Return-Path: Received: from [65.54.241.216] (HELO hotmail.com) by logan.com (CommuniGate Pro SMTP 4.2) with ESMTP id 363887 for flyrotary@lancaironline.net; Fri, 13 Aug 2004 13:53:41 -0400 Received-SPF: none receiver=logan.com; client-ip=65.54.241.216; envelope-from=lors01@msn.com Received: from hotmail.com ([65.54.168.110]) by hotmail.com with Microsoft SMTPSVC(5.0.2195.6713); Fri, 13 Aug 2004 10:53:09 -0700 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Fri, 13 Aug 2004 10:53:09 -0700 Received: from 65.54.98.150 by bay3-dav6.bay3.hotmail.com with DAV; Fri, 13 Aug 2004 17:53:09 +0000 X-Originating-IP: [65.54.98.150] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Answer to when is 2 gallons enough?Re: DeltaT Coolant was : [FlyRotary] Re: coolant temps Date: Fri, 13 Aug 2004 13:53:05 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0070_01C4813C.DBE056F0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.10.0006.2205 Seal-Send-Time: Fri, 13 Aug 2004 13:53:06 -0400 Message-ID: X-OriginalArrivalTime: 13 Aug 2004 17:53:09.0733 (UTC) FILETIME=[65294950:01C4815E] Return-Path: lors01@msn.com This is a multi-part message in MIME format. ------=_NextPart_000_0070_01C4813C.DBE056F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed, That answer was so well done I'd like to ask permission to use it = on my website, with full credit to the author of course. Tracy ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Friday, August 13, 2004 10:14 AM Subject: [FlyRotary] Answer to when is 2 gallons enough?Re: DeltaT = Coolant was : [FlyRotary] Re: coolant temps I'm sorry, Mark, I did not show that step. You are correct the weight = (mass) of water(or any other cooling medium) is an important factor as = is its specific heat. In the example you used - where we have a static 2 gallons capacity = of water, It would actually only take 8*2 =3D 16 lbms *10 =3D 160 BTU to = raise the temp of the water 1 degree F. The difference is in one case = we are talking about raising the temperature of a fixed static amount of = water which can not readily get rid of the heat, in the other (our = radiator engine case) we are talking about how much heat the coolant can = transfer from engine to radiator. Here the flow rate is the key factor. = But lets take your typical 2 gallon cooling system capacity and see = what we can determine. If we take our 2 gallons and start moving it from engine to radiator = and back we find that each times the 2 gallons circulates it transfers = 160 BTU (in our specific example!!). So at our flow rate of 30 gpm we = find it will move that 160 BTU 15 times/minute (at 30 gallons/minute the = 2 gallons would be transferred 15 times). So taking our 160 BTU that it = took to raise the temp of our 2 gallons of static water 10F that we now = have being moved from engine to radiator 15 times a minute =3D 160*15 = =3D 2400 BTU/Min. Amazing isn't it? So no magic, just math {:>). So = that is how our 2 gallons of water can transfer 2400 BTU/min from engine = to radiator. It also shows why the old wives tale about "slow water" = cooling better is just that (another story about how that got started) In the equation Q =3D W*deltaT*cp that specifies how much heat is = transferred ,we are not talking about capacity such as 2 gallons = capacity of a cooling system but instead are talking about mass flow. = As long as we reach that flow rate 1 gallon at 30 gpm or 1/ gallon at = 60 gpm or 1/4 gallon at 120 gpm all will remove the same amount of heat. = However if you keep increasing the flow rate and reducing the volume = you can run into other problems - like simply not enough water to keep = your coolant galleys filled {:>), so there are limits. Our 2 gallon capacity is, of course, simply recirculated at the rate = of 30 gpm through our engine (picking up heat- approx 2400 BTU/min in = this specific example) and then through our radiator (giving up heat of = 2400 BTU/Min to the air flow through the radiators) assuming everything = works as planned. IF the coolant does not give up as much heat in the = radiators (to the air stream) as it picks up in the engine then you will = eventually (actually quite quickly) over heat your engine. The 240 lb figure I used in the previous example comes from using 8 = lb/gal (a common approximation, but not precise as you point out) to = calculate the mass flow. The mass flow =3D mass of the medium (8 lbs/gallon for water) * Flow = rate(30 gpm) =3D240 lbs/min mass flow. Looking at the units we have (8 lbs/gallon)*(30 Gallon/minute) canceling out the like units = (gallons) leaves us with 240 lb/minute which is our mass flow in this = case. Then using the definition of the BTU we have 240 lbs of water that = must be raised 10F. Using our heat transfer equation=20 Q =3D W*deltaT*cp, we have Q =3D 240*10*1 =3D 2400 BTU/minute is = required to increase the temperature of this mass flow by 10F Using the more accurate weight of water we would have 8.34*30 =3D = 250.2 lbm/minute so the actual BTU required is closer to 2502 BTU/min = instead of my original 2400 BTU/Min, so there is apporx a 4% error in = using 8 lbs/gallon. If we could ever get accurate enough where this 4% = was an appreciable part of the total errors in doing our back of the = envelope thermodynamics then it would pay to use 8.34 vice 8, but I = don't think we are there, yet {:>). Now the same basic equation applies to the amount of heat that the air = transfers away from out radiators. But here the mass of air is much = lower than the mass of water so therefore it takes a much higher flow = rate to equal the same mass flow. What makes it even worse is that the = specific heat of air is only 0.25 compared to water's 1.0. So a lb of = air will only carry approx 25% the heat of a lb of water, so again for = this reason you need more air flow. =20 if 30 gpm of water will transfer 2400 bTu of engine heat (using = Tracy's fuel burn of 7 gallon/hour), how much air does it require to = remove that heat from the radiators? Well again we turn to our equation and with a little algebra we have = W =3D Q/(DeltaT*Cp) =3D 2400/(10*1) =3D 240 lbm/min. Not a surprise as = that is what we started with.