Received-SPF: none
 receiver=logan.com; client-ip=67.15.10.31; envelope-from=bob@bob-white.com
Date: Fri, 13 Aug 2004 16:27:09 -0600
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Answer to when is 2 gallons enough?Re: DeltaT
 Coolant was : [FlyRotary] Re:  coolant temps
Message-Id: <20040813162709.42116d46.bob@bob-white.com>
In-Reply-To: <list-364003@logan.com>
References: <list-364003@logan.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

My dad had exactly that same experience on a mid 50's model Ford.  His
thermostat failed closed, so he took it out and didn't replace it.=20
The car overheated.  His analysis was the obvious one that the water
went thru the radiator too fast to cool. It was years before I ever
found out what was really happening, and AFAIK he never did.

Bob White


On Fri, 13 Aug 2004 15:31:51 -0400
"ericruttan@chartermi.net" <ericruttan@chartermi.net> wrote:

> Let me add a trifle.
>=20
> Car racers I ran with as a kid with less creativity and more "results=20
> oriented" said the same thing, not because they had any fancy
> thermometers, but because they raced with the thermostats out, and
> boiled over.
>=20
> The reasoning was hard to argue with.  Put the thermostat (read
> restriction) in and the car ran fine.  Take it out and it would boil
> over.
>=20
> How can a student of physics argue with that!
>=20
> Years later I found out that the water pump was cavitating due to the=20
> reduced pressure.  With the restriction the pressure was higher and
> the cavitating less likely.
>=20
> With the addition of a better water pump vane design the boil overs
> stopped when the thermostats where removed, and the cars ran cooler,
> and faster.
>=20
>=20
> Ed Anderson wrote:
> > Ok, David, since you asked.
> >=20
> > In the early days of car racing (and still) some folks decided to do
> > some data collection about the effects of different factors.
> >=20
> > Being aware of the value of data they placed "Mom's" cooking=20
> > thermometers at the entrance and exit of a radiator mounted next to
> > the still.  With a fire burning under the still they proceeded to
> > pump hot water ....  OK, Ok, getting serious.
> >=20
> > Here is what let to the mistaken belief that "Slow Water cools
> > better".
> >=20
> > Folks observed that if they measure the entry and exit temperature
> > of water as it passed through a radiator an interesting thing.  The
> > slower the water flowed the greater the temperature difference
> > between the water entering and the water exiting the radiator.  AND=20
> > that observation is absolutely correct.  The reason of course is the
> > longer the water stays in the radiator the more heat is removed from
> > the water before it exits the radiator.  So far they were on solid
> > ground in their observations - however their interpretation of the
> > data is where they went afoul.
> >=20
> > The assumed the greater temperature drop of the slower water was
> > good as it showed more heat went out of the water - I mean how can
> > you argue with that??  Therefore slow water must be better at
> > cooling  - right?  Well, actually NOT!!!
> >=20
> > Where they failed is in considering the effects of the "slower"
> > water on the ENTIRE system  - not just the radiator, but the engine
> > which this is all about in the first place.  In reality lessening
> > the flow of the coolant(while it will cause a great deltaT of the
> > coolant flowing through the radiator) will fail to remove heat from
> > the engine as fast as faster moving water will as the recent
> > examples show. However, there are folks to this day will swear by
> > "Slow" water.  I argued with old man Lou Ross for 45 minutes on the
> > phone one time trying to reason it through with him but to no avail.
> >  It only stopped when I got a bit
> > frustrated and stated "Well, Lou, if slow water cools better ---=20
> > then Stopped water must cool best!!"" He of course knew that wasn't
> > the case, but still clung to that belief.
> >=20
> > Now, I have read that in some cases restrictors have helped cooling
> > - but not by slowing the water flow.  In some cases, it supposedly
> > reduced cavitation of the water pump, kept head pressure in the
> > block higher, promoted nucleated boiling and a number of things that
> > I never bothered to look into.  But all things equal more coolant
> > flow equals more heat removed from the engine (always assuming you
