On 10/7/06, James Newtons Massmind <jamesnewton@massmind.org> wrote:
> > > http://techref.massmind.org/techref/other/zeolitefridg.htm
> >
> > That one is very interesting.  A couple of  questions:
> >
> > - what is the purpose of the heat exchanger?  Could the water
> > freeze in there and cause maintenance problems?
>
> To cool the refrige box. If the water freezes, it will only stop operation
> long enough for the ice to melt.

I thought that the water evaporating in the box did the cooling?

> > - how much vacuum is required?  I'm thinking an electric
> > vacuum pump made for hot rods might be useful.  They
> > generally turn on at < 15 psi and pump until 25 psi is reached.
>
> The purpose of the vacuum is to make the water boil at a lower temperature.
> So the amount of vacuum needed is enough to make the water boil at the
> temperature you want the refrige to maintain.

Looking at this link:

http://www.chemistrycoach.com/vapor_pressure_of_water.htm

if you wanted to get down to -10*C, you would need a pressure of
2.1mmHg.  Even at 0*C, you need 4.6mmHg (0.08895psi), which is a very
low pressure.  Am I looking at the right chart?

BTW this site does nice conversions:
http://www.convert-me.com/en/convert/pressure
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