X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.1.12) with ESMTP id 2362019 for flyrotary@lancaironline.net; Mon, 01 Oct 2007 10:06:58 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Received: from edward2 ([24.74.103.61]) by cdptpa-omta06.mail.rr.com with SMTP id <20071001140619.ZQZV3972.cdptpa-omta06.mail.rr.com@edward2> for ; Mon, 1 Oct 2007 14:06:19 +0000 Message-ID: <004601c80434$4078d3d0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Another cooling question Date: Mon, 1 Oct 2007 10:06:24 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0043_01C80412.B91FA380" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 This is a multi-part message in MIME format. ------=_NextPart_000_0043_01C80412.B91FA380 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ok, Mark That is better. With a 15F Deg delta T, depending on your coolant flow = rate, you are rejecting approx 2500 BTU/min if a 20 gpm flow rate of = coolant or as much as 5000 BTU/min if flow rate were 40 gpm. So that = is much better correlation with what you are seeing than the 4 deg F = delta T for coolant you reported earlier which would only account for = considerably less heat rejection. Ed ----- Original Message -----=20 From: Mark Steitle=20 To: Rotary motors in aircraft=20 Sent: Sunday, September 30, 2007 8:21 PM Subject: [FlyRotary] Re: Another cooling question Ed, Tracy, Lynn, George, etc ,=20 Thanks for the explanations, now I just need to find someone to = explain it to me. ;-) I figured the numbers were wrong, just didn't = know exactly why. I recalibrated my coolant sensors today using a candy "mercury" = thermometer from Wally-World. The EM-2 sensor was ok at 212, but was = reading high at ambient (84*). After recalibration it appears much = closer throughout the entire range. =20 The EFIS/One was also ok at 212* but was off further down the line. = Using the candy thermometer, I went through the drill of heating the = water to boiling, holding it there for everything to stabilize, then = removing the heat and monitor the thermomter and EFIS/One as the temps = fell. They should now be good to within +/- a couple of degrees. Next = weekend I hope to do the same to the oil temp sensors. =20 So, I had to go fly and try it out. I didn't get all the numbers, but = coolant temps now show a spread of 15*. OAT was 24C and in an easy = cruise (5200 rpm, 117 knts), the coolant temps were 160* out of engine = and 145* return. So, if I had an operable cowl flap, I surely could = have closed it up some to reduce my cooling drag. There were too many = cumulus clouds to go above 2900', but the preliminary information looks = promising. Also, I need to "open 'er up" and see what happens to the = temps. Hopefully, the extra dynamic pressure will be more than enough = to handle the extra BTU's. =20 Oil temps settled in at 210* out of the engine, 185* return from oil = cooler. =20 I may experiment with reducing the coolant inlet duct and see if I can = get the oil and water a bit closer. I also need to instrument each = cooler with manometers to check for balance. But for now, after seven = years of building, I'm happy that everything is staying in the green.=20 Thanks to all for your input. This is definitely one for the = archives. =20 Mark =20 =20 On 9/30/07, Ed Anderson wrote:=20 ----- Original Message -----=20 From: Mark Steitle=20 To: Rotary motors in aircraft=20 Sent: Sunday, September 30, 2007 6:28 AM Subject: [FlyRotary] Another cooling question =20 ED wrote: Mark, if you really had excess air flowing through your radiators = the coolant would drop more than 4 Deg F. In fact, the more air flow = the more coolant Delta T you would drop through the radiator.=20 That's exactly what I HAD thought, until I was told that the air = could pass through too fast and not pick up as much heat. This didn't = make sense to me. Maybe I wasn't listening closely and missed the point = altogether (wouldn't be the first time). =20 This is one of the oldest myths around - that air or coolant will = flow too fast to pick up the heat. It just IS NOT factual. The more = mass flow you have, the more heat you will carry away. It appears that = some early experimenters noted that if you slowed the flow of coolant = through a radiator that there was a greater temperature drop of the = fluid than if it flowed through faster. This apparently gave rise to = the myth as you can still find references to that experiment supporting = the slower is better myth. I once had an debate with a fererent = believer in that myth, after about 30 minutes of getting no where in = convincing the individual of the factual side, I resorted to this line.=20 "So you claim that slow water cools better than fast water, the = response was "Yes", then I replied "If slower and slower water cools = better and better then stopped water must cool best - right?" A long = silence, then the individual hung up the phone. =20 The fact is the coolant (in this example of slowing coolant = through the radiator) will indeed lose more heat to the air - if you = slow its flow through the radiator, because that slug of coolant spends = more time exchanging heat with the air. However, the slower flow also = means you are removing less heat from your engine - which is the real = objective. =20 We know that molecules of air transport the vast majority of the = Heat (there is a very small amount radiated away) in our installations = through contact with the metal of the radiator. The average speed of = these molecules (in air) is approximate the speed of sound (1100 = feet/sec at sea level). So any velocity of the macro airstream in our = ducts and cores are insignificant compared to the air molecules = velocity. So speeding up this air flow or slowing it down has no = measurable effect on the frequency at which the molecules contact the = metal. Turbulent flow has more impact than velocity change. Now = changing the velocity of the flow does effect the mass flow through the = core and therefore our overall cooling effectiveness, it just does not = effect the "speed" with which the heat is transfer from metal to air.=20 What I DO know is that the air is flowing faster through the water = radiator than the oil radiator. (I'm not sure I have the ASI's hooked = up correctly, but they're both hooked up the same). I have a pitot = behind each radiator hooked up to two separate ASI's. In slow cruise, = say 125-130 kts, the water radiator ASI will read about 110knts and the = oil ASI will read about 90 kts. =20 110 kts would give you a dynamic pressure of approx 7.8 " H20. = Now what that is measuring depends on how your ASIs are hooked up. = Since they are differential pressure gauges they are measuring the = difference between the static pressure under your cowl and what ever = reference their static side accesses. If they reference the ampient = outside air pressure (as you static system does) then you are measuring = Cowl pressure relative to ambient. If there static lines are simply = open to the cabin, then since cabin pressure in normally a bit lower = than ambient pressure, it would exaggerate the reading a bit.=20 But, in any case, it appears to me that you are measuring = localized cowl pressure. If you had a pitot tube before the core with = its static referencing ambient pressure, then it would be the dynamic = pressure (converted to a static pressure increase). If you had the = pitot tube before the core and the static accessing the cowl, then you = would be measuring pressure across your core. If you have the pitot tube = under the cowl and the static referencing ambient you would be measuring = your cowl pressure. So it depends on your static reference as well as = where you have the pitot tube position as to what you are measuring.=20 The way it was behaving before I opened up the exit, it appeared = that the air from the water radiator was trying to exit backwards = through the oil inlet. I say this because of how high the oil temps = were reading. I enlarged the cowl exit, and both the water and oil = temps dropped significantly. =20 I would say your analysis is correct. Dennis also found that = enlarging his exit area improved the cooling.=20 The ASI's are referencing the static port for these readings; = should they be referencing cowl or cabin pressure instead? Airspeeds = readings seem awfully high to me. =20 Referencing the static port would then give you under the cowl = pressure. If you reference the cowl then you would be measuring the = localized dynamic pressure of the air (greater than existing under the = cowl pressure) exiting the core which I would expect to be small since = your duct should have converted most of the dynamic pressure to a static = pressure increase before the core . Mark (Going to the airport today to recalibrate temp sensors) ------=_NextPart_000_0043_01C80412.B91FA380 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ok, Mark
 
