Clean It Up
UK Window Cleaning Forum => Window Cleaning Forum => Topic started by: nathanharrison on January 06, 2010, 08:20:47 am
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Hot water freezes quicker than cold water? ??? ??? ???
I've seen quite a few posts saying this but surely that can't be true?
If you put water on the floor at say 50deg I know it will loose its heat quicker than water at say 8deg. But, if for instance the warm water cools down to 2deg in 5mins and by some miracle the 8deg water cools to 2deg in the same time (even tho I'd have thought it would cool quicker than that), are you seriously saying that the water that started off warmer is going to continue cooling at a faster rate and, in effect, overtake the other cool water in its fall to freezing point and freeze first???!!!
The logic and Physics in this process seems quite simple to me or am I missing something?
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Put an ice cube in the sink,run hot water over it til it melts. Do the same with cold water to a new ice cube. The ice cube will melt much quicker using cold. Don't ask me why. Not exactly answering your question directly, but i guess the theory is the same there somewhere. ;)
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An extract copied from another site.
Some choose not to believe it, but this phenomenon can be demonstrated in your own freezer under the proper conditions.
If you have two pails filled with equal amounts of water, one hot and one cold, and you set them out in the snow on a cold winter's morning, what happens?
What Should Happen
Any reasonable person would think that the hot pail would take longer than the cold pail to freeze. After all, the hot water needs extra time to reach the same temperature as the cold pail. When the hot pail finally does reach the same temperature as the cold pail initially was, the cold pail should already be frozen.
Back to the Top
What Actually Happens
There are several things that help the hot pail freeze faster than the cold pail. Here are what is thought to be the most significant factors:
Layer of ice forms on the top of the cold water.
The hot water is more likely to be supercooled. This means that the hot water's temperature is more likely to cool to temperatures below zero degrees Celsius. In the cold non-supercooled water, ice crystals form and float to the top, forming a sheet of ice over the top of the water, creating an insulating layer between the cooler air and the water. This ice sheet also stops evaporation. In the hot water that has become supercooled (thus, no longer hot) the water, when it does freeze, freezes throughout, creating more or less of a slush before freezing solid.
Why is hot water more likely to be supercooled? Because hot water is less likely to contain tiny gas bubbles. Gas bubbles form from dissolved gasses as the water cools. When the hot water was heated, these dissolved gasses may have been driven out. In cold water, ice crystals use the tiny bubbles as starting points for formation (in physics, we call them nucleation points). But in the hot water, there are no bubbles, so there aren't as many starting points for the ice crystals.
Dissolved gasses also lower the freezing point. Since heated gas is less likely to contain dissolved gasses, it's more likely to freeze first.
Water in the hot water pail evaporates at a much faster rate than the cold water. This does two things.
First, the process of evaporation is endothermic, which means it takes energy for something to evaporate. As a molecule of water evaporates, it leaves the surface of the water and flies into the atmosphere. Thus, in simplified terms, the molecule converted heat energy into kinetic energy (energy of motion). Since the hot water evaporates quicker than the cold water, it loses heat energy quicker than the cold energy.
Second, since some of the hot water evaporates away, there is less water left to have to freeze.
The hot water pail will melt the surrounding snow. Later, as it begins to freeze, the snow around the pail will freeze back so that it more closely "touches" the pail. The cold water pail is then only sitting in fluffy airy snow, while the hot water pail is in a form fitting ice-crust. The ice-crust will obviously conduct the cold better that the airy snow.
Other factors, such as convection currents (the movement made as hot water rises while cool water sinks) may or may not play a role in this odd phenomenon.
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Nathan, it's freezing outside your place now right? Clear a patch of about a square foot, tip a cup of cold water on the ground and see how long it takes to freeze. Then do the same with hot water. Hot freezes instantly. Remeber your physics classes at school mate? ;D
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Mpember effect. named after the student who dicovered it. Google it.
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If the wtaer is flowing and say 40, when it hits the glass ( the constant flow of wfp) it will warm the glass up. A window which would freeze with cold water doesn't with hot as the window heats from the constant flow of water.
That's what I noted last year. It freezes slower in the pipes (possibly due to lack of evaporation). But yes, it freezes faster on the floor. - Unless that is, it is a constant warm flow which warms the floor up and that slows/ prevents freezing.
