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Refrigeration and Cryogenics Maciej Chorowski. Faculty of Mechanical and Power Engineering. Refrigeration - definition. Refrigeration systems. Refrigerant. Chemical structure of refrigerants. Refrigerant R12, CF 2 Cl 2. Demanded properties of refrigerants.
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Refrigeration and CryogenicsMaciej Chorowski Faculty of Mechanical and Power Engineering
Demanded properties of refrigerants • Today the preservation of the ozone layer is the first priority of refrigeration selection
Why do we need ozone in the atmosphere • The atmosphere surrounding the earth contains small quantities of ozone - a gas with molecules consisting of three oxygen atoms (O3). If all the ozone in the atmosphere were compressed to a pressure corresponding to that at the earth's surface, the layer would be only 3 mm thick. • But even though ozone occurs in such small quantities, it plays an exceptionally fundamental part in life on earth. This is because ozone, together with ordinary molecular oxygen (O2), is able to absorb the major part of the sun's ultraviolet radiation and therefore prevent this dangerous radiation from reaching the surface. • Without a protective ozone layer in the atmosphere, animals and plants could not exist, at least upon land. It is therefore of the greatest importance to understand the processes that regulate the atmosphere's ozone content.
How does the ozone protect us against uv? • Ozone is formed in the atmosphere through the splitting of ordinary oxygen molecules (O2) by ultra-violet radiation from the sun. The oxygen atoms thereby liberated react with the molecular oxygen. The ozone that is formed in this process is also dissociated by solar radiation to form an oxygen atom and an oxygen molecule. This cyclic process leads to a natural steady-state concentration of stratospheric ozone. These three reactions are called the "Chapman cycle" : O2+ uv-light -> 2OO+O2+M -> O3+MO3 + uv-light -> O2 + O where M is a random air molecule (N2 or O2).
How is the ozone depleted by CFC’s Stratospheric Ozone Depletion by CFC’s (Catalytic Cycle): Net Reaction: 2 O3 -> 3 O2
The Nobel Prize in Chemistry 1995 The Royal Swedish Academy of Sciences has decided to award the 1995 Nobel Prize in Chemistry to Paul Crutzen, Mario Molina and F. Sherwood Rowland for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone.
