•A study found that regular microwaves don't heat liquids evenly
•The temperature difference between the top and bottom of a container can be more than 7°C
•But a silver-lined glass can heat liquids more evenly
We've all been there – we make a nice hot cup of tea or coffee and then forget about it. Instead of starting again from scratch, we pop it into the microwave to heat it up.
Some people might disagree, but unless it's hot chocolate, any microwaved beverage tastes like hot garbage.
And finally, science is backing this up. A study published in AIP Advances shows just what happens to liquids in the microwave. And their answer will hopefully settle the debate once and for all.
•Heat convection
The researchers used a run-of-the-mill microwave to heat water, alcohol and rice – and then compared the results to the same substances heated from the bottom on a stove.
With the latter, the temperatures ended up being even throughout the container.
It all boils down to heat convection. On a stove, for example, the process of convection allows the liquid at the bottom of the container to move to the top, resulting in a uniform temperature throughout.
One might assume that when you heat water in the microwave it will heat up like on a stove plate, but that's not how it works. In a microwave (which doesn't work with convection), the water at the top of the cup ends up being significantly hotter than the water at the bottom – about 7.8°C difference to be exact.
•Fixing the problem
But the researchers didn't stop there. They wanted to find a way to fix the temperature issue in microwaves.
They, therefore, created a container specifically for microwaving, using existing microwave rice cookers as inspiration.
They added silver plating to the rim of the glass to block the heating process at the top, creating a convection process similar to stovetop heating, which resulted in more uniform heat distribution.
They had to address the problem of arcing (sparks in the microwave when electromagnetic waves strike a metallic surface), though, and as one of the researchers explained, 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.
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