From: Jonathan Cohen (jonecoco@yahoo.com)
Date: Fri Nov 10 2000 - 13:44:20 PST
Message-ID: <20001110214420.28338.qmail@web2102.mail.yahoo.com> Date: Fri, 10 Nov 2000 13:44:20 -0800 (PST) From: Jonathan Cohen <jonecoco@yahoo.com> Subject: superheating and boiling
I have a couple of questions about boiling and heating
for which I would love some explaination.
1. A friend of mine recieved terrible burns (he
recovered wonderfully) in a freakish way that I never
understood. An overhead light fixture in a basement
apartment became filled with water due to a plumbing
leak overhead. Although the fixture nearly filled up
with water, it never shorted out. My unlucky friend
went up on a ladder to empty this overhead fixture. In
the process the water fell on him. It was scaldingly
hot. I know it wasn't visibly boiling but it must have
been close because he was badly burned.
Does the process has something to do with induction of
kenetic energy into the water molecules by the
alternating current? Why wouldn't the draw on the
circuit required to heat the water blow the circuit
breaker/fuse?
2. Attached is a message that someone refered to me in
the tradition of "You're a science teacher so.."
- Is this for real? How does it work?
- What is the connection with boiling chips used in
chem classes for boiling in beakers?
Is the vapor pressure of water at 100 celcius not
enough by itself to form bubbles?
Subject: Fwd: Microwaving water - BE Careful!
>Well, I am not sure I believe this, but just in case
it is true, thought I would pass it on. Better to be
safe than sorry, right?? >
>
Microwaving Water to Heat it Up:
I feel that the following is information that any one
who uses a microwave oven to heat water should be made
aware of. About five days ago, my 26 year old son
decided to have a cup of instant coffee. He took a cup
of water and put it in the microwave to heat it up
(something that he had done numerous times before). I
am not sure how long he set the timer for but he told
me he wanted to bring the water to a boil.
When the timer shut the oven off, he removed the cup
from the oven. As he looked into the cup he noted
that the water was not boiling.
Instantly the water in the cup "blew up" into his
face. The cup remained intact until he threw it out of
his hand but all the water flew out onto his face due
to the buildup of energy. His whole face is blistered
and he has 1st and 2nd degree burns to his face,
which may leave scarring. He also may have lost
partial sight in his left eye.
> > > >
While at the hospital, the doctor who was attending
to him stated that this is a fairly common occurrence
and water (alone) should never be heated in a
microwave oven. If water is heated in this manner,
something should be placed in the cup to diffuse the
energy such as a wooden stir stick, tea bag, etc. It
is however a much safer choice to boil the water in a
tea kettle.
> > > >
Please pass this information on to friends and family.
> > > >
Here is what our science teacher has to say on the
matter:
> > > >
"Thanks for the microwave warning. I have seen this
happen before. It is caused by a phenomenon known as
super heating. It can occur anytime water is heated
and will particularly occur if the vessel that the
water is heated in is new. What happens is that the
water heats faster than the vapor bubbles can form. If
the cup is very new then it is unlikely to
have small surface scratches inside it that provide a
place for the bubbles to form. As the bubbles cannot
form and release some of the heat that has built up,
the liquid does not boil, and the
liquid continues to heat up well past its boiling
point. What then usually happens is that the liquid is
bumped or jarred, which is just enough of a shock to
cause the bubbles to rapidly form and expel the hot
liquid. The rapid formation of bubbles is also why a
carbonated beverage spews when opened after having
been shaken."
Please pass this on to everyone you know, it could
save a lot of pain and suffering. >>
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