Non-imaging Device Research Articles

A New Approach for Design Optimization and Parametric Analysis of Symmetric Compound Parabolic Concentrator for Photovoltaic Applications

A compound parabolic concentrator (CPC) is a non-imaging device generally used in PV, thermal, or PV/thermal hybrid systems for the concentration of solar radiation on the target surface. This paper presents the geometric design, statistical modeling, parametric analysis, and geometric optimization of a two-dimensional low concentration symmetric compound parabolic concentrator for potential use in building-integrated and rooftop photovoltaic applications. The CPC was initially designed for a concentration ratio of “2×” and an acceptance half-angle of 30°. A MATLAB code was developed in house to provoke the CPC reflector’s profile. The height, aperture width, and concentration ratios were computed for different acceptance half-angles and receiver widths. The interdependence of optical concentration ratio and acceptance half-angle was demonstrated for a wide span of acceptance half-angles. The impact of the truncation ratio on the geometric parameters was investigated to identify the optimum truncation position. The profile of truncated CPC for different truncation positions was compared with full CPC. A detailed statistical analysis was performed to analyze the synergistic effects of independent design parameters on the responses using the response surface modeling approach. A set of optimized design parameters was obtained by establishing specified optimization criteria. A 50% truncated CPC with an acceptance half-angle of 21.58° and receiver width of 193.98 mm resulted in optimum geometric dimensions.

Collector characterisation and heat loss tests on a novel batch solar water heater with CPC reflector for households

ABSTRACTThis solar water-heating unit is an integration of the older concept of batch water heating with the modern trends in solar water-heating technologies i.e. incorporating a concentrator in the design. The concentrator used is the compound parabolic type (CPC) which is a non-imaging device having wider acceptance angle (64°) and supported on a wooden cradle, which comprises the two arms of the parabola. To suppress the heat loss, an air gap has been introduced in the arms of the CPC. The collector is a single larger diameter drum which serves both as an absorber and storage unit positioned at the focus of CPC. The parametric study of the model showed the thermal efficiency of the collector as high as 38% and maximum water temperature attained was 53°C. Heat loss tests performed on the collector on a 24-hr cycle period showed good long time performance estimates. The response time of collector computed and performance characteristic curve plotted to predict system response under any given conditions of solar insolation and ambient temperature.

A parametric study of a concentrating integral storage solar water heater for domestic uses

A parametric study of a concentrating integrated collector storage solar water heater was undertaken. The concentrator used was the Compound Parabolic Concentrator (CPC), an optical non-imaging device, a wider acceptance angle was used (64°) so that only occasional tracking is needed making this suitable for household purposes. The reflective concentrator was supported on a wooden cradle which comprised the two parabolas of the compound parabolic concentrator. Unlike conventional CPC systems with a large number of smaller diameter tubes, here is a single larger diameter drum was positioned at the focus of the CPC. Experimental studies were carried out and the mean collector efficiency computed on the model with an air gap introduced in the side walls (arms of the CPC). The parametric study of the design by EES at solar noon was in good agreement with the collected experimental results. The maximum thermal efficiency of the collector was 38% and the maximum water temperature attained was 53°C.

Design of a rotational three-dimensional nonimaging device by a compensated two-dimensional design process

A compensation process has been developed to design rotational three-dimensional (3D) nonimaging devices. By compensating the desired light distribution during a two-dimensional (2D) design process for an extended Lambertian source using a compensation coefficient, the meridian plane of a 3D device with good performance can be obtained. This method is suitable in many cases with fast calculation speed. Solutions to two kinds of optical design problems have been proposed, and the limitation of this compensated 2D design method is discussed.

