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NiChrome Power Source? Answered

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So, I'm doing a project that needs to boil maybe 8-10 drops of water very quickly. I was thinking of using NiChrome wire to do this as in the included diagram (sorry low quality, MS Paint). However, I can't seem to find an appropriate power source. So, I need some easy to obtain powersource that is also relatively small. Something like batteries, a capacitor bank, or anything similar. Remember, it has to be able to boil of those 8 drops pretty fast, lest they condense in another part of the pipe before the desired pressure is reached. 

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jeff-oBest Answer (author)2010-09-15

I wonder if it might be more effective to short out a high-current power supply through the water, rather than heating it indirectly. That way, the water would effectively "explode" rather than boil, in far less time.

A big capacitor bank ought to do the job.

Of course, the water itself will need to be less than pure, and the pipe must be non-conductive.

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LiquidLightning (author)jeff-o2010-09-15

What if the pipe were conductive but the wire half insulated and immersed in the water.

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jeff-o (author)LiquidLightning2010-09-15

Well, I suppose the pipe itself could be one of the conductors (ground) and the other wire could be suspended in the liquid. Just make sure they never touch, or something else might blow up when you pull the trigger!

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LiquidLightning (author)jeff-o2010-09-15

Sooo, something like this?

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jeff-o (author)LiquidLightning2010-09-16

Well, you don't have to wrap the wire around the pipe nearly so much; a single connection point close to the water should be enough.

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LiquidLightning (author)jeff-o2010-09-16

That would be electrical tape, not wire.

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jeff-o (author)LiquidLightning2010-09-17

Ok... as insulation, I assume?

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jeff-o (author)LiquidLightning2010-09-18

Well, let us all know if it works! And try not to electrocute yourself, OK? Until you know it's "safe," operate it from a distance.

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jeff-o (author)LiquidLightning2010-09-16

And really, your original diagram would work just fine; just eliminate the nichrome wire and make sure the wires don't touch.

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frollard (author)2010-09-14

Your steam-gun looks promising -- putting a hundred watts into that small area should do the trick. A modified ATX power supply should work -- search atx power supply -- theres a few ibles on the topic.

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LiquidLightning (author)frollard2010-09-14

A hundred watts? It seems a bit much for 8 drops of water and 1cm of NiChrome. Are you sure?

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kelseymh (author)LiquidLightning2010-09-14

Why not do the math and see how much power you need? All of the information you need is freely available, with just few seconds of Google or Wikipedia searching (provided you know what words to search for).

Assume the water is initially at room temperature (20C). Then you're going to need to raise it by 80C to get to the boiling point, then add the extra heat of vaporization to turn it to steam.


  • 8 drops (gtts) is 0.5 mL, or about 0.5 g = 0.0005 kg.
  • The specific heat of liquid water is 4.2 kJ/(kg K).
  • The heat of vaporization of water is 2257 kJ/kg.


You will need 4.2 kJ/(kg K) * 80 K * 0.0005 kg = 168 J to heat it up to 100C, and an additional 2257 kJ/kg * 0.0005 kg = 1128 J to turn the water to steam. That's a total of about 1300 joules.

If you have a 100W power supply (the equivalent of an incandescent bulb), it will take 13 seconds (W = J/s) to boil your 8 drops of water to steam.

Suppose instead that you put your half milliliter of water into a 1500W microwave oven. In that case, you'd flash it to steam in less than 1.2 seconds.

Now, figure out what you need to hook up to your nichrome wire to get the job done.

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LiquidLightning (author)kelseymh2010-09-14

Actually, in the microwave, it would take substantially longer because even though the magnetron emits at that amount of power, all of the microwaves do not hit the water evenly, or at the same time.

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kelseymh (author)LiquidLightning2010-09-14

True, for a real engineered microwave oven :-) But to do the calculation in that case, you need to know how uniformly the RF fills the cavity, and what (tiny!) fraction of the cavity is occupied by your 0.5 mL pipette. I just tried 1 mL (in a cough medicine cap) and even 30 seconds wasn't enough to fully evaporate the water.

My suspicion is that you're going to need a fairly high-power, high-current supply, maybe something along the lines of a capacitor bank, if you really want to generate steam quickly. It's hard to overcome that 2 megajoules per kilo.

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LiquidLightning (author)kelseymh2010-09-15

Actually, a capacitor bank sounds like a good idea. Maybe 4 or 5 20v 200uF caps could do the job.

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user

Energy stored = 1/2 X C X V2 If we plug in your numbers....1000uF x 200 =0.001 x 200 = ...0.2J....

Nope. That won't work either.

Steve

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steveastrouk (author)kelseymh2010-09-15

I agree with Kelsey's maths, and Rick's solution. Preheat the chamber, and inject the water hard and fast.

Steve

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rickharris (author)2010-09-15

It would be more effective to spray your water in a fine mist into a hot chamber.

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user

Would it? I think that it may seem to be, but it'll take the same amount of energy to boil it off.

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user

It would take a lot more energy this way since you have to heat the body of the chamber and the air inside the chamber to get the steam.

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