Well, yes and no.
The real numbers can be had by building the proposed system on a test stand
in an effort to remove as many variables as is possible.
Car radiators from the early days probably did produce such drag numbers,
because the individual razor sharp edged tubes stuck up into the tanks an 1/8"
or so and thus produced a flow disaster. Both in inlet and outlet of the tubes.
Vena contracta stuff you know.
Modern radiators and heat exchangers in general are much improved in this
regard. The thinking here is the quest for more fuel mileage. So, less drag,
smaller water pumps, more mileage. Easy.
Some modern radiators have plastic end tanks that are crimped in place with
many little finger wrapped around the tank flange. These radiators will not
support very high coolant pressures. A failed seal or head gasket will/can
blow a tank clear off the core. My wife's car did that.
The really good radiator designs had diagonal dents in each tube with those
on the opposite side at a reversed angle in order to turbulate the coolant
and keep the tube surface scrubbed of cooled coolant which tends to cling to the
tubes surface and insulate hotter coolant. Worse if antifreeze is in the
mixture. So, limit anti freeze to what you have to have for your area. Use
distilled water, 10% or as needed anti freeze
and 1/2 teaspoon full of Dawn dishwashing detergent. (because Dawn is easy
on your hands).
Why a double pass?
It puts both inlet and outlet on the same end tank. Handy for some
installations.
You can imagine that it just makes the radiator twice as wide (tube length)
with half the tube count. The down side is the drag from coolant leaving one set
of tubes and entering another to get back to the first end tank and half the
tube count.
This works great in racing. It is a pain to convert an existing radiator to
double pass. One outlet must be moved to another tank. The hole must be covered.
Best to order the double pass from a racing radiator manufacturer.
Why a triple pass?
Usually done to existing copper radiators but can be done to aluminum if
you have a TIG machine. No outlets need be moved. Just install two baffles
through the tanks using a hack saw cut. Solder in place or TIG if aluminum.
Imagine a radiator three times as wide with 1/3 the tube count. The down
side is drag from the tube count and two junctions where coolant re-enters the
tubes to get to the outlet.
How can my little water pump get coolant through all of that drag?
That little water pump is designed to provide enough flow to keep the
engine alive as you cross Death Valley on a really hot day with the air
conditioning running.
In the airplane you will be turning the pump two or three times as fast as
in the car. In the race car at 9,600 RPM maybe 5 times as fast.
So, the stock pump is plenty big enough for aircraft use.
What is that about a restrictor and or a thermostat?
The stock thermostat in the Mazda is a Rube Goldberg design that has
everything involved but a mouse with a candle on its back and a bowling ball.
The major thought should be: thermostats fail in the closed position. That
special fluid leaks out of the brass bellows and the thermostat snaps shut.
Never to open again. Pulling off power may get you another few minutes to look
for "Nearest" or maybe not. Worse if you normally have high coolant temps.
The design is a result of the Peoples Republic of California having
different pollution rules than all of the other states. Rapid warm up to
limit HC. So, that odd thermostat opens a loop for engine only
circulation when cold. Then when hot opens the radiator loop and closes off
the engine only loop with a foot valve. Most users just tap the foot valve hole
for a 1/2" pipe thread and install a pipe plug. A hex drive plug looks very
nice.
Then a conventional "American" thermostat can be installed, if you have to
have one like in the Great White North. You can drill three 1/8" holes
through the rim of the thermostat in Southern climes or just two in the North,
and a thermostat failure will not kill you right away. With a power reduction,
the engine can cool really well with coolant flowing through
just 3 such holes. Pull the power back, push nearest, turn the heater fan
up full blast. Declare a screw up.
Note here that good thermostats already have a hole in them to allow flow
and bubbles to pass through even when they are closed. This assures that heated
coolant can get to the thermostat and cause it to open. In some cases a caged BB
is involved, but the idea is that there must be at least one hole.
Should I use a restrictor?
In aircraft, probably not. A restrictor is used to keep the suction side of
the pump from pulling the inlet below ambient pressure (14.7 PSI at sea level).
