AN ANALYSIS OF VORTEX TUBES FOR COMBINED GAS-PHASE FISSION-HEATING AND SEPARATION OF THE FISSIONABLE MATERIAL

In order to achieve the high exhaust gas temperatures, which are desirable if the full potential of nuclear fission as an energy source for rocket propulsion is to be realized, it seems essential that the fissionable material be maintained in a gaseous mixture with the propellant. It is then necessary to separate the fissionable material from the propellant before discharging the latter, since the loss of fissionable material is prohibitive otherwise. This report presents an analytical evaluation of the characteristics of a vortex tabe which achieves the desired separation by means of a centrifugal field. Propellant is fed into the tube tangentially, at the periphery, and diffuses radially inward through a cloud of fissionable gas, picking up the fission heat as it goes. The fissionable gas is held against this radial propellant flow by the centrifugal vortex field generated by the tangentially entering propellant. The analysis involves several assumptions, the most important of which are that the flow is laminar and that it is inviscid. A set of non-linear first order differential equations is obtained which is sufficient to describe the fissionable gas concentration, temperature, and pressure distributions in the tube. These equations have been integrated numerically for a very wide range of conditions. The analysis predicts that the vortex tube is capable of maintaining rather high concentrations of fissionable gas, such that the density of the fissionable gas is of the same order as that of the propellant, with negligible loss of the fissionable gas, and with ratios of propellant exit temperature to entrance temperature up to ten. (auth

ANALYTICAL STUDY OF SOME ASPECTS OF VORTEX TUBES FOR GAS-PHASE FISSION HEATING

Several problems connected with vortex cavity reactors were studied analytically. They include, the generation of high-strength vortices by utilization of bleed through a porous tube wall to stabilize the shear layer on the wall; the nuclear criticality problem; the suitability of various compounds of plutonium as gaseous fissionable materials; and the problem of retaining the fission fragments within the vortex tube. It is concluded that the shear layer on the vortex tube wall can be stabilized if a mass flow greater than or equal to the vortex through flow is bled through the porous wall, and that the tangential Mach numbers which can be obtained are then slightly more than one-half the inviscid values. Beryllium oxide or graphite-moderated reactors of reasonable size and weight can attain criticality if the product of the hydrogen pressure in the vortex core and the maximum value of the ratio of fissionable gas density to hydrogen density in the tube is greater than about 100 atm. The reactor weights are then in the order of 10,000 lb or less. Of the several compounds of plutonium considered as gaseous fuel carriers, plutonium trifluoride and plutonium tribromide appear to be the most promising. It is probable that they can be held in gaseous form in hydrogen, under the desired concentrations. The rate of loss of fission fragments from the vortex tube can be reduced to a small fraction of the rate of their generation by making the vortex tubes about twice the minimum size that is allowable for satisfactory retention of the fissionable material. (auth

Characterization of open-cycle coal-fired MHD generators. Quarterly technical summary report No. 2, October 1--December 31, 1976. [Negative ion formation, electron/slag interaction, and alkali/slag interaction]

A study on how nonfuel components of coal will affect the electron and alkali seed chemistry in a high temperature coal combustion system like those envisioned for direct fired MHD generators is described. Three specific problems are being considered. The first problem area is to characterize the formation of negative ions due to electron attachment processes in the combustion flow. While some stable negative ions may be formed from hydrocarbon combustion species (OH, HCO/sup -//sub 3/), the bulk of the stable negative ions are expected to be formed from oxidized inorganic coal slag constituents (CO/sup -//sub 2/, PO/sup -//sub 2/, AlO/sup -//sub 2/, etc). Negative ion formation can reduce the conductivity of the MHD plasma, particularly at the low temperature end of the MHD channel, thus decreasing the efficiency of power generation. This phenomena is expected to be particularly severe in electrode boundary layers, and particular attention will be paid to conditions characteristic of flow along the electrodes. The second problem area involves the role slag condensation may play in determining the electron density through recombination, also adversely affecting conductivity in the core flow. The competitive balance between thermionic emission from slag droplets and electron/ion recombination on the droplet surfaces may be severely tipped in favor of electron loss processes, depending on the slag properties. Also, the heterogeneous interaction of alkali seed with particles formed by slag condensation in the generator channel is studied. Alkali seed material can be chemically bound into the molten slag particles tightly enough that seed recovery becomes prohibitively expensive. The loss of significant amounts of alkali seed with the slag could have a serious economic impact on proposed MHD systems. An approach, involving both theoretical modeling and experimental measurements, has been devised to explore the negative ion formation, the electron/slag interaction, and the alkali/slag interaction problems

Characterization of open-cycle coal-fired MHD generators. Quarterly technical summary report No. 3, January 1--March 31, 1977. [Negative ion formation, electron/slag interaction, and alkali/slag interaction]

The purpose of this contract effort is to understand how nonfuel components of coal will affect the electron and alkali seed chemistry in a high temperature coal combustion system like that envisioned for direct fired MHD generators. Three specific problems are being considered during this contract period. The first problem area is to characterize the formation of negative ions due to electron attachment processes in the combustion flow. While some stable negative ions may be formed from hydrocarbon combustion species (OH/sup -/), the bulk of the stable negative ions are expected to be formed from oxidized inorganic coal slag constituents (BO/sup -//sub 2/, PO/sup -//sub 2/, AlO/sup -//sub 2/, etc). Negative ion formation can reduce the conductivity of the MHD plasma, particularly at the low temperature end of the MHD channel, thus decreasing the efficiency of power generation. The second problem area involves the role slag condensation may play in determining the electron density through recombination, also adversely affecting conductivity in the core flow. The competitive balance between thermionic emission from slag droplets and electron/ion recombination on the droplet surfaces may be severely tipped in favor of electron loss processes, depending on the slag properties. The third problem area is the heterogeneous interaction of alkali seed with particles formed by slag condensation in the generator channel. Alkali seed material can be chemically bound into the molten slag particles tightly enough that seed recovery becomes prohibitively expensive. The loss of significant amounts of alkali seed with the slag could have a serious economic impact on proposed MHD systems. A coupled approach, involving both theoretical modeling and experimental measurements, has been devised to explore the negative ion formation, the electron/slag interaction, and the alkali/slag interaction problems. Research progress is reported

Microfabrication of a high pressure bipropellant rocket engine

A high pressure bipropellant rocket engine has been successfully micromanufactured by fusion bonding a stack of six individually etched single crystal silicon wafers. In order to test the device, an innovative packaging technique was developed to deliver liquid coolant and gaseous propellants to the rocket chip at pressures in excess of 200 atm at temperatures above 300°C. Testing continues on the 1.2 g devices, which have been run to date at a chamber pressure of 12 atm, generating 1 N of thrust, and delivering a thrust power of 750 W