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[en] In this work, a new sun-tracking concept was proposed, and the optical performance of solar panels with such sun-tracking system was theoretically investigated based on the developed mathematical method and monthly horizontal radiation. The mechanism of the proposed sun-tracking technique is that the azimuth angle of solar panels is daily adjusted three times at three fixed positions: eastward, southward and westward in the morning, noon, and afternoon, respectively, by rotating solar panels about the vertical axis (3A sun-tracking, in short). The analysis indicated that the tilt-angle of solar panels, β3A, azimuth angle of solar panels in the morning and afternoon from due south, φa, and solar hour angle when the azimuth angle adjustment was made in the morning and afternoon, ωa, were three key parameters affecting the optical performance of such tracked solar panels. Calculation results showed that, for 3A tracked solar panels with a yearly fixed tilt-angle, the maximum annual collectible radiation was above 92% of that on a solar panel with full 2-axis sun-tracking; whereas for those with the tilt-angle being seasonally adjusted, it was above 95%. Results also showed that yearly or seasonally optimal values of β3A, φa and ωa for maximizing annual solar gain were related to site latitudes, and empirical correlations for a quick estimation of optimal values of these parameters were proposed based on climatic data of 32 sites in China.
[en] The paper presents a mathematical solution of the one node transient equation for a flat-plate collector by removing approximations like mean fluid temperature and constant initial temperature used in earlier solutions of the equation. Analytical expressions have been obtained for many cases of practical interest. Test procedures for flat-plate collectors often involve transient studies. Deconvolution of these results and extraction of the desired parameters of the collector become easier with the analytical expression obtained here as compared to the numerical methods used earlier. The theory also allows us to predict the performance of the collector under various pumping conditions and can be applied to actual field conditions when storage and load are included
[en] In order to increase the efficiency of solar-thermal flat-plate collectors at temperatures above 100 °C or with low solar irradiation, we implement a double glazing with a low-emitting (low-e) coating on the inner pane to improve the insulation of the transparent cover. Since commercially available low-e glazing provides only insufficient solar transmittance for the application in thermal flat-plate collectors we are developing a sputter-deposited low e-coating system based on transparent conductive oxides which provides a high solar transmittance of 85% due to additional antireflective coatings and the use of low-iron glass substrates. Durability tests of the developed coating system show that our low e-coating system is well suitable even at high temperatures, humidity and condensation.
[en] Experimental investigation to study the effect of coupling a flat plate solar collector on the productivity of solar stills was carried out. Other different parameters (i.e. water depth, direction of still, solar radiation) to enhance the productivity were also studied. Single slope solar still with mirrors fixed to its interior sides was coupled with a flat plate collector. It has been found that coupling of a solar collector with a still has increased the productivity by 56%. Also the increase of water depth has decreased the productivity, while the still productivity is found to be proportional to the solar radiation intensity.(Author)
[en] The fresh water floating collector solar pond was investigated both experimentally and theoretically in a previous work, and it is now matched, by simulation, with the heat load requirements of a greenhouse. Results of the simulation indicate that such a pond is a potential energy source for greenhouse heating. This is especially true when the material properties are such that solar absorption and storage are enhanced. This paper reports that to demonstrate this point, three sets of collectors constructed with materials of different physical (radiation) properties were tested. One set is constructed of common materials which are readily available and are normally used as covers for greenhouses. The second set made of improved materials which are also available but have a smaller long-wave transmittance. The last set made of ideal material which additionally possesses selective radiation absorption properties. Collectors made of ideal materials make a superior solar pond; thus, manufacturing films with improved properties should become a worthwhile challenge for the agricultural polyethylene-films industry. Preliminary economic studies indicate that even with the low oil (<$20/Bbl) prices which exist between 1986-1989, the fresh water floating collectors solar pond provides an economically attractive alternative to the conventional oil-burning heating system. This is especially true in mild climate areas and when the large initial investment is justified by long-term greenhouse utilization planning
