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posted by Fnord666 on Wednesday August 05 2020, @03:33AM   Printer-friendly
from the shut-up-and-take-my-money dept.

The Problem with Microwaving Tea:

Typically, when a liquid is being warmed, the heating source — a stove, for example — heats the container from below. By a process called convection, as the liquid toward the bottom of the container warms up, it becomes less dense and moves to the top, allowing a cooler section of the liquid to contact the source. This ultimately results in a uniform temperature throughout the glass.

Inside a microwave, however, the electric field acting as the heating source exists everywhere. Because the entire glass itself is also warming up, the convection process does not occur, and the liquid at the top of the container ends up being much hotter than the liquid at the bottom.

A team of researchers from the University of Electronic Science & Technology of China studied this nonuniform heating behavior and presents a solution to this common problem in the journal AIP Advances, from AIP Publishing.

By designing a silver plating to go along the rim of a glass, the group was able to shield the effects of the microwave at the surface of the liquid. The 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, resulting in a more uniform temperature.

Placing silver in the microwave may seem like a dangerous idea, but similar metal structures with finely tuned geometry to avoid ignition have already been safely used for microwave steam pots and rice cookers.

Journal Reference:
Peiyang Zhao, Weiwei Gan, Chuanqi Feng, et al. Multiphysics analysis for unusual heat convection in microwave heating liquid [open], AIP Advances (DOI: 10.1063/5.0013295)


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  • (Score: 1) by deepgrey on Wednesday August 05 2020, @07:22AM (15 children)

    by deepgrey (6542) on Wednesday August 05 2020, @07:22AM (#1031613)

    Heating water for tea in the microwave is decently common in the US where we only have 120 V mains. I don't know anyone with an electric kettle. If they were as great here as they are in the UK I'd buy one, but I'm unfortunately stuck with a stovetop kettle.

    I'm pretty sure China has 220 V service though, so I guess it was just an interesting emag problem to solve.

  • (Score: 0) by Anonymous Coward on Wednesday August 05 2020, @08:50AM

    by Anonymous Coward on Wednesday August 05 2020, @08:50AM (#1031622)

    Electric kettles are crucial. It boils faster than a stove ever can, so you can pour boiling water into a pot and cook faster.

  • (Score: 2) by driverless on Wednesday August 05 2020, @12:13PM (8 children)

    by driverless (4770) on Wednesday August 05 2020, @12:13PM (#1031658)

    You have Amazon, they sell Zojirushi's at 110V, there's no excuse to ever use a microwave.

    • (Score: 1, Disagree) by deepgrey on Wednesday August 05 2020, @03:01PM (6 children)

      by deepgrey (6542) on Wednesday August 05 2020, @03:01PM (#1031750)

      A 120 V kettle isn't nearly as good as a 240 V kettle, so yes, there is an excuse. I prefer to use a kettle on my stove though because it makes better tea and actually boils water in a semi-reasonable amount of time, unlike a wimpy electric kettle. You have to realize that the current handling capability of the circuit is roughly the same for your 240 and our 120, but the voltage is halved, so the power is rougly halved. Your kettles heat much faster than ours.

      • (Score: 2) by drussell on Wednesday August 05 2020, @09:56PM (4 children)

        by drussell (2678) on Wednesday August 05 2020, @09:56PM (#1031979) Journal

        Just put a NEMA 6-15 receptacle on your countertop, buy the 3000W kettle from the UK and put the North American 240v 15A plug on it (the 6-15, with sideways blades) and you're golden.

        Most semi-modern kitchens are already wired with split-duplex plugs on the countertop, so all you do is remove one of those that has two circuits to it for the top and bottom, and simply install the 6-15 in place of the standard 5-15.

        You're totally allowed to have 240v plugs in North America.... It isn't even difficult.

        My neighbor's Tesla charges at 11 mi/h instead of 3 just by changing to a 240v plug in their parking stall and the appropriate $20 adapter from Tesla for the charger cable included with her model 3... All it takes is a 6-15 plug and a double-pole 15A GFCI breaker instead of the single. Wrap the ends of the white (formerly neutral) wire in red electrical tape to denote that it's the other phase of 240, put the cover back on and charge away. :)

        • (Score: 2, Touché) by Anonymous Coward on Wednesday August 05 2020, @10:53PM (2 children)

          by Anonymous Coward on Wednesday August 05 2020, @10:53PM (#1031999)

          If somebody doesn't already know how to do that, the correct way to instruct them is to say "Hire an electrician."

          • (Score: 2) by drussell on Thursday August 06 2020, @02:09PM (1 child)

            by drussell (2678) on Thursday August 06 2020, @02:09PM (#1032258) Journal

            Obviously if you aren't competent or comfortable doing a particular job, especially something like electrical work, you should hire a professional to do the job. (hopefully, correctly!) You need to at least know that something is possible, though, before you can ask said professional to do some particular thing for you.

