I see another picture of cavitation damage, just inside the pump inlet.
> > The water boils due to the low pressure right at the suction
> > opening and along the face of the vanes.
> > Coolant boiling temperature AND pressure determine boiling
point.
> > So an effective system can loose pressure and begin to
cavitate the
> > pump. Even stock engines can do this. In a cast iron
housing it
> may take
> > some long time for this kind of damage to become obvious.
In an
> aluminum
> > housing, damage can be sudden. The damage may eliminate
some of the
> > cavitation through reducing performance, but overall system
> performance will
> > suffer from a reduction in GPM.
> > Sharp edges should be removed from the pump cavity. This
> will increase
> > pump performance and raise the GPM where cavitation takes
place.
> >
> > It is no accident that the lower radiator hose on every
car is bigger
> > than the upper radiator hose. The lower hose is the water
> pump inlet.
>
> An effort is made to provide coolant to the suction side of the
>pump at the
> > highest volume and pressure possible. This, so the minimum
amount of
> > pump possible can do the job. Few cars have way too much
water pump
> > installed from the factory.
> > >
> > Raising the boiling point with a higher pressure cap
setting helps.
> > Using higher boiling point chemicals in the coolant works.
> > Slowing the pump a bit works. And restricting pump output
works.
>If the
> > restriction is down stream from the block, then pressure
inside
>the block
> > will be slightly higher, and so, the boiling point inside
the block.
> > >
> > I use a 5/8" restriction on the outlet of the thermostat
housing.
> > I use a 10% ethylene glycol and a bottle of Red Line Water
Wetter.
> the crank pulley is from racing beat, and is smaller than
stock.
>We shift
> > at 9,600 RPM. No cooling grooves in the rotor housing. No
cavitation
> > damage to an aluminum pump and housing in 15 years of
racing. No
>cracks
> around the plug holes. Never an overheat problem. 244.8 HP at
>9,400 RPM.
> >
> > Lynn E. Hanover
> >
> > Water outlet with 5/8" restricter welded on.
> > The clutch discs are Lamar Engineering/Tilton
> >
> > I would not use that disk on a street car as Robin would
complain
> > if she had to drive it :) No springs.
> >
> > I suspect a lot of damage people attributing to
caviatation is
> > caused by low water.
> > I can't imagines the Mazda engineers designing something that
> > cavatates in our rev range.
> > >
> > > Paul Lamar
> > >
> >
> >
> >
> > Lynn, how many pounds of pressure/cap?
> > Steve Beckham
> >
> >I use a 16 pound lever cap, but Stant makes caps up to 32
pounds. *
> >
> >Lynn E. Hanover
> >
>
>Lynn
>
>Just so I got this correct. It sounds like you are pulling the cooler
>water from the bottom of the radiator into the pump and from the pump
>into the engine block and then it exits the block back into the
top of
>the radiator through a smaller size hose. I don't know the
orientation
>of your radiator whether it is stock straight up or laying at an
angle.
>I am curious as to where and how you located the pressure cap.
>
>Doug in Japan
>
>The restrictor is on the water outlet, and the top hose is the
same size
>as a street Mazda. The radiator is a Griffin double pass aluminum.
3" by
>19" by 31" Two rows of 1 1/4" tubes. Both inlet and outlet on the
>passenger side.
>
>Here is a picture of a cooling system that has worked for me since
1980.
>I added the Rol-air-trol. A home made version of a air/water
separator.
>I used to manufacture heat transfer packages that used a giant
version.
>I thought Bell and Gosset made those but now I don't see one in their
>catalogue. When pumping hot water around a building, you must
remove all
>of the air from the loop. When air goes through a pump, it expands
>violently (cavitates) at the pump inlet and may damage the pump,
and it
>makes an awful noise at the pump, and going through fin tube
cabinets in
>each room. Nothing is as funny to school kids as a fin tube
cabinet that
>sounds like it is having a diarrhea attack. So air in the loop is just
>not allowed. The air removing device helped me get the air out quickly
>without hurting the engine, as my system may be drained often. It is
>difficult to remove air from the rotary when it is level. More so
if it
>is not level. The rest of the system is what you would have found on
>every RX-2 and RX-3. The pressure bottle is kept 1/3 full of coolant.
