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What is Static Pressure when referring to electric fans?

DanR

Diamond Level Sponsor
Curious as to your thoughts?

Found this on Electric Fans from Old Air


TECH

What is Static Pressure when referring to electric fans?

Static pressure is the amount of restriction in front of and behind the fan. It's measured in inches of H2O (water). Some companies advertise fans using the CFM (Cubic Feet per Minute) output at zero static pressure. This means the CFM output was measured without any restrictions. In real life applications, your cooling fan will be moving air through the front grill, A/C condenser, and radiator. The back side of the fan will be exhausting air against the engine and engine compartment. All of these factors create static pressure.


What is the normal static pressure range created by a condenser and radiator in an average vehicle?

The average vehicle will have a static pressure of about .5 to .7 inches H2O static loads. Ask for the fan output rating in these static load conditions when shopping for a good fan. A reputable fan manufacturer or distributor will have a complete cure chart of CFM ratings, static pressures and amperage demands available for your use.
Listed below is a chart showing the general operating range of our fan product versus some of our competitors. As you will see our Heavy Duty High Static Load 16" fan (#17-16VHP-S) is much stronger than anyone else in our industry while our High Performance 16" fan (17-16SHP-S) is still equal or more efficient than our competitors.
Be careful when purchasing an electric fan, some manufacturers and/or distributors advertise high CFM ratings that are inaccurate and misleading to consumers as shown in the performance chart below. Do not be misled by high CFM numbers at zero static pressure that do not accurately apply to your vehicle's actual working conditions.

TUacMAfRQDMhW06ZKllaShPY7oMMtXHh8Jbb6zi3_9wbGJgytG96dTuW54RKEbGKvXi1kxOetlT9fx2f16uVuJcTwz9jZaufbW99Kt1MA0o1Zjl6PVJemAZ5VNByzoZOBHetu8MvTOxNXYftKwjvXeV3mqr3t_ETgtg=s0-d-e1-ft

7Abb9LHJrySlxzcPSyz53i8M1DxYxggCjK7lFlGpv_a-64hUr3jMYbPZvIAJFqWCn2qizVs80PTqXsEicuO_992cpxT1po0ymyYrs6ngTn9iWO9B07f3pddI6ZM99E6tDznyyNyGXjhyM7an-DTGDDWvTs7QTIOWmWs=s0-d-e1-ft




I have read a lot, as most of you, about a Tiger/Alger/Other Modification and even a stock Alpine with heating problems and how to resolve them. Nothing is ever really simple or purely effective at all times.

From opening the hood (Bonnet) allowing an air flow, to louvers and even side vents to allow air (heat) removal as a means of "cooling" the Alpine/ Tiger has been tried. Still we have some difficulty at times cooling our cars.

One particular part of the above article; "The back side of the fan will be exhausting air against the engine and engine compartment," is most interesting to me.

How can it be determined how much air has to be moved to cool our cars? How can we determine what degree of restrictions are present behind the radiator/fan ?
 

65beam

Donation Time
Dan,
I've never had an Alpine that had a cooling problem . I keep the radiators clean, now use a 50/50 pre blended coolant and use a 180 thermostat. Yes ,if parked in traffic or in line at some event the temp will rise but don't remember one going to the danger point. I open the heater, run the engine speed up and again no problems. What operating temp do you see on your V6 under normal driving? How about other owners of V6 powered cars and Alpine 4 cylinder cars. What temps do you see and what changes have you made under the hood? Do all owners of V6 conversions use the same fan? Will more CFM of air flow make a difference if you have another problem such as timing or restrictions . Just wondering.
 

Barry

Diamond Level Sponsor
Dan,

First things first.

Cooling an automotive engine is a complex multi-step process.

Heat energy always moves from a higher temperature to a lower temperature. If there is no temperature difference, there is no heat transfer. The greater the temperature difference, the faster the heat transfer.

Combustion gases are hotter than the metal of the engine, so heat energy transfers from the combustion gases to the metal of the engine.​

The metal of the engine is hotter than the engine coolant, so heat energy transfers from the metal of the engine to the engine coolant.​

The engine coolant is hotter than the inside metal surface of the radiator, so heat energy transfers from the engine coolant to the inside metal surface of the radiator.​

The inside metal surface of the radiator is hotter than the outside metal surface of the radiator, so heat energy transfers from the inside metal surface of the radiator to the outside metal surface of the radiator.​

The outside metal surface of the radiator is hotter than the air moving through the radiator, so heat energy transfers from the outside metal surface of the radiator to the air.​

The coolant cools the engine, the radiator cools the liquid coolant, the air cools the radiator and round & round it goes. Total cooling "system" performance is no better than the weakest link in the system.​

OTBE, a "bigger" radiator (more coolant / metal and metal / air surface areas) can transfer (get rid of) more heat energy than a smaller radiator and moving more air through a given radiator will result in transferring more heat energy from the radiator to the air.​

Normally aspirated gasoline engines at near full load are about one-third efficient. In general terms, about one-third of the total heat energy produced by the internal combustion process is converted to rotational energy (aka, crankshaft power), about one-third of the total heat energy produced by the internal combustion process goes out the exhaust (in the form of hot gas) and about one-third of the total heat energy produced by the internal combustion process is disposed of (aka, wasted) by the engine cooling system.

At full power, a 99 gross HP Series V Alpine needs to dispose of about 250,000 BTU's per hour via the cooling system.

A 150 HP engine at full power needs to dispose of about 375,000 BTU's per hour via the cooling system.

A 200 HP engine at full power needs to dispose of about 500,000 BTU's per hour via the cooling system.​

A GM "thermal systems" engineer once told me that a minimum of 10 CFM per HP through the radiator core was a good starting point for typical passenger vehicles.

