Return-Path: Received: from fed1mtao03.cox.net ([68.6.19.242] verified) by logan.com (CommuniGate Pro SMTP 4.1.5) with ESMTP id 2645203 for flyrotary@lancaironline.net; Tue, 21 Oct 2003 11:00:29 -0400 Received: from BigAl ([68.107.116.221]) by fed1mtao03.cox.net (InterMail vM.5.01.06.05 201-253-122-130-105-20030824) with ESMTP id <20031021150028.YHWS23864.fed1mtao03.cox.net@BigAl> for ; Tue, 21 Oct 2003 11:00:28 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: temps behind radiator? Date: Tue, 21 Oct 2003 08:00:29 -0700 Message-ID: <000001c397e4$11823730$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C397A9.65235F30" 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 V6.00.2800.1106 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C397A9.65235F30 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable =20 Since the oil specific heat is only about 1/2 that of water, it requires approx twice the flow rate (based on that difference along) of coolant to bring the same amount of heat to the cooler. Then if the airflow through the oil cooler is impeded in any way (or you are pumping hot air into it) the situation becomes worst.=20 =20 There's not really much we can do about oil flow rate, short of not restricting it. Does the oil typically flow at double the rate of the coolant in the stock configuration? I've never really thought about that, but I can't see how it could. =20 =20 If the oil doesn't flow that much faster than water, and it has half the heat rejection of water, then do we need to size the oil cooler the same as the radiator? I've been amazed at how little radiator I need, compared to how hard it is to cool the oil, so this is starting to make sense. =20 =20 =20 Don=92t forget that the amount of heat rejected to the oil is about 40% = of what goes into the water. The specific heat of oil is actually about 70% that of a 50/50 mix of water/glycol (.6 vs .84 in metric) My dyno test showed the flow rate of water just a bit more than double that of the oil if you have a thermostat in the coolant circuit (triple without the thermostat). Now you put in the factor of typically allowing the oil about 20 F higher the coolant, and you have the air flow right, it works out that the heat transfer area (core volume, if you wish) of the oil cooler can be just a bit less than half the radiator. And Mazda had things figured correctly. =20 This, of course, assumes that you have the same incoming air temp to both. Putting the oil cooler behind the radiator throws a big wrench into optimizing the cooling systems; and is a bad idea from the git-go. Heat rejected is pretty much proportional to the temp difference between the air and the coolant/or oil. But if that=92s your only configuration option, and the air temp increase through the rad is, say, 35F; and you want to climb out on a 90F day, you can expect to need an oil cooler core volume of roughly 1 =BD times normal; or about =BE the size of the = rad. =20 This is rough estimating and assumes equal effectiveness of rad and cooler; but you get the idea. =20 Al =20 ------=_NextPart_000_0001_01C397A9.65235F30 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message

    

Since the oil specific heat = is only about 1/2 that of water, it requires approx twice the flow rate (based = on that difference along) of coolant to bring the same amount of heat to the cooler.   Then if the airflow through the oil cooler is = impeded in any way (or you are pumping hot air into it) the situation becomes = worst. 

 

There's not = really much we can do about oil flow rate, short of not restricting it.  Does = the oil typically flow at double the rate of the coolant in the stock configuration?  I've never really thought about that, but I can't = see how it could. 

 

If the oil = doesn't flow that much faster than water, and it has half the heat rejection of = water, then do we need to size the oil cooler the same as the radiator?  I've = been amazed at how little radiator I need, compared to how hard it is to cool = the oil, so this is starting to make sense. 

 

 

Don’t = forget that the amount of heat rejected to the oil is about 40% of what goes = into the water. =A0The specific heat of oil is actually about 70% that of a 50/50 = mix of water/glycol (.6 vs .84 in metric) My dyno test showed the flow rate of = water just a bit more than double that of the oil if you have a thermostat in the = coolant circuit (triple without the thermostat). =A0Now you put in the factor of = typically allowing the oil about 20 F higher the coolant, and you have the air flow right, = it works out that the heat transfer area (core volume, if you wish) of the = oil cooler can be just a bit less than half the radiator.=A0 And Mazda had = things figured correctly.

 <= /font>

This, of = course, assumes that you have the same incoming air temp to both.=A0 Putting the = oil cooler behind the radiator throws a big wrench into optimizing the = cooling systems; and is a bad idea from the git-go. =A0Heat rejected is pretty = much proportional to the temp difference between the air and the coolant/or oil. But if = that’s your only configuration option, and the air temp increase through the = rad is, say, 35F; and you want to climb out on a 90F day, you can expect to need = an oil cooler core volume of roughly 1 =BD times normal; or about =BE the size = of the rad.

 <= /font>

This is rough estimating and assumes equal effectiveness of rad and cooler; but you = get the idea.

 <= /font>

Al

 

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