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Design of a Stagnation Heater for the Rarefied Gas Wing Tunnel

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Master's thesis

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This report covers the fluid mechanic, heat transfer, and structural design of a stagnation heater for the Berkeley rarefied gas wind tunnel. The heater is to provide a low mass flow rate of gas for electron beam or laser diagnostic applications and is compatible with oxidizing gases at mass flow rates of 0.1 to 0.3 gs, with an output temperature of up to 2000 K. The heater consists of an inner zirconia tube for the source gas to pass through, which is surrounded by a pressure vessel. The source gas and the pressure vessel are designed to be at up to 2000 psi 136 atm. The heater will operate at pressure ratios of up to one million, producing gas flows of at least Mach ten. Fluid mechanic analysis shows that the source gas is in laminar flow through the heater, and has a transit time of 2-3 seconds. An extensive parametric study is presented of heater outlet diameter versus source gas type, temperature, pressure, and mass flow rate. The heat transfer analysis assumes uniform axial temperature in the core of the heater i.e. a constant temperature boundary condition, then finds 1-D radial heat transfer by accounting for simultaneous radiation and conduction. Heat losses at the ends are estimated iteratively by sequential 1-D conduction through the end of the heater and radiation to the wind tunnel. The structural design of the heater focuses on how the pressure vessel is sealed, including determining the size and number of bolts to keep the vessel safely intact. The vessel measures approximately 16-in. in length, and is 9.5-in. in diameter. Steel and zirconia are the primary structural materials. Tantalum wire in an argon atmosphere is used for heating. Total power requirements for the heater are estimated at 2700 Watts.

Subject Categories:

  • Air Conditioning, Heating, Lighting and Ventilating
  • Test Facilities, Equipment and Methods
  • Thermodynamics

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