A SHOCK TUBE STUDY OF THE COUPLING OF THE 02-Ar RATES OF DISSOCIATION AND VIBRATIONAL RELAXATION

WRAY, KURT L.

doi:10.21236/ad0274095

Cited by 5 publications

(6 citation statements)

References 3 publications

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“…lr\ such an environment, the number of vibrationally excited molecules that can dissociate are fewer, and the dissociation rate is slower than in the case when vibration is equilibrated. 6 Since the maximum temperature encountered during a typical entry flight of a vehicle from an Earth orbit is over 30,000 K, keen interests have been aroused to determine the dissociation rate in such a regime. The first of such endeavors is the work of Hammer ling et al 7 They considered the simplest possible gas model: the molecules have no rotational motion, the vibrational motion is harmonic, the cross sections for the collision-induced dissociation from individual vibrational states are independent of their vibrational quantum numbers, and the vibrational states are populated according to a Boltzmann distribution corresponding to a vibrational temperature T v .…”

Section: Nomenclaturementioning

confidence: 99%

“…This point agrees with the experimentally observed behavior behind a shock wave. 6 The increase of the average vibrational energy e v is approximately proportional to the vibrational temperature. During the period in which significant dissociation occurs, that is, for />10~4 s, the average energy loss due to the dissociation process, e, is around 27,000 cm" 1 , which is about 33% of the dissociation energy of the molecule.…”

Section: Relaxation Behavior In Heating Casementioning

confidence: 99%

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Rate parameters for coupled vibration-dissociation in a generalized SSH approximation

Sharma

Huo

Park

1992

Journal of Thermophysics and Heat Transfer

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We report a theoretical study of vibrational excitations and dissociations of nitrogen undergoing a nonequilibrium relaxation process upon heating and cooling. The rate coefficients for collisional induced vibrational transitions and transitions from a bound vibrational state into a dissociative state have been calculated using an extension of the theory originally proposed by Schwartz, Slawsky, and Herzfeld (SSH). High-lying vibrational states and dissociative states were explicitly included, but rotational energy transfer was neglected. The transition probabilities calculated from the SSH theory were fed into the master equation, which was integrated numerically to determine the population distribution of the vibratiqnal states, as well as bulk thermodynamic properties. Our results show that 1) the transition rates have a minimum near the middle of the bound vibrational levels, causing a bottleneck in the vibrational relaxation and dissociation rates, 2) high vibrational states are always in equilibrium with the dissociative state, 3) for the heating case, only the low vibrational states relax, according to Landau-Teller theory, 4) for the cooling case, vibrational relaxation cannot be described by a rate equation, and 5) the average vibrational energy removed in dissociation is about 30% of the dissociation energy. QtA,Qtb Nomenclature= parameter in Landau-Teller equation = dissociation energy = energy of the vibrational level v measured from minimum of the vibrational potential = average vibrational energy per molecule = Planck's constant = forward (dissociation) reaction rate coefficient, in cm 3 s~1 = rate coefficient for equilibrium vibration in the CVD model, in cmV 1 = reverse (recombination) reaction rate coefficient, in cm 3 s~1 = transition rate coefficient for v->c (continuum) transition, in cm 3 s~1 = transition rate coefficient for v -*» v' transition, in cn^s" 1 = Boltzmann constant = second moment of vibrational transition rate, see Eq. (35) -number of vibrational levels = reduced mass of colliding molecules = number density = temperature exponent in rate coefficient = probability of collisional induced vibrational transition = pressure in atmosphere = velocity-dependent probability of collisional induced vibrational transition = translational partition function for atoms A and B, respectively Q v = partition function for level v q = the vibrational quantum number above which quasi-steady-state approximation holds R = matrix element of relative motion r = distance between the centers of mass of the colliding molecules 5 = parameter in semiempirical rate equation of Park Si,s 2 = vibrational coordinates of molecules 1 and 2 T = translational temperature T a = geometrical mean temperature T d = characteristic temperature of dissociation T v = vibrational temperature r v i, r v2 , !T V 3 = three definitions of vibrational temperatures in a nonequilibrium flow t = time Uo,Uf = initial and final velocity of relative motion between two molecules V = interaction potential between two colliding molecules...

