Microwave oven field distribution

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

Domestic microwave oven. The cheapest and most popular equipment used in organic synthesis is the domestic microwave oven (with a limited power of 800-1,000 W). The distribution of electric field is heterogenous and the sample is always subjected to maximum power levels for varying time periods. In the... 

The electric field is a crucial condition in microwave heating and the design of microwave ovens. If electric field distributions within empty microwave ovens are well known, the problem is totally different if loaded microwave ovens are considered. Perturbation theory can be used if the sample is very small. In fact, the magnitude of the perturbation is proportional to reactor-to-applicator volume ratio. The perturbation could be negligible if this ratio is close to 10 and most laboratory and industrial devices have higher ratios [120]. 

One of the most important problems detected in microwave ovens is the presence of hot spots . Conventional fixed-frequency microwave heating suffers from local spatial fluctuations in the electromagnetic field that causes nonuniform power distribution within microwave cavities, thus leading to rmeven heating and potentially poor product quality [24]. 

In multimode cavities (conceptually similar to a domestic oven) the microwaves, which enter the cavity, are reflected by the walls and the load over the typically large cavity. A mode stirrer ensures that the field distribution is as homogeneous as possible. 

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