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The water and salt transport properties of ionizing radiation crosslinked poly(vinyl alcohol) (PVA) membranes were investigated. The studied membranes showed high permeabilities and low selectivities for both water and salt. The results were found to be in accord with a modified solution-diffusion model for transport across the membranes, in which pressure-dependent permeability coefficients are employed.
Analysis of 50-MeV particle data from ICE and 1-GeV data from eight high-latitude neutron monitors of the February 16, 1984 solar cosmic ray event indicates that an exponential with scattering mean free path of greater than 2 AU and with index in the 1.3-1.7 range provides a better description of particle anisotropies than the first-order form, confirming the prediction from cosmic ray transport theories which incorporate the effect of adiabatic focusing into the usual pitch angle scattering formalism. The time profile of the event is largely a reflection of coronal transport processes, with good fits provided by a coronal diffusion coefficient of about 10 to the 18th sq cm/s and with velocity-dependent escape. The simple method of predicting the interplanetary scattering parameters has application where particle injection is nearly continuous, but where previously accelerated particles have filled the heliosphere with a large omnidirectional background.
Potential curves for the higher-lying states of NO are used together with a general scattering code to compute accurate values of transport collision integrals for N(4S/0/)-O(3P) interactions. It is found that the major contribution to the collision integrals comes from these higher-lying states of NO. New values of the collision integrals for N(4S/0/)-N(4S/0/) and O(3P)-O(3P) interactions are computed as well. The tabulations of the collision integrals cover a broad range of temperatures from 250 to 100,000 K and can be used to determine transport properties such as viscosity, thermal conductivity, and the diffusion coefficient to the second order.
A marching Euler solver, GEM3D, was used to predict the Mach 3 flow field for the wing and body of a High-Speed Civil Transport concept. The analysis focused on a typical cruise lift coefficient of 0.1 at alpha = 3 deg. The Euler solution indicated that embedded shocks formed on the upper surface of the inboard wing panel and at the leading-edge of the outboard wing panel, due to its supersonic leading edge condition. According to a simple static-pressure criterion, the embedded wing upper-surface shocks were sufficiently strong to separate a turbulent boundary layer. Comparison of aerodynamic coefficients from the Euler solver with those from linear theory shows that the linear theory estimates of lift and drag are optimistic, which would lead to optimistic estimates of cruise range.
A Capillary Pumped Two-Phase Heat Transport Loop (CAPL) Flight Experiment, currently planned for 1993, will provide microgravity verification of the prototype capillary pumped loop (CPL) thermal control system for EOS. CAPL employs a heat pipe heat exchanger (HPHX) to couple the condenser section of the CPL to the radiator assembly. A prototype HPHX consisting of a heat exchanger (HX), a header heat pipe (HHP), a spreader heat pipe (SHP), and a flow regulator has been designed and tested. The HX transmits heat from the CPL condenser to the HHP, while the HHP and SHP transport heat to the radiator assembly. The flow regulator controls flow distribution among multiple parallel HPHX's. Test results indicated that the prototype HPHX could transport up to 800 watts with an overall heat transfer coefficient of more than 6000 watts/sq m-deg C. Flow regulation among parallel HPHX's was also demonstrated.
The evaporation of LOX under supercritical and subcritical conditions was studied experimentally and theoretically. In experiments, the evaporation rate and surface temperature were measured for LOX strand vaporizing in helium environments at pressures ranging from 5 to 68 atmospheres. Gas sampling and chromatography analysis were also employed to profile the gas composition above the LOX surface for the purpose of model validation. A comprehensive theoretical model was formulated and solved numerically to simulate the evaporation process of LOX at high pressures. The model was based on the conservation equations of mass, momentum, energy, and species concentrations for a multicomponent system, with consideration of gravitational body force, solubility of ambient gases in liquid, and variable thermophysical properties. Good agreement between predictions and measured oxygen mole fraction profiles was obtained. The effect of pressure on the distribution of the Lewis number, as well as the effect of variable diffusion coefficient, were further examined to elucidate the high-pressure transport behavior exhibited in the LOX vaporization process.
