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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61 views

How do fluids behave in space?

In outer space under absence of any external force (like gravity) can a free liquid develop pressure due to cohesive forces? Will the liquid be in spherical shape and will pressure increase towards ...
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45 views

Doubt about Clausius Inequality

In his text "On the Application of the Theorem of the Equivalence of Transformations to Interior Work", Clausius wrote If the cyclical process is not reversible, the equivalence values of the ...
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1answer
30 views

Entropy and internal energy + molecule

Internal energy can be defined theoretically for one molecule (U = 1/2 Kb T) for example but entropy is defined for a system thus for many molecules. Then we define temperature equal to $ \delta U $ / ...
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1answer
42 views

Fraction of blackbody energy below the peak of the blackbody curve

I don't know how to determine the fractions of blackbody energy that lie below and above the peak of the blackbody curve. Should I use the Planck distribution to solve this problem?
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10 views

What happens to carbon deposits in car engines when heated?

I am trying to determine the characteristics of carbon deposits in a gasoline automobile engine. Will the carbon deposits in and around the cylinders of an automobile engine soften, harden, or ...
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32 views

Thermodynamic reversibility, Landauer's principle, and Maxwell's demon

A lot of the literature surrounding Landauer's principle (and relating it to Maxwell's demon) talks about whether or not a logically irreversible process can be thermodynamically reversible. But why ...
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32 views

Could one, practically or hypothetically, capture energy from heat using magnetic fields? [closed]

I have had this idea, and I'm not sure if it would work. Heat is a form of chaotic kinetic energy, right?. Would it be possible to create a magnetic field within a gas or liquid so that when the ...
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38 views

Is there any relation between the entropy of a system and the kinetic energy of molecules in the system?

The kinetic energy of the molecules in the system increases when we provide heat to the system,thereby increasing its temperature under certain conditions. Similarly providing heat to a liquid ...
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3answers
93 views

Why doesn't power generated by thermal radiation violate Carnot's theorem?

It seems to me that you could use thermal radiation to drive an engine that does not require a cold reservoir. Carnot's theorem states that the only way to convert heat into work is with a temperature ...
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102 views

Why don't I see green flames more often?

I was just thinking today that I usually see red flame, and have seen plenty of blue flame, but not green. My naive presumption for coloration of flames would suggest that I would see more green, so ...
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36 views

Cyclic model of the universe and second law of thermodynamics

Cyclic model from wikipedia The above link shows some theories on cyclic model. It states that a scientist named Richard C. Tolman showed that the cyclic model proposed by Einstein can not be ...
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74 views

Why is the derivative of the Fermi-Dirac distribution negative?

Why the derivative of Fermi-Dirac distribution function at absolute zero temperature becomes negative of Dirac_Delta function. The Fermi-Dirac distribution function is \begin{equation} ...
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36 views

Do liquids creep from cold to hot like gases?

Consider the U-tube water experiment below with the left red block at 10C and the right red block at 90C. I think the right level will become about 3% higher than the left level simply because hotter ...
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44 views

effect of pressure in thermodynamic system

$W$ = $P_{ext} \Delta V$ Now my questions How do we calculate the work done if the external pressure changes with change in volume of the system? Is there any effect of the internal pressure on ...
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49 views

Time dependent heating of a conductor

I have a conductor that's being heated with current. I want to know the temperature of the conductor Steady state soultion is: ...
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1answer
29 views

Ideal solution fugacity coefficient

I am super confused about ideal solution behavior. I know that an ideal solution implies that pure component fugacity is equal to the mixture fugacity but apparently that does not mean that the ...
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1answer
86 views

Discrete time simulation of gas liquid equilibrium in a tank

I am trying to write a discrete time simulation of liquid/gaseous oxygen in a pressurised cryogenic fuel tank. For now I am assuming that the only external change to the system is the influx of heat ...
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1answer
25 views

Joule-Kelvin coefficent what does $p$ and $T$ represent?

