新型平板热管式太阳能PV/T集热系统的性能研究

文章搭建了新型平板热管式太阳能PV/T集热系统实验台,测试了该集热系统的热电性能。此外,建立了该集热系统的数学模型,并将该集热系统的测量结果和模拟结果进行对比分析,以验证该数学模型的准确性。最后,在相近的测试条件下,对新型平板热管式太阳能PV/T集热系统和传统圆形热管式太阳能PV/T集热系统的热电性能进行对比分析。分析结果表明,在相近的测试条件下,与传统圆形热管式太阳能PV/T集热系统相比,新型平板热管式太阳能PV/T集热系统的日平均热效率和日平均电效率分别提升了16.8%和3.5%,总集热量和总发电量分别提升了78.4%和35.5%。     

新型CPC热管式集热器的设计与模拟分析

基于CPC型集热器的发展现状,设计出新型CPC热管式集热器.介绍了该集热器的聚光面和接收器的结构设计计算过程,并对集热器进行了集热分析.采用MATLAB建模仿真技术对该集热器进行建模和动态仿真来预测该新型CPC热管式集热器的运行情况,得出新型CPC热管式集热器的有效输出能量、出口温度、瞬时集热效率的变化图.通过试验研究证实了新型CPC热管式集热器可以产生蒸汽,可用于制冷,尤其是热源品位要求较高的氨吸收式制冷,同时还可用于汽轮机发电和太阳能海水淡化等场合.     

太阳能对流型集热管

分析了太阳能集热器在应用中存在的诸多问题,提出一种新型的太阳能集热元件——对流型集热管。 给出了该集热元件的性能对比试验结果。由这种新型集热管组成的集热器具有更高的热效率、更好的可靠性、 更长的使用寿命和更高的性价比。     

磁纳米流体热管太阳能集热装置换热性能试验

设计了一套换热系统试验台,分别把磁纳米流体和水作为热管的工质,对玻璃真空管内插热管式太阳能集热器进行对比试验,分析两种集热器处于不同倾角、不同天气条件、不同总辐射量下的光热转换瞬时效率及日平均效率。此外,比较了玻璃真空集热器和热管内插式集热器的平均热损失系数。研究表明:内插热管式集热器的平均热损失系数约为全玻璃真空管集热器的2.32%,远小于全玻璃真空集热管,且工质为纳米流体的热管式玻璃真空管太阳能集热器的热损失系数比水工质热管真空集热管更低,其瞬时效率及日平均效率更高,运行更加高效、安全、稳定。     

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。     

CPC热管式真空管集热器的集热效率研究

介绍了CPC(compound parabolic concentrator)热管式真空管集热器的结构,对CPC热管式真空管太阳能集热器进行了传热分析,并对CPC热管式真空管集热器、热管式真空管集热器和CPC热管式集热器的集热效率进行了对比计算。CPC热管式真空管集热器的集热效率的理论计算和试验结果表明:CPC热管式真空管集热器的集热效率最佳。     

热管式真空管太阳能集热器研制成功

热管式真空管太阳能集热器研制成功１９９４年９月２０日，北京市太阳能研究所研制生产的热管式真空管太阳能集热器通过鉴定，标志着我国太阳能热利用基础元件的研究与生产步入世界先进行列。集热器是太阳能热利用领域中最关键的基础部件，它的发展经历了问晒式、平板式、...     

重力热管平板集热器的热性能研究

本文在热管平板集热器传热分析的基础上,对铝-丙酮和铝-氨重力热管(无芯网或槽道的光管)在太阳能平板集热器的热流密度下的传热特性进行了实验研究,发现热管工质的最佳充装量约为25％左右。实验表明,在低热流密度条件下,热管蒸发段的换热系数较低,集热器系统的设计又不允许热管有过长的冷凝段,使热管对载热质的总传热系数略低于常规平板集热器流道中的对流换热系数。故热管集热器的效率因子将略低于同类型常规集热器。实验结果还指出,热管集热器的热容小,起动快,它的全日效率略高于常规集热器。重力热管集热器系统能防冻、防腐,其热性能优于双回路系统,有进一步研制的价值。     

