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  • 11
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    Cosmic dust analogue material condensation in microgravity: The Stardust programme - First results and future activities (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Initial results are presented from airborne experiments investigating the vapor phase condensation in microgravity, carried out in the framework of the Stardust international program. Special attention is given to the design and operation of the experimental equipment, which includes the furnace for producing vapors from different materials and the cloud chamber in which the vapor nucleation occurs. A two-part mathematical model was developed to describe the transport processes in the nucleation chamber. Results obtained from three experimental series were conducted with Mg and Zn aboard NASA's KC-135 reduced-gravity research aircraft showed that nucleation front (smoke cloud) was quite different in appearance in microgravity from that typically observed at 1-g condition. The Mg and Zn particles exhibited significant differences in shape; there was some evidence of coagulation.
    Keywords: ASTROPHYSICS
    Type: IAF PAPER 92-0933
    Format: text
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  • 12
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    Microgravity nucleation and particle coagulation experiments support (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Researchers at NASA Goddard Space Flight Center have embarked on a program to study the formation and growth of cosmic grains. This includes experiments on the homogeneous nucleation of refractory vapors of materials such as magnesium, lead, tin, and silicon oxides. As part of this program, the Chemical Engineering Department of the University of Virginia has undertaken to develop a math model for these experiments, to assist in the design and construction of the apparatus, and to analyze the data once the experiments have begun. Status Reports 1 and 2 addressed the design of the apparatus and the development of math models for temperature and concentration fields. The bulk of this report discusses the continued refinement of these models, and the assembly and testing of the nucleation chamber along with its ancillary equipment, which began in the spring of 1988.
    Keywords: MATERIALS PROCESSING
    Type: NASA-CR-183282 , NAS 1.26:183282 , UVA/528260/CHE89/103
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  • 13
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    Microgravity nucleation and particle coagulation experiments support (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A hollow sphere model is developed to predict the range of supersaturation ratio values for refractory metal vapors in a proposed experimental nucleation apparatus. Since the experiments are to be carried out in a microgravity environment, the model neglects the effects of convection and assumes that the only transfer of vapors through an inert gas atmosphere is by conduction and molecular diffusion. A consistent set of physical properties data is assembled for the various candidate metals and inert ambient gases expected to be used in the nucleation experiments. Transient partial pressure profiles are computed for the diffusing refractory species for two possible temperature distributions. The supersaturation ratio values from both candidate temperature profiles are compared with previously obtained experimetnal data on a silver-hydrogen system. The model is used to simulate the diffusion of magnesium vapor through argon and other inert gas atmospheres over ranges of initial and boundary conditions. These results identify different combinations of design and operating parameters which are liekly to produce supersaturation ratio values high enough to induce homogeneous nucleation in the apparatus being designed for the microgravity nucleation experiments.
    Keywords: MATERIALS PROCESSING
    Type: NASA-CR-181541 , NAS 1.26:181541 , UVA/528260/CHE88/101
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  • 14
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    Microgravity nucleation and particle coagulation experiments support (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This project is a part of a program at GSFC to study to formation and growth of cosmic dust grain analogs under terrestrial as well as microgravity conditions. Its primary scientific objective is to study the homogeneous nucleation of refractory metal vapors and a variety of their oxides among others, while the engineering, and perhaps a more immediate objective is to develop a system capable of producing mono-dispersed, homogeneous suspensions of well-characterized refractory particles for various particle interaction experiments aboard the Space Shuttle and Space Station Freedom. Both of these objectives are to be met by a judicious combination of laboratory experiments on the ground and aboard NASA's KC-135 experimental research aircraft. Major effort during the current reporting period was devoted to the evaluation of our very successful first series of microgravity test runs in Feb. 1990. Although the apparatus performed well, it was decided to 'repackage' the equipment for easier installation on the KC-135 and access to various components. It will now consist of three separate racks: one each for the nucleation chamber, the power subsystem, and the electronic packages. The racks were fabricated at the University of Virginia and the assembly of the repackaged units is proceeding well. Preliminary analysis of the video data from the first microgravity flight series was performed and the results appear to display some trends expected from Hale's Scaled Nucleation Theory of 1986. The data acquisition system is currently being refined.
