X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [24.25.9.102] (HELO ms-smtp-03-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 5.0.7) with ESMTP id 964323 for flyrotary@lancaironline.net; Wed, 01 Feb 2006 20:44:27 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.102; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-025-165.carolina.res.rr.com [24.74.25.165]) by ms-smtp-03-eri0.southeast.rr.com (8.13.4/8.13.4) with SMTP id k121heFm005631 for ; Wed, 1 Feb 2006 20:43:41 -0500 (EST) Message-ID: <002701c6279a$1c474f00$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] sutability of NPG for rotary engine use Date: Wed, 1 Feb 2006 20:43:47 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0024_01C62770.3329DDC0" 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-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0024_01C62770.3329DDC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thanks for your assessment, Monty. Scares me a bit that we all (more or less) agree that the NPG is = probably not well suited to the stock rotary coolant system {:>) Ed ----- Original Message -----=20 From: M Roberts=20 To: Rotary motors in aircraft=20 Sent: Wednesday, February 01, 2006 8:35 PM Subject: [FlyRotary] sutability of NPG for rotary engine use I wouldn't worry about the theory behind mdot*Cp*deltaT too much. This = has been tested thoroughly. As long as your Cp number is correct the = calculation will be nuts on. The place you get into trouble is measuring = the constants for Cp or for a heat transfer coefficient. Your analysis = looks good to me Ed. The point Ernest made is a valid one. Cp is per = unit mass. A more dense fluid will transfer more heat per volume flow = than a less dense fluid. Bill S. also makes some good points. The main thing I have to add is: it would be nice to know what the = convection coefficient is for NPG. That is what gives the heat transfer = between the hot metal and the coolant. A more viscous fluid would tend = to have a thicker boundary layer and less turbulence. That could cause = problems. The turbulence and mixing of the boundary layer help to = transfer heat.=20 I also would be cautious about the vapor pressure. Boiling is not a = bad thing. It is a good thing. The heat transfer coefficient for a phase = change (liquid to gas) is infinite. This helps to cool a hot spot. We = are talking about sub cooled boiling here where the bulk liquid is = cooler than the boiling point. Locally the liquid boils and transfers = all the heat the metal can move. The limiting factor is actually the = metal conduction for this case. The bubbles of vapor are cooled by the = surrounding coolant and collapse. Put a pot on the stove and watch as = you transfer from sub-cooled to nucleate and finally bulk boiling. You = can see the process happen.=20 Both bulk and nucleate boiling are to be avoided. Sub cooled boiling, = a thin boundary layer and turbulence are all good things. NPG strikes = out on all three. In addition it requires more power to pump and the = pressure drop through the evaporator core type coolers at low temps is = suspect.=20 In short: The 13b was developed to use water/glycol as a coolant. To properly validate NPG you need a dyno and a lot of thermocouples, = plus a way to measure the mass flow of the coolant, pressure drops, pump = power, and the heat transfer coefficient.=20 Anybody got that laying around in their hangar? Do you want to be a guinea pig? I would not use NPG. Monty ------=_NextPart_000_0024_01C62770.3329DDC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thanks for your assessment, Monty.
 
Scares me a bit that we all (more or less) agree = that the=20 NPG is probably not well suited to the stock rotary coolant system=20 {:>)
 
Ed
----- Original Message -----
From:=20 M=20 Roberts
Sent: Wednesday, February 01, = 2006 8:35=20 PM
Subject: [FlyRotary] sutability = of NPG=20 for rotary engine use

I wouldn't worry about the theory = behind=20 mdot*Cp*deltaT too much. This has been tested thoroughly. As long as = your Cp=20 number is correct the calculation will be nuts on. The place you get = into=20 trouble is measuring the constants for Cp or for a heat transfer = coefficient.=20 Your analysis looks good to me Ed. The point Ernest made is a valid = one. Cp is=20 per unit mass. A more dense fluid will transfer more heat per volume = flow than=20 a less dense fluid. Bill S. also makes some good points.
 
 
The main thing I have to add is: it = would be nice=20 to know what the convection coefficient is for NPG. That is what gives = the=20 heat transfer between the hot metal and the coolant. A more viscous = fluid=20 would tend to have a thicker boundary layer and less turbulence. That = could=20 cause problems. The turbulence and mixing of the boundary layer help = to=20 transfer heat.
 
I also would be cautious about the = vapor=20 pressure. Boiling is not a bad thing. It is a good thing. The heat = transfer=20 coefficient for a phase change (liquid to gas) is infinite. This helps = to cool=20 a hot spot. We are talking about sub cooled boiling here where the = bulk liquid=20 is cooler than the boiling point. Locally the liquid boils and = transfers all=20 the heat the metal can move. The limiting factor is actually the metal = conduction for this case. The bubbles of vapor are cooled by the = surrounding=20 coolant and collapse. Put a pot on the stove and watch as you = transfer=20 from sub-cooled to nucleate and finally bulk boiling. You can see the = process=20 happen. 
 
Both bulk = and nucleate boiling are=20 to be avoided. Sub cooled boiling, a thin boundary layer = and turbulence=20 are all good things. NPG strikes out on all three. In addition it = requires more power to pump and the pressure drop through the = evaporator core=20 type coolers at low temps is suspect. 
 
In short:
 
The 13b was developed to use = water/glycol as a=20 coolant.
 
To = properly validate NPG you need=20 a dyno and a lot of thermocouples, plus a way to measure the mass flow = of the=20 coolant, pressure drops, pump power, and the heat transfer = coefficient.=20
 
Anybody got that laying around in = their=20 hangar?
 
Do you want to be a guinea = pig?
 
I would not use NPG.
 
Monty
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