I can heat water faster in my microwave
than I can on my stovetop.
Is a microwave "more efficient" at heating water ?
If so, can anyone see a time where
the heat source for a home water heater
would be microwave rather than heating elements ?
The microwave heats faster cause there is no warm-up time.
AND be carefull to never heat plain water in a MW as it may damn near
"explode" when you go to use it due to surface tension issue.
I.E. put cocoa in before heating, ditto tea bag.
And because it's usually not heating the container either. You can
put food in it on a paper plate, plastic container, neither of which
get heated up much, and even if they do, have a very small thermal
mass compared to a metal pot on a stove. And there is less loss to the
surrounding environment. The microwave directly vibrates the water
molecules transferring energy to them. With a pot on the stove a lot
of the heat goes to the air, surrounding stove metal, etc.
It definitely uses less electricity to warm the cup of water in the
microwave than on the stove. However, an electric water heater is
100% efficient at converting the incoming electricity to heat because
it's a simple resistance heating element surrounded by water.
Microwaves would offer no advantage in a storage tank water heater.
In fact, it would use MORE electricity, because the electronics that
create the microwaves are not 100% efficient.
The kitchen version of the water heater is an electric kettle. It's
basicly a metal teapot type appliance that has a 1500W heater
inside. I can have a quart of water boiling in just a few minutes,
much faster than on the stovetop. Again, it's going to be more
efficient because most of the heat is going directly to the water.
Agree. If you're going to heat water to near boiling, it should have
something in it. If it's pure water, it can become super heated,
where it's actually just a tiny bit above the boiling point without
actually boiling. Then the slightest disturbance can trigger it all
to suddenly boil at once.
Well, I have used the microwave for years to heat my coffee. As a lapsed
lab. chemist, I have a fair handle on volumes and just pour the required
amount of instant coffee from the jar straight into my mug, top up with
water and zap in the MW for the relevant time (depending upon the power of
the MW). IIRC, I haven't had a volcanic eruption to date. I might regret
having said that!
It saves energy rather than using the kettle and I don't use a spoon, (not
using milk or sugar). Very efficient, I find it.
Actually, superheating is a wellknown phenomenon. For water to boil, it
has to go to vapor phase (steam). That usually (in a pan on a fire of
some kind) at very hot places on the pan's surface. That's when the
water is starting to "sing". In a MW there is no such hot surface and
boiling has to start somewhere. This is then usually on a floating speck
of dust. The MW energy has heated the water in the meantime to higher
than the boiling temperature, so when a teensy "boil" starts, suddenly
this is the seed for much more water to become steam. Steam is also
much, muc more voluminous than water, hence the force of the boiling
water and steam.
When a chem student having to heat solvents on a heated water bath, it
was official policy to add "boiling stones" to the containers in order to
have a controlled boiling, rather than a little explosion. But that is
another story ...
Oh, yeah. 1 mole of water is 18 grams, just over half an ounce.
Visualize that volume. At "normal" conditions (0degrees C, 1 atmosphere
pressure), the volume of an ideal gas is 22.4 liters. Since pV=RT, that
volume would be 373/273 times as much at 100 degree C (boiling), or about
31 L, or close to 8 gallons. Visualize 18 milliliters expanding to 31
liters, roughly 2000 fold. That's the power of steam.
That explains why you eed be careful pulling the Saran wrap off of a
microwaved food container. Less than 4 tablespoons of water will convert
to 8 gallons of steam when overheated to boiling.
No microwave is NOT more 'efficient' at heating water.
It may be 'faster' at heating small quantities of water in small
containers that themselves do not absorb much heat.
But from basic physics the question makes no sense. It is all a matter
of how quickly the units of heat from watts of electrcity get into the
water by some means, so as to raise the temperature of the water.
A typical microwave uses maybe 1200 watts (1.2 kilowatts per hour);
and takes maybe a minute or so to heat a cup of water to say same
temperature as hot water out of the tap.
So that''s 1/60 of 1.2 kilowatt hour. Ignoring the losses in the
inefficiency of the magnetron, the little light that comes on inside
and the small amount of electrcity used by the controller module with
its display etc.
Less total amount of electrcity would be used in a properly insulated
hot water tank, more slowly, by its 3000 watt heater; or alternatively
one of those 'instant on' heaters; to heat the same amount (cup) of
water. Some of those instant hot water heaters can use 9 kilowatts or
more for the short periods they are on.
Compared to water heating on stove top: Element has to heat up, the
pan or kettle has to absorb the heat and there is heat loss to the
room, so it is a 'slower' process. But it is a 'convenient' way to
heat water for tea or coffee or cooking despite the heat losses.
There is a complete difference between 'how fast' and 'how efficient'
There are some ceramics designed to absorb microwaves, heat up and help
heat the contents. Those are more efficient. Some microwave foods place
a microwave "magnet" in the bottom of the tray to heat the food faster.
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