Return-Path: Received: from fed1rmmtao04.cox.net ([68.230.241.35] verified) by logan.com (CommuniGate Pro SMTP 4.2.3) with ESMTP id 432674 for flyrotary@lancaironline.net; Sun, 26 Sep 2004 01:44:04 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.35; envelope-from=ALVentures@cox.net Received: from BigAl ([68.107.116.221]) by fed1rmmtao04.cox.net (InterMail vM.6.01.03.04 201-2131-111-106-20040729) with ESMTP id <20040926054334.FJFB11627.fed1rmmtao04.cox.net@BigAl> for ; Sun, 26 Sep 2004 01:43:34 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Oil viscosity Date: Sat, 25 Sep 2004 22:43:45 -0700 Message-ID: <000001c4a38b$c9d249c0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C4A351.1D7371C0" 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 V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C4A351.1D7371C0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =20 Ah-h-h; something doesn't compute here, at least not for me. Did you = start from the same temp? Was the air a lot cooler? More air blowing through = the cooler? More oil in the pan? A slight reduction in viscosity can't = account for the difference. The flow rate will be essentially the same, as I = think your pressure drops confirm; so-o-o-o what makes the heat rejection rate double? Same temp, same everything. The only diff was the oil viscosity. One = of the reasons I tried this was because Bruce T mentioned that thinner oil would transfer heat better than thick oil. Do you disagree with that? =20 =20 Well, no; but. The specific heat is the same and the flow rate around = the loop is (roughly) the same. The lower viscosity will result in more = flow through the bearings and rotors (less bypassing through the pressure = control valve) providing more effective cooling of the rotors. But it has = little effect on the heat rejection (other than slightly better heat transfer coefficient), so, one might expect the oil to heat up at the same rate, = or a bit faster. =20 Unless there is something major I'm missing. =20 Al =20 ------=_NextPart_000_0001_01C4A351.1D7371C0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message

 

Ah-h-h; something doesn’t compute here, = at least not for me.  Did you start from the same temp?  Was the air a = lot cooler?  More air blowing through the cooler? More oil in the = pan?  A slight reduction in viscosity can’t account for the = difference.  The flow rate will be essentially the same, as I think your pressure drops = confirm; so-o-o-o what makes the heat rejection rate double?

Same temp, same everything.  The only = diff was the oil viscosity.   One of the reasons I tried this was = because Bruce T mentioned that thinner oil would transfer heat better than thick oil.  Do you disagree with that? 

 

Well, no; but. The specific heat = is the same and the flow rate around the loop is (roughly) the same.  The = lower viscosity will result in more flow through the bearings and rotors (less bypassing through the pressure control valve) providing more effective = cooling of the rotors.  But it has little effect on the heat rejection = (other than slightly better heat transfer coefficient), so, one might expect the oil = to heat up at the same rate, or a bit faster.

 

Unless there is something major = I’m missing.

 

Al

 

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