微波化学动力学

Dynamics of Microwave Chemistry

微波促进化学反应具有加热速度快、效率高、选择性加热等优势,对于节能减排具有重要的意义,但在工程应用过程中存在微波功率反射大、加热不均匀和热失控等问题,限制了微波能的进一步应用。为了解决以上问题,设计出高效的微波化学反应器,必须在宏观上深入研究微波促进化学反应的动力学过程,将电磁场方程、热传导方程和反应动力学方程等多个微分方程相互耦合。然而,现有研究一直缺乏以上方程之间的严格耦合关系。因此,本文介绍了化学反应的极化及微波在化学反应中的耗散,建立了微波促进化学反应过程的宏观动力学耦合模型。首先,梳理了微波化学的宏观动力学耦合模型,并对该模型存在的挑战进行了总结,即现有模型缺乏微波在化学反应中的极化过程及耗散过程。其次,针对微波在化学反应中极化过程的挑战,引入了新的介电特性表征,结果表明,反应体系的介电特性由反应物浓度和生成物浓度的概率分布函数对应的1阶勒让德多项式展开式的系数决定。然后,针对微波在化学反应中耗散过程的挑战,根据能量守恒,引入了新的耗散功率公式,结果表明,微波在反应体系中的耗散由微波在反应物中的耗散、在生成物中的耗散及生成物和反应物耦合产生的耗散等部分组成。最后,通过实例,阐述了微波促进化学反应的宏观动力学应用,以推动微波化学工程化的进一步发展。

Microwave heating of chemical reactions offers the advantages of rapid heating,high efficiency,and selective heating,contributing to energy conservation and emission reduction.However,challenges such as significant microwave reflection,non-uniform heating,and thermal runaway hinder its broader applications.Addressing these issues and designing high-performance microwave reactors requires an in-depth study of the macro-level dynamics of microwave chemistry,encompassing Maxwell’s equations,the heat transfer equation,and the chemical kinetic equation.Unfortunately,existing research lacks the necessary coupling among these equations.This paper aims to establish a dynamic model of microwave heating in chemical reactions at the macro level,incorporating polarization and power loss of microwaves during chemical reactions.The initial focus involves reviewing the coupling model for the dynamics of microwave heating,acknowledging the challenge of neglecting polar-ization and power loss in chemical reactions.To overcome this,a new dielectric characterization is introduced,revealing that the dielectric proper-ties of chemical reactions are determined by the coefficients of the first-order Legendre polynomial expansion.To address the issue of microwave power loss in chemical reactions,a dissipation power formula is proposed based on the law of energy conservation.Results demonstrate that mi-crowave power loss in chemical reactions comprises three components:power loss in reactants,power loss in products,and power loss generated by the coupling between products and reactants.Finally,an illustrative example is provided to demonstrate the application of the proposed dynam-ic model in practical scenarios.