Experimental And Theoretical Study On Flammability And Inhibition Characteristics Of Refrigerants

Refrigerant is the key medium to realize normal operation and energy conversion of refrigeration system.In response to global warming,the Kigali amendment to the Montreal Protocol has officially entered into force,and the gradual reduction and even phase-out of refrigerants with high GWP(global warming potential)have begun.By analyzing the existing refrigerant alternatives,it can be found that the perfect refrigerant that can take into account the characteristics of environmental protection,thermophysical properties,high energy efficiency,safety,and reasonable cost has not yet appeared.Most of the existing environmentally friendly refrigerants have varying degrees of flammability,so safety and environmental friendliness are often difficult to balance.Due to the continuous constraints of environmental policies,environmentally friendly and flammable refrigerants are still an indispensable component of alternative solutions.In view of the frequent occurrence of safety accidents related to refrigerant leakage and explosion,it is urgent to conduct systematic and in-depth research on the basic explosion and suppression characteristics of refrigerants.In this paper,HFOs,HFCs,HCs,ethers and other refrigerants with low GWP and their mixtures were taken as the research objects.The basic combustion and explosion characteristics of some typical environmentally friendly refrigerants and their mixtures,the influence of specific factors on their combustion characteristics,and the inhibition of several flame retardants on the flammability of refrigerants were studied by theoretical and experimental methods.First of all,the existing research objects on the flammability limit are mainly limited to hydrocarbons or non-halogenated compounds.Therefore,based on the stoichiometric concentration method,this paper combined the theoretical analysis of chain reaction and the chemical bond energy in molecules,and then proposed a new theoretical prediction method for the lower flammability limit(LFL)of flammable refrigerants.The characteristics of the new method were as follows:(1)it has wide applicability and can unify the calculation formulas of LFLs of hydrocarbons,halogenated compounds and some ethers;(2)the prediction accuracy of the new method is very high by comparing with the literature values.According to ASTM E681-2009 standard,a test system for the ignition and combustion characteristics of refrigerants was improved.The flame characteristics of a variety of low GWP refrigerants and their mixtures were measured and analyzed,and a large number of basic flammability limit data was obtained.Secondly,in view of the current requirements for burning velocity in the safety assessment of alternative refrigerants,a new test system for the burning velocity of refrigerants was designed and built with reference to the ISO 817-2014 standard.Then,the longitudinal flame propagation images of R152 a and its mixture were obtained.Meanwhile,the average flame propagation speed and burning velocity data at multiple times were analyzed and obtained.Three prediction methods for the burning velocity of binary flammable mixture were proposed.By comparing the calculated values with the experimental values,it is concluded that the component concentration equivalent method has the highest prediction accuracy among the three methods.Secondly,the actual environment of refrigerant leakage is not a static or quasi-static,but the research on the ignition and combustion characteristics of flammable refrigerants caused by gas disturbance is very scarce.Based on the above-mentioned test system for ignition and explosion characteristics,a new test method and process were designed.Then,the effect of different airflows on the flame characteristics and LFLs of several flammable refrigerants was studied.The results show that specific airflows can enhance the flammability of refrigerants.According to the obtained special experimental phenomena and the different effects of different test methods or test conditions,a new study on the critical flammability limit judgment method was carried out.And it is recommended to determine the LFL from multiple angles and multiple parameters.In addition,in order to reduce the flammability of R1234 yf,the inhibition of several flame retardants on the ignition and combustion characteristics of R1234 yf was experimentally studied.The results showed that the inhibitory effects of DFR1 and DFR3 were better than that of DFR2 and DFR4.At the same time,the comprehensive parameter IC(inhibition characteristics)of the inhibition characteristics of the flame retardants was proposed.Through its three secondary parameters,the inhibition characteristics of different flame retardants could be better analyzed and compared.Then the chemical inhibition mechanism of conventional flame retardants was analyzed theoretically.Different from conventional flame retardants,a new idea of indirect flame retardant using lubricating oil as a carrier was put forward.And the influence of lubricating oil on the flammability of refrigerant,and the influence of indirect flame retardant on the flammability of refrigerant with lubricating oil were studied.The results show that indirect flame retardants have the potential to inhibit the flammability of refrigerants or refrigerants with oil.At present,there are few studies on the concentration of HF,one of the combustion products of fluorine-containing refrigerants,and the research methods are different.Therefore,this paper proposed a closed test method of refrigerant combustion products.Based on the original test system of flammable characteristics,a concentration test system of refrigerant combustion product was established by adding a pressure relief system and a dilution test system.Then,the HF concentration characteristics of the combustion product of R161 were tested and analyzed.Through the analysis of the experimental value and the theoretical prediction value,a method for predicting the concentration of the refrigerant combustion product HF is proposed.The results of this study have positive significance for the replacement of refrigerants and the safe application of new environmentally friendly refrigerants.