I just thought I would post an update about the Idea of Liquid Nitrogen for cooling the
nutrient solution.
Unfortunately this does not seem feasible. Although the temperature of Liquid Nitrogen is about -320 F, It rapidly evaporates/boils away when introduced to the atmosphere. The density of Liquid Nitrogen is lighter than water so like oil and water the Liquid Nitrogen does not mix with the water but just floats on top until it all evaporates/boils away. Even though I poured 1 Letter of Liquid Nitrogen directly into the nutrient tank for my strawberry's, the direct contact between the Liquid Nitrogen and water did not seem to transfer any of the cold temperature of the Liquid Nitrogen into the water before it all evaporated/boiled away (in about 5-7 min). I didn't have a thermometer to put into the nutrient tank but I felt the water temp before and after adding the Liquid Nitrogen to it, and unfortunately I didn't find that there was any difference in temperature.
The only way I can see to use Liquid Nitrogen to cool the
nutrients is in a pressurized recirculation system (I don't have the funds to experiment with this right now). Because the Liquid Nitrogen would freeze any
pump and make it unusable (I am sure), the system would need to be pressurized to be able to get the Liquid to flow through a set of metal coils that can be submerged into the nutrient tank. Because the direct contact with with metal will cause the metal to reach a temperature of something like -40 F, the metal coils would then directly cool the nutrient solution.
A system like this would need to consist of two holding tanks for the Liquid Nitrogen, with the coils between them to run the Liquid Nitrogen back and forth through. Each holding tank would need a pressure relief valve, a pressure gauge and an open and close valve leading to the coils. As well as a fitting for injecting the compressed air and a sealable opening for filling with Liquid Nitrogen. You would also need a air compressor to pressurize the system. It would also take some research to find out what pressure range to use, and the system of coarse would need to be able to withstand pressure higher than its intended use (this could be tricky because nobody has done it before).
Like me, this might be a bit much to invest in (time and money) but for larger operations, even commercial Hydroponic farms in very hot regions of the world it may be a reasonable alternative to other methods (once the bugs were all worked out). Although I am not sure how large operations are addressing this problem but I would imagen that the "Geothermal (underground)" method is probably still the most efficient.
As for me I am looking into better ways of insulating my Hydro systems, nutrient tanks, fill and drain lines. I am also considering renting a back hoe to dig into the the rockey ground here in the desert of Lake Havasu AZ.. But the nutrient tank would need to be deep enough and surrounded with dirt to get the best Geothermal affects. This makes it more perminate and hard to take out and clean with every nutrient solution change as well as making the pump need to pump the solution another 3-4 feet high. I will probably need another higher volume pump for that.