As a crosscheck, 500,000 BTU (for a 200 HP engine at full power) and 2,000 CFM through the radiator core would mean an air temperature rise across the radiator of about 100+ degrees F. which seems realistic.

A bigger radiator certainly provides more cooling capacity than a small radiator, but the available space in a Series Alpine severely limits the maximum radiator size. The only cooling system variable that can readily be changed in a Series Alpine is the quantity of air moving through the radiator core. As per the Old Air article, a typical electric radiator fan will not move anywhere near the advertised CFM in the real world.
 
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65beam

Donation Time
Barry,
So what's the difference in cooling between the early Alpine cross flow radiator and the six blade fan and the later radiator and a four blade fan? Other than early series 1 the Alpines use the same water pump. I've never been able to get an answer as to why the series 1 and 2 radiators are set at an angle with the right side being lower. ????? When the series Alpine was dropped in favor of the fastback the radiator was changed to a three row instead of the original two row style but quite a bit more space under the hood.
 

Bill Blue

Platinum Level Sponsor
Dan,
I've never had an Alpine that had a cooling problem . I keep the radiators clean, now use a 50/50 pre blended coolant and use a 180 thermostat. Yes ,if parked in traffic or in line at some event the temp will rise but don't remember one going to the danger point. I open the heater, run the engine speed up and again no problems. What operating temp do you see on your V6 under normal driving? How about other owners of V6 powered cars and Alpine 4 cylinder cars. What temps do you see and what changes have you made under the hood? Do all owners of V6 conversions use the same fan? Will more CFM of air flow make a difference if you have another problem such as timing or restrictions . Just wondering.
More CFM will always make a difference. Sometimes it will compensate for the underlying problem, usually just helps. The most popular V6 fan, the Volvo 242, moves an incredible amount of air when run at water pump speed. Enough that it solves the problem in all but the most egregious situations. Plugged radiator, timing really off, etc.

Bill
 

DanR

Diamond Level Sponsor
Bob, Not all V6 Guys utilize the same type fans. Dennis came up with the Volvo fan which works very well as Bill says. Some, including me, use the Mutt II four blade also a good one. But I have several of the stock six blade fans with plans to modify the mount holes for the V6 and will see what difference that will make.

CFM surely makes a difference. So intake must not exceed the output as I understand it ?

And Barry provided a bunch of TECH Data which will take me a while to decipher:) All or most of what He said is in direct relation to why I was posting the article.

I like to use 3 row 17 fin copper radiators. They have proven to be excellent for me.

I would like to know, if a certain amount of air (CFM) comes thru the radiator, how can you tell the resistance to it from the area inside the engine compartment?


I have been looking at the inside of my V6 engine compartments and don't see a lot of area whereby the air can escape. The more CFM entering or attempting to enter via the fan blades has to go out and seems to me it should be done with less resistance to what comes in! Am I wrong?

A lot of Tigers have heating problems and owners have attempted to resolve them by running with the Bonnet open, louvers and even side vents to allow air (heat) removal as a means of "cooling" the Alpine/ Tiger has been tried. Still we have some difficulty at times cooling our cars.

Anyone know of a way to determine if we or I am getting the best flow based upon our radiator and fan and outlets in the engine compartments ???

Maybe I can find a good heating and air guy that can help....
 

65beam

Donation Time
Dan,
Have you ever read the study on engine cooling that Tiger Tom posted on the TE/AE site? I was there the weekend that he was working with fan blades by changing mainly the pitch of various blades. Very interesting.
 

DanR

Diamond Level Sponsor
Dan,
Have you ever read the study on engine cooling that Tiger Tom posted on the TE/AE site?

Yes, Bob! I have read it several times with much interest in several portions of the report/article. The article is a must read for all and I repeat ALL Alpine/Tiger/V6/Alger/ etc., etc owners

Here is an extract I find most interesting and runs along my line of questioning back pressure inside the engine compartment. Please note the BOLD and Italics are mine!!!!
Quote: Besides the electric fan testing, as an assist to idle cooling, we also cut openings into the upper part of the inner fenderwells behind where the voltage regulator and servo are mounted. The opening was about the same size and location used for the Tiger LAT 41 side vents. In theory this provides an exit for hot air pushed by the fan(s) at an idle, also when the engine is shut off but still building heat. We made some evaluations of these vents open and closed before and after airflow enhancements were incorporated. We only detected about a two degree improvement with these open during idle [fig. 21]. Since most Alpines and Tigers do not have these openings and it is difficult to make this change neatly we elected not to recommend this change.

The popular Griffin aluminum radiator was one of the better performers on the highway and performed well at idle, but only with the airflow improvements [fig. 27]. An extremely important point about this radiator was, until airflow increased to a certain level, it was one of the poorer performers at an idle (it was always great on the highway). The copper/brass radiators were more responsive at lower airflow rates. So if you have an aluminum radiator without maximizing airflow at an idle, you may not be doing yourself a favor. Unquote.
 

DanR

Diamond Level Sponsor
Another point that seems to be missed in the TEAE article even thought they cut out some sheet metal they did not address backpressure inside the engine compartment. The added openings they cut surely helped to allow more air to escape thus helping the CFM thru the radiator.

Hope Tiger Tom and whom ever will revisit this.
 

Warren

Bronze Level Sponsor
I hate the look but pulling driving with the hood open at back helps.
Nevermind rule no 1 in California any black interior car in direct summer sun is torturous. Even my 6 cylinder Falcon it was especially bad as to every little ill fitting firewall crack. Baked or fried in a convection oven comes to mind.

A nice thing to have would be a solid rubber E shaped piece that would drop into the gutter channel under hood and keep the flapping fiberglass LAT hood stable or make your metal one look like it's supposed to be that way.
 
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