基于动态传热分析的平板型太阳能集热器设计软件开发

平板型太阳能集热器的热性能受到环境因素、运行条件和设计因素的共同影响。为提升太阳能热利用工程的应用效果,需要针对环境和运行条件,对平板型太阳能集热器进行优化设计。本研究通过分析平板型太阳能集热器内部以及与环境间导热、对流、热辐射等动态传热过程,建立了计算集热量、集热效率以及集热器瞬时效率曲线的平板型太阳能集热器三维动态传热模型与差分求解算法,开发了具有传热过程分析和运行性能预测的平板型太阳能集热器设计软件,提高了不同环境因素、设计因素以及运行参数影响下集热器热性能分析速度和准确度。     

中温水平环路热虹吸管蒸汽发生器传热特性

将水平环路热虹吸管(HLTS)蒸汽发生器拓展用于槽式集热器(PTC),有望降低系统成本,解决现有槽式集热系统关键技术难题。本文设计了一种基于中温水平环路热虹吸管蒸汽发生器的槽式太阳能集热器(HLTS-PTC),分析得到其400～1000 W/m2太阳直接辐射工况下的有效传输功率为2.0～5.6 k W/m2。另外,对HLTS的传热特性和产蒸汽特性进行了实验研究。结果表明:HLTS的产蒸汽能力和传热性能随着热流的升高而显著提升。在加热热流为8.49 k W/m2时,系统4 h可产生8 MPa蒸汽,此外,该加热热流下系统的换热效率达72.7%。若该HTLS系统应用在更高热通量的PTC系统中且进一步优化环路热管的保温性能,其产蒸汽能力和传热性能会得到进一步提升。     

屋顶太阳能集热器对顶层房间冷热负荷的影响研究

屋顶太阳能集热器的存在改变了屋顶的太阳辐射得热,在一定程度上影响建筑的冷热负荷,特别是对于顶层房间,屋顶是受室外热作用影响最大的外围护结构。本文通过实验测量有太阳能集热器的屋顶和无太阳能集热器的屋顶的外表面温度,建立一维非稳态传热模型,对屋顶的内表面温度及传热量进行数值求解,获得屋顶的热流量数据并对实验结果进行分析。实验结果表明:太阳能集热器的存在会减少屋顶的辐射得热,降低建筑物的夏季冷负荷,增大建筑物的冬季热负荷。     

有限体积法求解二维双层半透明介质辐射-导热耦合传热

为了研究双层半透明介质内的辐射-导热耦合传热特性,采用基于有限体积法的开源C++程序库OpenFOAM,开发了求解二维双层半透明介质辐射-导热耦合传热问题的计算程序,并验证了计算程序的准确性。分析了折射率对耦合传热特性的影响,研究结果表明:当nj/ni不变时,折射率的变化对复合层温度场影响很小,介质层辐射热流密度随着介质折射率的增大而增加;当复合层高温侧介质折射率ni大于低温侧介质折射率nj时,复合层内温度扩散深度较ni相似文献   

数学模型对水冷型PVT围护结构热性能的影响研究

本文针对PVT围护结构分别建立了一维传热模型和二维传热模型,分析了数学模型对水冷型PVT围护结构热性能的影响,结果表明:一维传热模型增大了冷却水得热量、墙体得热量和电池片发电量,减小了热损失,与一维传热模型的结果相比,二维传热模型由于考虑了吸热板和电池片在流体流动方向的导热,可以获得吸热板和电池片的温度分布,其计算结果具有较高的精度,对PVT围护结构的设计具有重要指导作用。     

基于可再生能源的地板辐射供暖传热分析

结合甘肃河西地区的气候特点和当地丰富的可再生能源,研究了以太阳能和沼气互补的低温热水地板辐射供暖传热性能,建立了低温地板辐射供暖系统二维稳态传热数学模型,通过有限元法对不同管间距和供回水平均温度下地板表面的热流密度及地板表面温度分布进行分析研究,探讨了以可再生能源作为系统驱动热源的可行性,为可再生能源在低温热水地板辐射供暖系统中的应用提供一定的技术参考。     

地板辐射采暖系统若干问题的研究

本文在分析低温热水地板辐射采暖系统传热规律的基础上,建立了地板辐射采暖系统的二维稳态传热数学模型;进而利用有限单元法对不同地面层材料及布置方式进行分析,求出了数学模型的数值解;最后给出并分析了地面层材质与厚度、管间距、管径、水温及室温等因素对地板地面温度和热流密度影响的定性及定量关系.对于地板辐射采暖系统的优化设计、安全可靠地运行具有一定的参考价值.     

