X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail14.syd.optusnet.com.au ([211.29.132.195] verified) by logan.com (CommuniGate Pro SMTP 5.2c2) with ESMTPS id 2470880 for flyrotary@lancaironline.net; Tue, 13 Nov 2007 20:15:13 -0500 Received-SPF: none receiver=logan.com; client-ip=211.29.132.195; envelope-from=lendich@optusnet.com.au Received: from george (d220-236-71-208.dsl.nsw.optusnet.com.au [220.236.71.208]) by mail14.syd.optusnet.com.au (8.13.1/8.13.1) with SMTP id lAE1ERPd009731 for ; Wed, 14 Nov 2007 12:14:29 +1100 Message-ID: <002a01c8265b$b9f48b70$d047ecdc@george> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Rebutal to the rebutal {:>) Thick vs Thin was : Diffuser Configuration Comparison Date: Wed, 14 Nov 2007 11:14:36 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0027_01C826AF.8A84CB30" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Antivirus: avast! (VPS 0657-0, 12/12/2006), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0027_01C826AF.8A84CB30 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed,=20 Understanding your concerns, I have searched the net and confirmed that = 1HP =3D 746 Watts and 1Btu=3D 0.293 watts, therefore 746/0.293 =3D2546 = btu/hr=3D1hp. 2546/60 =3D 42.43 ( 3 recurring).btu/min. Same site gave 42.44 btu/min. So the 42.5 is my rule of thumb, but anyone can use it if they want. So your 5,000 Btu's ( water only) for 175hp must have been fairly = accurate( good memory). I wanted to know Btu's per min/per Hp, as I assume that Radiator = suppliers/ manufacturers need that info to confirm sizes of cores etc.=20 On another tack there is a rule of thumb that the first 1/2 of the Rad = does 3/4 of the cooling - is there some truth to that claim?=20 George (down under) George, That was just for the coolant (did not include the oil) and it = was just a best recalled guess - the amount of heat really did not = matter for the discussion point. So don't go using it as if it were = cast in stone {:>) Ed ----- Original Message -----=20 From: George Lendich=20 To: Rotary motors in aircraft=20 Sent: Tuesday, November 13, 2007 5:40 PM Subject: [FlyRotary] Re: Rebutal to the rebutal {:>) Thick vs Thin = was : Diffuser Configuration Comparison Ed, Can't wait for that information to see if fits with my present = notes. I have also taken a note of that equation you mention. However I have a question, is that 5,000 Btu's the 66 percent ( 2/3) = of heat the water has to deal with ( oil manages 1/3 of the heat, I = believe). That would make 7,500 BTu's in total for 175 hp or 42.857 Btu's per = HP. I have notes on Mistral's figures, 100,000 Btu/hr is sufficient for = oil cooler, 200,000 is sufficient for water. I can't remember their Hp = rating. One hp =3D 2545Btu's per hour/60 =3D42.41per min. That's pretty close, so I guess I can use 42.5 Btu's per min/per Hp = or is there a more accurate number to use. George ( down under) Hi Dave, Sure had me going for a spell, however, I got out the equations = and believe I can point out a different view point. If I understood you correctly, your basic assertion is that the = same mass flow is required for both thin and thick radiators and since = the thicker radiator has a smaller frontal area it must therefore have = a higher velocity air flow to generate the same mass flow to remove the = same heat. Furthermore the higher velocity also translates into more = drag (even with the reduced frontal area due to the drag being = proportional to the square of the velocity) - but all the above is not = necessarily true. In fact I found a NACA study where they looked at the effects of = using thicker radiators and I have worked out the equations on a = spreadsheet which I believe sheds some concrete facts on the old thin Vs = Thick debate - but, it is complex and I'll wait a bit before springing = it {:>). =20 However back to your contention that both radiators the thin and = the thick required the same mass flow to remove the same amount of heat = - it just isn't so and here is why. =20 First, we have two radiators one is 1" thick and 1 square ft in = frontal area, the second one is 1/2 square feet of frontal area and = twice (or more) as thick. Now turning to our trusty equation for heat = rejection and mass flow. Q =3D m*Cp*DeltaT is the basic equation that tells us how much = heat we remove for a mass flow "m", a specific heat (air =3D 0.24) and = temperature increase in the medium (air) or DeltaT. =20 Taking a specific example of say - 5000 Btu/min (which is about = the amount of heat an NA 13B generates at 175 HP that needs to be = rejected by the coolant). We know the Cp so that leaves the DeltaT and = that is what makes the difference. We have to assume a DeltaT, lets say = 50F (yes, it could easily be different but bear with me) then we have m =3D 5000/(0.24)*(50)/60 =3D 6.94 lbm/sec of mass flow . and = lets say we have a 1 square foot radiator to get rid of that heat. Then = the velocity requires V1 =3D m/(p1A1) =3D 6.94 lbm/min/(.0765*1) =3D 90 = ft/sec =3D 61.36 mph through the 1 square foot radiator. Perhaps a bit = higher than desirable but that's what we get. Now if I understood you correctly your point is that the same = mass flow is also required for the smaller radiator (1/2 sq ft) to = remove the same amount of heat and therefore since frontal area is 1/2 = the size, the velocity must be double that of the larger radiator to = get the same mass flow and remove the same quantity of heat. But, it = just isn't necessarily so. Taking the same conditions as before, except this time I use