The Construction Of A New Type Of Granary Phase Change Roof And Its Heat Transfer Characteristics

Grain is not only necessity of people’s life,but also strategic material for the country.Guaranteeing food security is the priority of governing and rejuvenating a country.The policy of long-term storage in granary was implemented in China.Thus,ensuring the quantity of grain is the basic requirement of guaranteeing national food security.It is important to maintain a preferred quality in the long-term grain storage period to meet with the rising requirement of people’s high living standard.However,the quality of grain was greatly affected by the external environment and the grain itself,especially in the high temperature in summer.In particular,the temperature of the air layer in the grain bin may even be 60℃,which will cause lots of loss and quality reduction of grain.Therefore,to improve the thermal insulation performance of granary’s roof is greatly concerned by engineers and researchers.With experimental and numerical simulation method,phase change material was corporated into cement-based material to product a new granary roof.Its heat transfer performance was then investigated.A new test platform was designed and built to test its heat transfer characteristics.Then,the effect of energy saving of this granary roof was evaluated.The main contents are as following:(1)A composite phase change material was developed to apply in granary roof structure.According to the melting blending method,the solid-liquid mixture of paraffin with different proportions was prepared by 58 # solid paraffin and the liquid paraffin.The composite phase change material was prepared with expanded graphite and high-density polyethylene.A scanning electron microscope was used to observe the microstructure of these materials.The differential scanning calorimeter was utilized to measure the thermal properties of these material.The results showed that the phase change temperature and latent heat of the composite phase change material are 33.8℃ and 79.95 k J/kg,respectively,which is appreciate for granary roof structure.(2)The preparation and thermal properties of phase change mortar layer on granary roof were studied to seek the optimal proportion of composite phase change material.Based on the made composite phase change materials,cement-based phase change energy storage mortar is developed by volume sand replacement method.The thermal adaptability test platform was designed to study the thermal stress variation with temperature and its thermal storage capacity.Finally,the optimum proportion of phase change mortar is determined to be 30%.(3)A new phase change granary roof was then constructed.The granary roof board is formed by phase change energy storage mortar and ordinary structure layer.A test platform was bulit to test its heat transfer performance.The ANSYS numerical model was established based on the test model.The effect of thickness and latent heat of phase change layer on the heat transfer characteristics of the roof panel under high temperature in Guangzhou is also ansyzed.Taking the ordinary granary roof board as a reference,the interior surface temperature of the phase change granary roof can be reduced by 4.2℃ when the thickness is 30 mm and phase change latent heat is 200 k J/kg,as well as 9% energy saving.