Calling hydraulic engineers - or just some smart people.
I need to spec an oil-air heat exchanger. Basically a radiator, like for your car, but oil runs through it instead of antifreeze.
I don’t understand the calculations…how do I size this thing?
I’ve got a 150 gallon oil tank and the hydraulic circuit is building the temp of this tank by approx 10 degrees per hour…up to around 160 degrees, which is too high for this system.
I need to maintain it around 130 degrees or less.
How do I figure the best way to size both my radiator’s surface area, and the gpm of my pump, so that I cool the oil enough?
The manufacturers of various heat exchangers are less than helpful, and want me to give them all the information first…instead of helping me figure it out. Google needs me to ask more specific questions than I have been (for the last hour) but it presumes I understand the language of hydraulic engineering…in order to ask the right questions…
150 gallons = 20 cubic feet. Specific gravity is about 0.9, so density is 56 lb/ft^3 (Because water is 62.3 lb/ft^3). So you’ve got about 1121 pounds of hydraulic fluid.
Specific heat of HF is about 0.4 BTU/(lb*degF).
10 degrees per hour? I’ll assume that’s Fahrenheit (160C would be really hot HF).
So your thermal power rate is 1121 pounds * 0.4 BTU/(lb*degF) * 10 degF/hr = 4485.6 BTU/hr. In SI, that’s 1.313 kilowatts. In crazy units, that’s 1.761 horsepower.
Now you know how much thermal power you need to dump through your heat cooler. An off-the-shelf hydraulic fluid cooler will list that as one of its performance specs. here’s some; and here’s one that specs 10 heat horsepower at temps up to 250F. That’s about five times more than you need, but that assumes (according to their specs - see “Additional Information” tab at that link) your oil is coming in at 100F above ambient. If you’re trying to keep the tank at 130F in an 80F room, then that’s roughly half of the inlet temperature they want. So something like this is probably close to appropriate for your needs. If you don’t want the fluid to get too cool, then you’ll need to control the fan and/or pump with a thermostatic switch.
Wow. Thanks! I’m smart enough to understand what you just told me, but I had absolutely no idea how to get from where I was to what you just showed me.
Thanks again! If I come up with any other questions I’ll tack them on below.
I copied your post and have it saved.
Although I certainly don’t work with Hydraulics like I used to I am still asked questions that some thought i understood.
An example,
A large Blasthole Drill that was overheating shortly after some major work and the ambient temp was -10 <> F and the 1350 CFM at 63 psi compressor (G-D Screw) would overheat in about 8 min.
The 3 ft diameter cooling fan blade had been replaced with a different pitch and I got the ball rolling on replacing the new blade by showing the air flow reduction simply by tossing a welding glove up to the vertical heat exchanger fin tubes and the glove would slide right down off and when this was done on another drill rig the glove would have to be peeled from the exchanger.
The Senior engineer commented that my troubleshooting wasn’t very scientific but certainly got the job done. I have that incorrect fan blade with the plans on using it as a windmill to charge battery’s at my hunting shack, Someday
