Numerical And Experimental Study On The Diffusion And Ignition Properties Of Difluoromethane

With the increasing emphasis on environmental issues and the protection of the ozone layer, the replacement of refrigerants become an important issue now. HCFC substances currently in use as the main refrigerant is HCFC-22which has long been widely used in a variety of high, medium and low temperature refrigeration and air conditioning field instead of CFC refrigerant in some cases. However, HCFC-22still contains a chlorine atom, and its ozone depleting potential is0.055, so it is disabled, requiring that its replacement refrigerants’ODP value should be zero, i.e., alternative refrigerants should not contain chlorine atom. HFC-32(difluoromethane), with high energy efficiency, high production of cold, excellent thermal properties and high cooling efficiency, no chlorine atom thus harmonious to ozone layer, etc., is a promising new generation of refrigerant, as a main alternative to R22refrigerant which is currently widely used. But difluoromethane has certain flammability which is a barrier to its application.Therefore it’s needed to study the leakage and ignition characteristics under realistic scenarios and analyze its safety and fire risk.Based on literature research, numerical simulation, simulating experiments and real machine experiments were carried out to study the leakage and ignition characteristics of HFC-32. Through simulation, some HFC-32’s leakage diffusion law were found that whether the leakage point is high or low, R32leaked in the process exhibited obvious settling; in height above the drain port and above the air vents there were rare R32;when leakage point was located in low height (cabinet air conditioners scene), R32diffused from the leakage point, and then making it as the center, spread from the near to the distant; and in the leakage process, the concentration near the leakage point was higher than that in other areas in the same plane; when the leakage point was located higher (wall-mounted air conditioners scene), in some areas there would be the lowest concentration value at intermediate height; and because of the impact of the initial velocity, the concentration in places closest to the leakage point was not higher than that of the surrounding in the same z plane that was lower than the leakage point; in above two conditions,soon after HCF-32reached far wall surface, the concentration close to the wall would get to the peak under the influence of turbulence. Simulating experiments corroborated the leakage laws in numerical simulation study, which there was significant subsidence phenomenon. And we also found that whether candles, electric stoves or high-voltage electronic ignition could not cause fire with flame, but HF gas was detected by HF gas detectors and sensors in long-term leakage experiments, indicating that candle flames, fires of electric stove and arc fires were able to bring reaction to leaked difluoromethane, making it decompose to produce HF gases. In real machine experiments, with limited amount of HFC-32charge and self-protection in the machine, concentrations of HFC-32in the space was lower, and in this case, obvious HF failed to be detected in the leakage and ignition process. Overall, HFC-32refrigerant in normal use particularly in the case of household real machine has low fire hazard.