And now for some good news.

[rubato]

The hole in the ozone layer which had stopped growing (allowing for normal fluctuation) has now started shrinking.

An example of how successful we can be if we follow the science and respond more quickly to problems.


http://www.vox.com/2014/9/10/6132991/oz ... to-recover

Sometimes the world really can get together and stop a major environmental catastrophe before it's too late. A new UN report finds that the Earth's protective ozone layer is finally starting to recover — after efforts in the 1980s to phase out CFCs and other destructive chemicals.

"Scientists have finally detected signs that the ozone layer is healing"

Back in the 1970s, scientists first realized that we were rapidly chewing a hole through Earth's stratospheric ozone layer, which protects us from the sun's harmful ultraviolet rays.

The culprit? Chlorofluorocarbons (CFCs) — chemicals that were widely used in refrigerators and air conditioners. These chemicals had already created a massive "hole" in the ozone layer around Antarctica and had the potential to destroy even more stratospheric ozone elsewhere in the world.

Had we destroyed the ozone layer elsewhere, skin-cancer rates likely would have skyrocketed — as they already have in Puentas Arenas, Chile, which lies under the existing ozone hole. What's more, the sun's UV rays could have done severe damage to crops and the marine food chain.

Fortunately, that apocalyptic scenario never came to pass. Scientists discovered the problem in time. And, under the 1987 Montreal Protocol, world leaders agreed to phase out CFCs (despite industry warnings that abolishing the chemicals would impose steep costs). The hole in the ozone layer stopped growing. The global economy thrived.

Now comes further good news. The latest UN assessment, by some 300 scientists, has found that the ozone layer is just now starting to heal — and should be back to relatively healthy 1980 levels by 2050, although there will be ups and downs along the way. ... "

The ozone-depleting CFCs were replaced with non-ozone depleting CFCs and now we are in the process of replacing those with ones which contribute less to global warming. (mandated in europe already and soon to be here too)

http://www.honeywellnow.com/tag/low-glo ... rigerants/

I think the new refrigerant is tetrafluoro propane.


yrs,
rubato

[Big RR]

rubato--if I recall correctly, TFP is flammable, and the new refrigerant is a mixture of a few compounds which form a nonflammable mixture, but TFP is a major component.

[rubato]

Actually, I think it might be tetrafluoropropene. But I'm not certain. I'll ask.



yrs,
rubato

[rubato]

I checked, and it is tetrafluoropropene. A good friend worked on it. Actually it was a German company* who claimed it was flammable because it ignited on contact with a surface hotter than 400C. Testing in the US showed the the prior refrigerants all ignite at 350C and are even more flammable. It was formulated for a while with trifluoroiodomethane as an azeotroping mixture which was less flammable but this was abandoned because Iodide is a good leaving group and thus it decomposed into something which destroyed the equipment. So it is now just tetrafluoropropene.

it is worthwhile to note that the increased regulation of CFCs has made automotive cooling systems much more leak-proof. Back in the 1970s you expected to have to re-fill with coolant every 3 years or so. We have had cars lasting 17, 13, and 14 years which were never re-filled and never needed it.


yours,
rubato

* Mercedes-Benz, they resent it when a non-German company beats out their own chemical industry.

[Guinevere]

The MSDS says it's quite flammable.

[rubato]

Correct, but the existing materials are even more flammable. They have a lower ignition temperature per the testing.

Flammability cannot be a 'killer defect' for a material used in a vehicle with 15 gallons or more of highly flammable motor fuel and/or hundreds of pounds of batteries filled with lithium hexafluoro phosphate which ignites spontaneously in air and burns hellishly hot. Its just an engineering problem.

CO2 has been used as a refrigerant and has an even lower global warming potential and its cheap. But. It is an Asphyxiant so a release in a confined space can be dangerous. And it requires much higher pressures which burns more fuel (your car engine has to work harder to maintain that pressure) and its a more powerful bomb if there is a rupture or overpressure due to heating. All of these are just engineering problems too, and can be managed except possibly for the inherent inefficiency problem. Maybe there will be a solution for that, I'm not a mechanical engineer.

The main point is that we have a number of choices and can move forward if we will only do so.

yrs,
rubato

[Big RR]

Guin--from what I recall, there are two different flammability parameters examined--if a gas (like this) can be ignited by an ignition source at room temperature, which it can, it is considered a flammable gas (for liquids it is somewhat different and flammability is determined by the flash point, the temperature at which the liquid has a vapor pressure high enough that is can be ignited). The second is the autoignition temperature--the temperature at which a substance can be ignited by bringing it into contact with a heated surface as the only ignition source. Tetrafluoropropene is a gas that can be ignited (by an ignition source such as a spark or match) in air at room temperature and atmospheric pressure, and will autoignite (again in air) above 400 degrees C (according to rubato). This makes it fairly flammable, but its autoignition temperature appears below that of other non-Freon refrigerants.

One of the most desirable properties of the freons is that they were generally nonflammable (some were even used in fire suppression systems), and there has been singificant research into trying to find other nonflammable refrigerants that don't have the ozone-depleting properties CFCs have.

rubato--in the gas tank, the vapor pressure of gasoline is such that it will not ignite at room temperature and pressure (heat it a bit hotter and it will though); motor oil and brake fluid are similar. Yes, it is an engineering problem to contain the refrigerant, but as the refrigerant is circulated through the engine compartment, is under pressure, and will empty quickly if a line develops a leak, using it poses a hazard--one that can be reduced by proper engineering, but a hazard nonetheless. We need to work on both sides of the equation to get the optimal refrigerant.

