Flat Plate Reflector Research Articles

Increase in Distillate Productivity by Inclining the Flat Plate Reflector of a Tilted-Wick Solar Still in Summer

Abstract: A tilted-wick solar still with a flat plate reflector inclined backwards is theoretically analysed to predict the distillate productivity of the still on a summer solstice day at 30oN latitude. We are proposing a new geometrical model to calculate the solar radiation reflected by the inclined reflector and then absorbed onto an evaporating wick. Using this method, we performed a numerical analysis of heat and mass transfer in the still in order to determine the effectiveness of the inclination of the reflector. We found that the benefit of a vertical flat plate reflector is negligible, while an inclined reflector can increase the distillate productivity of the still, and that the reflector angle should be set at about 20o backward from vertical on a summer solstice day. The benefit of the inclined reflector is less in summer than in winter, but the daily amount of distillate can be increased about 9% or 6% by using an inclined reflector when the length of the reflector is a half of the still’s length and the still’s angle is 10o or 30o. Key words: Solar still; Solar distillation; Solar desalination; Tilted-wick; Reflector; Inclined; Summer

Solar thermal collector augmented by flat plate booster reflector: Optimum inclination of collector and reflector

In this report we present a theoretical analysis of a solar thermal collector with a flat plate top reflector. The top reflector extends from the upper edge of the collector, and can be inclined forwards or backwards from vertical according to the seasons. We theoretically predicted the daily solar radiation absorbed on an absorbing plate of the collector throughout the year, which varies considerably with the inclination of both the collector and reflector, and is slightly affected by the ratio of the reflector and collector length. We found the optimum inclination of the collector and reflector for each month at 30°N latitude. An increase in the daily solar radiation absorbed on the absorbing plate over a conventional solar thermal collector would average about 19%, 26% and 33% throughout the year by using the flat plate reflector when the ratio of reflector and collector length is 0.5, 1.0 and 2.0 and both the collector and reflector are adjusted to the proper inclination.

Experimental study of vertical multiple-effect diffusion solar still coupled with a flat plate reflector

Abstract A vertical multiple-effect diffusion solar still, consisting of a glass cover and a series of closely spaced vertical and parallel partitions in contact with saline-soaked wicks, coupled with a flat plate reflector was constructed and examined in outdoor experiments at Fukuoka, Japan. The vertical partitions make it possible to reduce the diffusion gaps between partitions to increase distillate productivity. The overall daily productivity of the proposed still with 6-effect and 5 mm diffusion gaps was about 13.3 kg/m 2 day at maximum when the global solar radiation on a horizontal surface was 13.4 to 15.7 MJ/m 2 day and radiation on the glass cover was 20.2 to 22.9 MJ/m 2 day. The productivity of the still would be greater than or approximately equivalent to other types of multiple-effect diffusion still. The discrepancy between experimental results and theoretical predictions was observed in several experiments, and a discussion on this discrepancy is also presented.

Tilted wick solar still with external flat plate reflector: Optimum inclination of still and reflector

We present a theoretical analysis of a tilted wick solar still with an external flat plate reflector. The reflector is assumed to be able to be inclined forwards or backwards according to the seasons. We theoretically predicted the daily amount of distillate of the still throughout the year, which varies with the inclination angle of both the still and reflector. We found the optimum inclination angle of the still as well as the optimum inclination angle of the reflector for each month at 30°N latitude. The daily amount of distillate of the still can be increased by adjusting the inclination of both the still and reflector for any season, thus producing an average of about 21% more than a conventional tilted wick still throughout the year.

Effect of inclination of external reflector of basin type still in summer

In this paper, we present a geometrical model to calculate the radiation reflected from an external reflector inclined backwards and then absorbed onto a basin liner of a basin type still. The effect of the inclination of the external reflector on the distillate productivity of the still with both the internal and external flat plate reflector on a summer solstice day at 30°N was theoretically predicted. We found that the distillate productivity of the still can be increased by inclining the external reflector even in summer, but the augmentation is smaller than in winter. Further, the benefit of both the internal and the inclined external reflectors of the basin type still would be considerably less in summer than in winter.

