When you heat liquids like water, milk and tea in microwave, you must have noticed a difference as compared to heating on stove. Of course, the process is faster and that's the reason we choose microwave over stove for heating. But you must have also realised that your glass or container also gets heated up, and while the top layer of liquid is hot, the bottom liquid is not so much. Do you know what that is?
Stove cooking or heating uses the process of convection, wherein the bottom of the vessel gets heated and the heat gradually moves up to heat the content throughout. Whereas, in the microwave, the electric field is spread throughout the microwave, which prevents the convection process to happen. What happens is that the container gets heated and the heat touches the topmost layer of the liquid first with not much heat passing through to the bottom layer. Hence, there is uneven heating of the liquid.
A team of researchers from the University of Electronic Science & Technology of China studied this non-uniform heating behaviour of microwave and found a solution for the issue.
"There are two ways to improve the uniformity of microwave heating: one is improving the uniformity of the electromagnetic field in the microwave cavity and the other is improving the uniformity of microwave energy absorption in materials," said Peiyang Zhao, one of the researchers.
The team placed a silver cup on the glass containing liquid and because of the good heat conductivity of sliver, there was uniform temperature movement and heating of the liquid. The results were published in the journal AIP Advances. Whether it's safe to place silver in the microwave with current structures, is still not proven. But, microwave manufacturers can certainly pick this cue to modify them.
"Because of the good conductivity of silver, we plated a layer of metallic silver on the top of the glass, as shown in Fig. 7, and the cup is placed in the center of the ceramic plate; since the wall of the glass is very thin, the silvered part of the glass can be considered as a circular waveguide. Because the cup is placed in the center of the microwave oven, the distance between the cup and the cavity wall is far and the possibility of ignition is also small. Besides this, we also simulated the temperature distribution of heated water after adding a metal cover to the glass, "Peiyang Zhao added.