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i tested this theory when i was working with warm water yesterday doing a contract that was in the shade....it was minus 4 at the time......i got all the work done within 2 hours with the warm water no freezing at all even to the hose which did hit the ground, (only thing that did freeze was the outside of the pole).....i used a container of cold water at the last set of 2 windows ( froze within two seconds, the whole kit, i made sure i didnt damage anything though as i was right next to the pump and switched it off).
so while warm water freezes quicker when you put it directly into freezing air/ground it did not freeze at all contained within my pump system and hoses.
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If you have 2 buckets of water one at 40c and the other 80C put them outside in 0C they both start to cool which gets to 0C first?
Dunno.
But when the one at 80C falls to 40C its going to be cooling at the same as the one that was 40C when it was first put out there.
By which time the 40C one will be cooler already and therefore the first to reach 0C
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Thanks for everyone's reply. It's great to know we have some intellectual window cleaners!!!
I have done some research on the Mpemba effect where hot water freezes quicker and also done a little experiment of my own. I poured a pint of warm water (35deg) from my aquarium heated water in my tank and a pint of cold water (8deg) on the floor in the shade at home, to check which froze first. Once poured out the puddle was aprox 3mm deep Same conditions for both volumes of water. I waited until I felt they had reached dangerous slippery conditions (ie frozen), the cold water froze first by a good 3mins. This is what I expected and makes sense to me.
The Mpemba effect has a number of explanations, most of which do not apply to our situation in window cleaning because of the volume of water we drop onto the floor at each window and the temp it will be by the time it reaches the floor. By the time our warm water hits the floor and splashes, the depth of the water will not allow convection currents or have container walls to aid the super cooling effects that the strange Mpemba effect requires.
Either way, I have bought 500w of aquarium heater yeaterday and insulated my 400l tank which got the water to 35deg overnight and enabled me to work all day today without freezing up, so whether warm water feezes quicker or not I am going to contniue using it!!!
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There are many,many variables/scenarios with this statement.
It can happen but doesn`t always.
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when water is heated it changes its (whatever) and therefore freezes quicker . put hot water in your freezer and you will have crystal clear ice put cold water in and your ice will be cloudy looking , put warm water in your freezer and you will probably be somewhere inbetween
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when water is heated it changes its (whatever)
Molecular structure?
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when water is heated it changes its (whatever) and therefore freezes quicker .
In my experience heating water tends to make it boil
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put hot water in your freezer and you will have crystal clear ice
put warm water in your freezer and you will probably be somewhere inbetween
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Time to get back to work?
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It can do but not all the time. It's called the Mpemba effect. No one really knows why but generally you speaking of temperatures of say 70c freezing before 30c water. Best thing in this weather is tepid water, say up to about 40-50c, that doesn't freeze too fast, it will even melt frost off of windows.
Simon.
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Thanks for everyone's reply. It's great to know we have some intellectual window cleaners!!!
I have done some research on the Mpemba effect where hot water freezes quicker and also done a little experiment of my own. I poured a pint of warm water (35deg) from my aquarium heated water in my tank and a pint of cold water (8deg) on the floor in the shade at home, to check which froze first. Once poured out the puddle was aprox 3mm deep Same conditions for both volumes of water. I waited until I felt they had reached dangerous slippery conditions (ie frozen), the cold water froze first by a good 3mins. This is what I expected and makes sense to me.
The Mpemba effect has a number of explanations, most of which do not apply to our situation in window cleaning because of the volume of water we drop onto the floor at each window and the temp it will be by the time it reaches the floor. By the time our warm water hits the floor and splashes, the depth of the water will not allow convection currents or have container walls to aid the super cooling effects that the strange Mpemba effect requires.
Either way, I have bought 500w of aquarium heater yeaterday and insulated my 400l tank which got the water to 35deg overnight and enabled me to work all day today without freezing up, so whether warm water feezes quicker or not I am going to contniue using it!!!
Perhaps it would have been more of a scientific experiment if you actually used the same water, not from your aquarium, which is obviously going to be a lot different in it's chemical makeup.
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Last year on the local news they did an experiment where they had two cars in the freezing cold, side by side.
A bucket of cold water was thrown onto the windscreen of one car and a bucket of hot water was thrown onto the windscreen of the other car.
The windscreen with the hot water froze first; in just a few seconds; you could see it freezing.
I'm fairly sure it was explained that this happened because hot water is less dense than cold water; or something!