Half Acceptance Angle Research Articles

Optical and thermal performance of a three-dimensional compound parabolic concentrator for spherical absorber

For medium range temperature applications, focusing type collectors like Compound Parabolic Concentrator (CPC) are most commonly used. Considerable research work has been carried out to improve the performance of the two-dimensional compound parabolic concentrator (2D CPC). The three-dimensional compound parabolic concentrator (3D CPC) was found to be more efficient than 2D CPC because of the higher concentration ratio. In the present work a 3D CPC was fabricated with a half acceptance angle of 4° for a spherical absorber of radius 100 mm. UV stabilized aluminized polyester foil having high reflectivity (0·85) was pasted on the reflector for a total height of 441mm and an aperture width of 540 mm. The optical efficiency was estimated theoretically and compared with the experimental value. Experimentally determined values of optical and thermal efficiencies were in good agreement with theoretically predicted value. The experimental results shown that the optical efficiency obtained from the 3D CPC (0·626) was significantly higher than that of the 2D CPC (0·570) of similar dimensions. Since the optical efficiency of the 3D CPC was increased, the thermal efficiency of the collector was also increased. In addition to that, time constant of the concentrator was also calculated. The time constant of the 3D CPC (431 s) was fairly high when compared with the 2D CPC (110 s). An attempt was made to generate low pressure steam using 3D CPC in the in situ steam generation mode. The efficiency of the steam generation was about 38%, which was one of the possible applications of 3D CPC module.

Two-phase flow modelling of a solar concentrator applied as ammonia vapor generator in an absorption refrigerator

A detailed one-dimensional numerical model describing the heat and fluid-dynamic behavior inside a compound parabolic concentrator (CPC) used as an ammonia vapor generator has been developed. The governing equations (continuity, momentum, and energy) inside the CPC absorber tube, together with the energy equation in the tube wall and the thermal analysis in the solar concentrator were solved. The computational method developed is useful for the solar vapor generator design applied to absorption cooling systems. The effect on the outlet temperature and vapor quality of a range of CPC design parameters was analyzed. These parameters were the acceptance half-angle and CPC length, the diameter and coating of the absorber tube, and the manufacture materials of the cover, the reflector, and the absorber tube. It was found that the most important design parameters in order to obtain a higher ammonia–water vapor production are, in order of priority: the reflector material, the absorber tube diameter, the selective surface, and the acceptance half-angle. The direct ammonia–water vapor generation resulting from a 35 m long CPC was coupled to an absorption refrigeration system model in order to determine the solar fraction, cooling capacity, coefficient of performance, and overall efficiency during a typical day of operation. The results show that approximately 3.8 kW of cooling at −10 °C could be produced with solar and overall efficiencies up to 46.3% and 21.2%, respectively.

Analytic solutions for the geometric and optical properties of stationary compound parabolic concentrators with fully illuminated inverted V receiver

Stationary low concentrator collectors ( C < 2), of the CPC type, are of great interest to supply thermal energy for industrial processes, at temperatures below or around 90 °C. In particular, concentrators with fully illuminated inverted V absorbers have attractive properties for thermal energy production. Two classes of CPC’s with inverted V absorber are identified, according to the relationship between the vertex angle of the absorber ( γ) and the acceptance angle of the cavity ( θ a), ( γ ⩾ θ a) or ( γ < θ a). The first class of CPC’s ( γ ⩾ θ a) converge to the fully illuminated CPC with horizontal flat receiver when ( γ = 90°). The second class of CPC’s ( γ < θ a) converge to the fully illuminated CPC with vertical flat receiver when ( γ = 0°). Both limiting cases have been published in the technical literature. This paper analyzes the class of concentrators satisfying ( γ ⩾ θ a). The ideal concentrator corresponding to a fully illuminated wedge absorber and ( γ ⩾ θ a) is a circular involute plus three parabolic segments. Closed-form analytic solutions are derived for its geometric and optical properties: reflector geometry, aperture, height, reflector length, angular acceptance function and average number of reflections for any degree of truncation. The equations obtained can be used as important design tools, for simulation techniques and optimization purposes. The collectible energy for North–South and East–West oriented collectors, for various receiver vertex angle and acceptance angle, was calculated. A cost-benefit figure, given by the relationship between collectible energy and reflector surface, is also estimated. Numerical results for any degree of cavity truncation are presented. As the degree of truncation varies, a clear minimum of the length over aperture ratio ( L/A) occurs. The geometric and optical characteristics of different low concentration CPC’s ( C, between 1 and 2, range of interest of stationary concentrators) show that the cavities with the minimal relationship between the length or height of the reflector surface and the aperture, ( L/A) and ( H/A), and the lower average number of reflections 〈 n〉 correspond to the lowest angular acceptance concentrator (highest nominal concentration). If a concentration of 1.2 is desired, then the smallest ratios of ( L/A), ( H/A) and 〈 n〉, within the set of concentrators with maximal concentration ( C) between 1 and 2, occur for ( C = 2) (nominal acceptance half angle θ a = 30°). Collectible energy results together with a cost-benefit relationship enable to conclude that a good choice for a well-designed collector for the city of Recife-PE, Brazil is: (a) East–West orientation; (b) receiver vertex angles ( γ) of the order of (65°); (c) acceptance angle of the CPC ( θ a = 30°) and (d) concentration of the truncated cavity ( C t) in the interval (1.0–1.2).

