Microwave

Tea is the most popular beverage in the world after water. Not only good tea, but also the quality of water, skill of the tea maker, heating process as well as the heating source are so important for a good cup of tea. As AIP Publishing had reported, when a liquid is being warmed, the heating source (a stove, for example) heats the container from below. This process is called convection, as the liquid warms up from the bottom of the container, it becomes less dense and moves to the top, allowing a cooler section of the liquid to contact the source. This results in more uniform temperature throughout the glass. Inside a microwave, the electric field acting as the heating source exists everywhere. Since the entire glass itself is warming up, the convection process does not happen, and the liquid at the top of the container ends up being hotter than the liquid at the bottom.

A group of scholars from the University of Electronic Science & Technology of China (UESTC) have studied this non-uniform heating behavior and suggests a solution to this issue. By designing a silver plating to go along the rim of a glass, researchers have been able to shield the effects of the microwave at the surface of liquid. The silver acts as a guide for the waves, minimizing the electric field at the top and blocking the heating. This facilitates convection process similar to traditional approaches.

Similar metal structures with finely tuned geometry to avoid ignition have already been safely used for microwave steam pots and rice cookers. So placing silver in the microwave is not dangerous.

As Prof. Baoqing Zeng, at UESTC said, “After carefully designing the metal structure at the appropriate size, the metal edge, which is prone to ignition, is located at weak field strength, where it can completely avoid ignition, so it is still safe”

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References

1. AIP Publishing: https://publishing.aip.org/publications/latest-content/the-problem-with-microwaving-tea/