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Stability Characterization of Refractory Materials Under High Velocity Atmospheric Flight Conditions. Part 2. Volume 3. Facilities and Techniques Employed for Hot Gas/Cold Wall Tests

Report Number: AFML TR 69-84 Part 2 Volume 3
Author(s): Kaufman, Larry; Nesor, Harvey
Corporate Author: ManLabs Inc.
Laboratory: Air Force Materials Laboratory
Date of Publication: 1969-12
Pages: 136
Contract: AF 33(615)-3859
Project: 7312
Task: 731201
AD Number: AD0865316

Abstract:
The oxidation of refractory borides, graphites, and JT composites, hypereutectic carbide-graphite composites, refractory metals, coated refractory metals, metal oxide composites and iridium coated graphites in air over a wide range of conditions was studied over the spectrum of conditions encountered during reentry or high velocity atmospheric flight as well as those employed in conventional furnace tests. Elucidation of the relationship between hot gas/cold wall (HG/CW) and cold gas/hot wall (CG/HW) surface effects in terms of heat and mass transfer rates at high temperatures was a principal goal. This report deals with facilities and techniques employed for performing HG/CW tests in the Model 500, ROVERS and Ten Megawatt Arc installations at Avco and the Wave Superheater at Cornell. Stagnation pressures between 0.002 and 4.0 atm, stagnation enthalpy between 2000 and 16,000 BTU/lb, cold wall heta flux between 100 and 1500 BTU/Ft^2sec and exposure times between 20 and 23,000 seconds were employed. Diagnostic measurements included continuous recording of surface temperatures and radiated heat flux. Color motion picture coverage was also provided. Although most of the testing was performed on flat faced right circular cylinders some hemispherical capped samples and some pipes were also tested.

Heat flux measurements were made in the Model 500 and ROVERS facilities of the variation of heat flux with radial distance across the model. Model size was varied to asceertain the effect of size on the heat flux. Stream diameter was 0.60 inches and 2.25-3.00 inches in the Model 500 and ROVERS facilities, respectively. Calorimeters with diameters of 0.125 to 0.750 inches were employed with 0.500 and 1.500 inch diameter shrouds. The Model 500 results were described by a + or - 10% band independent of diameter. The heat flux showed a peak near a diameter of 0.375 inches.

The heat flux was independent of calorimeter radius in the ROVERS facility. The heat flux observed with a 0.500 inch diameter shroud was larger than observed with a 1.500 inch shroud. However, while the expected ratio is square root of 3 or 1.73, the observed ratio was about 1.20. The values obtained for the 0.500 inch diameter shrouded calorimeter were about 10% higher than the values predicted on the basis of a Fay-Riddell calculation, while the 1.500 inch shrouded calorimeter results were 50% higher than that calculated.

In-depth temperature measurements were performed in the Model 500 and ROVERS facilities. A micro-optical pyrometer was employed to measure the temperature at the base of a cavity drilled from the rear of the model to within 0.100 inch of the heated face. For oxide forming materials like ZrB2 and Hf-Ta-Mo, the temperature at the in-depth station was found to range from 500 to 1900R lower than the surface temperature.

Sixteen refractory material models were exposed to the high velocity flow of air in the Mach 6 Wave Superheater Hypersonic Tunnel. Data were taken in two 15 second tests of eight models, each at a velocity of 10^4 ft/sec, a stagnation pressure (at the model nose) of one atmosphere and a tunnel flow rate of 2.5 lb/sec. The stagnation enthalpy was 2200 BTU/lb while the cold wall heat flux was 600 BTU/ft^2sec.

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