Atomic Recombination in Nozzles : Methods of Analysis for Flows with Complicated Chemistry
The object of this review is to study the feasibility of performing accurate calculations on the non-equilibzWm flow of a complicated gas mixture through nozzles, with partioular reference to the propulsive nozzle of the hypersonic ramjet. Equations are given for the steady, quasi-one-dimensional, adiabatic flow of a general reacting gas mixture, consisting of rl species related through N chemical reactions. A number of alternative methods of obtaining numerical solutions to these equations are described and evaluated. The formulation of the system of chemical reactions is also discussed, together with the availability of the large amount of thermodynamic and chemical kinetic data which is required before a numerical solution can be attempted. It is found that by far the most serious difficulti to be overcome, before accurate non-equilibrium nozzle calculations can be performed, is obtaining reliable data on the rates of the many chemical reactions which may be involved.
The determination of optimum nozzle profiles to delay chemically frozen flow in the expansion of high temperature gas mixtures
An approximate method is presented which yields the supersonic nozzle profile necessary to keep an expanding high temperature gas mixture approximately in chemical equilibriurrio From equilibrium calculations for given chamber conditions, the freeze area ratio is determined by use of a modified Bray criterion. A plot of area ratio versus a function of nozzle geometry defines a limiting nozzle angle beyond which freezing is forecast to occur. This permits fen,,expa*sion angle at each area ratio to be chosen to keep the flow near equilibrium. The effectiveness of the resulting nozzle profile is evaluated by comparing exact calculations with equilibrium calculations. Contouring is shown to be effective for small nozzles when a correction factor is applied. The hydrogen-oxygen system is used as an example.
Synthesis of 2,4-dideoxy-.beta.-D-erythro-hexopyranosyl nucleosides
The synthesis of 1-(2,4-dideoxy-β-D-erythro-hexopyranosyl)thymine (12) 1 was accomplished using two different synthetic routes. It was obtained starting either from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose or from tri-O-acetyl-D-glucal. The other modified nucleosides, with either a cytosine, guanine, or adenine moiety, were synthesized using the second reaction scheme. Deoxygenation reactions were accomplished with the (2,4-dichlorophenoxy)thiocarbonyl derivatives generated in situ