Development and Calibration of a Cold Wire Probe for Use in Shock Tubes

Abstract

Th e use of a fine unheated wire for making s hock tube flow measurements is investigated. The operation of the instrument depends on the transient nature of the shock tube flow. The wire is referred to here as a cold wire; it operates in a non-steady manner which is completely different from the usual hot wire operation. This report describe s the construction and calibration of the cold wire. The experimental law for the rate of gain of heat to the wire 1n air is determine d over a range of Mach numbers from 0.4 to 1.9 and a range of Reynolds numbers from 0.035 to 3,500 based on the wire diameter and the conditions in the hot flow following the initial shock wave. Similar measurements are reported for argon. The heat transfer measurements cover the continuum region, the slip and transitional regions, and extend into the free-molecule flow region. The dimensionless results are compared with hot wire measurements obtained in wind tunnels and are found to differ slightly. A difference exists because the cold wire gains heat from the fluid while the hot wire loses heat to the fluid. The measurements are very repeatable and self-consistent, and they indicate that the wire can be used to give an accurate flow measurement in the shock tube. Some potential applications of the wire for the study of shock-tube flows are presented. It is concluded that the fine unheated wire is a versatile tool that can be used to great advantage in the shock tube.

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