碟式聚光太阳热发电技术

太阳热发电技术是利用太阳集热器把太阳能聚集起来,将工质加热到一定的温度,驱动热机带动发电机发电。由于整个系统的热源来自太阳能,所以称为太阳热发电技术。太阳能热发电系统一般由聚光系统、集热系统、热传输系统、蓄热贮能系统、热机系统等组成。当前太阳热发电技术主要有以下5种:(1)中央塔式(2)槽式(3)单碟独立电站和碟群体系(4)太阳烟囱(5)太阳池。本文通过介绍国外碟式太阳热发电技术的现状及发展趋势,提出发展我国碟式热发电技术的建议与思考。1碟式太阳热发电技术的历史与现状a.碟式热发电系统现代碟式太阳能热发电技术在20世纪70…     

Solar thermal storage systems using phase change materials

Using Fourier series expansion of the involving temperatures and the forcing parameters i.e. the solar radiation and the ambient temperature, an iterative procedure has been developed to solve the heat transfer problem with moving boundaries. Calculations specific to a typical summer and winter day in Delhi have been presented for a numerical appreciation of the developed analysis. Experiments have been performed to validate the developed theoretical analysis. A good agreement is seen between theoretical and experimental results with in the domain of the applicability of theory.     

Optimum power from a solar thermal power plant using solar concentrators

In this paper, the optimum temperature of operation of a solar concentrator and thus the maximum power obtained from a solar thermal power plant has been calculated. Results are plotted graphically and discussed.     

Detailed optical and thermal analysis of trough-like concentrators using tubular absorbers

A detailed analysis for studying the optical and thermal properties of trough-like concentrators using tubular absorbers is presented. Effective emissivity as a function of number of reflections, acceptance angle, emittance from reflector and aperture, and wall angle has been evaluated. Effective emissivity ε_eff increases with an increase in the concentration factor. Angle factor as a function of wall angle has also been calculated. Variations of collector and thermal efficiencies with ε_eff have been predicted. The paper includes graphs to aid in the design of trough-like concentrators.     

Solar flux distributions from circular cylindrical concentrators

Solar flux distributions produced by circular cylindrical concentrators have been determined. An integral relationship for evaluating the energy density distribution on receivers of arbitrary shape has been developed. The solar intensity distributions have been calculated for flat and cylindrical receivers. The developed formulae are applied to uniform and non-uniform source intensity distributions. The effect of longitudinal defocussing on the intensity distributions on receivers has also been considered. In case of cylindrical receivers, the local concentration decreases with an increase in the radius of receiver as well as with rim angle β of the receiver.     

Solar thermal electric power systems in Japan

The major subjects of this paper are to report the outline of the recent basic research and technical development for solar thermal electric power systems in Japan. Solar thermal electric power systems are presently being developed as one of the most important systems in Sunshine Projects which were initiated in 1974 to develop the utilization systems of new energy resources. Conceptional designs of solar thermal power systems were already done on the basis of the results of the supporting researches and two pilot plants of solar thermal electric power systems of a capacity of 1000 kWe are under construction on the basis of the conceptional and detailed designs and would be constructed by 1981. The present conditions of these pilot plants and the major researches which are thought to be most important subjects in the basic researches and technical developments for solar thermal electric power systems are described in this paper.     

Solar thermal systems: Advantages in domestic integration

Pollution represents a major issue, and so does the ability to utilize, when available, renewable energy sources instead of traditional ones. If, on the one hand, it is possible to utilize renewable energy sources in many contexts, on the other hand they are not exploited because of the high cost of the initial investment needed for the installation of these systems, above all when domestic usage is taken into account.This paper proposes a quantitative approach able to forecast the profitability of the introduction of domestic solar thermal systems operating in parallel with the most common systems for heating domestic sanitary water. The approach is developed firstly by analyzing the most common system for heating sanitary water from both the engineering and economic point of view. At the same time the technical–economic solutions related to the most commercialized solar heating systems, and their compatibility with the most common traditional heating systems are studied. This is carried out by using a differential economic analysis of different possible scenarios in which different matches between traditional and solar heating systems are shown, and their profitability is assessed as a function of the power installed.     

