Hydraulic Cooler Sizing (cross post)

[jeevsie]

I posted this in the wrong forum before. Perhaps a mod can delete the previous one?

I'm trying to size a cooler based on actual heat created in a system. In a closed loop circuit, do I consider leakage from the charge pump (10-15% of charge flow * charge setting), leakage through the pump case (10-15% of max flow * Delta P), and leakage through the motor case (10-15% of max flow * Delta P)? Just want to make sure I'm not doubling up on the pump and motor case.

For Delta P in the pump and motor case I am using (pressure setting - charge setting). I am running two cases to determine worst case -- high speed, low pressure and low speed, high pressure. HP of the prime mover limits high speed, high pressure instance.

Comments?

 

[hydtools]

Is this a hydraulic motor driven hydraulic pump? Hydrostatic transmission?
Are you also considering system losses(heat) in addition to pump and motor losses?
I have yet to see a system that had too much cooling capacity.

Ted

 

[jeevsie]

Diesel driven hydraulic power unit. I'm asking specifically about the hydrostat circuit. I have inefficiency of the open loop, cases in the motors, valve drains to also consider.

This is mobile equipment, so space is a premium. I can't just use the largest cooler I can find like I'd like to. I really need to size it right.

Thanks,

J

 

[kcj]

Not sure what you mean by charge pump losses. All of charge pump flow is a loss. I figure 5-10% of the charge flow is leaking out from the actual loop at high pressure, say worst case of 5000 psi. The other 90-95% is still a loss, going across relief or flushing valve at 300-400 psi.
There might be some port to port leakage at the valve plate of the rotating group, but realisitically most of it goes to case.

Also add a bit for the case churning heat from the pump rotating.

A big variable is the cooler efficiency: just alight coating of dust, or slower air flow, make sa big difference. Mfr tests are usually optimistic, at least in my environment.

I am cautious and conservative. I don't think I have ever been beaten on because a cooler was too big. They just run it harder and longer until complaining of heat.
I know space is a premium, but it costs a whole lot more to find that space after the machine is built....

 

[IceStationZebra]

I have done these types of calculations before. If you are running steady state it will be easier to just subtract the useful work from the power supplied - a majority of the difference needs to be rejected as heat. (there will be some mechanical friction in bearings, wheels, etc.)

And I agree with kcj - slightly oversize the cooler to account for dirt/debris buildup. The extent you over-design it will depend on the application and clientele.

And lastly, it pays to try out different fans, fan spacers and shrouds. In general the fan should be not be tight against the engine nor the radiator/cooler. I had a bunch of different length spacers and would do an optimization test. I have picked up 5-15% airflow just by changing the fan spacer or fan. In general the longer you can make the shroud the better, and if you can avoid sharp edges and corners even better. Look at the shroud on FWD cars to get an idea of the best shapes and contours.

ISZ