【作者】 欧阳莉；

【导师】 刘伟；

【作者基本信息】 华中科技大学 ， 工程热物理， 2008， 博士

【摘要】 太阳辐射具有分散性和断续性的特点,是太阳能利用中最大的困难。如何有效地收集和蓄积太阳能,对太阳能的利用效率有着非常重要的影响。太阳能在建筑采暖和农业日光温室的应用中,太阳墙是太阳能收集和蓄积的关键技术,是实现太阳能—建筑一体化的重要组成部分,也是世界各国学者普遍研究和关注的课题。因此,太阳墙的研究有着非常重要的意义。本文综合分析了国内外“太阳墙”的研究现状,集多孔介质复合Trombe墙和太阳能多孔集热墙优点为一体,设计了一种多孔介质太阳墙,并采用数值模拟的方法对多孔介质太阳墙的传热机理及应用进行了研究。从简化的角度出发,建立描述多孔介质太阳墙传热与流动特性的一维数学模型,对作为媒质的空气在多孔墙内的流动,以及与多孔墙之间的换热机理进行了初步的研究。结果表明:多孔墙能收集与蓄积太阳能,并加热空气;降低多孔墙入口空气速度,能够提高空气的温度;在保证所需的太阳辐射吸收率的条件下,增大多孔墙的孔隙率与渗透率,能够提高空气的温度:当多孔固体材料采用金属与非金属材料时,出口空气温度有着较大的差别。当多孔骨架材料采用铝时,空气的温升幅度较大,出口空气温度高,而采用岩石,空气的温升幅度较小。在实际应用中,应合理选择渗透率和多孔骨架材料,尽可能地降低初投资。基于对多孔墙的热分析,为降低多孔墙与环境之间的辐射与对流换热损失,从结构上对多孔墙进行改进,设计了一种新型的多孔太阳墙系统。在多孔墙的集热面与环境之间设玻璃盖板,形成玻璃通道。利用玻璃通道的“温室效应”降低热损失和收集热空气。在多孔墙内侧通道内设有风机,在风机的作用下,室外空气流入多孔墙,与多孔墙进行热交换后,被加热到一定的温度,用于冬季的供暖。基于二维稳态Navier-Stoke方程、饱和多孔介质Brinkman-Forchheimer Extended Darcy模型和能量双方程模型,对这种设有风机并附加玻璃通道的新型的多孔太阳墙系统内的传热与流动特性进行数值模拟。结果表明:风机的设计对系统内温度场和流场有较大的影响;降低空气入口流速,可减小空气流动阻力,提高多孔墙的集热效率;附加玻璃通道的多孔太阳墙可减小长波辐射损失,并具有收集热空气的作用。因此,它具有较高的集热效率。设计了一种多孔蓄热墙-温室系统。将温室北墙设计为由“半透明”的等径、均匀的多孔球堆积而成的多孔墙,能吸收和蓄积太阳能,加热温室空气,而且能够主动地调节温室内的热环境。将温室与多孔蓄热墙结合起来,充分发挥两者的作用。从而提高了温室的太阳能利用效果。借助带内热源的饱和多孔介质能量双方程模型和Brinkman-Forchheimer Extended Darcy模型以及k-ε紊流模型,对该太阳能温室系统的传热与流动特性进行预测。在此基础上,进一步模拟分析了孔隙率分层多孔墙对温室系统特性的影响。结果表明:温室系统的入口参数和多孔墙的结构对温室内的温度场、流场和压力场有较大的影响。因此,针对一定结构的温室系统,应根据温室热环境的要求,合理地设计多孔墙本体,调节风机的运行工况。设计了两种通风方式下的多孔太阳墙采暖系统。采用饱和多孔介质Brinkman-Forchheimer Extended Darcy模型、带内热源的能量双方程模型以及k-ε紊流模型,对采暖系统内的传热与流动特性进行计算、分析和比较。结果表明,多孔太阳墙采暖系统的送排风方式,对采暖房内的温度场、流场有很大的影响,它直接影响到系统的保温作用,对多孔墙的热利用率有较大的影响。因此,在实际应用中,应合理地设计多孔太阳墙采暖系统,提高多孔墙的热利用率,从而降低多孔墙的热价。对局部和斜坡地板送风式多孔太阳墙采暖系统内的传热与流动进行了数值模拟,得到了两种系统内的温度分布、流场分布。分析了架空地板的结构、地板送风口尺寸对采暖房内温度场和流场的影响;分析了建筑南墙对室内温度的影响。结果表明:采用地板送风方式,能够保证采暖房内均匀的温度场和流场;采用斜坡式地板送风方式,更有利于保证各送风口流量分布均匀。在实际应用中,应注意建筑承重墙的隔热,防止“热蚀”现象发生。针对多孔墙的结构特点,采用描述填充结构的多孔介质模型,进一步分析了多孔墙的结构特性。结果表明:增大颗粒直径和孔隙率能够降低系统的阻力。这一结果提供了优化多孔墙的结构参数。设计了多孔太阳墙测试系统,该系统能用于测试多孔太阳墙系统的阻力,多孔墙的吸收率和体积换热系数等特性参数。但由于太阳辐射的模拟是一个难点,因此,为了精确测试多孔墙的热性能,还需对测试系统进行改进。更多还原

