It was late 1988, and I was teaching physics without maths to students of a community college. That is when I understood clearly (this happens in an environment where equations do not obfuscate the critical issues) how to explain superheating of liquid. It is all about nucleation, indeed, lack of it in one instance. I will come to it presently.
Why
does the Old Faithful be so faithful,
erupting with an approximate period of an hour? The pressure head of water
column and the internal heat. How does a pressure cooker work? Superheating!
Now,
I take you to 1987. I was baby-sitting a house for a friend who had gone out-of-station
with his family for a couple of days and I had the run of a lake-front house, a
Jacuzzi, and a microwave oven, handy for coffee-in-a minute, any minute.
I
took water (just tap water in those days), and set the cup in the oven, for two
minutes (wasn’t sure one minute would do the job). Took out the tea cup and
dropped a spoonful of freeze-dried instant coffee powder.
My
cup did runneth over, literally! It was a mess with coffee all over the counter
top, the floor and on my hands, trying to scald them. That was my Road to Damascus moment. Tap water was
pure enough (no suspended particles), the walls of the cup were super clean
(dishwasher) and so was the measurement spoon.
The
water had gone into superheated state with no outlet – no suspended particles
to nucleate around. The granules of instant coffee powder came in handy!
Back
in India, after getting a microwave oven and waiting for years for this idea to
pop up in my mind, I finally did my experiment, with as clean a cup I can get
my hand on after rinsing it with water from RO filter (home version), filled
with RO water and set for two minutes and thirty six seconds (so that the ear
of the cup would be in a position for easy access).
Yes,
my science did not fail me. Water bubbled up the moment I sprinkled coffee
powder and spilled over everywhere.
I
showed it to my wife, she just cussed me out for messing up her kitchen counter
– these ladies are so possessive of their kitchen!
I
keep repeating this experiment once a
month or so. I still believe neither my eyes nor my science. My ego needs to be stoked every so often. I just cannot
afford to take science casually.
I
do have to tip-toe around science, not let it know I am testing it. Yes, that
is how science needs to be treated.
Raghuram
Ekambaram
4 comments:
Something entirely new for me. But i won't experiment with any kitchen stuff. Ladies are possessive about the entire kitchen 😊
You have a perfect alibi, Matheikal! After all, you were trained in math and English, if I am not wrong. But, gather your courage and do the experiment. Then expect a fight from your wife!
Thanks.
Raghuram
hmmm....as the much maligned lady in the kitchen myself,I have faced this 'superheating of liquid', when in a relatively narrow vessel I heat water on stove and then add detergent to the (still on stove) hot water,in my quest to soak dirty kitchen towels for cleaning them. Hahaha.
OK, OK ... I'll give this tip to my boss at home! Thanks Aditi. Tell me, is the result as dramatic as it is in a microwave - the basic difference being in the microwave the cup does not get hot. If the surface gets heated up, bubbles form on it. Then, other superheated water molecules can coalesce around them. This does not happen in microwave. I would like you to observe perhaps closer than usual and let me know.
Thanks.
Raghuram Ekambaram
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