X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.2.16) with ESMTP id 3816781 for flyrotary@lancaironline.net; Tue, 18 Aug 2009 09:10:17 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Received: from computername ([75.191.186.236]) by cdptpa-omta03.mail.rr.com with ESMTP id <20090818130941100.NXAP16591@cdptpa-omta03.mail.rr.com> for ; Tue, 18 Aug 2009 13:09:41 +0000 From: "Ed Anderson" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Swirl pots Date: Tue, 18 Aug 2009 09:08:17 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0040_01CA1FE3.6CC33490" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 thread-index: AcofwNKLVJ1AtRyeThGt/VxXLNzoSQAPLh2A Message-Id: <20090818130941100.NXAP16591@cdptpa-omta03.mail.rr.com> This is a multi-part message in MIME format. ------=_NextPart_000_0040_01CA1FE3.6CC33490 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Heat transfer is a compromise of factors tailored to specific operation conditions. The entire ideal is to transfer heat from engine to air. Holding the coolant longer in the block (via a flow restrictor) will indeed increase the temperature and therefore the heat content of the coolant. However, my view is the ideal is NOT to hold the heat in the block but to promote its rapid exit from the block to the radiator. At times with extremely high rpm engines, restrictors have been used (and perhaps necessarily) to increase coolant pressure on the pump side to reduce/prevent cavitation of the water pump. This use of restrictors has often (wrongly) been used to come up with the rational that slower moving coolant/water cools better. When if fact, it has been the reduction of cavitation that has improved cooling - not the slower flow. But, my view is we are not (normally) seeing those kinds of rpm in our application. A Mazda Rx-7 racing engine may benefit for those reasons - but I don't see any benefit in our application. Also fuel efficiency is generally enhanced by running an engine just short of melt-down - racers generally want to run as close to this point as possible (without going over it) - so a hotter engine is not necessarily bad from their viewpoint - unless it gets too hot of course. Anything that impedes the flow of coolant from engine to radiator is going to impede the transfer of heat from block to air no matter what other benefit it may bring. The basic heat transfer equation Q (btu) = mf*Cw*DT show there are two significant ways of increasing heat transfer - one way is to increase the DT by increasing the temperature of the coolant - but this is also increases the internal temperature of the block (not necessarily what we want) - or by increasing the mass flow "mf". Increasing coolant temp in the block also has a point of diminishing returns as the coolant temp goes higher there is less transfer from block to coolant. The benefit comes when the hotter coolant reaches the radiator and the greater DT promotes more heat transfer from coolant to air. But, this benefit can be diminished or eliminated if the flow is too slow in removing heat from the engine. The second method of increasing heat transfer is by Increasing mass flow perhaps by increasing pump speed up to the point that flow losses become prohibitive is probably the best way of increasing heat transfer from engine to radiator. However, normally we can only effect pump rpm by using different size pulleys - and there are not a lot of ready made sizes to choose from - so we generally stick with our stock water pump and pulley set up. The bottom line as we know is that coolant is one big compromise of opposing factors and the system needs to be tailored to your application not some other application where the environment, operating parameters, or incentives may be different. My $0.02 Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Tuesday, August 18, 2009 2:01 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Swirl pots I respectfully disagree with the idea of the putting a flow restriction at the exit of the engine. True, it does increase the coolant pressure in the block, and that's good. But it reduces flow, and that's bad. Reduced flow increases the delta T around the loop and reduces the cooling capacity of the radiator, and in an aircraft application we don't like to add additional radiator size. As far as increasing the pressure in the block, you can get about the same affect by plumbing the filler/pressure cap to the inlet side of the pump rather than the outlet, so the pressure drop around the loop is not seen by the cap. A swirl pot works, but is not necessary. You need an air bleed from the high point of the engine (usually the outlet of the pump, and from other places that the air may get trapped, like the rad tank. A small bleed line (3/16" o.d. aluminum is good) from the point the air gets trapped back to the filler neck/bottle. Since the filler neck is plumbed to the low pressure side of the loop, any air gets drawn back there. I connected the turbo coolant port on the rear iron of my 20B back to the port on the pump outlet to bleed air from the rear iron, and a manual bleed plug at the pump outlet to vent air during fillup. I have small bleed lines from each of two custom radiator tanks back to the filler neck (which is connected to the line just before the pump inlet). After fillup, one run cycle purges all the air back to the filler neck. BTW; the cold to hot expansion for my 20B system is about 2/3 of a quart. Works for me, but of course each installation is different; but the concept is the same. Al G __________ Information from ESET NOD32 Antivirus, version of virus signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ------=_NextPart_000_0040_01CA1FE3.6CC33490 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Heat transfer is a compromise of = factors tailored to specific operation conditions.

