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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Estimate heating wires temperature

Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption. I've tried to measure the ...
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38 views

Inversion and Isenthalpic Curves for van der Waals EOS

When I plot the isenthalpic curves in P-T plane, I see Joule-Thomson coefficient is positive in the lower inversion curve but it must be negative. Some authors consider the minimum inversion ...
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3answers
85 views

Evaporation of water

Consider a cylinder that there is water inside it. The volume (and so the pressure) of the cylinder is adjustable by a piston. The thickness of the cylinder and piston is very negligible. The cylinder ...
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1answer
26 views

Statiscal treatment of multiparticle system (Thermodynamics) [closed]

If a system of two energy levels with energies $\epsilon_1$ and $\epsilon_2$ is populated N particles at temperature T. The degeneracy of both levels is one. The particles populate the microstates to ...
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1answer
50 views

Can a High Enough Temperature Create a Black Hole?

My very basic understanding of GR leads me to think that if a substance has a high enough temperature, it can transform into a black hole without a mass required to create a black hole. The equation ...
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4answers
46 views

How can removing energy from a system do work? (ice)

Water freezing into ice expands, damaging roads, breaking rocks, etc. To my understanding, this is doing work (in a physics sense) by removing energy from the system. How is this possible?
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36 views

how to calculate enthalpy and internal energy in relation to heat capacities?

I remember that $\mathrm du=c\mathrm dT$ and $\mathrm dh=c\mathrm dT$ with $c$ being two different heat capacities, but I can't find anything about it, any help?
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1answer
39 views

Thermodynamics: efficiency of a heat engine [closed]

How can we calculate efficiency of a real heat engine? Do we have to consider volume of an object while calculating efficiency? Like in this question If so, how we have to proceed? Thanks in ...
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3answers
31 views

specific volume in a saturated steam mixture

In saturation temperature, we have both gas and liquid. In the steam tables, I don't know if the liquid is in form of droplets inside the steam or in the form of normal liquid water at the bottom of ...
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10 views

Acoustic energy

Let's Assume that I'm sitting in a hypothetical container(room) whose 6 walls are PERFECTLY AND IDEALLY rigid and also are PERFECTLY reflective. Now if I start speaking anything in this room and so ...
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3answers
132 views

Does entropy always increase with temperature? [duplicate]

For any system can we always say that entropy increases with temperature. In other words: $$\left(\frac{\partial S}{\partial T} \right)_{\{\alpha\}}\ge0$$ where $\{\alpha\}$ is the set of parameters ...
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1answer
133 views

Obtaining the temperature from Bose-Einstein and Fermi-Dirac distribution

Lets say you are given a distribution function $f(p)$ and you want to define a temperature, $T_f$, for this distribution. (I assume $\mu = 0$.) It is then natural to define a temperature the ...
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3answers
49 views

Clausius Inequality with three reservoirs

Deriving Clausius inequality in the case of two reservoirs is quite simple. We assume that there is a thermal machine operating between two reservoirs, the first at temperature $T_1$ and the second at ...
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1answer
64 views

2 times the velocity, 4 times the energy, 8 times the heat

In SpaceX's webcast today they talked about the first stage getting back to Earth with twice the velocity as usual. I quote: "So 4 times as much energy means harder on the stage, and 8 times as much ...
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2answers
98 views

How do ceiling fans cool or heat?

Why does a ceiling fan blowing air downward cool in the summertime: whereas a ceiling fan sucking air upwards heats in the wintertime: ? Why isn't it the other way around?
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1answer
36 views

How do I find the temperature of an object being heated on one side and cooled on the other [closed]

Ok so i'm trying to figure out what temperature a beam would be when one end is put into the ground and the other side is in the open air above. Assuming the beam is perfectly insulated besides the ...
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1answer
83 views

Intuition about the cosmological significance of the chemical potential

A definition of the chemical potential that has always served me well is $$\mu_i = \Big(\frac{\partial U}{\partial N_i}\Big)_{S,V},$$ that is, the amount of energy one would have to add to a system ...
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21 views

Liquid Temperature Profile

Suppose I have a one meter cubed box of liquid and I know that it is in a $-4^\circ~\rm C$ room for some amount of time, but was at a uniform $25^\circ ~\rm C$ when it was placed inside. I know I can ...
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1answer
37 views

Why does increasing heat conductivity decrease Nusselt number?

