Kinetic limitations on the diffusional control theory of the ablation rate of carbon.

Maahs, Howard G.

doi:10.2514/3.30367

Cited by 10 publications

(6 citation statements)

References 11 publications

(5 reference statements)

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“…In addition, carbon erosion by oxygen has been the subject of Refs. [11][12][13][14][15][16][17][18][19]. This data has not been widely applied to rocket motor design because the data was not correlated into a useful form, or the data did not provide sufficient information about the complex interactions of reactants and inhibitors such as HC1 or CO.…”

Section: Reaction Characteristicsmentioning

confidence: 99%

Kinetic Reaction Rates for Consumption of Pyrolytic Graphite by Combustion Gases

Schaefer

Tong

Bedard

1975

Journal of Spacecraft and Rockets

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An experimental program using an arc plasma generator was conducted to determine the kinetic mass consumption rate of pyrolytic graphite in simulated propellant atmospheres. These results, which include a wide range of gas species partial pressures and ablation rates, were successfully correlated using an equation with a functional form determined from phenomenological considerations. These correlations were in turn incorporated as an integral part of a prediction procedure which includes the simultaneous consideration of boundary-layer diffusion, equilibrium gas-phase chemistry, kinetically controlled surface chemistry, sublimation, indepth heat conduction and, surface mass transfer. The end product of this program was a procedure for predicting pyrolytic graphite ablation rates in rocket motor nozzles under conditions where surface kinetic effects are important.

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Section: Reaction Characteristicsmentioning

confidence: 99%

Kinetic Reaction Rates for Consumption of Pyrolytic Graphite by Combustion Gases

Schaefer

Tong

Bedard

1975

Journal of Spacecraft and Rockets

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“…This behaviour can be seen upon close inspection for some of the data in Figure 2.1. As a consequence of this, Maahs [46] noted that the maximum mass loss rate due to oxidation will be kinetic-controlled and not diffusion-limited for a wider range of conditions than was previously thought.…”

Section: Oxidationmentioning

confidence: 86%

“…The exact terminology used varies between authors [46,69,72], although the same trends are observed. In the kinetic-limited regime, also known as reaction limited or chemistry limited, the surface temperature and flow conditions are sufficient to allow surface reactions to occur and are limited by the reaction rates.…”

Section: Introductionmentioning

confidence: 89%

“…Due to the high costs associated with in-flight testing, ground testing stands as a cost-effective method for reducing modeling uncertainties. Ablation testing has often been conducted in long-duration facilities such as arc jets [12,44,46,[68][69][70]. These facilities are capable of providing representative surface heat fluxes and excel at investigating the in-depth response of TPS materials.…”

Section: Introductionmentioning

confidence: 99%

“…Ablation testing is generally conducted in long-duration facilities such as arc jets [12,44,46,[68][69][70], which are suitable for investigating the in-depth material response due to their ability to provide representative heating rates for extended periods. They are, however, unable to reproduce a realistic in-flight shock layer due to low Reynolds numbers and, depending on the facility type, a high degree of thermal and chemical nonequilibrium in the freestream.…”

Section: Introductionmentioning

confidence: 99%

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Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Lewis¹

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During reentry into the atmosphere, a vehicle can encounter extreme convective and possibly radiative heating loads. Such spacecraft must rely on a carefully designed thermal protection system to maintain the integrity of the underlying structure, thus ensuring the survival of any cargo or crew it may contain. Despite many past developments and research efforts, to this day there remain large uncertainties associated with the prediction of heat shield performance. In particular, accurate modelling of ablation phenomena is critical to minimising uncertainties, reducing excess weight, and increasing safety. This includes thermochemical ablation by oxidation, nitridation, and sublimation, as well as the mechanical removal of material via spallation. Due to the high costs associated with in-flight testing, and the difficulty of mounting precision instruments and advanced diagnostics on flight vehicles, ground-based experiments stand as a cost-effective method for reducing modelling uncertainties.Ablation testing is generally conducted in long-duration facilities such as arc jets, which are well suited to investigating in-depth material response due to their ability to provide representative heating rates for extended periods. They are, however, unable to reproduce a realistic in-flight shock layer due to low Reynolds numbers and, depending on the facility type, a high degree of thermal and chemical nonequilibrium in the free-stream. In contrast, impulse facilities such as shock tubes and their variants are well suited to reproducing realistic flight conditions with free-streams that are a closer match for flows dominated by binary processes in terms of Reynolds number, temperature, and chemical composition. Due to their extremely short test times, however, ranging from the order of 10 µs to several milliseconds, they are unable to aerothermally heat test models up to representative in-flight temperatures, or recreate the quasi-steady heat and mass flux balance of flight. This key limitation of impulse facilities was recently overcome in experiments using the University of Queensland's X2 expansion tunnel by electrically pre-heating samples to temperatures approaching 2500 K immediately prior to a test.In this work, the pre-heating methodology was enhanced to generate maximum surface temperatures approaching 3300 K in order to study sublimation phenomena. It was found that although sublimation-regime temperatures could be achieved, the relevant surface processes themselves were suppressed due to the high pitot pressures of the conditions used. Instead, the nitridation process was studied by observing air shock layer CN emissions with pure graphite models heated to surface temperatures ranging from 1770-3300 K. These results were compared with numerical simulations which predicted a monotonic increase of emissions with surface temperature for all models considered, whereas the experiments showed an initial increase from 1770-2500 K and then remained relatively constant from 2500-3300 K. The simulations also su...

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Establishing a Connection for Students between the Reacting System and the Particle Model with Games and Stochastic Simulations of the Arrhenius Equation

Kraska

2020

J. Chem. Educ.

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These days, theoretical methods and simulations are widely spread in chemical science. However, in secondary and introductory chemistry, students learn little or nothing about such approaches. To introduce simulations at this educational level it is necessary to identify suitable chemical problems and simulation methods that allow setting up concise computer codes. In addition, it is useful to implement simulations in topics which are already part of the regular chemistry curricula. Here, we employ the Arrhenius equation in combination with a simple stochastic simulation method to illustrate how computer simulations can be used in chemistry to get insights in the temperature dependence of the reaction rate constant. The basis for the simulation is a board game, which puts the students in the position to elaborate the mathematical equations for the modeling of kinetics themselves in a playful manner. Such simulation allows students to establish a connection between the reacting system and the particle model. Furthermore, freely available educational programming software makes it possible for students to write their own simulation program based on the game within limited time and effort.

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Kinetic limitations on the diffusional control theory of the ablation rate of carbon.

Abstract: Nomenclature h= Planck constant k = Boltzmann constant m = molecular mass of oxygen m = mass-loss or reaction rate, g/cm 2 sec POZ = oxygen pressure, atm P i2 = stagnation pressure of air adjacent to the surface, atm R = gas constant, 1.987 cal/mole °K

Cited by 10 publications

References 11 publications

Kinetic Reaction Rates for Consumption of Pyrolytic Graphite by Combustion Gases

Kinetic Reaction Rates for Consumption of Pyrolytic Graphite by Combustion Gases

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Establishing a Connection for Students between the Reacting System and the Particle Model with Games and Stochastic Simulations of the Arrhenius Equation

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