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  • 1
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    Onset of condensation effects in cryogenic wind tunnels (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The onset of condensation effects in cryogenic wind tunnels which limits their minimum operating temperatures is examined. If this onset of effects occurs below saturation temperature, then the tunnels may be operated at the lower temperatures and additional benefits to cryogenic tunnel operation resulting in increased Reynolds number capability and reduced operating costs. Both homogeneous and heterogeneous nucleation processes are discussed as they pertain to continuous flow cryogenic wind tunnels. Examples from condensation experiments in the 0.3 m Transonic Cryogenic Tunnel are also reviewed.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: High Reynolds Number Res. - 1980; p 93-104
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Real-gas effects 1: Simulation of ideal gas flow by cryogenic nitrogen and other selected gases (1980)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The thermodynamic properties of nitrogen gas do not thermodynamically approximate an ideal, diatomic gas at cryogenic temperatures. Choice of a suitable equation of state to model its behavior is discussed and the equation of Beattie and Bridgeman is selected as best meeting the needs for cryogenic wind tunnel use. The real gas behavior of nitrogen gas is compared to an ideal, diatomic gas for the following flow processes: isentropic expansion; normal shocks; boundary layers; and shock wave boundary layer interactions. The only differences in predicted pressure ratio between nitrogen and an ideal gas that may limit the minimum operating temperatures of transonic cryogenic wind tunnels seem to occur at total pressures approaching 9atmospheres and total temperatures 10 K below the corresponding saturation temperature, where the differences approach 1 percent for both isentropic expansions and normal shocks. Several alternative cryogenic test gases - air, helium, and hydrogen - are also analyzed. Differences in air from an ideal, diatomic gas are similar in magnitude to those of nitrogen. Differences for helium and hydrogen are over an order of magnitude greater than those for nitrogen or air. Helium and hydrogen do not approximate the compressible flow of an ideal, diatomic gas.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: AGARD Cryogenic Wind Tunnels; 16 p
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Real gas effects 2: Influence of condensation on minimum operating temperatures of cryogenic wind tunnels (1980)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Condensation effects are responsible for the minimum operating temperatures of cryogenic wind tunnels at total pressures up to about 9 atmospheres. The two primary modes of condensation homogeneous nucleation and heterogeneous nucleation and the conditions with which either may limit minimum operating temperatures are reveiwed. Previous hypersonic and supersonic condensation data are reviewed as are data taken in the nitrogen gas, Langley 0.3 Meter Transonic Cryogenic Tunnel. Analysis of data in the 0.3 m tunnel suggests that the onset of homogenous nucleation may be approximated by an analysis by sivier and that the onset of heterogeneous nucleation is only apparent just below free stream saturation. Extension of the results from the 0.3 m tunnel to other nitrogen gas cryogenic tunnels is discussed and is shown to depend on length scales, purity of the liquid nitrogen injected for cooling, number of particulates in the flow, and the extent to which the injected liquid nitrogen is evaporated.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: AGARD Cryogenic Wind Tunnels; 21 p
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Pre-existing seed particles and the onset of condensation in cryogenic wind tunnels (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The condensation research at NASA Langley Research Center has used a variety of experimental approaches to gather information on seed particles that can act as sites for condensation growth. Total pressure measurements have suggested that condensation growth is caused by impurities in the flow and not by unevaporated liquid nitrogen (LN2) droplets resulting from the LN2 injected to cool the 0.3-Meter Transonic Cryogenic Tunnel. A separate test with an optical droplet sizing probe, which was designed to detect droplets in the 2- to 300-micron range, confirmed the conclusions from the total pressure measurements and also discovered what appears to be solidified oil droplets having diameters of about 3 microns. These oil droplets appear to be the dominant source of seed particles above 2 microns. However, computer simulations of static pressure test data suggest that the measured condensation effects are the result of more numerous, smaller seeds with number densities on the order of 10 to the 12th per kilogram of the gas and diameters on the order of 0.5 microns.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: AIAA PAPER 84-0244
    Format: text
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    NASA TECHNICAL REPORTS
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