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Heat and cold are two contrasting yet equally important properties and have their own unique benefits and relevance to various processes in the domestic and industrial sectors. Can you think of an example where you need a cold atmosphere in a hot climate? Well there are common examples of using an air conditioning system or a refrigerator to produces temperatures which are really cold.
Despite the low temperatures produces by A.C. or refrigerators, have you ever wondered that how cold is “cold enough"? Well if you haven’t figured out let me tell you that according to the law of thermodynamics the lowest temperature which could never be achieved is that of absolute zero degrees which is equivalent to -273.15 degrees Celsius. But you might be surprise to know that though absolute zero cannot be obtained, it has been possible to reach very close to this temperature and the section below tells us more about this process.
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Cryogenics - The Cool Science
Science is always a cool and interesting subject to study but cryogenics is cool in the literal sense for it refers to the science related to production of extremely low temperatures. As I mentioned previously the reason for not being able to attain absolute zero is that the amount of energy required for this would be infinite which is obviously non-feasible.
If the word seems All Greek then you are probably right for a paradoxical coincidence for it is actually so. The word cryogenics is actually made up from the combination of two Greek words namely “Kyros" and “Genic" which refer to “frost" and “produce" respectively, hence the meaning of producing frost or very low temperatures.
We cannot specify a particular date when Cryogenics can said to be born but there is sufficient evidence to indicate that even as long back as 150 years ago, the Swiss watchmakers used this technique albeit without knowing much about the internal workings of the process. They buried parts of their watches in snow and found that these parts got more durable. Similar techniques were used in other parts of the world as well where materials were subject to extreme heat and cold to make them stronger and longer lasting.
Though there may be disagreements regarding exact origins of Cryogenics, most experts would agree that the credit of transforming the concepts discussed above into a concrete science goes to NASA who utilized this technique to strengthen parts used in spacecrafts so that they can survive the extreme temperatures of the universe along their astral journey.
Initially the process was not understood at the microscopic level hence when various processes successfully used liquid nitrogen immersion technique, some processes resulted in very brittle parts associated with the phenomenon of thermal shocks.
Two people who distinctly stand out in developing cryogenics are Dr Randall Barron of Louisiana Technical University and Dr Hugh of the General Dynamics Corporation. Of course there have been several other researchers and academicians who have contribute a lot to this field.
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How on Earth it’s so Cold?
Obviously you do not expect a household refrigerator or an air conditioner to produce these sorts of temperatures. There are several methods which exist for the production of these super low temperatures though it would not be possible to enlist the detailed description of these methods in this introductory article.
The common vapour compression refrigeration cycle with which we are mostly familiar is not much use when temperatures below 40 degrees are being talked about due to several reasons including the relatively higher freezing point of common refrigerants used in vapour compression cycles e.g. F-113 has a freezing point of just -35 degrees Celsius, high vacuum requirement of the evaporator, high compression ratios required and so forth.
Most of the above mentioned difficulties are overcome by using multi stage compression though it has its own set of challenges. Other arrangements include using a two stage and three stage cascade systems, which use compound compression systems with inter-cooling and sub-cooling with liquid refrigerant itself.