The water and salt transport properties of ionizing radiation crosslinked poly(vinyl alcohol) (PVA) membranes were investigated. The studied membranes showed high permeabilities and low selectivities for both water and salt. The results were found to be in accord with a modified solution-diffusion model for transport across the membranes, in which pressure-dependent permeability coefficients are employed.
A nonlinear modeling technique was used to characterize response surfaces for non-dimensional longitudinal aerodynamic force and moment coefficients, based on wind tunnel data from a commercial jet transport model. Data were collected using two experimental procedures - one based on modem design of experiments (MDOE), and one using a classical one factor at a time (OFAT) approach. The nonlinear modeling technique used multivariate orthogonal functions generated from the independent variable data as modeling functions in a least squares context to characterize the response surfaces. Model terms were selected automatically using a prediction error metric. Prediction error bounds computed from the modeling data alone were found to be- a good measure of actual prediction error for prediction points within the inference space. Root-mean-square model fit error and prediction error were less than 4 percent of the mean response value in all cases. Efficacy and prediction performance of the response surface models identified from both MDOE and OFAT experiments were investigated.
Artificial ice shapes of various geometric fidelity were tested on a wing model based on the Common Research Model. Low Reynolds number tests were conducted at Wichita State University's Beech Memorial Wind Tunnel, and high Reynolds number tests were conducted at ONERA's F1 wind tunnel. The aerodynamic performance data from the two facilities were compared at matched or similar Reynolds and Mach number to ensure that the results and trends observed at low Reynolds number could be applied and continued to high Reynolds number. For both clean and iced configurations, the data from Wichita State University and F1 agreed well at matched or similar Reynolds and Mach numbers. The lift and pitching moment curves agreed very well for most configurations. There appeared to be 0.2-0.3deg offset in the angle of attack between the Wichita State University and F1 data, possibly due to different flow angularities in the test sections of the two facilities. There was also an offset in the drag values between the two facilities from an unknown cause. Overall, the data compared very well between the low Reynolds number test at Wichita State University tunnel and the high Reynolds number test at F1. This indicated that data from the low Reynolds number tests could be used to understand iced-swept-wing aerodynamics at high Reynolds number.
In this study, the solidus curve of the Cd0.8Zn0.2Te homogeneity range was constructed from the partial pressure measurements by optical absorption technique which provided the information of the melt growth parameters to process crystals with the required electrical resistivity. The melt growth of Cd0.8Zn0.2Te crystals were then processed by directional solidification under controlled Cd overpressure. During the growth experiments, several procedures have been developed to improve the crystalline quality: (1) minimizing the contamination of impurities (2) improving the structural defects and (3) minimizing the Te-precipitates within the grown crystals to enhance charge transport properties. Additionally, the thermal conductivity, electrical conductivity, and Seebeck coefficient of a vapor-grown CdTe and two melt-grown Cd0.8Zn0.2Te crystals were measured between 190oC and 780oC to provide an in-depth understanding of the thermal and electrical conduction mechanisms of the crystals as well as the prospect of its thermoelectric applications.
Accurate, robust, and efficient prediction of transition in viscous flows is a significant challenge in computational fluid dynamics. We present a coupled, high-fidelity, iterative approach that leverages the FUN3D flow solver and the LASTRAC stability code to predict transition in low-disturbance environments, initiated by the linear growth of boundary-layer instability modes. Our method integrates the ability of FUN3D to compute mixed laminar-transitional-turbulent mean flows via transition-sensitized Reynolds-Averaged Navier-Stokes equations with the ability of LASTRAC to perform linear stability analysis, all within an automated framework that requires no intermediate user involvement. Unlike conventional frameworks that rely on classical stability theory or reduced-order metamodels, our approach employs the parabolized stability equations to provide more accurate and reliable estimates of disturbance growth for multiple instability mechanisms, including Tollmien-Schlichting, Kelvin-Helmholtz, and crossflow modes. By accounting for the effects of mean-flow nonparallelism as well as the surface curvature, this approach lays the foundation for improved N-factor correlations for transition onset prediction in a broad class of flows. We apply this method to three distinct flow configurations: 1) flow over a zero-pressure-gradient flat plate, 2) the NLF-0416 airfoil with both natural and separation-induced transitions, and 3) a 6:1 prolate spheroid, where transition is primarily driven by crossflow instability. For the two-dimensional cases, a formulated intermittency distribution is used to model the transition zone in between the laminar and fully turbulent flows. The results include comparisons with experimental measurements, similar numerical approaches, and transport-equations-based models, demonstrating good agreement in surface pressure coefficients, transition onset locations, and skin-friction coefficients for all three configurations. Besides contributing a couple of new insights into boundary-layer transition in these canonical cases, this study provides a powerful tool for transition modeling in both research and design applications in aerodynamics.
