Turbulent manipulation of condensation at a shock tube's contact surface

Abstract

IntroductionA N improved understanding of condensation phenomena in gaseous flow would have tremendous application to technological and scientific problems including droplet induced erosion in turbine blades, production of undesirable environmental conditions due to the condensation trails left by jet engines, and the inhibition of combustion in combustors. The usefulness of the shock tube for condensation studies was established by Wegener and Lundquist 1 followed by Glass and Patterson, 2 Barschdorff, 3 Sislian and Glass, 4 Kotake and Glass, 5 and Glass et al. 6 The development of the theory of nucleation rate and growth rate of the clusters is elaborated in the work of Lothe and Pound, 7 ' 8 Dunning, 9 Wegener,[10][11][12][13][14][15] In recent experiments carried out by Britan et al., 16 the effects of condensation on the parameters of the flow behind shock waves in water vapor were investigated in detail. Another recent experiment conducted by Schnerr and Bohning 17 investigated the effects of the heat addition by homogenous condensation on the compressible turbulent boundary layer. Nonetheless, in spite of all of this work, the relationship between the governing thermodynamic parameters and the simplest parameters in nucleation (such as onset and droplet growth rate) is not well understood at all.It is particularly clear that no experimental treatment has determined either the role which turbulence plays in the observations, if any, or the implications for such a possible role in the development of a reliable physical model. Implicitly, all current theories for droplet sizes also assume no role for turbulence. We, therefore, examine in this paper the possibility of a relationship between condensation and turbulence using the reliable and predictable turbulent environment of a shock tube's contact surface as a test system for water vapor condensation. We do not concern ourselves, at this juncture, with the onset of condensation. Our main interest is to investigate experimentally the effect that turbulence has on an existing condensation front which is moving with the turbulent gaseous media.A pressure driven shock tube ( Fig. 1) consisting of a driver section of 60 x 5.2 in., a driven section with a test section of 60 x 5.2 in., and an extension tube of 76 x 5.2 in. was used to carry out the experiment. Aluminized Mylar® sheets of various thicknesses were used as the material for the diaphragm which separates the driver section from the driven section. The compressed air is supplied to the driver section from a reservoir where the relative humidity of the air could be controlled by controlling the temperature in the driver gas. A heating tape is wrapped around (outside) the entire driver section, and a thermocouple probe is used in the driver section to measure the initial temperature.The test section has three stations for optical diagnostics, two of which consist of four perpendicular glass ports; the other station has two inline glass ports. The test section is also equipped with several ports for pressur...