[en] This paper discusses developments in light collection which had their origin in efforts to construct high performance gas Cerenkov detectors for precision studies of hyperon beta decays at the ZGS. The resulting devices, know generally as open-quotes compound parabolic concentrators,close quotes have found applications ranging from nuclear and particle physics experiments to solar energy concentration, instrument illumination, and understanding the optics of visual receptors. Interest in these devices and the ideas underlying them stimulated the development of a substantial new subfield of physics: nonimaging optics. This progression provides an excellent example of some ways in which unanticipated - and often unanticipatable - applied science and open-quotes practicalclose quotes devices naturally emerge from first-rate basic science. The characteristics of this process suggest that the term open-quotes spinoffclose quotes commonly used to denote it is misleading and in need of replacement
[en] This work present a numerical and experimental investigation of the influence of transversal flow deflector on the cooling of a heated block mounted on a flat plate. The deflector is inclined and therefore it guides the air flow to the upper surface of the block. This situation is simulating the air-cooling of a rectangular integrated circuit or a current converter mounted on an electronic board. The electronic component are assumed dissipating a low or medium heat flux (with a density lower than 5000 W/m2), as such the forced convection air cooling without fan or heat sink is still sufficient. The study details the effects of the angle of deflector on the temperature and the heat transfer coefficient along the surface of the block and around it. The results of the numerical simulations and the InfraRed camera measurements show that the deviation caused by deflector may significantly enhance the heat transfer on the top face of block
[en] Highlights: • The theoretical and experimental study on a solar air heaters with different configurations were performed. • Design and analysis of experiment was used to analyze the data from experiment. • Agreement between theoretical and empirical results, verified the exactness of the experimental design. • The highest efficiency was obtained from double pass solar collector with quarter perforated 10D cover. - Abstract: An experimental investigation was performed on a solar air heater with different configurations. The configurations included testing the single- and double-pass solar collectors with normal and perforated covers and with wire mesh layers instead of an absorber plate. Design and analysis of experiment was used to develop a model for the tested solar air heater and IBM’s Statistical Package for the Social Sciences software was used to analyze the model. Strong agreement was found between the results obtained from the theoretical and experimental investigations. Both methods suggested the same configuration for attaining the highest thermal efficiency from the system, i.e., a double-pass solar collector with a quarter-perforated cover with 3-cm hole-to-hole spacing and a mass flow rate of 0.032 kg/s
[en] The paper focuses on the ion collection simulation by j x B scheme with collision and sputtering. The effects of the collector electricity parameters on the collection time, collision and sputtering characteristics are studied. The collecting rate is increased with increasing of the current js and djs/dt, descended with increasing of the plasma density. The influence of the space between collectors is complex, augmenting the space and the collimated empty, improving collecting rate
[en] Highlights: • Case study for 316 climate station conditions was carried out. • Strong linear dependence on total yearly DNI was found. • Simplified model shows accurate results in 12 latitudes worldwide. - Abstract: This paper proposes a simple method for estimating annual thermal performance of parabolic trough collectors (PTCs) based on a linear relation with annual DNI for a certain latitude. A case study with simulations for a novel concentrating solar collector in 316 locations for three operating temperature scenarios worldwide was carried out and showed promising results for the latitudes and continents investigated. For a certain latitude and mean operating temperature, the annual yield of a PTC was found to be linearly proportional to yearly DNI. The proposed method will serve as a simplified alternative to the steady-state and quasi-dynamic methods already used. Estimating performance based on yearly DNI can be used by design engineers to do quick preliminary planning of solar plants. Customers can also use this method to evaluate existing solar collector installations. A TRNSYS/TRNSED tool that uses a steady-state model has been developed to carry out the simulations and it has been validated against a PTC array at Technical University of Denmark (DTU). The results show that the simplified method can give reliable estimates of long-term performance of parabolic trough collectors.