物料干燥系统热湿传递及其交叉作用的热力学分析

发布时间：2018-04-11 14:54

本文选题：干燥过程 + 热力学分析　；参考：《兰州理工大学》2017年硕士论文

【摘要】：干燥是指物料中的水分受热后以水蒸汽的形式溢出,随后被流经的干燥空气所携带而离开物料系统,从而起到了降低物料系统水分的目的。物料受热时的传热过程,以及水蒸汽离开物料系统时的传质过程构成了干燥过程中两个基本的热力学过程。通过研究干燥过程中传热过程与传质过程的基本规律及其动力学特征,进而揭示干燥过程中传热过程与传质过程相互作用机制,即热湿交叉过程中蕴含的热力学机制,构成了本论文的基本研究内容。首先以干燥过程中的热量守恒定律与质量守恒定律为基础,分析了干燥过程中热量与湿分的传递规律,并以此为依据分析对比了不同类型干燥设备效率的高低。基于守恒定律进行干燥过程的分析时,研究对象的选取方式,要根据分析的侧重点的不同而不同。以控制质量的干燥系统为研究对象时,是以干燥设备几何尺寸的设计和干燥工艺条件选定为目的,而以控制容积的干燥系统为研究对象时,是为了便于对干燥过程进行实时的观测,并能够根据变量变化情况及时调整干燥的工艺条件。其次,对干燥过程传热传湿过程进行了动力学分析。通过对干物料中湿分的性质进行研究,揭示了不同干燥阶段热量传递与湿分传递的动力学特点。研究表明,由于干燥的本质是湿分的相变蒸发,因此,湿空气的受热相变过程中,温度随熵的变化规律,可以反映物料干燥时传热传湿过程的热动力学特征。最后通过研究物料干燥系统的热湿交叉作用,揭示了物料干燥时热湿交叉作用所蕴含的两种热力机制。当传热过程与传湿过程均为自发过程时,热湿交叉满足场协同机制,这时传热过程与传湿过程相互增强,即传热过程的增强可以导致传湿过程的增强。当传热过程为自发过程,传湿过程为非自发过程时,热湿交叉满足热力学耦合机制,传热过程的减弱可以强化传湿过程,即传湿过程的增强是以传热过程的减弱为前提。依据这两种热力学机制,可以在不同的干燥阶段通过控制传热过程达到最佳的传湿效果。
[Abstract]:Drying means that the moisture in the material overflows in the form of water vapor after being heated, and then carried by the dry air flowing through it and then leaves the material system, which plays the purpose of reducing the moisture content of the material system.The heat transfer process when the material is heated and the mass transfer process when the water vapor leaves the material system constitute two basic thermodynamic processes in the drying process.By studying the basic laws and dynamic characteristics of heat and mass transfer in drying process, the interaction mechanism of heat and mass transfer in drying process is revealed, that is, the thermodynamic mechanism in the process of heat and moisture intersecting.Constitute the basic research content of this paper.On the basis of heat conservation law and mass conservation law in drying process, the transfer law of heat and moisture content in drying process is analyzed and the efficiency of different drying equipment is analyzed and compared.In the analysis of drying process based on conservation law, the selection method of the research object should be different according to the emphasis of the analysis.When the drying system with controlled quality is taken as the research object, the design of the geometric dimension of the drying equipment and the selection of drying process conditions are taken as the purpose, while the drying system with controlled volume is taken as the research object.It is convenient to observe the drying process in real time and to adjust the drying conditions according to the variation of variables.Secondly, the kinetics of heat and moisture transfer in drying process is analyzed.The dynamic characteristics of heat transfer and wet fraction transfer in dry materials were revealed by studying the properties of moisture content in dry materials.The results show that since the essence of drying is vaporization of wet fraction, the change of temperature with entropy can reflect the thermodynamics of heat and moisture transfer process in drying process of wet air.Finally, by studying the heat and moisture crossover of material drying system, two kinds of thermal mechanism are revealed.When the heat transfer process is a spontaneous process and the moisture transfer process is a non-spontaneous process, the thermodynamics coupling mechanism is satisfied. The weakening of the heat transfer process can strengthen the moisture transfer process, that is, the enhancement of the moisture transfer process is based on the weakening of the heat transfer process.According to these two thermodynamic mechanisms, the optimal moisture transfer effect can be achieved by controlling the heat transfer process in different drying stages.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ028.67

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