Hydraulic oil cooler "net"

[dawz]

Dear all,

Is it a bad thing to add a net to the hydraulic oil cooler fin side? The mesh can be pulled up for cleaning. The cooler is mounted on a crawler transporter to be used in sandy and muddy places (forest/plantation). The reason this decision was made because of wanting to clear off leaves and debris from the cooler fin.

A question was raised that it will make the cooling worse, and with operators not inspecting/cleaning this thing on a daily basis, it might just cook the hydraulic system.

What do you think?

 

[RobertHasty]

I believe you will get less cooling power.
Because the net is the restriction to air flow, just like debris and leaves.

On the other hand, if the cooler is sized big enough it should work.

 

[IRstuff]

The question that needs to be answered is whether the mesh size shown is really necessary, compared to, say, a half as dense mesh, or a quarter as dense mesh. At some determinable mesh density, loss of pressure would be minimal and may still be adequate to block leaves and twigs. The mesh as shown won't stop dust and dirt anyway.

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[FluidPowerUser]

It will actually make little difference, here's why.

Analogous to driving a car in snow, where you see that very little snow hits the windscreen. The vast majority of the air moves laterally when it hits a surface. It is the same for air that hits the front of the cooler matrix. A lot of air goes across the front of the matrix and not through it.

Plenty of designers put things in front of larger cooler matrix faces and take advantage of the fact that the matrix area is oversized in relation to required heat rejection rate.

Plenty of coolers have the matrix painted and that paint also changes the heat transfer coefficient. The coolers still work.

Mobile plant machinery that works in dusty environments, or farms with straw or hay, see a massive reduction in air flow before the oil temperature starts to rise. At that point, the reversing fan control comes on and blows the dust and debris off the matrix. Not just the face, the dust coats the entire surface area and the cooler still works well enough.

Oil coolers have a large margin of operating performance and the design of the air flow is not at all optimised. If more cooling is required, they just put a bigger pump on to increase the flow of liquid against the available air mass flow.

All of these are reasons why I don't expect you see anything different on your system.

 

[LittleInch]

Any filter or screen will create a differential pressure which increases as the filter becomes clogged.

Now how much is difficult to judge.

One way is to increase the surface areas of the grill to account for the area of the metal work. So say the metal takes up 20% of the surface area, then makes the grill area exposed to the air 20% bigger than the radiator.

Most radiators are sized for worst case conditions in terms of ambient temperature and also have some allowance for fouling.

So I would make the area of the grill bigger than the surface area of the radiator and monitor the temperature of the hydraulic fluid/ respond to high temperature alarms.

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[FluidPowerUser]

You can look on the Parker Hannifin website for details of their coolers. They also offer screens to protect the matrix against dust and stones.

They also paint the matrix to make it look nice.

All of these things restrict the mass air flow through the cooler, but they are still perfectly capable of cooling the system in line with the published heat rejection kw/degree (delta T).

As you are driving the fan with an electric motor, the easiest thing to do is to measure the current with and without the screen. You will be able to see the load on the motor change if the screen is making much of the difference to the air flow.

 

[73lafuite]

You must reverse the direction of rotation for example for 5 seconds every 10 minutes.

 

[FluidPowerUser]

Why?

 

[LittleInch]

To blow all the leaves off I suspect.

Is that fan pushing or pulling air through the matrix?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dawz]

Thanks for your input so far guys.

The fan is pulling out air from the matrix (from inside)

How is the reversal function work? Never heard of it before. Is it some sort of an automated sensor that reversed the polarity?

 

[FluidPowerUser]

It's not about sensing the pressure drop to cause the motor to reverse, that would be very expensive. It would be time based or oil temperature based to trigger a reversal of the motor. If it's DC motor, then an H bridge circuit will work.

In response to LittleInch, yes I know why the reversal of the air flow is required, I was just questioning the wording of "5 seconds every 10 minutes". 5 seconds isn't enough time to get up to speed and do anything effective and every 10 minutes is too frequent. At most it would need to be done once a day. Of course this is dependent on the environment, but if it's that bad, then there will be bigger problems that a blocked matrix, the hydraulic system will have died long before because of dirt ingress.

Back to the action of reversing the motor. The most effective way is to monitor the heat increase in the hydraulic system and use the output from a temperature switch (thermal switch) to operate an H bridge to reverse the motor direction for 1-2 minutes.

