ht. J. Hew, Moss Transfer. Vol. 36, No. 16, pp. 3897-3907, 1993 0017-9310/93%6.00+0.00 Printed in Great Britain 0 1993 Pergamon Press Ltd Study of 3-D mixing of a cold jet with a transverse plasma stream ZOUHIR NJAH,? JAVAD MOSTAGHIMI,$ M. FAGHRQ and MAHER BOULOSt t Plasma Technology Research Centre (CRTP), University of Sherbrooke, Sherbrooke, Quebec, Canada, JlK 2Rl 3 Department of Mechanical Engineering, University of Toronto, Toronto, Ontario, Canada, M5S IA5 5 Department of Mechanical Engineering and Applied Mechanics, University of Rhode Island, RI 02881, U.S.A. (Received 8 December 1992 and in final form 4 May 1993) Abstract-The present study involves both experimental and mathematical modelling of the 3-D mixing of a single jet with a transverse main stream. In the first part of this study, the interaction between a laminar nitrogen jet and a cross-flowing argon stream is studied under isothermal flow conditions. Results show that the numerical predictions of the nitrogen concentration fields, downstream of the injection point, are in good agreement with the experimental measurements. In the second part of this study, calculations of the mixing pattern between a single cold jet and a transverse plasma stream are presented. Results reveal a much slower gas mixing process under plasma conditions due to the increasing viscosity of the main stream. It is also shown that the mixing characteristics depend strongly on the ratio of jet to main stream mass fluxes (R, = p~v,/p,w,). 1. INTRODUCTION THE QUESTION of mixing of a cold jet introduced in a thermal plasma reactor is of great interest in plasma chemistry applications. A successful plasma chemical process depends to a large extent on the knowledge of the velocity, temperature and concentration fields in the region where the reactants are injected. Plasma flows are characterized by their high temperature and the presence of steep temperature gradients. As the viscosity of gases increases with temperature, the flow pattern in the mixing zone of a cold jet with a plasma stream is significantly different from that for an iso- thermal flow at ambient temperature ; a substantial reduction of the mixing between the two streams under plasma conditions is observed despite the increased mass transfer coefficient in the high tem- perature region. This fact has been clearly dem- onstrated by Dundas [l] who reported concentration mapping for an argon/air system under isothermal ambient temperature and plasma conditions. In a plasma reactor the side jet could be either one of the reactants or a quench medium introduced to rapidly cool a reaction mixture and thus avoid prod- uct decomposition. It may be noted that in radio frequency (r.f.) plasma reactors, two techniques are commonly used to inject reactants into the plasma; these are either introduced by a side jet downstream of the coil region of the discharge, or through a central water cooled probe. Extensive reviews of the subject has been published by Akashi [2], Yoshida [3] and Boulos [4]. Because of the practical importance of jets dis- charging into transverse streams, a large number of experimental, analytical and computational inves- tigations have been carried out on this subject. Exper- imental investigations of the behavior of jets issuing normally into a cross stream have been mostly devoted to measuring the jet trajectory, jet spread, velocity, temperature and pressure fields. Jordison [S] was the first to determine experimentally the trajectory of a jet issuing perpendicularly into a cross flow. He defined the trajectory of the jet as the line joining the points of maximum velocity. Keffer and Baines [6], Keffer [7], and Platten and Keffer [8] studied the gen- eral features of a jet injected normally into a cross stream and presented data for the jet trajectory. A comprehensive physical description of the jet in a cross stream is given by Moussa zyxwvutsrqponmlkjihgfedcbaZ et al. [9]. Patrick [IO] reported velocity and concentration measurements for the mixing of a round turbulent jet with a trans- verse main stream. His results showed that the flow pattern is dominated by a pair of vortices attached to the jet, which promote rapid mixing. Gelb and Martin [ll], Wu et al. [12], and McMahon and Mosher [13] made measurements of the pressure fields resulting from the interaction of a jet with a cross stream. Margason [ 141,McMahon et al. [ 151and Mikolowsky and McMahon [16] studied the jet-wake interference effects associated with jets exhausting into a deflecting stream. Ramsey [17], and Ramsey and Goldstein [18] studied the interaction between a single heated jet and a cross stream and reported measurements of velocity, temperature, and turbulence fields. Campbell and Schetz [19] investigated the behavior of heated jets discharged into waterway and determined the growth of the jet for different discharge velocities and tem- peratures. Kamotani and Greber [20] reported measurements of the velocity, temperature, and tur- bulence intensity fields for single, multiple, opposing 3897