Application of similarity theory to predict operational characteristics of a DC plasma torch under low-pressure condition.

An extensive experimental investigation is carried out to construct a generalized model using theory of dynamic similarity for plasma spray torch behaviour in low-pressure environment. The generalized model is designed with a new set of dimensionless numbers to highlight the operational behaviour of the plasma torch at 10 mbar ambient pressure. These dimensionless numbers represent the effect of corresponding input parameters on the output behaviour of the plasma torch. A comparative analysis of these dimensionless numbers with their atmospheric counterparts highlights the effect of low pressure on the plasma torch operation. The current–voltage characteristics (CVC) and thermal efficiency of the plasma torch are experimentally measured at ∼ 10 mbar chamber pressures at different arc current values, in the range of 100–500 A, for three different anode exit diameters, e.g. 8, 13 and 17 mm. Nitrogen is used as plasma-forming gas having flow rate range of 24–64 LPM. In addition to CVC profile and thermal efficiency, the plasma jet length at 10 mbar chamber pressure is also characterized using a very high-speed camera. A generalized model is also constructed to predict the plasma jet length in low pressure. The output of the model is verified by comparing with the experimental data at different input parameters and found to be in good agreement with the experimental data. This study presents a generalized relationship between input controllable parameters and output behaviour of a plasma spray torch, which is valid in the pressure range of ∼ 10 to ∼ 30 mbar. [ABSTRACT FROM AUTHOR]