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S, brian whatcott pi?e:

I think you need to do a little more testing and a little more calculating.
5 minutes? at 200 watts input?? (optimistic) is not going to get you a usable
cool box. If? you could pump down to a few millibars in 5 min, so your water boils, then
the pressure goes up again - so you have to keep pumping.

Sounds like you did as physics class quite a few years ago: is that the way it was?

:-)

Brian W

Well I did physic class few decades ago... :D

..but you do not read my post. Let's explain again:
I have two boxes. One is near full of water and the second is filled full of zeolite. Both are connected with hose. Under atmospheric pressure nothing happens. So let's start with all temperatures at 24C. When I start to pump and reach 30mBar the water will start to boil. Reaching this point should be very quick (minute or two). With that pressure the water will boil and presure will balance. Here the zeolite come in action. It's work like sponge for water vapour. And they wil adsorb the water wapour. No ned to pump any more if I want 24 degres C. But as I wan't to go lower I sustain pumping. So the water will agresively boil as presure is so low. So I can't get 5mBar but just few mBar under current water vapour pressure. But the side efect of pumping that is that I pump the water vapour AND remaining air. And I want to evacuate the AIR as water vapour will always balance with temperature. So after reaching 30mBar @24 degres I ned to pump litle longer but the gauge wil stay at 30mBar. (wel it wil go lower as water is colled by evaporation).

I did that test with (borowed) vacum pump and it's work as is writen here.
The pump reach 30mBar after 20 second and I leave it running for full minute reaching 20mBar.
I switch pump off. And check after 10 minutes. The gauges reads 12mBar @ 10 degres C.
Then I start pump again for one minute. The pump reach 6 mBar and I stop it.
10 minutes later the gauge reads 2 mBar and temperature is -6 degres. The water is frozzen.
3 hours latter the result is same. After 6 hour the presure start to rise and temperature too. All that without insulation!.

and about of energy..
We need 2260 kJoule to evaporate 1 kg of water. And 4 kg of zeolite can eat 1kg of water wapour easy.
If I have 40cm X 40cm X 40cm colling box the surface of box is 1m2. I want 8 degres C in cold box and hottest out temperature is 30 degres. So difference is 22 degres C. With insulation R=1.5 I need (22 * 1 / 1.5)=14.6 J. With 2260000 Joules available that give me 154794 seconds working time. (2579 minutes or 43 hour)

ahh yes I need to explain why I don't evacuate that system at home with borrowed pump. I have 2 reasons.
1. Don't want to heat my cabin. The zeolite container get hot!!!. So I put it out of lodge and need to assemble it on place
2. After saturating zeolite that need to be heated and thus dried. It's easyer just to remove canister from system and heat it in the stove or whatever hot source and let wapour to go out. In other case I need the condenser in line but that gave problems. (ice build up and others)

So Again.. I NEED THE SIMPLE VACUUM PUMP.. I study options I have and this is best one to have. And cost me under $50 + pump...

Slavko.