REFRIGERANTS
of CFCs could leak slowly into the stratosphere when they would be exposed to shorter wavelength UV radiation. Molina demonstrated that this more energetic UV, which normally does not penetrate to troposphere, is absorbed by CFC molecules, in the following case CFC-12, causing them to split off chlorine atoms.
CCl2 F2 + UV Cl + CClF2
So, having shown that CFCs could degrade, what could happen next? In the stratosphere UV light is absorbed by oxygen molecules
generating oxygen atoms which in turn reacted with oxygen molecules to form ozone (O3
). O2 O2
+ UV O + O + O O3
By absorbing the most highly energetic UV the stratospheric
ozone layer protects the biosphere, including ourselves, from radiation damage. Rowland and Molina showed the Cl atom liberated from CCl2
attacks an ozone molecule generating oxygen and chlorine monoxide (ClO).
Cl + O3 ClO + O2 In a fi nal step ClO reacts with O atoms, also formed in the
stratosphere, to release the Cl atom. ClO + O Cl + O2
Refrigerant Solutions hp ACR Aug22.qxp_Layout 1 13/7/22 08:54 Page 1 ozone. Most importantly, since it is regenerated, a single Cl
Overall, the chlorine atom has destroyed one molecule for F2
atom can destroy a number of ozone molecules before it is removed for example by conversion to hydrogen chloride (HCl). Rowland and Molina concluded that: ‘Chlorofl uoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for 40-150 years, and concentrations can be expected to reach 10 to 30 times present levels. Photodissociation of the chlorofl uoromethanes in the stratosphere produces signifi cant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone.’ (Nature, 1974). The CFC manufacturers responded rapidly. Firstly, they jointly funded independent, academic atmospheric scientists to test the Rowland and Molina hypothesis, posing the question is it correct, or not? If it is correct, at what rate is stratospheric ozone being depleted? Secondly, manufacturers initiated their own research programmes to identify alternative products, notably refrigerants that avoided ozone depletion but retained the desirable properties of the CFCs – low toxicity, nonfl ammability, stability and effi ciency. By the late 70s the scientifi c results confi rmed that Rowland and Molina were correct, CFCs could deplete stratospheric ozone, but models indicated at a rate that was suffi ciently low allowing a phased introduction of non- ozone depleting substances to minimise the economic impact. The USA banned the use of CFCs in aerosols but their use as refrigerants continued. Then, in 1984, the Antarctic Ozone hole was discovered – but that is another story.
Following World War 2 the usage the CFCs
grew rapidly contributing to the increase in living standards in the
developed nations and fi nding new outlets,
particularly as aerosol propellants.
RS-53 (R470A)
THE ONLY NON-FLAMMABLE DROP-IN REPLACEMENT FOR R410A ON THE MARKET
FANS
• Low direct GWP Drop-in replacement for R410A • Similar energy efficiency to R410A • Close match for R410A in cooling capacity • Similar discharge pressure to R410A • Minimal changes to hardware required during retrofitting
Download the ACR News app today
• Compatible with lubricants commonly used with R410A • Replaces R410A in air conditioning & refrigeration applications
• Similar flow rate to R410A • Zero Ozone Depletion Potential • Non-flammable & low toxicity
www.acr-news.com • March 2024 25
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