a = DeltaT of 100F (hey! its permitted as I'm using a different core = here{:>) see further discussion on effects of thickness on DeltaT). Now = we have m =3D 5000/(0.24)*100/60 =3D 3.47 lbm/sec of mass flow is = required. That is 1/2 of the mass flow required with a DeltaT of 50F. Therefore even with 1/2 the frontal area, I can use the same air = velocity as before and remove the same amount of heat with 1/2 the mass = flow and with LESS drag because my frontal area is now 1/2 that of the = thinner larger radiator and the velocity is the same. Now you can say I = cheated by having a different radiator, but that is certainly what you = would do - as that is what we are discussing are the relative merits of = thinner vs thicker for our application. But, If you reduce the frontal area of the radiator, then you = must increase the thickness (or add more fins, turbulators, etc) to = increase its Heat transfer coefficient to continue to reject sufficient = heat to the air flow. Therefore, The air temperature coming out of a = thicker radiator is going to be higher than a thin radiator. The reason = is both radiators are flowing at the same velocity (remember I did used = the same velocity for both radiators), and since the velocity of the = flow is the same for both radiators, the air spends more time (twice, = three, four times depending on the thickness) in the thicker core of the = smaller radiator. The longer duration of the air in the thicker core = causes it to be absorb more heat and be raised to a higher temperature = than the thinner radiator, therefore the higher deltaT (for the same = velocity air). This probably did not/and will not convince you of the merits of = the thicker vs thinner and besides I know your reservations about my = deductive reasoning {:>). So I am working on understanding fully the = Naca study I found that addresses the effect of thickness on required = mass flow and heat rejection. I believe it would be considered a fairly = credible source and will hopefully enable all to reach their own = conclusion. I think its going to blow the socks off this thick vs thin = debate - but, then I've been wrong before {:>) Boy, this is fun!!! Sure keeps the old brain working (hopefully). Anyhow, Dave, I respectively disagree with your assertion (see = above) {:>) Best Regards Ed ----- Original Message -----=20 From: "Ernest Christley" To: "Rotary motors in aircraft" Sent: Tuesday, November 13, 2007 9:19 AM Subject: [FlyRotary] Re: Thick vs Thin was : Diffuser = Configuration Comparison > David Leonard wrote: >> Why is it going slower? BECAUSE YOU HAVE DESIGNED YOUR THIN = RADIATOR SYSTEM >> DUCTS SUCH THAT AN EQUAL AMOUNT OF AIR PASSES THROUGH AN EQUAL = VOLUME OF >> RADIATOR AS WOULD OCCUR ON A THICK RADIATOR SYSTEM. (This is = the big if... >> system design... but bear with me). ie, equal amount of air, = equal volume >> of radiator - in the thin radiator system the air will be = flowing more >> slowly. >> =20 >=20 > I agree with your concept, Dave, but I think you underestimate = the=20 > difficulty of fitting a large faced radiator into the physical=20 > constraints of the area available in a small airplane. I worked = on=20 > trying to use a large, 1" thick radiator for a while, and this = was in a=20 > delta planform. I had comparitively HUGE amounts of volume to = work=20 > with. I eventually gave up, as there was just no reasonable way = to get=20 > a duct built around it that would slow the air down. As you = increase=20 > the face area, you increase the size of the duct necessary to = expand the=20 > air without separation. The best radiator and duct ever created = will be=20 > useless if we have to leave it on the ground because it doesn't = fit in=20 > the airplane. >=20 > I think the flow chart for sizing a radiator for our needs = should follow=20 > something like this: >=20 > 1) Mark out a space for the largest volume that you can fit a = radiator=20 > and its associated ducting into. Insure that routing for the = hoses will=20 > be convenient, and the ducting can be made something resembling = efficient. >=20 > 2) Visit one of the websites like frigidair.com and find a = radiator that=20 > meets the dimensional specs you came up with. Or contact Jerry = and have=20 > him make you one of that size. >=20 > 3) If the core volume is less than 700 cubic inches, add = another. >=20 > 4) Go fly. If it is to cool (<160F), choke off the inlet a = little. If=20 > it is to hot (>200F), fiddle with the ducting. >=20 > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html=20 -------------------------------------------------------------------------= - No virus found in this incoming message. Checked by AVG Free Edition.=20 Version: 7.5.503 / Virus Database: 269.15.30/1126 - Release Date: = 12/11/2007 12:56 PM -------------------------------------------------------------------------= ----- No virus found in this incoming message. Checked by AVG Free Edition.=20 Version: 7.5.503 / Virus Database: 269.15.31/1129 - Release Date: = 13/11/2007 9:22 PM ------=_NextPart_000_0027_01C826AF.8A84CB30 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed,
Understanding your concerns, I have = searched the=20 net and confirmed that 1HP =3D 746 Watts and 1Btu=3D 0.293 watts, = therefore=20 746/0.293 =3D2546 btu/hr=3D1hp.
2546/60 =3D 42.43 ( 3=20 recurring).btu/min.
Same site gave 42.44 = btu/min.
So the 42.5 is my rule of thumb, but = anyone can use=20 it if they want.
So your 5,000 Btu's ( water only) for = 175hp must=20 have been fairly accurate( good memory).
 
