I Need Help Choosing a Accumulator For A Hot Oil System

[leopardforest]

Hi all,

I need help choosing a accumulator or something else appropriate for my task.

I have a pumping system with approximately 5 gallons of oil in it. It is a closed system. When I run the machine the temperature goes up (200°C system max) and as the temp increases so does the pressure due to thermal expansion of the oil. Currently I have to bleed off fluid to stay within the pressure rating of the system and this is undesirable for what we are trying to do (we are a research lab).

I would like to be able to maintain the system pressure from 0-100 psi.
Be able to run the system up to 200°C.
Flow rate of the system is 10-30 gpm.

I was looking at a piston type accumulator as when we heat the oil in the system the volatiles in the oil boil off and I want to prevent this by having no headspace while still allowing room for expansion.
Most piston type accumulators are rated to several thousand psi which I don't need and are rather expensive.

Do you guys have any suggestions for accumulator or other options??

Thank you!

 

[SceneryDriver]

If the system is sealed, why would it matter if some of the volatiles ended up in the headspace of a simple accumulator? I'm seeing a short, squat piece of larger diameter pipe with a cap on one end, and a small port on the other end. That port connects to the rest of your system. There would be (almost) no flow, little exchange of fluid, and if you kept the accumulator near room temp, less chance volatiles would evaporate.


SceneryDriver

 

[leopardforest]

SceneryDriver,

It matters as the viscosity changes if I lose volatiles and the system is very sensitive to a increase in viscosity. Putting a chiller on the accumulator would help by causing the volatiles to condense, but then I need to ensure that they enter back into the flow.

 

[MikeHalloran]

Closed system suggests the oil is used as a heat transfer medium. AFAIK the absolute flow rate is not real critical except in transient conditions, as in adding a cold brick or something.

We understand that the flow rate induced by a centrifugal pump in a circulating system will be influenced by the viscosity of the fluid.

Suppose you ran the system open/vented for a while, and let the volatiles boil off, and then foreverafter ran closed with the now thickened oil; could that work?

If not, maybe you need a gear pump or other PD pump.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Maybe bellows expansion joint(s) to allow for expansion of the plumbing.

Ted

 

[3DDave]

You need to specify:

the oil, for seal compatibility
the temperature range of the oil, for seal compatibility
the maximum volume change of the oil
the maximum pressure for the part of the system you will store oil from
the as-mentioned desire to have no free oil surface.
the type of fittings you are using in the rest of the system if you want commonality or the fitting you've chosen for making the connection
any size restrictions
any desired mounting provisions

Once gathered together, you will have enough information to work with a hydraulics component supplier.

The system flow rate probably doesn't matter. Since it is temperature related, a piston will be OK. You may need to insulate the accumulator if the oil properties vary enough to be noticeable; also because the accumulator may extend beyond the equipment and you want to avoid burns from skin contact. You might also plumb a line to the accumulator to allow more flexibility in locating the accumulator.

 

[Compositepro]

Is yours a fluid power application (at 200C!?) or a heating oil application? In heating oil applications fluid reservoirs (or expansion tanks) are used. The head space is usually pressurized with nitrogen to keep out oxygen, which does not react well with hot oil. The expansion tank is located at the highest elevation point and lowest pressure point in the flow loop. If the tank is piped so that oil does not flow through it, but is only connected at a tee in the loop, then the oil in the tank can usually be kept at close to room temp.
An accumulator is an energy storage device for holding high pressure fluid. If that is, in fact, what you require, then you have to have an additional expansion tank to deal with fluid expansion in your loop.

 

[leopardforest]

Compositepro,

I guess you could say that it is a oil heat application (sorry, I have to be vague). I would love to just use a expansion tank, but I can't have the head space where volatiles can boil off and get trapped (I think the volatiles would still boil off in a nitrogen atmosphere?). For what I need, an accumulator is overkill. I just found what I really need, a volume/thermal expansion compensator, but I don't know any good sources. As stated before the system is relatively low pressure (100 psi) and I am not trying to store energy, just to account for a volume change while maintaining the system pressure (within 0-100psi) while the temperature changes. Some of the ones I saw are stainless steel bellows which sounds like a good option as it would allow the higher temps I am looking for. Any thoughts?

 

[Compositepro]

Volatile pressure comes to an equilibrium almost instantly in the head space, and none is lost unless you vent gas from the head space. Don't vent and you won't loose volatiles. You do need a safety pressure relief valve on any closed system, however.

You are making your problem much more difficult than it really is. Dowtherm and Syltherm have very detailed handbooks on how to design oil heating systems.

If you keep your expansion tank at room temp., then volatiles become a trivial problem and you lessen heat losses.