Electrical conductivity channel for a shock tube ( Introduction,Int

Frank K Lu et al 2005 Meas. Sci. Technol. 16 1730-1740 Electrical conductivity channel for a shock tube Frank K Lu1, Hsuan-Cheng Liu2 and Donald R Wilson1
1 Aerodynamics Research Center, Mechanical and Aerospace Engineering Department, University of Texas at Arlington, Arlington, TX 76019-0018, USA
2 Aerospace Science and Technology Research Center, National Cheng Kung University, 198 Hsin-Sheng Street, Kuei-Jen, Tainan 711, Taiwan

E-mail: lu@... jonathan@... and wilson@...
Received 10 January 2005, in final form 7 June 2005
Published 25 July 2005
Print publication: Issue 9 (September 2005) Abstract. The design of an electrical conductivity measurement channel for a shock tube is described. This measurement channel is used for the study of weakly ionized, high-enthalpy flows of gases seeded with alkali salts. The theory for determining the dimensions of the measurement channel and the electrical power supply for the channel is based on Ohm's law. Data are shown which demonstrate that the channel performs well. However, the measured electrical conductivity was one or two orders less than theoretical values. The current traces for each case show that the peak current occurred behind the contact surface, which indicates that some of the seed was entrained behind the test gas originally in the driven tube. An analysis of the effect of Joule heating on the measured conductivity was conducted. The result of increased temperature due to Joule heating in the measurement channel is believed to be minimal. Reasons for the discrepancy are given.
Keywords: ionized gas, plasma, shock tube

doi:10.1088/0957-0233/16/9/004
URL: http://stacks.iop.org/0957-0233/16/1730
PII: S0957-0233(05)93105-6
PDF (356 KB) http://ej.iop.org/links/q34/Jk8991An2Y9fL9jpEb2YWQ/mst5_9_004.pdf
References excerpt p 1 of 11 1. Introduction
Interest in magnetohydrodynamic (MHD) accelerators and
decelerators [1, 2], hypersonic flow control [3], power
extraction from hypersonic flows [4, 5] and hypersonic
ground test facilities capable of true altitude simulation [6]
has emphasized the need for a better understanding of the
conductivity of the high-enthalpy, high-pressure gas involved.
For example, the MHD accelerator utilizes the Lorentz
J B body force to increase the fluid velocity, pressure and
temperature. The electrical conductivity of the operating
fluid therefore plays an important role in determining the
effectiveness of the accelerator. This requires that an MHD
accelerator is provided with an electric field E at a reasonable
electrode voltage range and an appropriate magnetic field B.
To ensure an adequate current, the gas flow must be electrically
conductive. This may be realized in a neutral gas such as air
by a preionization scheme or by seeding with a material which
possesses a low ionization potential, for example, caesium or
potassium salts.

The performance of MHD techniques with high-enthalpy
gas flows depends directly on the magnitude of the electrical
conductivity of the preionized or seeded gas. However, data
on electrical conductivity of gaseous species are scarce or
nonexistent at high pressures. For this reason, an electrical