摘要
为了研究稻谷在整个储藏周期的温度、含水率分布规律以及黄变情况,该研究以南昌地区混凝土结构浅圆仓为研究对象,基于多孔介质的传热传质理论和局部热平衡原理,建立了仓储稻谷储藏过程中粮堆内部流动和热湿耦合传递的数学模型,并结合稻谷黄变数学模型,采用数值预测的方法模拟分析了全年自然(密闭)储藏和全年自然(密闭)储藏加机械通风时仓储稻谷内部温度和含水率的分布规律以及稻谷黄变规律。研究发现,当稻谷全年自然(密闭)储藏时,由于谷物呼吸放热,粮堆内部大部分区域温度都非常高,超过了35.0℃,并且这部分区域的稻谷极易黄变;自然(密闭)储藏期间,在自然对流的微气流作用下,粮堆内部水分向粮面迁移,导致粮面附近的含水率升高。在自然(密闭)储藏期间进行机械通风时,粮堆内部温度下降,且由于太阳辐射的影响,粮堆高温区在南墙壁附近和靠近南侧的粮面附近,这部分区域的稻谷黄变也较严重;通风后的自然(密闭)储藏期间,在自然对流的微气流作用下,粮堆内部水分向仓底附近迁移,仓底附近的稻谷含水率较高。研究结果为粮食仓储企业安全储粮提供参考和理论依据。
A theoretical model was proposed to implement the heat transfer,moisture content,and momentum in the cylinder-shaped silos,where rice was stored.A yellowing model of rice was also developed,according to the kinetics of color change.A field experiment was then carried out to evaluate the present model.A systematic investigation was then made on the temporal and spatial distribution of temperature,moisture content,and yellowness of stored rice within the concrete silo in the Nanchang area of China during storage without and with mechanical ventilation in the whole year.The simulation results show that the temperature of bulk rice near the inner wall of the silo had fluctuated with the local atmospheric temperature,and the mean temperature of bulk rice in the silo was rising during sealed storage without mechanical ventilation.Since the grain was a very good insulator,the center of the silo stayed much warmer with the longer storage.The temperature of bulk rice was more than 35.0℃in the most area of the silo,due to the heat transfer between the silo with the local atmosphere and the exothermic heat of the grain respiration in the silo,where the rice was very easy to turn yellow during the sealed storage without mechanical ventilation.Moisture migration also occurred in the rice storage silo,resulting from some differences in grain under air temperatures.The cold air on the outside of the bin(cold air was much heavier)pushed the warm air into the center of the silo in autumn,where the warm air moved upward and eventually encountered the cool air at the top.The currents of natural convection were formed by the displacement of hot air by the dense cold air.The moisture content of grain bulk migrated to the vicinity of the grain surface by the natural air currents,resulting in the condensation and crusting in the surface of the bulk grain.The opposite process was found in spring and summer,particularly with the condensation and spoilage at the bottom of the bin.Therefore,mechanical ventilation was used to alternately alleviate the natural air currents and the moisture migration for the sealed storage.In this case,the higher temperature area of the grain bulk was observed near the south wall,and the grain surface on the south side,due to the solar radiation,where the rice was relatively yellowish.The internal temperature of grain bulk dropped significantly during ventilation,particularly after a period of sealed storage.The yellowness of rice was relatively lower than before for the sealed storage during ventilation over the whole year,indicating that the temperature posed a predominant effect on the color change.Meanwhile,the ventilation can widely be expected to balance the temperature differences in the bulk rice,the natural current,and moisture migration during storage.The findings can also provide a strong reference and theoretical basis for grain storage.
作者
王远成
余海
杨开敏
王柯
Wang Yuancheng;Yu Hai;Yang Kaimin;Wang Ke(College of Thermal Energy Engineering,Shandong Jianzhu University,Jinan 250101,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2022年第4期297-307,共11页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家重点研发计划项目(2016YFD0400100,2016YFD0401002)
国家粮食公益专项(201513001)。
关键词
稻谷
自然储藏
机械通风
热湿耦合传递
黄变
数值模拟
rice
sealed storage
mechanical ventilation
coupled heat and moisture transfer
yellowing
numerical simulation
作者简介
王远成,博士,教授,研究方向为复杂多孔介质传热传质。Email:wycjn1@163.com。