> > get rid of the heat through a radiator before the coolant returns to
> > the engine).
> >=20
> > There David, hope that answers your question.
> >=20
> > Ed
> >=20
> > Ed Anderson
> > RV-6A N494BW Rotary Powered
> > Matthews, NC
> > ----- Original Message -----=20
> > From: "David Carter" <dcarter@datarecall.net>
> > To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> > Sent: Friday, August 13, 2004 11:38 AM
> > Subject: [FlyRotary] Re: Answer to when is 2 gallons enough?Re:
> > DeltaT Coolant was : [FlyRotary] Re: coolant temps
> >=20
> >=20
> >=20
> >>Ed, I really like your explanations - the math and attention to
> >explaining>the units.  Good work.
> >>
> >>Now, about "slower water cooling better".  I'd like to hear "the
> >rest of
> >=20
> > the
> >=20
> >>story".   Here's why I ask:  I went into a car "window tint" shop 3
> >weeks>ago to shop for tint on 3 windows on south side of my house.=20
> >Took care of>that busines - and noticed some nice after-market
> >anodized blue aluminum>housings and stuff hanging on a wall display.=20
> >I asked if this was an>electric water pump and asked a question about
> >it.  The "tint" guy said,>"You'll have to ask ____, the speed shop
> >guy, who shares the 4 shop bays>with me."
> >>
> >>I went out and visited with the racing guy - yep, used electric
> >water
> >=20
> > pumps
> >=20
> >>and can fix me up with an in-line pump for my rotary engine on RV-6
> >since>aluminum housings are only for specific V-8s.  He was working
> >on his drag>racer and pointed to the thermosat housing and some large
> >washers.  "Then>thar washers are different sizes for restricting and
> >adjusting the flow
> >=20
> > rate
> >=20
> >>through the radiator.  Makes it cool better."  So, "thar you have
> >it".>Doesn't make sense to me
> >>
> >>David
> >>
> >>----- Original Message -----=20
> >>From: "Ed Anderson" <eanderson@carolina.rr.com>
> >>To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> >>Sent: Friday, August 13, 2004 9:14 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
> >=20
> > the
> >=20
> >>temp of the water 1 degree F.  The difference is in one case we are
> >=20
> > talking
> >=20
> >>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)
> >=20
> > we
> >=20
> >>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
> >=20
> > we
> >=20
> >>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
> >=20
> > would
> >=20
> >>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
> >=20
> > from
> >=20
> >>engine to radiator 15 times a minute =3D 160*15 =3D 2400 BTU/Min.
> >Amazing
> >=20
> > isn't
> >=20
> >>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
> >=20
> > story
> >=20
> >>about how that got started)
> >>
> >>
> >>In the  equation Q =3D W*deltaT*cp that specifies how much heat is
> >=20
> > transferred
> >=20
> >>,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.=20
> >However if you keep
> >=20
> > increasing
> >=20
> >>the flow rate and reducing the volume you can run into other
> >problems -
> >=20
> > like
> >=20
> >>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
> >=20
> > 30
> >=20
> >>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
> >=20
> > as
> >=20
> >>planned.  IF  the coolant does not give up as much heat in the
> >radiators
> >=20
> > (to
> >=20
> >>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
> >=20
> > the
> >=20
> >>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
> >>
> >>Q =3D W*deltaT*cp, we have Q =3D 240*10*1 =3D 2400 BTU/minute is requir=
ed
> >to>increase the temperature of this mass flow by 10F
> >>
> >>Using the more accurate weight of water we would have  8.34*30 =3D=20
> >250.2>lbm/minute  so the actual BTU required is closer to 2502
> >BTU/min instead
> >=20
> > of
> >=20
> >>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.=20
> >So a lb of air will
> >=20
> > only
> >=20
> >>carry approx 25% the heat of a lb of water, so again for this reason
> >you>need more air flow.
> >>
> >>if 30 gpm of water will transfer 2400 bTu of engine heat (using
> >Tracy's
> >=20
> > fuel
> >=20
> >>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
> >=20
> > we
> >=20
> >>started with.
> >>
> >>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
> >=20
> > heat
> >=20
> >>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
> >=20
> > like
> >=20
