Enthalpy and heat flux distributions in a triple torch plasma reactor

Summary form only given. In thermal plasma deposition, the precursor materials are injected into the plasma and transported by a plasma jet to the substrate. The strong non-uniformities of the plasma jet and of the distribution of the deposition precursors can lead to nonuniformities in the coating properties. The triple torch plasma reactor has been designed to alleviate this situation and offers an increased plasma volume by arranging three plasma torches in such a way that their jets coalesce. The deposition precursors are injected through a water-cooled probe into the region where the jets combine. In order to get an understanding of the interaction between the plasma and the deposition precursors as well as between the plasma and the substrate, the enthalpy flux and heat flux distributions in the reactor have been measured. A watercooled miniature enthalpy probe has been used, in conjunction with a novel miniature heat flux probe embedded in the substrate. Data have been obtained for different torch currents (250 and 300 A per torch), for different chamber pressures (100 to 600 Torr), and for different injectant carrier gas flow rates. An analysis for the substrate heat flux based on regular stagnation flow heat transfer has yielded results which are in acceptable agreement with the experimental data for the case of 600 Torr chamber pressure, but display significant discrepancies for a pressure of 300 Torr. Non-equilibrium effects appear to reduce the substrate heat flux.