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  • FLUID MECHANICS AND HEAT TRANSFER  (2,457)
  • 1985-1989  (2,457)
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  • 1
    Publication Date: 2019-08-28
    Description: The principal concepts related to the nature of the processes occurring in high-temperature heat pipes with a noncondensable gas are examined, and guidelines for the development of such heat pipes are presented. The discussion is illustrated by experimental results obtained for a horizontal sodium heat pipe (diameter, 18/1 mm; length, 710 mm). In particular, attention is given to the starting dynamics and mechanisms, the shape of the vapor-gas front, and the vapor-gas front velocity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TT-20015 , NAS 1.77:20015
    Format: text
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  • 2
    Publication Date: 2019-08-28
    Description: A geometrical interpretation of the grouping and variation rate terms of Reynolds stresses in compressible turbulent flow is presented. Examples of applications of the method are also given.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TT-20330 , NAS 1.77:20330
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  • 3
    Publication Date: 2019-08-28
    Description: The response of a tiny gas bubble under reduced pressure is investigated in its relation to cavitation. Equations of motion are formulated for gas mixtures inside the bubble and numerical calculations performed for several examples. The conclusions are as follows: (1) at the onset of bubble growth, the gas mixture inside it adiabatically expands and the temperature decreases. Condensed droplets appear inside the gas mixture due to a uniform nucleation and the temperature recovers, thus the motion of the bubble is apparently isothermal; (2) the evaporation and condensation coefficient largely affects bubble motions (maximum radius, period and rate of attenuation of the bubble oscillation) including the uniform contraction; (3) the oscillation period of the bubble is longer as the equilibrium bubble radius is larger when the surrounding pressure decreases stepwise. In this circumstance the temperature inside the bubble is kept constant due to condensation evaporation phenomena and is nearly isothermal; and (4) when the surrounding pressure decreases in a stepwise fashion, the critical pressure bubble radius relation becomes closer to that for the isothermal process if the bubble radius is larger than 8 microns.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TT-20343 , NAS 1.77:20343
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  • 4
    Publication Date: 2019-08-28
    Description: Data in the literature on heat transfer in the case of nucleate boiling of various liquids in the wicks of heat pipes are reviewed. It is shown that none of the known analytical relationships can be used to generalize, with sufficient accuracy, the experimental data found in the literature. It is further shown that the exponent of the specific heat flux in the heat transfer law changes as a function of the liquid and wick properties. A relationship is obtained which generalizes experimental data for heat transfer agents of moderate temperatures (water, acetone, ethanol, and R-11 and R-113 coolants) and ammonia.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TT-20108 , NAS 1.77:20108
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  • 5
    Publication Date: 2019-08-28
    Description: The requirements for fundamental experimental studies of the influence of free stream turbulence, pressure gradients and wall cooling are discussed. Under turbine-like free stream conditions, comprehensive tests of transitional boundary layers with laminar, reversing and turbulent flow increments were performed to decouple the effects of the parameters and to determine the effects during mutual interaction.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-88524 , NAS 1.15:88524
    Format: application/pdf
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  • 6
    Publication Date: 2019-08-28
    Description: This survey paper gives an overview of NASA's Aerothermodynamics program. The purpose is to present the elements of, example results from, and projected technology needs for hypersonic fluid and thermal physics. The NASA program is focused on improving the fundamental understanding of aerodynamic and aerothermodynamic flow phenomena over hypersonic vehicles operating in the continuum, transitional, and free molecule flow regime. Vehicle design capabilities, computational fluid dynamics, computational chemistry, turbulence modeling, aerothermal loading, Shuttle Orbiter flight data analysis, and aerothermal facilities are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 7
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    In:  CASI
    Publication Date: 2019-08-28
    Description: In the range of greater hydrazine vapor pressure, detonation speed depends exclusively on the extent of the ammonia decomposition in the second reaction stage. As vapor pressure decreases, the ammonia disintegration speed becomes increasingly slower and the reaction reached in the reaction zone increasingly decreases until finally, in the vapor pressure range between 53 and 16 Torr, the contribution of the second stage to detonation propagation disappears, and only the first stage remains active. Since the disintegration speed of the hydrazine in this pressure range has decreased markedly as well, no level, but rather only spinning, detonations occur. Temporary separations of the impact front and the reaction zone in the process lead to fluctuations of the detonation speed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-77922 , NAS 1.15:77922
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  • 8
    Publication Date: 2019-08-28
    Description: Results of experimental study of regularities of a natural transition of a laminar boundary layer to a turbulent layer at low subsonic air flow velocities are presented, analyzed and compared with theory and model experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-77985 , NAS 1.15:77985
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  • 9
    Publication Date: 2019-08-28
    Description: Two semiempirical theories which provide a basis for determining the turbulent friction and heat exchange near a wall are presented: (1) the Prandtl-Karman theory, and (2) the theory utilizing an equation for the energy of turbulent pulsations. A comparison is made between exact numerical methods and approximate integral methods for computing the turbulent boundary layers in the presence of pressure, blowing, or suction gradients. Using the turbulent flow around a plate as an example, it is shown that, when computing turbulent flows with external turbulence, it is preferable to construct a turbulence model based on the equation for energy of turbulent pulsations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-77996 , NAS 1.15:77996
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  • 10
    Publication Date: 2019-08-28
    Description: A thin film heat transfer gauge is applied to the measurement of heat transfer coefficients in the interaction regions of incident shock waves and fully developed turbulent boundary layers. It was developed to measure heat flux with high spatial resolution and fast response for wind tunnels with long flow duration. To measure the heat transfer coefficients in the interaction region in detail, experiments were performed under the conditions of Mach number = 4, total pressure = 1.2 MPa, 0.59 to approximately 0.65. Reynolds number = 1.3 to approximately 1.5 x 10 to the 7th power and incident shock angles from 17.8 to 22.8 degrees. The results show that the heat transfer coefficient changes complicatedly in the interaction region. At the beginning the interaction region, the heat transfer coefficient decreases at first, reaches its minimum value at the point where the pressure begins to increase, and then increases sharply. When the boundary layer begins to separate, even a small separation bubble causes significant changes in the heat transfer coefficient, while the pressure does not show any changes which suggests that the boundary layer begins to separate.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-77958 , NAS 1.15:77958
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