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fpereira
Hi all,

Maybe someone can help me with this:

Can someone tell me how long and how many BTU is needed to boil 1 once of water? This water is at atmosfere pressure and room temperature (70 F).

Thanks,

Fabio Pereira
adoucette
No, but I'll give you some hints

BTUs or British Thermal Units can be converted to calories

A Calorie is the amount of heat needed to raise 1 liter of water 1d C

Water boils at 212 F or 100 C

Arthur
fpereira
I think I found the answer:

http://www.mansfieldct.org/schools/mms/sta...ingcalories.htm

The link above explains how many calories is needed to steam water. According to it, 1 calorie will raise 1 gram of water 1 degree Celsius. Also, it takes 540 calories to turn 1 gram of water (at 100 degrees C) to steam.

So follows:

1 once of water = 28.349 grams

To raise the water temperature to boiling point, we will need:

Heat = Mass x (F-S)
Heat = 28.349 x (100 - 25)
Heat = 2123.175 calories

Now, to steam this water we will need:

Steam = Mass x calories
Steam = 28.349 x 540
Steam = 15308.46 calories

Total energy needed to steam 1 oz of water is:

Total = Heat + Steam
Toral = 2123.175 + 15308.46
Total = 17434.635 calories

Since 1 KWh = 860424.76302468 calories, then:

Total = 17434.635 / 860424.76302468
Total = 20.26282 Wh


Thanks anyways,

Fabio Pereira
El_Machinae
Remember, though, that our machines are not efficient. So while the water will contain that many calories, we will need to burn many more calories to get the water to steam (heat leaks out the sides of the kettle, or away from the burner, etc.)
fpereira
You are right. I agree.
Schneibster
Just a pedantic point: the "energy needed to turn water at 100C to steam" is called "latent heat of vaporization."
fpereira
That is an interesting term. Thanks.
frank nesci
if i can boil 10 grams of water from room tempurture to steam with a hand operated electric genorator (no aditional power input) with in 60 seconds, what does this mean about our genorator??
Lalbatros
An even more pedantic point: "the energy needed to turn water at 100C to steam at 100C" is called latent heat of vaporization at 100C."
The latent heat of vaporization depends on the conditions chosen for the water and the steam.

For some choice of these reference conditions (states) the latent heat of vaporization could even be zero.

And now a pedantic question: when could it be zero?
Enthalpy
It is zero at the critical point of water (+374C and 218b). It's a physical effect there, not a matter of convention or reference.

Greetings to you all!
walkingman
QUOTE (Schneibster+Feb 7 2006, 10:21 PM)
Just a pedantic point: the "energy needed to turn water at 100C to steam" is called "latent heat of vaporization."

just to be a little more padantic thats saturated steam smile
jah
OK to what temp will you need to heat a sealed container of water to get it to completely convert to steam upon un sealing the container?
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