Normally we expect that when heat conductivity(k) increases heat transfer is also increases. But for fluids increasing k decreases Nusselt number. My senses tell that using high conductive fluid cause ...
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1answer
35 views

Can condensation occur in a unsaturated vapor?

Consider that a gas mixture of vapor$+$inert gas is unsaturated with concentration (or molar fraction) $x_\infty$ far from a clear, cooled substrate of temperature $T_\text{w}$, i.e. $T_\text{w}<T_\...
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1answer
24 views

How can excite a semiconductor to make a photon just by heat in room temperature?

I want to know if a semiconductor in room temperature can excite by heat, producing photon, without any other source of energy?
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6answers
492 views

Do gases have phonons?

A phonon is a quantized unit of sound; they are encountered when quantizing lattice vibrations in solids. Now, even an ideal gas supports sound waves, but in such a case, interactions between atoms ...
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1answer
32 views

Two rising bubbles of differing temperatures

Consider two bubbles rising through some medium (water, for example). Given that the two bubbles have the same initial size, pressure, and temperature but differing velocities, which bubble will be ...
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1answer
63 views

If Black holes are maximal entropy how can they evaporate?

According to Hawking/Bekenstein a black hole represents the highest amount of entropy for a given volume, (actually the entropy is related to the surface area of the black hole but the fact that they ...
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0answers
29 views

Calculate Temperature change in a solid due to resistive heating

Trying to calculate temperature increase in a solid due to resistive heating by a current flow, is this along the right lines? First I have calculated resistance due to resistivity, then calculated ...
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0answers
18 views

Inductance heating, Temp Change [duplicate]

I am trying to find the temperature increase of a solid(copper) in a gas (air) due to an electric current passing through the solid (inductance). I need to encompass any temperature losses from the ...
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2answers
89 views

Entropy always increases in a closed system - what if the universe is open?

An interesting question I was asked: Entropy always increases in a closed system - what if the universe is open? Does that mean that entropy can decrease in such a system? Of course, I think there is ...
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1answer
24 views

Effect of wall friction on stagnation pressure and temperature

We have incompressible air flowing through a cylindrical pipe, from section A to section B. The process is considered to be stationary. My theory book says that, because of the frictional losses on ...
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1answer
14 views

Does frequency of mechanical vibration of material affect its blackbody radiation spectrum

Can we see the difference in emissivity for instance between the same object vibrating in two different frequencies ?
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1answer
31 views

Confusion about Isobaric processes

Suppose in a ballon of gas is given an extra bit of heat, so as to getting the ballon's internal energy slightly up and this will work out to achieve a little bulk for the ballon. Though the whole way ...
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16 views

Rugged Energy Landcapes (Free Energy vs Potential Energy Questions)

A spin glass has what is called a "rugged energy landscape." That is, when you cool down below a certain temperature, the system divides into many wells, all corresponding to slightly different ...
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1answer
29 views

Why do $C_p$, $\alpha$ and $\kappa_T$ all approach to infinity when two phases coexist at the mean time?

My textbook (writed by Chinese) says that when two phases of a system coexist at the same time, this system's isobaric thermal capacity $C_p=T(\frac{\partial S}{\partial T})_p$, coefficient of ...
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2answers
45 views

Maxwell's area construction, why?

In the standard derivation of Maxwell's area construction (which can be found on page 4 of this pdf) the following equation is often written: $$G(p_1,T)=G(p_0,T)+\int^{p_1}_{p_0}Vdp $$ When the two ...
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23 views

Project Orion pusher plate computer modeling

Linked from the space.stackexchange forum: http://space.stackexchange.com/questions/15051/orion-project-npp-pusher-plate-computer-models-and-survivability Project Orion is discussed as if it is a ...
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55 views

Would it be correct to state that all the forms of everyday matter (mountains, tables, buildings, people, etc.) are in a metastable state?