一种基于新结构的线性腔式太阳能集热器研究

提出一种适用于槽式太阳能热发电系统的新型线性腔式集热器。通过Tracepro模拟聚光镜焦距、弧形结构及开口宽度对系统光学性能的影响;采用热网络模型对该集热器的传热性能进行参数化研究,确定优化的集热器结构为优弧型,开口宽度为70 mm,与其匹配的聚光镜焦距为2100 mm。研究结果表明,当太阳直射辐射强度为500 W/m2,集热温度为650 K时,系统光热转换效率达65.3%。与一类传统真空管集热器的对比表明,该新型线性腔式集热器的集热性能优于UVAC Cermet直通式真空管集热器。另外,该线性腔式集热器生产和维护成本明显低于真空管集热器,对于促进槽式太阳能热发电技术具有重要意义。     

CPC内聚光式热管集热管温度特性研究

为提高太阳能热水系统的输出温度,将CPC聚光技术应用于热管式真空集热管中,开发了一种新型的CPC内聚光式热管集热管。对该集热管建立数学模型,模拟计算其传热过程,获得了导热肋片温度、热管冷凝段温度等参数随太阳辐射强度的变化规律,并通过试验验证了数学模型的可靠性;与常规热管式真空管集热管传热特性相对比,证实了该集热管可大幅提高太阳能热水器输出温度。     

Performance study and parametric analysis of a novel heat pipe PV/T system

A novel heat pipe photovoltaic/thermal (PV/T) system that could simultaneously supply electrical and thermal energy was proposed. Compared with a traditional water-type PV/T system, the heat pipe PV/T system can be used in cold regions without becoming frozen. A dynamic model of the heat pipe PV/T system was presented, and a test rig was constructed. Experiments were conducted to validate the results of the simulation. Based on the validated model, the performances of the heat pipe PV/T system were studied under different parametric conditions, such as water flow rates, PV cell covering factor of the collector, tube space of heat pipes, and kinds of solar absorptive coatings of the absorber plate.     

Simulated and experimental performance of a heat pipe assisted solar wall

Performance was evaluated for a passive solar space heating system utilizing heat pipes to transfer heat through an insulated wall from an absorber outside the building to a storage tank inside the building. The one-directional, thermal diode heat transfer effect of heat pipes make them ideal for passive solar applications. Gains by the heat pipe are not lost during cloud cover or periods of low irradiation. Simplified thermal resistance-based computer models were constructed to simulate the performance of direct gain, indirect gain, and integrated heat pipe passive solar systems in four different climates. The heat pipe system provided significantly higher solar fractions than the other passive options in all climates, but was particularly advantageous in cold and cloudy climates. Parametric sensitivity was evaluated for material and design features related to the collector cover, absorber plate, heat pipe, and water storage tank to determine a combination providing good thermal performance with diminishing returns for incremental parametric improvements. Important parameters included a high transmittance glazing, a high performance absorber surface and large thermal storage capacity.An experimental model of the heat pipe passive solar wall was also tested in a laboratory setting. Experimental variations included fluid fill levels, addition of insulation on the adiabatic section of the heat pipe, and fins on the outside of the condenser section. Filling the heat pipe to 120% of the volume of the evaporator section and insulating the adiabatic section achieved a system efficiency of 85%. Addition of fins on the condenser of the heat pipe did not significantly enhance overall performance.The computer model was validated by simulating the laboratory experiments and comparing experimental and simulated data. Temperatures across the system were matched by adjusting the model conductances, which resulted in good agreement with the experiment.     

Finite time thermal analysis of ground integrated‐collector‐storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated‐collector‐storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two‐dimensional transient heat conduction equation using an explicit finite‐difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.     

Experimental study of a refrigerant charged solar collector

The performance of a heat-pipe solar collector was investigated experimentally using refrigerants R11 as the working fluid. The unit is fabricated locally and its performance is evaluated under Beirut Solar conditions. The heat transfer from the heat pipes to the hot-water storage tank took place through a circular end condenser section of the heat-pipe integrated within the collector frame. Tests of single heat pipes showed that the thermal performance of the heat pipe were dependent on its tilt angle, condenser section length and configuration, and type of internal wick used. A circular condenser end of the heat-pipe performed better than a straight condenser due to increased surface area for heat transfer. The R11-charged solar collector with integrated condenser for secondary cooling of water had an efficiency in early operation hours that reached values higher than 60% for the forced circulation mode. The instantaneous system efficiencies varied from 60 to 20%, which are in the range of conventional water solar collectors. System response was fast and sensitive to the incident solar radiation. The thermosyphonic mode of the system operation generated build up of stored energy in the condenser, resulting in oscillating-type flow thus reducing system efficiency below values obtained with forced circulation. © 1998 John Wiley & Sons, Ltd.     

