Cylindrical Parabolic Collector Research Articles

An improved model to evaluate thermodynamic solar plants with cylindrical parabolic collectors and air turbine engines in open Joule–Brayton cycle

An improved model to analyze the performance of solar plants operating with cylindrical parabolic collectors and atmospheric air as heat transfer fluid in an open Joule–Brayton cycle is presented. In the new model, the effect of the incident angle modifier is included, to take into account the variation of the optical efficiency with the incidence angle of the irradiance, and the effect of the reheating of the fluid also has been studied.The analysis was made for two operating modes of the plants: with variable air flow rate and constant inlet temperature to the turbine and with constant flow rate and variable inlet temperature to the turbine, with and without reheating of the fluid in the solar field. When reheating is used, the efficiency of the plant is increased.The obtained results show a good performance of this type of solar plant, in spite of its simplicity; it is able to compete well with other more complex plants operating with different heat transfer fluids.

An evaluation of thermodynamic solar plants with cylindrical parabolic collectors and air turbine engines with open Joule–Brayton cycle

A performance analysis of innovative solar plants operating with cylindrical parabolic collectors and atmospheric air as heat transfer fluid in an open Joule–Brayton cycle, with and without intercooling and regeneration, is presented.The analysis was made for two operating modes of the plants: with variable air flow rate and constant inlet temperature to the turbine and with constant flow rate and variable inlet temperature to the turbine.The obtained results show a good performance of this type of solar plant, in spite of its simplicity; it seems able to compete well with other more complex plants operating with different heat transfer fluids.

Evaluation of a solar intermittent refrigeration system for ice production operating with ammonia/lithium nitrate

A novel solar intermittent refrigeration system for ice production developed in the Centro de Investigación en Energía of the Universidad Nacional Autónoma de México is presented. The system operates with the ammonia/lithium nitrate mixture. The system developed has a nominal capacity of 8 kg of ice/day. It consists of a cylindrical parabolic collector acting as generator–absorber. Evaporator temperatures as low as −11 °C were obtained for several hours with solar coefficients of performance up to 0.08. It was found that the coefficient of performance increases with the increment of solar radiation and the solution concentration. A dependency of the coefficient of performance was not founded against the cooling water temperature. Also it was found that the maximum operating pressure increases meanwhile the generation temperature decreases with an increase of the solution concentration.

Transient performance analysis of cylindrical parabolic concentrating collectors and comparison with experimental results

This paper presents the unsteady, one-dimensional performance analysis of cylindrical parabolic concentrating collectors through the first and second laws of thermodynamics. These laws, together, help to define the optimum system that satisfies the imposed thermal and economical constraints and minimizes exergy loss. The analysis considers the thermal masses of the absorber pipe, pyrex envelope and the working fluid of the system individually, in an unsteady state. The instantaneous exergetic and energy efficiencies for the cylindrical parabolic collectors are compared for daily insolation at different flow rates. The values measured using the MKE Institute Collector Test Facility are in good agreement with the predicted simulation results. The simulation results indicate that the exergetic efficiency is highly dependent on the mass flow rates and the arrangement of the cylindrical parabolic collector array. The optimum flow rates which provide minimum exergy loss were obtained from the simulation model.

Performance analysis and loadmatching for tracking cylindrical parabolic collectors for solar cooling in arid zones

Line concentrating collectors are being used for heating and cooling. The decisive advantage of these collectors in comparison with other flat-plate collectors when they are used to power absorption cooling systems is their higher working temperature leading to a higher chiller coefficient of performance (COP) and less collector area and chiller capacity. The line concentrator collector uses a small micro-motor to track the sun in its daily east-west cycle. Due to environmental problems in the site (humidity, dust and excessive heat) the tracking system has failed. Major design modifications are explained to run the system trouble free. Absorption chiller testing showed serious limitations in running the system under fired and at higher condenser temperature as the machine produces less than half the expected output. Running the system should be optimized by increasing the generator temperature and decreasing the cooling water temperature (open-cycle cooling from an underground well was used). The major concern for the solar air-conditioning systems is mainly after applying serious energy conservation measures and thermal insulation to the building. There is certain threshold value for system operation and below that limit the system should not operate or it will be wasting electrical energy not saving it.

Experience with a sun tracker system

A sun tracking system for use with various dimensioned collectors or platforms is discussed. Sun position sensing is successfully performed using phototransistors mounted in a simple structure. Some problems associated with this technique which were successfully overcome are mentioned. An electrical circuit block diagram with description is given as well as the tracking system's performance when connected to a 2.34-m 2 cylindrical parabolic collector. With this arrangement, the tracker consumes approx. 1 W of electrical power which is supplied by a small panel of solar cells with a rechargeable battery as a back-up and night time supply.

Thermal analysis of black liquid cylindrical parabolic collector

In the present paper a simple theoretical analysis and an experiment are carried out for a modified concentrating collector which consists of a cylindrical parabolic reflector, a transparent glass tube centered along the focal line, and a highly absorbent black liquid which flows in the glass tube to directly absorb the concentrated solar beam radiation. The analytical results are presented in normalized form and proved to be in very good agreement with the experimental results.

Performance analysis of a cylindrical parabolic focusing collector and comparison with experimental results

The efficiencies for focusing collectors which consist of a cylindrical parabolic reflector and a collector tube surrounded by a transparent envelope and which heat a fluid flowing through the collector tube have been predicted using heat transfer analytical methods. The analysis considers visible radiation transfer, IR radiation exchange, conductive and convective losses and energy transferred to a fluid flowing through the collector tube. The collector may have a tilted north-south axis, an east-west axis or it may fully track the Sun and geometric parameters associated with tracking the Sun are considered. Predicted results are in excellent agreement with recent collector performances measured using Sandia Laboratories' collector test facility.