3 ms·
Problem with that theory: 1. Temperature is monotonically related to energy content. A warmer system has more energy than a colder one, all else being equal.
by lisper 4y ago
Problem with that theory:
1. Temperature is monotonically related to energy content. A warmer system has more energy than a colder one, all else being equal.
2. To cool, a system must release energy. The rate at which a system can release energy is monotonically related to the difference in temperature between the cooling system and the cold sink to which its energy is being released. The bigger the temperature difference, the higher the rate of energy release (all else being equal).
For the Mbemba effect to be real, one of those two premises must be false. Which one is wrong?
- eternauta3k 4y agoThe second one is false. https://en.wikipedia.org/wiki/Leidenfrost_effect https://en.wikipedia.org/wiki/Leidenfrost_effect
- eternauta3k 4y agoBasically, heat transfer rate in a liquid goes down when a certain temperature is reached, because an insulating layer of vapor is formed.
- teraflop 4y ago> Temperature is monotonically related to energy content. A warmer system has more energy than a colder one, all else being equal. In equilibrium, the temperature of the water is directly related to the energy content, with the heat capacity being the conversion factor. But under the thermodynamic definition, the temperature of the system depends not only on its energy but also on its entropy. And one of the points the article is making is that even when we know the total amount of energy entering or leaving the system, its entropy may not be nearly so easy to measure or calculate when its state is far from equilibrium.
- lisper 4y agoSorry, but that is not true. The definition of the SI unit of temperature, the Kelvin, is given in terms of Boltzmann's constant, which has units of Joules (i.e. energy) per Kelvin.
- cycomanic 4y agoIIRC (my thermodynamics is a long time ago), but 2 applies only when the two (cooling system and sink) are near equilibrium, which is not the case here.
- extr 4y agoI don't think either one is false. To me, 2 looks false if you consider the "system" in question to be the entire glass of water. But my interpretation is that in this case the glass of water is really many very small systems (pockets of unequal amounts of energy) all interacting with each other. Let's say you're given a few hot potatoes and have to cool them down as fast as possible. You have a refrigerator but you can only keep one of them in it at a time. How do you decide which one to put in at any given time so they all reach temp the fastest? When the "system" involves many possible pairings of temperature differentials it feels very intuitive that some configurations would be better than others. So it removes the mind-bending thermodynamics law breaking aspect of it. Admittedly, this isn't really what the article says! I honestly don't get how my above intuition squares with the whole energy minima thing, and so while useful as a thought exercise to at least help me entertain the idea, I'm not really sure it's correct?