What are the properties of refrigerant gases?:
In its liquid form it generally occupies about 40 times less volume than it does as a gas. In other words 1 litre of liquid would expand to 40 litres of gas. As a gas it will readily compress into a smaller volume. As a liquid it will not compress, so extreme care should be taken when recovering or charging. Pressure vessels tolerate compressed gas but become almost glass like when filled fully with liquid. Never fill above 70%.
Refrigerants manifest themselves in many chemical compositions. The most common one that is now found in motor vehicle air conditioning systems is R134a. Some other gases used for refrigeration and cooling systems, such as R22, R406, and R11, are just a few of the many man made compositions. All of these have long chemical names and formulae. R134a is classed as a hydroflorocarbon or HCFC. Its chemical name is "Tetrafluoroethane", CF3CH2F. At normal room temperature and pressures it will only exist as a colourless gas. It has a smell not unlike dry cleaning spirit; some would regard it as a pleasant smell, just as some like the smell of petrol or hot tar.
In order for it to exist in a liquid form it must be kept in a sealed vessel or system, with room to spare for vapour. At room temperature in this sealed vessel it would set up a pressure of around 70-psi. It would quickly boil or flash off to a gas or vapour if the seal were broken, in the process absorbing tremendous amounts of heat from its surroundings. If this sealed vessel were warmed the vapour pressure would increase. Similarly if it were cooled the pressure would drop. Cooling the container to below about -30 Celsius, the vapour pressure would be practically the same as the atmospheric, allowing you to break the seal. The liquid would then remain, just like water sat in a glass. This temperature is in fact is about the boiling point of R134a. Any rise in temperature above this and you would see the liquid begin to boil off to a gas. The higher the temperature the faster it will boil.
Other types of refrigerants act in a similar way. The difference being mainly in the temperature at which they would boil at, and the vapour pressure that they generate for a given temperature. These different properties of other gases allow them to be used for other applications for example, where much colder temperatures are required.
Why Are CFCs and HCFCs Bad for the Environment?:
The stratospheric ozone layer makes it possible for life to exist by shielding the earth from harmful ultraviolet (UV-B) rays generated from the sun. Scientifically, it has now been proved those man-made compounds such as chlorofluorocarbons (CFCs); hydrofluorocarbons (HCFCs) and halons destroy ozone in the upper atmosphere (stratosphere). Decreased concentration of stratospheric ozone allows increased levels of UV-B rays to reach the earth's surface.
R134a has now replaced R12 as the refrigerant medium in the motor vehicle industry, mainly for this reason. R134a causes significantly less damage to the ozone layer than R12; however R134a is still a contributor to the greenhouse gas phenomenon, which is a totally separate issue.
Stratospheric ozone loss can result in potential harm to human health and the environment, such as:
· increased incidence of skin cancer and cataracts,
· damage to terrestrial and aquatic plant life,
· damage to our immune system,
· premature aging of the skin,
· increased formation of ground-level ozone (smog),
· Weathering of plastics.
Stratospheric ozone depletion is caused when chlorine contained in these refrigerants, reacts with ozone. Most of the chlorine entering the stratosphere is from man-made sources (82%), such as CFCs and HCFCs with the remaining 18% from natural sources, such as the ocean and volcanoes.
Man-made compounds of refrigerant gases are very stable and can exist in the atmosphere for a long time; consequently, these compounds can reach the stratosphere and cause destruction of the ozone layer.
Chlorine found in nature is water-soluble. Therefore, most is removed in the lower atmosphere by rain, snow and ice and does not reach the stratosphere. Of particular concern is the damage caused to terrestrial and aquatic plant life. In the late eighties and early nineties, levels of ozone depletion were so bad that it was becoming critical. Participating governments and organizations around the world drew up the "Montreal Protocol". This effectively banned the use of certain refrigerants altogether and gave specifics on the planned phase out of others. You may remember that Macdonald's got a lot of bad press during this time about the use of CFC's in producing their polystyrene burger cartons. This was only a very small part of the story. Some compounds or refrigerant gases are more harmful to the ozone layer than others. Each compound is measured in terms of its ozone depletion potential (ODP) and its global warming potential (GWP). The ODP and GWP of each compound are established relative to R11, where R11 has an ODP of 1.
Natural global warming keeps the world from falling back to around -18C from the average 15C. Mankind's activity is enhancing this natural global warming effect, causing the average temperature to rise above 15C.
