Return-Path: Received: from fed1rmmtao11.cox.net ([68.230.241.28] verified) by logan.com (CommuniGate Pro SMTP 4.2.8) with ESMTP id 611515 for flyrotary@lancaironline.net; Tue, 18 Jan 2005 10:36:30 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.28; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao11.cox.net (InterMail vM.6.01.04.00 201-2131-117-20041022) with ESMTP id <20050118153559.XPSX28808.fed1rmmtao11.cox.net@BigAl> for ; Tue, 18 Jan 2005 10:35:59 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Switching to Evans NPG+ Date: Tue, 18 Jan 2005 07:36:11 -0800 Message-ID: <000001c4fd73$707b9470$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C4FD30.625AC570" 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 V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C4FD30.625AC570 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Subject: [FlyRotary] Re: Switching to Evans NPG+ Marv, I agree completely with everything you said. I fully plan to keep = my pressure system in place and continue to monitor the pressure as a way = to detect leaks. The beauty of NPG is that if the system does loose = pressure, it does not change the ability to cool. Dave; Adding my 2 cents worth; don=92t overlook that it=92s ability to cool is seriously less than water, or 50-50 w/g in the first place. The = specific heat is 40% less (I notice that is not in their table), so, as you know, = for a given volume of flow it carries away 40% less heat. Couple that with = say a 10 times (depending on temperature) higher viscosity, which means = lower flow rate, and lower thermal conductivity; you have seriously changed = the temperature gradients and internal surface temps in the engine. I = don=92t know that it would damage the engine, but there is a risk. On the face = of it, these things are serious disadvantages, and suggest to me that it is = not likely the best path to a solution. And I haven=92t even mentioned the = higher pumping power requirements, but that is a second order effect. We have been all over this stuff in the past; and, personally, I = wouldn=92t do it; at least not with a stock coolant pump. Doesn=92t mean you = shouldn=92t try it; we will all get some more information. Don=92t they still tell you = that you should change the coolant pump? They used to sell the pumps as = well. And don=92t overlook that Evans is promoting sales; which includes hype, = and overlooks potential problems. Design the cooling system around the use = of NPG, and it should be fine. But it is difficult, at least for me, to see = how it is going to solve a problem cooling system. Whether or not it =93solves=94 problems in your cooling system depends = on where the problem is, and if it solves one it may cause others. Again, not = that you shouldn=92t try it; just that as a friend I wasn=92t comfortable in = not voicing my concerns. Al =20 You mention coolant vapor around hot spots. Evans touts its ability to resist that vapor film as one of its strongest points, and it makes = sense. Even unpressurized 370 + degree boiling point is worlds better than the 265*F boiling point of pressurized 50/50. So I do believe that NPG will = be better at preventing that vapor film than 50/50 even pressurized up into = the 25psi range. I'm not saying that this stuff is magic. And I don't believe it can compensate for an inadequate cooling system (like pure water might), but = it does offer some advantages that I am starting to appreciate. From the Evans Web site, here is some technical stuff: COMPARISON OF COOLANT PARAMETERS =20 =20 Water 50/50 EGW Evans NPG =20 Evans NPG+ =20 =20 =20 =20 =20 =20 Boiling Point =20 121=B0 C (250=B0 F) (1 atm plus 15 psig) 129=B0 C (264=B0 F) (1 atm plus 15 psig)=20 187=B0 C (369=B0 F) (1 atm plus 0 psig)=20 191=B0 C (375=B0 F) (1 atm plus 0 psig) _____ =20 Viscosity =20 =20 =20 =20 =20 10=B0 C (50=B0 F) cp 1.2 5.0 115 58 80=B0 C (176=B0 F) cp .37 1.0 4.5 3.7 100=B0 C (212=B0 F) cp .28 0.7 2.8 2.3 =20 _____ =20 Density =20 =20 =20 =20 =20 20=B0 C (68=B0 F) spec grav 1.00 1.066 1.038 1.091 20=B0 C (68=B0 F) lbs/gal 8.32 8.87 8.64 9.08 _____ =20 Specific Heat =20 =20 =20 =20 =20 80=B0 C (176=B0 F) Btu/lb/=B0F 1.00 0.81 0.68 0.64 100=B0 C (212=B0 F) Btu/lb/=B0F 1.01 0.82 0.71 0.66 _____ =20 Heat of Vaporization cal/mole 9,700 9,800 12,500 12,050 _____ =20 Vapor Pressure=20 =20 =20 =20 =20 =20 80=B0 C (176=B0 F) mm Hg=20 360 270 8 6 80=B0 C (176=B0 F) kPa 475 360 11 8 _____ =20 Surface Tension=20 =20 =20 =20 =20 =20 25=B0 C (77=B0 F) dyn/cm 72 56 36 44 _____ =20 =20 =20 =20 > > Try and remember that the rules for what happens inside an engine > at sea level > are different than what goes on at 15,000 feet. While the NPG+ > may not boil > until 396*F at sea level, I'm certain that it's a different beast > at altitude. > The guy who engineered the Eagle was livid when we told him that = Evans > recommended a pressureless system... part of the reason for the > pressure is to > keep the coolant pressed firmly against the metal surfaces it's trying = to > cool. Even if you have a high boiling point, when the metal = temperatures > exceed it the boiling will happen and without the pressure to > insure coolant > contact, pretty soon everything is surrounded by a cloud of PG > steam (well, > maybe not a "cloud", but all the hotspots will be working > overtime keeping the > coolant boiling next to them). Those metal temps quickly build, > the areas > where the coolant has turned to vapor grow, and the problem feeds > on itself > until the system goes completely out of control. At this point your > pressureless system vents itself, throwing out what's left of the > coolant and > the engine is toast. The point here is that there are more > reasons for having > a pressurized system in an airplane than meets the eye. > > One more thing... with a pressurized system you can alarm it for a low > pressure situation. If something goes wrong with the coolant > system (like you > spring a leak) the pressure will likely go down before you see a rise = in > temps. If the system is setup to run at 20psi and you alarm it > at 15, when > you see that master warning you know that pretty soon you're > probably going to > overheat. Just another chance to get a jump on things that you pass = up > without pressure. > > > =20 > > >> Homepage: http://www.flyrotary.com/ > >> Archive: http://lancaironline.net/lists/flyrotary/List.html=20 ------=_NextPart_000_0001_01C4FD30.625AC570 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Subject: [FlyRotary] Re: Switching to Evans NPG+

