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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Critical Transport Phenomena in Fluid Helium Under Low Gravity

The feasibility of carrying out measurements of certain critical transport properties of pure fluid under conditions of low gravity was studied. These properties are the thermal conductivity, kappa, the shear viscosity zeta and the diffusive relaxation time tau, which are predicted to diverge (tend to infinity) as the liquid-vapor critical point is approached. However, in this critical region, the Earth's gravity effect becomes very important. As the critical point is approached, the gravity effects increasingly distort the results. The reason for this is that the compressibility of the fluid also diverges and under the influence of gravity causes a vertical density gradient in the fluid, which is significant even when very thin fluid layers (typically 1 mm high) are being used. The result is that the temperature dependence of kappa, zeta, and tau tends to flatten off as T sub c is approached instead of continuing to increase, and therefore the predictions from the renormalization group and mode coupling theories cannot be subjected to a satisfactory test.

Meyer, H.↗
DOE OSTI2024

Simulations of Stochastic Fluid Dynamics near a Critical Point in the Phase Diagram

Here, we present simulations of stochastic fluid dynamics in the vicinity of a critical endpoint belonging to the universality class of the Ising model. This study is motivated by the challenge of modeling the dynamics of critical fluctuations near a conjectured critical endpoint in the phase diagram of quantum chromodynamics (QCD). We focus on the interaction of shear modes with a conserved scalar density, which is known as model H. We show that the observed dynamical scaling behavior depends on the correlation length and the shear viscosity of the fluid. As the correlation length is increased or the viscosity is decreased we observe a crossover from the dynamical exponent of critical diffusion, z≃4, to the expected scaling exponent of model H, z≃3. We use our method to investigate the time-dependent correlation function of non-Gaussian moments M n (t) of the order parameter. We find that the relaxation time depends in a nontrivial manner on the power n.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1974

Normalizing parameters for the critical flow rate of simple fluids through nozzles

The two-phase critical flow rate for the simple fluids of methane, nitrogen, oxygen, and argon were normalized using the parameter G* = the square root of (rho sub c x P sub c/Z sub c). The values of G* are given and the question of how to apply this procedure to normalize the critical flow rates of the quantum fluids para-hydrogen and helium was addressed. Experimental data for p-hydrogen, reduced pressures to 4.5 and reduced temperatures from 0.87, were analyzed.

Hendricks, R. C.↗
DOE OSTI2023

Systematic study on the phase transition of confined fluid mixture up to the critical region

Systematic experimental study on the phase transition of confined fluids up to the critical region has been performed, in which many new insights have been obtained. For confined pure fluids, compared to the bulk phase, the critical point shifts to lower pressure and temperature, but the relative shift of critical pressure is much larger than that of critical temperature. The behavior of the shift, i.e., the shift as a function of pore size, is dependent on the pore type. For confined fluid mixtures, compared to the bulk phase, the critical point also shifts to lower pressure and temperature, and the relative shift of critical pressure is also much larger than that of critical temperature. Confined fluid mixture behaves similarly to confined pure fluid, i.e., it exhibits hysteresis at lower temperature range and does not exhibit phase coexistence or phase envelope. An equation of state for confined pure fluids, based on the Generalized van der Waals partition function, has also been developed and demonstrated to accurately predict the capillary condensation of simple molecules in MCM-41. The parameters of the equation of state are derived from experimental critical point.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1974

Convective heat transfer to low-temperature fluids

Research into forced and natural convection processes in low-temperature (cryogenic) fluids is reviewed with primary emphasis on forced convection. Boundaries of the near-critical region are defined, fluid properties near the critical state are discussed, and heat-transfer processes around the critical point are described. The thermodynamics of the critical point is analyzed together with transport properties of a near-critical fluid, and the quantum states of low-temperature molecular hydrogen (para and ortho) are discussed. Experimental work on heat transfer in free, natural, and forced convection systems is briefly summarized. Graham's (1969) penetration model for near-critical fluids is outlined, near-critical heat transfer is discussed in relation to conventional geometric effects, and the effects of curvature on the properties of near-critical hydrogen are noted. Theoretical considerations in free and forced convection are examined.

