Study On A New Type Of Phase Change Energy Storage Granary Wall And Its Heat Transfer Characteristics

Grain is a necessity of life,while the food security is an important guarantee for China’s economic and social development.Grain is easily affected by the outdoor temperature during the long storage process.The outdoor temperature of granary wall can achieve the maximum temperature of 50℃,whereas the granary temperature demand is desired to no more than25℃.Then,the grain waste may be caused by the increase of indoor temperature in granary.The thermal insulation of granary structure is a key parameter on the quality of grain storage.Therefore,it is necessary to improve the thermal structure of granary wall to regulate the grain storage quality.A new phase change energy storage granary wall was proposed to improve the grain quality and reduce the grain storage loss.The new granary was formed by the ordinary wall and shape phase change plate with suitable grain storage temperature.The heat performance of phase change granary wall was analyzed by the combination of model experiment,theoretical analysis and numerical calculation.Meanwhile,the simulator was built to analyze the influence of parameters to optimize the granary wall.The thermal insulation of granary wall is enhanced by using the temperature regulate ability of phase change material,which provides theoretical basis for realizing the low-carbon operation of granary grain storage.The main investigations are as follows:(1)A shaped phase change plate suitable for the grain storage environment was developed.Through investigation and analysis,the phase change temperature of PCM should be higher 2～3℃ than the demand temperature.Therefore,the solid and liquid paraffin wax are melted according to different proportions to prepare mixed paraffin wax so that it can select the suitable mixed paraffin wax for grain storage environment.Then,the mixed paraffin,high density polyethylene and expanded graphite were melted to prepare the shaped phase change plate.It can be seen that when the blending ratio of solid and liquid is 7:3,the composite material of phase change temperature and latent heat were 28.5℃ and 150.7 k J/kg,respectively.The performance test of phase change plate shows that the thermal conductivity of the shaped phase change plate is improved.It can effectively meet the temperature requirements of grain storage in bin and is stable without leakage.(2)The heat transfer performance of phase change energy storage wall in granary is studied by building an experimental platform.An experimental platform was built by combining phase change plate with common granary wall.The experiment was used to test the heat transfer characteristics of the phase change wall,by comparing with the ordinary wall during the high temperature environment in summer of Zhengzhou.The results show that the phase change granary wall improves the thermal insulation of the wall,which can effectively reduce the heat transfer,internal surface temperature and heat flux density of the wall.The energy consumption of grain bin operation was saved to achieve the purpose of reducing carbon emission.(3)ANSYS numerical model is established to analyze the influence factors of heat transfer in the new phase change energy storage wall.A new type of phase change energy storage granary wall structure was constructed to simulate the effects of phase change temperature,latent heat,plate thickness and position on the thermal insulation performance of phase change energy storage granary wall under the typical ambient temperature in Zhengzhou.The results show that The heat transfer effect of the phase change wall is the best and the thermal insulation performance is significantly improved,when the phase change temperature is 28.5℃,the latent heat is 150.7 k J/kg.Furthermore,the plate thickness is 50 mm and is placed outside the granary wall.Compared with the ordinary bin wall,the maximum temperature on the internal surface of the phase change granary wall is 24.5℃.It is obviously that the maximum reduction of temperature,the average temperature delay time,the attenuation multiple and the energy saving rate were 1.65℃,14.86 h,17.35 and 17.8%,respectively.