Some radiator questions

[moondisc]

So it's the lack of turbulence, and not the fact that the coolant isn't staying in the radiator long enough to transfer the heat?

[HOTRODSRJ]

So it's the lack of turbulence, and not the fact that the coolant isn't staying in the radiator long enough to transfer the heat?

Yep.....slower the flow the lower the BTU transfer both in the radiator and block.

Have you ever went swimming in a large river where the top of the river when you dove in was nice and warm, yet only a few feet down it was cold as ice!  This is a perfect example of laminar flow.  The whole volume of water is not being used to transport heat.  Same thing happens in the radiaotor.  The outer part of the column of water is heated and cooled yet the center is relatively left unaffected.  Once you "turn" the water then the whole column gets involved in the process of heat transfer.

[moondisc]

I learn something new every day.
And my wife said I'm too old to learn!  

[Bruce Dorsi]

I learn something new every day.

.......... I do, too.  And that's good because I forget something old each day!    

And my wife said I'm too old to learn!  

.....No, Charlie. -- She only said you're too * old!  

[48builder]

So it appears my first choice should be the 2000 Durango aluminum radiator with 2 rows. I will give it a try and seee what happens.

Thanks for all the input.

Hey Charlie, when we et a weelend with bad weather, I'll run that manifold out.

[PeterR]

About a month ago a similar topic ran on this board.    The widely held notion "the higher the water flow, the better the heat transfer" was promoted.

I related the experience of the racing Coopers which were notorious for overheating, and attempts to cure this by removing the thermostat to increase flow rate only made the situation worse.    The factory produced a restrictor plate to install in the thermostat housing and this item improved cooling efficiency enormously.

Another contributor wrote "I have heard this exact story and was a common phenom in circle track cars/engines as well. The replacement of the "restrictor" actually made the system cooler than having no thermostat. While the effect was known, the cause was not"

The explanation offered was that the reduced water flow rate by itself would worsen the condition, but the benefit of turbulence caused by the orifice more than compensated for the lower flow rate.

The next time I looked the thread had died,  however now this topic is under discussion again I shall continue.

When the effectiveness of these restrictors became evident there were numerous theories of how they functioned.   One popular explanation did relate to the effect of turbulence, my conclusion at the time was without a thermostat water might stream out from the head passages allowing air or steam to accumulate and reduce the heat transfer from metal to water, while a restrictor plate would keep the passages full and more than make up for the reduced flow.

In an act of desperation an overheating vehicle without a thermostat had a clamp put on the radiator hose to squeeze it down, -with exactly the same results.   This was done to the lower hose due to the short length of the top hose.  So it reduced the flow but did nothing to keep the head passages full, and did nothing to add turbulence to water entering the radiator, completely dispelling both theories.

Further, if turbulence and high flow had both been advantageous, a better solution than the restrictor plate would have been to leave out the thermostat and slide a thin walled tube with an array of knobby fingers on the inside wall into the top radiator spigot.    This would generate turbulence as the water entered the top tank while retaining the highest possible flow rate.

The restrictor plate was not something cobbled up by a home mechanic but an official part produced by a manufacturer with a factory team which at the time was winning high profile events like the Monte Carlo back to back.   However races held in warmer regions were another issue altogether where they were plagued with overheating.  If the solution lay purely in increasing turbulance I find it difficult to believe that over all the years these vehicles raced, factory engineers with access to a huge research budget were incapable of producing something like the item described above which I conjured up in a period of about one minute.

So, under some circumstances reducing water flow is advantageous, even though it has been demonstrated over and over again the vast majority of overheating problems -particularly at idle are improved by increasing flow.
 
My belief -and obviously it is only a personal opinion is, the process of transferring heat energy from engine to water then water to air has a parallel to the transfer of energy in an electrical system.

It is widely believed that to increase the power drawn by an electrical load the load resistance should be made smaller allowing more current to flow.   Pep, Choco and others will remember from their student days maximum electrical energy transfer occurs when the load impedance equals the source impedance.    This means the belief that lowering load resistance increases power consumption only holds true in situations where the source resistance is zero, or very much lower than the load.

With a cooling system the situation is similar except energy direction flow is reversed. We are trying to shed energy and the proposition a high flow rate always results in high transfer rates assumes a zero impedance sink which is not correct. If the water flow rate is increased and consequently the exit temperature from the engine is lowered, then there is a smaller water/air temperature gradient resulting in reduced heat transfer to the air.  

My hypotheses, and I state again I have absolutely no scientific proof to support this is that for each engine and radiator combination there is an optimum flow rate which provides maximum heat transfer, and this is may well be related to equalising the temperature delta across each interface.    

For the majority of vehicles, particularly at idle when the pump rotation speed is low the flow rate is well below optimum and increasing the flow rate enhances the heat transfer and in turn improves cooling.

