Jim,
You make some interesting arguments; let's see if they "hold water" so to
speak. First of all, local boiling can and is a big problem in motors;
especially high performance types. The temperature you measure as the water
leaves the motor is the average temperature of the water. Local hot spots
can and do cause local boiling which drastically reduces heat flow and can
cause engine problems like predetonation, cracking, etc. Secondly, you
explain the improved cooling at low flow in terms of laminar versus
turbulent flow. Well, this is wrong on two counts; first, heat transfer
across a boundary (surface) is much higher with turbulent flow than laminar
flow ( I think this is usually covered in first or second quarter fluid
dynamics and I think is even fairly obvious intuitively), and second, if
heat transfer were better with laminar flow, then in this case the water
would actually get hotter while passing through the motor, not cooler (I'm
assuming that the temperature sensor is responding to water temperature at
the outlet of the motor as in a Tiger (and most other vehicles too I
believe). While I don't claim to fully understand all the issues relating
to the cooling system , I can usually recognize a spurious argument when I
hear one. Once these red herrings are disposed of, then we can get down to
figuring what actually is going on.
If you think we're a little confused about this subject, you should read an
artile that was passed to me by a friend. It appeared in either Circle
Track or Stock Car Racing (at least some Peterson publication) circa Nov of
'96. He faxed me a copy and didn't give the exact reference. The title of
the article is "Buying Racing Water Pumps" and is essentally a dialogue
between Danny Castillo, R&D engineer from Edelbrock, Steve Morrison,
president of Milodon, Ken Sink, director of marketing for Weiand Automotive,
and Robert Hone, general manager of Moroso Performance Products. Basically,
these guys are trying to give us good reasons to buy their expensive water
pumps, so a lot of what they say should be tempered with some skepticism.
For example, there's a claim of the water pump drawing twenty-five or thirty
horsepower from the motor which I find totally unbelievable. Statements
apropos to the issue of pressure include: (Hone) "Restrictors are used to
hold the water in the block longer in order to absorb more heat. They also
will increase the water pressure in the block." Well, take your choice
slower flow or greater pressure; which is it? Guess you know my opinion in
this regard. Another quote: (Morrison) "We are increasing the pressure in
the block, especially at the back where the cylinder meets the block. In
that area, it has dead flow. That is where the water goes in, dead ends and
comes out again. Normally water wouldn't flow there and you just get a
steam pocket. It gets real hot in that little corner. You get a hot spot
in the cylider wall at the No. 7 cylinder and that one cylinder detonates.
Now you have to back the timing off or reduce the mixture just because of
that one cylinder. With even cooling from the increased pressure, now all
the cylinders are running the same temperature." I'm not putting these guys
up as experts or even necessarily agree with much of what they are saying.
At times they make some good points and are completely off base at other
times. With the exception of Castillo, these are primarily marketing and
management types and it seems like you don't get these kind of jobs without
developing a disregard for sound engineering principles. On the other hand,
these guys probably do make some pretty nice water pumps. I know at least a
few Tigers that have used the Edelbrock pump. Is it really any better than
a stock pump with a good impeller (e.g., Motorsport or HiPo)? I'd like to
hear from some people with experience with these pumps. If they're going to
use twenty-five horsepower, however, I think I'll pass.
Hope this gives you and the rest of the gang a little to chew on for awhile.
I'm sure there is going to be much more
Bob
>With regard to:
>
>" Reducing water flow per se never improves cooling. The value
>of a restriction is that it builds pressure inside the engine, albeit
>at the cost of water flow. As long as the reduction in water
>flow is not excessive, then there's a net benefit. The trick is
>to add just the right amount of restriction, I guess only trial
>and error will work here."
>
>I gotta take issue here. Pressure does not improve or worsen cooling.
>Pressure only changes the point at which water is converted to steam.
>I grant that steam in contact with metal is not as good a heat transfer
>interface as water to metal but pressure itself will not help cooling as
>long
>as you maintain the liquid phase.
>
>Flow rates, on the other hand, can impact the macro system and the micro
>system in the sense that laminar flow (or flow below the transition point)
>will
>transfer heat better across boundry than will turbulent flow. Turbulent
>flow
>of several things; primarily, in our systems I think, flow rate and
>surface finsh.
>Since the surface finish of my water passages are relatively rough; slower
>flow
>gives me a better chance at maintaining maximal laminar flow and increasing
>
>cooling effeciency.
>
>Regards,
>
>Jim
>B9470139
>
>
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