 

The entire ideal is to transfer = heat from engine to air.  Holding the coolant longer in the block (via a flow restrictor) will indeed increase the temperature and therefore the heat = content of the coolant.  However, my view is the ideal is NOT to hold the = heat in the block but to promote its rapid exit from the block to the = radiator. 

 

At times with extremely high rpm = engines, restrictors have been used (and perhaps necessarily) to increase coolant pressure on the pump side to reduce/prevent cavitation of the water = pump.  This use of restrictors has often (wrongly) been used to come up with = the rational that slower moving coolant/water cools better.  When if = fact, it has been the reduction of cavitation that has improved cooling – = not the slower flow.

 

But, my view is we are not = (normally) seeing those kinds of rpm in our application.  A  Mazda Rx-7 = racing engine may benefit for those reasons – but I don’t see any = benefit in our application.  Also fuel efficiency is generally enhanced by = running an engine just short of melt-down – racers generally want to run = as close to this point as possible (without going over it) – so a hotter = engine is not necessarily bad from their viewpoint – unless it gets too hot = of course.

 

Anything that impedes the flow of = coolant from engine to radiator is going to impede the transfer of heat from = block to air no matter what other benefit it may bring.  =

The basic heat transfer equation Q = (btu) =3D mf*Cw*DT show there are two significant ways of increasing heat = transfer – one way is to increase the DT by increasing = the temperature of the coolant – but this is also increases the = internal temperature of the block (not necessarily what we want) – or by increasing the mass flow “mf”. Increasing coolant temp in = the block also has a point of diminishing returns as the coolant temp goes higher = there is less transfer from block to coolant.  The benefit comes when the = hotter coolant reaches the radiator and the greater =  DT  promotes more heat transfer from coolant to air.  But, this benefit can be diminished or eliminated if the flow is too slow in removing heat from = the engine.

 

The second method of increasing = heat transfer is by  Increasing mass flow perhaps by increasing pump = speed up to the point that flow losses become prohibitive is probably the best = way of increasing heat transfer from engine to radiator.  However, = normally we can only effect pump rpm by using different size pulleys – and = there are not a lot of ready made sizes to choose from – so we generally = stick with our stock water pump and pulley set up.

 

The bottom line as we know is that = coolant is one big compromise of opposing factors and the system needs to be = tailored to your application not some other application where the environment, = operating parameters, or incentives may be different.

 

My = $0.02

 

Ed

 

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Tuesday, August 18, = 2009 2:01 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = Swirl pots

 

I respectfully disagree with the = idea of the putting a flow restriction at the exit of the engine.  True, it = does increase the coolant pressure in the block, and that’s good. But = it reduces flow, and that’s bad.  Reduced flow increases the = delta T around the loop and reduces the cooling capacity of the radiator, and in = an aircraft application we don’t like to add additional radiator = size.  As far as increasing the pressure in the block, you can get about the = same affect by plumbing the filler/pressure cap to the inlet side of the pump = rather than the outlet, so the pressure drop around the loop is not seen by the = cap.

A swirl pot works, but is not necessary.  You need an air bleed from the high point of the engine (usually the outlet of the pump, and from other places that the air may = get trapped, like the rad tank.  A small bleed line (3/16” o.d. aluminum = is good) from the point the air gets trapped back to the filler neck/bottle. =  Since the filler neck is plumbed to the low pressure side of the loop, any air = gets drawn back there.

I connected the turbo coolant = port on the rear iron of my 20B back to the port on the pump outlet to bleed air = from the rear iron, and a manual bleed plug at the pump outlet to vent air = during fillup.  I have small bleed lines from each of two custom radiator = tanks back to the filler neck (which is connected to the line just before the = pump inlet).  After fillup, one run cycle purges all the air back to the = filler neck.

BTW; the cold to hot expansion = for my 20B system is about 2/3 of a quart.

Works for me, but of course each installation is different; but the concept is the = same.

Al G

 



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The message was checked by ESET NOD32 Antivirus.

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