Bean had?

Jun 9th, 2009

You may have noticed reports in several newspapers and tech sites today of the Heinz Beanzawave, a USB powered microwave. In total, according to Google News, the story appears to have been covered by over fifty different outlets including the UPI, CrunchGear, Cnet and the Daily Mail. Not to mention a number of popular blogs, such as BoingBoing. While some of these articles have users raising criticisms in the comments, none of the news sources I checked bothered to run a critical eye over the story. (If you find one, please post it in the comments so the good guys can get some acknowledgements.)

The news seemingly originated from a press-release form the ‘Microwave Association,’ working in association with Heinz. Unfortunately for fans of beans and fancy USB gadgets the story appears to be, well, a load of old beans1.

Even a quick critical eye will spot some key flaws. The average modern microwave has an output of 850W, with even weaker models outputting at least 650W. By comparison, the USB 2.0 standard provides a maximum current of 500mA, at 5V; which works out as a maximum power output of just 2.5W2. The former figures should be familiar to anyone who has cooked something in the microwave, as the output is printed on the front, and you are expected to adjust cooking times accordingly. The latter meanwhile should be obvious in part to anyone who has hooked up a printer. While simple devices like mice can obtain sufficient power from a USB socket, the same can’t be said for more power-hungry devices such as printers, which need their own power supplies. Indeed, the power supply units of most computers aren’t certified to deliver 850W of power, with possibly only high quality gaming rigs fitted with a hefty enough PSU; even then, powering a microwave would leave scant remainder for the processor and graphics card.

So we’ve already seen that such a device would have to operate at a significantly lower power output than most modern microwaves. Such a device would be unlikely to be marketed as a novelty, and instead would be positioned to replace most standard microwaves. However is it possible that such improvements have been made, and we are in fact looking at vastly superior technology. In short, not likely, unless they have also managed to break the laws of thermodynamics in creating this miracle microwave.

In demonstrating how truly impossible their claims are we need to consider some physics.

The specific heat capacity of a substance is used to describe how much energy is required to raise its temperature; for water, this is given as approximately 4.2 joules per gram per kelvin. This means that for every gram of water, you must supply 4.2 joules of energy, to raise the temperature by 1 kelvin, or 1 degree Celcius3. Therefore, for a 200g tub of beans (which we shall approximate by assuming it is all water.) it takes 4.2 x 200 = 840 joules to raise the temperature by a single degree.

So how does this translate to our microwave? Well fortunately, the measurement watts tells us how many joules of energy are transferred each second. In other words 1 watt = 1 joule per second. So if we are to assume that our microwave is 100% efficient, that all energy it uses goes directly into heating the beans, we can discover how long it will take to deliver the required 840((And here is a good illustration of the inefficiency of standard microwaves. As by this calculation the beans should be ready in just under a second.)) joules to raise the temperature of the beans by a single degree. Simply divide 840 by 2.5 and… oh dear… 336 seconds. Five minutes, 36 seconds to warm the beans by a single degree. If you want them boiling hot4, then you are going to be waiting over 7 hours.

What bothers me most about this story isn’t the dubious nature of the original press-release. It was clearly constructed by marketing bods in an attempt to gain free column inches. In that respect it worked, and I’m only adding to the effect by writing this. What bothers me is the way the press regurgitated it, unthinkingly, unquestioningly, delivering advertisements as news. Not only this, but it is clear that in most cases, they didn’t even stop to pass a critical eye over it. This isn’t just churnalism, this is factually incorrect churnalism. When the media sacrifices its credibility in terms of fact checking, and ends up falling slave to marketing, what does it have left? And when we lose one of the key methods of fact distribution, of investigation and exposure, what do we have left? Blogs and citizen journalism go so far, but an effective and trustworthy media is is important for everyone; this story is only one of many that makes me wonder how much of one we have left.

I have already contacted the Microwave Association in the E-mail provided in the press-release, and have invited them to respond. I’ll update this entry as soon if I hear anything from them, and leave the comments open if they wish to contribute there. (Although I encourage you do do so via my E-mail, as that way I can be sure the response is genuine. Also, please bear in mind that comments from new users will be held for moderation, and may not get published immediately.)

  1. See, you don’t have to be part of the tabloid press to make terrible puns []
  2. Power is the product of current and voltage []
  3. The scale of Celcius and kelvin is identical. Only the position of the zero position changes, with 0 kelvin being equal to -273.15 °C []
  4. Assuming room temperature 20 °C and a boiling temperature 100 °C []
  5. See, you don't have to be part of the tabloid press to make terrible puns []

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One Response to “Bean had?”

  1. Good point James. You also forgot to mention the most important point: Not to put the tin in the microwave!!!

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