Lube Oil Cooler, unecessary?
Lube Oil Cooler, unecessary?
(OP)
We are installing a Pall lube oil purification skid that will remove particulates, free water, and dissolved water. Each tank is around 600 gallons and our skids will operate as kidney loops.
The existing system uses a filtration skid (only some free water removal) and a oil cooler that uses a fan to cool it down. Question is, since it's simply a kidney loop, is it necessary to have an oil cooler? The new skid has a built in heater that can be set to kick in when needed. The whole skid will shut down when the temperature of the oil gets too high. Flow rate is around 5 gpm.
Just wanted some operating experience regarding using these type of air oil coolers.
The existing system uses a filtration skid (only some free water removal) and a oil cooler that uses a fan to cool it down. Question is, since it's simply a kidney loop, is it necessary to have an oil cooler? The new skid has a built in heater that can be set to kick in when needed. The whole skid will shut down when the temperature of the oil gets too high. Flow rate is around 5 gpm.
Just wanted some operating experience regarding using these type of air oil coolers.





RE: Lube Oil Cooler, unecessary?
With a flow rate of 5 gpm and a fluid volume of 600 gallons, your system turnover rate is 120 minutes (2 hours). Whether or not you need a heat exchanger will be determined by the heat rejected into the oil and what temperature you need to maintain the oil at. With such a slow turnover rate, the answer is probably no. But you still should run some calculations to verify.
Hope that helps.
Terry
RE: Lube Oil Cooler, unecessary?
When you say doing calculations, if I need the temperature of the oil coming.back to the tank could I do a heat sink calculation to find out what the average temp of the oil may be at any given point?
RE: Lube Oil Cooler, unecessary?
Heat load will have to be calculated based on the heat removed from the bearings and gears (if any). This you can easily get from the bearing design/designers. The operating oil temperature and the heat removed will together have to be used for the heat load calculations. In all cases oil temperature is very critical for bearing operations.
You will have to calculate the area required to reduce the oil temperaure for operating conditions. This area will determine if you nee an oil cooler. If your reservoir size is too huge, such that the oil can cool inside (based on surfae area) then you might not need an oil cooler, else you would need one.
To start with you can use the below equations:
Q=m.cp.(T2-T1)
Q=U.A.LMTD
Q = Heat load
m = mass flow rate
cp = specific heat
T2 = Oil inlet temp
T1 = Oil outlet temp
U = Overall heat transfer coefficient
A = Area
LMTD = Log mean temp difference
Hope this helps.
RE: Lube Oil Cooler, unecessary?
First of all, if there are bearings/gears involved, the temperature of the incoming oil flow, the oil mass flow rate, and the temperature rise of the oil, are what matters. With a very low oil flow turnover rate in your system, it is quite likely that there will be enough ambient convective heat transfer in the reservoir walls, piping, etc. such that a supplementary cooler will not be necessary.
RE: Lube Oil Cooler, unecessary?
Ted
RE: Lube Oil Cooler, unecessary?
RE: Lube Oil Cooler, unecessary?
I believe the tank is large enough to that we do not need a cooler. The entire skid is set to shutdown is the incoming oil is over 180degF, which is in the PLC's program.
RE: Lube Oil Cooler, unecessary?
the return to main tank, drain from bearings can run very close to, if not above 180F (fossil). I don't recall average bearing return on Nuke, but would expect it around 170F. As a "kidney" unit, I would think the supply would be just from the reservior. Thus depending on the optimum temperture for the Pall unit, a cooler might be used occsional.
If the supply to the Pall will be from bearing header, then that should be controlled at 110 to 120F
RE: Lube Oil Cooler, unecessary?
The suction of the skid will take oil towards the bottom of the lube oil tank so the hotter oil will reside on the top part of the tank, from my understanding. I can't imagine oil from the feedwater pump and feedwater pump turbine being anything over 120F....I think
RE: Lube Oil Cooler, unecessary?
I just realized I was thinking bearing metal temps in the post above, SORRY.
RE: Lube Oil Cooler, unecessary?
RE: Lube Oil Cooler, unecessary?
The feedwater pumps operate at 13000 gpm and 2280 ft of head. If I know the RPM I may be able to better analyze just how hot that lube oil is coming back into the tank. When it comes back into the tank, it's actually on the opposite side of where our new skid is taking in the oil.
RE: Lube Oil Cooler, unecessary?
Ted
RE: Lube Oil Cooler, unecessary?
RE: Lube Oil Cooler, unecessary?
Using lube oil impingement to cool rotating components like gears and bearings is a very inefficient process. This is mostly due to the extremely brief period of time the oil is in intimate contact with the gear or bearing surfaces. The oil is squirted on and immediately flung off. The temperature rise in the oil in these situations is usually only about 30 to 40degF at best. Due to this inefficient heat transfer process and the low specific heat of lube oil, it can take a surprisingly large mass flow of lube oil to adequately cool components like gears and bearings.
You should also remember that lube oil cooling systems are usually designed to deal with some potential combined set of worst case operating conditions. As a result, the system is usually way over-designed for normal operating conditions. While it's a good idea to collect some oil in/out temperature data from a similar system operating at nominal conditions, just make sure you apply a reasonable factor to your calculations to allow for extreme cases before deciding whether or not a cooler is really necessary.
Good luck.
Terry