how long does it take water to boil

[Optical]

Originally posted by TwoSpoons
specific heat of water is 4.2J/K/ml

so it takes 4.2 joules to heat 1 ml of water by 1 degree C.

Now go get your calculator and work the rest out.

Though personally I'd go with the 6m53s.

[nerd]

Theres also the latent heat of vaporisation to consider at ~22.6 j / ml

[/nerd]

[part2wanksta]

oh i really didnt think about tthat

[Squalish]

[nerdier]
There's the light itself, how many lumens it projects, and the spectrum of the light.

There's the start up graph of the light's output as it warms up, which typically takes 5-10 minutes.

There's the reflector and type of reflector, the simplest being a spherical aimed at the arc. Its theoretical best absorption(steel is supposedly 65%), and its actual surface imperfections.

There's a correction for the amount of light that gets accurately aimed into the container, which can be affected by arc size.

There's the amount of light hitting the container itself, which varies with the size of the container, the distance from the lamp, etc.

There's also the amount of secondary heat that radiates from the enclosure, what type of cooling it has, how much heat it transmits outside the system, etc. This(and all the the stuff above this, other than lumens) can be negated if you insulate the box and make infrared rays leaving the water's other side the only means of cooling, but this doesn't give a meaningful number.

And there's the transmisivity, reflectance of both surfaces, "thermal mass", etc of the container that the water's in.

There's the amount of water.

And there's the amount that is absorbed by the water, which varies with the thickness of the channel and an absorption graph of water.

Then there's some variance, per conduction(since we're dealing with relatively uniform vertical heating of a liquid), in the temperature of the water, a gradient in which the water at the top could get to 100C before the water at the bottom. There's another thermal gradient overlayed on top of that to account for nonuniform absorption of spherically radiated light on a flat surface.

There's the amount of energy needed to be absorbed by the water to heat it up to 100C, determined by the specific heat. This needs to be converted into joules.

Then there's the latent heat of vaporization, the amount of energy needed to bring 100C water to 100C steam. This can be ignored if you only want to wait until the water STARTS to boil.

And there's the amount of energy that's released through radiation of the water itself.
[/nerdier]

To do a much easier estimation, we have to stipulate a lot: relying on a 400 watt heater[with no start up time] inserted into a perfectly insulated (from photonic as well as conductive losses) vat of 20C water, with perfectly absorbing water and a perfectly functioning stirrer to make sure that the water has a uniform temperature, it would take 840 seconds to begin boiling per each 1 liter of water(negating pre-flashpoint evaporation), if TwoSpoons is right on that number .

[Hezz]

Part2wanksta,

I take it from your post that you have found that good IR glass is not real cheap and so your are pursuing other options.

Here is one possible idea:

The glass that most tall high rise buildings use is a type of archetectural IR glass called heat glass. Probably not quite as good as that from Edmonds but I bet if you found a local glass company that did commercial glass replacement they would have some broken scraps they would give you which you could cut down to size. The problem may be finding some of the non tinted kind which is often used for sky lights.

Hezz

[Bigg'un]

Do you plan on adding a biocide to teh water so it dosn't turn green on you too?

[shipto]

Originally posted by TwoSpoons
specific heat of water is 4.2J/K/ml

so it takes 4.2 joules to heat 1 ml of water by 1 degree C.

Now go get your calculator and work the rest out.

Though personally I'd go with the 6m53s.

If i remember correctly thats the formula with atmospheric pressure if its a sealed unit the pressure will rise and so will the boiling point of the water.

[Me2!]

The spectral pattern of a stove is much better quality than your bulb. Expect inferior IR patterns compared to the black body radiator.

Does your water care? The real question is how much thermal energy from your bulb will be absorbed by the water and how much water? It will take longer if you add a bit of salt.

Will the bubbles interfere with your projection?! Ha, you didnt think of that one did you?

[justme]

I would think that if you are seriously considering this you would also be considering a pump and a seperate heatsink/radiator to dissipate the heat.