内置式PV-Trombe墙空气流动与传热的数值模拟
发布时间：2018-08-02 08:47
【摘要】：绿色建筑技术利用新能源和可再生能源进行供暖通风和空气调节,具有节能环保的优点,是近年来国内外的研究热点课题。Trombe墙是一种利用太阳能进行供暖和通风的建筑节能技术。PV-Trombe墙则通过把太阳能电池贴于Trombe墙玻璃盖板,从而实现了发电和供暖、通风的联供。然而太阳能电池阻碍了太阳辐射进入Trombe墙流道内部,从得热率的角度看,Trombe墙的太阳能利用效率将降低。为了更好地利用太阳能,本文提出了一种新型内置式PV-Trombe墙,它将光伏电池贴在Trombe墙的集热墙表面,太阳辐射完全穿过玻璃盖板进入Trombe墙内,并被集热墙表面的光伏电池和通道内的空气所吸收。其中,一部分太阳能被转换成电能,其余部分则用于加热通道内的空气,实现建筑采暖、通风和发电等功能。本文以水平进口内置式PV-Trombe墙为研究对象,基于计算流体力学原理,运用FLUENT软件对模型流道内的空气流动情况和对流换热特点进行了模拟研究。采用rNG κ-ε湍流模型、DO辐射模型以及SIMPLEC算法对温度场和流场进行计算,得到了流道内空气温度、压力和速度分布的详细结果。文中探讨了太阳辐射和结构尺寸对模型通风和传热性能的影响,分析了流道内部空气的温度、速度、流态、局部换热系数和质量流量以及模型热电性能的变化情况。通过对各变量进行量纲分析,引入无量纲准则数Nu数、Re数、Ra*数和热效率ηth等,基于最小二乘法原理,对各无量纲数进行线性拟合分析,得到了表征内置式PV-Trombe墙通风传热性能的拟合关联式。通过本文研究,得到以下主要结论：(1)流道内部空气沿着宽度方向,温度与速度分布并不是均匀一致。在玻璃盖板和光伏电池的近壁处,存在明显的温度和速度边界层,边界层厚度随着太阳辐射的增强而增大,边界层内温度梯度和速度梯度较大,而远离壁面的主流区,温度和速度变化较为平缓。(2)空气在竖直流道内流动属于有限空间自然对流,其流态可以用以流道宽度b为特征尺寸的Ra*数来判断。通过流线图和理论分析可知,空气的流态随着太阳辐射和高度的增加变化较小,而宽度才是影响流道内空气流动状态的关键参数。(3)流道内空气的局部对流换热系数分布存在入口段和充分发展段两个区段；太阳辐射和模型高度的增加有助于提高模型的通风性能,而空气质量流量随着宽度的增加却出现先增大然后逐渐减小的情况；空气在流道内流动产生的回流会增强局部对流换热系数,却会阻碍空气流动,降低模型通风性能。(4) 已经定义出表征模型的平均对流传热系数Nu数、表征模型通风量大小的Re数、表征模型结构尺寸和壁面热流密度变化的Ra*数以及热效率ηth,并通过线性拟合方法得到各无量纲数之间的通用幂函数关联式,为模型计算和工程应用提供参考。
[Abstract]:Green building technology uses new and renewable energy for heating, ventilation and air conditioning, which has the advantages of energy saving and environmental protection. Trombe wall is a kind of building energy saving technology using solar energy for heating and ventilation. PV-Trombe wall can realize the joint supply of power generation, heating and ventilation by attaching solar cells to Trombe wall glass panels. However, solar cells prevent solar radiation from entering the channel of Trombe wall, and the efficiency of solar energy utilization of Trombe wall will be reduced from the point of view of thermal efficiency. In order to make better use of solar energy, a new type of built-in PV-Trombe wall is proposed in this paper. The photovoltaic cell is attached to the surface of the collector wall of the Trombe wall, and the solar radiation is completely passed through the glass cover into the Trombe wall. It is absorbed by the photovoltaic cells on the surface of the collector wall and the air in the passage. Some of the solar energy is converted to electricity, while the rest is used to heat the air in the passage to provide building heating, ventilation and power generation. Based on the principle of computational fluid dynamics (CFD), the air flow and convection heat transfer characteristics in the model runner are simulated by using FLUENT software based on the horizontal inlet built-in PV-Trombe wall. The temperature field and flow field are calculated by using rNG 魏-蔚 turbulence model and SIMPLEC algorithm. The detailed results of air temperature, pressure and velocity distribution in the channel are obtained. The effects of solar radiation and structure size on the ventilation and heat transfer performance of the model are discussed. The variation of air temperature, velocity, flow state, local heat transfer coefficient and mass flow rate and the thermoelectric properties of the model are analyzed. Through dimensionality analysis of each variable, the dimensionless criterion number Nu and re number Ra* and thermal efficiency 畏 th are introduced. Based on the principle of least square method, linear fitting analysis is carried out for each dimensionless number. A fitting correlation is obtained to characterize the ventilation heat transfer performance of built-in PV-Trombe walls. The main conclusions are as follows: (1) the temperature and velocity distribution of the air in the channel is not uniform along the width direction. There are obvious temperature and velocity boundary layers in the near wall of the glass cover and photovoltaic cells. The thickness of the boundary layer increases with the increase of solar radiation. The temperature gradient and velocity gradient in the boundary layer are larger, but far from the mainstream area of the wall. The variation of temperature and velocity is relatively gentle. (2) the flow of air in vertical channel belongs to natural convection in finite space and its flow pattern can be judged by Ra* number of channel width b as characteristic size. According to the streamline diagram and theoretical analysis, the flow state of the air changes little with the increase of solar radiation and height. The width is the key parameter to affect the air flow state in the channel. (3) there are two sections of the local convection heat transfer coefficient distribution in the channel: the inlet section and the fully developed section; The increase of solar radiation and the height of the model helps to improve the ventilation performance of the model, but the air mass flow increases first and then decreases gradually with the increase of the width. The circumfluence caused by air flow in the channel will enhance the local convection heat transfer coefficient, but it will hinder the air flow and reduce the ventilation performance of the model. (4) the average convection heat transfer coefficient Nu number that characterizes the model and the re number representing the model ventilation rate have been defined. The Ra* number and the thermal efficiency 畏 _ (th) of the structural size and the wall heat flux change are characterized, and the general power function correlation between the dimensionless numbers is obtained by the linear fitting method, which provides a reference for the model calculation and engineering application.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU83
