1.1This test method covers the calculation from heat transfer theory of the stagnation enthalpy from experimental measurements of the stagnation-point heat transfer and stagnation pressure.
1.2Advantages:
1.2.1A value of stagnation enthalpy can be obtained at the location in the stream where the model is tested. This value gives a consistent set of data, along with heat transfer and stagnation pressure, for ablation computations.
1.2.2This computation of stagnation enthalpy does not require the measurement of any arc heater parameters.
1.3Limitations and Considerations—There are many factors that may contribute to an error using this type of approach to calculate stagnation enthalpy, including:
1.3.1Turbulence—The turbulence generated by adding energy to the stream may cause deviation from the laminar equilibrium heat transfer theory.
1.3.2Equilibrium, Nonequilibrium, or Frozen State of Gas—The reaction rates and expansions may be such that the gas is far from thermodynamic equilibrium.
1.3.3Noncatalytic Effects—The surface recombination rates and the characteristics of the metallic calorimeter may give a heat transfer deviation from the equilibrium theory.
1.3.4Free Electric Currents—The arc-heated gas stream may have free electric currents that will contribute to measured experimental heat transfer rates.
1.3.5Nonuniform Pressure Profile—A nonuniform pressure profile in the region of the stream at the point of the heat transfer measurement could distort the stagnation point velocity gradient.
1.3.6Mach Number Effects—The nondimensional stagnation-point velocity gradient is a function of the Mach number. In addition, the Mach number is a function of enthalpy and pressure such that an iterative process is necessary.
1.3.7Model Shape—The nondimensional stagnation-point velocity gradient is a function of model shape.
1.3.8Radiation Effects—The hot gas stream may contribute a radiative component to the heat transfer rate.
1.3.9Heat Transfer Rate Measurement—An error may be made in the heat transfer measurement (see Method E469 and Test Methods E422, E457, E459, and E511).
1.3.10Contamination—The electrode material may be of a large enough percentage of the mass flow rate to contribute to the heat transfer rate measurement.
1.4The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4.1Exception—The values given in parentheses are for information only.
1.5This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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