Heat is energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objects and systems, but its origin and properties can be understood in terms of their microscopic ...
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72 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 ...
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 ...
3
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1answer
52 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 ...
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1answer
132 views
Optical element is heated by laser: is it possible to get oscillating heat distribution?
Imagine that we have thin optical element, which is irradiated by laser. Laser heats element, so there is some heat distribution in element. There is a heat sink through upper and lower element faces ...
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1answer
58 views
Could we really charge metal plates using microwaves?
While skimming through Dielectric heating, I read that they use microwaves to charge the plates. How do they do that?
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1answer
451 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
45 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
58 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
82 views
Is the heat required to alter the Higgs field an 'absolute heat'?
I have read and heard that manipulating the Higgs field would require heating up a local geometry to ridiculous temperature. I am trying to understand if there are stars or places in the universe ...
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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
72 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
88 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
220 views
Why do phonons cause excellent heat conduction in diamonds?
Phonons are the quantum of lattice vibrations in crystals and are not to be confused with photons, the gauge bosons of the electromagnetic force. Apparently, they contribute to heat conduction, but I ...
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1answer
183 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
72 views
Mechanical Equivalent of Heat
Recently I have been looking up James Joule's experiment regarding the mechanical equivalent of heat. After viewing some drawings of the apparatus, I assumed that the lines holding the weights would ...
4
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0answers
121 views
Thermodynamic relations from Gibbs-Duhem
Given the Gibbs-Duhem relation
$V dp = S dT - N d \mu$, I am having trouble deriving the following identity:
$\ (\frac{\partial N}{\partial \mu})_{V,T} = N (\frac{\partial \rho}{\partial p})_T$
...
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0answers
41 views
Photon pumping in Laser
Let's consider a ring laser where the laser must pass through the gain material before it is sent toward a partially reflective surface $\ R=1-T $. The other mirrors are perfect reflectors with $\ ...
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0answers
142 views
Does a thermally expanding torus experience internal stress?
I'm trying to learn continuum mechanics and thermo-mechanics.
As we know, heating an object increases the mean atomic distance $a_0$ of the atoms in a rigid body. Let's assume it is a linear elastic ...
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0answers
25 views
Interface condition for heat exchange
I would like to compute the heat distribution of a piece of metal with some surrounding material. The heat is assumed to propagate by diffusion, so inside the metal piece and also on the outside, the ...
2
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0answers
31 views
In a non-degenerate plasma, why are e-e collision negligible compared to e-ion for thermal conduction?
I'm trying to make some order of magnitude estimates of heat transfer in stars - to better understand 1) why conduction is said to be negligible (for non-degenerate matter) and 2) when convection ...
2
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0answers
100 views
Problems in the modern semiconductor/electronics technology?
From what I have read, the problem with modern semiconductors/electronics seems to be quantum tunnelling and heat. The root of these problems is the size of the devices. The electrons are leaking out, ...
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0answers
405 views
When do I know if energy stored in an object is 0 or nonzero? (Heat transfer)
There is uniform internal heat generation at $\dot{q}=5\times10^{7} \frac{W}{m^{3}}$ is occurring in a cylindrical nuclear reactor fuel rod of 50 mm diameter and under steady state conditions the ...
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0answers
604 views
What are typical values of the critical thickness of insulation?
As most people who've had any elementary heat transfer course are aware, when insulating a pipe, wire, etc, there is a critical thickness for the insulation below which it causes greater heat transfer ...
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0answers
354 views
Heat equation and Bessel's function
Could someone please explain why if the time-independent heat equation can, via changing of variables, take the form of Bessel's equation that the $\sqrt\lambda$ should take the values of the zeros of ...
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0answers
48 views
Calculate how hot PLA will become
I am trying to attach the shaft of a brass heating tip to a PLA component. My problem is that the tip will have to reach a temperature of about 200°C and the PLA can only handle a temperature of about ...