At the other extreme where an engine is working close to maximum power shedding huge amounts waste of heat energy and the water pump is running at about ten times idle speed without a thermostat, reducing the flow rate can bring it back closer to optimum.

So there you have it, make of it what you will, all comments welcomed.

[HOTRODSRJ]

About a month ago a similar topic ran on this board.    The widely held notion "the higher the water flow, the better the heat transfer" was promoted.

I related the experience of the racing Coopers which were notorious for overheating, and attempts to cure this by removing the thermostat to increase flow rate only made the situation worse.    The factory produced a restrictor plate to install in the thermostat housing and this item improved cooling efficiency enormously.

Another contributor wrote "I have heard this exact story and was a common phenom in circle track cars/engines as well. The replacement of the "restrictor" actually made the system cooler than having no thermostat. While the effect was known, the cause was not"

Hey Peter.......I think I contributed to the fray and made the comments that you are referring to.  I would like to add more for what I think is going on respectfully.

First, and I like to say this alot.....racing does not translate to street very well, if at all! Simply too much other things going on with completely a differing application and use.  Higher rpms, differently designed cooling systems etc.  For example, racing motors turn higher rpms for longer periods of time.  Just think of that GT40 sceaming down the track at Lemans at top RPMS and what that means to the cooling system?  Simply put, racing is just different.  It's like comparing oranges and apples.  Take my word for it....I know them both.

Also, being an electrical engineer, I can't exactly equated that electricity  and fluids do behave anywhere near the same so to speak. Each has it's own indigneous physics that you have to understand.

Now having said that.....I will tell you that no experience that I have had in my professional career of designing high efficiency cooling systems and high efficiency industrial heat exchangers, automotive cooling systems or any text book in my thermodynamics library does reducing the flow (by practicality or theory for that matter) mean better cooling for any reason.  If you reduce the flow and your application "cools better" then something else is going on. This is why I made the "cause and effect" statement.......often the wrong conclusions are made.

I analysed your story and it makes perfect sense to me knowing alot about both street and racing cooling systems.  But I don't agree with your conclusions necessarily.  Your description of how you reduced the flow (and you really don't know what you did sense you probably did not have conclusive monitoring) and this helped in the cooling can be not only related to turbulence but also affecting the pumps efficiency.  While I don't  know the exacting design of the pump and so forth, I can easily build a case for the pump's design/cavitation issues being reduced or affected by this "damning" effect.  This happens all the time in racing.  Impellers flying around at warp like speeds are really an anomolous subjects.  You don't know how you may affect the output by tweaking the input unless you literally are doing comprehensive fluid dynamics studies. Also, internal flows can get effected by high flowing situations.  When the Chevrolet IRL engines first came together they too had a cooling issue that could not be readily addressed.  They too found that reducing the flow made for a "better sitution" and did some head scratching.  They really wanted the engine to run even cooler but when they turned the wick up it got worse?  They found out evenually that the internal castings of the block and heads (left over from Aurora days) were designed with internal "channels" if you will that had too many and too sharp of a bend in them.  These sharp and restrictive bends where setting up eddy currents and cavitation issues that introduced air into the stream making for a less efficient system.  After recasting the modifications needed the engines where able to flow about 40% more coolant and all was happy.  So, my point is that internals or the whole system design can determine and cause side effects that are completely unknown to the "outside" observer.  As long as you stay within the boundaries then adding flow will always enhance cooling.

So, under some circumstances reducing water flow is advantageous, even though it has been demonstrated over and over again the vast majority of overheating problems -particularly at idle are improved by increasing flow.
 
My hypotheses, and I state again I have absolutely no scientific proof to support this is that for each engine and radiator combination there is an optimum flow rate which provides maximum heat transfer, and this is may well be related to equalising the temperature delta across each interface.

This has some truth to it because the overall system "design and capability" is what is in play.    

For the majority of vehicles, particularly at idle when the pump rotation speed is low the flow rate is well below optimum and increasing the flow rate enhances the heat transfer and in turn improves cooling.

This is true for different reasons even tho flow is not the problem.  One has to stay within the boundaries of the system design or you can create all kinds of anomolies.......resulting in effects that are unknow.  My point here.

So, for the most part in street cooling applications (and this is why hi flowing pumps were invented) adding flow is a key to cooling better.

Does this make sense??

[Bruce Dorsi]

Thank you, Peter and Steve, for your prticipation in this thread and the previous thread to which Peter referred.

I always learn from your posts, and you both challenge my brain cells by stimulating thought.  ...I encourage your continued participation here, if for no other reason than, to increase my  knowledge.  ....Selfish, but true!

I do not have the formal education which you gentlemen have had, so I obviously defer to most of your statements.  .... I tend to look at other examples from the past, and see if the same principles apply to the present concern.  

