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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Bubble Departure from Metal-Graphite Composite Surfaces and Its Effects on Pool Boiling Heat Transfer

The formation and growth processes of a bubble in the vicinity of graphite micro-fiber tips on metal-graphite composite boiling surfaces and their effects on boiling behavior are investigated. It is discovered that a large number of micro bubbles are formed first at the micro scratches and cavities on the metal matrix in pool boiling. By virtue of the non-wetting property of graphite, once the growing micro bubbles touch the graphite tips, the micro bubbles are sucked by the tips and merged into larger micro bubbles sitting on the end of the tips. The micro bubbles grow rapidly and coalesce to form macro bubbles, each spanning several tips. The necking process of a detaching macro bubble is analyzed. It is revealed that a liquid jet is produced by sudden break-off of the bubble throat. The composite surfaces not only have higher temperatures in micro- and macrolayers but also make higher frequency of the bubble departure, which increase the average heat fluxes in both the bubble growth stage and in the bubble departure period. Based on these analyses, the enhancement mechanism of pool boiling heat transfer on composite surfaces is clearly revealed.

Chao, David F.↗
DOE OSTI2022

System and method for rapid, high throughput, high pressure synthesis of materials from a liquid precursor

The present disclosure relates to a system and method for synthesis of condensed nano-materials to at least one of create nanoparticles or modify existing nanoparticles. In one embodiment the system may have a source of liquid precursor, with the liquid precursor including a compound therein. A flow control element and a compression wave generating subsystem are also included. The flow control element is in communication with the source of the liquid precursor and creates a jet of liquid precursor. The compression wave generating subsystem drives a compression wave through at least a substantial portion of a thickness of the jet of liquid precursor to sufficiently compress the jet of liquid precursor, and to increase pressure and temperature of the jet of liquid precursor, to at least one of create nanoparticles or modify existing nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

System and method for rapid, high throughput, high pressure synthesis of materials from a liquid precursor

The present disclosure relates to a system and method for synthesis of condensed, nano-carbon materials to create nanoparticles. In one embodiment the system may have a source of liquid precursor, a flow control element and a shock wave generating subsystem. The flow control element is in communication with the source of the liquid precursor and creates a jet of liquid precursor. The shock wave generating subsystem drives a shock wave through at least a substantial portion of a thickness of the jet of liquid precursor to sufficiently compress the jet of liquid precursor, and to increase a pressure and a temperature of the jet of liquid precursor, to create solid state nanoparticles.

Armstrong, Mike↗
NASA NTRS1994

A combined Eulerian-volume of fraction-Lagrangian method for atomization simulation

The tracking of free surfaces between liquid and gas phases and analysis of the interfacial phenomena between the two during the atomization and breakup process of a liquid fuel jet is modeled. Numerical modeling of liquid-jet atomization requires the resolution of different conservation equations. Detailed formulation and validation are presented for the confined dam broken problem, the water surface problem, the single droplet problem, a jet breakup problem, and the liquid column instability problem.

Seung, S. P.↗
NASA NTRS1965

Jet penetration into a liquid

Stagnation pressure and displaced liquid analysis of gas jet impingement on and penetration into liquid at subsonic and supersonic speeds

IMPINGEMENT↗
NASA NTRS1973

Impinging jet separators for liquid metal magnetohydrodynamic power cycles

In many liquid metal MHD power, cycles, it is necessary to separate the phases of a high-speed liquid-gas flow. The usual method is to impinge the jet at a glancing angle against a solid surface. These surface separators achieve good separation of the two phases at a cost of a large velocity loss due to friction at the separator surface. This report deals with attempts to greatly reduce the friction loss by impinging two jets against each other. In the crude impinging jet separators tested to date, friction losses were greatly reduced, but the separation of the two phases was found to be much poorer than that achievable with surface separators. Analyses are presented which show many lines of attack (mainly changes in separator geometry) which should yield much better separation for impinging jet separators).

Bogdanoff, D. W.↗
NASA NTRS1995

Cryogenic and Simulated Fuel Jet Breakup in Argon, Helium and Nitrogen Gas Flows

Two-phase flow atomization of liquid nitrogen jets was experimentally investigated. They were co-axially injected into high-velocity gas flows of helium, nitrogen and argon, respectively, and atomized internally inside a two-fluid fuel nozzle. Cryogenic sprays with relatively high specific surface areas were produced, i.e., ratios of surface area to volume were fairly high. This was indicated by values of reciprocal Sauter mean diameters, RSMD's, as measured with a scattered- light scanning instrument developed at NASA Lewis Research Center. Correlating expressions were derived for the three atomizing gases over a gas temperature range of 111 to 422 K. Also, the correlation was extended to include waterjet breakup data that had been previously obtained in simulating fuel jet breakup in sonic velocity gas flow. The final correlating expression included a new dimensionless molecular-scale acceleration group. It was needed to correlate RSMD data, for LN2 and H2O sprays, with the fluid properties of the liquid jets and atomizing gases used in this investigation.

