Dynamic modelling and verification of a flat-plate solar collector

In the modelling of flat-plate solar collectors the dynamic effects have often been neglected. But because the solar collector is inherently exposed to variable weather conditions, its dynamics may be important to the design and control.It is demonstrated that it is not necessary to ignore the dependence of the various temperatures on the location in the direction of flow (which is often done to avoid complications) provided the model is developed in the frequency domain.The linearised model has been verified in the frequency domain by means of a least squares estimator. The verification was performed with a part of a full-size collector, as has been applied in some solar houses, and an artificial sun. It is concluded from the results of the verification that the developed model describes the collector dynamics quite satisfactorily. The differences between the theoretical and estimated heat resistances was about 10 per cent. The verification and estimation procedure proved to be a useful tool for comparing various collectors because the collector has to be fitted with only two temperature sensors.It is shown that the simple models have been discussed in the literature give responses which are not representative of the collector's dynamics. For well-designed collectors a simplified model is derived. Finally, some desirable sampling rates are given.     

Dynamic simulation and parametric sensitivity studies on a central solar domestic hot water system

A computer simulation program for a central solar domestic heat water (DHW) system has been developed and validated by comparing it with the actual performance data obtained from a real-life system. A computer simulation language, CSMP, was used for the simultaneous solution of the differential equations describing the system. The program was developed from basic principles and defined parameters. It was utilized to study the dynamic behavior of the system and to perform parametric studies to determine the effects of various system parameters on its performance.Parametric sensitivity studies were carried out to determine the response of the central solar DHW system performance to the following parameters: flow rate of heat-exchange fluid in the solar collector loop, consumption rate in the consumer loop, start-up time (i.e., activation of the collector loop circulation pump), and storage tank capacity.The concept of consumption management is analyzed and discussed in order to emphasize the fact that solar loop productivity, both qualitative and quantitative, is not independent of load. As a corollary, we show that it is possible, when the situation allows, to maximize solar loop productivity by controlling the consumer loop consumption schedule.     

Performance of a flat-plate solar collector

The design of a simple solar collector made from corrugated, galvanized-iron sheet is given. Its performance during summer at Allahabad, India, at various flows is presented. To obtain hot water at temperatures higher than 170 deg F, temperature being averaged over an eight-hour period, a flow of only about 1 lb/hr-ft² should be allowed. The supply of hot water from the collector will be used in an absorption-type solar cooler.     

基于高温工质R245fa的太阳能平板集热器集热过程动态模拟

提出了一种以R245fa为循环工质的气液分离双级太阳能集热系统.对第一级集热系统的集热过程进行了动态数值模拟.结果表明,系统的集热过程受太阳辐射强度的影响最大,受系统肩动温度的影响较小.当系统从环境温度启动达到工质蒸发状态时.减少循环工质的质量或增大集热面积均能有效地减少系统的运行时间,而增大系统集热面积是较佳方案.     

Experimental and numerical investigation of a flat-plate solar collector

In the present paper we present an experimental analysis and a thermal and hydrodynamic modelling of a newly designed flat-plate solar collector characterized by its corrugated channel and by the high surface area directly in contact with the heat transport fluid. The thermal and hydrodynamic modelling of the collector has been performed by means of the Finite Element Method (FEM), validated with analytical results for a well-known fin-and-tube type solar collector. The thermodynamic efficiency of the collector is analyzed by means of its experimental heating curves. The yield of the new collector has been compared to a previously existing commercial collector of related geometry but with less area in direct contact with the heat transport fluid. The experimental results are seen to adequately fit the simulation predictions, and a methodology to use in order to compute the parameters characterizing the thermal behavior of the collector is introduced.     

Thermodynamic optimization of solar flat-plate collector

Second-law modeling of flat-plate collectors is performed with the objective of describing collector performance when entropy generation is minimum. Effects of irreversibility are demonstrated. Factors mostly effecting the generation of entropy are discussed.     

一种新型平板式太阳能集热器

本产品是采用新型合金材料和特殊结构制造的平板式太阳能集热器。它既可安装成建筑物瓦面和幕墙,也可用于热水工程和家用太阳能热水器,实现了建筑瓦面与散户安装的统一和兼容。     

Model calculations on a flat-plate solar heat collector with integrated solar cells

A detailed physical model of a hybrid photovoltaic/thermal system is proposed, and algorithms for making quantitative predictions regarding the performance of the system are presented. The motivation for the present work is that solar cells act as good heat collectors and are fairly good selective absorbers. Additionally, most solar cells increase their efficiency when heat is drawn from the cells. The model is based on an analysis of energy transfers due to conduction, convection and radiation and predicts the amount of heat that can be drawn from the system as well as the (temperature-dependent) power output. Special emphasis is laid on the dependence of the fin width to tube diameter ratio. We attribute values to the model parameters, and show that hybrid devices are interesting concerning system efficiency as is also confirmed by previous experiments. Possible applications of such systems are also proposed.     

