Evaporative air conditioning is different than the typical type of air conditioning used in refrigerators, commercial businesses, and homes. Rather than continually compressing and pumping a liquid refrigerant over and over, evaporative air conditioning simply uses the warm air around a coolant to change the vapor pressure within it.
The process is as simple as pulling the warm air surrounding a coolant through moist evaporative pads and into a chamber with the coolant pooled at the bottom. This, in turn, causes air temperature cooling through natural evaporation.
At this point, the air is whisked away by a fan and is pumped into whatever area it is supposed to be cooling. Because this process relies on the beginning air temperature being much higher than that of the coolant and the fact that it adds a lot of moisture to the cooled air, these air conditioners are particularly well suited for areas that have both high temperatures and low humidity levels.
While it may seem unlikely, this evaporative cooling process can be used to reach extremely low temperatures which is the reason that a lot of cryogenic research uses some type of evaporative air conditioning.
Cryogenic research is the study of how things behave at extremely low temperatures. Typical cryogenic research being around minus 238 degrees Fahrenheit and continues all the way down to absolute zero (minus 459.67 degrees Fahrenheit). At extremely low temperatures materials begin to behave much differently than they do at normal temperatures. For example, gases at low temperatures become liquids, metals lose much of their electrical resistance and begin to super conduct, and living tissues can be preserved without decay for significant periods of time.
Evaporative Cooling and Cryogenics
Due to the way an evaporative cooler works, in order for it to provide air temperatures anywhere near those cryogenic work demands, a special coolant must be used. Generally, a highly-compressed gas such as Helium-3 can be used in an evaporative cooler to reach cryogenically suitable temperatures.
Researchers like using evaporative cooling for this type of cooling because it is relatively cheap to run and the temperature it puts out is consistent and stable. As a result, cryogenic applications of evaporative air conditioners vary greatly. These super air conditioners are used while researching everything from how food can be better preserved over time to research into new rocket fuels and superconducting magnets.
The main disadvantage of evaporative air conditioners in cryogenics is that because the cooling process is dependent on the vapor pressure of the coolant being used, there is a bottom limit temperature which the unit will not be able to cool below. However, to cross this limit scientists still sometimes use evaporative coolers because the coolers with the greatest cooling efficiency use an evaporative air conditioning and compressed vapor conditioning in tandem.
By using the evaporative process to super cool the compressed vapor before it returns to the compressor, cooling units can reach unbelievably low temperatures, allowing researchers to continue to expand their knowledge of cryogenic science.