X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao102.cox.net ([68.230.241.44] verified) by logan.com (CommuniGate Pro SMTP 5.2c2) with ESMTP id 2470971 for flyrotary@lancaironline.net; Tue, 13 Nov 2007 21:12:18 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.44; envelope-from=alventures@cox.net Received: from fed1rmimpo03.cox.net ([70.169.32.75]) by fed1rmmtao102.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20071114021140.MMYG18714.fed1rmmtao102.cox.net@fed1rmimpo03.cox.net> for ; Tue, 13 Nov 2007 21:11:40 -0500 Received: from BigAl ([72.192.143.193]) by fed1rmimpo03.cox.net with bizsmtp id CSBf1Y00C4AaN600000000; Tue, 13 Nov 2007 21:11:39 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Radiator delta T Date: Tue, 13 Nov 2007 18:11:58 -0800 Message-ID: <001501c82663$bc810910$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0016_01C82620.AE5DC910" 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_0016_01C82620.AE5DC910 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On another tack there is a rule of thumb that the first 1/2 of the Rad does 3/4 of the cooling - is there some truth to that claim? George (down under) It could be roughly true. The heat transfer is proportional to the temp difference between the core matrix surfaces and the air. As the air heats up going through, that difference decreases, and the heat transfer is reduced. To make the most effective use of the core volume, you want the air to still be cooler than the matrix at the exit - by maybe about 30- 40F at the design point (another rule of thumb) but is dependant of other conditions. So if your design point is high power climb with max coolant temp at say, 210F; and you want to do this on a 90F day, then I guess you could design for the max delta T through the rad of about 70-80F. Since I dump the rad exit air into the cowl, I chose to design for a 50F delta T to give me some margin, and keep the in-cowl temps down. Al G ------=_NextPart_000_0016_01C82620.AE5DC910 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

On another tack there is a = rule of thumb that the first 1/2 of the Rad does 3/4 of the cooling - is there = some truth to that claim? 

 

George (down = under)

 

It could be roughly true.  = The heat transfer is proportional to the temp difference between the core matrix surfaces and the air.  As the air heats up going through, that = difference decreases, and the heat transfer is reduced.  To make the most effective use = of the core volume, you want the air to still be cooler than the matrix at the exit = – by maybe about 30- 40F at the design point (another rule of thumb) but = is dependant of other conditions.  So if your design point is high power climb = with max coolant temp at say, 210F; and you want to do this on a 90F day, then I = guess you could design for the max delta T through the rad of about 70-80F.  = Since I dump the rad exit air into the cowl, I chose to design for a 50F delta T = to give me some margin, and keep the in-cowl temps down.

 

Al G

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