Fordnatics List Archive

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Mail From: "STEPHEN H 'STEVIE' GROSSEN" <(email redacted)>


Well guys, here it goes. I am an engineer and I will try to explain why
you should run a thermostat. My references are a experience running with
and without a thermostat and a heat transfer class taken 5 or six years
ago.
I believe we are confusing the specific heat of the cooling system
with the thermal conductivity of the system.
The cooling fluid in the engine / radiator has a certain capacity
to hold heat. So many calories of heat will raise the temperature of x
pounds of the fluid y number of degrees. However, this says nothing about
how quickly the heat is transferred and how quickly the temperature rises.
For example water has a specific heat of 1.00 Btu/lb-F. One Btu will
raise the temperature of 1 pound of water 1 degree F. This says nothing
about the amount of time it takes to do this.
To tie in the time we need the thermal conductivity of the fluid and the
other materials in the system. Thermal conductivity has the units of
Btu/hr-ft^2 F. Note that not only is time included but also area. To raise the temperature 1 degree F over 1
hour with an area of 1 ft^2 takes a certain number of Btus.
So what does this all mean. Well, we have an energy balance.
Heat must be soaked up in the engine and then dissipated in the radiator.
Heat is soaked up in the engine at a certain rate, and then dissipated by
the radiator at a certain rate. Those rates are dependant on the
specific heats of the fluids and radiator and engine material. (Why does a
bigger radiator work better, it has larger area to dissipate heat.) If the
the water is moving too fast through the system, it will not have time to
soak up all the heat it could, and therefore cannot dissipate all the heat
it could, and the system overheats. If the system is plugged and the fluid
moves too slowly, the fluid can not pick up all of the heat that is being
produced and the engine overheats. There is an optimum speed at which
the fluid should flow, and the thermostat provides the restriction to
provide the correct mass flow.
Now that is just my humble opinion. This and $.50 will buy you a
soda. Please feel free to comment, flame (I have my asbestos underoos on)
or what not.

steve

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Mail From: Lev Lvovsky <(email redacted)>

Maybe I'm not understanding this post too well, but I'll include my own
experiences with and w/o a thermostat. When I bought my car, it had a
funny habit of taking a long time to warm up. At the time, I was car
illiterate, and just thought of it as a given with old cars. Then, in
shop class we were going over cooling systems, and how they worked. We
were assigned to change the thermostat in our cars. When I took the
themostat housing off of the intake, I was surprised that there was no
themostat in there, and I asked the instructor why this was. He told me
that some people had the notion that theremostats cause overheating.
This couldn't be further from the truth. The only thing that a
thermostat does is keep the fluid that is contained in the engine block
from circulating with the fluid in the radiator when cold. When warm the
thermostat is open, and depending on the quality of the thermostat, has
little or no restriction oon the flow of the fluid. The thermostat has
no effect on the overeheating characteristics of the car. After putting
in my thermostat, the car warmed up faster, and got bettter gas mileage.
And as we all know a hotter engine is more efficient(to a point). Did I
get the jist of the post???

___________________________________________
|From: Lev Lvovsky; Castaic, CA
|Most cherished possesion: '66 Ford Mustang
|e-mail: (email redacted)
|Q:What do you think about American Culture?"
|A:"I think it's a good Idea."
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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Mail From: Roberto Arturo Schafer <(email redacted)>

As far as the engineering explaination went. The heat transfer rate is
also dependent on the relative difference in temperature of the two
materials. Therefore one would think that a faster flowing fluid would
allow a greater heat transfer. Faster fluid in and of itself should not
reduce the efficiency of heat transfer (assuming an infinitely large
source of cold fluid).

Me thinks, as Randy Hasson suggested, the added pockets of air (or are
they a vacuum?) due to the faster fluid flow are more responsible for the
lack of heat transfer. Still I don't have my degree yet and still must
rely on intuition and lower level physics and heat transfer classes.

So who is right? Anyone out there work for Modine?

Rob

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Mail From: "STEPHEN H 'STEVIE' GROSSEN" <(email redacted)>


> As far as the engineering explaination went. The heat transfer rate is
> also dependent on the relative difference in temperature of the two
> materials. Therefore one would think that a faster flowing fluid would
> allow a greater heat transfer. Faster fluid in and of itself should not
> reduce the efficiency of heat transfer (assuming an infinitely large
> source of cold fluid).

