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I'd need a formula

Hi!

Suppose I have 1 litre of water in a plastic tank, its temperature is ambient temperature, i.e. 20 C. Now I want it to reach 50 C in, say, 10 minutes, using an electrical resistor as heater.

How many watts does the resistor need to be? Is the above a good way to warm up a liquid (talking about cheap/simple ways, of course)?

I'd like to build myself a heater for my ferric perchloride tank and for the sur-tin one, because otherwise the former will be very slow and the latter won't work at all..

By the way, will silicone be adequate to isolate the wires? Even if no electrolysis took place, the acid will corrode the leads.. so I need to isolate them.

Thanks! It's cold here, you know! ;) John

Reply to
JJ
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Hmm, back to basic science...

A calorie raises 1 gram of water by one degree Celsius; you've got 1000 grams to raise by 30C so you need 30,000 calories. That's 125600 joules or watt-seconds, 2093.33 watt-minutes, so the required wattage for desired temperature rise in 10 minutes is 209.333 watts. That doesn't include any losses during the heating period, and there will be some through the walls of your tank unless you choose to insulate it.

I'd suggest looking for a hot plate or some similar heating element; it'll be lot cheaper than buying a 209 watt power resistor.

Reply to
Garrett Mace

In article , snipped-for-privacy@invalid.com mentioned...

[snip]

That's a very important point. The ambient temperature, and the container insulation make a great difference. If the container is foam plastic, the liquid's going to get warmer faster and with less power than if the container is glass, for example.

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Reply to
Watson A.Name - "Watt Sun, Dar

Actually, if a power resistor is immersed in water, then even a 10W resistor is sufficient. As long as the resistor is surrounded by liquid water, then the case of the resistor cannot be hotter than 100C!

I have used this trick when I wanted to test a 20A 12V Power Supply under load. I used a 10W aluminum jacketed resistor suspended in a beaker of water as a dummy load. The 240W of dissipation didn't harm the resistor at all...

MikeM

Reply to
MikeM

That's a great point, but unfortunately the original poster is dealing with corrosive fluids. Short of some elaborate heat-exchanger setup, I don't think using a resistor for immersion heating is going to work out too well.

Also, the case of the resistor *can* get hotter than 100C...once the contacting water reaches vapor phase, a bubble of steam will form around the resistor and you might get it to run away from you. I still stick to the plan of a mundane hotplate element under the tank, and maybe not being so ambitious about the time required to reach temperature. Household resistive heating elements are in everything and cost pennies at any thrift store.

Reply to
Garrett Mace

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