大功率柴油机双段喷射的仿真研究

以16V280ZJ型柴油机为例,通过建立该柴油机电子喷射系统的整机模型,对直喷柴油机典型的双段喷射方案进行了燃烧过程仿真计算。计算过程参数通过与试验结果的对比进行了修正,计算结果有效地反映了两次脉冲喷射的油量分配比例和喷射脉冲间隔角对排放特性及燃油经济性的影响规律,并以改善柴油机排放和降低压力升高率为目标,找出了双段喷射模式下的喷油规律优化方案。     

Optical and thermal analysis of trough-like concentrators

This paper presents an investigation of the optical and thermal properties of trough-like concentrators. The radiative and convective heat transfers through a trough concentrator have been evaluated. A simple analytical technique for calculating the average number of reflections and optical losses has been developed. Effective emissivity ε_eff and the collector efficiency η increase with an increase in the concentration factor. Further, the efficiency decreases with an increase in the temperature of the absorber.     

Solar ICS systems with two cylindrical storage tanks

Two types of ICS solar water heaters designed, constructed and tested. The systems consist of two cylindrical storage tanks, which are connected in series and are horizontally incorporated in a stationary asymmetric CPC type mirror. The efficient operation of the system is due to the thermal losses suppression of the two inverted cylindrical surfaces and the effective use of the two tanks during sunshine period. Low cost and durable materials are used to construct the systems. The mean daily efficiency and the thermal performance of the hot water storage during night are calculated from outdoor experimental data. The results show that the proposed ICS systems are efficient and suitable for practical use as DHW systems.     

Optical and thermal properties of compound parabolic concentrators

Compound Parabolic Concentrators (CPC) are relevant for solar energy collection because they achieve the highest possible concentration for any acceptance angle (tracking requirement). The convective and radiative heat transfer through a CPC are calculated, and formulas for evaluating the performance of solar collectors based on the CPC principle are presented. A simple analytic technique for calculating the average number of reflections for radiation passing through a CPC is developed; this is useful for computing optical losses. In most practical applications, a CPC will be truncated because a large portion of the reflector area can be eliminated without seriously reducing the concentration. The effects of this truncation are described explicitly. The paper includes many numerical examples, displayed in tables and graphs, which should be helpful in designing CPC solar collectors.     

A solar engine using the thermal expansion of metals

A thermal engine with solid metal as the single-phase working substance is described. The engine can consist of nothing more than a metal tube mounted in a bearing at either end so that it is free to rotate about its axis, with a flywheel mass at its midpoint. When the tube is heated on its upper surface, the region of its maximum compressive bending stress, it will rotate and produce steady power. Compared to engines using a gas or a liquid as the working substance, this engine has the disadvantage of low thermal efficiency but the advantage of simplicity. The solid metal phase engine may be useful for converting solar energy into small amounts of mechanical energy in underdeveloped regions of the world.     

Solar thermal electric power systems: Comparison of line-focus collectors

Three types of line-focusing collectors: parabolic though, fixed slats with movable absorber and movable slats with fixed absorber, are evaluated to find those systems that are capable of producing the lowest costs of electrical energy. Minimum costs per kW-hr are found using sequential optimization techniques that consider variations in rim angle, reflectance, aperture width, length, orientation, tracking, contour error, slat width, slat curvature, tangent slat angle, slope, installation methods, materials, fabrication methods, absorptance, emittance, cover transmittance, field shape, layout, pipe sizes, insulation thicknesses and turbine-generator-cooling lower efficiencies and designs. This approach provides a uniform treatment of both cost and performance for a solar thermal electric power system. This uniform treatment of solar thermal electric power systems for all collector types insures that valid comparisons are made.     

直喷式柴油机两段喷射计算模拟

以KIVA-3为计算平台，计算模拟4气门直喷式柴油机不同预喷油提前角的两段喷射燃烧历程。其结论是：150CA BTDC以后的预喷提前角，其预喷与主喷柴油都以扩散燃烧为主；预喷柴油燃烧与缸内流动的共同作用，使缸内温度、质量分数分布更加复杂。氧质量分数分布差异是不同预喷油提前角对主喷燃烧放热率影响的主要因素。     

The effect of using two PCMs on the thermal regulation performance of BIPV systems

