Heat Capacity of Tranny Fluid

[flousberg]

I am sure someone on here knows the heat capacity of tranny fluid. I am sizing the cooler for my 4R70W and I know the flow rate is 1gpm, and I am using the worst case temps, 220 to 150°F. All I need now is the heat capacity. Don't really feel like trial and error on this.

Thanks

 

[bronko69er]

Heat Capacity is Density x Specific Heat.
Per the table in the back of my Thermo book:
Density of unused motor oil (closest I can get to tranny fluid) @ 100 *C is 840 kg/m^3.
Specific heat of the same is 2219 J/kg-*C

A little quick math puts the Heat capacity at 1864 J/cc-*C.
Somebody double check my conversions.

I can do more unit conversion if you need it........

 

[flousberg]

I meant specific heat capacity. In energy/mass*temp. Actual heat capacity is energy/temp. I need it for Tranny fluid. I believe it is quite different then motor oil? My understanding is it is a very pure mineral oil. Maybe I will use that.

Is your numbers from Dewitt Fundamentals of Heat and Mass Transfer?

 

[bronko69er]

My Source:
Introduction to Thermodynamics and Heat Transfer
Dr. Yunus Cengel
University of Nevada, Reno
Irwin/McGraw-Hill 1997

On the table A-18 page 876 there is a soucre defined as:
Heat and Mass Transfer
Frank M. White
Addison-Wesley, Reading, MA 1988, pp. 677-688 and 692-694


Multiply Heat Capacity times your volume and the volume drops out leaving you with energy/temp.

Here's another (in English units this time):
Light oil @ 225*F
Density = 53.5 pounds mass/ ft^3
Specific Heat = 0.515 BTU /lbm-*F
Calculated Heat Capacity = 27.55 BTU/ft^3-*F

So multiply that number by your volume (in cu ft) and you get the units you want: Energy / Temp = BTU / *F

Sound right? or am I way off somewhere?

Handy Calculator

 

[00gyrhed]

hydraulic fluid is closer than motor oil, but all you really need is the API gravity. Specific heat capacity is pretty much linear in relation to temperature. I have a nomograph that will give an estimate but in that temperature it will range from .45 to .55 BTU/(LB)(DEG F) dependant upon the actual API gravity.

Why are you trying to run such a tight delta T with such a low leaving fluid temperature? 220 to 150 may reaquire an unnecessarily large exchanger.

 

[bronko69er]

Corection: Mineral oil Cp is .4 per this site

 

[flousberg]

B&M has tranny coolers listed in BTU/hr. If I want my tranny fluid to run at 180 then what temperature does it come back from the cooler, 140? 150?. Is a 40°F drop realistic?

so, 1 gal/min / 7.481gal/ft3 X 60min/hr X 54 lbs/ft3 X 0.5 Btu/lb°F X 40 = 8,674 btu/hr.

200-140~13,000 BTU/hr

So they have 9,800 Btu/hr up to 14,000 Btu/hr. I am not sure how they rate these because it will depend on the cooling fluid temperature and mass flow? Anyway, I need an exchange with a rated duty of say 14,000 worst case.

The 14,000 Btu/hr is 11" long by 5-3/4" wide. So if I assume crawling in the mountains with a summer temperature of 85°F and an altitude of 10,000 ft then the density of air is 0.052 lbs/ft3. The Cp of air is 0.26 Btu/lb °F. Surface area is .44ft2, assume a velocity of 30 mph or 158,400 fphr, the volumetric flow rate is 69,696 cfh. Mass flow rate is 3,624 lbs/hr. Then the temperature differential would have to be 15°F.

I don't know if this is realistic and I am finding out that the cooler manufacturers do not provide enough information to actually do a educated sizing for the cooler. So, I guess I will go with the largest one I can fit in front of the radiator. %)

 

[00gyrhed]

I am really sorry. You are fine for some reason I thought you were talking about power steering fluid. I don't know why, I read transmission but power steering clicked.

You probably want to keep the transmission under 250 so that you have some safety factor. If you do a lot of crawling you might just want to really oversize it. Like 2X. You can spend a lot of money on an automatic transmission and the most common reason for failure is heat.

BS in Chemical Engineering and I still can't read. sorry.

 

[flousberg]

Where did you go to school? I graduated in '98 from Colorado School of Mines. It is a good time to be a Chem. Eng.

 

[Broncobowsher]

I need to sobor up a little efore I try looking at those equasions.

Simple answer, get the biggest cooler you cna get.