In aircraft the pump is running at? 4,000/ 5,000 RPM?
This keeps cavitation from damaging the pump and the radiator tubes near
the outlet. Not a factor in aircraft, but a yes in racing where the shifts are
at 9,600 RPM and the pump is screaming.
You have noticed that the suction side outlets on car radiators are bigger
than the inlets.
And, the suction side hose has a wire support spring inside.
That is to prevent that hose from collapsing when you scream the stock
engine. See a pattern here?
A restrictor may also raise the water pressure in the block just a bit
which is good news.
Is Stewart Warner just lying to sell stuff like the super high flow
water pumps and the trick thermostats with hoes in the edge.
Did you hear a Turnip truck go by?
No, they have collected real data to back up each statement and run it by
the lawyers. It may not have been recovered from the same engine, or even the
same radiator, or during the same year, but I bet they have the DATA to
support each statement.
Stewart Warner sponsored my car for a year and I found them to be
supportive of racing, and never had a problem with any of the products we used.
Very nice people. And thank you for you're support.
In any case rig up a test stand and prove or disprove any such claims, and
publish your findings here.
This is just my opinion, and may be completely wrong.
Lynn E. Hanover
Rotary engines since 1980
In a message dated 6/16/2012 8:08:16 A.M. Eastern Daylight Time,
eanderson@carolina.rr.com writes:
Here is a link to Steward Warner site with tips and
information on radiator parameter. Very good information
I've found no
better, credible source of information that is easy to understand -
the best part -> no math required {:>)
Regarding double pass radiators - like anything else
there are pros and cons. Here is an extract from that site:
Double pass radiators require 16x more pressure
to flow the same volume of coolant through them, as compared to a single pass
radiator. Triple pass radiators require 64x more pressure to maintain the same
volume. Automotive water pumps are a centrifugal design, not positive
displacement, so with a double pass radiator, the pressure
is doubled and flow is reduced by approximately
33%. Modern radiator designs, using wide/thin cross sections
tubes, seldom benefit from multiple pass
configurations. The decrease in flow caused by multiple passes offsets
any benefits of a high-flow water pump.
The one basic equation of heat transfer Q = mDT/Cp. So if you reduce the mass flow m by 33%- that
is going to have equal reduction in heat transfer (Q). Now if the double
pass causes a better DT then you recover some of the
heat transfer, but all 33% lost to less mass flow?
Now if you can get the flow back up then the
double pass offers benefits. A higher capacity/higher pressure
pump capable of producing 16 times more pressure - or some
means to increase flow would seem desirable.
The bottom line is you can not consider just one aspect
of a cooling system and overly optimize on it. You cooling system is
exactly that - and it is a system which is no better than the weakness
link in the cooling chain, be it coolant flow, heat transfer characteristics
(# fins/sq inch, thickness, surface area, etc), air flow, specific heat of
coolant and on.
Frequently you will find (as Tracy recently
pointed out) that it is the small details that makes one system successful and
another seeming similar system not.
Will a double flow work - certainly it will - given
enough heat transfer surface and airflow across it almost any cooling system
can be make to work. The question is what (as always) are
the trade offs?
Ed
Sent: Friday, June 15, 2012 11:17 PM
Subject: [FlyRotary] Re: inlets and outlets
The double pass radiator increases the
efficiency of the radiator by about 50%.
You have tanks on both sides. One side has a
partition in the tank with the inlet at the top and outlet at the
bottom.
The coolant flows across the top half of the
core into the non-partitioned tank then back across the lower half back to the
partitioned tank and out the outlet.
That's the way I went with a custom Ron
Davis radiator.
On Fri, Jun 15, 2012 at 9:49 PM,
<CozyGirrrl@aol.com> wrote:
I can certainly see the logic in a single pass radiator of in on top
and out on bottom.
With a dual pass design (tanks top and bottom) what would be the
advantage of inlets and outlets on the bottom -vs- the top in a case with
the water pump above the top of the radiator?
In both cases their would be a vent line to the swirl pot from the
top tanks.
...C&R
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