日光温室不同厚度土墙蓄放热特性研究

发布时间：2017-12-27 03:20

本文关键词：日光温室不同厚度土墙蓄放热特性研究　出处：《山东农业大学》2017年博士论文　论文类型：学位论文

【摘要】：土质墙体的日光温室因具有蓄放热性能好、取材方便、成本低等优点,深受广大农民的青睐。目前,我国日光温室土墙的厚薄差异较大,甚至有很大一部分为超厚土墙,墙体占地面积加大,造成土地资源浪费。日光温室是我国独有的温室类型,其夜间维持作物生长的热量主要来源于日间温室墙体及地面吸收的太阳辐射热量,研究日光温室不同厚度土质墙体蓄放热、接受太阳辐射得热量及土墙体传热特性,对日光温室土墙体建造的轻便化设计和提高土地利用率都具有十分重要的理论及实践意义。本研究选取泰安市山东农业大学南校区建造的2栋土墙厚度不同的下挖式日光温室为研究对象,在温室北墙中间部位按不同高度设置5个测试层,每层水平布设温度传感器,室内墙体表面布设热流传感器及辐射计。基于各测试层监测的温度、太阳辐射照度和热流密度等数据,研究了不同天气情况下土墙内温度变化规律、各测试层太阳辐射量分布特性及土墙传热特性。主要结果如下:1.日光温室土墙体内温度变化分析及墙体放热效率评价以泰安市3.0 m厚土墙下挖式日光温室为研究对象,基于温室北墙5个测试层最冷季节(30 d)温室内气温、墙体温度、室外气温及室外太阳辐照度测试数据,分析了土墙日光温室内部空气温度及墙体内温度的分布规律。结果表明:各测试层墙体表面及由表面至墙内0.1~0.6 m处测点的温度均呈现出随温室内气温周期性变化而变化的规律,且随着墙体厚度的增加温度的波动幅值逐渐减小,时间相位明显后移;0.7 m以后各测点的温度波动幅值变化很小且趋于稳定,处于稳态向室外的导热过程;由此可以推定:日光温室后墙体内侧约0.7 m的厚度为昼夜间蓄放热的关键厚度。基于墙体温度分布、墙体白天蓄热量、夜间的放热量分析,计算得出墙体夜间放热效率约为43%,表明土墙白天蓄积热量的43%用于改善夜间温室内热环境。2.阴晴天情况下,日光温室不同厚度土墙墙体蓄放热特性基于晴好天气(2015年12月30日—2016年1月2日)及连阴天气(2016年1月4—6日)数据分析可知:连续晴好天气及连阴天时,1#温室厚墙体(顶宽2.0m,底宽6.0 m)和2#温室薄墙体(顶宽1.0m,底宽3.0 m)的5个测试层的放热量均为从第1层至第5层逐渐增加,两温室土墙体各层次的温度变化趋势相同;连续晴好天气(2015年12月30日—2016年1月2日)时,1#厚墙体温室和2#薄墙体温室的5个测试层的每天平均蓄热量分别为1971.2 k J和1888.9 k J,平均放热量分别为808.1 kJ和763.1 kJ,1#和2#温室的蓄热量和放热量的差值分别为82.3 k J和45.0 k J,数值差异很小。连阴天气(2016年1月4—6日)的前两天云层较薄有些散射光时,1#和2#温室的蓄热量都很小,第三天云层较厚,散射光也很弱,蓄热量甚至为零,基本为全天放热,平均放热量分别为1551.4 k J和935.5 k J,两温室差值为615.9 k J,数值差异较大;虽然温室厚墙体放热量明显高于薄墙体放热量,但距离墙体内表面0.1 m处的平均气温也只差0.6℃,温室内较前部的气温差异更小。从维持整个温室内最低气温的效果来看其作用也是甚微。3.不同天气状况下日光温室墙体5个测试层辐射得热量分布及墙体传热量分布特性基于多云、多云转阴、雾霾及晴好天气2#温室5个测试层采集数据,分析了各测试层接受太阳辐射量分布。结果表明:室外气象条件对温室接受太阳辐射强度的影响较大。晴好天气时墙体各测试层接受的太阳辐射量明显高于多云和轻度雾霾天气,重度雾霾(测试天PM2.5指数253)和阴天接受辐射量非常小。墙体表面不同高度接受的太阳辐射量从上至下为第2测试层最大,其次是第3测试层,2和3测试层辐射总量值比较接近;再次为第4、第1和第5测试层。同时,基于上述不同天气的墙体5测试层采集数据,分析了墙体5个测试层及后屋面向室外传热量分布特性。结果表明:北墙1~5个测试层的传热量占总传热量的比例依次为:第1测试层(墙体厚度为147 cm)约为21%,第2测试层(墙体厚度为186 cm)约为19%,第3测试层(墙体厚度为224 cm)约为17%,第4测试层(墙体厚度为263 cm)约为14%,第5测试层(墙体厚度为300 cm)约为12%,后屋面约为17%;温室内热量向室外的传递从低处至高处依次增强,因此,保温隔热措施应该是顺势加强。4.构建了日光温室墙体温度场模型基于ANSYS有限元分析软件构建了求解日光温室墙体温度场的计算模型,以墙面实测温度为自由度约束施加于模型边界上,采用稳态传热方法,模拟了阴晴天条件下不同时刻墙体内温度场变化,并对模拟数据与实测数据进行比较分析,结果发现模拟曲线拟合较好,其模拟值与实测值的平均误差为±1.0℃之内。利用ANSYS热分析方法构建的墙体温度场计算模型可以有效地预测温室墙体内部温度场的变化,能为泰安地区墙体设计及传热特性分析提供理论参考。
[Abstract]:The solar greenhouse in the soil wall has the advantages of good heat storage and heat storage, convenient material extraction and low cost, which are favored by the vast majority of farmers. At present, there is a large difference in the thickness of the earth wall in China's solar greenhouse, and even a large part of the earth wall is super thick, and the area of the wall is increased, which causes the waste of land resources. Solar greenhouse is our unique greenhouse type, the night to maintain calorie crop growth mainly from solar radiation heat wall and ground absorb daytime greenhouse, greenhouse of different thickness of soil wall heat storage, solar heat and heat transfer characteristics of the wall body, on greenhouse soil wall design and construction of light improvement has great theoretical and practical significance of land utilization. This study selected 2 wall thickness to build Tai'an city Shandong Agricultural University South Campus under different dig in greenhouse as the research object, in the middle part of the north wall of the greenhouse with different height to set up 5 test layers, each layer level distributed temperature sensor, indoor wall surface heat flux sensor and radiometer layout. Based on the data of monitoring temperature, solar irradiance and heat flux, the temperature variation rule of the earth wall, the distribution characteristics of the solar radiation and the heat transfer characteristics of the earth wall under different weather conditions are studied. The main results are as follows: analysis and evaluation of 1. greenhouse wall heat release rate in wall temperature changes in Tai'an city 3 m thick wall dug under the sunlight greenhouse as the research object, based on the north wall of the 5 layer of greenhouse test the coldest season (30 d) in the greenhouse temperature, wall temperature, outdoor air temperature and solar irradiance data. Analysis of temperature distribution of the internal wall of greenhouse air temperature and wall. The results showed that the test layer of wall surface and wall surface by 0.1~0.6 to m temperature measuring points were shown with the temperature indoor temperature cycle which changes with the increase of the thickness of wall temperature fluctuation amplitude decreases obviously after temporal phase shift; 0.7 m after each measuring point amplitude the temperature fluctuation is small and stable, steady heat conduction process to the outside; it can be presumed: greenhouse walls inside about 0.7 m thickness of the thickness of the heat storage key day and night. Based on wall temperature distribution, wall heat storage during the day and heat release at night, it is calculated that the night heat release efficiency of the wall is about 43%, indicating that 43% of the daily thermal storage capacity of the earth wall is used to improve the thermal environment in the greenhouse at night. 