Tea drinkers have been saying this for years. Water heated in a microwave oven is simply not the same.
Usually, when heating a liquid, the heating source – a stove, for example – heats the vessel from below. Through a process called convection, as the liquid to the bottom of the container heats up, it becomes less dense and moves to the top, allowing a cooler portion of the liquid to come into contact with the source. This eventually leads to the same temperature throughout the cup.
Inside the microwave, however, the electric field acting as a source of heating exists everywhere. As the cup itself is also heated, the convection process does not take place and the liquid at the top of the container turns out to be much hotter than the liquid at the bottom.
A team of researchers from the University of Electronic Science and Technology in China studied this uneven behavior in heating and presented a solution to this common problem in the journal. AIP advances, from AIP Publishing.
By designing a silver coating to run along the rim of the cup, the group was able to protect the effects of the microwave on the surface of the liquid. Silver acts as a guide for the waves, reducing the electric field at the top and effectively blocking the heating. This creates a convection process similar to traditional approaches, leading to a more uniform temperature.
Placing silver in the microwave may seem like a dangerous idea, but similar metal structures with fine-tuned geometry to avoid ignition are now safely used for microwave steamers and rice cookers.
“After carefully designing the metal structure with the appropriate size, the metal edge, which is prone to ignition, is located at low field strength, where it can completely avoid ignition, so it is still safe,”
Solids do not undergo convection, so letting your residue heat evenly is a completely different challenge.
“For solids, there is no easy way to design a bowl or a plate to achieve a much better heating result,” Zen said. “We can change the distribution of the field, but the change is very small, so the improvement is limited.”
The group is considering other ways to improve the unevenness of solid foods, but the methods are currently too expensive for practical use. For now, they are focusing on working with a microwave oven manufacturer to commercialize their microwave liquid accessories.
A future in which tea can be microwaved without ridicule may not be too far away.
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Materials provided by American Institute of Physics,, Note: Content can be edited for style and length.