Proposal of Radiation Fluxmeter for Measurement of Asymmetric Radiation Field

In this study, CPC (Compound Parabolic Concentrator) radiation fluxmeter was newly developed for the measurement of the asymmetric radiation field such as urban street canyon with the strong solar radiation especially in summer. The developed fluxmeter consists of the CPCs and radiation flux sensors, and can collect the limited directional radiation from solid angle decided by the acceptance half-angle of the CPC. The optical characteristics of the CPC and the heat balance at the radiation flux sensor were numerically analyzed from a viewpoint of radiative heat transfer. Furthermore, a prototype CPC radiation fluxmeter was made and validated by fundamental experiments.

Design and analysis of solar thermoelectric power generation system

This article reports on the design and performance analysis of a solar thermoelectric power generation plant (STEPG). The system considers both truncated compound parabolic collectors (CPCs) with a flat receiver and conventional flat-plate collectors, thermoelectric (TE) cooling and power generator modules and appropriate connecting pipes and control devices. The design tool uses TRNSYS IIsibat-15 program with a new component we developed for the TE modules. The main input data of the system are the specifications of TE module, the maximum hot side temperature of TE modules, and the desired power output. Examples of the design using truncated CPC and flat-plate collectors are reported and discussed for various slope angle and half-acceptance angle of CPC. To minimize system cost, seasonal adjustment of the slope angle between 0° and 30° was considered, which could give relatively high power output under Bangkok ambient condition. Two small-scale STEPGs were built. One of them uses electrical heater, whereas the other used a CPC with locally made aluminum foil reflector. Measured data showed reasonable agreement with the model outputs. TE cooling modules were found to be more appropriate. Therefore, the TRNSYS software and the developed TE component offer an extremely powerful tool for the design and performance analysis of STEPG plant.

Maximum concentration for ideal asymmetrical radiation concentrators

A new relation between the maximum geometric concentration factor C and the angular acceptance interval for asymmetrical ideal non-imaging concentrators is proposed. A generalization of the well-known relation for the two-dimensional case, sin θ c = 1/ C where θ c is the acceptance half-angle, results in the proposed relation sin θ 2 − sin θ 1 = 2/ C, where θ 1 and θ 2 are the angles of the acceptance interval limits relative to the normal of the entrance aperture. The proposed relation is valid for any ideal 2D concentrator, symmetrical or asymmetrical. A proof based on conservation of phase space is provided.

Comparison of the optics of non-tracking and novel types of tracking solar thermal collectors for process heat applications up to 300 °C