【Abstract】 The characteristics of discontinuity and disperse of solar radiation give a great difficulty in solar energy applications. The absorption and storage of solar radiation has important effect on the utilization efficiency of solar energy. In heating buildings and greenhouses, the solar wall is a key part to incorporate the utilization of solar energy with the building, and also subject studied by researchers at home and abroad. So, it is very important to study the solar wall. In this paper, actualities of investigations on solar wall at home and abroad are analyzed. A new porous solar wall is designed by using the excellences of the porous composite Trombe wall and the porous absorption solar wall. In addition, based on numerical simulation, the application and heat transfer performances of the porous solar wall are studied.For simplification, one-dimensional mathematic model is used to describe the heat transfer and flow in the porous solar wall. The flow and heat transfer in the porous wall with the air as heat transfer medium are investigated primarily. To reach such conclusions, the porous wall can collect and store solar energy, and heat air; The air temperature will increase with a decrease in the inlet velocity; On the premise of demand for solar radiation collection, the air temperature will increase with an increase in the porosity and permeability of the porous wall; There are different results when metal and nonmetal are used as the material of the porous matrix, respectively. The increase speed of the air temperature is quicker when aluminum is used as the material of the porous wall. In contrast, the increase speed of the air temperature becomes slower when rock is used as the material of the porous wall. Consequently, the permeability and material of the porous wall should be carefully selected to reduce the cost of the porous solar wall.Based on the thermal analysis, the structure of the porous solar wall is improved and a new porous solar wall is designed to reduce convection and radiation heat exchanges between the porous wall and the ambient. The glass plate is located between the porous wall and the ambient to form a glass duct, which can reduce heat losses and collect hot air by using "greenhouse effective". Additionally, the fan is located in the duct near the inside surface of the porous wall. Under the action of the fan, the ambient air flows into the porous wall and exchanges heat with the porous wall. Then the air is heated to certain value to demand for heating in winter. Based on the two-dimensional steady Navier-Stokes equations, Brinkman-Forchheimer Extended Darcy model and energy two-equation model for saturated porous medium, the flow and heat transfer in the new porous solar wall system with glass duct and fan are simulated. The results show that the design of the fan has significant influence on the flow field and temperature field, the flow resistance will decrease and the thermal efficiency of porous wall will increase with a decrease in the inlet velocity, the porous wall with the glass duct can decrease length-wave radiation and collect hot air. So the new porous solar wall system can obtain a higher thermal efficiency as compared with a conventional one.A new greenhouse with heat-storage porous wall is designed, in which the north wall is a heat-storage porous wall. Equal diameter, uniform and semitransparent porous balls are used as the material of the porous solar wall, which can collect and store solar energy to heat the air in the greenhouse, and condition the thermal environment in the greenhouse. Their effect both can be exerted fully by combining the greenhouse with the heat-storage porous wall, which causes the higher solar energy utilization efficiency. Based on Brinkman-Forchheimer Extended Darcy model and energy two-equation model with internal heat source for saturated porous medium, k-εturbulent model, the flow and heat transfer characteristics of solar greenhouse system are simulated. Additionally, the influence of the porous wall with layered porosity on the characteristics of the greenhouse is also analyzed by numerical simulation further. The results show that the inlet parameters of the greenhouse and the structure of the porous wall have great effect on the temperature field, the flow field and the pressure field. So, for a certain structure of the greenhouse, the porous wall should be designed and the fan operation should be also conditioned reasonably according to the admired thermal environment in the greenhouse.Two kinds of new solar heating systems with a new porous heat storage wall are designed, which have different ventilation patterns. Based on k-εturbulent model, Brinkman-Forchheimer Extended Darcy model and energy two-equation model for saturated porous medium, the coupled heat transfer and flow characteristics in the new solar heating system are simulated, analyzed and compared. The results show that ventilation pattern has great effect on temperature field and flow field, which also has important influence on the insulation of the heating system and the thermal efficiency of the porous heat storage wall. Thus in real applications, the solar heating system with porous heat storage wall should be designed properly in order to increase the thermal efficiency of porous solar wall and decrease the heating price for porous wall.The flow field and temperature field are available by simulating the flow and heat transfer in two kinds of porous solar wall heating system with partial and slope under floor distribution system, respectively. The effect of the structure and air supply vent dimension of the under floor distribution system on flow field and temperature field are analyzed. The effect of the south wall on the temperature in the heating room also is studied. The results show that uniform temperature field and flow field in the heating room can be ensured by using the under floor distribution system, while the slope under floor distribution is good to obtain uniform mass flow rate for every supply air vent. In real applications, the south main wall of building should be insulated to prevent the phenomenon of "heat-erode".Based on the mathematical model used to describe the structure filled with uniform and equal diameter porous balls, the structure characteristics of porous solar wall are investigated further. The results show that the flow resistance will decrease with an increase in particle diameter and porosity. The results also provide parameters for an optimization of the porous wall.The porous solar wall experiment system is also designed, which can be used to investigate such performance parameters as the flow resistance of the porous solar wallsystem, the absorptivity and volume convection heat transfer coefficient of the porous wall,etc. But simulation of solar radiation is so difficult that the porous solar wall experimentsystem should be developed further to test the thermal performance of the porous wallaccurately.更多还原