In the Joule-Kelvin expansion we take a gas at one pressure $p_1$ and throttle it through a valve to another pressure $p_2$ where these two pressures are taken to be constant. The Joule-Kelvin ...
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29 views

Compression of a gas in a cylinder

On my test I had a question: A movable, friction-less, and rigid piston stands upright with a 10 kg weight resting on top like this, compressing the gas inside. If the piston is turned on its side, ...
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22 views

Internal energy of a body

I have a really fundamental question regarding the internal heat energy of a body. From textbooks, we know: $$\Delta Q = m \cdot c \cdot \Delta T$$ where $m$ is the mass of the body, $c$ its specific ...
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49 views

Maxwell Boltzmann distribution: Going from momentum to energy

I am learning about the Maxwell Boltzmann distribution, and am trying to convert the equation from momentum into energy, but I'm stuck on changing $d^n p$ into $dE$. I have the equation: $$ ...
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71 views

Why is such huge mount of heat released by brute-force GPG cipher?

Please see GnuPG FAQ. I'm really interested in how to derive to "boil the ocean" by using the Landauer bound and the Margolus–Levitin limit. Any suggestion is welcome.
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54 views

How does heat damage the body? [closed]

Let's take an example : If I put my hand in cold water (let's say 20°C), it doesn't hurt, and it doesn't burn. But if I put my hand in hot water (let's say 90°C), it hurts and my hand can get burnt. ...
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60 views

How much effect does wind have on cooling an object?

I was reading a question on how to cool frying oil on the cooking SE, and in a comment I suggested that having moving air would speed up the cooling as the heat transfer from the oil to the air would ...
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57 views

Maximum Temperature?

I have been reading a lot about wavelengths of light and Planck's law and such. Curious as to whether a minimum wavelength of $h$ (Planck's Constant) indicates that there is in some way an absolute ...
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47 views

Is it Possible to Burn a fuel (coal especially) without a flame or spark? [closed]

Actually there was a topic of quality determination of coal where it was heated up to 750-950 degrees in order to burn its mixed volatile substances. I was wondering how coal itself wouldn't burn. ...
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1answer
36 views

How much Oxygen is in ζ-phase metallic Oxygen?

I am playing with a sci-fi idea of Oxygen storage for breathing. I wonder how do some compressed forms of Oxygen compare to human-breath-Oxygen (room temperature, room pressure) in terms of density. ...
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34 views

At what temperature does the vibrational degree of freedom becomes significant for an ideal diatomic molecule?

For ideal diatomic molecules such as $\text{H}_2$, $\text{N}_2$ and $\text{O}_2$, at what temperature does the vibrational degree of freedom significantly contributes to the calculations such as that ...
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45 views

Calculating change in gas volume over time given a constant number of molecules and a changed weight

I was watching a video, and a question came to my mind. Suppose I have a cylindrical piston. I have a rock that rests on a roof, which keeps the gas underneath at a constant pressure & volume. ...
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41 views

First law of thermodynamics with additional term

I read in a paper that a "known expression for the heat received by a body" is $$dQ=dU+pdV-\mathbf{v}\cdot d\mathbf{P}$$ where $\mathbf{P}$ is the linear momentum of the body, $p$ is the pressure, ...
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118 views

General Definition of Steady State

According to many sources (including Wikipedia, Stephani&Kluge, D.J. Acheson) a steady state ist: In systems theory, a system in a steady state has numerous properties that are unchanging in ...
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1answer
52 views

How to calculate max temperature craft needs to withstand near the Sun

The Solar Probe Plus fact-sheet states that the craft will approach to the distance of 9 solar radii to the surface of the Sun (Approx 6.26e6 km) and its heat shields must withstand 1644K of heat. I ...
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23 views

Thermal conductivity of a binary gas mixture

I want to estimate the thermal conductivity of binary gas mixture, say water vapor+nitrogen. I assume the mixture as ideal gas. The molar fraction and thermal conductivities of the components are ...
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132 views

Why are cooling towers at nuclear power plants shaped the way they are?

