New Practice for Inferring the Bulk Enthalpy and Total Temperature of Multi-Species Plasma Gas Mixture in an Arc-jet Column using a Thermochemically-Closed Sonic-Flow Inversion Method
1. Scope
This practice describes a methodology for inferring the bulk enthalpy rise and total temperature of multi-species plasma gas flows upstream of a choked nozzle using a thermochemically-closed sonic-flow inversion. The method is based on measured total pressure, total mass flow rate, gas composition, and nozzle throat geometry, combined with thermochemical closure obtained from a chemical equilibrium or frozen chemistry model. This practice is applicable to electric arc-heated and inductively coupled plasma facilities operating under steady-state, choked-flow conditions. The inferred bulk enthalpy rise represents an effective upstream reservoir state governing the choking condition and may differ from local or spatially resolved enthalpy values in the flow. This practice does not require calorimetric energy balance measurements or optical diagnostics.
Keywords
total temperature; nozzle; sonic-flow; plasma; arc-jet; thermochemical inversion; characteristic velocity
Rationale
Bulk enthalpy is a primary parameter for interpreting arc-jet and plasma facility tests and for defining boundary conditions in computational simulations. Existing techniques, such as calorimetric energy balance, may exhibit high uncertainty when temperature differences are small or facility losses are poorly characterized. Optical diagnostic techniques may require species-specific calibration and optical access. This new standard is agnostic to any of the formerly listed issues and can infer enthalpy from facility measurements that are already being collected by arc-heaters and/or inductively-coupled plasma torch facilities (total pressure, total mass flow rate, gas composition, and nozzle throat geometry) as long as the flow is choked.
