Results for “dielectric fluid” — Page 2

NASA NTRS2004

Controllable Sonar Lenses and Prisms Based on ERFs

Sonar-beam-steering devices of the proposed type would contain no moving parts and would be considerably smaller and less power-hungry, relative to conventional multiple-beam sonar arrays. The proposed devices are under consideration for installation on future small autonomous underwater vehicles because the sizes and power demands of conventional multiple-beam arrays are excessive, and motors used in single-beam mechanically scanned systems are also not reliable. The proposed devices would include a variety of electrically controllable acoustic prisms, lenses, and prism/lens combinations both simple and compound. These devices would contain electrorheological fluids (ERFs) between electrodes. An ERF typically consists of dielectric particles floating in a dielectric fluid. When an electric field is applied to the fluid, the particles become grouped into fibrils aligned in rows, with a consequent increase in the viscosity of the fluid and a corresponding increase in the speed of sound in the fluid. The change in the speed of sound increases with an increase in the applied electric field. By thus varying the speed of sound, one varies the acoustic index of refraction, analogously to varying the index of refraction of an optical lens or prism. In the proposed acoustic devices, this effect would be exploited to control the angles of refraction of acoustic beams, thereby steering the beams and, in the case of lenses, controlling focal lengths.

Bar-Cohen, Yoseph↗

NASA NTRS1985

The effect of power law body forces on a thermally-driven flow between concentric rotating spheres

A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

Macaraeg, M. G.↗

NASA NTRS1986

The effect of power-law body forces on a thermally driven flow between concentric rotating spheres

A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

Macaraeg, M. G.↗

NASA NTRS1976

Studies of earth simulation experiments

The low gravity environment of earth orbit offers the potential for performing experiments involving baroclinic Geophysical Fluid Dynamics (GFD) on spherical surfaces. These experiments in turn have the potential for providing deeper understanding of large scale planetary and solar circulations. However, to perform these experiments, one requires an experimental technique whereby a radially directed body force can be generated to simulate a radial gravitational force field. One viable technique is the use of dielectric fluids with temperature dependent dielectric permittivity in a radially directed electric field. Application of the Boussinesq approximation to the equations of motion for this system and restrictions on the size of certain electrodynamic terms in the energy equations yields a set of equations which are analogous to the equations of motions of geophysical systems like the earth's atmosphere on term by term basis. The theoretical design of GFD experiments for performance in earth orbit are described along with results of preliminary tests of a prototype.

Hart, J. E.↗

NASA NTRS1971

Dielectric siphons.

The normally weak polarization force density, exerted on insulating dielectric liquids by a nonuniform electric field, is enhanced if high pressures are used. The nonuniform electric field acts as an elastic ?wall' to contain and guide the dielectric fluid. A general theory for these electrohydrodynamic (EHD) conduits has been developed. An illustrative example of the EHD conduits is the dielectric siphon consisting of two U-shaped electrodes held adjacent to each other by insulating nylon screws.

Jones, T. B.↗

NASA NTRS1965

Three-dimensional wire-mesh capacitor system measures fluid density

Gaging system automatically measures the bulk density of a stored, electrically nonconductive fluid containing varying portions of liquid and vapor. The system employs a three-dimensional wire-mesh capacitor whose capacitance varies with the bulk density of the fluid dielectric medium between the capacitor plates.

Source record↗

NASA NTRS1965

Electromagnetic flowmeter.

Transducer and electronic detector of electromagnetic flow meter for volumetric flow measurement for both electrically conducting and dielectric fluids

FLOW METER↗

NASA NTRS1973

Electrohydrodynamically coupled Kelvin-Helmholtz instability

An inviscid model of the surface dynamics at the interface between two parallel-flowing insulating dielectric fluids, subject to a tangential electric field with a weak gradient, is developed. The two flows are oppositely directed, resulting in an electrohydrodynamically coupled Kelvin-Hemholtz instability. A simple stability criterion is used successfully to correlate experimental data obtained with a test configuration.

Perry, M. P.↗

NASA NTRS1974

RF gauging efforts with liquid hydrogen and liquid oxygen as applicable to subcritical space vehicle systems

The RF gauging concept is based on the interaction between a fluid dielectric medium in an enclosed metallic cavity and electromagnetic fields set up within that cavity. In RF gauging systems, the fundamental measurement relies on the interpretation of changes in the resonant RF frequencies of an enclosed tank as the mass of the propellant contained in the tank is changed. In addition to a discussion of the basic principles of operation of these systems, the study presents a description of the current breadboard implementation with typical test arrangements, along with supporting test data. The experimental testing of the RF gauging technique for liquid cryogen mass gauging indicates that this technique is a feasible approach to liquid oxygen and liquid hydrogen gauging under all attitude or reduced gravity environments.

