Watchmojo bitcoin stock price
22 comments
Nxt castor bot
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.
The ideal working fluid or often called refrigerant would have favorable thermodynamic properties, be noncorrosive to mechanical components, and be safe, including freedom from toxicity and flammability. It would not cause ozone depletion or climate change. Since different fluids have the desired traits in different degree, choice is a matter of trade-offs. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization , a moderate density in liquid form, a relatively high density in gaseous form, and a high critical temperature.
Since boiling point and gas density are affected by pressure , refrigerants may be made more suitable for a particular application by appropriate choice of operating pressures. The inert nature of many halons , chlorofluorocarbons CFC , and hydrochlorofluorocarbons HCFC , particularly CFC and CFC, made them preferred choices among refrigerants for many years because of their nonflammability and nontoxicity.
However, their stability in the atmosphere and their corresponding global warming potential and ozone depletion potential raised concerns about their usage.
However, these refrigerants still have global warming potentials thousands of times greater than CO 2. Therefore, they are now being replaced in markets where leaks are likely, by using a third generation of refrigerants, most prominently HFOyf , which have global warming potentials much closer to that of CO 2.
Some other refrigerants such as propane and ammonia are not inert, and are flammable or toxic if released. In order from the highest to the lowest potential of ozone depletion are: 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.
Early mechanical refrigeration systems employed sulfur dioxide , methyl chloride and ammonia. Being toxic, sulfur dioxide and methyl chloride rapidly disappeared from the market with the introduction of CFCs. Occasionally, one may encounter older machines with methyl formate , chloromethane , or dichloromethane called carrene in the trade.
Chlorofluorocarbons were little used for refrigeration until better synthesis methods, developed in the s, reduced their cost. Their domination of the market was called into question in the s by concerns about depletion of the ozone layer.
Following legislative regulations on ozone depleting chlorofluorocarbons CFCs and hydrochlorofluorocarbons HCFCs , substances used as substitute refrigerants such as perfluorocarbons FCs and hydrofluorocarbons HFCs have also come under criticism.
They are currently subject to prohibition discussions on account of their harmful effect on the climate. In , the EU adopted a Regulation on fluorinated greenhouse gases , which makes stipulations regarding the use of FCs and HFCs with the intention of reducing their emissions.
The provisions do not affect climate-neutral refrigerants. Refrigerants such as ammonia R , carbon dioxide and non-halogenated hydrocarbons do not deplete the ozone layer and have no ammonia or only a low carbon dioxide, hydrocarbons global warming potential.
In these settings their toxicity is less a concern than in home equipment. Emissions from automobile air conditioning are a growing concern because of their impact on climate change.
One of the most promising alternatives is CO 2 R Carbon dioxide is non-flammable, non-ozone depleting, has a global warming potential of 1. R can be used as a working fluid in climate control systems for cars, residential air conditioning, hot water pumps, commercial refrigeration, and vending machines.
Some refrigerants are seeing rising use as recreational drugs , leading to an extremely dangerous phenomenon known as inhalant abuse. Under Section of the United States' Clean Air Act it is illegal to knowingly release refrigerants into the atmosphere. When refrigerants are removed they should be recycled to clean out any contaminants and return them to a usable condition.
Refrigerants should never be mixed together outside of facilities licensed to do so for the purpose of producing blends. Some refrigerants must be managed as hazardous waste even if recycled, and special precautions are required for their transport, depending on the legislation of the country's government.
Various refrigerant reclamation methods are in use to recover refrigerants for reuse. Refrigerants may be divided into three classes according to their manner of absorption or extraction of heat from the substances to be refrigerated: The R- numbering system was developed by DuPont corporation which owns the Freon trademark , and systematically identifies the molecular structure of refrigerants made with a single halogenated hydrocarbon.
The meaning of the codes is as follows: For example, Ra has 2 carbon atoms, 2 hydrogen atoms, and 4 fluorine atoms, an empirical formula of tetrafluoroethane. The "a" suffix indicates that the isomer is unbalanced by one atom, giving 1,1,1,2-Tetrafluoroethane. R without the "a" suffix would have a molecular structure of 1,1,2,2-Tetrafluoroethane—a compound not especially effective as a refrigerant. The same numbers are used with an R- prefix for generic refrigerants, with a "Propellant" prefix e.
Recently, a practice of using abbreviations HFC- for hydrofluorocarbons , CFC- for chlorofluorocarbons , and HCFC- for hydrochlorofluorocarbons has arisen, because of the regulatory differences among these groups.
Below are some notable blended HFC mixtures. There exist many more see list of refrigerants. All R R-4xx and R R-5xx hydroflurocarbons are blends, as noted above. Air is so frequently used as a coolant that air cooling is seldom mentioned in a refrigeration context. Due to the low boiling point of its constituents and low heat-carrying capacity, air is infrequently used as a refrigerant. The reason why air is not more widely used as a general-purpose refrigerant is because there is no change of phase , and is therefore too inefficient to be practical in most applications.
However, an explosion could result from vapors or atomized refrigerant-type compressor lubricating oils being compressed together with air, in a process similar to a diesel engine. Water—natural, non toxic, low cost, environmentally friendly, and widely available—is widely used in water cooling , and if evaporated in the process may be called a "refrigerant".
Water also commonly serves as a heat transfer and storage material ,and in large systems it may actually fill all of these roles. The simplest and lowest cost open-cycle cooling systems, known as swamp coolers in the south-west United States, do not even need power for a compressor, merely a blower fan, so humidified cooled air is simply vented into the living space.
However, if these systems are improperly implemented the drawbacks are multiple and severe. The total cooling power of the unit is limited by the fact that neither coolant nor air can be recirculated. If the cooling unit does not have a supply of fresh dry air and the waste air is not effectively vented, stagnant humid air will make the space more uncomfortable than if it were merely ventilated.
An additional limitation of such systems would be that if the air outside is already humid , cooling power is severely limited. This is why such units are not found in areas of frequent and high humidity, such as the south-east United States.
In these instances more-complex systems such as two stage, indirect-direct or hybrid will be needed. While all the drawbacks can be addressed in various ways, the complexity and initial cost of these systems increases to the point that the installation cost comes into competition with common refrigerant based direct cooling systems. At this price point, direct cooling systems are often chosen even though the long term energy cost of evaporative systems may be lower.
From Wikipedia, the free encyclopedia. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. December Learn how and when to remove this template message. This section's factual accuracy is disputed. Relevant discussion may be found on Talk: Please help to ensure that disputed statements are reliably sourced. May Learn how and when to remove this template message. Retrieved June 21, American Public Health Association, Retrieved 20 December Retrieved 25 December Archived from the original on Archived from the original on 1 June Retrieved from " https: Heating, ventilating, and air conditioning Refrigerants Industrial gases.
All articles with dead external links Articles with dead external links from January Articles needing additional references from December All articles needing additional references All articles with unsourced statements Articles with unsourced statements from December Accuracy disputes from May All accuracy disputes Articles with unsourced statements from August Articles with unsourced statements from March Views Read Edit View history.
In other projects Wikimedia Commons. This page was last edited on 14 May , at By using this site, you agree to the Terms of Use and Privacy Policy.