滚筒干燥器内丝状物料的传热传质特性研究

干燥涉及众多生产领域,卷烟加工过程中存在干燥环节,滚筒烘丝机是用于干燥烟丝的主要设备。在滚筒烘丝机内,烟丝与周围环境进行热质交换,不同的运行控制条件,将直接影响烟丝的品质。由于干燥过程受众多因素的影响,至今烟草加工企业对烘丝机内部烟丝的传热传质特性缺乏深层次的认识,不利于烟丝品质的提高。针对上述背景,本文基于传热传质学、流体力学、多相流动等相关理论,通过计算机数值模拟方法,建立并求解滚筒内的传热传质数学模型,获得不同操作条件下烟丝温度、含水率变化的详细信息,并将所得结果与实际生产数据相验证。研究结果表明,烟丝与气流逆流流动条件下,干燥过程存在三个阶段：预热段、恒速段、降速段,烟丝含水率先升后降,烟丝温度经历先升高、后降低、再升高的过程;顺流流动条件下,干燥过程存在两个阶段：预热段与恒速段,烟丝含水率沿程单调下降,烟丝温度在预热段急剧上升,在恒速段平缓上升。

Heat and Mass Transfer Characteristics of Filamentary Materials in Rotary Dryer

Drying involves many areas of production, it＇s one of procedures in cigarette processing, and the rotary dryer is the major equipment in cut tobacco drying. In a rotary dryer, there is heat and mass transfer between cut tobacco and its surroundings, and the operating conditions will affect the quality of cut tobacco directly. As the drying process affected by many factors, cigarette processing enterprises still lack in-depth understanding of the heat and mass transfer in rotary dryer. It is not desirable for improving the quality of cut tobacco. So based on the theories of heat and mass transfer, fluid mechanics, multiphase flow, and others related, this article established a mathematical model, solved it through computer numerical method, and obtained the changes of cut tobacco temperature and moisture content in detail under different operating conditions. The results were verified with the actual production data. The results show that, under countercurrent airflow condition, there are three stages of the drying process： preheat period, constant period and deceleration period; the cut tobacco moisture content increases first and then decrease, and the temperature increases first, then decrease and then increases again. Under co-current flow condition, there are preheat period and constant period, the cut tobacco moisture content decreases monotonically, and the temperature increases sharply in preheating period, and slowly in constant period.