Study and design of a cryogenic propellant acquisition system

The development of an acquisition system for supplying subcooled liquid hydrogen and liquid oxygen under in-orbit conditions is discussed. The system will be applied to the integrated cryogenic feed requirements for space systems such as a space shuttle cryogenic auxiliary propulsion system (APS) and main propulsion for an advanced spacecraft propulsion module (ASPM). Concepts that use the favorable surface tension characteristics of fine mesh screens are emphasized. The specific objectives of the program are: (1) to evolve conceptual designs for candidate acquisition systems, (2) to formulate the analytical models needed to analyze the systems, and (3) to generate parametric data on overall candidate system performance, characteristics, and operational features in sufficient depth to establish critical design problems and criteria to support a sound system design and evaluation

Study and design of cryogenic propellant acquisition systems. Volume 2: Supporting experimental program

Areas of cryogenic fuel systems were identified where critical experimental information was needed either to define a design criteria or to establish the feasibility of a design concept or a critical aspect of a particular design. Such data requirements fell into three broad categories: (1) basic surface tension screen characteristics; (2) screen acquisition device fabrication problems; and (3) screen surface tension device operational failure modes. To explore these problems and to establish design criteria where possible, extensive laboratory or bench test scale experiments were conducted. In general, these proved to be quite successful and, in many instances, the test results were directly used in the system design analyses and development. In some cases, particularly those relating to operational-type problems, areas requiring future research were identified, especially screen heat transfer and vibrational effects

Study and design of cryogenic propellant acquisition systems. Volume 1: Design studies

An in-depth study and selection of practical propellant surface tension acquisition system designs for two specific future cryogenic space vehicles, an advanced cryogenic space shuttle auxiliary propulsion system and an advanced space propulsion module is reported. A supporting laboratory scale experimental program was also conducted to provide design information critical to concept finalization and selection. Designs using localized pressure isolated surface tension screen devices were selected for each application and preliminary designs were generated. Based on these designs, large scale acquisition prototype hardware was designed and fabricated to be compatible with available NASA-MSFC feed system hardware

Development and Performance of a Digital Image Radiometer for Heliostat Evaluation at Solar One