Thompson, H. E.↗

NASA NTRS1984

Electroformed Electrodes for Electrical-Discharge Machining

Copper electrodes replace graphite electrodes in many instances of electrical-discharge machining (EDM) of complex shapes. Copper electrodes wear longer and cause less contamination of EDM dielectric fluid than do graphite electrodes.

Werner, A.↗

NASA NTRS1985

Computation of flow regimes in parameter space for the AGCE

This report describes the results of a small study program in support of the design studies for NASA's proposed Atmospheric General Circulation Experiment (AGCE). The proposed experiment will model the atmosphere using a hemispherical layer of a dielectric fluid such as silicone oil, heated at the equator, and with a large radial AC electric field producing a temperature-dependent radial body force similar to radial gravity. The effect of terrestrial gravity on the experiment can be eliminated by doing the experiment in space flight. The author developed a series of three computer models to support these design studies. The first two calculate axisymmetric solutions and their stability to small non-axisymmetric perturbations. The third computes three-dimensional solutions. These codes allow the option of solving problems in a cylindrical geometry as well as a rather generally defined spherical layer.

Roberts, G. O.↗

NASA NTRS1986

A mixed pseudospectral/finite difference method for the axisymmetric flow in a heated, rotating spherical shell

For a Spacelab flight, a model experiment of the earth's atmospheric circulation has been proposed. This experiment is known as the Atmospheric General Circulation Experiment (AGCE). In the experiment concentric spheres will rotate as a solid body, while a dielectric fluid is confined in a portion of the gap between the spheres. A zero gravity environment will be required in the context of the simulation of the gravitational body force on the atmosphere. The present study is concerned with the development of pseudospectral/finite difference (PS/FD) model and its subsequent application to physical cases relevant to the AGCE. The model is based on a hybrid scheme involving a pseudospectral latitudinal formulation, and finite difference radial and time discretization. The advantages of the use of the hybrid PS/FD method compared to a pure second-order accurate finite difference (FD) method are discussed, taking into account the higher accuracy and efficiency of the PS/FD method.

Macaraeg, M. G.↗

NASA NTRS1987

Environmental projects. Volume 1: Polychlorinated biphenyl (PCB) abatement program

Six large parabolic dish antennas are located at the Goldstone Deep Space Communications Complex north of Barstow, California. Some of the ancillary electrical equipment of thes Deep Space Stations, particularly transformers and power capicitors, were filled with stable, fire-retardant, dielectric fluids containing substances called polychlorobiphenyls (PCBs). Because the Environmental Protection Agency has determined that PCBs are environmental pollutants toxic to humans, all NASA centers have been asked to participate in a PCB-abatement program. Under the supervision of JPL's Office of Telecommunications and Data Acquisition, a two-year long PCB-abatement program has eliminated PCBs from the Goldstone Complex.

Kushner, L.↗

NASA NTRS1992

Microgravity experiments and numerical simulations of rotating convection in a hemispherical layer

Hart el al. (1986) has previously described Spacelab experiments on rotating convection in a hemispherical layer with a spherically symmetric body force. A body force is induced on the dielectric fluid (silicon oil) by applying an electrostatic potential across the gap. Various configurations of temperature forcings are applied on the inner and outer spherical boundaries, which along with the rotation rate and the strength of the body force define the external parameters for each experiment. The present paper will present a review of the past experimental results and some new results from a numerical model of previous and planned experiments.

Miller, Timothy L.↗

NASA NTRS1998

Microgravity Experiments and Numerical Modeling of Rotating Buoyant Convection in a Spherical Shell with Latitudinal Thermal Gradients

The results of numerical model calculations are compared with space laboratory experiments for rotating, thermally driven flow in a hemispherical shell, and various flow regimes are described. A spherically symmetric body force, analogous to gravity, is imposed in the radial direction through the use of a dielectric fluid and an electrostatic potential difference across the gap. The spherical boundaries are maintained at constant temperature profiles (with the pole and the inner sphere being the warmer surfaces), and the equatorial wall is an insulator. Typical parameter combinations result in highly nonlinear, but laminar, flow. For weak enough buoyant forcing, the flow is axisymmetric. It consists of a single meridional cell, rising in warm latitudes (in this case, near the pole) and sinking in cool latitudes, with prograde flow in the equatorial region and near the inner hemisphere for other latitudes, and retrograde motion elsewhere. For fast rotation, the first transition due to the instability of this simple flow is also axisymmetric, consisting of rings of convection in the polar region, which propagate poleward. The first nonaxisymmetric convection occurs at Rayleigh numbers which increase with rotation rate. The form of the convection near the transition also depends upon the rate of rotation. Selected flow patterns near the transition as well as those beyond it are studied numerically. For those cases where there exist laboratory experiments with which to compare, the numerical and experimental results agree very well.