It takes a certain amount of time for heat to transfer from the
cooling fluid to the radiator and the surrounding air. If the coolant
is moving too fast through the radiator, it is not spending enough time in the
radiator to transfer this heat.
I agree with the relative temperature difference. A radiator will
remove heat better in January near zero temperatures than it will in
July when it is in the 80's. This is why cars are more likely to overheat
in the summer than in the winter. Of course you can overheat in the
winter if the the coolant has froze in the radiator and essentially
blocked it off.

> Me thinks, as Randy Hasson suggested, the added pockets of air (or are
> they a vacuum?) due to the faster fluid flow are more responsible for the
> lack of heat transfer. Still I don't have my degree yet and still must
> rely on intuition and lower level physics and heat transfer classes.

A coolant system operates (or should) operate at 7-14psi. This has the
effect of elevating the boiling point of the coolant. There may be local
"steam pockets", but the higher pressure is supposed to help eliminate
these as well as the cavitation of the fluid due to overspeeding of the
water pump impeller. Taking this to extremes, winston cup cars use
something like 22psi caps and really underdrive the water pumps. Some even
have quick attach fittings to add fluid to the system under pressure.
Flow in a cylinder head is very complex and has not been
characterized very well (IMHO). After all, look at most V-8 engines, the
block is cooled first, then the head. Isn't the head (and the top of
the cylinder) where most of the heat is at? We ought to be cooling those
valves first. Chevy now does it on the new LT1. How about the new
modular engine? I am not sure.

I know, I'm long winded.
later
steve

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Mail From: (email redacted) (Brian Kelley)


STEVIE GROSSEN writes:

> It takes a certain amount of time for heat to transfer from the
> cooling fluid to the radiator and the surrounding air. If the coolant
> is moving too fast through the radiator, it is not spending enough time in
> the radiator to transfer this heat.

Ever stick your hand under a hot faucet? Think of your hand as a
radiator. At any given temperature, the faster the water flow, the
faster you get burned. I suppose you're also going to tell me that my
air conditioner cools me faster on low than on high?

Will I pull more heat out of my workstation with a slow or a fast fan?
Once that air is heated, what makes you think the situation is
different when we're trying to extract the heat from the air? The
faster it moves by the cooling surface, the better. The greater the
_difference_ in temperature, the faster the heat transfer (assuming
not cavitation, etc).

Brian


- ---
(email redacted)

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Mail From: "STEPHEN H 'STEVIE' GROSSEN" <(email redacted)>


Brian,

> > It takes a certain amount of time for heat to transfer from the
> > cooling fluid to the radiator and the surrounding air. If the coolant
> > is moving too fast through the radiator, it is not spending enough time in
> > the radiator to transfer this heat.
>
> Ever stick your hand under a hot faucet? Think of your hand as a
> radiator. At any given temperature, the faster the water flow, the
> faster you get burned. I suppose you're also going to tell me that my
> air conditioner cools me faster on low than on high?

Poor analogy (IMHO) with the hot water in the sink, but I will work with
it. I think the scale factor is not appropriate. Instead, look at it this
way, think of the sink as the radiator. Set the faucet and drain to hold
a sink full of water, with water flowing in and out. Record the
temperature of the water comming in and that of the water going out after
things have stabilized. Now change the speed of the water flow in and out
to faster and slower than the baseline and record the difference in
temperature again. There is an optimum flow rate that will give the
lowest temperature in the sink. The same is true for the cooling system
There is an optimum flow rate for coolant in the radiator. That doesn't
mean the system won't work at different flow rates, it just won't work as
well. A cooling system in otherwise perfect shape will probably work ok
without a thermostat, but it will work better with one.

Air conditioner analogy is apples and oranges. The air conditioner on high
increases the fan speed, not of the freon in the internal system.
Compressor output is relatively constant. A better analogy would be a
multi speed radiator fan. The faster the fan runs the better, to a point
where stagnation and blockage become a factor. Beyond that increasing
the fan speed does no good.

>
> Will I pull more heat out of my workstation with a slow or a fast fan?
> Once that air is heated, what makes you think the situation is
> different when we're trying to extract the heat from the air? The
> faster it moves by the cooling surface, the better. The greater the
> _difference_ in temperature, the faster the heat transfer (assuming
> not cavitation, etc).

