[Vwdiesel] Hydraulics and heat: was,

[Val Christian]

The real issue here is where is the heat coming from.  What is the primary
source of heat being introduced at the injector pump?  Thusfar, we have
suggested that it might be the flyweights sloshing in the fuel, or that 
it may be losses in the pump.  

My relatively uninformed position is that the flyweights sloshing in the 
fuel account for the bulk of the heat gain.  We could do an experiment 
where we take a similar assembly and slosh it around in a container of
fuel oil, and measure the temperature gain of that fuel oil.  Someone
handy with a buzz box could fab an assembly similar in form, and 
attach it to a 1/4" shaft.  A drill press, and an old thermos jug,
and some fuel oil, and we'd be measuring heat gains in the fuel oil.
The specific heat of the fuel oil is known within a range, and an estimate
of the energy loss from swinging weights around in oil could be made.

If one chooses to argue that the heat gain is from the pump component of
the injector pump, one approach to validate that is to calculate the 
potential power consumption of the pump.  The displacement and pressure
would be a good start.  We know the top end speed.  

A place to start is to make a estimate of the power (heat) from the 
injector pump assembly.  Hagar could do that by measuring the fuel oil
temperature going into the pump, and the temperature coming out of
the pump, and the fuel flow.  That will give us a bogie number for the
total system heat loss.  

Once we have the total system heat loss for the injector pump assembly, 
then we can attempt to rationalize where the heat is coming from.


Lee, just a few clarifications...my reference to the tractor hydraulic pump
was assuming it was in bypass mode, and that the system was pressurized to
3500 PSI.  I have a neat little lever that lets me do that, and the pump
does get warm, but not untouchable.  What REALLY gets warm is the bypass
valve housing.  I'd argue that is where the frictive losses, turbulent flow
and all those other power wasting things are happening.  To be fair, the 
pump is cooled by the total system hydraulic fluid load, which also bathes
the transmission, and consequently, the total system has allot of thermal
mass, and a reasonable radiator area.  

It's those same frictive, and turbulent flow losses that I'm arguing come
from the flyweights sloshing in the injector pump.

Anyone with industrial mixer experience?  Perhaps we can estimate the 
wetted area of the parts in the injector pump, and approximate the 
drag they'd have in fuel oil, running at a speed like 2500 RPM 
(I realize that'll be at or slightly above top end on the engine).

Can anyone give us the plunger dimensions on the injection pump, 
along with the max displacement?  Figure 5000 RPM on the engine,
which would be about 5000 strokes per minute.  We then know the 
power input needed.

Another thought...if heat loss is flow times pressure (V*I), then 
for the pump portion of the pump to get hot, it would have to leak
considerable fuel, since the flow is ultimately low (8 liters per hour
perhaps?).  If the leak flow was very high, then the pump metering
would be way off, and it would be difficult to maintain fuel metering.

It'll be interesting to see where the heat comes from.  

