Comparing group (a) and group (b) in Fig. 6, the loss factor of
the circulating water inside the cavity had a significant influence
on the intensity of temperature in the sample. Although the patterns
were similar for both groups, reducing the loss factor of circulating
water by half (from e00
r ¼ 2:70 for tap water to e00
r ¼ 1:35
for deionized water) would result in a 23–37% increase in temperature.
The reason was that the amount of microwave energy dissipated
to heat is different in different circulating waters. For higher
lossy circulating water such as tap water, a relatively large amount
of the microwave energy was absorbed by the water reducing the
amount of energy that may be absorbed by the food. For relatively
lower lossy water such as deionized water, less microwave energy
was absorbed by the circulating water. This made most of the incident
microwave energy available to food material, producing
higher heating rate and final temperature of the food. In actual processing
in the MATS system, during the application of microwave
power to the heating cavities, there is an average of 2–3 C increase
in temperature of the circulating water (i.e., from 122 C to 124–
125 C) showing that water indeed absorbed microwave energy.
The microwave energy absorbed by the water is then subsequently
taken off by the chilling water through a heat exchanger attached
to the MATS system, which then reduces the temperature back to
122 C before entering the microwave heating section.