2. sunny days under greenhouse of different thickness of wall wall heat storage based on the characteristics of fine weather (December 30, 2015 - January 2, 2016) and overcast weather (January 2016 4 - 6 days) data analysis shows that: continuous fine weather and cloudy, greenhouse 1# thick wall (top width 2.0m, bottom width 6 m) and 2# thin greenhouse the wall (top width 1.0m, bottom width 3 m) 5 test layer heat is gradually increased from first to fifth, the two levels of greenhouse temperature change trend in the same soil wall; continuous fine weather (December 30, 2015 - January 2, 2016), the 5 layer of 1# thick wall temperature test chamber and 2# thin the average daily room wall temperature heat storage were 1971.2 K J and 1888.9 K J, the average heat release were 808.1 kJ and 763.1 kJ, the difference between 1# and 2# in greenhouse heat storage and heat release were 82.3 K J and 45 K J, the numerical difference is very small. Overcast weather (January 2016 4 - 6 days) two days before the thin cloud layer and some scattered light, the heat storage capacity of 1# and 2# in greenhouse is very small, the third day of thick clouds, scattered light is very weak, the heat storage capacity or even zero, is exothermic heat all day long, the average was 1551.4 K J and 935.5 K J, two of the greenhouse difference was 615.9 K J, numerical differences; although the greenhouse heat release was significantly higher than that of thick wall thin wall heat, but the average distance between the wall surface temperature at 0.1 M is only 0.6 degrees Celsius, the temperature in the greenhouse in front of the difference is smaller. The effect of maintaining the minimum temperature in the whole greenhouse is very small. 3. different weather conditions in the solar greenhouse wall 5 test layer of radiation heat distribution and wall heat transfer based on distribution characteristics of cloudy, cloudy, sunny weather haze and greenhouse 2# 5 layer test data collection, analysis of the test layer to receive solar radiation distribution. The results show that outdoor weather conditions have great influence on solar radiation intensity in greenhouse. The amount of solar radiation in sunny weather when the wall test layers accept was significantly higher than that in cloudy and mild haze, heavy haze (test day PM2.5 index 253) and cloudy accept the amount of radiation is very small. The solar radiation from different heights of the wall surface is second from the top to the bottom, the test layer is the largest, followed by the third test layer, 2 and 3, the radiation level of the test layer is relatively close, and the second is fourth, first and fifth test layer. At the same time, based on the different weather wall 5 test data acquisition layer, analyzed the 5 test layer and the back wall outside the room for heat distribution characteristics. The results show that the heat transfer from the north wall 1~5 test layer of total heat transfer ratio is as follows: first the test layer (wall thickness of 147 cm) is about 21%, second test layer (wall thickness of 186 cm) is about 19%, third test layer (wall thickness of 224 cm) is about 17%, fourth the test layer (wall thickness of 263 cm) is about 14%, fifth test layer (wall thickness of 300 cm) is about 12%, the back surface is about 17%; the greenhouse heat transfer to the outside from low to high in the enhancement, therefore, insulation measures should be strengthened with. 4. build the model of solar greenhouse wall temperature field based on finite element analysis software ANSYS to build a computing model for the solar greenhouse wall temperature field of the wall to measured temperature as degrees of freedom constraint imposed on the model boundary, the steady-state heat transfer method, simulated cloudy sunny conditions at different wall temperature change, and the simulation data and the measured data were compared, results showed that die
【学位授予单位】：山东农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S625.1

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