    Keywords: MATERIALS PROCESSING
    Type: NASA-CR-189899 , NAS 1.26:189899 , UVA/528260/CHE92/106
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  • 15
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    Microgravity nucleation and particle coagulation experiments support (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A preliminary model for diffusion between concentric hemispheres was adapted to the cylindrical geometry of a microgravity nucleation apparatus, and extended to include the effects of radiation and conduction through the containment walls. Computer programs were developed to calculate first the temperature distribution and then the evolving concentration field using a finite difference formulation of the transient diffusion and radiation processes. The following estimations are made: (1) it takes approximately 35 minutes to establish a steady temperature field; (2) magnesium vapors released into the argon environment at the steady temperature distribution will reach a maximum supersaturation ratio of approximately 10,000 in the 20-second period at a distance of 15 cm from the source of vapors; and (3) approximately 750W electrical power will be required to maintain steady operating temperatures within the chamber.
    Keywords: MATERIALS PROCESSING
    Type: NASA-CR-181540 , NAS 1.26:181540 , UVA/528260/CHE88/102
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  • 16
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    Stardust - Aggregation of cosmic dust analogues in microgravity (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The condensation behavior of refractory grains near stars was investigated in an experiment which used a specially designed apparatus flown aboard NASA's Reduced Gravity aircraft. The apparatus consisted of a furnace in which a solid material (Zn or Mg) is vaporized into a temperature- and pressure-controlled chamber. Light scattered from the grains was recorded using a video system, and temperature measurements in the chamber were recorded throughout the microgravity period. The video and the temperature data are compared to models that predict the time dependence of the temperature- and vapor-pressure profiles to deduce the condensation behavior of the material. The joint U.S.-Italian program (named Stardust) for these experiments, designed to study refractory grain formation and aggregation, was set up to develop experimental and computational techniques for condensation studies under microgravity conditions.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: AIAA PAPER 93-0577 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 8 p.
    Format: text
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  • 17
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    Microgravity nucleation and particle coagulation experiments support (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Modifications to the nucleation apparatus suggested by our first microgravity flight campaign are complete. These included a complete 'repackaging' of the equipment into three racks along with an improved vapor spout shutter mechanism and additional thermocouples for gas temperature measurements. The 'repackaged' apparatus was used in two KC-135 campaigns: one during the week of June 3, 1991 consisting of two flights with Mg and two with Zn, and another series consisting of three flights with Zn during the week of September 23, 1991. Our effort then was focused on the analysis of these data, including further development of the mathematical models to generate the values of temperature and supersaturation at the observed points of nucleation. The efforts to apply Hale's Scaled Nucleation Theory to our experimental data have met with only limited success, most likely due to still inadequate temperature field determination. Work on the development of a preliminary particle collector system designed to capture particles from the region of nucleation and condensation, as well as from other parts of the chamber, are discussed.
    Keywords: MATERIALS PROCESSING
    Type: NASA-CR-190159 , NAS 1.26:190159 , UVA/528260/CHE92/107
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  • 18
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    Nucleation experiments in a microgravity environment (1986)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A simple experimental apparatus is described in which a wide variety of vapor phase nucleation studies of refractory materials could be performed aboard NASA's KC-135 Research Aircraft. The chief advantage of a microgravity environment for these studies is the expected absence of thermally driven convective motions in the gas. The absence of convection leads to much more accurate knowledge of both the temperature distribution in the system and the time evolution of the refractory vapor concentration as a function of distance from the crucible.The evolution of the apparatus will be described as more experience is gained with the microgravity environment. Such experiments will be used to prepare for similar ones carried out aboard either the shuttle or Space Station where considerably longer duration experiments are possible.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA. Lyndon B. Johnson Space Center Space Station Planetology Experiments (SSPEX); 2 p
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