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 6.0c1) with ESMTP id 5727065 for flyrotary@lancaironline.net; Fri, 24 Aug 2012 09:07:32 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=2.0 cv=OtDNOlDt c=1 sm=0 a=g3L/TDsr+eNLfIieSKfGkw==:17 a=AHkS0RJitIMA:10 a=05ChyHeVI94A:10 a=4AhhwAmbf7EA:10 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=r1ClD_H3AAAA:8 a=sy4fRFA90_s7ArpuiiQA:9 a=pILNOxqGKmIA:10 a=E93lBu2AAAAA:8 a=FY9-5c58jLz_rmIdPJcA:9 a=_W_S_7VecoQA:10 a=hO30gm18fF0A:10 a=MpuOTR30KwMA:10 a=ITy1QvswKHoA:10 a=mvWFUSSifWkA:10 a=C1REVoR1p7wA:10 a=NWVoK91CQyQA:10 a=g3L/TDsr+eNLfIieSKfGkw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.170.10 Received: from [174.110.170.10] ([174.110.170.10:53509] helo=EdPC) by cdptpa-oedge01.mail.rr.com (envelope-from ) (ecelerity 2.2.3.46 r()) with ESMTP id E1/8E-29356-27C77305; Fri, 24 Aug 2012 13:06:59 +0000 Message-ID: <1925E35F189F4471BADF6B94D24596F6@EdPC> From: "Ed Anderson" To: "Rotary motors in aircraft" Subject: Spreadsheet Cooling Section Date: Fri, 24 Aug 2012 09:06:59 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0008_01CD81D7.D1A75A90" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_0008_01CD81D7.D1A75A90 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Regarding the cooling section of the spreadsheet. =20 Calculations do compensate for the effects of less air density at = altitude which for the same airspeed results in less air mass cooling = flow at altitude compared to sea level. However, changes in Air = Temperature at altitude are not automatically compensated for - you need = to ensure that your engine intake air temperature is adjusted for = altitude - if you are that into it. =20 The cooling section also includes a factor that adjusts cooling flow = rate based on engine rpm - higher engine rpm =3D higher coolant flow = rate. =20 Concept: Basically the cooling section uses air mass flow and cooling mass flow = to calculate heat transfer. Air mass flow primarily dependent on: 1. Airflow velocity in duct for climb configuration =3D 0.3*airspeed 2. Air Mass flow which factors air density, frontal area of heat = exchangers and the velocity of the air in the duct 3. Air density compensation for altitude and temperature 4. Specific heat of air =3D 0.25 cp Cooling mass flow is dependent on: 1. A 0.7 cp compared to pure water of 1.0 Cp - this compensates for the = typical anitfreeze dilution of the specific heat of water. =20 2. Mass flow of coolant dependent primarily on engine/pump rpm There are some other factors which get a bit esoteric, but play a lesser = role. So the results are a bit conservative - for example if you don't = use antifreeze then theoretically you would pick up a 30% improvement in = cooling capacity due to the higher specific heat value for pure water. So these factors are used to calculate how many BTU/min the cooling = system can reject for the selected operational values. Then this is = compared to the BTU of waste heat the engine needs to reject based on = the power it is producing. The radiator and oil cooler can compensate = to some degree for a deficiency in capacity in each. So if the oil = cooler for example is showing overheating by 1% and the radiator shows a = + 10% excess cooling capacity - it will reject some of the heat not = being rejected by the oil. So as long as the overall capacity is = adequate you are probably OK. =20 Again, this is just a 1st order SWAG at cooling and its has only been = compared to tractor installations. It fairly accurately predicts my = cooling capacity at Sea level and altitude. So if your cooling results were adequate for the power = setting/temperature at sea level and all you do in the cooling = spreadsheet is change the altitude, your cooling may no longer be = adequate due to the less air mass flow at altitude due to the lessen air = density. But, since you will probably be traveling at a higher airspeed = which would increase your air mass flow, the two factors in real life = would tend to offset each other to some degree. If you also increase = your airspeed (as would probably happen at cruise) along with the = altitude increase then you would likely find you cooling is back to = adequate. But, as stated before the cooling section is on less solid ground due to = the fact that installation variables play such a large role in cooling = and they are not taken into consideration. But, you can play with it to = see the effects of changing several variables on cooling. Ed Edward L. Anderson Anderson Electronic Enterprises LLC 305 Reefton Road Weddington, NC 28104 http://www.andersonee.com http://www.eicommander.com ------=_NextPart_000_0008_01CD81D7.D1A75A90 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
Regarding the cooling section of the = spreadsheet. =20
 
