No abstract

Time-resolved measurements of the oxygen atom concentration during shock-wave initiated combustion of low-density (25 5 p 5 175 kPa) H2--02--CO-402-Ar

Recombination in highly diluted, lean hydrogen-oxygen-argon mixtures with H,/O, ratios of 0.50 and 0.33 has been investigated with a shock tube over the temperature range 1150 0 -1850 0 K for reaction pressures of 0. 85-5.41 atm. An OH ultraviolet line absorption technique was used to follow the progress of the reaction after substantial equilibration of the rapid bimolecular reactions which form OH initially. It was determined that under these conditions the recombination process is third order and its rate, R reo , obeys the empirical relationshipRreo=keffkeff was found to decrease slightly with increasing temperature and to depend to a small extent upon the composition of the reacting mixture. The experimental results indicate that the reaction ! H+O,+M->HO,+M dominates the recombination process. Further analysis of the data made it possible to obtain from keff a value of k(M=Ar) = 1.42 X 1011 ee l /mole 2 sec at 1500 0 K and an estimate of k(M=H,O)/k(M=Ar) of about 30. This value of k(M=Ar) has been combined with other experimental determinations to obtain the expression k(M=Ar) =8.6XI0 14 exp(1280±90/ RT) cc'/mole 2 sec which describes the data to within 20% over the entire temperature range from 225° to 1850 0 K.

No abstract

The deposition conversion is estimated as bhe average of the lowest and highest possible conversions which, on the first time through the program, are 0 and 100%. For each iteration, the program determines if the previous conversion estimate is too high or too low by solving both the kinetic and diffusion equations, resets either the highest or lowest possible conversion to the new estimated value, and then reaverages. The conversion is soon found with a high degree of accuracy. For each conversion estimate, the bulk stream, interfacial and film compositions, and the physical properties of the bulk stream and film are recomputed.From these values and the flow rate, the thickness of the diffusion barrier is calculated. The interfacial compositions are then determined from the Stefan-Maxwell equations. Since initially the film composition was estimated, an iterative procedure was used where the results of the previous iteration were used as the estimated interfacial composition for the next iteration. When two successive iterations agree, this set of interfacial compositions is used to calculate the deposition rate from the kinetic equations for the particular system. If this kinetic rate agrees with the rate calculated from the estimated deposition conversion, the program is completed and the interfacial compositions, conversions, etc., are printed out. If there is poor agreement, the deposition conversion is estimated again to give better agreement, and the iterative procedures repeated.If the kinetic expression is unknown and the deposition rate is known to be diffusion controlled, such as with the tungstenhexduoride-hydrogen system, the test for high or low deposition rate can be a sign test on interfacial compositions. For all positive values of film composition, the deposition conversion is obviously too low, while a negative value for the concentration of any component indicates the conversion is too high. In estimating rates in systems where no experimental kinetic data are available, thermodynamic equilibria have also been employed to test if efficiency was either too high or too low. This paper describes experimental measurements of diffusion rates in three ternary gas systems in which two gases are simultaneously diffusing through a third species.The results are used to check the validity of the StefanMaxwell equations under these conditions.The Stefan-Maxwell equations describe in differential form diffusion in isothermal, isobaric ideal gas mixtures (1 to 4 ) . Whereas the number of cases for which these equations have been solved is limited to a few restrictive situations in ternary systems ( 5 to l o ) , even fewer actual experimental tests of the validity of the solutions are available (6, 9 to 11). Thus although the recent extensive work of Duncan and Toor with ternary equimolal countercurrent diffusion (11) does offer very convincing proof of the applicability of the Stefan-Maxwell equations in real gas systems, we wish to present further evidence of this fact from a stud of cocurrent diffusion of...