冲缝吸热板渗透型太阳能空气集热器性能研究

介绍了冲缝吸热板渗透型太阳能空气集热器的结构,建立了传热数学模型。采用Matlab程序对传热数学模型进行求解,模拟研究了结构参数、运行参数对集热器热性能的影响。集热器出口空气温度的实测结果与模拟结果的平均偏差为0.99K,证明传热数学模型准确可靠。集热量随吸热板外表面发射率增大而降低,随集热器出口空气流量、太阳辐射强度的增大而升高,随环境温度的增大先降低后升高。集热器出口空气温度随吸热板外表面发射率、集热器出口空气流量的增大而降低,随太阳辐射强度、环境温度的增大而升高。     

板式地板辐射供暖系统传热性能模拟研究

建立了板式地板辐射供暖的二维稳态传热模型。采用有限元分析软件ANSYS,分析了地板表面温度分布、传热计算单元内部温度分布、地板表面热流密度的影响因素及地板表面平均温度的影响因素,在考虑地板向下传热时对模拟计算结果进行了修正。供、回水平均温度是影响地板表面热流密度和平均温度的主要因素。当室内温度为20℃时,在维持适宜的地板表面平均温度范围24~28℃的前提下,供、回水平均温度的变化范围为27~34℃,考虑地板向下传热后,应控制在30~35℃。考虑地板向下传热后,应将模拟计算结果乘以一个不小于0.9的修正系数。     

严寒地区太阳能槽式集热器影响因素研究

以大庆地区为研究背景,分析了LS-2型太阳能槽式集热器光热转化过程中的能量传递,综合利用Sol Trace软件与Fluent软件计算了集热器的光学效率及瞬时效率。研究内容包括聚光面积、环境温度、流量以及管长对集热器瞬时效率的影响。结果表明:针对该模型而言,太阳能槽式集热器的瞬时效率随着聚光面积的增加而增大;环境温度在-20~20℃的变化范围内,瞬时效率有小幅度的提高,约为1%;且对于流量及管长来说,均存在一个使瞬时效率趋于稳定的值。本文的研究结果可以为严寒地区利用太阳能光热转换技术提供支撑和技术参考。     

太阳能平板集热器关键参数对其热性能的影响

为了提升太阳能在建筑能源供给体系中的比重,形式多样的太阳能集热设备及其系统在建筑领域得到了广泛应用。基于机理分析法,建立了具有单层玻璃盖板的管板式太阳能平板集热器的稳态传热模型。并且针对集热管间距、集热管内径、工质入口温度和工质质量流量等关键参数对集热器集热效率的影响特性进行了数值模拟与分析。结果表明,建立的该稳态传热模型是可行的;此外,在其余参数值保持不变的情况下,减小集热管间距或增加集热管内径均可使集热器瞬时效率增大;增大工质入口温度会导致集热器瞬时效率下降;而增大工质质量流量会提升集热器瞬时效率。这些结论对于太阳能平板集热器在太阳能建筑一体化的实际应用中,具有一定的参考作用。     

Experimental study and analysis of air heating system using a parabolic trough solar collector

An experimental study of air heating system was carried out using a parabolic trough collector with a U-tube aluminium heat exchanger. An evacuated tube placed at the focal length of the parabolic trough collected the solar radiations reflected from the surface of parabolic trough. The air was used as a working fluid, which was heated by passing it through a U-shaped aluminium heat exchanger placed inside the evacuated tube. It was found that efficiency of the parabolic trough collector depends on the mass flow rate, solar intensity and use of fins. It was observed that by using fins at a high mass flow rate of 4.557?kg/h, the maximum temperature of 126°C was achieved which is 13.27% more than the maximum temperature obtained without fins. Furthermore, for a low-mass-flow rate of 1.69?kg/h, the maximum temperature obtained was 149°C.     

Experimental investigation and analysis of the hybrid solar collector

Hybrid solar collector is a new and innovative technique to harness all the spectrum of sunlight and hence generate a system to harness sunlight. This project deals with the fabrication of a parabolic trough which suits the required design of the solar collector. This project deals with the study of heat transfer across the receiver tube and mode of heat transfer across the hybrid solar collector, to optimise the design, to minimise the losses and maximise the heat and photon transfer to the receiver and power generating unit. Our aim is to study the heat exchange process across tube and to prevent the heating of solar panels from the radiations emitted by the receiver tube when light is focused on it and direct the working of solar collector to a maximum efficient way. We consider the radiation spectrum of sun to be of different waves and utilising each component of it – that is, visible and UV (consisting most of photons) and infrared (consisting of heating radiation) – and try to segregate them with the help of a water jacket and bring the temperature of the PV panels to an optimum condition.     