Val



> 
> 
> 
>   OK, time to hit the books. I'm not a scientist, but I do have plenty of
> practical experience and a selection of reference material. No slight meant.
> 
> 
> 
> 
> > I would be inclined to argue otherwise.  There is little energy
> > released when a rather incompressible fluid is decompressed.
> > This much is calculable.  The number will be small.  And this is
> > why hydraulic systems are so neat.
> 
> 
> 
> 
>  From 'Using Industrial Hydraulics', T.C. Frankenfeld, ISBN #0-932905-01-3,
> page 1-17:
> 
>  "Unfortunately, the newcomer to hydraulics, until he gets burnt, so to
> speak, with his first system, really has no way of realizing just how
> efficient a heater a hydraulic system can be. We must remember that flow
> multiplied by pressure is the hydraulic equivalent to horsepower. Wherever
> we have flow from point A to point B in a system, with any loss in pressure,
> there is an equivalent loss of horsepower between points A nad B. Since, a
> pressure loss occours without doing useful work (causing mechanical motion)
> a percentage of the input horsepower is wasted. This wasted horsepower shows
> up in the hydraulic system in the form of heat. Of course, the higher the
> pressure loss and the higher the flow, the more we waste horsepower. Some
> typical examples where pressure is lost without doing useful work are
> summarized as follows:
> 
>  Heat is generated when there is a drop in pressure as oil flows:
> - through pipes & fittings
> - through flow controls
> - over relief valves
> - across counter balance valves
> - internal leakage of pumps and motors
> 
>  If we know the flow rate (GPM), and the loss in pressure (PSI) across any
> device that does not produce mechaniical motion, we can calculate the heat
> generated.
> 
>  Since the hydraulic system either does work, or creates heat, the units of
> heat may be expressed in any units of work or energy. However, we more often
> see heat expressed in BTU (British Thermal Units) than we do in ft-lbs of
> heat.
> 
> 1 BTU=778 ft-lbs
> 
>  In effect, this shows that one BTU cntains enough energy to move a one
> pound object 778 feet."
> 
>  There's some more, but it just explains the formulae they use to explain
> this formula:
> 
> 1 HP = 42.4 BTU/min = 2545 BTU/hr  or BTU/HR = 1.5 x GPM x PSI, where PSI is
> the loss in pressure that does no useful work.
> 
>  If you want, I can supply formulae for heat dissapation, pressure loss
> through pipes, etc.
> 
> 
> 
> > I won't begin to dispute your experience with your pumps.
> > However, I can tell you that my tractor hydraulic pump,
> > which runs about 3500 psi bypass, doesn't begin to get
> > hot.  It's a small pump, and it doesn't seem to get
> > much warmer than the surrounding engine area.  I could
> > measure it sometime, but I doubt if it's 50F hotter than
> > the surrounding area, even under heavy load.
> >
> > What DOES get hot is the bypass valve area.  That's not
> > because of the pressure differential.  It is because of the
> > turbulent flow, and the heating secondary to that turbulent
> > flow.
> 
> 
> 
>  I disagree; the reason it gets hot IS because of the pressure differential.
> 
>  The only thing that prevents your positive displacement tractor pump from
> melting down is that your system is designed to use open-spool hydraulic
> valves. There is essentially zero pressure at the pump unless you move one
> of the valves and direct fluid to a cylinder, motor, or whatever. Otherwise,
> all of the pump flow simply flows through the open center spool in the valve
> back to tank with no pressure generation and thus no (or at least
> negligible) heat generation.
> 
>  Try this: run a hydraulic cylinder to it's limit, deadheaded,  and hold the
> lever there, so that the fluid bypasses continuously over the bypass in the
> pump. (Don't do this for more than a minute or so, or you will begin burning
> up the fluid!) Now, go and VERY carefully feel the pump. You might want to
> wear gloves for this.
> 
>  That should be a good practical lesson in how much heat is generated
> passing over a relief valve where no work is being done.
> 
> 
> >
> > The VW injection pump has less flow than the tractor hydraulic
> > pump.  And the tractor hydraulic pump creates higher pressure.
> > So there's more power put into it.  But the hydraulic pump is
> > cooler than the VW injection pump.
> >
> > Why?
> >
> > I submit that it is because of turbulent flow.  Yes, some from
> > the release of pump blow-by.  But likely more from the stirring
> > of the fuel with the flyweights.
> 
>   See above.  :-))
> 
> 
> 
> >
> > Look, I really don't mean to be argumentative.  I'm just sharing
> > some of my reasoning, and "common sense" aquired through life.
> > Just like your electrically driven pump story.  Perhaps this
> > question would be a good one to have a ME student work out,
> > and give us some sample numbers.  Can anyone give a textual
> > description of the flywheels, including an estimate of their
> > wetted area, and rotational velocities?
> 
> 
>  Nor do I mean to be argumentative. Read over what I copied verbatim and see
> if that changes your mind. If it doesn't, feeling your tractor pump bypass
> after deadheading it for a while, that  should.
> 
> 
> 
> > I'm a scientist by profession, and we work lots of things out
> > by numbers.  But we also try to shortcut the numbers with
> > intuition and other experience.  I may be real wrong in guessing
> > the source of the heat, but my best guess is the turbulent flow,
> > vs. the pressure release.  There just isn't much energy to
> > derive from simply releasing pressure on a liquid.
> 
> 
>   Agreed, I know hydraulic fluid is about .5 to 1% compressible, primatily
> due to entrained air. But, we're not releasing pressure generated by the
> compressibility of the fluid; we're passing fluid that is held at pressure
> by the pump over an orifice.
> 
>  Interesting side note: Brand-new hydraulic fluid right out of the drum is
> "lazy". It contains sigificantly more entrained air than used fluid does.
> You need to "work" the fluid to drive the air out.
> 
> 
> >
> > Guessing isn't really necessary, because a student experienced
> > with hydraulics, fluid flow, and the like can readily calculate
> > the different components involved.  We can then see if his or
> > her prediction comes close the the heat gain we see in Hagar's
> > test environment.
> 
> 
>   I guess we need to gather and plug in numbers to the equations I provided
> above.
> 
> 
> 
> >
> > Val
> > [COM-ASMEL, CFI-AI, N2EPO (work HF at all?)]
> 
> 
> 
>   No, not much HF. Most of my hamming lately is done VHF/UHF mobile on my
> hour-long commute or when I volunteer at the many public service events my
> club supports as well as others that they don't, like the Boston Marathon
> or, coming up, the Maine Forest Rally. Can't wait for that one, I love to
> watch rally racing and this one is run mostly on paper mill company roads
> out in the puckerbrush of northern Maine.
>  All I have for HF equipment is an old, borrowed Swan 350 with no antenna
> tuner. I had a Windom dipole strung up but it didn't work too well. I dunno
> if the tubes are shot or what but I was only seeing a few watts out. I need
> to bring that to a club member who is up on Swans and see if he can tune it
> up for me. I was able to work Europe occasionally, though, that was kind of
> fun.
> 
>  ....Jealous of the COM-ASMEL, CFI-AI......
> 
> 73 DE Lee KB1GNI
> 
> 
>   Lee
>   Oo-v-oO
>   PP-ASEL
>   KB1GNI
> 
> 
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