3 ms·
I transcribed the data and fitted dual exponentials to it. When time t is in minutes, the data seem to follow T(t) = 20 + 25e^(-2.3*t) + 54e^(-0.034*t) T
by kqr 7mo ago
I transcribed the data and fitted dual exponentials to it. When time t is in minutes, the data seem to follow
T(t) = 20 + 25e^(-2.3*t) + 54e^(-0.034*t)
This is very close to what the LLMs suggested. If I wanted to make an initial guess at this as accurate as the LLMs, what would I need to know? My interpretation of the coefficients is:
(a) 20 ℃ represents the room temperature this will eventually reach.
(b) 25 ℃ is how much of the temperature the mug will absorb as it is heating up.
(c) The decay -2.3 represents how fast heat is transferred to the mug. (It will be halfway after 20 seconds.)
(d) 54 ℃ is the differential between room temperature and starting temperature once we've accounted for the loss of 25 ℃ to heat the mug.
(e) The decay -0.034 is how fast heat is transferred out of the mug to the room. (It will be halfway to room temperature after 20 minutes.)
I'm okay with (a), and I could probably have guessed (d) once I know the other parameters.
I can also sort of see myself figuring out (b): I would guess the heat capacity of the mug would be maybe 500 × 0.6 = 300 J/K, do the same for the water (4000×0.2 = 800 J/K). Some work later this comes out to a temperature loss of 20 degrees. Close enough.
But even if I tried to use my intuition for how hot the mug feels as these processes go on, I would have ended up nowhere near -2.3 and -0.034 for the decay coefficients. What would I need to know about convection, mug materials, and air properties to guess that more accurately?
Is it a neat coincidence or a good, very approximate rule of thumb that heat transfer to air is about 60× slower than that to ceramic-like solids?
- azalemeth 7mo agoThis is all known physics. It's almost exactly Newton's Law of cooling -- see https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling#Standard_formulation https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling#Stan... -- which has been known for a long time and is a mono exp. The biexponential behaviour is because the _actual_ relevant differential equation, the Thermal Diffusion Equation, has a Fourier mode solution and you've picked out two coefficients. An infinite sum of them _is_ the answer. How you pick out the coefficients is the fun game of https://en.wikipedia.org/wiki/Spectral_methods https://en.wikipedia.org/wiki/Spectral_methods
- dynm 7mo agoAck, I'm sorry you had to waste your time transcribing the data! I uploaded it here: https://dynomight.net/img/coffee/temps.csv https://dynomight.net/img/coffee/temps.csv
- kqr 7mo agoIt is really no bother when [1] exists. It took a couple of minutes at most. These are the differences between the transcribed data and the CSV values: https://i.xkqr.org/transcracc.png https://i.xkqr.org/transcracc.png [1]: https://web.eecs.utk.edu/~dcostine/personal/PowerDeviceLib/DigiTest/index.html https://web.eecs.utk.edu/~dcostine/personal/PowerDeviceLib/D...