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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74 views
How do you determine the heat transfer from a P-V diagram?
I doubt this question has been addressed properly before, but if there are similar answers, do direct them to me.
I am currently studying the First Law of Thermodynamics, which includes the p-V ...
3
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2answers
176 views
Ideal gas concentration under temperature gradient
I'm trying to calculate the concentration of an ideal gas in an adiabatic container as a function of position where the top and bottom plates of the container are fixed at temperatures $T_1$ and ...
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2answers
94 views
Why is Entropy expressed in terms of Enthalpy?
Why does ${\Delta}S_{m(fusion)} = \frac{{\Delta}H_{m(fusion)}}{T}$ ?
I always thought ${\Delta}S = \frac{dQ}{T}$
In this case does it mean $dQ = {\Delta}H$ ??
Why is it so?
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2answers
140 views
Behaviour of individual terms in Einstein-Smoluchowski fluctuation-dissipation relation
Consider a bath of Brownian particles at temperature $T$. If we sprinkle some larger particles in this (eg: pollen grains in water or dust motes in air), they'll diffuse with diffusion constant $D$ ...
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2answers
119 views
Measurement of the energy of an atom using a cold substance
An atom was prepared in a superposition of ground state and excited states.I propose to measure the state by coupling the system to a cold enough substance.
By cold enough I mean $$kT\ll E_1,$$ where ...
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1answer
617 views
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 ...
6
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1answer
1k views
LED Thermal Modeling (How to solve heat equation with constant heat source)
I have a mechanical design with LEDs that generate heat. I want to estimate the temperature at the LED junction vs. time, but especially at steady state.
Knowing the LED voltage drop and current, I ...
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1answer
325 views
What meaning does the slope of the efficiency path on a Mollier diagram have in terms of temperature?
Let's say I have a steam turbine that I have modified to increase its isentropic efficiency. As a specific case, consider the modification outlined in the Mollier diagram below. The arrows represent ...
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1answer
53 views
How can I understand a Vortex Tube and its efficiency?
A Vortex Tube takes a pressurized input stream, most typically of a gas, and creates two output streams with a temperature differential. Apparently, it has been described as a Maxwell's Demon.
Both ...
3
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1answer
59 views
Amount of energy to separate Gases - relationship to concentration
I want to understand the efficiencies of separating mixed gases, and for that I want to understand the thermodynamic limit case. Looking at the wikipedia page for entropy of mixing, I find the ...
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1answer
282 views
Coffee cooling in a cup
Will coffee in two differant size styrofoam cups in the same room conditions cool at the same rate? One cup is 8 oz. and the other would be 12 oz.
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1answer
94 views
Joule-Thomson effect of Van der Waals gas
I'm supposed to calculate the inversion pressure $p_i$ of a Van der Waals gas. The state equation of the Van der Waals gas is: $$(p + \frac{a}{V^2})(V-b) = RT.$$ To get a hold of the inversion ...
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1answer
57 views
How long does it take a warm object to cool in air?
This is a work-related question. A warm steel torus of a given diameter & thickness is left in a room held at a controlled temperature, how long does it take to reach equilibrium? Assume the air ...
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1answer
35 views
Can Joule's First Law of Thermodynamics be Applied to Atomic Charges?
James Joule established that all forms of energy were basically the same and interchangeable. My question is if thas law is relevant in particle physics. Can a positive charge and a negative charge be ...
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1answer
456 views
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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1answer
199 views
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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1answer
180 views
Maxwell's Demon bug, trapdoor space and time
What about the size of the door (space) and how long has it to be opened (time)?
I think Maxwell's demon would have a problem with space, if the door is too wide (more than one particle size), then ...
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1answer
47 views
Calculating the coefficient of thermal expansion in liquid
I am trying to write a matlab function that calculates the coefficient of thermal expansion of water from a given temperature. From what I understand the thermal expansion coefficient is calculated as ...
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1answer
48 views
Time constant of ice melt
I'm familiar with problems of "how much ice can you melt given some amount of energy", but I'm writing to get some clarification on the time constant of this event. This question might be somewhat ...
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1answer
18 views
Gas transformation for different molar number
When a gas at normal conditions (1atm, 273K, 22.4L) we say like the $$\frac{PV}{T} = 0.0820...$$
And by the know equation: $$PV = nRT$$
Where R is equals to $0.08205...$ and $n$ is the number of mols ...
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1answer
59 views
Indicators on how even the heat is distributed?