Demonstration of Infrared-Photovoltaics for a Full-Spectrum Solar Energy System

A nonimaging (NI) device and infrared-photovoltaic (IR-PV) array for use in a full-spectrum solar energy system has been designed, built, and tested (Dye et al., 2003, “Optical Design of an Infrared Non-Imaging Device for a Full-Spectrum Solar Energy System,” Proceedings of the ASME International Solar Energy Society Conference; Dye and Wood, 2003, Infrared Transmission Efficiency of Refractive and Reflective Non-Imaging Devices for a Full-Spectrum Solar Energy System,” Nonimaging Optics: Maximum Efficiency Light Transfer VII, Proc. SPIE, 5185; Fraas et al., 2001, Infrared Photovoltaics for Combined Solar Lighting and Electricity for Buildings,” Proceedings of 17th European Photovoltaic Solar Energy Conference}. This system was designed to utilize the otherwise wasted infrared (IR) energy that is separated from the visible portion of the solar spectrum before the visible light is harvested. The IR energy will be converted to electricity via a gallium antimonide (GaSb) IR-PV array. The experimental apparatus for the testing of the IR optics and IR-PV performance is described. Array performance data will be presented, along with a comparison between outdoor experimental tests and laboratory flash tests. An analysis of the flow of the infrared energy through the collection system will be presented, and recommendations will be made for improvements. The IR-PV array generated a maximum of 26.7W, demonstrating a conversion efficiency of the IR energy of 12%.

Optical Design of an Infrared Non-Imaging Device for a Full-Spectrum Solar Energy System

A full-spectrum solar energy system is being designed by a research team lead by Oak Ridge National Laboratory and the University of Nevada, Reno. [1,2] The benchmark collector/receiver and prototype thermophotovoltaic (TPV) array have been built [3], so the work performed here is to match the two systems together for optimal performance. It is shown that a hollow, rectangular-shaped non-imaging (NI) device only 23 cm long can effectively distribute the IR flux incident on the TPV array mounted behind the secondary mirror. Results of the ray-tracing analysis of the different systems tested are presented.

Discrimination of osteoporotic patients with quantitative ultrasound using imaging or non-imaging device

Objectives. – Quantitative ultrasound (QUS) has emerged as a new tool in the assessment of fracture risk. The aim of this study was to compare the clinical utility of QUS parameters measured using imaging and non-imaging devices in the discrimination of osteoporotic patients. Methods. – QUS (Broadband Ultrasound Attenuation, BUA dB/MHz, and Speed of Sound, SOS m/s) were measured and then statistical analyses were performed. Results. – The 106 women included were 65 ± 8 years aged. Using DXA, T score was ≤–2.5 at either lumbar spine or hip in 59% of patients, and 25% had osteoporotic fractures. QUS results were different among devices, and these differences were highly dependent on the measured value. There was a similar effect of age and duration of menopause for all parameters. To obtain 90% of sensitivity for the diagnosis of osteoporosis, the thresholds were 50.80 and 71.70 dB/MHz for BUA and 1544.80 and 1551.50 m/s for SOS, using imaging and non-imaging devices, respectively. Belonging to the highest tertile of QUS had a negative predictive value for osteoporosis ranging from 59% to 65%. In the lowest tertile of QUS, the proportion of osteoporotic women was between 73% and 80%. All QUS parameters, except BUA measured with the non-imaging device, were able to discriminate post-menopausal women with fractures after adjustment for age and hip BMD. Conclusions. – Our data suggest that an imaging system improves the utility of BUA measurement, but not SOS, for post-menopausal osteoporosis assessment.

Identification des patientes ostéoporotiques par analyse ultrasonore osseuse avec ou sans imagerie