A review is presented of the development, performance, and operation of a digital image radiometer (DIR) used to evaluate and enhance heliostat optical and tracking performance at the Solar One 10 MWe pilot plant at Daggett, Calif. The system, termed the beam characterization system (BCS), is based on digitizing, calibrating, and computer-processing video images of heliostat-reflected beams displayed on four 30-by 40-ft targets located on the tower beneath the receiver. Additionally, the radiance distribution of the sun is simultaneously recorded by a separate, specially modified solar-tracking video camera. The basic theory and analytical techniques used to determine beam centroid error {i.e., heliostat pointing errors), the actual incident beam power, spillage power off the receiver, and solar radiance distribution are described. The computer system is presented including the automatic data acquisition mode, the interface with the heliostat array controller (HAC), and the data acquisition system (DAS). Data display for plant operator purposes and additional data acquired and stored for more detailed engineering evaluations are discussed. Advanced applications of the DIR such as determination of total incident flux on a receiver from a field of heliostats, reflectance monitoring, and measurement of atmospheric attenuation are presented. Introduction Early in the development of solar central receivers, it was recognized that some means of aligning, monitoring, and evaluating large numbers of heliostats would be required. To meet these objectives, a digital image radiometer (DIR) was conceived in 1974 at McDonnell Douglas Astronautics Co. as part of a company-funded solar research and development program. This early DIR system consisted of a video camera, video digitizer, elevated target with several radiometers, and computers. This system was used to evaluate heliostats in desert tests conducted in 1974-1975 and 1976-1977 at the Naval Weapons Center An improved version was installed in late 1977 at the MDAC Huntington Beach Solar Energy Test Facility and used to evaluate various mirror modules and heliostats. A similar device was developed at Sandia National Laboratories Central Receiver Test Facility in 1979, and used extensively in the evaluation of various heliostats The basic DIR approach was originally selected because it offered high resolution, high acquisition rates, and real-time visual monitoring, used passive targets, required little maintenance, and was the lowest cost system when compared Contributed by the Solar Energy Division and presented at the Solar Energy Conference, Las Vegas, Nev., 1984. Manuscript received by the Solar Energy Division, November, 1984. with calorimeters or arrays of moving or stationary point detectors mounted on the tower. These advantages, coupled with successful experience with the first DIR systems at MDAC and Sandia, led to selection of the DIR as the beam characterization system (BCS) at the Solar One 10 MWe pilot plant in Daggett, Calif. Additional requirements imposed on this system involved automatic operation, sophisticated integration with other subsystems, and a variety of options for acquiring, storing, and analyzing on-line and off-line data. This system provides an automatic update of heliostat-tracking-aimpoint biases and monitors heliostat optical performance; it has been operational since September 1982 [7]. Improvements were made in 1984, such as the addition of a camera to track the sun and determine the solar radiance distribution simultaneously with each beam scan. The BCS now provides comparisons of observed beam shape with computer codes that use solar radiance distribution data and theoretical heliostat optical characteristics to evaluate performance. Beam Characterization System (BCS) Design The Solar One beam characterization system characterizes the reflected beam from a heliostat or mirror module, with respect to flux distribution and beam size, shape, centroid, and power. The BCS is used to align and evaluate heliostats as part of the pilot plant functional and integrated acceptance test program, and provides operational support for collector subsystem realignment, performance evaluation, and maintenance throughout plant operation. The overall system design and special component design features are described below. System Design. The BCS is based on the DIR measuring and recording instrument and is shown in Additional radiometers located in the field as part of the data acquisition subsystem (DAS) determine incident solar irradiance, which is used to establish heliostat reflective efficiency as measured at the target. Beam centroid data are obtained to establish heliostat aimpoints. Component Design Features Video Camera. The video camera is a Model 2850C-207 low-light television camera manufactured by COHU, Inc., Electronics Division. The camera is equipped with an RCA Model 4532 B/H silicon diode array vidicon tube and a COHU Model 2820 C-204 10:1 zoom lens with a 2X extender. Features include remote or automatic iris and zoom control, antiglare shields, sealed environmental housing, dual-tone modulated frequency (DTMF) control from the BCS computer interface, and a stable platform to minimize camera movement and wind-induced vibration. The antiglare shields eliminate stray light from clouds, receiver, sun, etc., which could cause erroneous measurements. The shields are formed to match the shape of the target and two or three are used as multiple light baffles. Circuit modifications eliminate automatic gain control types of responses and a black-level mask located at the edge of the image is used as a reference to ensure constant black level over a wide temperature range. These modifications allow the camera to operate as a radiometer, with light level controlled by iris settings and filters. The camera has a relay lens for the black-level mask and space for a variety of filters used to flatten the response of the camera over its spectral response range. Dual Tone Modulated Frequency (DTMF) Camera Control System. Camera selection and light control are accomplished by a noise-resistant tone-command system composed of a transmitter in the camera control rack and a remote receiver near each camera. The transmitter is a COHU Model DTMF 100 modified for Solar One application. Integral manual control switches are provided to select the desired camera, apply power, and control the iris or place it in automatic mode. Reed relay outputs from the MODCOMP Model 1136 module in the BCS computer provide programmable camera selection and iris control. Camera control commands are encoded to digital form and transmitted to the selected receiver over standard twisted-pair wires using audio tones to represent the digital information. The transmitter also sends camera-select commands to route the desired video input through the video switch to the digitizer. The COHU Model DTMF 200 receiver decodes the command data from the transmitter and provides power and iris control commands to the associated video camera. Video Switch. The video switch is a Pelco Model VS504R switching matrix, which routes the selected video input (north, south, east, west, or sunshape camera) to the video digitizer. Video Digitizer. The video digitizer system is a Quantex Model DS-12 digital image memory/processor. This system (1) accepts the video signal from the video camera (conforming to the EIA RS-170 standard), (2) converts the signal to a digital form, (3) stores the digital data, and (4) transmits the data to the BCS computer upon command over an IEEE 488 interface. Incoming composite video is stripped of sync and applied to a high-speed A/D converter. Data from the A/D passes through the arithmetic process where it may be combined with a memory data through hardwired arithmetic processes that include summation with data already in memory, averaging, and subtraction. The resulting data are then stored in memory. The IEEE 488 interface connects the digital memory port and the system control microprocessor to the MODCOMP Model 5488 controller in the BCS computer. This interface connects the digitizer to a direct memory access channel of the BCS computer and allows block transfer of image data and program control of the digitizer functions. A standard EIA RS-170 video output is routed to the BCS monitor CRT in the receiver console in the control room. Processed data are routed through a D/A converter to the digitizer or unprocessed data may be selected. Operation. Automatic BCS operation normally occurs when the plant is operational. Heliostats are automatically selected from a file, or heliostat candidate list, so that 60 heliostats can be tested each day. To avoid stray beams from heliostats in an adjacent quadrant, opposite quadrants and targets are tested; that is, the north and south field heliostat beams are sequentially moved onto the north and south targets while the east and west field heliostats