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I'm curious why these devices don't use water
filled pressure compensation?
Positives:
1) Water is a MUCH better heat
conductor
2) The viscosity of water is much lower than oil,
leading to less internal drag
3) No environmental concerns. Cheap and easy to
handle.
Negatives:
1) Corrosion must be considered. Ferrite
magnets, steel laminations, etc.
The metal-working community uses
various amounts and types of oil in coolant water to
reduce or
effectively eliminate corrosion. I wonder if this can mitigate this big
concern.
2) If you have a leak, you won't know until enough
salt & minerals diffuse into the motor to create problems
3) Must use distilled water (tap water
has additional minerals which may deposit onto surfaces)
Neutral:
1) Both water and oil are compressible to about the
same amount. Water is about 0.34% per KSI, and Oil is about 0.5% per
KSI.
Either fluid will require a
flexible bladder/accumulator to compensate for volume reduction at
significant depths.
2) Both oil and distilled water are
non-conductive.
3) Dielectric strength would seem to be irrelavant
for a low voltage motor.
Thoughts?
Mark
----- Original Message -----
Sent: Sunday, July 29, 2007 9:08 AM
Subject: Re: [PSUBS-MAILIST] Diver
Lockout.... serious question here!!
Vance,
Air is the least effective means to cool
something that is enclosed. The problem with air, if it is exchanged in a fast
enough rate, it works great. On the other hand....if you can't exchange the
air, you end up with an oven. Oil on the other hand can carry
more heat away faster. The density is the factor here. Air is
not very dense, so it will only absorb so much thermal energy per unit.Oil
will absorb many more btu per unit than air. Also because oil will
thermocycle.....the oil will transfer the heat to the container that contains
it faster.
I think an air filled thruster would work good
too, but there are problems with compression. If there are any bearings housed
within the casing......they will bind under extreme pressure if filled with
air. An oil filled enclosure will not compress as far. There will still
be compression problems, but not to the extent of an air filled
unit.
There was a project a few years ago....a guy made
a gaming computer that used oil to keep all the expensive parts cool. You
should look it up. It worked really well. (Oil cooled computer)
I do not plan at this point to run a reduction
gear. BLDC motors are real good at direct drive.
I would like to build smaller thrusters that can
go very deep.
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