Abstract A novel heating efficiency analysis of the microwave heated stop-flow (i.e. stagnant liquid) and continuous-flow reactors has been presented. The thermal losses to the surrounding air by natural convection have been taken into account for heating efficiency calculation of the microwave heating process. The effect of the load diameter in the range of 4–29 mm on the heating efficiency of ethylene glycol was studied in a single mode microwave cavity under continuous flow and stop-flow conditions. The variation of the microwave absorbing properties of the load with temperature was estimated. Under stop-flow conditions, the heating efficiency depends on the load diameter. The highest heating efficiency has been observed at the load diameter close to the half wavelength of the electromagnetic field in the corresponding medium. Under continuous-flow conditions, the heating efficiency increased linearly. However, microwave leakage above the propagation diameter restricted further experimentation at higher load diameters. Contrary to the stop-flow conditions, the load temperature did not raise monotonously from the inlet to outlet under continuous-flow conditions. This was due to the combined effect of lagging convective heat fluxes in comparison to volumetric heating. This severely disturbs the uniformity of the electromagnetic field in the axial direction and creates areas of high and low field intensity along the load length decreasing the heating efficiency as compared to stop-flow conditions.

中文翻译：

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在停流和连续流条件下负载大小对微波加热效率的影响

摘要 对微波加热的停流（即停滞液体）和连续流反应器进行了新的加热效率分析。在计算微波加热过程的加热效率时，已经考虑了自然对流对周围空气的热损失。在连续流和停流条件下，在单模微波腔中研究了负载直径在 4-29 mm 范围内对乙二醇加热效率的影响。估计负载的微波吸收特性随温度的变化。在停流条件下，加热效率取决于负载直径。在接近相应介质中电磁场半波长的负载直径处观察到最高的加热效率。在连续流动条件下，加热效率线性增加。然而，传播直径以上的微波泄漏限制了在更高负载直径下的进一步实验。与停流条件相反，在连续流条件下，负载温度不会从入口到出口单调升高。这是由于与体积加热相比滞后对流热通量的综合影响。这严重扰乱了轴向电磁场的均匀性，并在负载长度上产生了高场强和低场强的区域，与停流条件相比，降低了加热效率。与停流条件相反，在连续流条件下，负载温度不会从入口到出口单调升高。这是由于与体积加热相比滞后对流热通量的综合影响。这严重扰乱了轴向电磁场的均匀性，并在负载长度上产生了高场强和低场强的区域，与停流条件相比，降低了加热效率。与停流条件相反，在连续流条件下，负载温度不会从入口到出口单调升高。这是由于与体积加热相比滞后对流热通量的综合影响。这严重扰乱了轴向电磁场的均匀性，并在负载长度上产生了高场强和低场强的区域，与停流条件相比，降低了加热效率。