I'm wondering if there are any good indicators on how even the heat is distributed on an object (for simplicity, a flat object maybe)? What are the possibly reasonable ways to maximize the evenness if ...
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1answer
217 views
How much energy Maxwell's demon will earn?
Suppose we have one mole of one-atom ideal gas at temperature $T$.
Suppose Maxwell's daemon has separated molecules into two sections, one with speed below mean and another with speed above mean.
...
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1answer
54 views
Problem evaluating moles in a an isochor transformation
I have a problem with an isochor transformation.
Me and my group of study made an experiment that want to check Gay-Lussac’s law.
We registered the equilibrium states and fitted the $P = nRT / V$, ...
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1answer
212 views
Expressions for canonical partition function and probabilities $p(E_i)$
Given an atom with 4 allowed states corresponding to the energy levels
$E_1 = 0$, $E_2 = E$, and $E_3 = 2E$ with degeneracies 1, 1, and 2 respectively.
How do I find the expressions for the ...
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1answer
69 views
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas?
I think that you need work to preserve this process and you bring thermal ...
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1answer
44 views
Heisenberg's uncertainty and $0 K$ temperature
when a body is subjected to $0 K$ temperature, it becomes rigid. hence if we see in terms of quantum the lattice vibration decreases, resulting in no change in the direction of the Random velocity, ...
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1answer
73 views
The effects of heat on gravitational fields
In boiling soapy water, globs of soap coalesce as the temperature increases to boiling. Does this mean that temperature increases the gravitational pull of bodies?
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1answer
91 views
Sensible heat question (solving for temperature)
If $55 034.175 \rm{kJ }$ of heat are transferred to $150 \rm{kg}$ of ice at a temperature of $-12.15 ^\circ \rm{C}$, calculate the temperature of the resulting water.
Using $Q = mc(t_2-t_1)$ or ...
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1answer
184 views
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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0answers
26 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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0answers
36 views
Relation for Temperature and Pressure starting from chemical potential
Assume we have a system filled with a specific substance. Inside the system there is a small box with an opening. Usually this would mean $T,p,\mu$ would all be the same inside the box and outside. ...
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35 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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0answers
36 views
State equations in magnetic systems
Assume there is an isotropic magnetic material in a homogeneous field $\vec{H}$ inside of a long coil. The work done to the material is given by $\delta A = H dM$, where $M$ is the magnetisation of ...
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0answers
18 views
Flow of the component of a hidrostatic system
I have a problem that asks me to prove, from notions of thermodynamic chemichal potential, that at constant temperature, air (or any component of a hidrostatic system) will flow to lower pressures, ...
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0answers
195 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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0answers
40 views
Entropy of binding two rigid bodies together in a closed system (e.g. forming a diatomic out of two monatomic gas particles)
When I bind two molecular complexes together, or in the simplest case, form a diatomic out of two atoms in a monatomic gas, the entropy of my (closed) system will decrease. We can perhaps understand ...
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0answers
59 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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0answers
131 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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0answers
70 views
Pressure changes and external pressure
The questions I'm about to ask are standard thermodynamics but within a context of a refrigeration cycle if that is of any use to you. Anyways, I'm going to be going over my thoughts of how it works ...
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0answers
179 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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0answers
37 views
Relation between maximum entropy thermodynamics and entropy bounds
Here is a question which I've been thinking about, I'm sorry if it's little too vague, maybe you could point me to some source to read, if there's no clear direct answer.
The whole concept of ...
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0answers
257 views
Carnot efficiency, coefficient of performance for a refrigerator
I was reading that a new type of refrigerator might reach a coefficient of performance (COP) of 10. This seems quite the achievement and the authors state that their approach might achieve a Carnot ...
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0answers
109 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).
...
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0answers
122 views
what is the physics just at bubble formation.
ie do a couple of molecules with more energy bang out a volume in the liquid where molecular attraction is overcome and the energetic molecules can move at random?
where can I find out more about ...
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0answers
78 views
2 streams going into an engine and 2 come out. Find the enthalpy?
Problem: Steam supply to an engine is made of two streams that mix before entering the engine. Stream 1 flows at a $.01\frac{kg}{s}$ with an enthalpy of $2952\frac{kJ}{kg}$ and a velocity of ...
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0answers
55 views
Newton's cooling law
I want to know few things regarding the practical of Newton's cooling law.
1). What are the other possible ways of making external conditions constant except using two calorimeters one within one?
...