> >>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>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
> >=20
> > 69.75
> >=20
> >>ft/sec airflow velocity through our radiators  or 47.56 Mph.  Now
> >that>sounds more reasonable doesn't it??
> >>
> >>Now all of this is simply a first order estimate.  There are lots of
> >=20
> > factors
> >=20
> >>such as the density of the air which unlike water changes with
> >altitude,
> >=20
> > the
> >=20
> >>temperature of the air, etc. that can change the numbers a bit.=20
> >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.
> >>
> >>Hope this helped clarify the matter.
> >>
> >>Ed
> >>
> >>
> >>Ed Anderson
> >>RV-6A N494BW Rotary Powered
> >>Matthews, NC
> >>  ----- Original Message -----=20
> >>  From: Mark Steitle
> >>  To: Rotary motors in aircraft
> >>  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
> >=20
> > takes
> >=20
> >>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,
> >=20
> > where
> >=20
> >>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
> >=20
> > the
> >=20
> >>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
> >>
> >>    Below  is one semi-official definition of BTU in English units.=20
> >1 BTU>is amount of heat to raise 1 lb of water 1 degree Fahrenheit.
> >>
> >>    So with Tracy's 30 gpm flow of water =3D 240 lbs/min.  Since its
> >>temperature is raised 10 degree F we have
> >>
> >>    BTU =3D 240 * 10 * 1 =3D 2400 BTU/min
> >>
> >>    I know I'm ancient and  I should move into the new metric world,
> >but
> >=20
> > at
> >=20
> >>least I didn't do it in Stones and Furlongs {:>)
> >>
> >>    Ed
> >>
> >>    The Columbia Encyclopedia, Sixth Edition.  2001.
> >>
> >>    British thermal unit
> >>
> >>
> >>    abbr. Btu, unit for measuring heat quantity in the customary
> >system of>English units of measurement, equal to the amount of heat
> >required to
> >=20
> > raise
> >=20
> >>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
> >=20
> > also
> >=20
> >>be defined for the temperature difference between 59=B0F and 60=B0F. One
> >Btu
> >=20
> > is
> >=20
> >>approximately equivalent to the following: 251.9 calories; 778.26
> >>foot-pounds; 1055 joules; 107.5 kilogram-meters; 0.0002928
> >kilowatt-hours.
> >=20
> > A
> >=20
> >>pound (0.454 kilogram) of good coal when burned should yield 14,000
> >to>15,000 Btu; a pound of gasoline or other .
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>    Ed Anderson
> >>    RV-6A N494BW Rotary Powered
> >>    Matthews, NC
> >>      ----- Original Message -----=20
> >>      From: DaveLeonard
> >>      To: Rotary motors in aircraft
> >>      Sent: Thursday, August 12, 2004 8:12 PM
> >>      Subject: [FlyRotary] Re: DeltaT Coolant was : [FlyRotary] Re:
> >=20
> > coolant
> >=20
> >>temps
> >>
> >>
> >>      Ed, are those units right.  I know that the specific heat of
> >water
> >=20
> > is
> >=20
> >>1.0 cal/(deg Celsius*gram).  Does that also work out to 1.0
> >BTU/(deg.>Farhengight * Lb.) ?
> >>
> >>      Dave Leonard
> >>      Tracy my calculations shows your coolant temp drop is where it
> >=20
> > should
> >=20
> >>be:
> >>
> >>      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.
> >>
> >>      Q =3D W*DeltaT*Cp  Basic Heat/Mass Flow equation  With water as
> >the
> >=20
> > mass
> >=20
> >>with a weight of 8 lbs/ gallon and a specific heat of 1.0
> >>
> >>      Q =3D BTU/min of heat removed by coolant mass flow
> >>
> >>       Assuming 30 GPM coolant flow =3D 30*8 =3D 240 lb/min mass flow.
> >=20
> > specific
> >=20
> >>heat of water  Cp =3D 1.0
> >>
> >>
> >>       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
> >>
> >>      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>
> >>       a 50/50 coolant mix but something closer to pure water.  But
> >in any>case, certainly in the ball park.
> >>
> >>      You reported 10-12F under those conditions, so I would say
> >condition>is 4. Normal operation
> >>
> >>      Ed
> >>
> >>      Ed Anderson
> >>      RV-6A N494BW Rotary Powered
> >>      Matthews, NC
> >>
> >>
> >>
> >>
> >>>> Homepage:  http://www.flyrotary.com/
> >>>> Archive:   http://lancaironline.net/lists/flyrotary/List.html
> >=20
> >=20
> >=20
> >=20
> >>> Homepage:  http://www.flyrotary.com/
> >>> Archive:   http://lancaironline.net/lists/flyrotary/List.html
> >=20
> >=20
>=20
>=20
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>=20
>=20


--=20
http://www.bob-white.com
N93BD - Rotary Powered BD-4 (soon)