Evacuated CPC (compound parabolic concentrator) collectors with non-tracking reflectors are compared with two novel tracking collectors: a parabolic trough and an evacuated tube collector with integrated tracking reflector. Non-tracking low concentrating CPC collectors are mostly mounted in east–west direction with a latitude dependent slope angle. They are suitable at most for working temperatures up to 200–250 °C. We present a tracking evacuated tube-collector with a trough-like concentrating mirror. Single-axis tracking of the mirror is realized with a magnetic mechanism. The mirror is mounted inside the evacuated tube and hence protected from environmental influences. One axis tracking in combination with a small acceptance angle allows for higher concentration as compared to non-tracking concentrating collectors. Ray-tracing analysis shows a half acceptance angle of about 5.7° at geometrical concentration ratio of 3.2. Losses of well constructed evacuated tube collectors (heat conductivity through the manifolds inside the thermally insulated terminating housing are low) are dominated by radiation losses of the absorber. Hence, reducing the absorber size can lead to higher efficiencies at high operating temperature levels. With the presented collector we aim for operating temperatures up to 350 °C. At temperatures of 300 °C we expect with anti-reflective coating of the glass tube and a selective absorber coating efficiencies of 0.65. This allows for application in industrial process heat generation, high efficient solar cooling and power generation. A first prototype, equipped with a standard glass tube and a black paint absorber coating, was tested at ZAE Bayern. The optical efficiency was measured to be 0.71. This tube-collector is compared by ray-tracing with non-tracking market available tube-collectors with geometrical concentration ratios up to 1.1 and with a low cost parabolic trough collector of Industrial Solar Technology (IST) with an acceptance half angle about 1.5°, a geometrical concentration ratio of 14.4 and a measured optical efficiency of 0.69.

Development and performance analysis of compound parabolic solar concentrators with reduced gap losses—‘V’ groove reflector

A system has been developed to use compound parabolic concentrators to collect solar energy and to generate steam. A CPC reflector profile with a V groove at the bottom of the reflector to reduce the gap losses was designed with a half acceptance angle of 23.5° for a tubular absorber of OD 30 mm. Five troughs fabricated with fiberglass substrate pasted over with UV stabilized self-adhesive aluminized polyester foil having high specular reflectivity joined together side by side comprise the CPC module with an aperture area of 2.04 m 2. Copper tubes coated with NALSUN selective coatings and enclosed by borosilicate glass envelope act as absorbers. The reflector absorber assembly housed in a single glass wool insulated wooden box forms the CPC collector. Using water as the heat transfer fluid efficiency tests were carried out with different inlet temperatures. In situ steam generation testing and possible application to steam cooking were also carried out. A theoretical modeling was developed by setting up different heat balancing equations and a reasonable agreement between theoretical computed values and the experimental values was observed.

Development and performance analysis of compound parabolic solar concentrators with reduced gap losses – oversized reflector

A severe energy shortage already exists in many parts of the developing world. In an attempt to find a technical solution, several solar energy collection technologies have been developed. A system has been designed to use compound parabolic concentrating collectors to collect solar energy and to generate steam. A compound parabolic concentrator (CPC) profile with oversized reflector and thereby reduced gap losses was designed with a half-acceptance angle of 23.5 o for a tubular absorber of OD 19 mm. Five troughs fabricated with a fiberglass substrate pasted over with UV stabilized self-adhesive aluminized polyester foil having high specular reflectivity joined together side by side make the CPC module with aperture area of 0.72 m 2. Copper tubes coated with NALSUN selective coatings and enclosed by borosilicate glass envelopes act as absorbers. The reflector–absorber assembly placed in a single glazed glass wool insulated wooden box forms the CPC collector. Using water as heat transfer fluid, efficiency tests were conducted with different inlet temperatures. Even at high temperature, the system operates with a reasonably high efficiency of 50%. In situ steam generation testing was also conducted. The fabricated CPC collector was used for steam cooking by connecting it to a pressure cooker. Cooking tests were conducted and the results are compared with earlier works. This cooker unites the characteristics of reflector cookers, steam cookers, pressure cookers and heat accumulating solar cookers. The fabricated CPC can be of immense and wide spread use for rural applications, such as water heating, steam cooking and sterilization.

Localization of chromophore absorption signals in TEM with an improved prism-mirror-prism filter.

A corrected prism-mirror-prism electron energy filter with curved entrance and exit faces was designed and incorporated into a Zeiss EM902 transmission electron microscope. The installation of the new filter required little modification to the existing microscope geometry and electronics. The filter had an energy resolution of 1.1 eV over the full image plane (acceptance half angle 10 mradian). The improved energy resolution was applied in studies of the low electron energy loss region that includes molecular orbital excitations or chromophore energy absorptions. Chromophore signal behaviour under electron irradiation was characterized using embedded crystals of hematin and of the dye mercury orange. Images of these crystals confirmed the expected decrease in signal intensity on shifting the selected energy loss from the region of molecular orbital excitations (less than approximately 5 eV) to higher energy losses. Electron irradiation-induced fading of the chromophore signal from hematin and mercury orange yielded similar 1/e dose values of 1.1 x 10(5) e(-) nm(-2) and 1.4 x 10(5) e(-) nm(-2) respectively. In a cellular context, chromophore signals were obtained from energy-filtered images of RIF-1 cell sections containing the photosensitizer chlorin e6 and from sections of BS-C-1 cells with cytoskeletal labelling via FITC-conjugated antibodies. The respective signals were extracted using a dose-dependent method or a shift in selected energy. Chromophore signal distributions were in agreement with fluorescence light microscopic images, but provided detail at higher spatial resolution.