That is better.  With a 15F Deg delta T, = depending on=20 your coolant flow rate, you are rejecting approx   2500 = BTU/min if a=20 20 gpm flow rate of coolant or as much as 5000 BTU/min if flow rate were = 40=20 gpm.   So that is much better correlation with what you are = seeing=20 than the 4 deg F delta T for coolant you reported earlier which would = only=20 account for considerably less heat rejection.
 
Ed
 
 
----- Original Message -----
From:=20 Mark = Steitle=20
Sent: Sunday, September 30, = 2007 8:21=20 PM
Subject: [FlyRotary] Re: = Another cooling=20 question

Ed, Tracy, Lynn, George, etc
,
Thanks for the explanations, now I just need to find someone to = explain=20 it to me.  ;-)  I figured the numbers were wrong, just = didn't know=20 exactly why.
 
I recalibrated my coolant sensors today using a candy "mercury"=20 thermometer from Wally-World.  The EM-2 sensor was ok at 212, but = was=20 reading high at ambient (84*).  After recalibration it appears = much=20 closer throughout the entire range. 
 
The EFIS/One was also ok at 212* but was off further down the = line. =20 Using the candy thermometer, I went through the drill of heating the = water to=20 boiling, holding it there for everything to stabilize, then removing = the heat=20 and monitor the thermomter and EFIS/One as the temps fell.  They = should=20 now be good to within +/- a couple of degrees.  Next weekend = I hope=20 to do the same to the oil temp sensors.   
 
So, I had to go fly and try it out.  I didn't get all the = numbers,=20 but coolant temps now show a spread of 15*.  OAT was 24C and in = an easy=20 cruise (5200 rpm, 117 knts), the coolant temps were 160* out of engine = and=20 145* return.  So, if I had an operable cowl flap, I surely could = have=20 closed it up some to reduce my cooling drag.  There were too = many=20 cumulus clouds to go above 2900', but the preliminary information = looks=20 promising.  Also, I need to "open 'er up" and see what happens to = the=20 temps.  Hopefully, the extra dynamic pressure will be more than = enough to=20 handle the extra BTU's. 
 
Oil temps settled in at 210* out of the engine, 185* return from = oil=20 cooler. 
 
I may experiment with reducing the coolant inlet duct and = see if I=20 can get the oil and water a bit closer.  I also need to = instrument each cooler with manometers to check for balance.  But = for=20 now, after seven years of building,  I'm happy = that everything=20 is staying in the green.
 
Thanks to all for your input.  This is definitely one for = the=20 archives. 
 