continue to track on the receiver. Later, the east and west field heliostats are sequentially tested. Three runs are taken during the day (morning, noon, afternoon) so that the tracking aimpoint variations can be assessed and a nominal aimpoint selected. This procedure is used because heliostat aimpoints often exhibit a diurnal variation. At the end of the day, the aimpoint data, based on the measured beam intensity centroids, are used to bias the heliostat tracking data in the heliostat array controller (HAC) and thus correct the aimpoint. The HAC controls the heliostats so that each beam is moved on and off the target as required. As each selected heliostat is trained on the target, the appropriate video camera is switched to view the beam and the video signal is digitized and transmitted to the BCS computer. The BCS computer processes the digitized data, correlates the data with absolute intensity measured by target-mounted radiometers, and outputs the processed data on a CRT display terminal that has hardcopy capability. A computer program resident in the BCS determines which heliostats could block or shadow the test heliostat. The beam from the test heliostat is then moved from the receiver to a standby aimpoint, the interfering heliostats are commanded to face-up stow positions, and the test heliostat beam is then directed at the target. The 8-bit video digitizer takes an "image grab" and the computer analyzes the data. If the beam is too bright (the digitizer shows saturated values) or too dim (peak values less then 150), the camera iris is adjusted automatically to obtain the correct brightness range. Five image grabs are then taken and stored in rapid succession. A calibration curve is constructed from the digitized brightness values at the three points on the target where the radiometers are located and the corresponding radiometer measurements of irradiance (W/m 2 ). A total of 15 data points is obtained, from which a curve relating brightness to irradiance is determined. A message is then sent from the BCS to the HAC that the beam scans are complete, the HAC moves the beam off the target, and a rapid series of background image grabs is taken. The background brightness values are subtracted from the previous beam brightness values taken 5 to 30 seconds previously. The calibration curve is used to obtain the net irradiance corresponding to each pizel. Calculations are then made of beam centroid, beam power, spillage power, etc., as described in the following sections. Immediately after the last beam scan, an image grab is taken of the sun and the corresponding irradiance is measured by an adjacent Eppley pyrheliometer. Correlation of the digitized video image of the sun and the measured irradiance gives the radiance (W/m 2 steradian). This procedure is followed sequentially at a rate of roughly 15 to 30 heliostats per hour with most of this time period required for repositioning interfering heliostats. Principle of Operation. The BCS acquires a large number (256 x 256) of relative brightness values (termed DIR numbers) with a video scan. These qualitative brightness data can be transformed into quantitative irradiance data using the calibration technique that associates the brightness at several points on the target with simultaneous, quantitative radiometer measurements taken at those points. The calibration curve obtained is then applied to all of the brightness values so that the irradiance at each pixel, the net beam power, the centroid of the beam, and the isoflux contours can be determined. In order to achieve reasonable accuracies, however, a number of requirements must be met, as discussed below. Alignment. The principal requirement for accurate power measurement is that the beam must cover at least one of the three central radiometers, preferably with the higher irradiance region of the beam. Because the Solar One heliostats have a single mirror-module cant angle configuration, beam irradiance for outer row heliostats shows a central maximum and a gradual decrease with increasing radius from the beam center. Close-in heliostats show little overlap and exhibit a great deal of nonuniformity; each mirror module is distinguishable, as are the spaces between the modules. As a result, close-in heliostats may cover a radiometer with a rapidly varying irradiance distribution or slope, and heliostat movement further changes the irradiance on the radiometer. These effects decrease accuracy by increasing the data spread for the calibration curve. Power measurement accuracy is therefore greater for outer field heliostats that normally give good calibration-curve results. Because of this close-in heliostat nonuniformity, multiple heliostat scans are taken (usually five) from which 15 data points correlating irradiance and brightness are obtained. The increase in data improves the curve fit. Heliostat initial alignment has some relatively large errors (centroid error up to 1 to 3 meters) and thus some beams barely cover even one radiometer. In this case, power measurement results are not accurate, but the beam centroid data are in general accurate and a bias update can be achieved. Subsequent tests of this redirected beam give more accurate beam power and centroid results. Shading Corrections. Response over the vidicon tube face normally exhibits a relatively flat maximum near the center and drops off in the outer region. This nonunifority is corrected by an algorithm that increases the brightness (or DIR number) in the proper proportion, depending on the pixel position. The correction data are obtained by periodically pointing the camera into an integrating sphere that has uniform illumination. An image grab is taken and stored as a corrective "white file." Similarly, an image grab is taken without any light to obtain a black file. The correction is then applied as a proportional increase of the actual image file, pixel by pixel, based on the response to uniform illumination. Brightness/Irradiance Correlation. Accurate results are dependent on the correlation of a brightness value obtained at a point on the target with the corresponding irradiance measured at that point at nearly the same instant. Either of two methods is used to accomplish this. The first method uses a shutter at each radiometer, coated with the target paint. When the shutter is open, the radiometer measures the irradiance and immediately after the shutter is closed, the video digitizer takes a "frame grab." The brightness of that particular spot on the beam can then be correlated with the irradiance reading immediately prior to shutter closure. The time between the two measurements is approximately 0.5 to 1 second. This technique is workable for beams having reasonably uniform irradiance and little rapid beam movement. For beams having an irregular irradiance distribution, and beam movement, the correlations show increased scatter. The second method is to leave the shutters open and obtain data on brightness from the adjacent pixels. This approach was originally used for the NWC tests [1], The average brightness is then correlated with the radiometer reading taken at the same instant. This technique has proven to be more accurate and efforts are planned to improve this technique by reconfiguring the shutter opening and further reducing the time delay. In principle, the radiometer as seen by the camera is darker than the immediate surrounding target area, but since the radiometer and target hole size can be less than the characteristic dimensions of a pixel (~ 5 cm/pixel), the camera response to this dark region is slight. In addition, iteration techniques are used to determine the brightness that would have been observed at the radiometer, if the target hole were negligibly small and the target reflectance were thus uniform. Background. The target background irradiance is time and position dependent as a result of incident light variations on the target from the sun, clouds, ground, and especially, wideangle scattering from the heliostats. The time between a power scan and background scan is approximately 5 to 30 seconds, and slight background changes can occur. Since background area is several times the beam area, a relatively small change in background can introduce a nonnegligible error in net beam power. Several techniques are used to minimize this effect. First, if incident solar irradiance is changing rapidly, a flag is set, alerting an evaluator that conditions may be changing rapidly. Second, the background brightness on the target periphery is monitored continuously and the background values adjusted so as to nearly correspond to the values during the time the individual beam scans were taken. Third, the region outside the beam is examined by an algorithm that adjusts the difference so that it becomes minimal. In effect, the region outside the beam should have a net irradiance of zero when the total irradiance minus the background irradiance is examined

