A 2-FLUID MODEL OF TURBULENCE FOR A THERMAL PLASMA-JET

In this paper, a turbulent argon plasma jet issuing into a stagnant argon environment at 1 atm is studied by applying a two-fluid turbulence model, in order to advance our understanding of thermal plasma jets. The mathematical model has some similarities to the models of two-phase flows, so that the turbulent plasma jet is treated as a two-phase mixture. The governing equations include the transport equations for mass, momentum, and energy for two different fluid parcels (in-moving parcels and out-moving parcels). Auxiliary relations that govern the physical phenomena of the interfluid mass, momentum, and energy exchange are presented together with a description of the mechanisms that control the growth or diminution of the fragment size. The results are presented in conditional- and unconditional-averaged forms and compared with experimental results from enthalpy-probe measurements. A well-known nondimensional form (a Gaussian error function) can represent the radial distributions of the measured- and predicted-unconditional mean axial velocity and temperature in consecutive sections (20-45 mm from the nozzle exit). Further insight into the behavior of turbulent plasma jets can be gained by looking at the conditional fluid properties. The results show that this model can predict phenomena that escape more conventional models, e.g., the unmixing phenomenon.