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Three models have been applied to very rapid compression of oxygen in a dead-ended tube. Pressures as high as 41MPa (6,000psi) lead to peak temperatures well in excess of the autoignition temperature (750K) of polytetrafluoroethylene (PTFE). These findings are in accord with experiments that have resulted in ignition and combustion of the PTFE, leading to the melting and/or combustion of the stainless steel braiding and catastrophic failure.
A purely thermodynamic model assumes filling to be complete upstream of a flow-limiting orifice before any gas passes through the orifice. Results show that peak temperatures as high as 4,800K can result from recompression of the gas after expanding through the orifice. An approximate transient model without an orifice was developed assuming an isentropic compression process. Results indicated that fill times can be considerably shorter than valve opening times. The third model was a finite difference, 1-D transient compressible flow model. Results from the code show the recompression effect but predict much lower peak temperatures than the thermodynamic model. The difference is due mostly to the complete lack of mixing in the thermodynamic model.
oxygen, compressible flow, fluid mechanics, thermodynamics
assistant professorNASA/ASEE Summer Faculty Fellow, New Mexico State UniversityWhite Sands Test Facility, Las CrucesLas Cruces, NMNM