One step azimuth tracking tilted-wick solar still with a vertical flat plate reflector

This paper presents a theoretical analysis of a one step azimuth tracking tilted-wick solar still with a vertical flat plate reflector. The still is assumed to be rotated manually just once a day at southing of the sun. We performed numerical analysis of heat and mass transfer in the still to determine the distillate productivity of the still on four typical days: the spring and autumn equinox and summer and winter solstice days at 30°N latitude. We theoretically determined the optimum tilt angle of the still and the optimum orientation of the still on these four days. We also found that the increase in the daily amount of distillate of a tilted-wick still would average about 41% for four days, and can be achieved by the simple modification of using a flat plate reflector, setting the still at proper tilt angle according to seasons and rotating the still just once a day.

A study of roadside passive reflectors for improvement in the radar reliability on curves and at intersections

The use of radar in automotive applications such as adaptive cruise control is limited to detecting target vehicles directly in front of the host vehicle. Vehicles around a curve on a highway and cross-traffic vehicles at an intersection cannot be detected by current radar systems. This is primarily due to the limited beam width angle of the radar. This paper examines and evaluates the novel concept of using passive roadside reflectors (PRRs) to increase the utility of the radar system. PRRs on the shoulder and the median of a road are designed which would enable the radar system to pick up cross traffic at highway intersections. Both simulations and experiments demonstrate that this concept could be effectively used for cross-traffic distance measurement. A limitation of this technology is that cross traffic cannot be detected when the radar-equipped vehicle is close to the intersection, owing to the lateral offset of the radar from the location of the PRR. However, the system is still valuable for providing future warning of cross traffic at rural intersections. A number of options are explored for the use of PRRs to improve radar measurements on highway curves. These include the use of tangential flat-plate reflectors, skewed flat-plate reflectors, and convex reflectors. Algorithms for distance measurement with each of these options are derived and evaluated through simulations. The use of skewed flat-plate reflectors is also evaluated experimentally and found to work effectively. The effective range of the radar on highway curves could be doubled by the use of the developed system.

Improvement of the tilted wick solar still by using a flat plate reflector

This paper presents a numerical analysis to investigate the effect of the vertical flat plate external reflector on the distillate productivity of the tilted wick solar still. We propose a geometrical method to calculate the solar radiation reflected by the external reflector and absorbed on the evaporating wick, and also performed numerical analysis of heat and mass transfer in the still to predict the distillate productivity on four days (spring and autumn equinox and summer and winter solstice days) at 30°N latitude. We found that the external reflector can increase the distillate productivity in all but the summer seasons, and the increase in the daily amount of distillate averaged over the four days is predicted to be about 9%.

Outdoor experiments of a vertical diffusion solar still coupled with a flat plate reflector

We are presenting the results of outdoor experiments for a vertical single-effect diffusion solar still. This structure is equivalent to the first distilling cell of a vertical multiple-effect diffusion solar still, coupled with a flat plate reflector. The proposed multiple-effect still has a very high rate of productivity in spite of its simple structure and it may be possible for local technicians in the developing countries to construct and maintain the still. First, we performed theoretical analysis to determine the optimum angle of the flat plate reflector and the optimum orientation of the still, both of which would vary according to month, throughout the year at Kurume, Japan (33.2EN latitude) assuming that the angle of the flat plate reflector is fixed throughout the day and the orientation of the still is changed just once a day at southing of the sun. After that, we performed outdoor experiments with the vertical single-effect diffusion still coupled with the flat plate reflector from July to November 2005 at Kurume, Japan. Time variations of the distillate production rate of the still as well as temperatures in the still showed a fairly good agreement between the experimental results and the theoretical predictions, and the experimental results of the daily productivity of the still agree with the theoretical predictions with about a ±7% error margin except for the results on a cloudy day. This indicates that the solar absorption of direct, diffuse and reflected radiation on the first partition of the proposed still can be well calculated with a geometrical model described in our previous paper [23].

Numerical analysis of the vertical multiple-effect diffusion solar still coupled with a flat plate reflector: optimum reflector angle and optimum orientation of the still at various seasons and locations

