Experimental Investigation of an Arc Heater

Abstract

An electric arc heater, intended to provide a steady flow of high stagnation temperature gas (up to 10,000°K) into a convergent-divergent nozzle, was designed at the GALCIT Hypersonic Laboratory. Section 2 first gives a few preliminary calculations which have been made for the arc heater-nozzle combination, using argon, at stagnation pressures of 1 and 2 atm., and assuming equilibrium flow. In particular, the Mach number in the test section of a fixed nozzle will depend on the thermodynamic properties at the reservoir. In the heater, the direct-current arc is axially constricted by a channel parallel to the gas flow. A description of the design and instrumentation is given in Sections 2 and 3. For two series of experiments, using argon, the central electrode was either the cathode, as in the conventional arrangement, or the anode: both configurations were thoroughly investigated. Provided a sharp edge exists at the end of the flow constricting channel, the configuration with anode in the center was found to give, generally, a more stable functioning, with a voltage drop about twice as large, higher efficiency and thus higher average temperature for the same mass flow of gas, as compared to the case where the cathode is in the center. In the ranges of power (up to 13 Kw) and mass flow (up to 6.00 gr/sec) investigated, it was found that the best efficiency is obtained for a swirl close to the central electrode and large gas mass flows. When the anode is in the center, a long and narrow constricting channel leads to the optimal conditions. With the reversed polarities, the geometry of the downstream channel is not very important. Finally, a tentative explanation of the results is given, emphasizing in particular that the "anode in the center" case corresponds to a "long" arc, and the "cathode in the center" to a "short" one with poorer transfer of energy from the arc to the gas.

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