Performance evaluation of two-dimensional compound elliptic lens concentrators using a yearly distributed insolation model

Optical performance of a two-dimensional compound elliptic lens (2D-CEL) for a photovoltaic static concentrator module has been studied as a function of half-acceptance angle using an yearly distributed insolation model. The maximum yearly averaged optical concentration ratio of 1.75 was obtained for global radiation when the 2D-CEL was installed at a tilt angle equal to the latitude of Tokyo (N35°). Also, the 2D-CEL was found to be more advantageous for collection of direct and diffuse radiations than a conventional, compound parabolic concentrator. In the case where the 2D-CEL is installed at a tilt angle of 20–35°, the maximum yearly integrated irradiance collected on the receiver was found to be 1.45 at a suitable half-acceptance angle.

Improved design of a three-dimensional, static concentrator lens using meteorological data

A three-dimensional, rectangular concentrator lens (3D lens) has been designed by combining two kinds of two-dimensional compound elliptic lenses and meteorological data. Optical concentration ratios of the 3D lenses designed at various half-acceptance angles are calculated and measured as a function of light incidence angle. Yearly integrated irradiance and yearly averaged module efficiency are simulated using the calculated optical concentration ratios and meteorological data. A performance index—a product of entry aperture and cell occupation ratios—is defined to compare with that of flat-plate modules. Consequently, designed half-acceptance angles are optimized at 40° and 70° in north–south and east–west directions. The occupation area of solar cells can be reduced to 62% using this lens although module area increases to only 1·16 times that of the flat-plate module. Copyright © 1999 John Wiley & Sons, Ltd.

Improved design of a three‐dimensional, static concentrator lens using meteorological data

A three-dimensional, rectangular concentrator lens (3D lens) has been designed by combining two kinds of two-dimensional compound elliptic lenses and meteorological data. Optical concentration ratios of the 3D lenses designed at various half-acceptance angles are calculated and measured as a function of light incidence angle. Yearly integrated irradiance and yearly averaged module efficiency are simulated using the calculated optical concentration ratios and meteorological data. A performance index—a product of entry aperture and cell occupation ratios—is defined to compare with that of flat-plate modules. Consequently, designed half-acceptance angles are optimized at 40° and 70° in north–south and east–west directions. The occupation area of solar cells can be reduced to 62% using this lens although module area increases to only 1·16 times that of the flat-plate module. Copyright © 1999 John Wiley & Sons, Ltd.

Preparation and properties of photovoltaic static concentrators

To realize further cost reduction of photovoltaic solar systems, several kinds of refractive static concentrators have been investigated. Using a ray tracing method, a two-dimensional lens was designed to obtain an optical concentration ratio of 1.75. As for a three-dimensional lens, a higher optical concentration ratio of 2.3 was developed for half-acceptance angles of 30 and 45°. In addition, to clarify the issues for commercial use, a long-life static concentrator was fabricated using a glass-lens with three kinds of Tedlar rear films in a mini-module. These results suggest that the refractive static concentrators are feasible to decrease cost reduction of the current flat-plate modules by reducing an occupation area of costly cells.

An asymmetric line-axis compound parabolic concentrating single basin solar still

An asymmetric line-axis compound parabolic concentrating single basin solar still of concentration 1.15, exit aperture 0.24 metres and length 0.48 metres, 30° inclination and 60° half acceptance angle has been designed fabricated and tested.

The fabrication and testing of a line-axis compound parabolic concentrating solar energy collector

The fabrication with locally available materials, installation and testing of a line-axis compound parabolic concentrating solar energy collector is described. The system is 2.0 metres long with a 0.2 metre exit aperture. The acceptance half-angle is 36°, and the angle of inclination is 26° 10′.