>When air is delivered to the pressure bottle, it pops to the top and
>only airless coolant can be forced back into the system when a
>temperature/volume change occurs. In two or three heat cycles the
system
>will be solid coolant. The bottle must be refilled after each heat
>cycle, but not over 1/3 full. I have a Shrader valve on my bottle,
so I
>can be at relief pressure before the engine starts. Probably not
>required for airplanes. You could also add the pressure gage on or
close
>to the bottle for easy reading, and or, a gage on the dash to view
>coolant pressure. The racing organizations require that catch
tank, but
>there is never anything in it.
>
>I used a stock RX-2 pressure bottle, but a better choice would be an
>aluminum aftermarket bottle to get a good selection of cap pressures.
>The pressure cap is on the bottle. Not on the swirl pot. That cap is
>solid and used to fill the system.
>
>Lynn E. Hanover
>
>
Lynn,
Thanks for your fine diagram. Can you tell me the pressure drop across
your radiator or pressure before your restrictor? As I understand it,
your radiator is a dual pass 3" x 19"x 31". It sounds like the water
flows to port side and reverses back to starboard side. That means you
have two rows of 1 1/4 high tubes traversing a total radiator length of
62 inches or more than 372 square inches of wetted surface area within
the radiator. That is quite some restriction in its own right. I
can't understand why you would restrict the flow even more. Perhaps
without it the coolant would be forced out at high revs?
Doug in Japan
The theory behind the restrictor is it increases the pressure in
the block
which delays over all boiling. However it reduces the flow rate
which is a bad
trade off. It is better to just use a higher pressure cap. Also this
is a car
and a thermostat is necessary. The thermostat also acts as a
restrictor. In an
airplane it is better to use a cowl flap to control engine
temperature which
reduces the cooling drag when closed. Cooling drag can be as high as
30% of the
over all drag on an airplane and therefore cowl flaps can be worth
as much as 50
HP more in the engine when it comes to top speed. As Kays and London
say;
"At a given set of temperatures at a given air density, the heat
dissipated by a
heat exchanger is nearly proportional to the velocity of the air
through its
core. The power required to force the air through the core, however,
varies
approximately with the cube of the air velocity. Thus, by reducing
the air
velocity through the core, the ratio of heat dissipated to drag
power absorbed
is reduced, even though the size of the heat exchanger must be
increased
correspondingly to dissipate the heat from a given engine installation."
Paul Lamar
The lower radiator hose on a street car has a wire stiffener so that it
cannot be collapsed by ambient air pressure. Well how is that possible
we ask? Because even though a 14 or 16 pound pressure cap is common. The
dynamic of flow through the system where the highest drag or restriction
is the radiator, will often produce below ambient pressure on the
suction side of the pump. If that be the case, there must be a higher
pressure elsewhere in the system. So where would that be? Everything
between the outlet of the pump and the inlet to the radiator would be
the higher pressure area. That includes the engine block. Good news.
Much of this is speculation on my part, and may be slightly right,
slightly wrong, or bass akwards.
The many small tubes in the pressure side of the radiator stick out of
the manifold wall a bit. Each of those
produces a vena contracta at the tube opening. The higher the pressure
the more effective the contracta.
I suspect that raising the pressure in the inlet manifold of the
radiator, does not produce a linear increase in coolant flow. Or,
doubling the pressure probably does not double the flow. So I suspect
that there might be a small range of pressure that produces the highest
flow rate vice pressure. In aluminum radiators where the tubes are
epoxied into the manifold, and the epoxy is close to the end of the
tube, unlike a soldered radiator, very little vena contracta would occur
and the pressure function would be close to linear. Even so, there are
dents in a cross pattern to produce turbulence and help scrub chilled
coolant from the tube walls where it tends to stick. So a double pass
has twice the length of tubes, and half the number.
So as long as the flow rate of the whole system is low enough that the
radiator is not the maximum restriction, the suction side of the pump
will not be starved of coolant. So the total flow rate is a function of
the restrictor, not the radiator. The restrictor is small and is sharp
edged on both sides. We had to race in 50 degree weather once, and I
installed a 180 degree thermostat that I had drilled three 1/8" holes
around the rim to let bubbles through. In the morning warm up, the
engine got up to 120 degrees. I taped over 1/3 of the radiator and we
got up to 150 during the race.
I have no data for inlet or outlet temps or pressures. The radiator is
typical in big block dirt cars. Massive over-kill is my cure.
Lynn E. Hanover
Mazda eliminated the built in restrictor in the 13B water pump and went to a
wide open system in the RX8 engine. Less restriction.... more water flow.
There is no sweet spot. We proved that with our water pump dyno while you were gone.
Paul Lamar
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
Youtube key word UTUBPLEASE
Copyright 1998-2008 All world wide rights reserved.
