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通过数值模拟来研究微波加热化学反应这一非线性过程,重点讨论了温度场的时空变化及相关的热点、热失控现象.设被加热物体为无限长圆柱体,入射电磁波为平面波,于是导致了一个二维多物理场的耦合计算问题.计算中采用矩量法求解电磁场积分方程,采用半解析法求解热传导方程,并提出一种微波加热化学反应过程中反应物等效复介电常数的确定方法.对水和一假定的化学反应(A)的计算结果表明,微波加热过程中的热点现象广泛存在,其普遍规律是:当被加热物体半径较小时,电磁波的聚焦作用使物体内部某些地方出现最高温度;当半径增加到一定程度时,电磁波的趋肤效应开始逐渐明显,最高温度出现在物体表面附近,呈现出月牙形的高温区域.这和电磁波传播的基本物理规律相符.在半径值固定的条件下,水在加热过程中热点位置并无变化,而反应A在少数半径值下则有热点的移动.计算研究还发现,无论是水还是反应A,在半径值较小时,热失控现象易发生,即半径值微小的不同会使物体的最高温度有很大不同;相反,在半径值较大时,则热失控现象不明显.值得一提的是,水的最高温度随半径增大呈现震荡减小的趋势,而反应A则几乎是单调减小.这种差别是否只是偶然产生,还需要进一步做出研究.
The non-linear process of microwave heating chemical reaction is studied through numerical simulation, focusing on the spatio-temporal variations of temperature field and related hot spots and thermal runaway phenomena. When the object to be heated is an infinitely long cylinder and the incident electromagnetic wave is a plane wave, A two-dimensional multi-physics coupling problem is solved by using the moment method to solve the integral equation of the electromagnetic field. The heat conduction equation is solved by the semi-analytical method and the equivalent complex permittivity of the reactants in the microwave heating is determined The calculation results for water and a hypothetical chemical reaction (A) show that there are many hot phenomena in the microwave heating process. The general rule is that when the radius of the heated object is small, the focusing effect of the electromagnetic wave makes certain When the radius increases to a certain extent, the skin effect of electromagnetic waves begins to become noticeable, the highest temperature appears near the surface of the object, showing a crescent-shaped high temperature region.This is consistent with the basic physical laws of electromagnetic wave propagation.With the radius The value of the fixed conditions, the hot water in the heating process no change in position, and the reaction A in a few radius values There is a hot movement.Calculation study also found that both the water or the reaction A, when the radius value is small, the thermal runaway occurs easily, that is, the small radius of the object will make the maximum temperature is very different; the contrary, in the When the radius value is larger, the thermal runaway phenomenon is not obvious.It is worth mentioning that the maximum temperature of water shows a trend of decreasing the turbulence with the increase of radius, while the reaction A almost monotonically decreases.Is this difference only by chance Produced, but also need to make further research.