X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail08.syd.optusnet.com.au ([211.29.132.189] verified) by logan.com (CommuniGate Pro SMTP 5.2c2) with ESMTPS id 2470658 for flyrotary@lancaironline.net; Tue, 13 Nov 2007 17:41:10 -0500 Received-SPF: none receiver=logan.com; client-ip=211.29.132.189; envelope-from=lendich@optusnet.com.au Received: from george (d220-236-71-208.dsl.nsw.optusnet.com.au [220.236.71.208]) by mail08.syd.optusnet.com.au (8.13.1/8.13.1) with SMTP id lADMeJCa016324 for ; Wed, 14 Nov 2007 09:40:26 +1100 Message-ID: <002301c82646$34a69e00$d047ecdc@george> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Rebutal to the rebutal {:>) Thick vs Thin was : Diffuser Configuration Comparison Date: Wed, 14 Nov 2007 08:40:28 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001E_01C8269A.022B7280" 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_001E_01C8269A.022B7280 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 ------=_NextPart_000_001E_01C8269A.022B7280 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed,
Can't wait for that information to see = if fits with=20 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 the=20 66 percent ( 2/3) of heat the water has to deal with ( oil manages 1/3 = of the=20 heat, I believe).
That would make 7,500 BTu's in total = for 175 hp or=20 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=20 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 = velocity=20 also translates into more drag (even with the reduced frontal area due = to the=20 drag being proportional to the square of the velocity) - but all = the=20 above is not necessarily true.
 
  In fact I found a NACA study where they = looked at=20 the effects of using thicker radiators and I have worked out the = equations on=20 a spreadsheet which I believe sheds some concrete facts on the old = thin Vs=20 Thick debate - but, it is complex and I'll wait a bit before springing = it=20 {:>). 
 
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 how=20 much heat we remove for a mass flow "m", a specific heat (air =3D = 0.24) and=20 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 say=20 50F (yes, it could easily be different but bear with = me)  then we=20 have
 
m =3D 5000/(0.24)*(50)/60  =3D 6.94 =  lbm/sec=20 of mass flow  . and lets say we have a 1 square foot = radiator=20 to get rid of that heat.  Then the velocity requires V1 =3D = m/(p1A1)=20 =3D 6.94 lbm/min/(.0765*1) =3D 90 ft/sec =3D 61.36 mph through = the 1 square=20 foot radiator.  Perhaps a bit higher than desirable but that's = what we=20 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 area=20 is 1/2 the size,  the velocity must be double that of the larger = radiator=20 to get the same mass flow and remove the same quantity of heat.  = But, it=20 just isn't necessarily so.
 
Taking the same conditions as before, except = this time I=20 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). =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 = 50F.
 
Therefore even with 1/2 the frontal area, I = can use the=20 same air velocity as before and remove the same amount of heat with = 1/2 the=20 mass flow and with LESS drag because my frontal area is now 1/2 that = of the=20 thinner larger radiator and the velocity is the same.  Now you = can say I=20 cheated by having a different radiator, but that is certainly what you = would=20 do - as that is what we are discussing are the relative merits of = thinner vs=20 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 thin=20 radiator.  The reason is both radiators are flowing at the same = velocity=20 (remember I did used  the same velocity for both radiators), = and=20 since the velocity of the flow is the same for both radiators, the air = spends=20 more time (twice, three, four times depending on the = thickness) in the=20 thicker core of the smaller radiator.  The longer duration of the = air in=20 the thicker core causes it to be absorb more heat and be raised to a = higher=20 temperature than the thinner radiator, therefore the higher deltaT = (for the=20 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 my=20 deductive reasoning {:>).  So I am working on understanding = fully the=20 Naca study I found that addresses the effect of thickness on required = mass=20 flow and heat rejection.  I believe it would be considered a = fairly=20 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 = 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 in=20 a
> delta planform.  I had comparitively HUGE amounts of = volume to=20 work
> with.  I eventually gave up, as there was just no=20 reasonable way to get
> a duct built around it that would slow = the air=20 down.  As you increase
> the face area, you increase the = size of=20 the duct necessary to expand the
> air without = separation.  The=20 best radiator and duct ever created will be
> useless if we = have to=20 leave it on the ground because it doesn't fit in
> the=20 airplane.
>
> I think the flow chart for sizing a = radiator for=20 our needs should follow
> something like this:
>
> = 1) Mark=20 out a space for the largest volume that you can fit a radiator =
> and=20 its associated ducting into.  Insure that routing for the hoses = will=20
> be convenient, and the ducting can be made something = resembling=20 efficient.
>
> 2) Visit one of the websites like = frigidair.com=20 and find a radiator that
> meets the dimensional specs you came = up=20 with.  Or contact Jerry and have
> him make you one of = that=20 size.
>
> 3)  If the core volume is less than 700 = cubic=20 inches, add another.
>
> 4) Go fly.  If it is to = cool=20 (<160F), choke off the inlet a little.  If
> it is to = hot=20 (>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 = Edition.
Version: 7.5.503 / Virus Database: 269.15.30/1126 - = Release Date:=20 12/11/2007 12:56 PM
------=_NextPart_000_001E_01C8269A.022B7280--