EXPERIMENTS ON A REACTING PLUME - 1 - CONVENTIONAL CONCENTRATION STATISTICS

Experiments have been carried out under laboratory conditions to study turbulent mixing with chemical reaction. Such flows are common in the environment but there are few high-resolution measurements of them un der controlled conditions. The reaction NO + O-3 --> NO2 + O-2 + 200 k J (mel)(-1) (in the absence of UV radiation) has been used by introduc ing a non-buoyant reactive plume of NO into a turbulent grid flow dope d with O-3. The experiments have been conducted over a wide range of c onditions by varying the Damkohler number (the ratio of the flow times cale to that of the chemical reaction) by a factor of 6 and varying th e ratio of initial reactant concentrations by a factor of 30. The data are presented in two parts. Part 1 (present paper) presents conventio nal concentration statistics. Part 2 presents concentration statistics conditionally averaged by a mixing parameter and discusses their usef ulness for investigating the reactive behaviour of the plume. Speciall y developed chemiluminescent analysers are used to measure NO and O-3 concentrations with high-frequency response and a spatial resolution o f four Kolmogorov scales (in this flow). The mixing field of the plume is studied using conserved scalar theory and is compared to that obta ined in other non-reactive flows. Results for the means, variances and joint statistics of the reactive species are presented and compared w ith frozen and equilibrium limits obtained from the conserved scalar t heory for reacting flows. Statistics for NO show no significant trend with Damkohler number while those for O-3 and NO2 have increased react ion at higher Damkohler number. The reactive scalar means are bounded by the frozen and equilibrium limits as they should be according to co nserved scalar theory. Other reactive scalar statistics are not necess arily bounded by the limits. A simple relation between moments of O-3 and NO2 is found in the experimental results and is confirmed by conse rved scalar theory. Contribution to the mean reaction rate from the re actant covariance and product of means is compared and it is found tha t both are significant under the present conditions. Intensity of segr egation varies over a wide range and is sensitive to initial reactant concentrations. (C) 1998 Elsevier Science Ltd. All rights reserved.