Propane/air deflagrations and CTA measurements of turbulence inducing elements in closed pipes

The current paper presents experimental investigations on several influence parameters of deflagrations in long closed pipes. The experiments were carried out with different propane/air mixtures, various length-to-diameter ratios (up to L/D=143, D=0.159 m) and miscellaneous initial pressures. Maximum values of explosion pressures and flame speeds were found at stoichiometric propane/air compositions. With increasing L/D, the explosion pressures decreased while higher flame speeds were determined. In addition, elevated initial pressures led to rising explosion pressures. Furthermore, it is well known that turbulence inducing elements in pipes, ducts or vessels enhance the heat and mass transfer during reactive flows. This may lead to a significant acceleration of ongoing gaseous reactions and could finally cause a deflagration to detonation transition (DDT) aligned with much higher pressures and flame speeds. Therefore, constant temperature anemometry (CTA) measurements were carried out to describe the influence of frequently used flange assemblies and baffles on the velocity and turbulence distributions of air flows in steel pipes similar to those in the explosion measurements. The experiments showed that in contrast to flange assemblies, baffles caused a significant increase of the turbulence intensity in pipe flows.