Calculations do compensate for the effects of = less air=20 density at altitude which for the same airspeed  results in less = air mass=20 cooling flow at altitude compared to sea level.  However, changes = in Air=20 Temperature at altitude are not automatically compensated for - you need = to=20 ensure that your engine intake air temperature is adjusted for altitude = - if you=20 are that into it. 
 
The cooling section also includes a factor that = adjusts=20 cooling flow rate based on engine rpm - higher engine rpm =3D higher = coolant flow=20 rate.   
 
Concept:
 
Basically the cooling section uses air mass flow = and=20 cooling mass flow to calculate heat transfer.  Air mass flow = primarily=20 dependent on:
1.  Airflow velocity in duct  for = climb=20 configuration =3D 0.3*airspeed
2. Air Mass flow which factors air density, = frontal area=20 of heat exchangers and the velocity of the air in the duct
3. Air density compensation for altitude and=20 temperature
4.  Specific heat of air =3D 0.25 = cp
 
Cooling mass flow is dependent = on:
1. A  0.7 cp compared to pure water of = 1.0 Cp -=20 this compensates for the typical anitfreeze dilution of the specific = heat of=20 water. 
2. Mass flow of coolant dependent primarily = on=20 engine/pump rpm
 
There are some other factors which get a bit = esoteric, but=20 play a lesser role.  So the results are a bit conservative - for = example if=20 you don't use antifreeze then theoretically you would pick up a 30% = improvement=20 in cooling capacity due to the higher specific heat value for pure=20 water.
 
So these factors are used to calculate how many = BTU/min=20 the cooling system can reject for the selected operational values.  = Then=20 this is compared to the BTU of waste heat the engine needs to reject = based on=20 the power it is producing.  The radiator and oil cooler can = compensate to=20 some degree for a deficiency in capacity in each.  So if the oil = cooler for=20 example is showing overheating by 1% and the radiator shows a  + = 10% excess=20 cooling capacity - it will reject some of the heat not being rejected by = the=20 oil.  So as long as the overall capacity is adequate you are = probably=20 OK. 
 
Again, this is just a 1st order SWAG at cooling = and its=20 has only been compared to tractor installations.  It fairly = accurately=20 predicts my cooling capacity at Sea level and altitude.
 
So if your cooling results were adequate for the = power=20 setting/temperature at sea level and all you do in the cooling = spreadsheet is=20 change the altitude, your cooling may no longer be adequate due to the = less air=20 mass flow at altitude due to the lessen air density.  But, since = you will=20 probably be traveling at a higher airspeed which would increase your air = mass=20 flow, the two factors in real life would tend to offset each other to = some=20 degree.  If you also increase your airspeed (as would probably = happen at=20 cruise) along with the altitude increase then you would likely find you = cooling=20 is back to adequate.
 
But, as stated before the cooling section is on = less solid=20 ground due to the fact that installation variables play such a large = role in=20 cooling and they are not taken into consideration.  But, you can = play with=20 it to see the effects of changing several variables on = cooling.
 
Ed
 
 
Edward L. Anderson
Anderson Electronic = Enterprises=20 LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com
------=_NextPart_000_0008_01CD81D7.D1A75A90--