Actually Joe, you are correct in that compressible matter such as gases do
heat up as they are compressed. The key word is compressible; in hydraulics,
fluids are considered to be basically incompressible. Absolutely they do
expand with heat, it is just that the heating is not primarily due to
compression. The amount of force necessary to compress a true fluid like
water or oil at room temperature is huge. It is most unlikely that such
force could ever be brought to bear in a simple mechanical system.
Again a very old story. Back in the 50s my father was working in a lab that
was doing experiments in ultra-high pressures. Well UH for the time.
Basically what they would do is make a very thick steel pipe with a fine
thread all the way down to a closed bottom. Then they put a bit of fluid in
the bottom and wound a big bolt in the top. Once the bolt contacted the
fulid, they would twist it but good. When nice and tight they could get up
to a pressure of 30,000 tons per square inch in the water. All the pressure
was caused by deformation of the steel, the water didn't give a bit. (well
very very little)
One day they left the system under pressure and went home. That night the
material fatigued and the pipe broke. The resulting expansion/explosion
(whatever) of the bits of metal blew out 3 floors of the lab. It was a
miracle that it happened at night when nobody was there.
A few months later an american firm approached the British and asked them to
perform the same experiment at 50,000 tons. The staff resigned en masse.
Mark Hooper
-----Original Message-----
From: Joe Curry [mailto:spitlist@gte.net]
Sent: Thursday, June 21, 2001 2:33 PM
To: Mark Hooper
Cc: Randall Young; triumphs@autox.team.net
Subject: Re: Hydraulics
Mark Hooper wrote:
>
> I think you have a little circular logic in that one Joe! I think it is
the
> viscosity of the fluid as it is stirred in a system rather than the
> squeezing that causes it to heat up and expand.
>
> Mark
I don't think so. These are scientific principles at work here.
Compression causes heat (That is why intercoolers are so popular to cool the
air that is compressed by superchargers and turbochargers)
Heat typically causes expansion.
The two principles are irrefutable. Now, I won't say that in hydraulic
systems the principles apply to any great extent because as I said, the
fluids
are selected due to their properties that resist compression. And since the
action at the input is reciprocated by an action at the other end of the
system, not much compression takes place anyway. It is more an action of
displacement rather than compression.
Joe
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