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Topic: Maintaining a rolling boil of water in a Microwave  (Read 4779 times)

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Offline daveyboy

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Maintaining a rolling boil of water in a Microwave
« on: July 30, 2010, 05:22:18 PM »
I would like to be able to do this. I know you're supposed to use "microwave-safe" containers in there but I never had trouble with anything glass or ceramic and I intended to use a tea-pot or maybe a pyrex jug for this experiment. I am worried about the pyrex jug though as it has painted gradients and the paint might not be suitable for microwaving. Since I never had a single ceramic thing explode on me I think I will use tea pot.

I understand about superheating so intended to plonk a wooden pastry stick in the bottom plus the tea pot has holes for the spout to form bubbles on.

Is it actually possible to do this? What wattage would be the right wattage to maintain the water at 100 degrees C? I need to keep the water at a "rolling boil" like you would do on a hob, unfortunately mine just blew up and I can't afford another until next week. I assume there's a mathematical equation to it to calculate the right temperature or I could just try by trial and error.

It's my intention to keep the rolling boil going for 20 minutes. Can anyone help with this?

Offline daveyboy

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Re: Maintaining a rolling boil of water in a Microwave
« Reply #1 on: July 30, 2010, 05:54:46 PM »
Trying to work this out (I know nothing of these things), I find out:

The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C.

My microwave is 800 W output with 10 power levels so I presume it would put out 80 W on power level 1... I know I'm on the right track here...

So I boil the water in kettle first then try to use the microwave to maintain the boil. I've learned watts are joules per second.

A litre I want to maintain at 100C, so I need to know the temperature of the surrounding environment it is going to lose heat to but I don't know what that will be inside a microwave and that's getting me stuck. I assume the steam would fairly quickly bring the temperature up in the microwave to around the same temperature as the water or am I wrong?

Now I think a litre of water contains 418600.0 joules of energy. I guess to get it perfect I need to know the surface area of the container. There's no way I'm going to do that with a tea-pot so I can calculate how much will be lost by radiation. Perhaps I will give up and just start on power 1 and trial and error what it takes to keep the water at a boil :)
« Last Edit: July 30, 2010, 06:16:20 PM by daveyboy »

Offline daveyboy

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Re: Maintaining a rolling boil of water in a Microwave
« Reply #2 on: July 30, 2010, 07:56:52 PM »
By trial and error I found that with 800W microwave power level 5 was a little too low and power level 6 a little too high to hold 500ml water and 10 tea spoons of tea (see what I was doing now :D) at boiling point. This was in a thick ceramic tea pot which absorbed a lot of heat so I expect if it was done in a Pyrex jug then 5 would be the right level.

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