| Refrigerants are recognized as the blood of the refrigerating and heating systems. The mainly on using HCFCs (hydrochlorofluorocarbons) and partial HFCs (hydrofluorocarbons) refrigerants are not environmentally friendly, which will be phased out. The ideal new generation refrigerants are expected to be with the following characteristics:zero ozone depletion potential, lower global warming potential, better thermo-physical properties, energy efficiency, safety, nontoxic, lower flammability, suitable operating pressure, lower cost, suitable for the heat source, recyclable, policy allowance, etc. However, there is no perfect solution of refrigerants substitution right now.The current research results indicate that:R744, R290, R717, R600a, R1150, R1270, RE170, R32, R161, R152a, R1234yf, R1234ze (E) and their blends may play the vital roles in the process of refrigerants updating. But most of these prospective candidates possess a disadvantage of flammability (R744 exception). In recently years, the frequent accidents on the refrigerating systems rouse people to realize the importance of researching the leaking and flammability characteristics of refrigerants deeply, as well as the related prevention strategies. However, the existing achievements cannot meet the development requirements of the new generation refrigerants.This paper focuses on "refrigerant", and the research contents cover ①the properties of the available candidates, ②the fundamental flammability and explosion characteristics under various surrounding conditions, ③the flame suppression and inerting mechanism of multifarious retardants,④the solubility of various refrigerants and lubricating oils, ⑤ the theory on the generation division of working fluids, etc. The research objects include hydrocarbons, HFOs (hydrofluoroolefins), HCFCs, HFCs, ethers, and their blends. Many influence factors on the fundamental flammable characteristics of refrigerants have been studied experimentally and theoretically, such as the environmental temperature, relative humidity, ignition energy, lubricating oils, reaction vessels, and inerting agents. Combined with the theory of molecular bond dissociation energy, a new estimation method was proposed to calculate the flammability limits of refrigerants with accepted accuracy. In addition, the gaseous combustion essence was analyzed, as well as the typical flammability parameters of gases, and then an amendment was suggested to revise the maximum permissible charging amount of the flammable refrigerant in the monomer air conditioning.The leakage characteristic of refrigerant from a domestic air conditioning was studied by using the computational fluid dynamics (CFD) method. The concentration field distribution was simulated and discussed under the varying initial conditions. The results indicated that the following factors may increase the burning risk, ①the lower LFL of refrigerant, ②the bigger refrigerant charge, ﹖he slower velocity of air outlet,④ opening window seldom, ⑤losed to the ignition sources.Further, the author designed and built an experimental system to test the flammability of refrigerants and inhibitors on the basic of GB/12474-2008 and ASTM E 681-2009 standards, in which a good deal of tests have been carried out under complicated conditions. The value of the virtual LFL’(with Le Chatelier equation style) for fire retardant is proportional to the volumteric concentration ratio of the fire retardant to refrigerant, with the linear relationship. Finally, a new flammability inerting sensitivity indicator was proposed to indicate the flammability limits variation amplitude in case of the ratio of fire retardant to refrigerant changed.This paper also played attention to the combustion flame features and influence factors:surrounding temperature, free radical luminescence, oxidant concentration, electron transition, soot formation, heat absorbing, elements, lubricating oil as so on. In the flame propagation process, either the "go straight up" or "go up and back" phenomena can be observed under the two different testing methods. Besides, the flammability characteristics of the gaseous refrigerants and lubricating oil mixtures were tested under three conditions, which can be explained from the view of fugacity for vapor liquid phase equilibrium.The solubility of refrigerants (such as HCFCs, HFCs, ethers, blends) and lubricating oils (mineral oil, POE, mixture) has been studied. A new experimental system was built on the ground of SH/T 0699 and JIS K2211 standards. The research results showed that:Firstly some a HFC refrigerant dissolved in mineral oil; secondly the system charging with the HFCs/HCs mixture cannot use mineral oil but POE unless the ratio of HCs was more enough; thirdly, if charging the HFCs and POE into the refrigerating system, the residual original mineral oil will affect its solubility and heat exchanging. Finally a new proposed evaluation index was helpful for predicting the solubility of refrigerants and mineral oils. |
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