Experimental study of the heat and mass transfer in a high-frequency thermal plasma reactor

The present study reveals some of the important parameters which control the decomposition of ammonia introduced by radial injection into an induction plasma. Temperature and composition gradients of the plasma stream were evaluated with an enthalpy probe connected to a mass spectrometer. Axial and radial profiles are measured at the exit of the plasma torch to quantify the important mass and energy transfer mechanisms occurring at two levels of ammonia flow rate. Other experiments were made using the enthalpy probe at a “fixed point” along the centerline of the reactor, near the exit of the plasma torch. These experiments were useful in establishing: 1) the minimum radial flow rate that permits the ammonia to completely penetrated the plasma, and 2) to evaluate the maximum load of ammonia that could be decomposed by the plasma. Finally, the “fixed point” configuration is used in combination with a 2³ factorial experiment design to quantitatively determine the important parameters that affected the transport properties of the plasma during the NH₃ radial injection. The controlled experimental parameters employed for the factorial were the flow rate of ammonia, the plate power, the reactor pressure, and the flow rate of the central plasma gas, while the torch exit temperature and the N₂ and NH₃ concentrations formed the studied outputs. The findings of the factorial design showed that the plasma temperature inside the decomposition zone could only be modified by means of plasma plate power and ammonia flow rate changes or adjustments. The diffusion of species during ammonia decomposition is strongly affected by the four controlled experimental parameters under study