Marv, I agree completely with everything you said.  I fully plan to keep my pressure system in place and = continue to monitor the pressure as a way to detect leaks.  The beauty of NPG = is that if the system does loose pressure, it does not change the ability to = cool.

Dave;

Adding my 2 cents worth; don’t = overlook that it’s ability to cool is seriously less than water, or 50-50 = w/g in the first place. =A0The specific heat is 40% less (I notice that is not = in their table), so, as you know, for a given volume of flow it carries away 40% = less heat.=A0 Couple that with say a 10 times (depending on temperature) = higher viscosity, which means lower flow rate, and lower thermal conductivity; = you have seriously changed the temperature gradients and internal surface = temps in the engine.=A0 I don’t know that it would damage the engine, but = there is a risk.=A0 On the face of it, these things are serious disadvantages, and = suggest to me that it is not likely the best path to a solution.=A0 And I = haven’t even mentioned the higher pumping power requirements, but that is a = second order effect.

We have been all over this stuff in the = past; and, personally, I wouldn’t do it; at least not with a stock = coolant pump. =A0Doesn’t mean you shouldn’t try it; we will all get = some more information. =A0Don’t they still tell you that you should change = the coolant pump?=A0 They used to sell the pumps as well.

And don’t overlook that Evans is promoting sales; which includes hype, and overlooks potential problems. = Design the cooling system around the use of NPG, and it should be fine. But it is difficult, at least for me, to see how it is going to solve a problem = cooling system.

