Questions tagged [thermodynamics]
Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using tag: [statistical-mechanics].
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Efficiency of parallel and sequential heat pumps
Consider two identical heat pumps, for example, split-system air conditioners. There're two ways to make them work - in parallel or sequential. Parallel means that "hot" radiators of the machines are ...
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Thermal Energy from Friction on a Rope
Question:
A capstan is a rotating drum or cylinder over which a rope or cord slides to provide a great amplification of the rope's tension while keeping both ends free. Since the added tension in the ...
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Confusion regarding entropy, reference papers request
1.a In paragraph at Wikipedia/Entropy it is stated:
This is because energy supplied at a high temperature (i.e. with low entropy)
tends to be more useful than the same amount of energy
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How would I calculate the convection coefficient in transient convection?
So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I ...
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Transient radiation--heating a slab
Hey guys I really need help on this problem.
A ceramic slab of dimentions 5cm x 10 cm x .25 cm has to be heated to $177\,^{\circ}{\rm C}$. The ceramic slab travels on a conveyor belt traveling at $....
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Relation between external magnetic field intensity H, magnetisation M and the entropy?
How are the external magnetic field intensity H, magnetisation M and the entropy related to each other? i.e. if I change the magnetic field intensity by dH what will be the change in entropy dS in ...
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Connection between entropy and energy
An isolated system $A$ has entropy $S_a>0$.
Next, the isolation of $A$ is temporarily violated, and it has entropy reduced $$S_b ~=~ S_a - S,\space\space\space S\leq S_a.$$
Is it true to say: the ...
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Thermodynamics and cross entropy
I am facing with the concept of cross entropy. I would like to know the thermodynamic and statistical meaning of cross entropy (if exists)?
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System moves away from equilibrium $\rightarrow$ it has energy added?
Suppose there is an isolated system $A$ at time $(-\infty, t_1)$, whose entropy is $S=S_{max}$, i.e. it is at thermodynamical equilibrium.
Between moments $[t_1, t_2)$ the isolation is violated and ...
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Time it takes for temperature change
I have just been thinking about it for a while and would like to see if there is a way to do this problem.
The Setup:
We have an insulated cup with mass $m_c$ and specific heat $s_c$. The cup is at ...
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Reference paper to support information -- energy relation $\left(kT \ln2 \rm\frac{J}{bit}\right)\;.$
In answer to Maxwell's Demon Constant (Information-Energy equivalence) there is stated that one bit of information allows to perform $kT \cdot \ln2$ Joules of work. Which paper supports the thesis?...
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Is a closed system receiving heat guaranteed to have entropy below maximum?
Isolated system will preserve its entropy unchanged (for fully reversible system) or it will increase its entropy (for system with irreversible processes).
For a closed system, it can receive energy ...
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Why are volume and pressure inversely proportional to each other?
It makes sense, that if you have a balloon and press it down with your hands, the volume will decrease and the pressure will increase. This confirms Boyle's Law, $ pV=k=nRT $.
But what if the ...
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Why is glass a good conductor of heat?
AFAIK Glass is insulator, it doesn't have free electron. It's said metal is a good conductor of heat because it has free electron, glass doesn't have free electron, why it is a good conductor of heat?
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How would I go about solving this transient convection problem if the mean fluid temperature is constantly changing?
Let's say I have a ceramic slab on a conveyor belt that is initially at $450\,^{\circ}\mathrm{C}$ and there is air being blown over it at a speed of $35 \frac{m}{s}$ with an ambient temperature of $18\...
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Equations instead of psychrometric charts
I want to create a program that will accurately simulate a condensor. I want to use the data in psychrometric charts. But I cannot and hence want to use equations that show similar data. Any idea ...
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Interacting system and relaxation times
I got a question I'm not sure how to state precisely or is it even valid. Any help is most welcomed.
I stripped the question of all details because I wanted to emphasize my problem, but should ...
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nature of glass transition
I am reading in some book: "The glass transition is similar in appearance to a second-order phase transition, but it is not a true thermodynamic phase transition. This is because the transition ...
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Is there a simple way to derive a T-S diagram from a p-V diagram for arbitrary processes?
Often, for thermodynamic processes only a p-V diagram is shown.
Even without hard figures, the shape of the curve can be helpful to evaluate the process.
However, it is hard to figure out for real ...
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If I take a bottle of air into space, and open it, where does it go?
It seems to me that space doesn't have any/much air, and if my bottle is full of air, when I open it, where does the air go?
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Intuition behind the concept of heat
Even if elementary, I'm afraid I am still not comfortable with the concept of heat. I can picture heat as some kind of incompressible fluid that is transferred from a body to another in such a way ...
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Why did the microwave oven only heat my coffee half as much as expected?
A sticker on my microwave oven states its output effect to be $750\ \mathrm W$, which is $180$ calories per second. This means that heating $250\ \mathrm g$ of water by one degree Celsius would take $...