About a month ago a similar topic ran on this board.    The widely held notion "the higher the water flow, the better the heat transfer" was promoted.

The next time I looked the thread had died...

----Much to my disappointment, as well.  I was hoping to get answers to my questions in that thread.

...In an act of desperation an overheating vehicle without a thermostat had a clamp put on the radiator hose to squeeze it down, -with exactly the same results.   This was done to the lower hose due to the short length of the top hose.  So it reduced the flow but did nothing to keep the head passages full, and did nothing to add turbulence to water entering the radiator, completely dispelling both theories.

----While the hose clamp was effective, it MAY have kept the head passages full, and perhaps, did NOT reduce the flow.  

The flow characteristics of centrifugal pumps are greatly affected by throttling the suction side of the pump.  ....Sometimes flow is improved, in other cases flow is diminished.  ....It is possible, you created a "venturi" effect in the suction line, which actually aided pump performance.  

Off the top of my head, I can not give you the technical jargon or the explanations to back up this statement, but I can get them if necessary.  ...My best friend has been working as an engineer, doing flow testing and plotting pump curves on centrifugal pumps for the last 30 years.  ....We have discussed waterpump design and flows many times in the past, but he "loses" me about about half-way into the discussions.
   

So, under some circumstances reducing water flow is advantageous, even though it has been demonstrated over and over again the vast majority of overheating problems -particularly at idle are improved by increasing flow.

----I do not yet see any advantage to reducing water flow.

Perhaps my thinking is flawed here, but I equate the automotive cooling system to a hydronic closed-loop heating system in a house.
...If the flow-rate between the boiler and the radiators is low, a small amount of heat is released to the room.  Increasing the flow-rate will increase the amount of btu's transferred by the "heat-sink," even though the water returning to the boiler may be warmer than before.  ...The higher flow rate will equalize the temps in the boiler and heat-sink more quickly.

Raising the water temp at the boiler will increase the amount of heat given off from the heat sink.

If the water flow rate is increased and consequently the exit temperature from the engine is lowered, then there is a smaller water/air temperature gradient resulting in reduced heat transfer to the air.

---Accepted and agreed.    

My hypotheses, and I state again I have absolutely no scientific proof to support this is that for each engine and radiator combination there is an optimum flow rate which provides maximum heat transfer, and this is may well be related to equalising the temperature delta across each interface.

---No argument from me, but that optimum flow rate will vary with ambient air temp, airflow thru the raditor, and coolant temps generated in the engine.  ....Designing for steady-state conditions is relatively easy, so designing for worst-case conditions seems prudent.    

For the majority of vehicles, particularly at idle when the pump rotation speed is low the flow rate is well below optimum and increasing the flow rate enhances the heat transfer and in turn improves cooling.

---We must also consider that on engines with mechanical fans, increasing the pump speed also increases the fan speed, pulling more air thru the radiator.  Thus, any additional cooling at idle may be partially attributed to this.

At the other extreme where an engine is working close to maximum power shedding huge amounts waste of heat energy and the water pump is running at about ten times idle speed without a thermostat, reducing the flow rate can bring it back closer to optimum.

----Too high a pump rpm will induce cavitation or disturbance of flow in a centrifugal pump.  

Let's face it, most of the automotive waterpumps use crude, unshrouded, impellers with massive clearances between the impellers and housings.  ...High-performance aka high-efficiency, aka high-flow, pumps improve their performance by changing these factors, and do not rely on just changing pump speed or impeller diameter.  ...Impeller/housing design is a field of its own.


OUCH! --- All this thinking is making my head hurt!

[PeterR]

First, and I like to say this alot.....racing does not translate to street very well, if at all! Simply too much other things going on with completely a differing application and use. Higher rpms, differently designed cooling systems etc. For example, racing motors turn higher rpms for longer periods of time. Just think of that GT40 sceaming down the track at Lemans at top RPMS and what that means to the cooling system? Simply put, racing is just different. It's like comparing oranges and apples. Take my word for it....I know them both.

Agree absolutely, now that I see you are confining the discussion to typical street applications.

Still not convinced however increasing flow is beneficial in every case, though I am relying on my memory of forty years ago.

Leaving engines to one side for a moment.   Consider two heat exchangers in series running a common liquid transfer medium.

If the first exchanger has a capacity very much greater than the second, then at maximum throughput there will be a larger temperature gradient across the second element than the first.  Conversely if the second exchanger has a larger capacity most of the total temperature differential will appear across the first.

This means for any combination there will be an optimum liquid temperature at which the entire system has maximum heat throughput, and where this lies will depend on the relative capacities of the first and second element.     The fluid temperature for maximum heat transfer is not related to the optimum operating temperature.

If increasing fluid rate increased the system capacity it would be possible keep pushing ever larger amounts of heat into the system and watch it come out the other end by doing no more than running the transfer pump faster and clearly this is not so.  