Objectives: Quantitative ultrasound (QUS) has emerged as a new tool in the assessment of fracture risk. The aim of this study was to compare the clinical utility of QUS parameters measured using an imaging and a non-imaging devices in the discrimination of osteoporotic patients. Methods: QUS (Broadband Ultrasound Attenuation, BUA dB/MHz, and Speed of Sound, SOS m/s) were measured and then statistical analyses were performed. Results: The 106 women included were aged 65 ± 8 years. Using DXA, T score was ≤–2.5 at either lumbar spine or hip in 59% of patients, and 25% had osteoporotic fractures. QUS results were different among devices, and these differences were highly dependent on the measured value. There was a similar effect of age and duration of menopause for all parameters. To obtain 90% of sensitivity for the diagnosis of osteoporosis, the thresholds were 50.80 and 71.70 dB/MHz for BUA and 1544.80 and 1551.50 m/s for SOS, using imaging and non-imaging devices, respectively. Belonging to the highest tertile of QUS had a negative predictive value for osteoporosis ranging from 59% to 65%. In the lowest tertile of QUS, the proportion of osteoporotic women was between 73% and 80%. All QUS parameters, except BUA measured with the non-imaging device, were able to discriminate post menopausal women with fractures after adjustment for age and hip BMD. Conclusions: Our data suggest that an imaging system improves the utility of BUA measurement, but not SOS, for post menopausal osteoporosis assessment.

Ultracompact nonimaging devices for optical wireless communications

Advanced optical design methods using the tools of nonimaging optics (instead of conventional imaging tools) produce ultracompact devices that combine high collection efficiency with a concentration (or collimating) capability close to the thermodynamic limit. After a general overview covering the most important design methods and devices in nonimaging optics, two of these designs, the so-called RX and RXI, are presented. Even though it is designed within the nonimaging framework, the RX device nevertheless has imaging properties that complement its valuable performance as a nonimaging device. The RXI is extremely compact: its aspect ratio (thickness/aperture diameter) is less than 1/3. When working as a receiver, that is, by placing a photodiode in the correct position, it attains an increase in irradiance that takes it beyond 95% of the theoretical thermodynamic limit (i.e., a concentration of 1600 times with an acceptance angle of ±2.14 deg). As an emitter, similar intensity gains can be obtained within an angle almost as large as 95% of the thermodynamic limit. The combination of high concentration factors, relatively wide acceptance angles, simplicity, and compactness makes these devices almost unique. The measurements carried out with several RXI prototypes, all of them made by PMMA injection, are also presented.

Does transducer selection affect aortic arch velocities?

The hypothesis tested was that transducers of different types and shapes would produce different peak and mean ascending aortic (AAo) velocities. Additionally, we sought to determine if mean and peak velocity recorded from the descending aorta (DAo) were similar to velocities in the AAo. Twenty-eight consecutive individuals who had normal hearts were studied. AAo velocities were measured with four traneducers including a nonimaging device that transmitted Doppler at right angies to the transducer handie, a 30-degree angled continuous wave transducer, an imaging transducer that transmitted Doppler in line with the transducer handle, and a second imaging transducer that sectored at 25 degrees to the transducer handle. DAo was studied with a standard in-line imaging transducer. Results showed that mean and peak AAo velocities recorded by transducers that transmitted off the axis of the transducer handle were similar, but the transducer that imaged along the transducer handle axis produced significantly lower peak and mean velocities. The problem that caused lower velocity for the on-axis transducer was inabillty to image the area immediately posterior to the sternum to permit alignment in the azimuthal dimension. The continuous wave transducer provided a wide spectral dispersion. Mean DAo velocity was simllar to mean AAo velocity, but variabillty was large.

Monitoring ventricular function at rest and during exercise with a nonimaging nuclear detector

A portable nonimaging device, the nuclear stethoscope, for measuring beat to beat ventricular time-activity curves in normal people and patients with heart disease, both at rest and during exercise, is being developed and evaluated. The latest device has several operating modes that facilitate left ventricular and background localization, measurement of transit times and automatic calculation and display of left ventricular ejection fraction. The correlation coefficient of left ventricular ejection fraction obtained with the device and with a camera-computer system was 0.92 in 35 subjects. During bicycle exercise the ejection fraction in 15 normal persons increased from 44 to 64 percent ( P < 0.001), whereas among 12 patients with heart disease it was unchanged in 5 and decreased in 7.