| Chinese solar greenhouse is a kind of facility agricultural building which uses solar energy to produce off-season crops.At present,most of the existing greenhouse with heavy materials masonry wall,it belong to the passive sensible heat heat storage wall structure.This kind of wall is not only very thick and covers a large area,but also the thickness of the effective heat storage layer of the indoor side wall is small.As a result,there is a thick temperature stable layer inside the greenhouse wall,which will lead to the underutilization of the heat storage and release capacity of the wall material.In order to improve the internal temperature of the wall,increase the heat storage of the greenhouse wall and the ability of the wall to regulate and control the thermal environment in the solar greenhouse,a micro-heat pipe array heat storage wall for solar greenhouse was proposed in this paper,using the methods of experimental test and numerical simulation,focusing on the construction method of the micro heat pipe array heat storage wall of the solar greenhouse and the thermal characteristics of the heat storage wall,A series of researches have been carried out on the effect of the wall in improving the thermal environment of the greenhouse and the structural optimization of the micro heat pipe array heat storage wall.Firstly,through the literature summary of the current domestic and foreign scholars in the solar greenhouse wall heat storage and release performance of the study,the shortcomings of current solar greenhouse wall construction were analyzed.The results show that the thermal conductivity of the constant material is limited,which leads to the thin heat storage layer of the wall.Even though the use of phase change materials can effectively improve the heat storage and release performance of the greenhouse wall,there is still a thick temperature stable layer inside the wall.The active heat storage and release technology can significantly improve the heat storage and release performance of the greenhouse wall,but the active heat supply technology needs a higher initial investment,and the operation cost is high,and the management and maintenance technology is complex.Therefore,this paper proposes a kind of micro heat pipe array heat storage wall for solar greenhouse.During the heat storage period of the wall in the daytime,the evaporation section of the micro heat pipe array exposed on the surface of the wall to receive solar energy,and the internal working substance is evaporated to transfer heat quickly to the condensing section,and then the surrounding wall is heated by the condensing section,so as to improve the internal temperature of the wall.During the nighttime,the heat inside the wall is transferred from the condensing section to the evaporation section and then released to the air inside the greenhouse through the metal structure of the micro heat pipe array,so as to improve the control ability of the thermal environment inside the greenhouse at night.Secondly,through the test,the micro heat pipe array under different bending Angle and radius of curvature of the equivalent thermal conductivity coefficient,considering different structure of micro heat pipe array average equivalent coefficient of thermal conductivity,scope of work and decorate in the direction of wall depth,identify the better structure of micro heat pipe array with a bending Angle is 90° and curvature radius is 40 mm for solar greenhouse wall construction.Thirdly,in order to explore the thermal performence of the proposed wall with micro heat pipe array,a small greenhouse with micro heat pipe array heat storage wall and a greenhouse with common brick wall were built.Through testing of the thermal environment evaluation parameters of the solar greenhouse,the data of typical sunny days in winter were selected for comparative analysis.The results show that the temperature inside of the micro heat pipe array heat storage wall is higher than that of ordinary wall,especially near the location of micro heat pipe array condenser(120mm～240mm).The temperature difference between the proposed wall and ordinary wall has the largest value in the depth of 185 mm,which is about 5.5～7.0℃.The average temperature of 0～370mm area of the proposed wall is2.7～4.0℃ higher than the oridinary wall.During the heat storage period(9:00-17:00),the ambient temperature of the greenhouse with micro heat pipe array heat storage wall is slightly lower than that of the common greenhouse by 0.2～0.5℃,but during the heat release period at night(17:00 to 09:00 the next day),the average ambient temperature of the greenhouse with micro heat pipe array heat storage wall is 1.2～1.5℃ higher than that of the common greenhouse.The daily heat storage of the micro heat pipe array wall is 8.93%～14.35% higher than that of the common wall,and the daily heat release is 2.24%～8.07% higher than that of the common wall.From 23:00 at night to 07:00 the next day,the heat release rate of MHPA wall is higher than that of ordinary wall,with an average increase of 11.53%.Fourthly,in order to optimize the structural of the proposed heat storage wall,a 3D heat transfer model of the greenhouse with the same size as the experimental greenhouse was established to examine the reliability of the numerical calculation method,and the simulation was carried out using the experimental data as the boundary condition.The results show that the simulation values are in good agreement with the experimental values,and the average relative errors between the simulation values and the experimental values of the indoor air temperature and the wall surface temperature are 6.90% and 9.82%,respectively,which indicates that the numerical method is reasonable and reliable to be used for subsequent wall structure optimization simulation analysis.Fifthly,based on the common brick module of greenhouse wall,the 3D heat transfer model of common wall greenhouse with different arrangement depth is established.The results show that when the greenhouse insulation is closed(17:00),the maximum temperature at the embedded position of the micro heat pipe array inside the wall can reach 22.0℃.The maximum air temperature of the micro heat pipe array greenhouse at 9:00 of the next day was0.8℃,0.7℃ and 0.7℃ higher than that of the common greenhouse.According to the temperature distribution of the wall,among the layout depths of 154,204 and 254 mm respectively,the increase of the internal temperature of the wall is more obvious when the layout depth is 254 mm,and the influence depth of the temperature field of the wall is large.Finally,to explore the micro heat pipe array block in the north wall of greenhouse,a 3D model is established to study the arrangement of the dislocation of the micro heat pipe array block,which has double row arrangement and single permutation.The results show that at the end of the heat storage period at 17:00,from indoor to outdoor,in the depth of 0.35 m and0.45 m of the wall,the largest temperature value of dislocation arrangement,double row arrangement,single permutation and ordinary wall is 14.5℃,14.5℃,15.0℃,11.5℃,and11.75℃,11.75℃,12.0℃,11.0℃,respectively.All of the three arrangements can increase the temperature inside the wall,but single permutation will lead to heat concentration,which has a week influence on the temperature in the height direction of the wall.For double row arrangement,the distance of the top and bottom row of micro heat pipe array condensation section is larger,result in the delaytime of the temperature field in the wall height direction.At 9:00 the next day,the maximum air temperature of the micro heat pipe array greenhouse and the ordinary greenhouse was 8.8℃ and 8.0℃,respectively.The high temperature area of the air domain of the greenhouse under the dislocation arrangement was larger than that under the other two arrangements.Therefore,the dislocation arrangement was relatively better.The research results of this paper,which is the proposed solar greenhouse micro-heat pipe array heat storage wall and the optimization of its structural parameters,can provide a reference for the design and construction of solar greenhouse wall. |
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