Boundary Layer Effects on Chemical Kinetics Studies in a Shock Tube

Abstract

The effect of the cold boundary layer on kinetic parameters was studied behind reflected shocks in a single pulse shock tube. By inserting hollow cylinders into the test section, parallel to the tube walls, the surface relative to the volume was increased, and the lowering of the chemical conversion was determined as a function of the surface per unit volume. The test reaction studied was the unimolecular decomposition of perfluorocyclobutane (C4F8→2C2F4). It was shown that the lowering of the chemical conversion was proportional to the surface-to-volume ratio in the test section. A hypothetical cold layer δc in which no conversion occurred was found to be around 0.2 mm. It was concluded that in a shock tube of ∼ 2-in. i.d., at an initial pressure of p1 ≥ 100 torr the cold boundary layer has very little effect on kinetic parameters obtained in a single-pulse shock tube. At lower pressures and in smaller diameters shock tubes these effects should be considered when interpreting kinetics results.

Detailed Simulations of Shock-Bifurcation and Ignition of an Argon-diluted Hydrogen/Oxygen Mixture in a Shock Tube

“…6,26 Further, residual gas motion behind the reflected shock can also contribute to local pressure inhomogeneities. 27 Although it has recently been recognized that these effects require consideration, 7,28,29 a satisfactory theoretical characterization has so far not been established. This is primarily due to the fact that the boundary layer interaction and shock bifurcation occur in the transitional and turbulent flow regime and are largely dependent on geometry and conditions behind and in front of the shock.…”

The Competitive dehydrohalogenation of 1,1,1‐trifluoro‐2‐chloroethane in reflected shock waves

“…This can be achieved by the correct selection of tube geometry and leads to the sample of reactants and products being finally located between the end plate and ball valve. The effects of the cold boundary layer have been investigated [7], and attempts were made in this study to minimize these effects.…”