Techno-economic model of a solar still coupled with a solar flat-plate collector

In this paper, a techno-economic model has been developed for a solar still coupled with a flat-plate collector through a heat-exchanger. The model is based on the establishment of periodic steady-state conditions. The economic criterion used in the model is based on the least cost of a unit mass of distilled water evaluated from the life-cycle costing of the system. To evaluate the model, numerical calculations have been made corresponding to the climate of Delhi (India). It is concluded that the addition of a solar collector enhances the distillate yield; however, this is not always economical. This system therefore needs careful and economic system design.     

平板式太阳能空气集热器流道改进的试验研究和数值模拟

对传统平板式太阳能空气集热器的流道进行了改进,把对角型进出口流道改为多进出口式流道。对改进的集热器的性能进行了试验测试。新的进出口流道消除了吸热板和空气换热不均的现象,出口温度提升明显。在相同条件下,集热器的瞬时效率增加约20%。用CFD方法对集热器内部的流场结构和传热进行的数值模拟对比表明,传统集热器内部存在流动死区,中心截面温度分布不均匀,吸热板上有局部的高温区域,改进后的集热器流场和温度场分布得较均匀。     

Performance of a thermal trap flat-plate solar energy collector

The performance of a thermal trap flat-plate solar energy collector has been investigated theoretically and validated experimentally, from the point of view of stagnation temperature. The theoretical model is based on the periodic solution of the heat conduction equation and takes into account the internal emission of the thermal trap material. The model explains the experimental measurements fairly well. It is found that the trap material should have an optimal thickness in order to obtain the maximum plate temperature.The thickness of the air gap between the trap material and the cover has only a very marginal effect on the stagnation temperature.     

Analysis and performance of flat-plate solar collector arrays

A new discrete numerical model is proposed to calculate the flow and temperature distribution in solar collector arrays. The flow nonuniformity, the longitudinal heat conduction, and the buoyancy effect are all taken into account in the analysis. The numerical results of pressure and temperature distribution are found in agreement with the experimental results. It is found that the flow nonuniformity has detrimental effect on the thermal performance of collector array.     

Heat transfer analysis of a flat-plate solar energy collector

A model is developed for the heat transfer in a flat plate solar collector with a rectangular channel for water or air flow. This 2-dimensional geometry offers the maximum area of contact between the fluid and the collecting surface exposed to the Sun. The analysis yields temperature and heat flow distributions in both dimensions of the collector. Thermal boundary layer development is investigated. Overall efficiencies are calculated for uniform solar heat influx with variable heat losses from the plate. The thermosyphonic effect, due to natural convection, is evaluated and the collector's geometry optimized with respect to this effect.     

一种新型的平板太阳能集热器

平板太阳能集热器就是让太阳光通过透明盖板,照在吸热板上,使光能变为热能,通过与吸热板紧密接触的管道,把热量传给水. 平板太阳能集热器的主要缺点是自然对流热损和辐射热损失大,理想的平板太阳能集热器就是要抵制自然对流热损失,同时降低辐射热损失.     

Domestic solar water-heating system with a thermal-trap flat-plate solar-energy collector

Based on the periodic solution of the heat conduction equation, an analysis has been developed to study the thermal performance of a simple domestic solar water-heating system consisting of a thermal-trap solar-energy collector, connected to a water tank. To study the effects of typical parameters such as the thickness of the trap material and the presence/absence of the glass cover on the thermal performance, numerical calculations have been performed to correspond to the daily variations of the ambient temperature and solar intensity on a typical cold winter day in New Delhi.     

平板型太阳集热器瞬时效率曲线的统一性分析

平板太阳能集热器的效率方程和对应的效率曲线是判断集热器热性能的重要依据,前人分别用3个不同方程和3条不同曲线定量地描述了集热器效率.文章阐释了3条曲线的异同点,并提出将3条太阳热水器瞬时效率曲线统一起来的具体解决办法.     

General thermal analysis of parallel-flow flat-plate solar collector absorbers

Improved equations are formulated for the transfer of heat in flat-plate solar collector absorbers, including a shape factor accounting for details of flow duct designs, and developing heat transport in the ducts. Approximate, analytical solutions are obtained in terms of perturbation series, which are applicable to practical collectors with lengths much greater than the distance between flow ducts.The primary result of the analysis is a universal-type design equation, or chart, which determines the collector efficiency factor for any duct design, heat transfer development, or other absorber-plate parameter. Collector performance is stated in terms of an effectiveness/number-of-transfer-unit relationship. Ease of use and utility of the design chart is illustrated by examples.