You can't pull out any more heat than is produced inside. Once you
flow air past the components to remove all of the heat that is being
produced, any other airflow is waste. You can't cool the board any cooler
then the media being used too cool it. 70 degree air will only cool the
board to 70 degrees, no matter how fast a fan pulls it through (assuming
subsonic flow that is).

I don't want to use anymore bandwith on this than necessary. I am sure
a lot of folks are already perturbed with my longwindedness. You or
anyone else, may e-mail me directly, and we can continue the discussion
off line if you so choose.

steve

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Mail From: Dan Malek <(email redacted)>


> Date: Tue, 28 Mar 1995 08:26:32 -0500 (EST)
> From: STEPHEN H 'STEVIE' GROSSEN <(email redacted)>
>
>

>It takes a certain amount of time for heat to transfer from the
>cooling fluid to the radiator and the surrounding air. If the coolant
>is moving too fast through the radiator, it is not spending enough time in the
>radiator to transfer this heat.

OK, I can't watch this stuff go by any longer. You guys are going to
have to start supporting these arguments with some of mother nature's
laws of physics. I certainly don't have all of the answers, and the
information I have is gleaned from racing product publications and
acutally building custom cooling systems. The only piece of information
I have that relates to the speed of the coolant concerns cavitation.
Basically, you want to avoid it. Below that speed it just does not
matter, unless you can't get the coolant out of the block before it
overheats.

The rules are pretty simple. The radiator has to dissipate more BTUs/min
than the engine is capable of generating, and you don't want to cavitate
the coolant. We have some engines with thermostats, some without. One
car has louvers in front of the radiator to control the air flow. The
more air, the more cool. We measure coolant flow, temperature increases
across the engine, and decreaes across the radiator. Maybe someone with
a mechanical engineering degree can explain it with lots of equations,
but for us, the rules are pretty simple.

>A coolant system operates (or should) operate at 7-14psi. This has the

The pressure reflects whatever temperature above atmospheric boiling
point you want to achieve. There is no "must" or "should" here. I
personally try to run as low as possible, since that reduces the risk
of leaks.

>... Taking this to extremes, winston cup cars use
>something like 22psi caps and really underdrive the water pumps. Some even
>have quick attach fittings to add fluid to the system under pressure.

The water pumps are really underdriven because you don't want your
pump to keep up with the 8000+ RPM you are running all day. You basically
determine the water flow you want to maintain at top speed down the
back straight, determine the engine RPM at that point as well, then
find a set of pulleys that does it. The 22 psi caps are used because
the radiator is just minimally big enough to do the job, and you have to
cover the peak overheating cases.

> Flow in a cylinder head is very complex and has not been
>characterized very well (IMHO). After all, look at most V-8 engines, the

Well, yes and no. Our dyno test engines have lots of temperature probes,
so we have a pretty good idea how the head is cooled.

>block is cooled first, then the head. Isn't the head (and the top of
>the cylinder) where most of the heat is at? We ought to be cooling those
>valves first. Chevy now does it on the new LT1. How about the new
>modular engine? I am not sure.

The rules change when you start running aluminum heads on cast iron
blocks. When racing regulations require stock block and pump
configuration you don't have much choice either. Street engines rarely
care how they are cooled, and racing engines do what is necessary when
the regulations allow. IMHO, the LT1 is expensive engineering publicity
for a non-problem.


-- Dan

This read-only message was archived from a public mail list.
Mail From: (email redacted)

>>Heat is soaked up in the engine at a certain rate, and then dissipated by
the radiator at a certain rate. Those rates are dependant on the specific
heats of the fluids and radiator and engine material. (Why does a bigger
radiator work better, it has larger area to dissipate heat.) If the the
water is moving too fast through the system, it will not have time to soak up
all the heat it could, and therefore cannot dissipate all the heat it could,
and the system overheats. If the system is plugged and the fluid moves too
slowly, the fluid can not pick up all of the heat that is being produced and
the engine overheats. There is an optimum speed at which the fluid should
flow, and the thermostat provides the restriction to provide the correct mass
flow.<<

I understand the theory, I just doubt the practicality of it in most
real-world applications. I don't think that for the average street app, the
water pump, even without a thermostat, is moving the water fast enough to
keep the water from tranferring enough heat.