            My point was simply that you CAN get a "proper" 3000W 240v kettle and have a proper, safe, valid plug for it in your kitchen. The same plug also works for things like one of those small countertop-sized commercial deep fryers if you're tired of attempting to make your wings and fries or fish or whatever in tiny batches in a wimpy little 1500W residential joke of a deep fryer.

            Believe me, I've seen my fair share of scary electrical work, even relatively simple things like changing a plug, that were obviously done by clueless homeowners or handymen. On one renovation we did many years ago, someone had changed all the plugs on the main floor of the home, and only two of the plugs were even wired with the correct polarity. The other 20 or so were all wired with the hot and neutral reversed. Egads!

            If you don't know what you're doing, hire a professional! :)

            • (Score: 0) by Anonymous Coward on Thursday August 06 2020, @10:30PM

              by Anonymous Coward on Thursday August 06 2020, @10:30PM (#1032550)

              When you get to the point of instructing what color tape to put on exposed wires, you are a bit past "it's easy and fairly cheap to get 240 volts in your kitchen, an electrician can do it in a few minutes".

        • (Score: 1) by deepgrey on Thursday August 06 2020, @04:26AM

          by deepgrey (6542) on Thursday August 06 2020, @04:26AM (#1032147)

          Yeah, I'm just happy to have a ground in my kitchen. You can forget trying to easily change mine to 240 V. It's not split duplex. In fact, I just realized that I've never put a GFCI outlet in there, and I probably should.

      • (Score: 2) by kazzie on Friday August 07 2020, @06:52AM

        by kazzie (5309) Subscriber Badge on Friday August 07 2020, @06:52AM (#1032784)

        My family in Canada use 120V kettles, but that may be a cultural/family thing, given that they emigrated there from the UK.

    • (Score: 2) by driverless on Friday August 07 2020, @05:34AM

      by driverless (4770) on Friday August 07 2020, @05:34AM (#1032765)

      A Zojirushi is actually something completely different, it's a Japanese-made triple-vacuum-insulated thermopot that boils the water once and then uses a small trickle of power to keep it warm, so you get hot water on demand whenever you want it. Runs just as well off 110V as 220V since it uses (for my 4L one) 17W to keep the water at temperature.

  • (Score: 2) by driverless on Wednesday August 05 2020, @12:16PM

    by driverless (4770) on Wednesday August 05 2020, @12:16PM (#1031660)

    Heating water for tea in the microwave is decently common in the US

    Sean Connery's comment on this practice [youtube.com].

  • (Score: 2) by wisnoskij on Thursday August 06 2020, @12:47PM (2 children)

    by wisnoskij (5149) <{jonathonwisnoski} {at} {gmail.com}> on Thursday August 06 2020, @12:47PM (#1032233)

    I absolutely guarantee you that no one outside of a restaurant has ever used a 220v kettle.

    • (Score: 3, Informative) by drussell on Thursday August 06 2020, @02:17PM (1 child)

      by drussell (2678) on Thursday August 06 2020, @02:17PM (#1032261) Journal

      I'm assuming you must have been meaning "in North America" or something...

      Everyone in the UK (where it can nearly cause a blackout due to overload when they all turn on their 3000W kettles at the same time after some televised event or something) would beg to differ.

      eg: https://www.johnlewis.com/browse/electricals/kettles/3000w/_/N-ahtZ1z0ejjz [johnlewis.com]

      Standard ring mains in UK homes are 32A at 240V, so plenty of power for things like 3000W kettles in virtually every home.

      • (Score: 2) by wisnoskij on Thursday August 06 2020, @03:01PM

        by wisnoskij (5149) <{jonathonwisnoski} {at} {gmail.com}> on Thursday August 06 2020, @03:01PM (#1032275)

        We typically get double 120v in NA, at least residential. We use the 240v almost exclusively for stove/clothes dryer/air conditioning. Their is practically nothing else that uses it unless you purchase a welder (and they have been making some pretty good 120v welders lately), I think it is pretty much considered something only an expert should install/screw with.

        You can boil a cup of water in like 30 seconds on 120v over a thin electrical cord, so what would be the benefit of anything higher? I think we max out at about 3000w appliances as well, I think I have seen toasters that put that out (120v).

  • (Score: 0) by Anonymous Coward on Thursday August 06 2020, @06:56PM

    by Anonymous Coward on Thursday August 06 2020, @06:56PM (#1032416)

    I have an electric kettle in the US, it works just fine. You can even get the fancy Japanese ones here, and they work even better.