=20 But now taking the 240 lbm/min mass flow and translating that into = Cubic feet/minute of air flow. We know that a cubic foot of air at sea = level weighs approx 0.076 lbs. So 240 lbm/(0.076 lbm/Cubic foot) =3D = 3157 cubic feet/min to equal the same mass as the coolant. But since = the specific heat of air is lower (0.25) that water, we actually need = 75% more air mass or 1.75 * 3157 =3D 5524.75 CFM air flow at sea level. = Now I know this sounds like a tremendous amount of air but stay with me = through the next step. Taking two GM evaporator cores with a total frontal area of 2*95 =3D = 190 sq inches and turning that in to square feet =3D 1.32 sq ft we take = our=20 5524.75 cubic feet minute and divide by 1.32 sq ft =3D 4185 ft/min for = the required air velocity to move that much air volume through our two = evaporator cores. To get the air velocity in ft/sec divide 4185/60 =3D = 69.75 ft/sec airflow velocity through our radiators or 47.56 Mph. Now = that sounds more reasonable doesn't it?? =20 Now all of this is simply a first order estimate. There are lots of = factors such as the density of the air which unlike water changes with = altitude, the temperature of the air, etc. that can change the numbers a = bit. But, then there is really not much point in trying to be more = accurate given the limitations of our experimentation accuracy {:>). Also do not confuse the BTUs required to raise the temperature of 1 lb = of water 1 degree F with that required to turn water in to vapor - that = requires orders of magnitude more BTU. =20 Hope this helped clarify the matter. Ed Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC ----- Original Message -----=20 From: Mark Steitle=20 To: Rotary motors in aircraft=20 Sent: Friday, August 13, 2004 8:32 AM Subject: [FlyRotary] Re: DeltaT Coolant was : [FlyRotary] Re: = coolant temps Ed, Please humor me (a non-engineer) while I ask a dumb question. If it = takes 1BTU to raise 1lb of water 1 degree, and you factor in 30 gpm flow = to come up with a 2400 BTU requirement for a 10 degree rise for 1 lb of = water, where does the number of pounds of water figure into the = equation, or do we just ignore that issue? Water is 8.34 lbs/gal, and = say you have 2 gallons of coolant, that would be 16.68 lbs. Seems that = we would need to multiply the 2400 figure by 16.68 to arrive at a total = system requirement of 40,032 BTU/min. What am I missing here? Mark S. At 09:58 PM 8/12/2004 -0400, you wrote: Right you are, Dave =20 Below is one semi-official definition of BTU in English units. 1 = BTU is amount of heat to raise 1 lb of water 1 degree Fahrenheit. =20 =20 So with Tracy's 30 gpm flow of water =3D 240 lbs/min. Since its = temperature is raised 10 degree F we have =20 BTU =3D 240 * 10 * 1 =3D 2400 BTU/min =20 I know I'm ancient and I should move into the new metric world, = but at least I didn't do it in Stones and Furlongs {:>) =20 Ed =20 The Columbia Encyclopedia, Sixth Edition. 2001. =20 British thermal unit =20 =20 abbr. Btu, unit for measuring heat quantity in the customary = system of English units of = measurement, equal to the = amount of heat required to raise the temperature of one pound of water = at its maximum density [which occurs at a temperature of 39.1 degrees = Fahrenheit (=B0F) ] by 1=B0F. The Btu may also be defined for the = temperature difference between 59=B0F and 60=B0F. One Btu is = approximately equivalent to the following: 251.9 calories; 778.26 = foot-pounds; 1055 joules; 107.5 kilogram-meters; 0.0002928 = kilowatt-hours. A pound (0.454 kilogram) of good coal when burned should = yield 14,000 to 15,000 Btu; a pound of gasoline or other . =20 =20 =20 =20 =20 =20 =20 Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC=20 ----- Original Message -----=20 From: DaveLeonard=20 To: Rotary motors in = aircraft=20 Sent: Thursday, August 12, 2004 8:12 PM=20 Subject: [FlyRotary] Re: DeltaT Coolant was : [FlyRotary] Re: = coolant temps Ed, are those units right. I know that the specific heat of = water is 1.0 cal/(deg Celsius*gram). Does that also work out to 1.0 = BTU/(deg. Farhengight * Lb.) ?=20 Dave Leonard=20 Tracy my calculations shows your coolant temp drop is where it = should be:=20 My calculations show that at 7 gph fuel burn you need to get rid = of 2369 BTU/Min through your coolant/radiators. I rounded it off to = 2400 BTU/min.=20 Q =3D W*DeltaT*Cp Basic Heat/Mass Flow equation With water as = the mass with a weight of 8 lbs/ gallon and a specific heat of 1.0=20 Q =3D BTU/min of heat removed by coolant mass flow=20 Assuming 30 GPM coolant flow =3D 30*8 =3D 240 lb/min mass flow. = specific heat of water Cp =3D 1.0=20 Solving for DeltaT =3D Q/(W*Cp) =3D 2400/(240*1) =3D 2400/240 = =3D 10 or your delta T for the parameters specified should be around = 10F=20 Assuming a 50/50 coolant mix with a Cp of 0.7 you would have = approx 2400/(240 *0.7) =3D 2400/168 =3D 14.2F so I would say you do not = fly with=20 a 50/50 coolant mix but something closer to pure water. But in = any case, certainly in the ball park.=20 You reported 10-12F under those conditions, so I would say = condition is 4. Normal operation=20 Ed=20 Ed Anderson=20 RV-6A N494BW Rotary Powered=20 Matthews, NC ------=_NextPart_000_0070_01C4813C.DBE056F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed,  That answer was so well done I'd like to ask permission = to=20 use it on my website, with full credit to the author of = course.
 
