Study On Explosion Theory And Inhibition Mechanisms Of Combustion And Explosion Of Flammable Refrigerants

Using natural substances as refrigerants safely has become the trend of development of refrigeration technology while the flammability of some natural refrigerant is the main obstacle to utilization of natural refrigerants. Study on explosion theory and inhibition mechanisms of explosion limit of flammable refrigerants was conducted in this dissertation, the main conclusions and results are the followings: 1 Study on the factors affecting explosion limit The functions applied to compute flame temperature and explosion pressure of flammable refrigerant containing atom F were derived. Computations and analysis demonstrate that the theoretical combustion temperature and the explosion pressure of HFCs are affected by the βnumber, the ratio of the of atom F to H: In the case ofβ=1, the refrigerant has high combustion temperature and explosion pressure; in the case ofβ<1, is flammable, and the combustion temperature and the range of explosion power the refrigerant decreases with the reduce of β. It can be concluded that there is deference between test value and actual value of explosion limit of a flammable refrigerant. Test conditions should be determined and security coefficient should be taken into account before parameters of explosion limit are selected. 2 Study on explosion limit of refrigerant mixture The experimental equipment was developed to test explosion limit of flammable refrigerants. R134a, R125, and R227ea were mixed with R290, R600, R600a, R32, R143a, and R152a respectively to obtain 18 experimental curves of explosion limits. The models were established to calculate explosion limit of mixture respectively. According to the conditions when ternary mixture with nonflammable agent reaches critical inhibitor concentration, the models were established to compute critical inhibitor concentration of mixture. The errors of the models are generally lower than 10% compared with the experimental results. The models can be used to calculate explosion limits and critical inhibitor concentrations. By using the models provided in this dissertation to direct explosion limit test experiment, experiment times can be reduced, test quickened, and the cost of experiment cut down. 3 Study on inhibition effectiveness of nonflammable refrigerants The inhibition efficiency of flame velocity of flammable refrigerants were calculated by the improved Group Distribution Method. Relative burning velocity varies with the concentration of flammable refrigerant was achieved by the inhibition exponential model. The burning velocity of flammable refrigerant decreases exponentially with the increase concentration of inhibitor, and CHs requires higher minimum inhibitor concentration than HFCs. To flammable HFCs, the smaller the ratio of atom H to atom F is, the less inhibitor concentration is required. The relationship curves of the concentration of R134a, R125 and R227ea with the explosion limit of R290, R600, R600a, R32a, R143a, R152a were achieved experimentally. 4 Study on the flammability of leaking flammable refrigerants According to the theory of efflux the models were setup for simulating speed and concentration fields of leakage flammable refrigerants. The simulating results prove that there is a local area which may produce fire or explosion hazards outside the leakage point. The local flammable concentration should be taken into account when the danger of flammable refrigerants are analyzed. A dynamic model was established to calculate the leakage velocity and the flammable concentration range. According to the simulating results, the concentration of flammable agent changed obviously. Thereby the gas-phase leakage must be taken into account when critical flammable concentration is determined. For zeotropes containing flammable agents, low boiling point nonflammable agent should be used to inhibit high boiling point flammable agent, because smaller amount inertia agent is needed, the effectiveness is better, and the possibility of explosion is lower when leakage taking place. 5 Analysis on the safety of leakage of flammable refrigerants A model was established to calculate flammable refrigerant concentration in room after leaking, the result of computation shows, for small air conditioning unit, the possibility of explosion triggered by the leakage of flammable refrigerant is confined a local region outside the leakage point. Three methods were used to analyze damage range, and the damage level of the explosion with flammable refrigerant leakage. The results show the damage range is within 1 meter for small amount of refrigerant. Only with the development of technology and the improvement of security measure, flammable refrigerants will be used besides the field of small air conditioning unit. A new Pressure Relief Equation with restriction was derived, which has definite physical meaning and tallies with the practice.