X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao105.cox.net ([68.230.241.41] verified) by logan.com (CommuniGate Pro SMTP 5.2c2) with ESMTP id 2470330 for flyrotary@lancaironline.net; Tue, 13 Nov 2007 14:49:53 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.41; envelope-from=alventures@cox.net Received: from fed1rmimpo02.cox.net ([70.169.32.72]) by fed1rmmtao105.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20071113194914.EHSW28248.fed1rmmtao105.cox.net@fed1rmimpo02.cox.net> for ; Tue, 13 Nov 2007 14:49:14 -0500 Received: from BigAl ([72.192.143.193]) by fed1rmimpo02.cox.net with bizsmtp id CKpD1Y00H4AaN600000000; Tue, 13 Nov 2007 14:49:14 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Rebutal to the rebutal {:>) Thick vs Thin was : Diffuser Configuration Comparison Date: Tue, 13 Nov 2007 11:49:31 -0800 Message-ID: <000001c8262e$4f5a05b0$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C825EB.4136C5B0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C825EB.4136C5B0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Sorry; Ed, your argument is bogus. You changed horses in the middle of = the stream, and that is not allowed. You cannot suddenly change your = assumed delta T, because that also requires changing the inlet scoop, which = changes the mass flow rate. =20 You size the inlet scoop to give you a mass flow needed at a given delta = T. If I expand that air to a large, thin core, it's velocity is slow, and I = get the given delta T. If I now expand the air half as much for a frontal = area that is half as large and the velocity is double, To get the same delta = T (whatever that thickness is, probably double) I will get a pressure drop about 4 times as high for the same delta T. =20 You have to compare them based on the same heat removal - same mass = flow, same delta T =20 Al=20 =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson Sent: Tuesday, November 13, 2007 10:06 AM To: Rotary motors in aircraft Subject: [FlyRotary] Rebutal to the rebutal {:>) Thick vs Thin was : Diffuser Configuration Comparison =20 Hi Dave, =20 Sure had me going for a spell, however, I got out the equations and = believe I can point out a different view point. =20 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. =20 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 =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 =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. =20 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 =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 =20 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. =20 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. =20 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. =20 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. =20 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). =20 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 = {:>) =20 Boy, this is fun!!! Sure keeps the old brain working (hopefully). =20 Anyhow, Dave, I respectively disagree with your assertion (see above) = {:>) =20 Best Regards =20 Ed =20 =20 =20 =20 =20 =20 ----- Original Message -----=20 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 Configuration Comparison =20 > 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 = > 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 = > 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 ------=_NextPart_000_0001_01C825EB.4136C5B0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Sorry; Ed, your argument is = bogus.  You changed horses in the middle of the stream, and that is not = allowed.  You cannot suddenly change your assumed delta T, because that also = requires changing the inlet scoop, which changes the mass flow = rate.

 

You size the inlet scoop to give = you a mass flow needed at a given delta T.  If I expand that air to a = large, thin core, it’s velocity is slow, and I get the given delta = T.  If I now expand the air half as much for a frontal area that is half as large = and the velocity is double, To get the same delta T (whatever that thickness is, probably double) I = will get a pressure drop about 4 times as high for the same delta = T.

 

You have to compare them based on = the same heat removal = – same mass flow, = same delta = T

 

Al

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Tuesday, November 13, 2007 10:06 = AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] = Rebutal to the rebutal {:>) Thick vs Thin was : Diffuser Configuration = Comparison

 

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 {:>). 

 

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. 

 

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. 

 

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 = -----

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 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.
>>  
>
> I agree with your concept, Dave, but I think you underestimate the =
> difficulty of fitting a large faced radiator into the physical
> constraints of the area available in a small airplane.  I = worked on
> trying to use a large, 1" thick radiator for a while, and this = was in a
> delta planform.  I had comparitively HUGE amounts of volume to = work
> with.  I eventually gave up, as there was just no reasonable = way to get
> a duct built around it that would slow the air down.  As you = increase
> the face area, you increase the size of the duct necessary to = expand the
> air without separation.  The best radiator and duct ever = created will be
> useless if we have to leave it on the ground because it doesn't fit = in
> the airplane.
>
> I think the flow chart for sizing a radiator for our needs should = follow
> something like this:
>
> 1) Mark out a space for the largest volume that you can fit a = radiator
> and its associated ducting into.  Insure that routing for the = hoses will
> be convenient, and the ducting can be made something resembling = efficient.
>
> 2) Visit one of the websites like frigidair.com and find a radiator = that
> meets the dimensional specs you came up with.  Or contact = Jerry and have
> him make you one of that size.
>
> 3)  If the core volume is less than 700 cubic inches, add = another.
>
> 4) Go fly.  If it is to cool (<160F), choke off the inlet a little.  If
> it is to hot (>200F), fiddle with the ducting.
>
> --
> Homepage:  http://www.flyrotary.com/ > Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrot= ary/List.html

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