Tracy
----- Original Message -----
From: Ed Anderson
To: Rotary motors in = aircraft
Sent: Friday, August 13, 2004 = 10:14=20 AM
Subject: [FlyRotary] Answer to = when is 2=20 gallons enough?Re: DeltaT Coolant was : [FlyRotary] Re: coolant = temps

I'm sorry, Mark, I did not show that = step. =20 You are correct the weight (mass) of water(or any other cooling=20 medium) is an important factor as is its specific = heat.
 
 In the example you used  - = where we=20 have a static 2 gallons capacity of water, It would actually only take = 8*2 =3D=20 16 lbms *10 =3D 160 BTU to raise the temp of the water 1 degree = F.  The=20 difference is in one case we are talking about raising the temperature = of a=20 fixed static amount of water which can not readily get rid of the = heat, in the=20 other (our radiator engine case) we are talking about how much heat = the=20 coolant can transfer from engine to radiator. Here the flow rate is = the key=20 factor. 
 
But lets take your typical 2 gallon = cooling=20 system capacity and see what we can determine.
 
If we take our 2 gallons and start = moving it from=20 engine to radiator and back we find that each times the 2 gallons = circulates=20 it transfers 160 BTU (in our specific example!!). So at our flow rate = of 30=20 gpm we find it will move that 160 BTU 15 times/minute (at 30 = gallons/minute=20 the 2 gallons would be transferred 15 times).  So taking our 160 = BTU that=20 it took to raise the temp of our 2 gallons of static water 10F = that we=20 now have being moved from engine to radiator 15 times a minute =3D = 160*15 =3D 2400=20 BTU/Min. Amazing isn't it?   So no magic, just math=20 {:>).  So that is how our 2 gallons of water can transfer 2400 = BTU/min=20 from engine to radiator.  It also shows why the old wives tale = about=20 "slow water" cooling better is just that (another story about how that = got=20 started)
 
 
In the  equation Q =3D = W*deltaT*cp that=20 specifies how much heat is transferred ,we are not = talking=20 about capacity such as 2 gallons capacity of a = cooling=20 system but instead are talking about mass flow.  = As long=20 as we reach that flow rate  1 gallon at 30 gpm or 1/ gallon at 60 = gpm or=20 1/4 gallon at 120 gpm all will remove the same amount of heat. =20 However if you keep increasing the flow rate and reducing = the volume=20 you can run into other problems - like simply not enough water to = keep=20 your coolant galleys filled {:>), so there are limits.
 
