【作者】 戴巧利；

【导师】 左然；

【作者基本信息】 江苏大学 ， 热能工程， 2009， 硕士

【摘要】 太阳能是新能源中分布最广、使用最方便、最清洁的可再生能源。我国的大部分地区太阳能资源较丰富,具有利用太阳能的良好条件。但是我国的太阳能热利用目前仍然集中在太阳能热水器,利用太阳能的温室增温技术发展缓慢,远未实现市场化。因此,太阳能温室增温技术有着广阔的应用前景。本论文研制一种以空气为载热介质的太阳能空气集热-土壤蓄热的增温系统,应用于农业温室。论文主要包括以下内容:1.设计研制一种新型的主动式太阳能空气集热-土壤蓄热温室增温系统。该系统包括空气集热系统和土壤蓄热系统两部分。其中集热系统由平板型空气集热器组成,集热器布置在南北走向的温室大棚的东西两侧,面向正南。土壤蓄热系统由两根布置在温室内土壤80cm深处的东西两侧的纵向主管和若干根横穿温室土壤的PVC散热管组成。白天利用太阳能空气集热器加热空气,由风机把热空气抽入地下,通过地下管道与土壤的热交换,将热量传给土壤储存。夜间热量缓慢上升至地表,从而使土壤保持恒温。当夜间温室气温过低时,系统将自动启动风机,把地下贮存的热量,通过气流带到地上。由于土壤巨大的热容量,不仅可以将热量保持至夜间,甚至可以保持多天,供阴雨天加温,从而达到节约能源,使作物高产的目的。2.设计制作了带空气夹层的双层薄膜覆盖保温层和保温门。加温温室的保温覆盖材料采用双层0.08mm厚的聚氯乙烯长寿无滴塑料薄膜,在两层塑料薄膜之间有10cm厚的空气层,用很轻的泡沫做成的长圆柱管支撑,既廉价又实用。与对照温室相比,采用带空气夹层的双层保温覆盖具有良好的保温效果,可有效避免温室在夜间的逆温现象。此外,在温室大棚的进出口处采用有隔层的保温门,可有效避免冬季人员进出温室引起的棚内热空气和棚外冷空气之间的强对流热损失。3.对所设计的主动式太阳能空气集热—土壤蓄热温室增温系统进行了连续加温试验。试验结果表明:利用太阳能空气集热—土壤蓄热的温室增温系统,可使温室内气温平均每天提高3.3℃,地温平均每天提高2.5℃。夜间地温提高2.3℃,气温提高3.8℃。且温室增温系统具有良好的蓄热性能,白天的蓄热量可达228.9～319.1MJ,平均蓄热功率密度为211.9～295.5 W/m~2。试验结果表明,利用太阳能空气集热—土壤蓄热的温室增温系统是可行的,具有明显的白天蓄热、夜间放热的效果,并且还具有长期蓄热的潜力,可以满足农作物在连续阴天时的地温需要。4.分析了主动式太阳能温室地下土壤的传热机理,在此基础上建立土壤蓄热系统的二维非稳态模型,并对其进行数值计算。此外,还分析了普通塑料大棚的能量收支情况,在此基础上对太阳能加温温室的保温覆盖材料、室内空气、室内水分、室内表层土壤进行了热平衡分析,并建立了各自的热平衡方程。5.对温室地下土壤蓄热系统和主动式太阳能温室分别建立了三维数学模型,采用管道热空气进口速度和温度、天空辐射温度、室外空气温度、室外太阳辐照度、温室围护结构外表面的对流辐射换热系数、温室内1m深土壤温度等作为边界条件,选用标准k—ε湍流模型,运用Fluent6.0的分离隐式求解器进行三维非稳态数值模拟。通过模拟结果发现,模拟的土壤温度的变化规律与实际的土壤温度测量值的变化规律相同,实验值和模拟值吻合较好,二者的差值不超过2℃。更多还原

【Abstract】 Solar energy is one of the most widely distributed,convenient and clean renewable energies.Mostly areas in China are rich in solar energy resources which provide favorable conditions to the utilization of solar energy.At present,we focus mainly on the solar water heaters in solar thermal utilization field.Technology of greenhouse heating using solar energy develops very slowly,which is far from market.Accordingly, there exists a vast market of prospects for the use of solar energy in greenhouse heating.In this thesis,a new solar active heating system with air collectors collecting and soil heat storage is studied for greenhouses heating.The thesis includes following aspects:1.A new solar active heating system for greenhouses which is comprised of solar air collectors and soil heat storage system has been designed and built.The solar air collecting system is made up of flat-plate air collectors which are laid at two sides of the south-north-trend greenhouse.Soil heat storage system is made of two domain air collecting PVC pipes and some radiator PVC pipes.In this system,outside air is heated by solar air collectors and then pumped into underground pipes.The heat carried by air is transferred through pipes to the soil and stored for use at night.In the night,heat rises slowly to the ground surface to maintain the soil at constant temperature.When the air temperature in the heated greenhouse is lower than a certain one,the fan will work to get the cold air in greenhouse to be heated by the underground hot soil.2.An insulation cover which is made of two PVC films has been designed to reduce thermal loss of the heated greenhouse.Two films are supported by several long and light foam cylindrical tubes to form an air layer of 10 cm thickness.The insulation cover shows good insulation effect which can effectively avoid temperature inversion in contrast to the compared greenhouse which is covered with the same monolayer film.In addition,we design an insulation gate at the inlet of the greenhouse.This attempt can avoid strong convective thermal losses between indoor hot air and outdoor cold air when workers go into the greenhouse on cold days.3.An experiment with the active solar heating system for greenhouses has been performed for days continuously.The emphasis is to study the heating effect of the solar heating system on air and soil temperature in the heated greenhouse.The results show that,in winter of Zhenjiang Jiangsu Province,in a sunny daytime,the air temperature increases about 3.3℃by daylight and 3.8℃at night by an average in the heated greenhouse than that of the greenhouse without heating during the heating experiment.Also the soil temperature is 2.5℃and 2.3℃higher at daytime and night respectively than that the compared greenhouse.The system shows good heat storage performance,which can store 228.9～319.1 MJ heat and 211.9～295.5 W/m~2 by daylight.The experimental results show that using solar air heating system with soil heat storage can increase the air and soil temperatures for greenhouse effectively in cold days.The heating system can storage solar energy at daytime and release heat at night.Also the system has the potential to storage heat for a long time and may be satisfy the needed energy for plants for several cloudy days.The solar active heating system has good prospect for applications in greenhouses.4.Heat transfer mechanism of the soil heat storage is anlynized for active solar greenhouses.On the basis of it,the soil heated model in the heated greenhouse is established and solved the model with numerical analysis method.In addition,the energy budget of unheated solar greenhouse has been analyzed.On the basis of thermal analysis,we establish heat balance equations of the insulation cover,indoor air, indoor moisture and ground surface of the active solar greenhouse.5.The 3-D mathematical models of the soil heat storage system and active solar greenhouse have been established and simplified in this thesis respectively.The boundary conditions are based on hot air temperatre of pipe inlet,solar radiation,sky radiative temperature, external air temperature,wind velocities and soil temperature at 1.0m deep inside.Conservation equations are solved using unsteady simulations by Computational Fluid Dynamics technique and soil temperatures in active solar greenhouse are simulated in time and in space.The simulation results show that:the differences between the simulated soil temperatures at 10cm,20cm,30cm and 40cm depth and the measured values are being no than 2℃respectively.The simulation results are in good agreement with the experimental test.更多还原