太阳能空气-热水两用集热器设计与实验研究

提出一款针对北方农宅应用的太阳能空气-热水两用集热器,采暖季用之加热空气进行热风采暖、非采暖季用之加热热水提供生活热水。并根据ASHRAE标准,对集热器加热空气和热水的热性能分别进行稳态工况测试。结果表明,加热空气时,当空气流量从80 m~3/h增至120 m~3/h,最大热效率从0.5148增至0.5591。集热器两端压力仅损失约100 Pa。加热热水时,最大热效率可达0.6506。该集热器可大大提高全年利用率,经济适用,适合在北方农村推广,解决农户采暖和生活热水的不同需求。     

槽式太阳能供热光伏系统集热器集热性能的实验研究

文章基于沧州地区的气候特点,通过实验分析了传热工质进口温度、直射辐射量对槽式太阳能供热光伏系统中集热器集热性能的影响情况。实验结果表明:沧州地区3月份晴朗天气条件下,槽式太阳能供热光伏系统的集热效率为0.35～0.65;当运行温度为20～100℃时,随着传热工质入口温度逐渐升高,槽式太阳能供热光伏系统中集热器的集热效率和火用效率均得到明显提高;直射辐射量的增大,会导致槽式太阳能供热光伏系统中集热器的集热效率和火用效率随之升高。     

双层中空玻璃盖板太阳能平板集热器集热性能实验测试研究

文章提出了一种采用双层中空玻璃盖板且吸热板表面镀有蓝钛膜的太阳能平板集热器,并在不同的工质流量和进口温度条件下对该集热器的集热性能进行实验测试,得到该集热器的瞬时集热效率曲线。研究结果表明,该集热器的集热效率曲线截距为0.83,热损系数为3.1 W/(m~2·K),该集热器的集热性能明显优于其他结构的平板集热器。此外,文章建立了该集热器的数学模型,得到该集热器的总热损系数和热迁移因子的数学表达式。     

非成像聚光太阳能集热器供暖应用研究

基于非成像聚光集热器的太阳能供暖系统相比于传统的供暖系统具有突出的优势,非成像聚光集热器集三种常见集热器(平板型、真空管、聚光集热器)优点于一身。文中详细介绍了非成像聚光太阳能集热器的运行原理及特点,并对其性能进行了测试分析,该集热器的时间常数为450 s,最大瞬时效率为59. 31%。同时结合典型的工程应用案例对非成像聚光太阳能集热器+电辅热及非成像聚光太阳能集热器+空气源热泵供热系统分别进行了分析和总结。     

蓄能型空气式太阳能集热器热效率研究

针对以水为传热介质真空管太阳能集热器存在的低温冻裂、过高温炸裂和使用间断性等问题,将太阳能集热器的真空管进行改进设计,并在其中设置相变蓄能棒,采用空气为传热介质,研制了一种新型空气式太阳能集热器。实验测试表明：在平均辐照强度为727 W/m2条件下,可延长供热3 h,并随着辐照强度增加供热时间延长;无相变材料的真空管太阳能集热器平均集热效率为36%,相变蓄能棒平均等效集热效率为60%,新型蓄能型空气式太阳能集热器综合集热效率为96%;与传统以水为介质的内插式真空管太阳能集热器平均集热效率为58%相比,该新型集热器集热效率有显著提高。     

遮阳板式太阳能相变集热器的实验研究

研制了遮阳板与集热器一体化的新型太阳能相变集热器,通过搭建的实验测试平台对其集热性能及隔热特性进行了实验测试。该建筑构件具备遮阳隔热及太阳能集热功能,为在建筑中高效利用太阳能,实现太阳能与建筑一体化提供一种新的工程应用模式。通过实验测试,对该集热器在不同工况下的集热性能、隔热特性及其影响因素进行了系统分析研究,提出了该集热器的累积集热量、集热效率、隔热特性等性能评价指标。测试结果表明,遮阳板式太阳能相变集热器的平均集热效率可达12.3%,隔热效果优于普通遮阳板。     

单、双风道折形折流板式空气集热器对比分析

为了进一步提升太阳能空气集热器的集热效率,文章在单风道折形折流板空气集热器的基础上,提出了双风道折形折流板式空气集热器,通过在集热器中加入回风通道,并按照一定的比例将新风和回风进行配比,以增加集热器的热利用率。研究结果表明,双风道折形折流板式空气集热器的集热效率高于单风道折形折流板空气集热器,双风道折形折流板式空气集热器的压损系数低于单风道折形折流板式空气集热器;随着进口温度逐渐升高,两种空气集热器的集热效率均逐渐下降,单风道折形折流板式空气集热器全新风和全回风集热效率分别为53.35%,49.17%;在全新风工况下,双风道折形折流板式空气集热器的集热效率最高,为59.89%,在全回风工况下,双风道折形折流板式空气集热器的集热效率最低为59.09%;随着进口风速逐渐增大,双风道折形折流板式空气集热器的集热效率和压力损失均逐渐上升,该集热器的最高集热效率为70.49%;冬季,当太阳能空气供暖系统的进口风速为0.3 m/s时,室内的舒适度最佳。     