Building Integrated Photovoltaics (BIPVs) is one of the most promising applications for Photovoltaics (PVs). However, when the temperature in the BIPV increases, the conversion efficiency deteriorates. A PV/PCM system using Phase Change Materials (PCM) for BIPV thermal control has been experimentally and numerically studied previously. One of the main barriers for this application is how to improve the low thermal conductivity of the PCM in order to achieve a quick thermal dissipation response with longer thermal regulation in PVs. Although the metal fins inserted inside the PCM can improve the heat transfer, the thermal regulation period declines as the volume of the PCM is substituted by the metal mass of the PV/PCM system. A modified PV/PCM system integrated with two PCMs with different phase transient temperatures for improving the heat regulation needs to be investigated. The use of combinations of PCMs, each with a set of different phase transient temperatures, is expected to enhance the thermal regulation effect of the PV/PCM system and lengthen the thermal regulation time in PVs. In this study a developed PV/PCM numerical simulation model for single PCM application has been modified to predict the thermal performance of the multi-PCMs in a triangular cell in the PV/PCM system. A series of numerical simulations tests have been carried out in static state and realistic conditions in UK. The thermal regulation of the PV/PCM system with a different range of phase transient temperature PCMs has been discussed.     

Activated carbon + HFC 134a based two stage thermal compression adsorption refrigeration using low grade thermal energy sources

A thermodynamic analysis is presented for the two stage thermal compression process for an adsorption refrigeration cycle with HFC-134a as the working fluid and activated carbon as the adsorbent. Three specimens of varying achievable packing densities were evaluated. The influence of evaporating, condensing/adsorption and desorption temperatures was assessed through three performance indicators, namely, the uptake efficiency, the coefficient of performance and the exergetic efficiency. Conditions under which a two stage thermal compression process performs better than the single stage unit are identified. It is concluded that two stage thermal compression will be a viable proposition when the heat source temperature is low or when adsorption characteristics are weak or when adequate packing densities are difficult to realize.     

Investigation in utilizing paraboloid concentrators for thermal perforation of metals

Paraboloid solar concentrators are used to investigate the feasibility of using concentrated solar energy to perforate metals. An electroplated paraboloid was used as the test rig, and experiments were conducted on the variation of temperature at the absorber location (focal point). Given the size of the aperture of the paraboloid, a concentration factor of around 3000 was achieved and temperature in excess of 840 °C was reported. Such temperatures are enough to melt most nonferrous alloys, and given the size of the absorber area (focal point size) the power developed are comparable to continuous-pulse laser machining are expected.     

Performance model for two-stage optical concentrators for solar thermal applications

A performance model has been developed for evaluating benefits associated with the addition of a nonimaging secondary concentrator to a conventional paraboloidal solar dish. The model uses a Monte Carlo ray-trace procedure to determine the focal plane distribution as a function of optical parameters and, by evaluating the trade-off between thermal losses and optical gain, calculates the corresponding optimized concentration and thermal efficiency as a function of temperature, both with and without the secondary. These comparative optimizations, carried out over a wide range of design parameters, show that the efficiency of a two-stage concentrator is always greater than that of a single stage if all other design parameters are the same. For example, for a reference design corresponding to a dish with a focal length to diameter ratio of 0.6 and a characteristic slope error of 5 milliradians operated at a receiver temperature of 1000°C, the optimized efficiency with a secondary is 0.70 compared to 0.59 for the primary alone. At fixed focal ratio, the relative performance advantage with a secondary increases, if either the temperature or the primary slope error or both, are increased, whereas it decreases if they are decreased. However, the advantage remains significant at temperatures above 400°C, even in the “high performance limit” of slope errors <2 milliradians.     

Solar heating using common building elements as passive systems

The paper reviews the first steps of a study on use of windows as passive solar air collectors, offsetting naturally the excess of heat in the thermal mass of the building itself, and of vertical solar collectors, with air as working fluid, and with storage systems designed as intergral parts of the building, incorporated in the concrete elements. Some examples of architectural solutions combining these principles in a modular design are suggested. Incorporated storage examples using ceilings and partitions with appropriate air transfer through them are proposed. The relevant thermal analysis on the use of windows as passive solar collectors is based on the Total Thermal Time Constant (TTTC) Method, developed by two of the authors. An analysis is also presented for a vertical flat-plate solar collector using air as working fluid and capable of integration in a blank (windowless) part of an external wall. Design and dimensioning of the fin surface are proposed for heat transfer from collector surface to fluid. The final section deals with experimental model based on the above principles and combining a vertical collector and heat storage for use in daytime and at night, respectively. The model was so dimensioned as to represent a 1:1 unit in modular building design. An overall thermal efficiency of about 18 per cent was obtained.