[Vwdiesel] PV=nRT and Hydraulics

[Val Christian]

You'll recall the ideal gas law, PV=nRT.

You'll also recall that release of gas pressure will cause cooling.  Works
with a rapidly decompressing gas cylinder, such as an O2 cylinder on a cutting
torch.  Or a CO2 fire extinquisher.  

n stands for the moles of gas in the system,

R is a constant, which is emphirically derived.  It can be thought of as
the compressibility of the gas.

I believe the gas law applies to fluids, such as water, hydraulic fluid
and diesel fuel.  R is just real small.  

This would suggest that in theory, the release of pressure on a hydraulic
line would cause a decrease in temperature.  A quick consult with my 
physical chemistry experts confirms this.  [Liquid exceptions exist, and
include water (4C to 0C), ATF in some pressure and temperature domains, 
etc.]  The compressibility of simple compounds is found in references such 
as CRC.

Soooo, Lee, in theory, that leakage past the pump should cause COOLING,
rather than heating.  I rest on my earlier assertion that the heat in 
the pump is primarily from losses due to turbulent flow, fluid friction
and the like.  

Val