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Is fire plasma?
Is Fire a Plasma?
If not, what is it then?
If yes why, don't we teach kids this basic example?
UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify the ...
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Maximum efficiency for a counter-current heat exchanger (double flux controlled motorized ventilation)
I am not sure if I can explain the question correctly because I don't know the name of this mechanism in English.
This is my explanation attempt: In a house, a tube is expelling the air from the ...
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How fast is heat transferred by conduction?
How fast is heat transferred by conduction? Is there some simple, but quantitative way that starts from some properties of the material (e.g. its thermal conductivity) and makes rough predictions, for ...
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Given constant T, why does P affect internal energy?
It has always bugged me that tables for water (and other) properties have the capability to look up internal energy as a function of both temperature and pressure. If we limit the discussion to ...
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What is lambda R in Richardson's Law?
I've got to calculate the thermionic emission through a diode, so I need to use Richardson's Law. However, one thing's got me confused - according to the Wikipedia page:
$$J = A_GT^2e^\frac{-W}{kt}$$
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When a color LCD/LED display is off it is black, when on it is colored. What color to light is an LCD/LED display
When a modern display using pixels is turned on its colors are different than the black that the screen is actually made up of. When put in light, such as sunlight, does the screen react to the color ...
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For how long can we make an air balloon stay flying via remotely controlled heat system?
I wonder how a function $$f=f(h, m_{\mathrm empty}, V_{max}, T_{h}), $$ with the top height $h$, the empty mass $m$, the maximum volume $V_{max}$, and the temperature of the heater $T_{h}$ would look ...
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Intuitive picture for spin-fluctuations contribution to specific heat of He3
Usually when discussing Fermi liquid theory, it is stated that due to the quasiparticles effectively behaving like a free electron gas with effective mass, the specific heat is linear in $T$ at small ...
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Why is oil a poor conductor of heat?
Why is oil a poor conductor of heat as compared to metals? It is used in transformers to conduct heat to external fins. But is it ever used for heat insulation?
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Is the efficiency of a stirling engine affected by dead volumes?
Consider the p-V diagrams of an ideal and real stirling cycle, as found here
The article suggests that dead volumes reduce the efficiency of a stirling engine. On the other hand, a simple thought ...
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Why is the lid of the cookware kept on induction cooker not hot?
Induction cookware cooks food by inducing an electro magnetic field in the ferro-magnetic cookware. Since iron offers a lot of resistance to the current, the current is converted into heat in the ...
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Per unit area, is there more heat transfer through the open top of a mug or the side walls?
I had a mug of hot coffee cool too rapidly for my liking the other day, which made me wonder what was the greater contributor to heat loss for a typical open-top ceramic mug: the open top, the walls, ...
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What is the physical or mathematical meaning of the Gibbs-Duhem equation?
The Gibbs-Duhem equation states
$$0~=~SdT-VdP+\sum(N_i d\mu_i),$$
where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?
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Microwave oven + water: dielectric heating or ion drag?
When you place a water or food in a microwave oven, it heats.
Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating?
AFAIK, in distilled water (which is a ...
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How to calculate the evaporative cooling rate needed to protect a house from forest fire
Recently in our area there has been a large forest fire and I've been looking into home defense from such things.
I am not a physicist - but can do some basic math.
I was wondering how I could ...
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How to express the heat capacity in terms of heat?
The first law of thermodynamics divides the internal energy change into contributions of heat and work.
$$\text dU=\omega_Q-\omega_W,$$
Here I chose the notation to emphasise that the two parts are in ...
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Boltzmann Brain Immortality
This is a somewhat philosophical question. Given that even after person A's death, there's a non-zero chance that a brain fluctuates into existence with exactly the same structure and memories as A's ...
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How much oxygen would be consumed on a 1 cm squared surface which is on fire?
I'm trying to figure out how much oxygen the Human Torch produces when he is on fire. I figure if I knew how much oxygen on average (per second?) is consumed by a 1 cm squared surface which is ...
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Why is compressible flow near the choke point so efficient?
Imagine a steady state, one-dimensional, compressible flow in a horizontal pipe of constant cross sectional area. This flow can be isothermal, adiabatic (Fanno), or diabatic (Rayleigh). As an example,...
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Finding electric power generated using heat transfer
I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$.
Given:
$\alpha_s = 0.83$
$...
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What's the classical limit of the pressure of the ultrarelativistic Bose gas
The pressure for the ultrarelativistic Bose gas is
$$p~=~U/(3V) ~\propto~ (kT)^4/(hc)^3.$$
It looks to me like it diverges for $h \to 0$. Looking at the derivation, it diverges because $h$ is the ...
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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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Does the second law of thermodynamics tell me how the entropy changes?
In thermodynamics I can e.g. compute the properties of ideal gases with certain energies $U_1,U_2$ in boxes with certain volumes $V_1$ and $V_2$. Say I have two such boxes and they have some specific ...
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