Newsgroups: sci.electronics
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uupsi!rodan.acs.syr.edu!amichiel
From: amichiel@rodan.acs.syr.edu (Allen J Michielsen)
Subject: Re: Microwave Water Heater
Message-ID: <1991Apr28.182011.3357@rodan.acs.syr.edu>
Organization: Syracuse University, Syracuse, NY
References: <12469@qisoff.phx.mcd.mot.com>
Distribution: usa
Date: Sun, 28 Apr 91 18:20:11 GMT

In article <12469@qisoff.phx.mcd.mot.com> hbg6@citek.mcdphx.mot.com writes:
>Why isn't there a microwave residential water heater on the market?
>It would seem ideal for both large tank heater and on-demand systems.
>Another thing, is the space inside a microwave oven tuned?

  Well, off-hand I can think of a few dozen serious problems to solve.
MWing water tends to create small pockets of superheated water (steam on the
droplet level).  This would just about require a tank circulation/mixing
system to keep this from getting to the 'user'.  The temperature shutoff sensor
would have the same difficulty.  Both of these would be really serious when
the flow rate is high (on demand).  Then, MW ovens are sorta tuned, and
depending on the design, would quite large or complex.  
Then there is always the WAG/ extrapolation problem.  I take a 500 watt
MW oven (which probably doesn't draw 500 watts, but...), and put a quart of
water in it at 50F.  It takes quite awhile, like 10 minnutes I'd guess to
bring the mix temp up to 200F. On most gas or electric 40 gallon or so water
heaters, the recovery time (fill with 40 gallons of 50F water and bring up
to 180F or so) is about 20 min or so.  All things equal, this would equate
to a power rating of a MW oven of about 100 times the original 500 watt job
or about 50 Kw.  
al



-- 
Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University
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