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Flammability Measurements of Difluoromethane in Air at 100 Deg C.


pdf icon Flammability Measurements of Difluoromethane in Air at 100 Deg C. (842 K)
Grosshandler, W. L.; Donnelly, M. K.; Womeldorf, C. A.

AJTE99-6142;

ASME/JSME Joint Thermal Engineering Conference, 5th Proceedings. American Society of Mechanical Engineers (ASME)/Japan Society of Mechanical Engineers (JSME). March 15-19, 1999, San Diego, CA, 1-8 pp, 1999.

Sponsor:

Air-Conditioning and Refrigeration Technology Institute, Arlington, VA

Keywords:

flammability measurements; difluoromethane; refrigerants

Abstract:

Difluoromethane (CH2F2, or R-32) is a candidate to repIace currently used ozone-depleting chlorofluorocarbon refrigerants. Because CH2F2 is flammable, it is necessary to assess the hazard posed by a leak in a refrigeration machine. The currently accepted method for determining flammability, ASTM E 681, has difficulty discerning the flammability boundary for weak fuels such as CH2F2. This paper describes an alternative approach to identify the limits of flammability, using a twin, premixed counter-flow flame. By using the extinction of an already established flame, the point dividing flammable from non-flammable becomes unambiguous. The limiting extinction mixture changes with stretch rate, so it is convenient to report the flammability limit as the value extrapolated to a zero stretch condition. In the burner, contoured nozzles with outlet diameters of 12 mm are aligned counter to each other and spaced 12 mm apart. The lean flammability limit of CH2F2 in dry air at room temperature was previously reported by the authors to be a mole fraction of 0.14, using the twin counter-flow flame method. In the current study, relative humidity was not found to affect the lean limit. Increasing the temperature of the premixed fuel and air to 100 deg C is shown to extend the flammability limit in the lean direction to 0.13. The rich Iimit of CH2F2 found using the counter-flow method is around 0.27. The uncertainties of the measurements are presented and the results compared to data in the literature.