Mark   

 
On 9/30/07, Ed=20 Anderson <eanderson@carolina.rr.com&g= t;=20 wrote:=20
 
----- Original Message ----- =
From: = Mark = Steitle
To: Rotary = motors in=20 aircraft
Sent: Sunday, September 30, = 2007 6:28=20 AM
Subject: [FlyRotary] = Another cooling=20 question

 
ED wrote:
<snip>
 Mark, if you really had excess air flowing through your = radiators the coolant would drop more than 4 Deg F.  In fact, = the=20 more air flow the more coolant Delta T you would drop through the=20 radiator. 
<snip>
 
That's exactly what I HAD thought, until I was told that the = air=20 could pass through too fast and not pick up as much heat.  = This=20 didn't make sense to me.  Maybe I wasn't listening closely = and missed=20 the point altogether (wouldn't be the first time). 
 
 
This is one of the oldest = myths around=20 - that air or coolant will flow too fast to pick up the = heat.  It=20 just IS NOT factual.  The more mass flow you have, the = more heat=20 you will carry away.  It appears that some early = experimenters=20 noted that if you slowed the flow of coolant through a radiator = that there=20 was a greater temperature drop of the fluid than if it flowed = through=20 faster.  This apparently gave rise to the myth as you can = still find=20 references to that experiment supporting the slower is better = myth. =20 I once had an debate with a fererent believer in that myth, after = about 30=20 minutes of getting no where in convincing the individual of the = factual=20 side, I resorted to this line.
 
"So you claim that slow = water cools=20 better than fast water, the response was "Yes", then I replied "If = slower=20 and slower water cools better and better  then stopped water = must=20 cool best - right?"  A long silence, then the individual hung = up the=20 phone. 
 
The fact is the coolant = (in this=20 example of slowing coolant through the radiator) will indeed lose = more=20 heat to the air - if you slow its flow through the radiator, = because=20 that slug of coolant  spends more time exchanging heat with = the=20 air.  However, the slower flow also  means you are = removing less=20 heat from your engine - which is the real = objective.  =20
 
 We know that = molecules of air=20 transport the vast majority of the Heat (there is a very=20 small amount radiated away) in our installations through = contact with=20 the metal of the radiator.   The average speed of = these=20 molecules (in air) is approximate the speed of sound (1100 = feet/sec at sea=20 level).  So any velocity of the macro airstream in our ducts = and=20 cores are insignificant compared to the air molecules = velocity.  So=20 speeding up this air flow or slowing it down has no measurable = effect on=20 the frequency at which the molecules contact the metal.  = Turbulent=20 flow has more impact than velocity change.  Now changing the=20 velocity of  the flow does effect the mass flow through = the core=20 and therefore our overall cooling effectiveness, it just does not = effect=20 the "speed" with which the heat is transfer from metal to air.=20
 
 
 
What I DO know is that the air is flowing faster through the = water=20 radiator than the oil radiator.  (I'm not sure I have the = ASI's=20 hooked up correctly, but they're both hooked up the same).  I = have a=20 pitot behind each radiator hooked up to two separate ASI's.  = In slow=20 cruise, say 125-130 kts, the water radiator ASI will read about = 110knts=20 and the oil ASI will read about 90 kts. 
 
110 kts would give you a = dynamic=20 pressure of approx 7.8 " H20.  Now what that is measuring = depends on=20 how your ASIs are hooked up.  Since they are differential = pressure=20 gauges they are measuring the difference between the static = pressure under=20 your cowl and what ever reference their static side = accesses.  If=20 they reference the ampient outside air pressure (as you static = system=20 does) then you are measuring Cowl pressure relative to = ambient.  If=20 there static lines are simply open to the cabin, then since cabin = pressure=20 in normally a bit lower than ambient pressure, it would exaggerate = the=20 reading a bit.
 
But, in any case, it = appears to me=20 that you are measuring localized cowl pressure.  If you had a = pitot=20 tube before the core with its static referencing ambient pressure, = then it=20 would be the dynamic pressure (converted to a static pressure=20 increase).  If you had the pitot tube before the core and the = static=20 accessing the cowl, then you would be measuring pressure across = your=20 core. If you have the pitot tube under the cowl and the = static=20 referencing ambient you would be measuring your cowl=20 pressure. So it depends on your static reference as well as = where you=20 have the pitot tube position as to what you are measuring. =
 
 
 The way it was behaving before I opened up the exit, it = appeared that the air from the water radiator was trying to = exit=20 backwards through the oil inlet.  I say this because of = how high=20 the oil temps were reading.  I enlarged the cowl exit, = and both=20 the water and oil temps dropped significantly. 
 
I would say your = analysis is=20 correct.  Dennis also found that enlarging his exit area = improved the cooling. 
 
The ASI's are referencing the static port for these readings; = should=20 they be referencing cowl or cabin pressure instead?  = Airspeeds=20 readings seem awfully high to me. 
 
Referencing the = static port=20 would then give you under the cowl pressure.  If you = reference the=20 cowl then you would be measuring the localized  dynamic = pressure of=20 the air (greater than existing under the cowl = pressure) exiting=20 the core which I would expect to be small since your duct should = have=20 converted most of the dynamic pressure to a static pressure = increase=20 before the core .
Mark
(Going to the airport today to recalibrate temp = sensors)
=
 

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