空調(diào)系統(tǒng)外文翻譯-在線瀏覽
2025-02-05 20:30本頁面
【正文】 ect contact with the air or water in the evaporator. The refrigerant is converted from a low quality, twophase fluid to a superheated vapor under normal operating conditions in the evaporator. The vapor formed must be removed by the pressor at a sufficient rate to maintain the low pressure in the evaporator and keep the cycle operating. All mechanical cooling results in the production of heat energy that must be rejected through the condenser. In many instances, this heat energy is rejected to the environment directly to the air in the condenser or indirectly to water where it is rejected in a cooling tower. With some applications, it is possible to utilize this waste heat energy to provide simultaneous heating to the building. Recovery of this waste heat at temperatures up to 65176。C (150176。 EPA 1993b) and international agreements (UNEP, 1987) have placed restrictions on the production and use of CFCs and HCFCs. Hydrofluorocarbons (HFCs) are now being used in some applications where CFCs and HCFCs 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 4 were used. Having an understanding of refrigerants can help a building owner or engineer make a more informed decision about the best choice of refrigerants for specific applications. This section discusses the different refrigerants used in or proposed for building air conditioning applications and the regulations affecting their use. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has a standard numbering system (Table ) for identifying refrigerants (ASHRAE, 1992). Many popular CFC, HCFC, and HFC refrigerants are in the methane and ethane series of refrigerants. They are called halocarbons, or halogenated hydrocarbons, because of the presence of halogen elements such as fluorine or chlorine (King, 1986). Zeotropes and azeotropes are mixtures of two or more different refrigerants. A zeotropic mixture changes saturation temperatures as it evaporates (or condenses) at constant pressure. The phenomena is called temperature glide. At atmospheric pressure, R407C has a boiling (bubble) point of –44176。F) and a condensation (dew) point of –37176。F), which gives it a temperature glide of 7176。F). An azeotropic mixture behaves like a single ponent refrigerant in that the saturation temperature does not change appreciably as it evaporates or condenses at constant pressure. R410A has a small enough temperature glide (less than 176。F) that it is considered a nearazeotropic refrigerant mixture. ASHRAE groups refrigerants (Table ) by their toxicity and flammability (ASHRAE, 1994).Group A1 is nonflammable and least toxic, while Group B3 is flammable and most toxic. Toxicity is based on the upper safety limit for airborne exposure to the refrigerant. If the refrigerant is nontoxic in quantities less than 400 parts per million, it is a Class A refrigerant. If exposure to less than 400 parts per million is toxic, then the substance is given the B designation. The numerical designations refer to the flammability of the refrigerant. The last column of Table shows the toxicity and flammability rating of mon refrigerants. 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 5 Refrigerant 22 is an HCFC, is used in many of the same applications, and is still the refrigerant 內(nèi)蒙古科 技大學(xué)畢業(yè)設(shè)計說明書 6 of c
研究報告相關(guān)推薦
鄂ICP備17016276號-1