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What is the speed of heat?

Anonymous Thu 23 Apr 08:13:40 2020 No.11594239 View Reply Original Report

Quoted By: >>11594262 >>11595080 >>11595223

Let's say I had a one meter long metal rod and on one end I attach a device that can measure even the tiniest increases in temperature at that end of the rod. If I start heating the opposite end how much time will it take before my device measures any temperature change? Is it the speed of sound in the material? The speed of light?

Anonymous

Anonymous Thu 23 Apr 2020 08:30:05 No.11594262 Report

Quoted By: >>11596860

>>11594239
It has to do with the specific heat capacity, the fastest possible transmission of heat is seen in liquid helium.

Anonymous

Anonymous Thu 23 Apr 2020 15:44:43 No.11595080 Report

Quoted By:

>>11594239
depends on how hot no?

Anonymous

Anonymous Thu 23 Apr 2020 15:52:41 No.11595104 Report

Quoted By: >>11596860

>heat
What you are really trying to say is what is the time rate of change of the temperature differential at different points in the rod. At a given point in the rod, you can use some basic thermodynamic principles to show that temperature obeys $\frac{\partial T}{\partial t}=\alpha\frac{\partial^2 T}{\partial x^2}$ where alpha is a constant that depends on the material. The bigger alpha is, the quicker temperatures move to equilibrium and the faster heat is transferred.

Anonymous

Anonymous Thu 23 Apr 2020 16:39:04 No.11595223 Report

Quoted By:

>>11594239
Well the energy is dissipated via phonons, so I guess you'd say the 'speed of heat' is the speed of sound in the material. Really though you'd use the heat equation to work out how the heat will dissipate so it's not particularly useful to think of a 'speed of heat'.

Anonymous

Anonymous Fri 24 Apr 2020 01:37:19 No.11596860 Report

Quoted By: >>11596916 >>11596974

>>11595104
>>11594262
i'm specifically not wondering about the rate of heat transfer. speed of heat as in m/s. in essence how long does it take in time for one end of the rod to "know" when the other end of the rod is warm.

Anonymous

Anonymous Fri 24 Apr 2020 01:57:46 No.11596916 Report

Quoted By: >>11596954 >>11597665 >>11597685

>>11596860
>i'm specifically not wondering about the rate of heat transfer. speed of heat as in m/s. in essence how long does it take in time for one end of the rod to "know" when the other end of the rod is warm.
Is this b8 or is OP just retarded?

Anonymous

Anonymous Fri 24 Apr 2020 02:14:57 No.11596954 Report

Quoted By: >>11597665

>>11596916
probably the latter, we get tons of unironic HS dropouts here. if he were actually smart he'd post in >>>/sci/sqt

Anonymous

Anonymous Fri 24 Apr 2020 02:21:03 No.11596974 Report

Quoted By: >>11597665 >>11597761

>>11596860
actually the speed of sound because heat is conducted (mainly) by phonons (at room temp).

So the first signal would get there at the speed of sound if you could measure it, but how fast you get enough higher energy phonons over there to actually measure a macroscopic signal depends on the thermal conductivity.

Anonymous

Anonymous Fri 24 Apr 2020 07:45:38 No.11597665 Report

Quoted By: >>11597766

>>11596954
>>11596916
Nah y'all are retarded and cant understand a simple fucking question. Congrats on passing 8th grade science and understanding thermal conductivity fucking bravo.
>>11596974
Thanks for an actual answer. I guess my lack of understanding was because I wasn't thinking of the quantization of the energy.

Anonymous

Anonymous Fri 24 Apr 2020 07:55:39 No.11597685 Report

Quoted By: >>11597744 >>11597771

>>11596916
>Is this b8 or is OP just retarded?
Are you?
Modelling heat using the standard heat equation leads to instantaneous heat propagation.
See https://link.springer.com/chapter/10.1007%2F978-3-7643-7794-6_2 for a finite speed model

Anonymous

Anonymous Fri 24 Apr 2020 08:44:26 No.11597744 Report

Quoted By: >>11597761

>>11597685
Started reading the paper and I’m pretty much out of my depth for everything after the first page. Is there any way to explain the rest of the paper in a way that an engineering undergrad can understand

Anonymous

Anonymous Fri 24 Apr 2020 08:56:34 No.11597761 Report

Quoted By:

>>11597744
It's incomplete because springer are nazis. So there's not much to actually get.
They just modified the flux in Fick's first law to include the speed of sound.

The answer to OP's question in general was given by >>11596974
You should read about phonons if you want to know more, my link was just to show the other anon is full of shit and it's actually a valid question

Anonymous

Anonymous Fri 24 Apr 2020 09:01:40 No.11597766 Report

Quoted By:

>>11597665
cope

Anonymous

Anonymous Fri 24 Apr 2020 09:04:32 No.11597771 Report

Quoted By: >>11597780

>>11597685
>instantaneous
FTL? How instantaneous?

Anonymous

Anonymous Fri 24 Apr 2020 09:10:09 No.11597780 Report

Quoted By:

>>11597771
>FTL? How instantaneous?
Arbitrarily fast, depending on your timestep and resolution

Anonymous

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Anonymous Fri 24 Apr 2020 10:50:31 No.11597918 Report

Quoted By:

>"cope"
>"Look guys i said the meme word does this mean I won the argument?!!!"

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