Main Anthropogenic Sources of Greenhouse Gases Refrigerants

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1 Main Anthropogenic Sources of Greenhouse Gases Refrigerants

2 Content Refrigerant definition Refrigerants Refrigerants as a source of GHG

3 Refrigerant Definition A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas and back again. Many working fluids have been used for such purposes. Fluorocarbons, especially chlorofluorocarbons, became commonplace in the 20th century, but they are being phased out because of their ozone depletion effects. Other common refrigerants used in various applications are ammonia, sulfur dioxide, and non halogenated hydrocarbons such as propane.

4 Refrigerants A chlorofluorocarbon (CFC) is an organic compound that contains only carbon, chlorine, and fluorine, produced as a volatile derivative of methane, ethane, and propane. They are also commonly known by the DuPont brand name Freon. The most common representative is dichlorodifluoromethane (R 12 or Freon 12). Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), and solvents. Because CFCs contribute to ozone depletion in the upper atmosphere, the manufacture of such compounds has been phased out under the Montreal Protocol, and they are being replaced with other products such as HFCs (e.g., R 410A), hydrocarbons, and CO 2. However, these replacements are sometimes considered pollutants in their own right.

5 Refrigerants Work on alternatives for chlorofluorocarbons in refrigerants began in the late 1970s after the first warnings of damage to stratospheric ozone were published. The hydrochlorofluorocarbons (HCFCs) are less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer. Nevertheless, a significant fraction of the HCFCs do break down in the stratosphere and they have contributed to more chlorine buildup there than originally predicted. Later alternatives lacking the chlorine, the hydrofluorocarbons (HFCs) have an even shorter lifetimes in the lower atmosphere. One of these compounds, HFC 134a, is now used in place of CFC 12 in automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane blend) are also used extensively in mobile air conditioning systems in Australia, the USA and many other countries, as they have excellent thermodynamic properties and perform particularly well in high ambient temperatures.

6 Refrigerants One of the natural refrigerants (along with ammonia and carbon dioxide), hydrocarbons have negligible environmental impacts and are also used worldwide in domestic and commercial refrigeration applications, and are becoming available in new split system air conditioners. Various other solvents and methods have replaced the use of CFCs in laboratory analytics.

7 Refrigerants

8 Refrigerants as a Source of GHG The inert nature of many halons, chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC), with the benefits of their being nonflammable and nontoxic, made them good choices as refrigerants, but their stability in the atmosphere and their corresponding global warming potential and ozone depletion potential raised concerns about their usage. In order from the highest to the lowest potential of ozone depletion are Bromochlorofluorocarbon, CFC then HCFC. Though HFC and PFC are non ozone depleting, many have global warming potentials that are thousands of times greater than CO2. Some other refrigerants such as propane and ammonia are not inert, and are flammable or toxic if released. New refrigerants were developed in the early 21st century that are safer for the environment, but their application has been held up due to concerns over toxicity and flammability.

9 Refrigerants gases trends.

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11 The Radiative Forcing bar chart: AR5 version Climate Change 2013: IPCC AR5 WG1 SPM, Fig. SPM 05

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14 Joule Thomson Coefficient When a fluid passes through a restriction such as a porous plug, a capillary tube, or an ordinary valve, its pressure decreases. The enthalpy of the fluid remains approximately constant during such a throttling process. The temperature of the fluid may remain unchanged, or it may even increase during a throttling process. The temperature behavior of a fluid during a throttling ( constant) process is described by the Joule Thomson coefficient, defined as

15 Joule Thomson Coefficient Thus the Joule Thomson coefficient is a measure of the change in temperature with pressure during a constant enthalpy process. Notice that if during a throttling process. Some constant enthalpy lines on the T P diagram pass through a point of zero slope or zero Joule Thomson coefficient. The line that passes through these points is called the inversion line, and the temperature at a point where a constant enthalpy line intersects the inversion line is called the inversion temperature.

16 Required Properties of Ideal Refrigerant 1) The refrigerant should have low boiling point and low freezing point. 2) It must have low specific heat and high latent heat. Because high specific heat decreases the refrigerating effect per kg of refrigerant and high latent heat at low temperature increases the refrigerating effect per kg of refrigerant. 3) The pressures required to be maintained in the evaporator and condenser should be low enough to reduce the material cost and must be positive to avoid leakage of air into the system. 4) It must have high critical pressure and temperature to avoid large power requirements. 5) It should have low specific volume to reduce the size of the compressor.

17 Required Properties of Ideal Refrigerant 6) It must have high thermal conductivity to reduce the area of heat transfer in evaporator and condenser. 7) It should be non flammable, non explosive, non toxic and non corrosive. 8) It should not have any bad effects on the stored material or food, when any leak develops in the system. 9) It must have high miscibility with lubricating oil and it should not have reacting properly with lubricating oil in the temperature range of the system. 10) It should give high COP in the working temperature range. This is necessary to reduce the running cost of the system. 11) It must be readily available and it must be cheap also.

18 Refrigerants Ammonia Has good heat transfer properties Not miscible with oil But Toxic Flammable Corrosive to copper pipes Carbon dioxide Non toxic Non flammable But Higher cost Halogens (freons) Non toxic Non flammable Have good heat transfer properties Lower cost But Miscible with oil Widely used despite miscibility

19 Main Anthropogenic Sources of Greenhouse Gases Refrigerants