An experimental evaluation of analytical techniques for predicting certain stability and control characteristics of a large flexible aircraft is presented. Analytical methods based on both the model approach and flexibility influence coefficients are developed to predict the aerodynamic characteristics of a flexible airplane. These methods are then applied to a flexibly scaled model of a supersonic transport configuration. Comparisons of wind-tunnel data, calculations based on the model approach, and flexibility influence coefficients are presented over the Mach number range from 0.6 to 2.7. An examination of the results obtained from this study indicates that both analytical techniques predict reasonably well the effect of flexibility on the basic longitudinal characteristics and that both techniques give generally comparable results.
Redox-active colloids (RACs) represent a novel class of energy carriers that exchange electrical energy upon contact. Understanding contact-mediated electron transfer dynamics in RACs offers insights into physical contact events in colloidal suspensions and enables quantification of electrical energy transport in nonconjugated polymers. Redox-based electron transport was directly observed in monolayers of micron-sized RACs containing ethyl-viologen side groups via fluorescence microscopy through an unexpected nonlinear electrofluorochromism that is quantitatively coupled to the redox state of the colloid. Via imaging studies, using this electrofluorochromism, the apparent charge transfer diffusion coefficient D CT of the RAC was easily determined. The visualization of energy transport within suspensions of redox-active colloids was also demonstrated. Our work elucidates fundamental mechanisms of energy transport in colloidal systems, informs the development of next-generation redox flow batteries, and may inspire new designs of smart active soft matter including conductive polymers for applications ranging from electrochemical sensors and organic electronics to colloidal robotics.
The effects of flow oscillations on axial energy diffusion in a porous medium, in which the flow is continuously disrupted by the irregularities of the porous structure, are analyzed. The formulation employs an internal heat transfer coefficient that couples the fluid and solid temperatures. The final relationship shows that the axial energy transport per unit cross-sectional area and time is directly proportional to the axial temperature gradient and the square of the maximum fluid displacement.
Carbon molecular sieve (CMS) membranes offer the best available combination of scalable economical processability with excellent separation performance. Physical aging of CMS membranes causes pore structure changes over time that affect CMS membrane performance. To provide fundamental insights into the structure evolution in CMS membranes during physical aging, a combined dual-mode sorption and transport model is used in this study to characterize the diffusion coefficients of gas molecules in fresh and 7-day vacuum aged CMS membranes. Further, the results show physical aging of CMS membrane is primarily “diffusion related” and such aging behavior simultaneously causes ultramicropore changes in the continuous phase and Langmuir phase of CMS membrane. The new insights offered in this study suggest strategies to control the physical aging of CMS membranes and even use it as a valuable tool to tune the separation performance of CMS membranes for demanding gas separations.
Bifurcation approximation for binary and thermal diffusion coefficients, mixture viscosity, and thermal conductivity of laminar boundary layer
A proposed study to measure aerodynamic and heat transfer coefficients within the thermo-fluid-dynamic range experienced by a tethered satellite and to compare the coefficients with previous correlations is discussed. Tests are proposed on a satellite of existing design, on a satellite design consisting of models carried aboard, and on a newly designed satellite devoted to energy, mass, and momentum transfer studies on particular geometries.
The diffusion of a multispecies component is complicated by the different diffusion coefficient of each species and the interconversion reactions among the species. A diffusion equation is derived that incorporates the diffusive fluxes of all species contributing to the component's concentration. The effect of speciation on diffusion is investigated experimentally by measuring concentration profiles of all species developed during diffusion experiments. Data on water diffusion in rhyolitic glasses indicate that H2O molecules predominate over OH groups as the diffusing species at very low to high water concentrations. A simple theoretical relationship is drawn between the effective total oxygen diffusion coefficient and the total water concentration of silicates at low water content.