| Temperature was one of the most important environmental factors in solar greenhouse.Whether greenhouse crops could achieve high yield or high quality was greatly restricted by temperature.The back wall and soil in solar greenhouse absorbed solar radiation energy by day and released heat during night,with action of heat preservation quilt,to form temperature environment needed by greenhouse crops,and the crops could pass through the winter season.For many years,researchers had done a lot of research on the heat absorption and temperature preservation of solar greenhouse,but the mechanism of heat absorption and temperature preservation and its relation with night temperature were not very clear.Based on the microscopic concept of temperature and heat flow of non-conductive solids and deep-bed solar greenhouse as study subject,the characteristics of heat absorb and release of back wall and soil during the initial stage of unsteady heat conduction and its influence on the night temperature were studied in order to point out the research direction for improving the heat absorption and temperature preservation performance of greenhouse.The experiment was carried out in the south campus of Shandong Agricultural University in Tai’an City.The length of the greenhouse is 50 m long,the span is 9.3 m wide,and the depth under the ground surface is 0.5 m deep;the upper part of the back wall is 2.0 m wide and the lower part is 3.5 m wide;the greenhouse was covered with heat preservation quilt at night.Temperature sensors and heat flow plates were set at different height of the back wall and different span positions of the span to measure the temperature and heat release volume of the back wall and ground,and the temperature sensors were set horizontally and vertically in the greenhouse space to measure the air temperature of that space.The experiment was in the winter of 2015,the observation time was 2015-12-15～2016-01-27,and tomatoes were planted and in full fruit period.The results were as follows:1.The attenuation curve was calculated to show the degree of temperature attenuation inside the back wall,and the physical model of temperature and heat conversion was constructed by using the attenuation curve to show basic characteristics of temperature and heat flow conversion during initial stage of non-conductive solids.2.There was a correlation between the accumulated heat absorbing and release volume and the temperature difference of heat absorbing and release of back wall and soil,which indicated that the model could reflect the process of temperature and heat conversion.The accumulated heat absorbing and release volume of the back wall was 1381.98 KJ/m2、1165.77 KJ/m2,respectively,the heat absorbing volume was 84.36%of that of heat release;and the accumulated heat absorbing and release volume of the soil was 1046.21KJ/m2、1272.89 KJ/m2,respectively,and the heat release volume was 121.67%of that of heat absorbing;the volume of heat absorbing and release of the soil was not balanced,and the overall temperature level decreased.The soil heat absorbing volume was 156.45%of that of the back wall,and the heat absorbing condition of the back wall was better than that of the soil;the heat release volume of the soil was 225.66%of that of the back wall,and the role of heat release of the soil in the formation of greenhouse night air temperature was greater than that of the back wall.3.The temperature of the back wall and soil decreased after releasing heat;temperature decreasing was external manifestation of heat releasing,and heat releasing was internal cause of temperature decrease.The heat releasing volume from the back wall increased gradually from top to bottom,and the volume from the middle of the wall also was more when the back wall absorb much heat during the day;The ratio between the temperature decreasing and the heat releasing was was not consistent with that of the back wall,and there was heat flowing from top to bottom inside the wall.The heat releasing volume from the soil was more on both sides and less in the middle of the span;the ratio between temperature decreasing and heat releasing volume in different span positions was also inconsistent,and there was heat flowing from north to south inside the soil.4.The heat releasing volume of the soil was more than that of the back wall,heat releasing volume of the soil was 75.61%～85.72%of the total of the back wall and soil,the soil heat release and the back wall heat release play a leading and auxiliary role in the formation of greenhouse temperature,respectively.The back wall and soil heat release was a passive heat release process driven by external low temperature.Influenced by the shape of the cover surface,the exothermic driving ratio on the back wall gradually increased with the height of the back wall decreasing,and the exothermic driving ratio on the ground increased gradually with the span distance increasing,resulting in the imbalance of the heat releasing.In this experiment,the integral values of exothermic driving proportional on the back wall and ground were 33.64,10.42,respectively,which was the reason that the soil heat release played a leading role in the formation of night air temperature.5.The mechanism of temperature and heat releasing volume of the back wall and soil on the formation of greenhouse temperature was the principle of heat absorption and temperature preservation in solar greenhouse.The higher the temperature of the back wall and soil,or the soil,the higher the greenhouse night temperature;the temperature of the back wall and soil,or the soil were the foundation of greenhouse air temperature,which has a direct impact on greenhouse night temperature.In this experiment,the night air temperature was basically 91%of the temperature of the back wall and soil,and was basically 93%of the soil temperature.Compared with the back wall temperature,the correlation between the back wall temperature and the greenhouse night temperature was low.The heat releasing volume of the back wall and soil affected the greenhouse air temperature by reducing the temperature of the back wall and soil and increasing the temperature difference of convection heat transfer.The more heat released from the back wall and soil,the more the greenhouse air temperature decreased,and the heat release volume had an indirect effect on the greenhouse air temperature. |
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