槽式太阳能集热器聚光面能流分布及传热特性

本文运用蒙特卡罗光线追踪法模拟了LS-2型槽式太阳能集热系统的聚光特性,并以此为边界条件,进一步研究传热工质为THERMINOL55合成导热油时该集热器内管壁和管内流体的温度分布特性和传热特性。结果表明,管壁和管内流体温度分布十分不均匀。并考察了不同导热油以及导热油的流速对传热效率的影响工质流速对管壁温度分布影响较大,当太阳直射辐照为1000 W/m^2,导热油入口温度为160℃,流速为0.05 m/s时,吸热管圆周方向最大温差为235℃左右,当流速增加到0.05 m/s时,最大温差减小到142℃左右。     

槽型抛物面聚光集热器分析

槽型抛物面聚光集热器是槽式太阳能热发电系统的关键部件。在热力学第一定律和热力学第二定律的基础上,结合槽式太阳能热发电系统模型,对槽型抛物面聚光集热器进行分析。以SEGS-VI槽式太阳能电站设计参数为根据,采用能量系统的白箱模型分析,计算得到各过程的耗散和槽式太阳能聚光集热器的损失和效率,并揭示系统中用能不合理的"薄弱环节"。     

U型管式全玻璃真空管太阳集热器的热性能

在U型管式全玻璃真空管集热器能量平衡分析的基础上，推导了集热器热损系数、效率因子等性能参数计算公式，其理论计算结果与实验数据吻合良好。计算分析表明：真空管热损系数与吸热管温和环境温度之差是非线性关系，将两者的计算关系式按环境温度分段整理将使计算结果更接近实际;涂层发射比对集热器效率影响较大，降低涂层发射比是提高集热器效率的有效途径;采取适当的措施降低吸热管与肋片接触热阻后，采用U型管连接方式不会对热水系统集热器效率造成太大影响。     

建筑一体化电热冷联产光伏组件能量特性研究

传统太阳能光伏或光热建筑一体化只能为建筑提供单一电能或热能。通过研究一种集成发电、集热、制冷3种功能的建筑一体化电热冷联产光伏组件,对其夏季工况下能量特性进行了实际检测。结果表明:白天,组件集热同时能有效降低光伏电池温度,组件工作温度高于环境温度约8~16℃,发电和集热效率分别为14.1%~13.7%和40.1%~15.7%;晴朗夜间,组件通过对流和辐射两种传热方式进行散热制冷,总制冷功率为26.0~268.5 W/m~2。电热冷联产光伏组件适合与热泵结合,为建筑提供所需能源。     

Thermal performance analysis of the glass evacuated tube solar collector with U-tube

In this paper, based on the energy balance for the glass evacuated tube solar collector with U-tube, the thermal performance of the individual glass evacuated tube solar collector is investigated by analytical method. The solar collector considered in this study is a two-layered glass evacuated tube, and the absorber film is deposited in the outer surface of the absorber tube. The heat loss coefficient and heat efficiency factor are analyzed using one-dimensional analytical solution. And the influence of air layer between the absorber tube and the copper fin on the heat efficiency is also studied. The results show that the function relation of the heat loss coefficient of the glass evacuated tube solar collector with temperature difference between the absorbing coating surface and the ambient air is nonlinear. In the different ambient temperatures, the heat loss coefficient of the solar collector should be calculated by different expressions. The heat efficiency factor will be subject to influence of air layer between absorber tube and the copper fin. Specially, the influence is remarkable when the heat loss coefficient of the collector is large. When the synthetical conductance amounts to 5 W/m K, the solar collector efficiency decreases 10%, and the outlet fluid temperature decreases 16% compared with the case which the air thermal resistance is neglected. And the surface temperature of the absorbing coating increases 30 °C due to the effect of air thermal resistance. So the surface temperature of the absorbing coating is an important parameter to evaluate the thermal performance of the glass evacuated tube solar collector.     

Coupled heat transfer modes for calculation of cooling load through hollow concrete building walls

A CFD model was developed to study thermal performance of hollow cement wall constructions of buildings under hot summer conditions. The approach employed couples conjugate, laminar natural convective flow of a viscous fluid in hollow building blocks with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the wall. A state-of-art building energy simulation program, ESP-r, was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the wall domain. A detailed parametric study showed that using a wider cavity within a building block does not necessarily reduce heat flux through the block. Radiation heat transfer between cavity sides may account for a significant fraction of heat flux through the block and neglecting its effect can lead to errors that could be as large as 46%. The geometry of the hollow blocks was demonstrated to affect the heat flux by as much as 30%.     

Conjugate conduction convection and radiation heat transfer through hollow autoclaved aerated concrete blocks

A computational fluid dynamics (CFD) model is developed to study thermal performance of hollow autoclaved aerated concrete (AAC) blocks in wall constructions of buildings under hot summer conditions. The goal is to determine size and distribution of cavities (within building blocks) that reduce heat flow through the walls and thereby lead to energy savings in air conditioning. The model couples conjugate, laminar natural convective flow of a viscous fluid (air) in the cavities with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the block. A state-of-the-art building energy simulation programme was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings, and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the AAC block domain. The results show a complex dependence of heat flux through the blocks on cavity and block sizes. In general, introducing large cavities in AAC blocks, being a construction material of low thermal conductivity, leads to greater heat transfer than the corresponding solid blocks. Several small cavities in a block may lead to small reductions in heat flux, but the best configuration found is a large cavity with a fine divider mesh in which case heat flux reductions of 50% are achievable.