From: SFPhysics@aol.com
Date: Sun Jul 25 2004 - 03:35:05 PDT
From: SFPhysics@aol.com Message-ID: <8c.1071b65a.2e34e6d9@aol.com> Date: Sun, 25 Jul 2004 06:35:05 EDT Subject: Jukebox Bubble Tubes...
Irene Yun asks:
>I was at a bar last night and noticed that in the jukebox with bubbler tubes
going up the >sides. The bubbles got SMALLER as they rose up the tube. The
bubbles I looked at last >night were reduced in volume by almost 5 times their
original size. Any clues what's going >on?
Hello Irene:
The bubbler tubes in the Wurlitzer Model 1015, etc., have no air in them.
The glass tube is filled with a low boiling point liquid and a space is left at
the top. The air in that space is evacuated with a vacuum pump but the liquid
fills up the remaining space with vapor at a reduced pressure and the tube is
then sealed. The space therefore is a partial vacuum above the liquid. When
heat is applied via a hot light bulb on the bottom, the vapor pressure of the
fluid there pushes the column of liquid upward. The liquid streams down the
sides as the vapor bubble rises and as the bubble rises it starts to cool.
Cooling makes the vapor pressure drop so the bubble gets smaller. The second
thing that happens is condensation. Most of the vapor bubble condenses back
into the liquid form before the bubble reaches the top. If the column were high
enough you could actually watch the bubble disappear at some point.
Now the bubbles in your beer are another story... They do start small and
get larger as they pick up more gas coming out of solution while they rise. You
were very astute to have noticed the two different processes.
I hope that explains it well enough.
Best wishes,
Al Sefl
Who has studied enough beers to become a real bubble head...
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