| In the past,the solar greenhouse mainly relied on wall and soil for heat storage,the utilization rate of solar energy was low,and the temperature difference between day and night was large,which led to the instability of the greenhouse environment and the poor growth of plants.Therefore,this experimental study designed a leafy production system with low cost and stable environment.The deep-water floating cultivation technology was used to collect and store solar energy with a large amount of nutrient solution as a carrier of heat storage and release to regulate the internal environment of the system.The experiment first studied the change law of heat transfer of nutrient solution.The temperature change of nutrient solution at different depths of leaf vegetable system was significantly different.The largest amplitude of temperature variation of nutrition solutions was at surface layer.The deeper the nutrient solution,the smaller was the variation.The highest temperature of nutrient solution in autumn decreased rapidly with increasing nutrient solution depth,and happened at 14:00,16:00,17:40 and 20:00for the solution depths of 0 cm,5 cm,10 cm and 15 cm respectively.Based on the daily range of temperature at different depths,nutrient solutions were divided into three temperature layers: heat exchange layer(daily range of temperature > 3?),heat buffer layer(daily range of temperature at 1-3?)and heat stability layer(daily range of temperature at 0-1?),which were located in the solution layers of 0-5 cm,5-10 cm and 10-15 cm,respectively.When the nutrient solution depth of leaf vegetable production system was 21.5 cm,the relationship between daily temperature difference and solution depth(0 cm,5 cm,10 cm,15 cm were expressed as 1,2,3 and 4 in the function)was described with the logarithmic function y =2.619ln(x)+ 4.215 2.That indicated that daily temperature difference at 20 cm below solution surface was0?.The above results indicated that energy was conducted on a layer-by-layer basis in the nutrient solution of hydroponic system.In order to improve the utilization rate of solar energy,the environmental effects of covering materials were studied on the leafy production system.In winter,the internal temperature of the system decreased from 13:00 to more than 5?/ h,the cooling rate decreased after covering the insulation material,aluminumfoil was 0.15?/ h,and the polyester and non-woven was 0.3?/ h.Although covering the insulation material could alleviate the low temperature at night and reduced the energy loss in the system,other supporting warming measures such as adding a heating wire to ensure the safe wintering of the leafy vegetables were still needed.In summer,the shading net was covered on the top of the leaf vegetable system,and the temperature droped rapidly.Shading at 10:00-16:30,the liquid temperature was below28? throughout the day.It could reduce the heat entering the system and alleviate the high temperature,but other supporting cooling measures were needed to ensure the safer summer of lettuce.It was found that the porous plate could dissipate some heat by evaporation,therefore,the effect of liquid surface covering with different materials on its environment was studied.The leaf temperature production system had a large air temperature change after the liquid surface covered the porous planting plate,and the liquid temperature was low overall.The heat storage and heat release of the transparent film were increased by 19.56% and 15.58%,respectively;A layer of film on the planting board could reduce evaporation,conducive to the improvement of rhizosphere temperature,stabilize the liquid temperature and reduce energy loss in the inner environment of the leafy vegetable production system,and was easy to operate.In short,the leafy vegetable production system that we studied and designed was feasible in actual production.Through the implementation of shading,cooling,heat preservation and other measures,the water environment was stable and suitable for leafy vegetable growth. |
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