Refrigeration and Cryogenics
Maciej Chorowski
Faculty of Mechanical and Power Engineering
Refrigeration - definition
Refrigeration systems
Refrigerant
Chemical structure of refrigerants
Refrigerant R12, CF2Cl2
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 -> 2O
O+O2+M -> O3+M
O3 + 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
How is the ozone depleted by CFC’s
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.
Ozone Depletion Potential (ODP)
Pressure-enthalpy diagram
CARNOT vapor cycle
CARNOT CYCLE
Single stage vapour compression cycle
Single stage vapour compression cycle
Vapour compression cycle
Refrigeration – basic definitions