X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.121] verified) by logan.com (CommuniGate Pro SMTP 5.2c2) with ESMTP id 2470677 for flyrotary@lancaironline.net; Tue, 13 Nov 2007 17:46:59 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.121; envelope-from=eanderson@carolina.rr.com Received: from edward2 ([24.74.103.61]) by cdptpa-omta03.mail.rr.com with SMTP id <20071113224622.OYOP19167.cdptpa-omta03.mail.rr.com@edward2> for ; Tue, 13 Nov 2007 22:46:22 +0000 Message-ID: <004801c82647$519657c0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Rebutal to the rebutal {:>) Thick vs Thin was : Diffuser Configuration Comparison Date: Tue, 13 Nov 2007 17:48:32 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0045_01C8261D.687D7A60" 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_0045_01C8261D.687D7A60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 = > 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 ------=_NextPart_000_0045_01C8261D.687D7A60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
George, That was just for the coolant (did not = include the=20 oil) and it was just a best recalled guess - the amount of heat really = did not=20 matter for the discussion point.  So don't go using it as if it = were cast=20 in stone {:>)
 
Ed
 
----- Original Message -----
From:=20 George=20 Lendich
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=20 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 of=20 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 Btu/hr=20 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=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 the=20 equations and believe I can point out a different view = point.
 
If I understood you correctly, your basic = assertion is=20 that  the same mass flow is required for both thin and thick = radiators=20 and since the thicker radiator has a smaller frontal area =  it=20 must therefore have a higher velocity air flow to generate the same = mass=20 flow to remove the same  heat.  Furthermore the = higher=20 velocity also translates into more drag (even with the reduced = frontal area=20 due to the drag being proportional to the square of the velocity) = - but=20 all the above is not necessarily true.
 
  In fact I found a NACA study where = they looked=20 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 the=20 old thin Vs Thick debate - but, it is complex and I'll wait a bit = before=20 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.  =
 
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 area=20 and twice (or more) as thick.  Now turning to our trusty = equation for=20 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.  =
 
Taking a specific example of say - 5000 = Btu/min (which=20 is about the amount of heat an NA 13B generates at 175 HP that needs = to be=20 rejected by the coolant).  We know the Cp so that leaves the = DeltaT and=20 that is what makes the difference.  We have to assume a DeltaT, = lets=20 say 50F (yes, it could easily be different but bear with = me)  then=20 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 square=20 foot radiator to get rid of that heat.  Then the velocity = requires V1 =3D=20 m/(p1A1) =3D 6.94 lbm/min/(.0765*1) =3D 90 ft/sec =3D 61.36 mph = through the 1=20 square foot radiator.  Perhaps a bit higher than desirable but = that's=20 what we get.
 
  Now if I understood you correctly = your point is=20 that  the same mass flow is also required for the smaller = radiator=20 (1/2 sq ft) to remove the same amount of heat and therefore since = frontal=20 area is 1/2 the size,  the velocity must be double that of the = larger=20 radiator to get the same mass flow and remove the same quantity of=20 heat.  But, it just isn't necessarily so.
 
Taking the same conditions as before, except = this time=20 I use a DeltaT of 100F (hey! its permitted as I'm using a different = core=20 here{:>) see further discussion on effects of thickness on = DeltaT). =20 Now we have m =3D 5000/(0.24)*100/60 =3D 3.47 lbm/sec of mass flow = is=20 required.  That is 1/2 of the mass flow required with a DeltaT = of=20 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 1/2=20 the mass flow and with LESS drag because my frontal area is now 1/2 = that of=20 the thinner larger radiator and the velocity is the same.  Now = you can=20 say I cheated by having a different radiator, but that is certainly = what you=20 would do - as that is what we are discussing are the relative merits = of=20 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 = continue=20 to reject sufficient  heat to the air flow.  Therefore, = The air=20 temperature coming out of a thicker radiator is going to be higher = than a=20 thin radiator.  The reason is both radiators are flowing at the = same=20 velocity (remember I did used  the same velocity for both=20 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 the=20 merits of the thicker vs thinner and besides I know your = reservations about=20 my deductive reasoning {:>).  So I am working on = understanding fully=20 the Naca study I found that addresses the effect of thickness on = required=20 mass flow and heat rejection.  I believe it would be considered = a=20 fairly credible source and will hopefully enable all to reach their = own=20 conclusion.  I think its going to blow the socks off this thick = vs thin=20 debate - but, then I've been wrong before {:>)
 
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 = AM
Subject: [FlyRotary] Re: Thick vs Thin was : = Diffuser=20 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 AIR=20 PASSES THROUGH AN EQUAL VOLUME OF
>> RADIATOR AS WOULD = OCCUR ON A=20 THICK RADIATOR SYSTEM.  (This is the big if...
>> = system=20 design... but bear with me).  ie, equal amount of air, equal=20 volume
>> of radiator - in the thin radiator system the air = will be=20 flowing more
>> slowly.
>>  
> =
> I=20 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=20 in a
> delta planform.  I had comparitively HUGE amounts = of=20 volume to work
> with.  I eventually gave up, as there = was just=20 no reasonable way to get
> a duct built around it that would = slow the=20 air down.  As you increase
> the face area, you increase = the=20 size of the duct necessary to expand the
> air without=20 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.
>
> I think the flow chart for = sizing a=20 radiator for our needs should follow
> something like = this:
>=20
> 1) Mark out a space for the largest volume that you can fit = a=20 radiator
> and its associated ducting into.  Insure that = routing=20 for the hoses will
> be convenient, and the ducting can be = made=20 something resembling efficient.
>
> 2) Visit one of the = websites like frigidair.com and find a radiator that
> meets = the=20 dimensional specs you came up with.  Or contact Jerry and have =
>=20 him make you one of that size.
>
> 3)  If the core = volume=20 is less than 700 cubic inches, add another.
>
> 4) Go=20 fly.  If it is to cool (<160F), choke off the inlet a = little. =20 If
> it is to hot (>200F), fiddle with the = ducting.
>=20
> --
> 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
------=_NextPart_000_0045_01C8261D.687D7A60--