The mesh might stop large stones from rupturing the matrix, but it won't stop leaves and other debris sticking to the face of the cooler. If you can measure and respond to the temperature of the oil, you can reverse the direction of the fan as and when you need to and you wont need the mesh, unless you want to use the mesh as protection against damage. In which case, the mesh can be added and won't affect the air flow that much and certainly not the oil temperature rise. The temperature rise rate in any case is a function of the duty cycle of the machine. If it's working hard, that is when the cooling performance is required.

Does the machine control system modulate the fan speed or is the fan running at full speed all of the time? If the speed is being modulated, then the machine control system is already measuring the temperature and controlling the fan speed, you just need a way of reversing the fan motor.

 

[LittleInch]

In terms of larger bits of debris like leaves, bits of paper etc, there is surely a velocity where it will just drop to the ground if you makes the outer cage far enough away from the radiator itself that the average velocity is less than ??0.5 m/sec?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

If it is picked up enough to get to the screen, it's staying there. They may drop off on their own when the fan stops running, but backwash is probably the best that can be done. The worst case is when stems get into the holes and the leaves need to be pulled loose. Or around pine needles. But it's better to have the screen that is removable for cleaning than to have people scraping it off the heat exchanger and won't plug much worse than the exchanger will, though I would tend towards pleating the screen to get the same total area as the exchanger, if there is room for that.

 

[dawz]

The most effective way is to monitor the heat increase in the hydraulic system and use the output from a temperature switch (thermal switch) to operate an H bridge to reverse the motor direction for 1-2 minutes.

Does the machine control system modulate the fan speed or is the fan running at full speed all of the time? If the speed is being modulated, then the machine control system is already measuring the temperature and controlling the fan speed, you just need a way of reversing the fan motor.

Thermal sensors might not be feasible i think? as temperature stays constantly warm during operation, but this is a good idea though. Perhaps a device with a potentiometer to adjust the reverse polarity trigger every, say, how many hours once, and running for like 30 seconds.

Once engine turns on, the fan will keep running at max speed in 12v, there is no sensor for the cooler fan.

In terms of larger bits of debris like leaves, bits of paper etc, there is surely a velocity where it will just drop to the ground if you makes the outer cage far enough away from the radiator itself that the average velocity is less than ??0.5 m/sec?

Hmm.. mixing with moist debris, it might get stuck and stay hardened, and like 3DDave mentioned, if there is enough leaves, it will create a vacuum and trap more leaves.

but backwash is probably the best that can be done.

there's a backwash system for cooler fins? reminds me of headlamp washer/wiper systems from BMW.

show you guys one of the photos from my customer's unit during inspection.

 

[3DDave]

The backwash from running the fan in reverse.

I would think a cyclonic separator would be more useful, but you would need a blower to get enough delta-P to make it work. They also need a capture box for the material that is pulled out of the airstream. If you have a lot of fine dust, and it looks like there is, a separate screen may not be enough to stop it, just increase the intervals between washdowns, which might be enough - a check on farm equipment operators, who are around a lot of dust and plant material indicates that's what they do. Pull the screen for the big stuff and rinse or use a compressed air gun to clean the radiator. Also, make sure no smart guy thinks a pressure washer would be even better.

 

[dawz]

The backwash from running the fan in reverse.

I would think a cyclonic separator would be more useful, but you would need a blower to get enough delta-P to make it work. They also need a capture box for the material that is pulled out of the airstream. If you have a lot of fine dust, and it looks like there is, a separate screen may not be enough to stop it, just increase the intervals between washdowns, which might be enough - a check on farm equipment operators, who are around a lot of dust and plant material indicates that's what they do. Pull the screen for the big stuff and rinse or use a compressed air gun to clean the radiator. Also, make sure no smart guy thinks a pressure washer would be even better.

hmm.. Space around the cooler is limited for now. Looks like a constant reverse fan trigger is the only feasible choice for an almost "maintenance free" operation. If fins are well covered with debris in plantation where there's no equipment, river water and manual washing is the way to go, although it's corrosive due to fertilizer leaking into river. Conditions are unfavorable for clean washing.

 

[LittleInch]

Your mesh won't stop that sort of dust and gunge.

The outer grill will clog up just the same

That's too small a set of fins for dirty environment

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dawz]

Your mesh won't stop that sort of dust and gunge.

The outer grill will clog up just the same

That's too small a set of fins for dirty environment

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Thank you. I guess it boils down to just inspecting and manually cleaning it on a frequent basis.