Be careful with a CO2 tank. If you are using a regulator to reduce pressure before your tank, it will get most of the cooling. If you go direct to your tank and the outlet gets frosted shut, it will explode in fairly short order. It the tank has much volume of CO2 in it when it goes, there could be "issues"...
The tanks are also heavy. It needs to be mounted so that it doesn't come loose in an accident, so safe for something like 20g's.
Does anybody know how those guys http://www.designengineering.com/catalog/cryo2-system-components
solve those issues?
If you design your own it's up to you. But their unit might blow up too if the exhaust got plugged. I'd certainly ask them how long that tank of CO2 lasts in one continuous blast.
There's a little error in their ad about it,
"The CryO2® system uses liquid carbon dioxide (CO2), stored at 80 degrees below zero (Fahrenheit), to super cool intake air, ...."
The temperature right at the small area where CO2 evaporates from a liquid to a gas is at ~-80°. That tank is not insulated to store
CO2 at -80°. When CO2 is stored at high pressure it can still be a liquid at higher temperatures. We used to have a very large CO2 tank for testing equipment to -72° F. The Co2 was stored in the tank at 300 psi with a refrigeration unit to cool the tank to ~0° F. Can you imagine the equipment it would take to cool & keep that CO2 car cylinder at -80°?
I found this at http://www.kegkits.com/Merchant2/mercha
"Note: Liquid CO2 should not be stored in the trunk or passenger compartment of any car. The temperatures inside a car can easily cross 120 degrees F and any full CO2 tank will vent (loose its charge) at these temperatures."
My note, the tank CO2 pressure would exceed the safety valve set point built into the regulator.