I wanted to know Btu's per min/per Hp, = as I assume=20 that Radiator suppliers/ manufacturers need that info to confirm sizes = of cores=20 etc. 
 
On another tack there is a rule of = thumb that the=20 first 1/2 of the Rad does 3/4 of the cooling - is there some truth to = that=20 claim? 
George (down under)
George, That was just for the coolant (did not = include=20 the oil) and it was just a best recalled guess - the amount of heat = really did=20 not matter for the discussion point.  So don't go using it as if = it were=20 cast in stone {:>)
 
Ed
 
----- Original Message -----
From:=20 George Lendich
To: Rotary motors in = aircraft=20
Sent: Tuesday, November 13, = 2007 5:40=20 PM
Subject: [FlyRotary] Re: = Rebutal to the=20 rebutal {:>) Thick vs Thin was : Diffuser Configuration = Comparison

Ed,
Can't wait for that information to = see if fits=20 with my present notes. I have also taken a note of that equation you = mention.
 
However I have a question, is that = 5,000 Btu's=20 the 66 percent ( 2/3) of heat the water has to deal with ( oil = manages 1/3=20 of the heat, I believe).
That would make 7,500 BTu's in = total for 175 hp=20 or 42.857 Btu's per HP.
 
I have notes on Mistral's figures, = 100,000=20 Btu/hr is sufficient for oil cooler, 200,000 is sufficient for = water. I=20 can't remember their Hp rating. One hp =3D 2545Btu's per hour/60 = =3D42.41per=20 min.
 
