[thedoc]

Jonathan Huygens  asked the Naked Scientists:
   
Hi,

My name is Jonathan Huygens, and I'm trying to create an artwork that involves rain.
I have however come into contact with some difficulties.

My intention is to make it rain inside a room in a manner that is child friendly....
and i've tried heathing up water until it evaporates and then coolingthat down.
Ithink this should do the trick however i need some better cooling equipment.
Do you have any suggestions?  It should be not too expensive, not big and non-toxic, but still be able to cool down a room of about 4m x 8m x 2m enough to create the rain.  The results of my experiments up till now have been: the evaporated water that starts to condensate onto the walls and ceilling and then starts to drip off, wich is not the result i'm looking for.

I have also been wondering is there a material that repels water? much like a balloon
can atract water (as show in kitchen science: bending water-static attraction).
That would mean that i could cover the walls of the room with this material and thus
making the evaporated water to concentrate itself into a certain area and making it
more easy tot make it rain.

If you could help me with this i would be really grateful.

What do you think?

[RD]

Rent a fog screen ? ... http://www.fogscreen.com/    http://vimeo.com/20595372
Maybe project a video of rainfall on this nebulous walk-thru screen.   

[evan_au]

Apart from the problems of water condensing on the walls (which you've already met), you could suffer from mildew.

Real rain comes from water vapour which rises until  it cools enough by expansion, reach 100% humidity which allows the vapour to condense into microscopic droplets - which we call "clouds" if its up high, or "fog" if its down low.

The microscopic droplets then collide many times until they get big enough to form droplets, which fall to earth as rain.

I've heard that the NASA Vehicle Assembly Building is so tall that clouds can form inside it (if they didn't have air-conditioning).

But in this small room, it is going to be hard to maintain 100% humidity, and the microscopic droplets of the fog are going to hit the wall or roof before they get big enough to form a raindrop. Even with a water-repellant coating, the tiny droplets will run down the wall.

I don't think that cooling the high air will work well, because cool air sinks down to where you are trying to heat up the water.

I think your best approach would be a water hose suspended under the roof, with tiny holes in the hose. This could make a rain of droplets.

Just ensure that the walls and floor are waterproof, with a drain, and a non-slip floor - like a giant shower stall!

[William McCormick]

Jonathan Huygens  asked the Naked Scientists:
   
Hi,

My name is Jonathan Huygens, and I'm trying to create an artwork that involves rain.
I have however come into contact with some difficulties.

My intention is to make it rain inside a room in a manner that is child friendly....
and i've tried heathing up water until it evaporates and then coolingthat down.
Ithink this should do the trick however i need some better cooling equipment.
Do you have any suggestions?  It should be not too expensive, not big and non-toxic, but still be able to cool down a room of about 4m x 8m x 2m enough to create the rain.  The results of my experiments up till now have been: the evaporated water that starts to condensate onto the walls and ceilling and then starts to drip off, wich is not the result i'm looking for.

I have also been wondering is there a material that repels water? much like a balloon
can atract water (as show in kitchen science: bending water-static attraction).
That would mean that i could cover the walls of the room with this material and thus
making the evaporated water to concentrate itself into a certain area and making it
more easy tot make it rain.

If you could help me with this i would be really grateful.

What do you think?

This is not a solution however it may give you some insight. Years ago I was working with a fellow that decided to bypass all the safeties on a large rack refrigeration system. The system held about 100 pounds of R-22 Freon. On a moist summer day, we turned the system on, the system instantly raised the temperature and pressure in the condenser, that was not receiving cooling water. Which is why the safety sensor was continually taking down the system.

The last safety in such a system is a mechanical pressure blow off valve mounted on the condenser. When the condenser reached the pressure the blow off was designed to relieve the pressure inside the condenser, it blew as it should. It released 100 pounds of Freon into the room in about ten seconds, and actually made it snow. I would think that what you are trying to do, might be better achieved without trying to condense the water vapor.

You could just blow very fine ice particles into the room and they would melt on the way down. Very realistic to clouds themselves. Or just drop the tiny ice through a man made fog cloud. That would fool me if I saw it.


                      Sincerely,

                            William McCormick

[richardtj]

The state of h2o is dependant upon the energy it contains.  The more energy in it, the more it's molecules vibrate and the more spaced out they are.  In order to condense from vapour back into droplets, they must first "get rid" of the excess energy and contact with a cooler surface allows the vapour to pass energy (in the form of heat) to the cool surface (window or wall).  In order to make rain inside a room, you will need to heat the walls and windows and ceilings and cool the atmosphere.  Then the vapour would have time to cool and condense. However, the height of the room would prevent it from coalescing into larger droplets as it would slowly fall to the floor before it had time for the modlecules to co-alesce into larger drops.  The reason that clouds can form in the Shuttle Assembly Building is it's height allows for vapour to rise to a point where it has had time to get rid of it's energy in the surrounding atmosphere.  By this time, it's too cool to condense on the walls and instead can condense in the upper atmosphere of the building.