MadSci Network: Physics

Re: How much voltage/amperage would it take to make a drop of water explode.

Date: Sat Nov 28 22:52:50 1998
Posted By: William Beaty, Electrical Engineer / Physics explainer / K-6 science textbook content provider
Area of science: Physics
ID: 906864330.Ph

Hi Michael!

It takes 1 calorie to raise 1 gram of water by 1C degree, and takes 540 calories to vaporize a gram of water.

If we start with a 1-gram drop of water at room temperature 30C (one gram is a fairly large droplet!), then it takes 70cal to get to boiling temperature, and 540cal to boil into vapor, for a total of 610 cal. Converting calories to Joules gives us a total of approx. 2600 joules of energy.

For fresh water, it takes quite a large voltage to drive a big current through the water, and the bigger the current, the faster the boiling is accomplished. If we use something like a 30,000-volt oil-capacitor bank to store our 2600 joules, maybe 10 or 20 microfarads would do nicely as a water-exploder. This is quite a large, expensive capacitor. Fairly huge conductors are required (copper bars or multiple ground-braids).

Dr. P. Graneau, along with Richard Hull of TBCOR recently reproduced the exploding water cannon and managed to penetrate 1/4" aluminum plates (or much thicker plywood.) This appears in issue 14 of the semi-pro journal ESJ This was part of Dr. Graneau's research into unexplained forces in fluid conductors, and he suspects that electrical water explosions are not simple boiling, but may be some sort of motor-force effect. Some researchers report neutron bursts from capacitor discharges through water or ice.

Also see my article on capacitor discharge demonstrations. Take the warnings seriously, this stuff is as dangerous as working with high explosives.

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