We had a fire going in the backyard of a friends house this weekend, and after thinking about the chemical reactions occurring in the wood (and anything else we threw into the pit), I started to ...
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1answer
53 views

Why are glass beads used in a fractionating column?

Most sources do not go beyond saying that glass beads help increase the surface area for condensation of the liquid of the higher boiling point while using the method of Fractional Distillation to ...
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0answers
32 views

How can I get the exit temperature of water entered 100 degree in a pipe surrounded by 30 degree water?

Assume any value for: Length of the pipe The material of the pipe Velocity Heat transfer coefficient. I tried considering it as parallel flow heat exchanger but the water in this example isn't ...
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1answer
54 views

Confusion about inverse square law and temperature increase of an object

I know the inverse square law means that radiation intensity decreases in proportion to the radial distance from the source (I is proportional to 1/r^2). Does this apply to the temperature increase ...
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3answers
102 views

What ds>dQ/T mean?

I read the derivation on page 216 over here: https://www3.nd.edu/~powers/ame.20231/notes.pdf First it considers an irreversible process between state 1 and 2 followed by a reversible process between ...
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3answers
57 views

When does the Boltzmann distribution apply?

What are the requirements for a system to be described by the Boltzmann distribution in equilibrium? For example, should all the particles be identical? No attractors in the phase space? ...
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1answer
46 views

Thermofluid mechanics inclined plane

As shown in the attacked image, a tank has an inclined wall at an angle of 450 to the horizontal. On this wall, there is a 1m square door that is hinged at A and has a simple latch at B. The distance ...
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2answers
43 views

Thermal Capacity

An electrical heating coil of power $P$ is used to transfer thermal energy to a body of mass $m$. In a time $t$ the body changes temperature by $\Delta T$ . What is the thermal capacity of the body?
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1answer
144 views

Does density of air decrease or increase with altitude and relation of this with temperature?

I think the air density decrease as due to gravity more air woul be near the earth but as the hot air raises up doesn't it have momentarily increased the density at height (like in up troposphere) ...
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1answer
18 views

Force applied between neighboring atoms resulting in increase in separation

I am attempting a past paper question in practice for an upcoming exam and I am a little lost with the following question: Using lennard Jones model for potential. An external force $F$ is applied to ...
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1answer
71 views

2nd law of thermodynamics - simple steam power plant problem [closed]

A steam power plant consists of a boiler, a turbine, a condenser and a pump. The temperature of the inner walls of the boiler is 350 °C and the temperature of the condenser cooling water is 20 °C. ...
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1answer
39 views

Entropy for $N$ number of particles [closed]

If there are $N$ number of non-interacting and distinguishable particles which have either Energy $E_1$ or $E_2$ , then a. What will be the entropy $S(n)$ for such system? ($n$ is the number of ...
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2answers
57 views

Increase in entropy principle

If we consider a system to undergo an irreversible process from state 1 to state 2 and a reversible process from state 2 to state 1, then through Clausius inequality $\int_{1}^{2} \frac{\delta Q_{...
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0answers
54 views

Maximum temperature possible on earth

What is maximum temperature that can we have on earth on a single day? Lets say an air mass is static over an area and there is no way for air mass to move, sun warming it up would increase ...
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28 views

Eddy current damping heat generation

Background According to this source (page 7): https://deepblue.lib.umich.edu/bitstream/handle/2027.42/109373/me450w10project16_report.pdf?sequence=1 the "braking" torque a magnetic field on a ...
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1answer
35 views

Are all heaters exactly as energy efficient as each other?

I many applications, efficiency is measured in terms of how much of the input energy is wasted generating heat instead of the actual type of energy you want. For example, lightbulbs generating heat ...