Whether or not it “solves” = problems in your cooling system depends on where the problem is, and if it solves = one it may cause others.=A0 Again, not that you shouldn’t try it; just = that as a friend I wasn’t comfortable in not voicing my = concerns.

Al

 



You mention coolant vapor around hot spots.  Evans touts its = ability to resist that vapor film as one of its strongest points, and it makes sense.  Even unpressurized 370 + degree boiling point is worlds = better than the 265*F boiling point of pressurized 50/50.  So I do believe = that NPG will be better at preventing that vapor film than 50/50 even = pressurized up into the 25psi range.

I'm not saying that this stuff is magic.  And I don't believe it = can compensate for an inadequate cooling system (like pure water might), but = it does offer some advantages that I am starting to appreciate.

From the Evans Web site, here is some technical stuff:

COMPARISON = OF COOLANT PARAMETERS

 

 

Water

50/50 EGW

Evans NPG

Evans NPG+

 

 

 

 

 

 

Boiling = Point

 

121=B0 C (250=B0 F)
(1 atm plus 15 psig)

129=B0 C (264=B0 F)
(1 atm plus 15 psig) =

187=B0 C (369=B0 F)
(1 atm plus 0 psig) =

191=B0 C (375=B0 F)
(1 atm plus 0 psig)

Viscosity

 

 

 

 

 

    10=B0 C (50=B0 = F)

cp

1.2

5.0

115

58

    80=B0 C (176=B0 = F)

cp

.37

1.0

4.5

3.7

   100=B0 C (212=B0 = F)

cp

.28

0.7

2.8

2.3

 

Density

 

 

 

 

 

    20=B0 C (68=B0 = F)

spec grav

1.00

1.066

1.038

1.091

    20=B0 C (68=B0 = F)

lbs/gal

8.32

8.87

8.64

9.08

Specific = Heat

 

 

 

 

 

    80=B0 C (176=B0 = F)

Btu/lb/=B0F

1.00

0.81

0.68

0.64

   100=B0 C (212=B0 = F)

Btu/lb/=B0F

1.01

0.82

0.71

0.66

Heat of = Vaporization

cal/mole

9,700

9,800

12,500

12,050

Vapor = Pressure

 

 

 

 

 

    80=B0 C (176=B0 = F)

mm Hg

360

270

8

6

    80=B0 C (176=B0 = F)

kPa

475

360

11

8

Surface = Tension

 

 

 

 

 

    25=B0 C (77=B0 = F)

dyn/cm

72

56

36

44

 

 

 


>
> Try and remember that the rules for what happens inside an = engine
> at sea level
> are different than what goes on at 15,000 feet.  While the = NPG+
> may not boil
> until 396*F at sea level, I'm certain that it's a different = beast
> at altitude.
>  The guy who engineered the Eagle was livid when we told him = that Evans
> recommended a pressureless system... part of the reason for the
> pressure is to
> keep the coolant pressed firmly against the metal surfaces it's = trying to
> cool.  Even if you have a high boiling point, when the metal temperatures
> exceed it the boiling will happen and without the pressure to
> insure coolant
> contact, pretty soon everything is surrounded by a cloud of PG
> steam (well,
> maybe not a "cloud", but all the hotspots will be = working
> overtime keeping the
> coolant boiling next to them).  Those metal temps quickly = build,
> the areas
> where the coolant has turned to vapor grow, and the problem = feeds
> on itself
> until the system goes completely out of control.  At this = point your
> pressureless system vents itself, throwing out what's left of = the
> coolant and
> the engine is toast.  The point here is that there are = more
> reasons for having
> a pressurized system in an airplane than meets the eye.
>
> One more thing... with a pressurized system you can alarm it for a = low
> pressure situation.  If something goes wrong with the = coolant
> system (like you
> spring a leak) the pressure will likely go down before you see a = rise in
> temps.  If the system is setup to run at 20psi and you alarm = it
> at 15, when
> you see that master warning you know that pretty soon you're
> probably going to
> overheat.  Just another chance to get a jump on things that = you pass up
> without pressure.
>
>   <marv>
>  
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html<= /span>

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