Photo credit: CSA Images - Getty Images
Photo credit: CSA Images – Getty Images

From Popular Mechanics

  • Should you prepare your cup of tea with water heated in the microwave or on the stovetop?

  • The verdict is in, according to research from the University of Electronic Science & Technology of China: the kettle is superior.

  • On August 4, the scientists published their results in the journal AIP Advances.

Scientists from the University of Electronic Science & Technology of China are spilling some tea in a new paper published in the journal AIP Advances.

In the study, they settle a seminal debate once and for all: Kettles are the superior apparatus to heat up water for your tea—not the microwave.

“Usually, the fluidity of liquids is considered to make the temperature field uniform, when it is heated, because of the heat convection, but there is something different when microwave heating,” the authors note in the paper’s abstract. “The temperature of the top is always the highest in the liquid when heated by microwaves.”

🔬 Science explains everything. Come find your answer.

So if you go the microwave route, the water in your mug might be the premium H2O you hoped it would be—but only at the very top. It’s the same deal as reheating a bowl of soup: the top might be scalding, but the layers underneath will be lukewarm and, scientifically speaking, subpar.

Let’s talk about convection. It’s basically the transfer of heat among bulk liquids, driven by changes in density. “Hot liquid will expand, becoming less dense, and will rise; cool liquid will contract, becoming denser, and so will sink,” writes John Campbell in the 2015 book Complete Casting Handbook.

Because you’re typically heating a liquid from beneath, like setting a kettle over a stovetop, the liquid at the bottom of the container warms up, becomes less dense, and floats to the top. At the same time, the cooler liquid at the top starts to sink closer to the heat source. Eventually, you get a uniform temperature throughout.

Photo credit: Encyclopaedia Britannica - Getty Images
Photo credit: Encyclopaedia Britannica – Getty Images

But microwaves are an entirely different beast. A magnetron inside the metal box generates microwaves, the kind of electromagnetic radiation that gives the appliance its name. Microwaves fall along the electromagnetic spectrum, just like the ultraviolet light you protect your skin from in the summer, or the X-ray scans your doctor might take.

From there, the magnetron converts electricity from your home into some pretty intense radio waves. A channel called a “wave guide” blasts the radiation into the microwave box to heat your meal or, in this case, water. A turntable rotates the food in question to evenly heat it.

Photo credit: ExplainThatStuff.com
Photo credit: ExplainThatStuff.com

The microwaves bounce all over the reflective metal walls until they ping your food or drink. Then, they blast right through the food, just like radio waves can travel through the walls in your home. This excites the molecules inside the food, causing them to vibrate more quickly, creating heat.

Because the electromagnetic waves are coming from all angles of the microwave unit, rather than just from the bottom, convection doesn’t occur at all. Instead, the liquid at the top is much hotter than the liquid at the bottom, which isn’t optimal for the seasoned tea connoisseur.

In the new paper, the scientists describe a silver plating that a tea drinker could place along the rim of the glass to circumvent this microwave issue. The silver acts like a guide for the electromagnetic waves, helping to reduce the electric field at the top of the mug, shielding the heat. In effect, it creates a pseudo-convection process for more even heat distribution.

This sounds a little dangerous, considering you aren’t supposed to put metal inside a microwave. But the special silver in this case is analogous to the metal structures used in steam pots and rice cookers—very particular geometries of the metal can make it safe.

You Might Also Like

source: yahoo.com

LEAVE A REPLY

Please enter your comment!
Please enter your name here