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0answers
28 views
Calculating the change in entropy in a melting process
I have a homework question that I'm completely stumped on and need help solving it.
I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
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0answers
30 views
What is the meaning of $h_L - h_H$ for a heat engine?
My problem gives me a Carnot cycle heat engine with water as its working fluid, with $T_H$, $T_L$, and the fact that it starts from saturated liquid to saturated vapor in the heating process.
I need ...
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0answers
70 views
How much money does an unused but plugged-in cellphone-charger waste in a year, if its not getting warm?
Is it right as xkcd states:
You can use heat flow to come up with simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day.
Or, more ...
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0answers
42 views
Several questions about spring chiller and LMTD
I'm designing a simple copper coil wort chiller. Digging formulas I'm having hard time to figure some things out, perhaps some simple guides may help me to go the right direction:
LMTD need inlet ...
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0answers
44 views
Can I estimate the long-term surface heat transfer coefficient based on a temperature difference between the air surface and ground surface?
I want to estimate the long-term or annual heat transfer coefficient for the earth's surface in a particular area where the mean annual air surface temperature is about 13$^\circ$C, and the mean ...
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0answers
44 views
What other factors effect the ability of a propigating field of pressure in a gaseous medium to predict gravitational collapse?
What other factors effect the ability of a propigating field of pressure in a gaseous medium to predict gravitational collapse?
Will the only factor influencing the Speed of Sound in this medium be ...
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0answers
166 views
Is the $mL_c$ value for triangular and rectangular fins the same value?
I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong.
...
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0answers
65 views
How to compute the heat flow for a specific material for some given boundary temperature?
Assume I have a bounded material with heat sources inside. The material is known (i.e. I know heat capacity and all relevant data) and the temperature of the boundary is fixed. I solved the (steady ...
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0answers
242 views
Maxwell's Demon - laser cooling
There’s an interesting article on Scientific American
that tells how to cool individual atoms can bee cooled to within a very tiny fraction of Absolute Zero.
It uses two laser beams acting on a very ...
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0answers
20 views
Total massflow through heat exchanger
I am working on a project and I stumbled on a problem. The project is to design a heat pump to replace the old system (actual problem, not some homework problem). There are 100 or so induction units ...
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0answers
19 views
Heat transfer in fluid between two horizontal plates vs unconfined case
I often see the correlation for turbulent heat transfer between liquid cells published by Globe and Dropkin (1959). In the original paper the fluid was confined between two horizontal plates and ...
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0answers
26 views
Heat of adsorption from fugacity data
I have a set of data relating the fugacity ($\approx$ pressure) to the loading for a given set of temperatures. There are three temperature sets each having five fugacity vs. loading points.
The ...
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0answers
32 views
Height of a piston in a heated cylinder containing H2O
I'm a first time user and I hope I won't be too enigmatic asking the following question:
I have a cylinder (radius= $6$ $\text{cm}$) with a frictionless piston on top of it and inside $30$ $g$ of ...
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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
59 views
How is pool boiling dealt with by today's process design methods?
Designing evaporators and industrial reboilers often requires at initial stages of dimensioning (i.e. when the support from a finite element software tool to model the system of interest, isn't yet ...
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0answers
533 views
What is the insulative value of water?
I am having a hard to finding what the R value of water is. I am trying to compare it to styrofoam (which has an R-Value of 5).
EDIT
Based on the assumption that water has an insulative property, ...
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0answers
59 views
MIT's 230% efficient LEDs. A reprise about cooling
This is a reprise of the question Can someone explain the science behind MIT's 230% efficient LEDs?
The PRL paper doesn't detail what the efficiency of heat-to-light energy conversion is, which in ...
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0answers
1k views
How to determine size of a Heat Exchanger?
I am designing a Tube heat-exchanger, similar to this:
My process requires water (at room temperature, 18C ~ 22C) that is being pumped out of a small tank (300 Liters) to be heated in a ...
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0answers
53 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?
...
