The chamber is made of stainless steel, and there are five teflon shelves placed inside, supported on frames on both sides of the chamber (see Fig. below), on which food products can be placed. The location of the shelves relative to the reference chamber remained unchanged. On the back wall of the chamber there are MW windows in through which microwaves enter to the chamber with food products, and MW mixer which ensure uniformity of the MW field. Additionally, chamber had been equipped with the necessary equipment to ensure process control (temperature and pressure sensors) and operational safety (propane and arc detection sensors). The temperature of the shelf with products was monitored using the fiber optic sensor.
The microwave heating system was based on two continuous-wave magnetrons LG 2M246–03TAG (nominal output power 1040 W at 2460 MHz) that work alternately, placed on the chamber’s back wall as presented in Fig. below. During trial tests, overheating of the magnetron was observed. Therefore, to prevent the magnetrons from overheating, additional instrumentation was required. In particular, the microwave isolator had been installed between the magnetron and the vacuum chamber. That device transmits the microwave in only one direction. Consequently, even if a significant amount of power returns into the magnetron direction, it is filtered by the mentioned isolator.
The MW prototype freeze-dryer (a) front view, (b) back view and (c) additional MW heating system equipment