Mpemba effect - just how a freezer works?

[bahamagreen]

I read the Wiki page, then read Nikola Bregović's paper which Wiki mentions was selected as the best idea of about 22,000 paper submissions called by the Royal Society of Chemistry in 2012...

I'm not seeing any solutions that indicate they take into account how a freezer works... a freezer responds to hot water differently than cool water because it has a thermostat..

Mpemba's original observation was from using a freezer; and a freezer was also what Nikola Bregović described as using in his paper for his experiments.

The point is, a freezer uses a thermostat to power the cooling function as required. The thermostat is measuring the air temperature in the freezer compartment (not the temperature of the water)...

Simply put, elevated air temperature in the freezer compartment makes the thermostat kick on the cooler. Imagine two identical freezers with identical thermostat settings. Put cool water into one and hot water into the other. Now measure frequency and durations with which the thermostats engage the cooling function for both freezers...

Keeping in mind that the cooling function is designed to present a temperature to the air well below the freezing point,.and well below the subfreezing setting for the thermostat; which freezer is going to be subject to a greater warming of the air in the compartment, and which freezer will therefore be more aggressively cooling the air temperature (more frequent and/or longer durations of running the cooling function) in its compartment?

Seems to me that the Mpemba paradox arises from the assumption that both the hot and cool water are subject to the same conditions (a "static" subfreezing air environment), but freezers don't present a static environment; they actively engage their cooling function in response to the temperature of the air inside.

I did notice that some who do this experiment get the result and others don't... maybe the former are using a single freezer for separate trials or two freezers one for each sample, whereas maybe the latter are using one freezer to hold both samples for each trial. That would be consistent with how freezers use their thermostats and cooling functions.

Any thoughts?

 

[mfb]

I'm not seeing any solutions that indicate they take into account how a freezer works... a freezer responds to hot water differently than cool water because it has a thermostat..

How can have that an effect if you put both pots of water in together? Yes it works with a single freezer.

 

[bahamagreen]

Hmm... well that's interesting. :)

 

[russ_watters]

Most fridges/freezers turn on the compressor instantly when you open the door, so I doubt the heat loss from the water would make much difference.

I did a fairly rigorous experiment on this a few years ago and the thread is around here somewhere. My conclusion is that if the effect is real at all, it only happens under very specific/contrived circumstances. It is not generally true.

 

[PJC01]

I find the Mpemba effect intriguing but also recognize that there are many variables at play in this phenomenon. While it is true that a freezer uses a thermostat to regulate its cooling function, there are also other factors such as the initial temperature of the freezer, the amount of water being frozen, and the surrounding environment that can affect the results.

It is also important to note that the Mpemba effect has not been consistently replicated in experiments, which suggests that there may be other factors at play that we are not yet aware of. It is possible that the effect may be more pronounced in certain types of freezers or under specific conditions.

I agree with your observation that the Mpemba paradox may arise from the assumption of a static subfreezing air environment. Freezers are designed to actively respond to changes in temperature, so it is possible that the cooling function may be more aggressive in response to the hotter water in the Mpemba effect.

Overall, I think more research needs to be done to fully understand the Mpemba effect and its underlying mechanisms. As scientists, it is important to approach this phenomenon with an open mind and consider all possible variables before drawing conclusions.