Maximum Work Rate Extractable from Energy Fluxes

A general formalism is developed to evaluate the amount of work extractable from energy fluxes. It covers nonequilibrium cases when the concept of exergy is not relevant. The rate of work deficiency, which has been previously introduced as the total loss of exergy, is defined here as the total loss of work, which would have resulted if all the work were lost to the environment. New performance indicators are proposed. First, the work content factor gives the proportion of extractable work in a given amount of energy. Second, the work deficiency factor is a measure of the potential of improvement for the operation of energy conversion systems. Previous results reported in literature are particular cases of the general results obtained here. The formalism is used to evaluate the work rate extractable from the solar energy flux. Results are shown in cases where solar radiation interacts with materials without energy bandgap (metals) and with energy bandgaps (semiconductors), respectively.

Research of Al2O3 and SiO2 fibers based heat protective materials behavior of based under the effect of concentrated solar energy flux

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Usage of solar shading devices to improve the thermal comfort in summer in a Romanian PassivHaus

The global trend is to increase the thermal comfort in all kinds of buildings, residential and non-residential. At the same time, minimization of energy consumption and improved building sustainability must be achieved. Only precise calculations can keep the balance between maximizing comfort and minimizing energy consumption. The PassivHaus (PH) is a special type of building with low heating energy consumption that fulfills special requirements defined by the Passivhaus Institut of Darmstadt, Germany. The PassivHaus concept has been successfully implemented in climates other than that of Germany. However, current practice in Southern European countries shows that PHs may exhibit overheating in the hot season, a phenomenon which is not very often encountered in Germany. Shading devices may be considered in these southern countries to improve the thermal comfort in PHs during summer. A model of the AMVIC PH office building located near Bucharest, Romania, has been developed using Simergy and EnergyPlus software. The model was validated and calibrated using measured data during summer. Measurements have been used to estimate the classical thermal comfort indices such as predicted mean vote and predicted percent of dissatisfied. Simulations have been performed to study the effect on thermal comfort of several shading devices, such as exterior blinds, exterior shades, and overhangs. Exterior blinds and exterior shades are generally more efficient than overhangs when the results are discussed with reference to transmitted solar energy flux through the windows.

Theoretical and Experimental Optical Evaluation and Comparison of Symmetric 2D CPC and V-Trough Collector for Photovoltaic Applications

This paper presents theoretical and experimental optical evaluation and comparison of symmetric Compound Parabolic Concentrator (CPC) and V-trough collector. For direct optical properties comparison, both concentrators were deliberately designed to have the same geometrical concentration ratio (1.96), aperture area, absorber area, and maximum concentrator length. The theoretical optical evaluation of the CPC and V-trough collector was carried out using a ray-trace technique while the experimental optical efficiency and solar energy flux distributions were analysed using an isolated cell PV module method. Results by simulation analysis showed that for the CPC, the highest optical efficiency was 95% achieved in the interval range of 0° to ±20° whereas the highest outdoor experimental optical efficiency was 94% in the interval range of 0° to ±20°. For the V-tough collector, the highest optical efficiency for simulation and outdoor experiments was about 96% and 93%, respectively, both in the interval range of 0° to ±5°. Simulation results also showed that the CPC and V-trough exhibit higher variation in non-illumination intensity distributions over the PV module surface for larger incidence angles than lower incidence angles. On the other hand, the maximum power output for the cells with concentrators varied depending on the location of the cell in the PV module.

Experimental Study on the Heat Exchanger Performance of Parabolic Trough Solar Water Heater

This paper introduces a new type of solar water heater——Parabolic trough solar water heater,the biggest feature of the solar water heater is that the parabolic trough reflector can reflect light onto the tube with reflective principles,which may lead to lots of advantages,such as more strong solar energy flux density,fewer losses,fewer tubes used.In a word,the cost is reduced while the performance is guaranteed.On this basis,we built a collector area of about 1.54 square meters of parabolic trough solar water heaters bench and made experiments to test.Instantaneous average efficiency and daily average efficiency of the water heater can be calculated.Efficiency curve can also be generated.Meanwhile we measured the heat loss coefficient of the water heater.The results showed that the daily average efficiency of the parabolic trough concentrating solar collector is between 30% and 50%,while at higher temperatures the collector showed its good insulation properties.

RAY-TRACING ANALYSIS OF A TWO-STAGE SOLAR CONCENTRATOR

A ray-tracing analysis was conducted on a 2-stage solar concentrator made of two parabolic mirrors created by Lunenburg Industrial Foundry & Engineering (LIFE). The effects of the secondary mirror’s focal length, the distance between the secondary mirror and the target, and the misalignment with the sun were studied. The focal length of the secondary mirror determines the maximum local solar energy flux Φ that can be achieve on the target. For the optimal focal length of 157.9ʺ, a maximum Φ = 1.2 x 104 MW/m2 was achieve compare to Φ = 1680 MW/m2 for the initial LIFE’s focal length of 158.8125ʺ. The concentrator concentrates all the incident energy from the sun on the target, and that independently of the secondary mirror’s focal length (within the range studied), as long as the target position is within an 11 cm zone. Small misalignments in the order of ±0.2° would bring the concentration efficiency to zero.