| The "Belt and Road",the national strategy of rural revitalization and the policy of benefiting farmers in western China have promoted the leap-forward development of solar greenhouse industry in Northwest China,which has played a huge role in the annual balanced supply of vegetables and the increase of farmers’ employment and income.Although Northwest China is rich in solar energy resources,the cold winter and large daily temperature range in this region,coupled with the passive heat storage and release mode of traditional solar greenhouse relying on wall materials,make the thermal environment construction and control technology of solar greenhouse in winter face new challenges.In order to improve the greenhouse wall heat storage capacity,improve the environment of greenhouse greenhouse thermal heat storage wall regulation ability,this article,on the basis of the principle of passive regenerative heat transfer enhancement in combination with micro-heat pipe technology,this paper proposes a sunlight greenhouse of micro heat pipe array phase change heat storage wall,adopt the method of experiment,the paper explores the heat transfer characteristics of heat storage wall and its effect on the improvement of the thermal environment of greenhouse,mainly in the following several aspects of research work.Firstly,the important progress made by scholars at home and abroad in greenhouse wall heat storage and improvement of greenhouse thermal environment was summarized through literature review,and the shortcomings of traditional solar greenhouse wall in heat storage and release,thermal insulation performance,construction methods and other aspects were analyzed.In this paper,the enhanced heat transfer technology of micro-heat pipe array and phase change heat storage technology are combined together.Based on the greenhouse wall heat storage,a construction method of phase change heat storage wall of micro-heat pipe array in passive solar greenhouse is proposed.The wall uses the large heat transport capacity of the winding micro-heat pipe array to transfer the excess solar energy in the greenhouse during the day into the wall.At the same time,the latent heat storage is carried out by the phase change material board.When the indoor temperature drops at night,the stored heat energy is released to the room in time to maximize the use of the heat storage capacity of the greenhouse wall itself.Secondly,according to the construction mode of the wall,the heat transfer performance test bed of the micro-heat pipe array was designed,and the heat transfer ability of the winding micro-heat pipe was quantitatively analyzed,and the influence law of the bending radius and bending Angle on the heat transfer performance of the micro-heat pipe array was sought.The experimental results show that the micro-heat pipe arrays with two lengths of 500 mm and750mm are bent into "Z" shape,and the micro-heat pipe arrays still have good geothermal transmission capacity.Based on the demand of greenhouse wall,taking the flat heat pipe with an inclination Angle of 90° as the comparison object,the axial temperature distribution on the surface of the heat pipe is more uniform after winding,and the isothermal property of the heat pipe increases in a certain temperature range,but winding will reduce the maximum heat transfer of the micro-heat pipe array.The equivalent thermal conductivity of the winding micro-heat pipe array is increased compared with that of the straight micro-heat pipe array.For the micro-heat pipe array of two lengths,under the same heating power,the effect of different bending radius on the equivalent thermal conductivity is not obvious.The shorter the horizontal part of the adiabatic section of "Z" winding micro-heat pipe array,the greater the heat transfer limit.After winding,the heat resistance of the heat pipe is reduced,and the heat resistance is mainly concentrated in the evaporation section.Therefore,the heat resistance of the evaporation section should be reduced as much as possible to obtain better heat transfer performance of the heat pipe.According to the above test results,considering the heat transfer capacity of micro-heat pipe array and the construction requirements of solar greenhouse wall,a "Z" shaped micro heat pipe array with a length of 500 mm,a bending radius of 40 mm and a bending Angle of 90° in the condensation section was selected to make micro-heat pipe block and construct the greenhouse heat storage wall.Finally,according to the bending of micro-heat pipe array size is determined,the winding micro-heat pipe with cement mortar laying bricks or stones of micro-heat pipe block array,and then a small-size greenhouse test bed was built by using the manufactured blocks and phase change board to carry out comparative tests.The heat storage,heat storage and release rate,indoor air temperature and the temperature of blackened and unblackened inner surface of the wall are analyzed.The results show that the maximum temperature of the inner surface of the wall is 48.05℃,47.84℃ and 49.69℃ for three consecutive days in typical sunny days in winter,which is 23.60% higher than that of the ordinary wall on average.The surface temperature of the test wall was increased by 5.54℃ on average compared with that of the ordinary wall in three consecutive complete heat storage and release cycles,in which the temperature was increased by 7.60℃ on average in the heat storage period and 4.49℃ in the heat release period.Before blackening the surface of the test wall,the surface temperature of the test wall in the heat storage period is 3.2℃ higher than that of the ordinary wall on average,and 5.8℃ higher than that of the ordinary wall after blackening,and the maximum temperature increases by 22.3% on average.The peak value of air temperature in the tested greenhouse was 0.77℃,0.68℃ and 1.93℃ higher than that in the ordinary greenhouse,respectively.From the end of heat storage to the end of heat release in the next morning,the air temperature of the experimental greenhouse decreased by 18.15℃,13.49℃ and 18.49℃,respectively,which decreased by 24% compared with the ordinary greenhouse on average.According to the analysis of the heat storage of the wall,the heat storage of the experimental wall in the typical sunny days in winter is increased by 89.71%,106.80% and91.68% respectively compared with the ordinary wall,and the heat release of the new wall is increased by 97.97%,95.97% and 95.27% respectively compared with the ordinary wall.In the heat storage period,the heat storage rate of the test wall is 87.99% higher than that of the ordinary wall,and the maximum heat release rate of the test wall is 76.93 W in the heat release period,which is 147% higher than the 31.15 W of the ordinary wall.The average heat release rate is 46.27 W,which is 98.86% higher than the 26.28 W of the ordinary wall.The combination of micro-heat pipe array and phase change board effectively improves the thermal performance of the greenhouse wall,increases the heat storage of the wall and increases the internal temperature of the wall,so that the wall can release more heat at night to maintain the indoor thermal environment.In this paper,a phase change heat storage wall with micro-heat pipe array and its construction method are presented.The thermal performance of the wall and its improving effect on the thermal environment of greenhouse are analyzed.The research results can provide reference for the construction of new solar greenhouse wall in the northwest of China. |
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