Graham, R. W.↗
DOE OSTI2020

Imaging viscous flow of the Dirac fluid in graphene

The electron–hole plasma in charge-neutral graphene is predicted to realize a quantum critical system in which electrical transport features a universal hydrodynamic description, even at room temperature. This quantum critical ‘Dirac fluid’ is expected to have a shear viscosity close to a minimum bound, with an interparticle scattering rate saturating1 at the Planckian time, the shortest possible timescale for particles to relax. Although electrical transport measurements at finite carrier density are consistent with hydrodynamic electron flow in graphene a clear demonstration of viscous flow at the charge-neutrality point remains elusive. In this work, we directly image viscous Dirac fluid flow in graphene at room temperature by measuring the associated stray magnetic field. Nanoscale magnetic imaging is performed using quantum spin magnetometers realized with nitrogen vacancy centres in diamond. Scanning single-spin and wide-field magnetometry reveal a parabolic Poiseuille profile for electron flow in a high-mobility graphene channel near the charge-neutrality point, establishing the viscous transport of the Dirac fluid. This measurement is in contrast to the conventional uniform flow profile imaged in a metallic conductor and also in a low-mobility graphene channel. Furthermore, via combined imaging and transport measurements, we obtain viscosity and scattering rates, and observe that these quantities are comparable to the universal values expected at quantum criticality. This finding establishes a nearly ideal electron fluid in charge-neutral, high-mobility graphene at room temperature4. Our results will enable the study of hydrodynamic transport in quantum critical fluids relevant to strongly correlated electrons in high-temperature superconductors9. This work also highlights the capability of quantum spin magnetometers to probe correlated electronic phenomena at the nanoscale.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1974

Normalizing parameters for the critical flow rate of simple fluids through nozzles

It is shown that two-phase critical nozzle flow of simple fluids almost obeys the principle of corresponding states. Quantum fluid departures from the principle are resolved as a function of temperature for para-hydrogen and helium. The critical flow rates are normalized, using a normalizing parameter for which the critical flow rates of all simple fluids reduce to a single isothermal curve. The expression obtained for the normalizing parameter is shown to provide good agreement with the experiment for the critical flow rates of nitrogen, oxygen, and para-hydrogen.

Hendricks, R. C.↗
NASA NTRS1992

Near-critical point phenomena in fluids (19-IML-1)

Understanding the effects of gravity is essential if the behavior of fluids is to be predicted in spacecraft and orbital stations, and, more generally, to give a better understanding of the hydrodynamics in these systems. An understanding is sought of the behavior of fluids in space. What should emerge from the International Microgravity Lab (IML-1) mission is a better understanding of the kinetics of growth in off-critical conditions, in both liquid mixtures and pure fluids. This complex phenomenon is the object of intensive study in physics and materials sciences area. It is also expected that the IML-1 flight will procure key results to provide a better understanding of how a pure fluid can be homogenized without gravity induced convections, and to what extent the 'Piston Effect' is effective in thermalizing the compressible fluids.

Beysens, D.↗
DOE OSTI2020

Nanoscale Critical Phenomena in a Complex Fluid Studied by X-ray Photon Correlation Spectroscopy.

The advent of high-speed x-ray photon correlation spectroscopy now allows the study of critical phenomena in fluids to much smaller length scales and over a wider range of temperatures than is possible with dynamic light scattering. We present an x-ray photon correlation spectroscopy study of critical fluctuation dynamics in a complex fluid typical of those used in liquid-liquid extraction (LLE) of ions,dodecane-DMDBTDMA with extracted aqueous Ce(NO 3 ) 3 . We observe good agreement with both staticand dynamic scaling without the need for significant noncritical background corrections. Critical exponents agree with 3D Ising values, and the fluctuation dynamics are described by simple exponential relaxation.The form of the dynamic master curve deviates somewhat from the Kawasaki result, with a more abrupt transition between the critical and noncritical asymptotic behavior. The concepts of critical phenomena thus provide a quantitative framework for understanding the structure and dynamics of LLE systems and a path forward to new LLE processes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2006

Multiphase Flow Technology Impacts on Thermal Control Systems for Exploration

The Two-Phase Flow Facility (TPHIFFy) Project focused on bridging the critical knowledge gap by developing and demonstrating critical multiphase fluid products for advanced life support, thermal management and power conversion systems that are required to enable the Vision for Space Exploration. Safety and reliability of future systems will be enhanced by addressing critical microgravity fluid physics issues associated with flow boiling, condensation, phase separation, and system stability. The project included concept development, normal gravity testing, and reduced gravity aircraft flight campaigns, in preparation for the development of a space flight experiment implementation. Data will be utilized to develop predictive models that could be used for system design and operation. A single fluid, two-phase closed thermodynamic loop test bed was designed, assembled and tested. The major components in this test bed include: a boiler, a condenser, a phase separator and a circulating pump. The test loop was instrumented with flow meters, thermocouples, pressure transducers and both high speed and normal speed video cameras. A low boiling point surrogate fluid, FC-72, was selected based on scaling analyses using preliminary designs for operational systems. Preliminary results are presented which include flow regime transitions and some observations regarding system stability.

McQuillen, John↗