Yearly distributed insolation model and optimum design of a two dimensional compound parabolic concentrator

Optimum acceptance angle of a compound parabolic concentrator (CPC) is studied by the use of an insolation model proposed in this paper. The insolation consists of two components; diffuse and direct. The direct radiation is supposed to be distributed in the field within ±23.5° of declination on the celestial hemisphere and the diffuse radiation is assumed to have uniform irradiance. This yearly insolation model suggests that the optimum half-acceptance angle at the two-dimensional CPC becomes 26° irrespective of the change of the diffuse radiation fraction. This result leads us to the conclusion that, almost all over the world, a common CPC could be used as an optimum concentration for many solar radiation collecting systems.

A simple magnetic spectrometer for radiotherapy electron beams

A small, lightweight, single-focusing magnetic spectrometer was designed, assembled, and tested for analysis of electron beams from radiotherapy electron linacs. The objective was to develop a low cost, simple device that could be easily replicated in other medical centers, and to demonstrate the practicality of individual electron counting for precise analysis of electron spectra. Two methods of spectroscopy have been developed. One method consists of counting electrons individually as a function of magnetic field setting. Electrons are deflected through 90 degrees in the magnetic spectrometer, through an exit slit, and into a scintillation detector. A second method consists of recording the complete spectrum of electron energies from the accelerator on a strip of film at a single magnetic field setting. A critical design element is the 10-cm long collimator for electrons entering the magnet gap, with defining apertures and scraper slits. The spectrometer's cleanliness of transmission, energy calibration, and resolution were all tested at 10 and 16 MeV using the nearly monoenergetic electron beam of the accelerator at the National Research Council of Canada (NRCC). These accelerator tests, and also Monte Carlo trajectory simulations, both show that contamination of the transmitted spectrum due to scattered or knock-on electrons is negligible. Low-energy characteristics were tested using a 90Sr + 90Y beta-particle source. The energy calibration of the 90 degree spectrometer mode was based on mapping the magnetic field and also electron trajectory computer simulations. That calibration agrees with the NRCC's own calibrated scale to 0.8% for the single-particle counting method and to 1.3% for the film method. The energy resolution was measured to be 2% at 10 MeV, which is adequate for radiotherapy linac measurements. The acceptance half angle is 0.5 degrees or less, depending on the aperture size, which is adequate for electron angular distribution measurements within the forward cone of the electron beam. Used with film, the spectrometer is a simple, accurate, and highly transportable device for measuring radiotherapy electron energy spectra.

Optimization and testing of an imaging energy spectrometer for high-resolution electron-energy-loss microanalysis

Electron energy loss (EEL) microanalysis is a powerful technique for studying the chemical composition of a specimen and the distribution of each constituent. The energy loss spectrum of the post-specimen electron beam, on which the technique is based, is obtained by the use of an energy spectrometer. In transmission electron microscopy, the most prevalent type of imaging energy spectrometer is the Prism-Mirror-Prism (PMP) design (Fig. 1). It is compact in size and easy to align. For an acceptance half angle (β in Fig. 1) of 10 mradian, which corresponds to the full field of view of a modified Siemens 102 microscope of our laboratory, an experimental PMP spectrometer with a straight-faced magnetic prism has an energy resolution of 25 eV at the microscope operating voltage of 80 kV. This resolution has permitted ionization energies of different elements to be resolved, thus making the elemental microanalysis possible. However, a resolution of 25 eV is inadequate for resolving and possibly imaging with characteristic molecular energy losses, that are located in the 1.5-10 eV region of the electron energy loss spectrum.

A new design of nontracking seasonally adjusted plane mirror linear trough solar concentrator with a flat horizontal absorber

This paper presents an optical design based on a single-reflection criterion, and performance characteristics of an east-west aligned nontracking seasonally adjusted linear trough solar concentrator with a flat horizontal absorber, using plane mirror elements. The design procedure allows the use of any desired number of mirror elements to reflect solar energy onto the base absorber in one reflection. The angle of inclination of each mirror element with respect to the absorber surface, and the width of the mirror element, are determined so that a ray incident on the extreme upper edge of the mirror element at a specified angle to the normal to the concentrator aperture (acceptance half-angle), after reflection, strikes the extreme edge of the absorber on the opposite side of the mirror element. Other rays making angles less than the design acceptance half-angle are also reflected onto the base absorber in one reflection. Concentrator designs resulting from this approach appear to have the important characteristic of relatively smaller heights, and hence appear highly cost-effective in terms of the amount of material required for fabrication. Some numerical calculations have been carried out to illustrate the performance of concentrators for different acceptance half-angles. Results obtained are presented in graphic and tabular forms, and are discussed.