Our  2 gallon capacity is, = of course,=20 simply recirculated at the rate of 30 gpm through our engine (picking = up heat-=20 approx 2400 BTU/min in this specific example) and then through our = radiator=20 (giving up heat of 2400 BTU/Min  to the air flow through the = radiators) assuming everything works as planned.  IF  the = coolant=20 does not give up as much heat in the radiators (to the air stream) as = it picks=20 up in the engine then you will eventually (actually quite quickly) = over heat=20 your engine.
 
The 240 lb figure I used in the = previous example=20 comes from using 8 lb/gal (a common approximation, but not precise as = you=20 point out) to calculate the mass flow.
 
The mass flow =3D mass of the medium = (8 lbs/gallon=20 for water) * Flow rate(30 gpm) =3D240 lbs/min mass flow. Looking at = the units we=20 have
(8 lbs/gallon)*(30 Gallon/minute) = canceling out=20 the like units (gallons) leaves us with 240 lb/minute which is our = mass flow=20 in this case.
 
Then using the definition of the BTU = we have 240=20 lbs of water that must be raised 10F.  Using our heat transfer = equation=20
 
Q =3D W*deltaT*cp, we have Q =3D = 240*10*1 =3D 2400=20 BTU/minute is required to increase the temperature of this mass flow = by=20 10F
 
Using the more accurate weight of = water we would=20 have  8.34*30 =3D  250.2 lbm/minute  so the actual BTU = required=20 is closer to 2502 BTU/min instead of my original 2400 BTU/Min, so = there is=20 apporx a 4% error in using 8 lbs/gallon.  If we could ever get = accurate=20 enough where this 4% was an appreciable part of the total errors in = doing our=20 back of the envelope thermodynamics then it would pay to use 8.34 vice = 8, but=20 I don't think we are there, yet {:>).
 
Now the same basic equation applies = to the amount=20 of heat that the air transfers away from out radiators.  But here = the=20 mass of air is much lower than the mass of water so therefore it takes = a much=20 higher flow rate to equal the same mass flow.  What makes it even = worse=20 is that the specific heat of air is only 0.25 compared to water's = 1.0.  So a lb of air will only carry approx 25% the heat of a lb = of=20 water, so again for this reason you need more air flow.  =
 
if 30 gpm of water will transfer 2400 = bTu of=20 engine heat (using Tracy's fuel burn of 7 gallon/hour), how much air = does it=20 require to remove that heat from the radiators?
 
Well  again we turn to our = equation and with=20 a little algebra we have W =3D Q/(DeltaT*Cp) =3D 2400/(10*1) =3D 240 = lbm/min. Not a=20 surprise as that is what we started with.
 
But now taking the 240 lbm/min mass = flow and=20 translating that into Cubic feet/minute of air flow.  We know = that=20 a cubic foot of air at sea level weighs approx 0.076 lbs.  = So 240=20 lbm/(0.076 lbm/Cubic foot) =3D 3157 cubic feet/min to equal  the = same mass=20 as the coolant. But since the specific heat of air is lower (0.25) = that water,=20 we actually need 75% more air mass or 1.75 * 3157 =3D 5524.75 CFM air = flow at=20 sea level. Now I know this sounds like a tremendous amount of air but = stay=20 with me through the next step.
 
Taking two GM evaporator cores with a = total=20 frontal area of 2*95 =3D 190 sq inches and turning that in to square = feet =3D 1.32=20 sq ft we take our
5524.75 cubic feet minute and divide = by 1.32 sq=20 ft =3D 4185 ft/min for the required air velocity to move that much air = volume=20 through our two evaporator cores.  To get the = air velocity in=20 ft/sec divide 4185/60 =3D 69.75 ft/sec airflow velocity through = our=20 radiators  or 47.56 Mph.  Now that sounds more reasonable = doesn't=20 it?? 
 
Now all of this is simply a first = order=20 estimate.  There are lots of factors such as the density of the = air which=20 unlike water changes with altitude, the temperature of the air, etc. = that can=20 change the numbers a bit.  But, then there is really not much = point in=20 trying to be more accurate given the limitations of our = experimentation=20 accuracy {:>).
 
 
Also do not confuse the BTUs required = to raise=20 the temperature of 1 lb of water 1 degree F with that required to turn = water=20 in to vapor - that requires orders of magnitude more BTU.  =
 
Hope this helped clarify the = matter.
 