That's pretty close, so I guess I = can use 42.5=20 Btu's per min/per Hp or is there a more accurate number to = use.
George ( down under)
Hi Dave,
 
Sure had me going for a spell, however, I = got out=20 the equations and believe I can point out a different view=20 point.
 
If I understood you correctly, your basic = assertion=20 is that  the same mass flow is required for both thin and = thick=20 radiators and since the thicker radiator has a smaller = frontal=20 area  it must therefore have a higher velocity air flow to = generate=20 the same mass flow to remove the same  heat.  = Furthermore=20 the higher velocity also translates into more drag (even with the = reduced=20 frontal area due to the drag being proportional to the square of = the=20 velocity) - but all the above is not necessarily=20 true.
 
  In fact I found a NACA study where = they=20 looked at the effects of using thicker radiators and I have worked = out the=20 equations on a spreadsheet which I believe sheds some concrete = facts on=20 the old thin Vs Thick debate - but, it is complex and I'll wait a = bit=20 before springing it {:>). 
 
However  back to your contention that = both=20 radiators the thin and the thick required the same mass flow to = remove the=20 same amount of heat - it just isn't so and here is why. =20
 
First, we have two radiators one is 1" = thick and 1=20 square ft in frontal area, the second one is 1/2 square feet of = frontal=20 area and twice (or more) as thick.  Now turning to our trusty = equation for heat rejection and mass flow.
 
Q =3D m*Cp*DeltaT is the basic equation = that tells us=20 how much heat we remove for a mass flow "m", a specific heat (air = =3D 0.24)=20 and temperature increase in the medium (air) or DeltaT. =20
 
Taking a specific example of say - 5000 = Btu/min=20 (which is about the amount of heat an NA 13B generates at 175 HP = that=20 needs to be rejected by the coolant).  We know the Cp so that = leaves=20 the DeltaT and that is what makes the difference.  We have to = assume=20 a DeltaT, lets say 50F (yes, it could easily be different but bear = with=20 me)  then we have
 
m =3D 5000/(0.24)*(50)/60 =  =3D 6.94=20  lbm/sec of mass flow  . and lets say we have = a 1=20 square foot radiator to get rid of that heat.  Then the = velocity=20 requires V1 =3D m/(p1A1) =3D 6.94 lbm/min/(.0765*1) =3D 90 = ft/sec =3D 61.36=20 mph through the 1 square foot radiator.  Perhaps a bit higher = than=20 desirable but that's what we get.
 
  Now if I understood you correctly = your point=20 is that  the same mass flow is also required for the = smaller=20 radiator (1/2 sq ft) to remove the same amount of heat and = therefore since=20 frontal area is 1/2 the size,  the velocity must be double = that of=20 the larger radiator to get the same mass flow and remove the same = quantity=20 of heat.  But, it just isn't necessarily so.
 
Taking the same conditions as before, = except this=20 time I use a DeltaT of 100F (hey! its permitted as I'm using a = different=20 core here{:>) see further discussion on effects of thickness on = DeltaT).  Now we have m =3D 5000/(0.24)*100/60 =3D 3.47 = lbm/sec of mass=20 flow is required.  That is 1/2 of the mass flow required with = a=20 DeltaT of 50F.
 
Therefore even with 1/2 the frontal area, = I can use=20 the same air velocity as before and remove the same amount of heat = with=20 1/2 the mass flow and with LESS drag because my frontal area is = now 1/2=20 that of the thinner larger radiator and the velocity is the = same. =20 Now you can say I cheated by having a different radiator, but that = is=20 certainly what you would do - as that is what we are discussing = are the=20 relative merits of thinner vs thicker for our = application.
 
But,  If you reduce the frontal area = of the=20 radiator,  then you must increase the thickness (or add more = fins,=20 turbulators, etc) to increase its Heat transfer = coefficient to=20 continue to reject sufficient  heat to the air flow.  = Therefore,=20 The air temperature coming out of a thicker radiator is going to = be higher=20 than a thin radiator.  The reason is both radiators are = flowing at=20 the same velocity (remember I did used  the same = velocity for=20 both radiators), and since the velocity of the flow is the same = for both=20 radiators, the air spends more time (twice, three, four times = depending on=20 the thickness) in the thicker core of the smaller = radiator.  The=20 longer duration of the air in the thicker core causes it to be = absorb more=20 heat and be raised to a higher temperature than the thinner = radiator,=20 therefore the higher deltaT (for the same velocity = air).
 