Ingebo, Robert D.↗
NASA NTRS1988

Experimental verification of the thermodynamic properties for a jet-A fuel

Thermodynamic properties for a Jet-A fuel were determined by Shell Development Company in 1970 under a contract for NASA Lewis Research Center. The polynomial fit necessary to include Jet-A fuel (liquid and gaseous phases) in the library of thermodynamic properties of the NASA Lewis Chemical Equilibrium Program is calculated. To verify the thermodynamic data, the temperatures of mixtures of liquid Jet-A injected into a hot nitrogen stream were experimentally measured and compared to those calculated by the program. Iso-octane, a fuel for which the thermodynamic properties are well known, was used as a standard to calibrate the apparatus. The measured temperatures for the iso-octane/nitrogen mixtures reproduced the calculated temperatures except for a small loss due to the non-adiabatic behavior of the apparatus. The measurements for Jet-A were corrected for this heat loss and showed excellent agreement with the calculated temperatures. These experiments show that this process can be adequately described by the thermodynamic properties fitted for the Chemical Equilibrium Program.

Graciasalcedo, Carmen M.↗
NASA NTRS1977

Hydrocarbon group type determination in jet fuels by high performance liquid chromatography

Thirty-two jet and diesel fuel samples of varying chemical composition and physical properties were prepared from oil shale and coal syncrudes. Hydrocarbon types in these samples were determined by a fluorescent indicator adsorption analysis, and the results from three laboratories are presented and compared. Two methods of rapid high performance liquid chromatography were used to analyze some of the samples, and these results are also presented and compared. Two samples of petroleum-based Jet A fuel are similarly analyzed.

Antoine, A. C.↗
NASA NTRS1990

Optical characterization of clouds of fine liquid-nitrogen particles

Characteristic drop size, D sub 32, of clouds of fine liquid nitrogen particles was measured with a scattered light scanning instrument developed at NASA-Lewis. Calibration of the instrument was accomplished with suspensions of monosized polystyrene spheres and the scattered light scanner was then used to investigate the mechanism of liquid nitrogen jet disintegration in high velocity gas flow. The Sauter mean diameter, D sub 32, was found to vary inversely with nitrogen gas mass-flux raised to the 1.33 power. Values of D sub 32 varied from 5 to 25 microns and the mass-flux exponent 1.33 agrees well with theory for liquid jet breakup in high velocity gas flow. Loss of fine particles due to the high vaporization rate of liquid nitrogen was avoided by sampling the spray 1.3 cm downstream of the nozzle orifice. The presence of high velocity and thermal gradients in the gas phase also made sampling of the particles quite difficult. As a result, it was necessary to correct the measurements for background noise produced by both highly turbulent gas flow and thermally induced density gradients in the gas phase.

Ingebo, Robert D.↗
NASA NTRS1988

Axisymmetric confined turbulent jet directed towards the liquid surface from below

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are compared with appropriate experimental data. The problems associated with the free surface boundary conditions for the turbulent quantities are discussed.

Hasan, Mohammad M.↗
NASA NTRS1989

Axisymmetric confined turbulent jet directed towards the liquid surface from below

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are compared with appropriate experimental data. The problems associated with the free surface boundary conditions for the turbulent quantities are discussed.

Hasan, Mohammad M.↗
NASA NTRS1994

Experimental Investigation of Jet-Induced Mixing of a Large Liquid Hydrogen Storage Tank

Experiments have been conducted to investigate the effect of fluid mixing on the depressurization of a large liquid hydrogen storage tank. The test tank is approximately ellipsoidal, having a volume of 4.89 m(exp 3) and an average wall heat flux of 4.2 W/m(exp 2) due to external heat input. A mixer unit was installed near the bottom of the tank to generate an upward directed axial jet flow normal to the liquid-vapor interface. Mixing tests were initiated after achieving thermally stratified conditions in the tank either by the introduction of hydrogen gas into the tank or by self-pressurization due to ambient heat leak through the tank wall. The subcooled liquid jet directed towards the liquid-vapor interface by the mixer induced vapor condensation and caused a reduction in tank pressure. Tests were conducted at two jet submergence depths for jet Reynolds numbers from 80,000 to 495,000 and Richardson numbers from 0.014 to 0.52. Results show that the rate of tank pressure change is controlled by the competing effects of subcooled jet flow and the free convection boundary layer flow due to external tank wall heating. It is shown that existing correlations for mixing time and vapor condensation rate based on small scale tanks may not be applicable to large scale liquid hydrogen systems.

Lin, C. S.↗