Person-Centredness In the Workplace: An Examination of Person-Centred Skills, Processes and Workplace Factors Among Medicaid Waiver Providers In the United States

Background: Existing research supports the effectiveness of person-centred practices in working with persons with physical, intellectual and developmental disabilities, but less clear is the influence of workplace factors on the implementation and quality of person-centred practices. Aims: This article explores the influence of workplace factors on job satisfaction and on the implementation and quality of person-centred practices in healthcare agencies that provide home- and community-based services through a Medicaid waiver in Mississippi, a state in the southeastern United States. Methods: Purposive sampling was used to collect data via online surveys to explore the interrelationships among person-centred workplaces, job satisfaction and person-centred practices. Results: Path analysis reveals that a person-centred workplace influences both skill implementation and person-centred processes. Job satisfaction was significantly correlated to skill implementation and person-centred processes in bivariate analysis but was not detected in the path model. Conclusion: This study suggests that organisations may improve the provision of person-centred practices by investing in policies that create a person-centred workplace

Direct reaction measurements with a 132Sn radioactive ion beam

The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the cross section. The magnitude of the nuclear effects was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N=82 shell closure. The data were analyzed using finite range adiabatic wave calculations and the results compared with the previous analysis using the distorted wave Born approximation. Angular distributions for the ground and first excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one neutron states beyond the benchmark doubly-magic nucleus 208Pb.Comment: 22 pages, 7 figure

Two-neutron transfer reaction mechanisms in 12^{12}C(6^6He,4^{4}He)14^{14}C using a realistic three-body 6^{6}He model

The reaction mechanisms of the two-neutron transfer reaction $^{12}$C($^6$He,$^4$He) have been studied at 30 MeV at the TRIUMF ISAC-II facility using the SHARC charged-particle detector array. Optical potential parameters have been extracted from the analysis of the elastic scattering angular distribution. The new potential has been applied to the study of the transfer angular distribution to the 2$^+_2$ 8.32 MeV state in $^{14}$C, using a realistic 3-body $^6$He model and advanced shell model calculations for the carbon structure, allowing to calculate the relative contributions of the simultaneous and sequential two-neutron transfer. The reaction model provides a good description of the 30 MeV data set and shows that the simultaneous process is the dominant transfer mechanism. Sensitivity tests of optical potential parameters show that the final results can be considerably affected by the choice of optical potentials. A reanalysis of data measured previously at 18 MeV however, is not as well described by the same reaction model, suggesting that one needs to include higher order effects in the reaction mechanism.Comment: 9 pages, 9 figure

Reactions of a Be-10 beam on proton and deuteron targets

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus Be-11 has been examined through the 10Be(d,p) reaction in inverse kinematics at equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of Be-10 on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of Be-10 on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in Be-11 were analyzed using the Finite Range ADiabatic Wave Approximation (FR-ADWA). Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4) respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor.Comment: 16 Pages, 10 figure