The iconic cooling towers at most nuclear power plants are shaped like hyperboloids. Wikipedia mentions that this is because the wide base promotes thin film evaporation and the narrow point ...
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32 views

Infrared light and heat

I know that mid wave IR, long wave IR, and far IR are all infrared light that we feel as heat. Often, even when it is cold and windy, if I face the sun in a sunny spot it feels like it is 80 degrees F ...
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1answer
49 views

Calculation of Entropy of Debye Solid at High T

I am calculating the kmolar entropy of a Debye solid at low temperature ($T << \theta_D$) and high temperature ($T >> \theta_D$). For the low temperature, I use $U = U_0 + \frac{9 k_B ...
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935 views

Why do particles in the molten wax near a burning candle wick get pushed away?

Have a look at this clip I made of my candle burning: I can accept that the molten wax gets sucked into the wick (though not quite sure why: capilary action?). But why does it also seem to get ...
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43 views

Conceptual Ice Water Equilibrium

We observe that when we apply pressure on on Ice Water equilibrium system then more of ice melts.. Ice(more Volume) + Heat ----><----- Water (Less volume) If we increase pressure then volume ...
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1answer
64 views

How to find the normalization constant of Fermi-Dirac distribution function?

The Fermi-Dirac distribution function is given by $$f(E):=\dfrac{A}{{\mathrm e}^{(E-E_{F})\,/\,(k_{B}T)}+1},$$ where A is the normalization constant. When we sum over all the states, we get $1$. ...
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1answer
75 views

What is the cause of this 'bump' in the heat capacity graph for a monatomic ideal gas?

I am trying to understand the heat capacity behaviour for an ideal gas as a function of temperature. The text I am learning from is Schroeder's An Introduction to Thermal Physics. This is an exercise ...
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24 views

Is there a way to make a heat pipe that can transfer heat downward?

Is there a way to make a heat pipe that can transfer heat downward? As in a 10 to 20 ft vertical pipe with 100°f at the top and 50°f at the bottom.
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16 views

Cooldown of a 1 meter wide sphere of water at 10C° in space [closed]

I am wondering how long would it take for such a sphere of water to totally be under 0C°. Let's suppose that the surface tension is enough to keep the topology of the sphere intact an that it will ...
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2answers
17 views

Comparing rates of cooling

There are 2 metallic spheres A and B. Mass of A is thrice the mass of B. Both the spheres are heated to the same high temperature from same initial temperature. The spheres are thermally insulated ...
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1answer
350 views

If I mix 1 unit of water at at 30C° with 1 unit of water at 60C°, is the resulting water at 45C°? [closed]

I'm curious how temperatures work when mixing water. I'm not very good at physics but I'm always learning. Let's say I've 1 gallon of water at 30C° and 1 gallon of water at 60C°, and I mix them ...
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2answers
52 views

How Much Does Roof Color Affect Energy Consumption?

I'm not sure whether this is off-topic; if so, I do apologize and will fully understand votes to close. That said: I live in a climate that's quite cold much of the year but gets pretty hot in the ...
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0answers
50 views

The effect of 8 hours 20 degrees C sunshine on the temperature of a stationary car's engine block? [closed]

What temperature of the engine block could be achieved by parking a car (Mazda 3) in full sunlight and facing south all day. Average day temperature 20 degrees Celsius no wind. And then how long to ...
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26 views

Difference Value of the Specific heats at constant Pressure and Temperature of Real Gases

As in ideal gases, we can have the equation of $C_p=C_v+R$, or to be precise, the difference of the Specific heats of ideal gases at constant pressure and volume is the universal gas constant. But, we ...
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37 views

Thermodynamics: Deriving inner energy from ideal gas equation of state [closed]

If we know equation of state for ideal gas $ PV = NkT$ where $P$ stands for pressure, $V$ for volume, $N$ for number of particles, $k$ is Boltzmann constant and $T$ is temperature, how can one ...
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129 views

On a molecular level, how does heat transfer take place?

When an ice molecule hits a water molecule, the water molecule adds kinetic energy to the ice molecule. Why do the water molecules lose kinetic energy? In other words, why does heat like to go where ...
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30 views

Maxwell Relations - Isentropic Compressibility to Isothermal Compressibility [closed]

I am trying to derive an expression for the isentropic compressibility in terms of thermal expansion coefficient $\alpha_P$, the isothermal compressibility $\kappa _T$ and the constant pressure heat ...