Leslie, Fred W.↗

NASA NTRS2017

Gravity Effects in Microgap Flow Boiling

Increasing integration density of electronic components has exacerbated the thermal management challenges facing electronic system developers. The high power, heat flux, and volumetric heat generation of emerging devices are driving the transition from remote cooling, which relies on conduction and spreading, to embedded cooling, which facilitates direct contact between the heat-generating device and coolant flow. Microgap coolers employ the forced flow of dielectric fluids undergoing phase change in a heated channel between devices. While two phase microcoolers are used routinely in ground-based systems, the lack of acceptable models and correlations for microgravity operation has limited their use for spacecraft thermal management. Previous research has revealed that gravitational acceleration plays a diminishing role as the channel diameter shrinks, but there is considerable variation among the proposed gravity-insensitive channel dimensions and minimal research on rectangular ducts. Reliable criteria for achieving gravity-insensitive flow boiling performance would enable spaceflight systems to exploit this powerful thermal management technique and reduce development time and costs through reliance on ground-based testing. In the present effort, the authors have studied the effect of evaporator orientation on flow boiling performance of HFE7100 in a 218 m tall by 13.0 mm wide microgap cooler. Similar heat transfer coefficients and critical heat flux were achieved across five evaporator orientations, indicating that the effect of gravity was negligible.

microscale↗

NASA NTRS2017

Gravity Effects in Microgap Flow Boiling

Increasing integration density of electronic components has exacerbated the thermal management challenges facing electronic system developers. The high power, heat flux, and volumetric heat generation of emerging devices are driving the transition from remote cooling, which relies on conduction and spreading, to embedded cooling, which facilitates direct contact between the heat-generating device and coolant flow. Microgap coolers employ the forced flow of dielectric fluids undergoing phase change in a heated channel between devices. While two phase microcoolers are used routinely in ground-based systems, the lack of acceptable models and correlations for microgravity operation has limited their use for spacecraft thermal management. Previous research has revealed that gravitational acceleration plays a diminishing role as the channel diameter shrinks, but there is considerable variation among the proposed gravity-insensitive channel dimensions and minimal research on rectangular ducts. Reliable criteria for achieving gravity-insensitive flow boiling performance would enable spaceflight systems to exploit this powerful thermal management technique and reduce development time and costs through reliance on ground-based testing. In the present effort, the authors have studied the effect of evaporator orientation on flow boiling performance of HFE7100 in a 218 m tall by 13.0 mm wide microgap cooler. Similar heat transfer coefficients and critical heat flux were achieved across five evaporator orientations, indicating that the effect of gravity was negligible.

microscale↗

NASA NTRS2018

Orientation Effects in Two-Phase Microgap Flow

The high power density of emerging electronic devices is driving the transition from remote cooling, which relies on con-duction and spreading, to embedded cooling, which extracts dissipated heat on-site. Two-phase microgap coolers employ the forced flow of dielectric fluids undergoing phase change in a heated channel within or between devices. Such coolers must work reliably in all orientations for a variety of applications (e.g., vehicle-based equipment), as well as in microgravity and high-g for other applications (e.g., spacecraft and aircraft). The lack of acceptable models and correlations for orientation- and gravity-independent operation has limited the use of two-phase coolers in such applications. Previous research has revealed that gravita-tional acceleration plays a diminishing role in establishing flow regimes and transport rates as the channel size shrinks, but there is considerable variation among the proposed microscale criteria and limited research on two-phase flows in low aspect ratio mi-crogap channels. Reliable criteria for achieving orientation- and gravity-independent flow boiling would enable emerging sys-tems to exploit this thermal management technique and streamline the technology development process. As a first step toward understanding the effect of gravity on two-phase microgap flow and transport, in the present effort the authors have studied the effect of evaporator orientation and mass flux on near-saturated flow boiling of HFE7100 in a 1.01 mm tall by 13.0 mm wide by 12.7 mm long microgap channel. Orientation-independence, defined as achieving similar critical heat fluxes, heat transfer coefficients, and flow regimes across evaporator orientations, was achieved for mass fluxes of 400 kg/m2-s and greater. The present results are compared to pub-lished criteria for achieving gravity-independence.

orientation↗