[rubato]

"...

We need to work on both sides of the equation to get the optimal refrigerant.

Yes, that is what I said.

And motor fuel is much more highly flammable and it is pumped through tubing close to the exhaust system and if it develops a leak will ignite. Motor fuel is the greater hazard you are just used to accepting it.



yrs,
rubato

[Big RR]

Well, I agree that motor fuel (and brake fluid and oil) are hazards as well, but we'll just have to disagree on what is a bigger hazard.

[rubato]

Fluorinated hydrocarbons produce less energy per mass and per mole than non-fluorinated ones during combustion because the F-C bonds cannot be oxidized during conditions found in normal combustion. So that propane (which is a gas at STP) is not only more flammable it produces more heat when it burns. Ca. 2lbs of tetrafluoropropene is nothing compared to the energy in ca 90 lbs of motor fuel or 20lbs of propane in a small standard-sized tank. It is objectively a lower hazard.

I have further information from my informant but that will have to wait; I'm off to dinner. But he said that carbon dioxide deserves to 'win' even though the best formulation still requires a pressure of 180lbs (vs 3-5 lbs for current systems) and it has to be mixed with a fluorinated hydrocarbon to reduce the pressure (azeotrope effect again).

yrs,
rubato

[Jarlaxle]

Oh, by the gods...that must be why the LOW side on most R-134a systems is 30-45psi.

[rubato]

Oh, by the gods...that must be why the LOW side on most R-134a systems is 30-45psi.

As I said, I was talking with a friend who developed the LGW refrigerant and he said it was 3-5lbs. Both r134a and HFO-1234ze boil at similar temperature at STP (-23C vs -19C) so it is a drop-in replacement while CO2 sublimes at -78C (goes from solid to gas) and requires very very high pressures to exist in a liquid at all. So while it has advantages it also has serious problems.

But to get back. He said that the only way to get the pressure down to 180lbs for CO2 was to add a fluorocarbon and essentially all of the patents are tied up by companies who won't license their use for that purpose. On the other hand, a lot of well-funded and intelligent people are backing CO2 so it may ultimately displace HFO-1234ze


http://www.ohio.edu/mechanical/thermo/A ... pter9.html

Chapter 9: Carbon Dioxide (R744) - The New Refrigerant
Introduction and Discussion

In the early days of refrigeration the two refrigerants in common use were ammonia and carbon dioxide. Both were problematic - ammonia is toxic and carbon dioxide requires extremely high presures (from around 30 to 200 atmospheres!) to operate in a refrigeration cycle, and since it operates on a transcritical cycle the compressor outlet temperature is extremely high (around 160°C). When Freon 12 (dichloro-diflouro-methane) was discovered it totally took over as the refrigerant of choice. It is an extremely stable, non toxic fluid, which does not interact with the compressor lubricant, and operates at pressures always somewhat higher than atmospheric, so that if any leakage occured, air would not leak into the system, thus one could recharge without having to apply vacuum.

Unfortunately when the refrigerant does ultimately leak and make its way up to the ozone layer the ultraviolet radiation breaks up the molecule releasing the highly active chlorine radicals, which help to deplete the ozone layer. Freon 12 has since been banned from usage on a global scale, and has been essentially replaced by chlorine free R134a (tetraflouro-ethane) - not as stable as Freon 12, however it does not have ozone depletion characteristics.

Recently, however, the international scientific consensus is that Global Warming is caused by human energy related activity, and various man made substances are defined on the basis of a Global Warming Potential (GWP) with reference to carbon dioxide (GWP = 1). R134a has been found to have a GWP of 1300 and in Europe, within a few years, automobile air conditioning systems will be barred from using R134a as a refrigerant.

The new hot topic is a return to carbon dioxide as a refrigerant. The previous two major problems of high pressure and high compressor temperature are found in fact to be advantageous. The very high cycle pressure results in a high fluid density throughout the cycle, allowing miniturization of the systems for the same heat pumping power requirements. Furthermore the high outlet temperature will allow instant defrosting of automobile windshields (we don't have to wait until the car engine warms up) and can be used for combined space heating and hot water heating in home usage (refer for example: Norwegian IEA Heatpump Program Annex28).
Recent update March 2013 - Volkswagen, Daimler, Audi, BMW and Porsche have announced plans to develop CO2 MAC (Mobile Air Conditioning) systems (refer: Environmental Leader)

CO2 does not have to be manufactured, only separated and purified which is a big advantage.

Fluorocarbons have to be made by first extracting fluorine from Calcium fluoride, which is very very energy intensive*, followed by reaction at ca 450C over a nickle catalyst with the hydrocarbon which is also very energy intensive.


yrs,
rubato

*and all of the piping has to be replaced every few years due to the effects of HF.

[Lord Jim]

As I said, I was talking with a friend who developed the LGW refrigerant and he said it was 3-5lbs. Both r134a and HFO-1234ze boil at similar temperature at STP (-23C vs -19C) so it is a drop-in replacement while CO2 sublimes at -78C (goes from solid to gas) and requires very very high pressures to exist in a liquid at all.

You must be pure magic at cocktail parties...

[Jarlaxle]

One more time for the rube: the LOW-pressure side on a typical R-134a system is 30-45psi...though the low pressure CUTOFF may activate at 5psi. (Though I suspect it will do so sooner...probably 10-12psi.)