利用条缝射流强化无盖板型太阳能集热器性能

为提升无盖板型太阳能空气集热器热性能，设计一种条缝射流型太阳能空气集热器，并利用数值模拟和实验验证对其热性能进行分析。集热器内部流动及换热特性的模拟结果表明，利用圆孔和挡片形成的条缝射流能对集热板形成有效覆盖，进而提高进气与集热板的对流换热。射流条缝存在最优结构参数，当圆孔直径为25 mm时，条缝宽度在3 mm处接近最优；集热效率则随挡片直径的增大而增大，是由于射流贴附效应在变强。实验结果表明，条缝射流型集热器的全天热效率稳定且高效。当处理气量为39 m3/h时，该集热器全天热效率稳定在约48%，优于传统的无盖板渗透型太阳能集热器。     

多功能太阳能采暖集热器研究

本研究设计了一种可转换冬季与夏季功能的太阳空气集热器,该集热器的集热板为一组叶片,叶片由传动装置联接在一起,吸热板叶片可以转动,并且能够跟踪太阳能运行,最大限度吸收太阳辐射。吸热板背面涂以热反射涂层,夏季叶片翻转180,°反射红外辐射隔热降温。文章分析了影响太阳空气集热器的瞬时集热效率的各种因素,并对其热性能进行了试验。     

不同气候条件下平板太阳能集热器动态热性能的解析

利用一种可结合环境气象数据等参数来计算平板太阳能集热器一段时间内集热效率动态分布的数学模型,对比研究了不同气候区典型城市年平均效率及逐月效率分布的差异,分析了入口温度与环境温度温差、太阳辐照度对集热器全年瞬时效率的影响,并将该模型与《太阳能供热采暖工程技术规范》中的集热效率计算方法进行了对比。通过分析说明了在研究太阳能集热器的集热效率时,应结合气象条件和运行参数动态进行研究分析,冬季的瞬时效率并非总是低于夏季。该模型可更精确地模拟实际工程情况来计算集热器平均效率,是一种更加适应不同气候地区的太阳能集热器热性能模型,为工程实例中平板太阳能集热器平均效率的选取提供了参考。     

Solar Collector Parameter Identification by Step Input Test Procedure

A fast test procedure is introduced for identification of solar collector parameters. The tests were accomplished by exposing the collector to the sun and then shielding it from the sun, with the flow rate and inlet temperature held constant. The transient heat up and cool down data points were used to identify the collector parameters specified for the first order and second order models. The experimental results of the collector performance by the step input test procedure were found in fairly good agreement with those of standard steady-state procedure.     

Design and analysis of solar thermoelectric power generation system

This article reports on the design and performance analysis of a solar thermoelectric power generation plant (STEPG). The system considers both truncated compound parabolic collectors (CPCs) with a flat receiver and conventional flat-plate collectors, thermoelectric (TE) cooling and power generator modules and appropriate connecting pipes and control devices. The design tool uses TRNSYS IIsibat-15 program with a new component we developed for the TE modules. The main input data of the system are the specifications of TE module, the maximum hot side temperature of TE modules, and the desired power output. Examples of the design using truncated CPC and flat-plate collectors are reported and discussed for various slope angle and half-acceptance angle of CPC. To minimize system cost, seasonal adjustment of the slope angle between 0° and 30° was considered, which could give relatively high power output under Bangkok ambient condition. Two small-scale STEPGs were built. One of them uses electrical heater, whereas the other used a CPC with locally made aluminum foil reflector. Measured data showed reasonable agreement with the model outputs. TE cooling modules were found to be more appropriate. Therefore, the TRNSYS software and the developed TE component offer an extremely powerful tool for the design and performance analysis of STEPG plant.     

Detailed comparison of the performance of flat-plate and vacuum tube solar collectors for domestic hot water heating

The performance of a DHW system fitted with flat-plate and vacuum collectors has been analysed. Simulations were carried out on the basis of equal aperture or gross areas of basis using TMY data for hour-by-hour dynamic simulation generated for 1036 sites located in different regions of the world. The performance indicators of solar fractions and number of days were determined for specific water mean temperatures in the storage tank of 37 °C, 45 °C and 55 °C. It has been shown that vacuum tube collectors provide slightly better DHW performance indicators than typical flat-plate collectors having the same aperture area. However, since the space that needs to be provided and directly or indirectly paid for is what matters to the user of solar heating systems, the analysis was also carried out on equal gross area basis; on this basis, the advantages of using vacuum collectors are not obvious.     

太阳能热风发电系统集热器热物理模型及分析

集热器是太阳能热风发电系统的重要组成部分.文章建立了集热器的热物理模型,分析了集热器各部分的传热过程和集热器效率的计算方法.介绍了集热器热损失的求解方法,即利用热阻法求解和根据经验公式求解.     

