Return-Path: Received: from fed1mtao06.cox.net ([68.6.19.125] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2923905 for flyrotary@lancaironline.net; Thu, 08 Jan 2004 22:06:52 -0500 Received: from BigAl ([68.107.116.221]) by fed1mtao06.cox.net (InterMail vM.5.01.06.05 201-253-122-130-105-20030824) with ESMTP id <20040109030648.JQGG11223.fed1mtao06.cox.net@BigAl> for ; Thu, 8 Jan 2004 22:06:48 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Series vs parralel rads Date: Thu, 8 Jan 2004 19:06:51 -0800 Message-ID: <000001c3d65d$a10c5b30$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C3D61A.92E91B30" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4024 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C3D61A.92E91B30 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit I've pondered about this issue and I think there may be a number of factors involved. (Group input is highly desired) We both used large hoses for our installations. 1.5" to the Y's and 1" from the Y's to the rads. (Actually, one of us used Y's and the other T's). I'm wondering if the large hoses after the Y was too little flow resistance thereby allowing most of the coolant to pass through one rad. I notice Tracey uses smaller hoses which may increase flow resistance to each rad and provide more of a balance. I think someone is using AN16 fittings which is 1" hose but by the time you get through the restrictive male coupling, the same factors may apply. Al G. may be able to help me with this one. Assuming a perfect world. what would the outlet temperature difference be between series rads vs, parallel. My guess is. if we had 215 degrees coolant entering the parallel rads and we get 180 degrees leaving the rads, there is a 35 degree drop, or about a 16.3% drop. Series rads would give a similar % drop divided by 2 for each. 215 - 8% = 199. Then the second rad sees 199 - 8% = 184 (I rounded off the numbers cuz 1 degree isn't an issue) By my calculation (which may be out in left field) the difference is negligible. In general, you will get better heat rejection with more flow, and with higher average temperature in the radiator cores (smaller delta T). Running the rads in parallel is better on both counts. Connecting in parallel results in a larger flow path and less pressure drop - less pressure drop results in more flow - more flow results in a higher average core temp. And using large diameter, low pressure drop lines is good because the lower the pressure drop, the greater the flow. If you had a positive displacement pump (so the flow wasn't dependant on pressure drop) the outlet temp would be about the same in either case, series or parallel, for the same amount of heat rejected. But with a centrifugal pump, the flow does drop off with higher pressure drop. So how much better parallel flow is depends on how much of an issue the pressure drop is. When connecting in parallel, the same flow will go to both cores only if the pressure drop (flow resistance) is the same in both loops. The coolant will take the path of least resistance, so it will automatically balance the pressure drop, not the flow. With large enough lines, most of the resistance is generally through the cores, so identical cores will likely balance well enough so you don't need to be concerned. But since it is unlikely that the air flow to the two cores is also balanced, getting equal flow isn't really the issue, and probably not very important. So if you want to get picky; it is likely best to make the temp drop (delta T) equal. So the idea is to measure the outlet temp from each core at operating conditions, and then orifice the flow to the core with the lowest delta T until the outlet temps are the same. It's not so tough really. Clamp on a thermocouple to each outlet pipe, cover with insulation. If you have a hose barb connection, get a brass washer with same o.d. (or just a little larger) as the connector tube on the core (grind as necessary). File out the i.d. until the area is maybe 60% of the inlet area of the tube. Place this on the inlet side tube and slip the hose over and clamp. Measure delta T's again - you guessed it - adjust the hole size in the washer until you get about the same delta T through both cores. So there you have my take on the issue. I connected two different rad designs in parallel, so I expect to have a little balancing to do. Al ------=_NextPart_000_0001_01C3D61A.92E91B30 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

   = ;         I’ve pondered about this issue and I think there may be a number of factors involved.  (Group input is highly desired)  We both used large = hoses for our installations.  1.5” to the Y’s and 1” = from the Y’s to the rads.  (Actually, one of us used Y’s and the = other T’s).  I’m wondering if the large hoses after the Y was = too little flow resistance thereby allowing most of the coolant to pass = through one rad.  I notice Tracey uses smaller hoses which may increase flow resistance to each rad and provide more of a balance.  I think = someone is using AN16 fittings which is 1” hose but by the time you get = through the restrictive male coupling, the same factors may apply.

 

   = ;         Al G. may be able to help me with this one…  Assuming a perfect world…  what would the outlet temperature difference be = between series rads vs, parallel.  My guess is…  if we had 215 = degrees coolant entering the parallel rads and we get 180 degrees leaving the = rads, there is a 35 degree drop, or about a 16.3% drop.  Series rads = would give a similar % drop divided by 2 for each.  215 – 8% =3D = 199.  Then the second rad sees 199 – 8% =3D 184  (I rounded off the = numbers cuz 1 degree isn’t an issue)  By my calculation (which may be out = in left field) the difference is negligible. 

 

 

In general, you will get better = heat rejection with more flow, and with higher average temperature in the = radiator cores (smaller delta T).  Running the rads in parallel is better on = both counts.  Connecting in parallel results in a larger flow path and = less pressure drop – less pressure drop results in more flow – = more flow results in a higher average core temp.  And using large diameter, = low pressure drop lines is good because the lower the pressure drop, the = greater the flow.

 

If you had a positive = displacement pump (so the flow wasn’t dependant on pressure drop) the outlet temp = would be about the same in either case, series or parallel, for the same amount of heat = rejected.  But with a centrifugal pump, the flow does drop off with higher pressure = drop.  So how much better parallel flow is depends on how much of an issue the = pressure drop is.

 

When connecting in parallel, the = same flow will go to both cores only if the pressure drop (flow resistance) = is the same in both loops.  The coolant will take the path of least = resistance, so it will automatically balance the pressure drop, not the flow.  = With large enough lines, most of the resistance is generally through the cores, so identical cores will likely balance well enough so you don’t need = to be concerned.

 

But since it is unlikely that the = air flow to the two cores is also balanced, getting equal flow isn’t = really the issue, and probably not very important.  So if you want to get = picky; it is likely best to make the temp drop (delta T) equal.  So the idea = is to measure the outlet temp from each core at operating conditions, and then orifice the flow to the core with the lowest delta T until the outlet = temps are the same.   

 

It’s not so tough = really.  Clamp on a thermocouple to each outlet pipe, cover with insulation.  If = you have a hose barb connection, get a brass washer with same o.d. (or just a = little larger) as the connector tube on the core (grind as necessary).  = File out the i.d. until the area is maybe 60% of the inlet area of the = tube.  Place this on the inlet side tube and slip the hose over and clamp.  = Measure delta T’s again – you guessed it – adjust the hole = size in the washer until you get about the same delta T through both cores. =

 

So there you have my take on the issue.  I connected two different rad designs in parallel, so I = expect to have a little balancing to do.

 

Al

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