The optimum angle of a flat plate reflector and the optimum orientation of a vertical multiple-effect diffusion solar still coupled with a flat plate reflector throughout the year are numerically determined with the assumption that the still is located at the equator and at 10°, 20°, 30° and 40° northern latitude. The optimum orientation of the still which maximizes the distillate productivity of the proposed still was calculated assuming that the orientation of the still is changed once during daytime at southing of the sun. The proposed still has very simple structure and consists of common materials such as thin stainless steel plates, glass plate, cotton cloth, a flat plate reflector and so on, which can be purchased in the developing countries, so the proposed still may be constructed and operated by local technicians in the developing counties. The proposed still consists of a glass cover and a number of vertical parallel partitions with narrow air gaps between partitions, and all partitions except for the outer one are in contact with saline-soaked wicks. Direct and diffuse solar radiation as well as the reflected radiation from the flat plate reflector are absorbed on the first partition, and the evaporation and condensation process is repeated on all partitions to increase the productivity of distillate. The proposed still is assumed to be rotated manually just twice a day (at near noon and before sunrise) to change its orientation and absorb more solar energy on the first partition. We found that the angle of the flat plate reflector should be basically fixed at 10° from horizontal and changed to be 0° during the winter season (around December) at higher latitudes, and the orientation of the still should be adjusted according to month at any latitude. The daily productivity of the proposed still was predicted to be more than 30 kg/m 2day at any latitude throughout the year except for the winter season (from November to January) at 40°N latitude.

Effect of inclination of external flat plate reflector of basin type still in winter

This paper presents a theoretical analysis of a basin type solar still with an internal reflector (two sides and back walls) and an inclined flat plate external reflector on a winter solstice day at 30° N latitude. We are proposing a new geometrical method for calculating the solar radiation reflected by the inclined external reflector and then absorbed on the basin liner. Using this method, we performed a numerical analysis of heat and mass transfer in the still in order to determine the effectiveness of the inclination of the external reflector. We found that the benefit of a vertical external reflector would be smaller or even negligible for a still with a larger value for the glass cover angle, while an inclined external reflector can increase the distillate productivity of the still at any glass cover angle, and the external reflector angle should be set at about 15° from vertical on a winter solstice day. The daily amount of distillate of the still with the inclined external reflector would be about 16% greater than that with the vertical external reflector, and about 2.3 times as large as that of the still with neither the internal nor the external reflector on a winter solstice day.

Factors influencing the productivity of a multiple-effect diffusion-type solar still coupled with a flat plate reflector

Parametric study was presented on a vertical multiple-effect diffusion-type solar still consisting of a flat plate reflector, a number of vertical parallel partitions in contact with saline-soaked wicks with narrow air gaps between partitions, and casters for manual azimuth tracking. The simple structure of the proposed still would make it possible for local technicians in developing countries to construct and operate it with common materials. However, poorness of construction and lack of operation skills of local technicians as well as low-grade materials would decrease the actual distillate production in practical operations. Therefore, we performed theoretical parametric investigations to determine the effect of these factors that could cause a decrease in the distillate productivity of the still, and found that although the distillate productivity of the still under practical conditions considering possible poorness of construction and operation skills would be about half of that under optimum conditions, the actual productivity under practical conditions would still be significantly greater than that of the conventional single-effect stills.

Noise temperature of a lossy flat-plate reflector for the elliptically polarized wave-case

This paper presents the derivation of equations necessary to calculate noise temperature of a lossy flat-plate reflector. Reflector losses can be due to metallic surface resistivity and multilayer dielectric sheets, including thin layers of plating, paint, and primer on the reflector surface. The incident wave is elliptically polarized, which is general enough to include linear and circular polarizations as well. The derivations show that the noise temperature for the circularly polarized incident wave case is simply the average of those for perpendicular and parallel polarizations.

The potential attractiveness and efficiency of amorphous silicon solar cells as compared with polycrystalline silicon solar cells

Ways to make the amorphous silicon solar cell (ASSC) more efficient than the polycrystalline silicon solar cell (PSSC) are discussed. This study proves that if we use two identical flat plate reflectors with their length equal to the width of the amorphous silicon solar panel at an angle of 60° to the level of the solar panel and we use an antireflecting (AR) coating layer over the layer of the ASSC, then its efficiency will be higher than the PSSC by a factor of 20–40%.

Combined collector-reflector systems

The use of flat-plate reflectors can substantially improve the performance of flat-plate collectors. We present the fundamental characteristics of a simulation program to estimate the optimum configuration of reflectors, which should be added to a solar plant, under a variety of design parameters, in order to yield the greatest economic benefit. The performance results for these collector-reflector plants are compared with traditional, single-cover collector plants, as well as with plants made up of collectors with different numbers of cover plates. The flat-plate reflector is incorporated in large-scale solar collector plants; the reflector-enhancement factor and its cost are taken into account. A sensitivity analysis is performed to visualize the behaviour of these novel systems under different cost and operating conditions.