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

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

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

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.)

You are right. I agree.

Just a pedantic point: the "energy needed to turn water at 100C to steam" is called "latent heat of vaporization."

That is an interesting term. Thanks.

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??

An even more pedantic point: "the energy needed to turn water at 100°C to steam at 100°C" is called latent heat of vaporization at 100°C."
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?

It is zero at the critical point of water (+374°C and 218b). It's a physical effect there, not a matter of convention or reference.

Greetings to you all!