Also, how is this system affected by the fact that the water spends less time
in contact with the engine as well, thus - allowing the engine to transfer
less heat to the water?

Additionally, could you run pulleys that slowed the speed of the H2O pump and
no thermostat to balance things out? Many of the cars here are already
running underdrive pulleys.

There are also several types of thermostats available - including high flow
models - how do they fit in to the picture?

Again, I don't doubt that this _could_ happen, but I suspect it is a lot less
common than the amount of press it gets.

-Tom

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Mail From: (email redacted) (Bob_Wise)

There are (at least) two temperature transfers taking place.

1) engine -> coolant
2) coolant -> air

Moving the coolant through the system quickly means that the heat
energy absorbed by any given volume of coolant in the engine is
reduced. This means that the temperature of that coolant once it gets
to the radiator is lower if it was moved through the engine quickly,
and hotter if moved through the engine more slowly. Hotter coolant
transfers its heat to the air faster because it has a greater
temperature differential.

On the other hand, hotter coolant inside the engine absorbs heat more
slowly, because again, the greater the temperature differential, the
greater the heat transfer.

On the gripping hand, this means that there is an optimal coolant flow
rate, which is neither as fast nor as slow as the coolant _could_ be
moved.

Given an "infinite" supply of coolant at a set temperature, the faster
the rate, the better (which I believe was Brian's point). However,
the radiator system is closed.

-Bob

On Mar 28, 12:57, Brian Kelley wrote:
> Subject: Re: Thermostat or no
>
> STEVIE GROSSEN writes:
>
> > It takes a certain amount of time for heat to transfer from the
> > cooling fluid to the radiator and the surrounding air. If the coolant
> > is moving too fast through the radiator, it is not spending enough time in
> > the radiator to transfer this heat.
>
> Ever stick your hand under a hot faucet? Think of your hand as a
> radiator. At any given temperature, the faster the water flow, the
> faster you get burned. I suppose you're also going to tell me that my
> air conditioner cools me faster on low than on high?
>
> Will I pull more heat out of my workstation with a slow or a fast fan?
> Once that air is heated, what makes you think the situation is
> different when we're trying to extract the heat from the air? The
> faster it moves by the cooling surface, the better. The greater the
> _difference_ in temperature, the faster the heat transfer (assuming
> not cavitation, etc).
>
> Brian
>
>
> ---
> (email redacted)
>
>-- End of excerpt from Brian Kelley






- --
- -----------------------------------------------------------------------------
| Bob Wise | INET:622-1322 | MCIMail:468-2222 | Pager:719-577-1928 |
| |-------------------------------------------------------|
| MCI | Phone:719-535-1322 | Internetemail redacted) |
- -----------------------------------------------------------------------------

This read-only message was archived from a public mail list.
Mail From: Matthew Prater <(email redacted)>

In Brian Kelley's letter-
|STEVIE GROSSEN writes:
|
|> It takes a certain amount of time for heat to transfer from the
|> cooling fluid to the radiator and the surrounding air. If the coolant
|> is moving too fast through the radiator, it is not spending enough time in
|> the radiator to transfer this heat.
|Ever stick your hand under a hot faucet? Think of your hand as a
|radiator. At any given temperature, the faster the water flow, the
|faster you get burned. I suppose you're also going to tell me that my
|air conditioner cools me faster on low than on high?
|Will I pull more heat out of my workstation with a slow or a fast fan?
|Once that air is heated, what makes you think the situation is
|different when we're trying to extract the heat from the air? The
|faster it moves by the cooling surface, the better. The greater the
|_difference_ in temperature, the faster the heat transfer (assuming
|not cavitation, etc).
|---
|(email redacted)

Not neccesarily.
Take the instance were a hot stream flows throw a 2 inch pipe.

But, seeing that this system is a circulation type, it doesn't matter that much.

What matters most is the temperature difference between the outside of the
rad, and the inside.

If your radiator is huge, push all the liquid you can.

I would say vary the fans, and don't worry about the flow rate.

Matt.

Matthew L. Prater/ 1700 Townsend, 170 DHH/ Houghton, MI 49931-1194/ 906-487-0269
(email redacted) "me.mtu.edu/~prater/" Michigan Tech. Univ.