In a poorly designed system or if used in a situation the designer never intended, the fluid temperature corresponding to maximum heat transfer may exceed the desired operating temperature of the equipment involved.  I suspect that was the situation with the Coopers, as exactly the same engine with the same pump at the same revs did not require the restrictor when used as an inline engine.

Something else that intrigues me is the use of large tube radiators.  Without doing any calculations I had imagined that the Reynolds number may have fallen below the magic 2000 level.

Also, being an electrical engineer, I can't exactly equated that electricity and fluids do behave anywhere near the same so to speak. Each has it's own indigneous physics that you have to understand.

It is interesting you say that, at the university where I studied engineering my Elec and Fluid Mechanics lecturers frequently discussed eachothers topics as though they were one, and it always amazed me.    

You also mentioned thermodynamics which I have to say was the least enjoyable subject I have ever taken.   Plotting those Mollier diagrams was so tedious I can still remember it forty years later.

[HOTRODSRJ]

Agree absolutely, now that I see you are confining the discussion to typical street applications.

Still not convinced however increasing flow is beneficial in every case, though I am relying on my memory of forty years ago.

That's what we are addressing here......not racing or high pressure industrial heat exchangers as well.  That's why I make the statement that flow is KING in these specific applications!   Everything else outside the street application is moot for most if not all the watching eyes. Designs outside this realm vary too much making for anomolies that need a whole semester to muster.

[PeterR]

Steve,
A company here is making an electric pump that fits into the lower hose.   It has a PWM speed controller taking a signal from the temp guage so the pump speed is independent of engine revs.   Have you seen these or had a chance to evaluate them.

The manufacturer claims there is considerable OEM interest.

[HOTRODSRJ]

Steve,
A company here is making an electric pump that fits into the lower hose.   It has a PWM speed controller taking a signal from the temp guage so the pump speed is independent of engine revs.   Have you seen these or had a chance to evaluate them.

The manufacturer claims there is considerable OEM interest.

Peter.......actually this is NOT a new idea.  YOu can go to www.stewartcomponents.com and see their "booster" pump.  They often have great demostrations at various shows to show the diffence....and WOW......it really boosts performance of the system.  This is great for blower motors or high hp motors needing flow.  But, you have to add a large fan to augment the demand for more heat exchange at the radiator too.  The two upgrades is awesome.

[PeterR]

The unit this company makes is intended to completely replace the original mechanical pump

http://www.daviescraig.com.au/main/display.asp?pid=8

[HOTRODSRJ]

The unit this company makes is intended to completely replace the original mechanical pump

http://www.daviescraig.com.au/main/display.asp?pid=8

Peter........wow....I am glad you posted this.  I can't believe that this pump is allocated to doing duty all by itself?  The reason is that the output of this is very low... a pultry 1300 gph/80Lpm or 21gpm max!  This is NOT enough flow for squat!  Also, they imply that you are going to save a heap of HP doing such when in fact most high efficiency water pumps only take two to three hp at full tilt also viewable at the link below! It used to be that old timey water pumps could take as much as 10hp at full tilt.

Check this link out at http://www.stewartcomponents.com/tech_tips/Tech_Tips_7.htm and look at the flow rates and hp analysis.  These guys are very good if not the best in the business for street, high performance and racing cooling issues.

FWIW, even high quality electric pumps having flow rates less than 55 gpm are susceptible to being over taxed under certain driving circumstances.  I have run into several guys going to Pigeon Forge for various car shows in the mountains of Georgia, North Carolina and Tenn that have pulled over due to overheating going up long moderate grades.  This was primarily due to their use of electric water pumps of volumes of less than 50gpm.  For example my 57 with the big 440hp+ 383 with the air on during summer conditions will flow over 70gpm at 2400 rpm engine speed.  The flow rates are pretty far apart.  I am using the TuffStuff series pumps which mirror the Stewarts Stage I....only chrome!

So, thus my contention that electric pumps are not yet ready for the sole cooling duty on street applications.  My understanding is that some OEM suppliers are working on a 75gpm model.  Now that is a pump that I will endorse if it's reliable?  Would meet or exceed all the conditions of street application......even moderate towing applications....which really produces high heat issues in the cooling systems.

[PeterR]

A brief article on this pump appeared in a trade magazine some time ago where there was mention of OEM interest, but until last night I had never been to their web site nor seen any specs.

The unit is much smaller than I had expected and the modest output caught me by surprise too. However there are very few vehicles here with engines larger than 250cu in, the most common being around 120~150 so I assumed it was intended for motors of this size where it probably would have been OK. But as soon as I saw  "trucks, buses and boats" they lost me.  

Also, I am always suspicious of any claims that an electric motor powered by a belt driven alternator is somehow more efficient than a straight belt drive.