Showing papers by "Vikram Sarabhai Space Centre published in 1981"

Thermal decomposition of polybutadienes by pyrolysis gas chromatography

Abstract: The thermal decomposition of cis-1,4-, trans-1,4-, and 1,2-polybutadienes (PBD) in the temperature range 450–900°C was investigated by pyrolysis gas chromatography (PGC). The cis- and trans-PBDs have closely similar product distribution and can be readily distinguished at lower temperatures of pyrolysis from the 1,2-PBD by the low amount of vinyl cyclohexene (VCH) produced by the 1,2 species. The amount of butadiene (BD) produced by 1,2-PBD varies with the tacticity of the polymer; the greater syndiotactic yields a lesser amount of BD. A method of determining the 1,4 and the 1,2 contents of PBD based on the ratios of peak heights of ethylene (C2) to VCH, propylene (C3) to VCH, and BD to VCH is presented. The advantages of this method are discussed. The nature and composition of the products of pyrolysis in the temperature range 540–900°C are presented and the mechanism of degradation at these elevated temperatures is explained.

Periodic orbits of the second kind in the restricted three-body problem when the more massive primary is an oblate spheroid

Abstract: Utilizing secular perturbing potential due to oblateness, the existence of periodic orbits of the second kind is established through analytic continuation using Delaunay's canonical variables in the planar restricted three-body problem when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion.

Transient Response of a Gas-Controlled Heat Pipe

Abstract: The paper presents a combined analytical and experimental investigation of the transient response of a gascontrolled heat pipe with an absorption gas reservoir. A mathematical model which considers the heat conduction in the condenser wall, the overall vapor core temperature, the diffusion of the vapor-gas interface, and the absorption of the control gas in the working fluid/wick structure matrix of the reservoir is developed for analysis. Experimental evaluation of the heat-pipe performance is made with methanol as a working fluid and ammonia and nitrogen as control gases. The combination of ammonia and methanol is considered for the soluble gas absorption reservoir, while nitrogen and methanol is considered for the standard gas reservoir. The performance of the two is compared. It has been observed that, to a limited extent, the performance can be improved by the absorption gas reservoir. Both theoretical and experimental results exhibit the same features of the performance of the heat pipe.

Estimation of heat-transfer coefficient in a rocket nozzle

Abstract: Ludwieg, H., "Erklarung der Wirbelaufplatzens mit Hilfe der Stabilitats Theorie fur Stromungen mit Schraubenlinien-formigen Stromlinien," ZeitschriftfurFlugwissenschaften, Band 13, 1965, pp. 437-442. Tsai, C. Y. and Widnall, S. E., "Examination of Group Velocity Criterion for Breakdown of Vortex Flow in a Divergent Duct," The Physics of Fluids, Vol. 23, May 1980, pp. 864-870. Nakamura, Y. and Uchida, S., "A Contribution to the Occurrence of Axisymmetric Type of Vortex Breakdown," Transactions of the Japan Society for Aerospace Sciences, Vol. 23, 1980, pp. 79-90. Faler, J. H. and Leibovich, S., "An Experimental Map of the Internal Structure of a Vortex Breakdown," Journal of Fluid Mechanics, Vol. 86, 1978, pp. 313-335. Kawazoe, H., "Experiments on Vortex Breakdown of Swirling Flows," Bachelor Thesis, Nagoya University, 1978. Uchida, S., Nakamura, Y., and Ohsawa, M., "On the Structure of Vortex Breakdown," Proceedings of the Eleventh Fluid Dynamics Conference, 1979, pp. 54-57. *

Condensation polymerization of pyromellitic dianhydride with aromatic diamine in aprotic solvent: A reaction mechanism

Abstract: Based on nuclear magnetic resonance (NMR) studies, a probable reaction mechanism was proposed for the condensation polymerization of pyromellitic dianhydride with aromatic diamines in aprotic solvent, N,N-dimethylacetamide (DMAc), to yield aromatic polyimides. The mechanism shows the essential role played by the solvent during polymerization reaction and in imidization. It explains the formation of polyamic acid and that of its high molecular weight buildup under the conditions in which solid dianhydride was added to the solution of diamine in DMAc. A prepolymer complex formation was observed, along with the main polyamic acid, when solid diamine was added to the solution of dianhydride in DMAc. The structure of the prepolymer was derived on the basis of NMR and its formation explained in the mechanism. The nature of the prepolymer was such that on treatment with anhydride it goes to polyamic acid.

The effect of vacuum and radiation on solid propellant properties

Abstract: To understand the changes occurring in solid propellants on storage under space environments, the effect of vacuum and radiation on different propellants were studied. It was found that propellants lost weight on vacuum storage and that the rate and extent of weight loss depended upon the plasticizer content, the exposed surface area and the vacuum level. Mechanical properties and burning rates were practically unaffected and the effect on thermal decomposition was marginal. On the other hand, irradiation with gamma rays resulted in a drastic deterioration of mechanical properties and in a large increase in the rate of thermal decomposition at 225 °C. Radiation had no effect on burning rates.

A simulation model for the determination of Flory's branching coefficient in infinite network systems

Abstract: The object of this paper is to present the features of a simulation model for the evaluation of the branching coefficient of complex polymer networks. A generalized computer program, developed for this purpose, has yielded values which are in good agreement with those obtained from the well-known theoretical equations for the simpler 3,2,1/2,1 system. Die vorliegende Arbeit hat zum Ziel, die Merkmale eines zur Bestimmung von Verzweigungskoeffizienten komplexer Polymernetzwerke anwendbaren Simulations-modells darzustellen. Ein zu diesem Zweck entwickeltes allgemeines Rechenprogramm hat Werte ergeben, die mit den sich fur das einfachere 3,2,1/2,1-System durch Anwendung der bekannten theoretischen Gleichungen ergebenden Werten gut uber-einstimmen.

Burning Rate Evaluation of Composite Solid Propellants. A simplified approach

Abstract: One of the principal parameters associated with a solid propellant is its linear burning rate. Many attempts have been made in the past to determine theoretically the burning rates of solid propellants by the use of appropriate combustion models. The object of the present paper is to propose a simplified theory of burning rate suitable for composite solid propellants. While the paper follows basically the scheme suggested for this purpose by Beckstead, Derr and Price using multiple flamelets, certain simplifying assumptions have been introduced with a view to make the model easier to operate. An attempt is also made in the paper to extend it to the case of aluminized solid propellants as well on the basis of a specific hypothesis regarding the role of aluminium. The relevant transcendental equations of combustion were solved on a digital computer. The burning rates and related characteristics were evaluated by this technique for two specific ammonium perchlorate-based solid propellants, one aluminized and the other non-aluminized, and the results obtained agree reasonably with the reported experimental trends.