Experimental study of the performance of a solar collector by closed-end oscillating heat pipe (CEOHP)

An experimental flat plate solar collector operating in conjunction with a closed-end oscillating heat pipe (CEOHP) offers a reasonably efficient and cost effective alternative to conventional solar collector system that use heat pipes. The CEOHP system described in this study relies on the natural forces of gravity and capillary action and dose not require an external power source. The flat plate collector consisted of a 1 mm thick sheet of black zinc covered by a glass enclosure with a collecting area of 2.00 × 0.97 m² , an evaporator located on the collecting plate, and a condenser inserted into a water tank. A length of 0.003 ID copper tubing was bent into multiple turns at critical points along its path and used to channel the working fluid throughout the system. R134a was used as the working fluid. Efficiency evaluations were conducted during daylight hours over a two month period and included extensive monitoring and recording of temperatures with type-K thermocouples placed at key locations throughout the system. The results confirmed the anticipated fluctuation in collector efficiency dependant on the time of day, solar energy irradiation, ambient temperature and flat plate mean temperature. An efficiency of approximately 62% was achieved, which correlates with the efficiency of the more expensive heat pipe system. The CEOHP system offers the additional benefits of corrosion free operation and absence of freezing during winter months.     

Optimal flow control of a forced circulation solar water heating system with energy storage units and connecting pipes

This paper focuses on pump flow rate optimization for forced circulation solar water heating systems with pipes. The system consists of: an array of flat plate solar collectors, two storage tanks for the circulation fluid and water, a heat exchanger, two pumps, and connecting pipes. The storage tanks operate in the fully mixed regime to avoid thermal stratification. The pipes are considered as separated components in the system so as to account for their thermal effects. The objective is to determine optimal flow rates in the primary and secondary loops in order to maximize energy transfer to the circulation fluid storage tank, while reaching user defined temperatures in the water storage tank to increase thermal comfort. A model is developed using mainly the first and second laws of thermodynamics. The model is used to maximize the difference between the energy extracted from the solar collector and the combined sum of the energy extracted by the heat exchanger and corresponding energies used by the pumps in the primary and secondary loops. The objective function maximizes the overall system energy gain whilst minimizing the sum of the energy extracted by the heat exchanger and corresponding pump energy in the secondary loop to conserve stored energy and meet the user requirement of water tank temperatures. A case study is shown to illustrate the effects of the model. When compared to other flow control techniques, in particular the most suitable energy efficient control strategy, the results of this study show a 7.82% increase in the amount of energy extracted. The results also show system thermal losses ranging between 5.54% and 7.34% for the different control strategies due to connecting pipe losses.     

An experimental heat transfer study for periodically varying-curvature curved-pipe

Experiments were conducted for water flowing through a varying-curvature curved-pipe inside a larger diameter straight pipe to form a double-pipe heat exchanger with water as the working medium. The heat transfer coefficients were obtained using the Wilson plot method. The effects of the Dean, Prandtl, Reynolds number and the curvature ratio on the average heat transfer coefficients and the friction factors are presented. A higher Dean number results in a higher heat transfer rate. It is found that the heat transfer rate may be increased by up to 100%, as compared with a straight pipe, while the friction coefficient increased by less than 40%. Therefore, it is promising to use S-shaped pipes instead of straight pipes for the performance enhancement for a heat exchanger such as a solar collector.     

The study of the heat-engineering characteristics of a solar heat collector based on aluminum heat pipes

This paper presents the results of studies into the heat-engineering characteristics of a flat heat solar collector based on aluminum heat pipes that is designed to be used in building facades. The principle of work and the structure of the solar collector are considered; the results of its comparison with a traditional flat solar collector are presented. The studies were performed at a heat carrier temperature range of +10–+30°C and at a solar heat flow density of 400–1000 W/m². The obtained experimental heat-engineering characteristics of the collector based on heat pipes show that they are at a level of traditional flow solar collectors; for example, its efficiency is 0.65–0.73. Meanwhile, the hydraulic resistance of the structure with heat pipes is by a factor of 2–2.4 smaller and ensures a high level of scalability, reliability, and maintainability, which is important when using it as an element of facade constructions of solar heat systems.