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Section: Nomenclaturementioning

confidence: 99%

Section: Relaxation Behavior In Heating Casementioning

confidence: 99%

Rate parameters for coupled vibration-dissociation in a generalized SSH approximation

Sharma

Huo

Park

1992

Journal of Thermophysics and Heat Transfer

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“…Steady state dissociation rate coefficients of molecular oxygen highly diluted in Ar. Experiments denoted by ® to ® are by Wray, 40 Anderson, 41 Breshears et al, 42 Cammac and Vaughan, 43 Watt and Myerson, 44 …”

Section: Discussionmentioning

confidence: 99%

“…Last of all, it should be noted that the experimental values for induction time have large uncertainties: the values scatter in a wide range and their estimated errors are reported to be very large 40 . Moreover, the reduction process of the experimental data contains a Landau-Teller type or strong vibrational bias model, which may have caused the agreement of the solution of the DHO model with the experimental values.…”

Section: Idnmentioning

confidence: 99%

An analysis of quasiclassical molecular collisions and rate processes for coupled vibration-dissociation and recombination

Mizobata

1997

35th Aerospace Sciences Meeting and Exhibit

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Coupled molecular vibration-dissociation and recombination of oxygen highly diluted and suddenly heated in argon were solved using only microscopic information of molecules. Rate coefficients for state-to-state vibrational transitions and detailed dissociations were evaluated by quasiclassical molecular collision analysis using a sum of pairwise potentials of diatoms whereas those for detailed recombinations were estimated by the detailed balancing rule. Molecular vibration, dissociation, and recombination were described simultaneously by a set of master equations and solved using the rate coefficients. Quasisteady state dissociation rate coefficients, dissociation induction times, and vibrational relaxation times were calculated from the solutions and compared with experimental data so that the quantitative validity and features of the method could be assessed. The calculated steady state dissociation rate coefficients showed good agreement with the experimental values at temperatures above 3,000 K, whereas the calculated induction times and vibrational relaxation times were smaller than those from experiments. (Author) AbstractCoupled molecular vibration-dissociation and recombination of oxygen highly diluted and suddenly heated in argon were solved using only microscopic information of molecules. Rate coefficients for stateto-state vibrational transitions and detailed dissociations were evaluated by quasiclassical molecular collision analysis using a sum of pairwise potentials of diatoms whereas those for detailed recombinations were estimated by the detailed balancing rule. Molecular vibration, dissociation, and recombination were described simultaneously by a set of master equations and were solved using the rate coefficients. Quasisteady state dissociation rate coefficients, dissociation induction times, and vibrational relaxation times were calculated from the solutions and compared with experimental data so that the quantitative validity and features of the method could be assessed. The calculated steady state dissociation rate coefficients showed good agreement with the experimental values at temperatures above 3,OOOK, whereas the calculated induction times and vibrational relaxation times were smaller than those from experiments.

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“…The previous approximations are consistent with the fact that vibrational relaxation is found to be much faster than dissociation-recombination relaxation at low and intermediate temperatures. 3 Mach number distributions for the vacuum plume of the rocket in question were available. These distributions were calculated by a method-of-characteristics computer program, 4 on the basis of a specific heat ratio of 1.30, the frozen value of 7 at the nozzle exit.…”

Section: Geometry and Properties Of The Plumementioning

confidence: 99%

Effect of rocket exhausts on infrared planet sensors.

French¹

1966

Journal of Spacecraft and Rockets

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Infrared trackers can incur serious errors when viewing a planet through the exhaust plume of a rocket engine. Quantitative prediction involves the evaluation of the distribution of plume properties, the spectral emission and absorption of the plume as a function of line of sight, and the integrated radiation power entering the tracker fields of view from both planet and plume. A numerical example of error calculations is presented for a radiation-balance tracker located on a space vehicle executing an earth-moon mission. The plume considered is that generated by a storable-propellant rocket with an exit diameter of 100 in. Tracker field angles of 5.45° to 17.3° are considered, and pointing errors are evaluated at earth ranges from 24,700 to 197,000 miles. Pointing errors up to the loss-of-track limit are encountered when the earth is viewed through the plume near the nozzle exit. The region of error is greatest for large tracker fields and large ranges. Nomenclature B = Planck function B e = rotational constant / = intensity 7co = spectral intensity M = Mach number TV = mole fraction P = pressure R = radius, or radial position R 0 = radial position of tracker S = tracker-to-plume distance T = temperature Y = axial position of tracker X = distance from nozzle exit a = integrated band absorption dp = pointing error jj. = volumetric absorption coefficient

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A SHOCK TUBE STUDY OF THE COUPLING OF THE 02-Ar RATES OF DISSOCIATION AND VIBRATIONAL RELAXATION

Cited by 5 publications

References 3 publications

Rate parameters for coupled vibration-dissociation in a generalized SSH approximation

Rate parameters for coupled vibration-dissociation in a generalized SSH approximation

An analysis of quasiclassical molecular collisions and rate processes for coupled vibration-dissociation and recombination

Effect of rocket exhausts on infrared planet sensors.

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