size radiator air inlet

[paintballJim]

How would I go about determining the required volume of air inlet for a radiator? I am tasked with determinimg if the air scoop opening is large enough for the Cummins diesel engine we are using.
I am assuming a simple bernoulli formula would be in order. Presure in would be atmosphere but would pressure out be the same? Velosity in would be 0, I'm not sure if P out would be as well. I assume volume out could be calculated from the opening of the radiator shroud. Is there a better method?

Thank you

Jim

 

[patprimmer]

Does this device have a fan or forward motion to push air through the opening.

Regards
Pat
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[MikeHalloran]

The pressure difference in these systems is typically limited to a few millimeters of water pressure. With a pressure difference so small, the air is often treated as incompressible.

Whoever supplies the actual radiator should be able to provide you with application help for sizing the air-side ducting.

Rule of thumb: Any 'scoop' needs as much transverse area as the radiator core.





Mike Halloran
Pembroke Pines, FL, USA

 

[paintballJim]

Yes, there is a fan to pull the air through the radiator, The "scoop" is also forward facing and the machine will be moving up to 30 mph, but not all the time, so there will be some force pushing the air part time.
Mike,
I was afraid that I would get the "same size the radiator" answer but was wondering if the size could be reduced with the fan pulling the air. I have sent a request to the radiator vendor but have not recived a reply yet.

Thank you

 

[L4189]

There are several things here. I thought Cummins would insist on furnishing the radiator cooling system with their engine. They know better than anybody what's required.

Another way to look at this is locomotives control the jacket water temperature by cycling the fan motors on and off. The radiators are horizontal so "thermo-syphon" works at idle but need everything going at full power.

The scoop area is a very sensitive design feature. You may remember that a lot of the WW2 fighter the P51 performance advantage over the P40 using initially the same engine, was that the cooling water scoop was about a third the area of the radiator and had a standoff from the fuselage out of the boundary layer. On the ground there was a flap that opened downstream of the radiator to keep things cool until the plane got into the air. In normal (flight) operation the ram air velocity was greatly reduced while passing through the radiator and the with the exhaust flap was adjusted so that there was an additional 300 lb. thrust due to the energy picked up from the radiator.

Anyway you probably should consut Cummins.

 

[IceStationZebra]

Cummings will sell the radiator, but it will be very expensive to sourcing your own. And in my dealings with them all they care about in the end is the cooling ability and air purging ability of the system. They generally assume 120°F ambient and a 212°F max top tank temp with pure water for coolant. I try to shoot for better to account for system degradation in the field. (dirt, corrosion, partial plugging, etc.)

As far as the cross sectional area, you can get away with something smaller than the radiator. Depending on the fin design, fins-per-inch, and number of rows, your radiator is blocking a significant portion of the area. I would keep the ducting just in front of the radiator the same size as the radiator for 6" minimum, then start tapering.

Another factor: puller or pusher fan? You can get away with a cruder scoop design with a pusher fan, but they are less efficient. In my experience with B-series engines in tight engine compartments the cooling is reduced about 10%. Try to keep the shroud as long as you can, it helps quite a bit by getting air to move through the corners and very center of the radiator. When you put the fan within a couple inches of the radiator you loose a lot of effective surface area.

ISZ

 

[paintballJim]

Thank you gentlemen,
The fan is a pulling fan and has a shroud on the outlet side to keep the air all comming through the radiator. The scoop actually is over the top of the engine pulling the air from the front of the machine and then directs the air to the rear of the unit turning it and then ends facing forward into the radiator with the engine sitting with the fan and radiator facing to the rear. I have given the dimensions and sketch to the radiator source for approval and cummings will be to approve everything before the unit is put into production. i was hoping to learn more to be able to better understand the requirements and maybe do some of my own work myself.
Again thank you for your insight.

 

[MikeHalloran]

Equally important: After the air leaves the shroud, it presumably flows over the engine (which radiates a fair amount of heat into it), and then leaves the vehicle by so far unspecified means. That path also has a pressure drop limit, and needs to be controlled/ designed/ planned. The heated air doesn't just disappear.


Mike Halloran
Pembroke Pines, FL, USA