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Q: Vaporization of Water with Pressure Differential ( No Answer,   3 Comments )
Subject: Vaporization of Water with Pressure Differential
Category: Science > Physics
Asked by: megahog-ga
List Price: $5.00
Posted: 03 May 2006 13:52 PDT
Expires: 04 May 2006 14:17 PDT
Question ID: 725202
Can the enthalpy of vaportization (latent heat of vaporization) be
"overcome" for saturated liquid water at 1000 kPa by creating a
pressure differential of 300 kPa via a pressure control valve?  I know
up to this point that energy must be put into the water to vaporize,
but can a change in pressure vaporize the water?
There is no answer at this time.

Subject: Re: Vaporization of Water with Pressure Differential
From: ansel001-ga on 03 May 2006 14:14 PDT
I remember in my high school chemistry class the teacher did a
demonstration.  She put water in a beaker and boiled it, not by
heating it but by putting it in a machine that created a vaccuum. 
When the air pressure inside was low enough, the water boiled at room
Subject: Re: Vaporization of Water with Pressure Differential
From: kottekoe-ga on 03 May 2006 19:23 PDT
As Ansel says, you can vaporize the water by reducing the pressure
below the vapor pressure at the water's temperature. You still need to
supply the heat of vaporization. If there is no source of heat, the
water will cool down as it vaporizes. This is how refrigerators work.

Subject: Re: Vaporization of Water with Pressure Differential
From: frde-ga on 04 May 2006 05:10 PDT
It sounds as if you are after what I call a 'heat knife'

Divide a set level of temperature into heat+ and heat- (cold)

I've been assured that it is not possible, which makes me suspect that it is.

We are basking in potential energy, kicking a rock of a mountain takes
little effort, but the avelanche at the bottom is pretty powerful.

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