My 9yr old is inspired to try to make ice with a vacuum after seeing an exhibit do just that at room temperature at the Exploratorium in San Francisco.
He's using a motorcycle vacuum brake bleed pump that pulls a 760mmhg vacuum, and we're putting water into a plastic container in that system and pulling the vacuum on that, it's not working, any ideas what we need to do to get this working? Is the vacuum strong enough? Would the water need to be cooled to begin with? We're not sure if the water in the Exploratorium exhibit was 'pre-chilled' to a specific temperature or not.
However it sounds like from other posts here the pressure we're able to get from the vacuum pump we're using should be enough to get the water to hit its solid/liquid/vapor triple point which should be enough to get it to freeze. Any ideas how to tweak this experiment to make it a success?
Best Answer
Three suggestions:
a small amount of water: you have to evaporate a large fraction to freeze it, and a large fraction of a lot of water is a lot of pumping
start with cold water: the colder the water, the higher the freezing pressure
keep it well insulated: energy flowing in the through the plastic container will warm it up
keep pumping: you have to evaporate about 15% of the water to freeze the rest
There’s more on this here.