy of a solid, liquid and gas vary with pressure. I have found no similar graphs on the internet that match the above. Instead I often find these ...
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40 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
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1answer
152 views

What causes a heat generating source to stabilize at a certain temperature? (Answered by myself, I think)

For example, we out a heat sink on a microprocessor to keep it cooler. I understand that if we run 100 watts of electricity through the microprocessor, it will generate 100 watts of heat, or 100 ...
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1answer
50 views

Heat generated on thin disc plate in magnetic field [closed]

There are the eddy currents in thin circular copper plate thickness h and radius a, in a harmonic magnetic field which is perpendicular to plate and the effect of auto-induction is negligible. Now we ...
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67 views

Given partial derivatives find the state function

I have to find the state function of a gas (which under very low pressures behaves as an ideal gas). So, first I tried writing it as part of an equation $ dV = \dfrac{\partial V}{\partial T}\ dT + ...
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39 views

Snowmaking in the tropics - an estimate of water evaporation

If I set up a snowmaker in the tropics and sprayed water with it how much water would I evaporate? How would I calculate?
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42 views

Do COBE, WMAP, and Plack have design flaws? [duplicate]

MRI expert Pierre-Marie Robitaille on the design flaws of COBE, WMAP, & Planck and the violation Kirchhoff's Law: Here are his talks: Pierre-Marie Robitaille: The Cosmic Microwave Background ...
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29 views

Heat energy in special theory of relativity [duplicate]

Is heat energy invariant under Lorentz transformation? If so then how?