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Milk keeps tea hot??
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18-01-2009 2:53pm#1
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To be honest I think she is repeating some myth she heard back in the dark ages because i doubt she has ever drank black tea, and certainly never enough to know that it gets colder quicker than milky tea.
As a engineer, who has spent many a long evening and night studying physics, I can't think of any good reason why milky tea stays hotter longer. Even if milk does hold heat better than tea/water, isn't it at about 5degrees when it's poured into tea so surely this would negate any inherent properties
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maybe......
a cup of tea without milk would be hotter and would lose its heat energy quicker due to the greater temp difference between it and the air???so it would seem to get colder quicker
That's what I was thinking. But because the milk will leave that drink cooler than a cup of tea to which milk hasn't been added, the temperature of the drink with milk will be lower, just not getting any cooler as quickly. If I could draw a graph to explain better I would
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That is it. If you introduce a hot or cold object to a room at a fixed temp, then the 2 will eventually arrive at an equal temperature. But as they get close and closer to the same temp it slows down. I like to think of things like that in extremes. Imagine heating a pin until it is red hot, it could be 700C, this will cool very quickly, losing lots of "degrees per second", but if your room is 20C, then the heat down from say 25C to 20C is a lot slower than the time taken to go from 700 to 695Ca cup of tea without milk would be hotter and would lose its heat energy quicker due to the greater temp difference between it and the air???so it would seem to get colder quicker
I have drawn manys the graph! I have done extensive testing on water boiler machine cool down times. It was actually a lot more linear than I expected. I design water boilers and have requests & queries about water temperature all the time. You have to be careful in finding out exactly what people mean, e.g. if you have a tank of water at 96C, and pour this into a cup it will usually be down to 93-94C right away, if going into a cold cup it can be 90C or less moments later. Heat is rapidly lost. Putting the milk in the cup first will slow the heat loss a little more too. If you put hot tea in then the cup will conduct the heat out, the cup could get quite hot, then the cold milk is added and if there is enough then the liquid could be reheated by the hot cup. By adding the milk first the cup should never have been heated higher than the mixture of the liquids.anotherlostie wrote: »If I could draw a graph to explain better I would.
The link gives good info but this bit is very relevant to home freezersi heard once that hot water will lose its temperature and freeze quicker than cold water?For example, one explanation for the Mpemba effect is that if the container is resting on a thin layer of frost, than the container holding the cold water will simply sit on the surface of the frost, while the container with the hot water will melt the frost, and then be sitting on the bottom of the freezer. The hot water will then have better thermal contact with the cooling systems. If the melted frost refreezes into an ice bridge between the freezer and the container, the thermal contact may be even better.
Obviously, even if this argument is true, it has fairly limited utility, since most scientific experiments are careful enough not to rest the container on a layer of frost in a freezer, but instead place the container on a thermal insulator, or in a cooling bath. So while this proposed mechanism may or may not have some relevance to some home experiments, it's irrelevant for most published results.0
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