Solar thermal energy combined with humidification–dehumidification process for desalination brackish water: Technical review

Water scarcity has become a chronic problem aggravated by climate change. One third of the world's population already lives in areas suffering moderate to high water stress; some 1.5 billion people lack ready access to drinking water. Desalination is in the course of becoming a major source of fresh water by tapping into the vast reserves of seawater and brackish water. Large scale desalination plants use either thermal or membrane processes which consume a great deal of energy. Economic implications of large energy requirements coupled with environmental concerns about carbon emissions spurred a growing interest in developing desalination processes that use renewable energy sources. Among these processes the humidification dehumidification (HD) of air, using solar energy, is a simple technology particularly suited for regions in developing countries where there is very low infrastructure and unskilled manpower.     

Development of advanced solar assisted drying systems

The Solar Energy Research Group in the Universiti Kebangsaan Malaysia has been set-up more than two decades ago. One of the activities is in the field of solar thermal process, particularly in development of solar assisted drying systems. Solar drying systems technical development can proceed in two directions. Firstly simple, low power, short life, and comparatively low efficiency-drying system. Secondly, the development of high efficiency, high power, long life expensive solar drying system. The group has developed four solar assisted drying systems namely (a) the V-groove solar collector, (b) the double-pass solar collector with integrated storage system, (c) the solar assisted dehumidification system for medicinal herbs and (d) the photovoltaic thermal (PVT) collector system. The common problems associated with the intermittent nature of solar radiation and the low intensities of solar radiation in solar thermal systems can be remedied using these types of solar drying systems. These drying systems have the advantages of heat storage, auxiliary energy source, integrated structure control system and can be use for a wide range of agricultural produce.     

Performance prediction of a solar water heater with intermittent output

A solar water heater constructed from readily available materials in the countryside has earlier been discussed in the continuous flow mode. Water flows in the tubes at a constant rate throughout the day. In any realistic situation, however, the rate of flow will be a function of time depending on the requirements of the user. In this paper a theoretical method is developed which is used to predict the outlet water temperature of the time dependent flows. The effect of various design parameters like the position of the water pipes, choice of sensible heat storage material etc. are discussed taking different functions of rate of flow. The inexpensive water heater can provide hot water for a small household even in the late evening hours provided no heat is withdrawn from the system during the day time.     

建筑物平屋顶圆柱吸热体真空管集热器的能量收益研究

对建筑物平屋顶水平面上南北向和东西向放置圆柱形吸热体真空管集热器的日、年能量收益,以及上述两种集热器管中心距与能量收益的关系进行了分析研究。结果表明:冬季水平面上东西向管集热器比南北向管集热器的日能量收益明显要高。水平面上南北向管集热器和东西向管集热器在管中心距等于2.0D时,可分别得到管中心距为5.0D时年能量收益的91%和96%。     

LONG TERM PERFORMANCE OF A SHADED COLLECTOR FIELD

A numerical model is presented to estimate the monthly average daily solar radiation absorbed by a collector field, with taking into account the effect of shading of the various collectors on each others. The field consists of N_Y rows of collectors, spaced uniformly by a distance Δy from each other, and each row contains. N_X collectors. Each collector has a length L and width W and tilted towards the equator by an angle equals to the latitude angle of the location. The model accounts for collectors with one or two glass covers. Calculations are carried out using the model at various parametric values. The results are used to establish charts which can be used for a collector field of any dimensions and located at any location on the surface of the earth. A case study is presented to demonstrate the application of results of the present model to determine the optimum spacing between rows and the monthly average daily solar thermal energy absorbed by the collector field.     

Comparative analysis of direct-absorption parabolic-trough solar collectors considering concentric nanofluid segmentation

Nanofluids have been actively used in direct-absorption solar collectors. In a direct-absorption parabolic-trough solar collector (DAPTSC) for medium-high temperature regime, the nanofluids used to be contained in a transparent glass receiver located at the focal line of a parabolic mirror so that the solar radiation is concentrated to the glass receiver and absorbed volumetrically inside the collector. In order to further increase the thermal efficiency of a DAPTSC, we propose to insert an extra glass tube inside the nanofluid so that the nanofluid is separated into two concentric segmentations (ie, an inner section and an outer section), and apply a nanofluid of lower concentration in the outer section while a nanofluid of a higher concentration in the inner section. The proposed idea is numerically tested on four pairs of DAPTSCs (the variants obtained depending on whether there is a vacuum envelope and whether there is a reflective semicylindrical coating on the receiver). The results show that at the same particle concentration parameter, the DAPTSCs with two concentric segmentations of nanofluids outperform those with one uniform nanofluid for all configurations considered in this work. For a transparent case without an envelope, this efficiency increase is as high as 12.5% point when the inlet temperature is 350 K. In addition, parametric studies are performed for this best configuration to evaluate the effect of absorption coefficient, mass flow rate, collector length, solar irradiance, and convection heat transfer coefficient on the collector performance.