Ed
 
 
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From:=20 Mark Steitle
To: Rotary motors in = aircraft=20
Sent: Friday, August 13, 2004 = 8:32=20 AM
Subject: [FlyRotary] Re: = DeltaT Coolant=20 was : [FlyRotary] Re: coolant temps

Ed,
Please humor me (a = non-engineer) while I=20 ask a dumb question.  If it takes 1BTU to raise 1lb of water 1 = degree,=20 and you factor in 30 gpm flow to come up with a 2400 BTU requirement = for a=20 10 degree rise for 1 lb of water, where does the number of pounds of = water=20 figure into the equation, or do we just ignore that issue?  = Water is=20 8.34 lbs/gal, and say you have 2 gallons of coolant, that would be = 16.68=20 lbs.  Seems that we would need to multiply the 2400 figure by = 16.68 to=20 arrive at a total system requirement of 40,032 BTU/min.  What = am I=20 missing here?

Mark S.


     At = 09:58 PM=20 8/12/2004 -0400, you wrote:
Right=20 you are, Dave
 
Below  is=20 one semi-official definition of BTU in English units.  1 BTU = is=20 amount of heat to raise 1 lb of water 1 degree = Fahrenheit.  =20
 
So with Tracy's = 30 gpm flow=20 of water =3D 240 lbs/min.  Since its temperature is raised 10 = degree F=20 we have
 
BTU =3D = 240 * 10 * 1 =3D=20 2400 BTU/min
 
I = know I'm=20 ancient and  I should move into the new metric world, but at = least I=20 didn't do it in Stones and Furlongs = {:>)
 
Ed
 
The Columbia = Encyclopedia, Sixth=20 Edition.  2001.
 
British thermal=20 unit
 
 
abbr. Btu, = unit for=20 measuring heat quantity in the customary system of English units = of=20 measurement, equal to the amount of heat required to raise the = temperature of one pound of water at its maximum density [which = occurs at=20 a temperature of 39.1 degrees Fahrenheit (=B0F) ] by 1=B0F. The = Btu may also=20 be defined for the temperature difference between 59=B0F and = 60=B0F. One Btu=20 is approximately equivalent to the following: 251.9 calories; = 778.26=20 foot-pounds; 1055 joules; 107.5 kilogram-meters; 0.0002928 = kilowatt-hours.=20 A pound (0.454 kilogram) of good coal when burned should yield = 14,000 to=20 15,000 Btu; a pound of gasoline or other=20 =
 
 
 
 
 
 
 Ed=20 Anderson
RV-6A N494BW Rotary Powered
Matthews, NC=20
----- Original Message -----=20
From: DaveLeonard=20
To: Rotary motors in = aircraft=20
Sent: Thursday, August 12, 2004 8:12 PM=20
Subject: [FlyRotary] Re: DeltaT Coolant was : = [FlyRotary] Re:=20 coolant temps

Ed, are those units right.  I know that the specific = heat of=20 water is 1.0 cal/(deg Celsius*gram).  Does that also work = out to=20 1.0 BTU/(deg. Farhengight * Lb.) ?=20
Dave Leonard =
Tracy my calculations shows your coolant temp drop is where = it=20 should be:=20
My calculations show that at 7 gph fuel burn you need to get = rid of=20 2369 BTU/Min through your coolant/radiators.  I rounded it = off to=20 2400 BTU/min.=20
Q =3D W*DeltaT*Cp  Basic Heat/Mass Flow equation  = With water=20 as the mass with a weight of 8 lbs/ gallon and a specific heat = of 1.0=20
Q =3D BTU/min of heat removed by coolant mass flow=20
 Assuming 30 GPM coolant flow =3D 30*8 =3D 240 lb/min = mass flow.=20 specific heat of water  Cp =3D 1.0=20
 Solving for DeltaT =3D Q/(W*Cp) =3D 2400/(240*1)  = =3D =20 2400/240 =3D 10 or  your delta T for the parameters = specified should=20 be around 10F=20
Assuming a 50/50 coolant mix with a Cp  of 0.7 you = would have=20 approx 2400/(240 *0.7) =3D 2400/168 =3D 14.2F so I would say you = do not fly=20 with=20
 a 50/50 coolant mix but something closer to pure = water. =20 But in any case, certainly in the ball park.=20
You reported 10-12F under those conditions, so I would say = condition=20 is 4. Normal operation=20
Ed=20
Ed Anderson=20
RV-6A N494BW Rotary Powered=20
Matthews, NC=20 =
= ------=_NextPart_000_0070_01C4813C.DBE056F0--