本文编号：2158878
[Abstract]:Green building technology uses new and renewable energy for heating, ventilation and air conditioning, which has the advantages of energy saving and environmental protection. Trombe wall is a kind of building energy saving technology using solar energy for heating and ventilation. PV-Trombe wall can realize the joint supply of power generation, heating and ventilation by attaching solar cells to Trombe wall glass panels. However, solar cells prevent solar radiation from entering the channel of Trombe wall, and the efficiency of solar energy utilization of Trombe wall will be reduced from the point of view of thermal efficiency. In order to make better use of solar energy, a new type of built-in PV-Trombe wall is proposed in this paper. The photovoltaic cell is attached to the surface of the collector wall of the Trombe wall, and the solar radiation is completely passed through the glass cover into the Trombe wall. It is absorbed by the photovoltaic cells on the surface of the collector wall and the air in the passage. Some of the solar energy is converted to electricity, while the rest is used to heat the air in the passage to provide building heating, ventilation and power generation. Based on the principle of computational fluid dynamics (CFD), the air flow and convection heat transfer characteristics in the model runner are simulated by using FLUENT software based on the horizontal inlet built-in PV-Trombe wall. The temperature field and flow field are calculated by using rNG 魏-蔚 turbulence model and SIMPLEC algorithm. The detailed results of air temperature, pressure and velocity distribution in the channel are obtained. The effects of solar radiation and structure size on the ventilation and heat transfer performance of the model are discussed. The variation of air temperature, velocity, flow state, local heat transfer coefficient and mass flow rate and the thermoelectric properties of the model are analyzed. Through dimensionality analysis of each variable, the dimensionless criterion number Nu and re number Ra* and thermal efficiency 畏 th are introduced. Based on the principle of least square method, linear fitting analysis is carried out for each dimensionless number. A fitting correlation is obtained to characterize the ventilation heat transfer performance of built-in PV-Trombe walls. The main conclusions are as follows: (1) the temperature and velocity distribution of the air in the channel is not uniform along the width direction. There are obvious temperature and velocity boundary layers in the near wall of the glass cover and photovoltaic cells. The thickness of the boundary layer increases with the increase of solar radiation. The temperature gradient and velocity gradient in the boundary layer are larger, but far from the mainstream area of the wall. The variation of temperature and velocity is relatively gentle. (2) the flow of air in vertical channel belongs to natural convection in finite space and its flow pattern can be judged by Ra* number of channel width b as characteristic size. According to the streamline diagram and theoretical analysis, the flow state of the air changes little with the increase of solar radiation and height. The width is the key parameter to affect the air flow state in the channel. (3) there are two sections of the local convection heat transfer coefficient distribution in the channel: the inlet section and the fully developed section; The increase of solar radiation and the height of the model helps to improve the ventilation performance of the model, but the air mass flow increases first and then decreases gradually with the increase of the width. The circumfluence caused by air flow in the channel will enhance the local convection heat transfer coefficient, but it will hinder the air flow and reduce the ventilation performance of the model. (4) the average convection heat transfer coefficient Nu number that characterizes the model and the re number representing the model ventilation rate have been defined. The Ra* number and the thermal efficiency 畏 _ (th) of the structural size and the wall heat flux change are characterized, and the general power function correlation between the dimensionless numbers is obtained by the linear fitting method, which provides a reference for the model calculation and engineering application.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU83
【参考文献】
相关期刊论文 前1条
1 苏亚欣;柳仲宝;;太阳能烟囱强化自然通风的研究现状[J];科技导报;2011年27期
，本文编号：2158878
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