This probably did not/and will not = convince you of=20 the merits of the thicker vs thinner and besides I know your = reservations=20 about my deductive reasoning {:>).  So I am working on=20 understanding fully the Naca study I found that addresses the = effect of=20 thickness on required mass flow and heat rejection.  I = believe it=20 would be considered a fairly credible source and will hopefully = enable all=20 to reach their own conclusion.  I think its going to blow the = socks=20 off this thick vs thin debate - but, then I've been wrong before=20 {:>)
 
Boy, this is fun!!!  Sure keeps the = old brain=20 working (hopefully).
 
Anyhow, Dave, I respectively disagree with = your=20 assertion (see above) {:>)
 
Best Regards
 
Ed
 
 
 
 
 
 
----- Original Message -----
From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" = <flyrotary@lancaironline.net>
Sent: Tuesday, November 13, 2007 9:19=20 AM
Subject: [FlyRotary] Re: Thick vs Thin was = :=20 Diffuser Configuration Comparison

> = David Leonard=20 wrote:
>> Why is it going slower?  BECAUSE YOU HAVE = DESIGNED=20 YOUR THIN RADIATOR SYSTEM
>> DUCTS SUCH THAT AN EQUAL = AMOUNT OF=20 AIR PASSES THROUGH AN EQUAL VOLUME OF
>> RADIATOR AS = WOULD OCCUR=20 ON A THICK RADIATOR SYSTEM.  (This is the big = if...
>>=20 system design... but bear with me).  ie, equal amount of air, = equal=20 volume
>> of radiator - in the thin radiator system the = air will=20 be flowing more
>> slowly.
>>   =
>=20
> I agree with your concept, Dave, but I think you = underestimate=20 the
> difficulty of fitting a large faced radiator into the = physical
> constraints of the area available in a small=20 airplane.  I worked on
> trying to use a large, 1" = thick=20 radiator for a while, and this was in a
> delta = planform.  I=20 had comparitively HUGE amounts of volume to work
> = with.  I=20 eventually gave up, as there was just no reasonable way to get =
> a=20 duct built around it that would slow the air down.  As you = increase=20
> the face area, you increase the size of the duct = necessary to=20 expand the
> air without separation.  The best = radiator and=20 duct ever created will be
> useless if we have to leave it = on the=20 ground because it doesn't fit in
> the airplane.
> =
> I=20 think the flow chart for sizing a radiator for our needs should = follow=20
> something like this:
>
> 1) Mark out a space = for the=20 largest volume that you can fit a radiator
> and its = associated=20 ducting into.  Insure that routing for the hoses will =
> be=20 convenient, and the ducting can be made something resembling=20 efficient.
>
> 2) Visit one of the websites like=20 frigidair.com and find a radiator that
> meets the = dimensional=20 specs you came up with.  Or contact Jerry and have
> = him make=20 you one of that size.
>
> 3)  If the core volume = is less=20 than 700 cubic inches, add another.
>
> 4) Go = fly.  If=20 it is to cool (<160F), choke off the inlet a little.  If =
>=20 it is to hot (>200F), fiddle with the ducting.
>
> = --
> Homepage:  http://www.flyrotary.com/
>=20 Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.html=20

No virus found in this incoming message.
Checked by AVG = Free=20 Edition.
Version: 7.5.503 / Virus Database: 269.15.30/1126 - = Release=20 Date: 12/11/2007 12:56 PM

No virus found in this incoming message.
Checked by AVG Free = Edition.
Version: 7.5.503 / Virus Database: 269.15.31/1129 - = Release Date:=20 13/11/2007 9:22 PM
------=_NextPart_000_0027_01C826AF.8A84CB30--