hbg6@citek.mcdphx.mot.com (04/26/91)
I was asked a question today and do not have a good answer. Why isn't there a microwave residential water heater on the market? Or is there? It would seem ideal for both large tank heater and on-demand systems. Another thing, is the space inside a microwave oven tuned? Thanks, John ..................................................................... John Schuch - Motorola Inc., Computer Systems Division (602)438-3008 All opinions expressed are mine and not Motorolas, their loss. .....................................................................
amichiel@rodan.acs.syr.edu (Allen J Michielsen) (04/29/91)
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 InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE
mzenier@polari.UUCP (Mark Zenier) (04/29/91)
In article <12469@qisoff.phx.mcd.mot.com> hbg6@citek.mcdphx.mot.com writes: >I was asked a question today and do not have a good answer. > >Why isn't there a microwave residential water heater on the market? >Or is there? >It would seem ideal for both large tank heater and on-demand systems. To convert electricity to heat, a resistor is 100% efficient. In a microwave water heater, you'd probably get as much heat from water cooling the magnetron than from the RF. Mark Zenier markz@ssc.uucp mzenier@polari.uucp
rogerm@hpfcso.FC.HP.COM (Roger Mitchell) (04/30/91)
Besides restiance heating elements are nearly 100 % efficent in this application. Roger Mitchell
strong@tc.fluke.COM (Norm Strong) (05/06/91)
In article <7480018@hpfcso.FC.HP.COM> rogerm@hpfcso.FC.HP.COM (Roger Mitchell) writes: }Besides restiance heating elements are nearly 100 % efficent in this application. } Roger Mitchell Yes. Too bad the process of turning coal into electricity and delivering it to your plug is only 25% efficient. :-( -- Norm Strong (strong@tc.fluke.com) 2528 31st S. Seattle WA 98144 USA
amichiel@rodan.acs.syr.edu (Allen J Michielsen) (05/07/91)
In article <@tc.fluke.COM> strong@tc.fluke.COM (Norm Strong) writes: >In article @hpfcso.FC.HP.COM> rogerm@hpfcso.FC.HP.COM (Roger Mitchell) >}restiance heating elements are nearly 100 % efficent in this application >Yes. Too bad the process of turning coal into electricity and delivering >it to your plug is only 25% efficient. :-( In Steam by Babcock & Wilcox 38th edition, it is implied that 85-89% is to be expected. The materials presented in undergraduate classes suggests this is optimistic, but a lower working limit of 65% is used. Then both Marks and Cooks Reference books use a working number of 80% for Transmission systems. That would make a working minimum value approaching 50% not 25%. Then it would only be fair to compare a microwave 'oven' and a antique resistance heating element in this application. It shouldn't take a lot of work to see that the antique is much higher than the microwave. al -- Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE
henry@zoo.toronto.edu (Henry Spencer) (05/07/91)
In article <1991May6.211620.6876@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >>Yes. Too bad the process of turning coal into electricity and delivering >>it to your plug is only 25% efficient. :-( > >In Steam by Babcock & Wilcox 38th edition, it is implied that 85-89% is >to be expected... Uh, for what? I would be very surprised if B&W had found a way to repeal the laws of thermodynamics, which make it very difficult to get an efficiency of more than 40-50% out of a heat engine. Methinks you are reading a number for only part of the process, perhaps the efficiency *after* the heat energy is converted to mechanical energy. -- And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology "beans are more important". | henry@zoo.toronto.edu utzoo!henry
gt8021a@prism.gatech.EDU (EASON) (05/08/91)
In article <1991May6.211620.6876@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >Then it would only be fair to compare a microwave 'oven' and a antique >resistance heating element in this application. It shouldn't take a lot >of work to see that the antique is much higher than the microwave. >-- >Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University Then again, how long does your microwave continue to heat up your kitchen and your house after you're through cooking? And how much does it heat up the surrounding space while it's cooking? My understanding is that, particularly for the short cooking jobs that microwaves tend to be used for, the reduced efficiency while cooking is largely offset by the lack of residual heat: "warm-up" and "cool-down" periods of a conventional oven where the heat that was *produced* with 100% efficiency is not being *used* with 100% efficiency. Something to think about... -Bill -- Bill Eason Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt8021a Internet: gt8021a@prism.gatech.edu
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (05/08/91)
In article <1991May7.153014.4344@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <1991May6.211620.6876@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >>>Yes. Too bad the process of turning coal into electricity and delivering >>>it to your plug is only 25% efficient. :-( >> >>In Steam by Babcock & Wilcox 38th edition, it is implied that 85-89% is >>to be expected... > >Uh, for what? I would be very surprised if B&W had found a way to repeal >the laws of thermodynamics, which make it very difficult to get an efficiency >of more than 40-50% out of a heat engine. Methinks you are reading a number >for only part of the process, perhaps the efficiency *after* the heat energy >is converted to mechanical energy. I have a much more efficient way to heat water than either the microwave system described or the coal burning/electrical resistive element method. Utilizing oxidative combustion methods, our proprietary system combines light hydrocarbon gasses under pressure with atmospheric oxygen providing direct creation of heat at the boiler, with no need for messy and inefficient electrical transmission systems. For more information on our patented "Gas Hot Water Heater," send us all your money please. --scott