Refrigerants (18 pages)

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Refrigerants



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Refrigerants

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Pages:
18
School:
San Jose State University
Course:
Me 113 - Thermodynamics
Thermodynamics Documents

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Refrigerants Background 1850 s 1870 s ammonia ammonia water CO2 Early 1900 s SO2 methyl chloride used for domestic refrigerators 1930 s halocarbon refrigerants discovered by Midgley R 12 R 22 R 114 R 22 Halocarbon advantages stable compounds favorable thermodynamic properties safer than existing refrigerants Ammonia still used for large low T industrial plants Ozone Depletion Molina Rowland 1974 hypothesized that Cl in CFC s contributed to depletion of ozone O3 in upper atmosphere CFC s HCFC s HFC s Ozone Depletion cont CFC s Most stable remain in atmosphere for many years allowing them to diffuse to high altitudes CFC s break down and Cl combines with and consumes some ozone HCFC s Hydrogenated Not as stable most of it breaks down before reaching high altitudes Less damaging to ozone Ozone Depletion cont HFC s Contains no Cl Causes no depletion of ozone Montreal Protocol 1987 Called for curtailment of production of CFC s Follow up conferences London Copenhagen Complete cessation of CFC production Eventual discontinuance of HCFC production Global Warming Short wavelength radiation from sun passes easily through atmosphere Earth emits long wavelength radiation Greenhouse gases block transmission of long wavelength radiation causing the earth to retain more heat Greenhouse gases are removed from the atmosphere by natural processes at varying rates NOTE THAT GLOBAL WARMING AND OZONE DEPLETION ARE DIFFERENT PROBLEMS WITH DIFFERENT CAUSES A lot of people mess up on this on exams TEWI Total Equivalent Warming Impact Consider direct contributions to global warming refrigerant emissions and indirect CO2 emitted due to electrical energy usage Indirect contributions are up to 98 of the total contribution System efficiency is important After redesign most HCFC and HFC systems now have lower a TEWI than CFC systems Kyoto Protocol 1998 Requires reduction in six greenhouse gas emissions to a level seven percent below what existed in 1990 Signed by US in 1998 but not ratified by



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