Microwave controlling factors

S.2 Controlling Factors of Grafting by Combination of Microwave Radiation and Free Radical Initiator (CAN)... 

Fig. 9.19 Controlling factors of microwave-assisted drying processes, and process intensification strategy.

Some software packages additionally offer pressure-controlled method development, which relies on the resulting pressure as a limiting factor. The microwave power is regulated by the adjusted pressure limit, and thus there is no influence on the resulting temperature. Because the reaction temperature is the most crucial parameter for successful chemical synthesis, this program variation is used only rarely. For preliminary experiments, it is recommended that temperature programs... 

The detailed study of the MCRs involving barbituric acids and 5-aminopyrazoles was published by Muravyova et al. [58]. The article describes the development of chemoselective cyclocondensations with help of microwave and ultrasonic irradiation. It was established that the temperature was the main factor in controlling the direction of the MCRs studied. 

Figure 1.3 Dielectric spectra for range of alcohols in the frequency range of 107-10n Hz. The absolute permittivities at low frequencies fall as the size of the alcohol increases and they began to respond to the microwave fields at lower frequencies because their relaxation times become longer. The loss factors that control the efficiency of conversion of microwave into thermal energies also reach their maxima at lower frequencies. The loss tangent is the ratio of the loss factor and permittivity at that frequency. (Idealised from the raw data illustrated in Ref. 10.)...

Also as discussed earlier, a difficulty can arise when a material being irradiated possesses a dissipation factor that increases with temperature. A microwave-driven thermal runaway can result unless the temperature is carefully monitored and the power controlled. On the other hand, solvents show a general decrease in dielectric constant with temperature. Efficiency of microwave absorption diminishes with temperature rise and can lead to poor matching of the microwave load, particularly as the fluid approaches the supercritical state. Solvents and reaction temperatures should be selected with these considerations in mind, as excess input microwave energy can lead to arcing. 

Recently the use of humidity sensors has greatly increased in a range of industries such as in the production of electronic devices, precision instruments and foodstuffs. As humidity is a permanent environmental factor, its measurement and/or control are of importance not only for human comfort but also for many industries and technologies. In recent years, major domestic applications of humidity sensors have been eg, automatic humidity control in air conditioners, automatic cooking by microwave ovens, and dew sensing on the cylinder heads of VTRs [1, 2]. 

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