Heat exchanger physics question
08-05-2009, 01:05 AM
#1
Registered
Thread Starter
Heat exchanger physics question
To increase effectiveness of a heat exchanger, whether it be an oil cooler or a closed cooling exchanger, which will be a bigger influence? Increasing the size (say 25%) or switching from a 2 pass to a 4 pass (of raw water) on the same exchanger?
.
.
08-11-2009, 06:57 PM
#3
Platinum Member
Platinum Member
you'd really have to determine whether your existing cooler was getting heat saturated. You have four deltas to contend with.
Delta 1 would be the temp rise of the cooling water in vs out.
Delta 2 would be the temp drop of the medium needing cooled in vs out.
Delta 3 would be the temp diff of the incoming water vs the incoming oil (if it was an oil cooler)
Delta 4 would be the temp diff of the outgoing cooling water vs the outgoing oil temp.
Sometimes you have a surface area issue, sometimes you have a flow volume issue. You need all 4 deltas to know.
Yes, though, the more surface area, the more heat transfer takes place. You almost always get more results out of more area. If, however, your flow volume is too low, added area won't do nearly as much. Your three main variables are: coolant flow, oil flow, transfer/surface area. They all contribute.
Lesser variables also contribute, such as heat conductivity of the tubing used, the internal and external cross section of the tubing used, the flow path through the unit, and all the other stuff...
Delta 1 would be the temp rise of the cooling water in vs out.
Delta 2 would be the temp drop of the medium needing cooled in vs out.
Delta 3 would be the temp diff of the incoming water vs the incoming oil (if it was an oil cooler)
Delta 4 would be the temp diff of the outgoing cooling water vs the outgoing oil temp.
Sometimes you have a surface area issue, sometimes you have a flow volume issue. You need all 4 deltas to know.
Yes, though, the more surface area, the more heat transfer takes place. You almost always get more results out of more area. If, however, your flow volume is too low, added area won't do nearly as much. Your three main variables are: coolant flow, oil flow, transfer/surface area. They all contribute.
Lesser variables also contribute, such as heat conductivity of the tubing used, the internal and external cross section of the tubing used, the flow path through the unit, and all the other stuff...
08-11-2009, 07:20 PM
#4
Registered
Thread Starter
mcollinstn!
I did not expect you to pipe in here but if definitely is up your alley.
Turns out I have been asking the same question different ways.
Without setting up a true laboratory setting where your deltas (changes) can become known values, let me give you my real world scenario. I use the big Teague coolers with raw water coming in after the strainers. My oil temps spike after a long hard run but come back down pretty quickly when cruising.
I have a stepped bottom, high X-dimension and sportmaster shortys. Others (with similar rigging) have found that too much air enters the pick ups at high speed, reducing cooling efficiency. My raw water pressure stays at 15lbs and my closed cooling ranges from 170-180. The heat exchanger is much bigger for the closed cooling but has the same copper nickel tubing inside a brass housings.
The next step in my real world application is to place cone top lids on the strainers, with a check valve and overboard transom dump. Hopefully this will eliminate air (steam) in the raw water side, improving the oil cooler's ability to cool the oil.
I did not expect you to pipe in here but if definitely is up your alley.
Turns out I have been asking the same question different ways.
Without setting up a true laboratory setting where your deltas (changes) can become known values, let me give you my real world scenario. I use the big Teague coolers with raw water coming in after the strainers. My oil temps spike after a long hard run but come back down pretty quickly when cruising.
I have a stepped bottom, high X-dimension and sportmaster shortys. Others (with similar rigging) have found that too much air enters the pick ups at high speed, reducing cooling efficiency. My raw water pressure stays at 15lbs and my closed cooling ranges from 170-180. The heat exchanger is much bigger for the closed cooling but has the same copper nickel tubing inside a brass housings.
The next step in my real world application is to place cone top lids on the strainers, with a check valve and overboard transom dump. Hopefully this will eliminate air (steam) in the raw water side, improving the oil cooler's ability to cool the oil.
08-12-2009, 09:28 AM
#5
Platinum Member
Platinum Member
#1: what sort of SPIKE in oil temps are you seeing?
mkay. yeah, you can be getting air thru the cooler and losing efficiency, but you're still getting decent total water volume else your closed cooling loop would be showing an overheat tendency as well.
Are you splitting after the strainers and sending water one way thru the oil coolers and another way thru the engine H/E ? Or are you running thru the oil cooler and THEN into the engine h/e?
Describe your raw water path, including any splits and dumps and restrictors, etc.
Normal strainers will pass air pretty easily since the in and out are both located at the top of the strainers. Industrial air/water separators use a cyclonic action to sling the water to the outside, and they extract from the center in order to purge/separate the air. I think your top purge idea for your strainers will ASSIST in removing air, but I think a lot of it will still go thru the system. BUT some air is probably okay as long as you aren't getting pockets trapped. I'm not sure how many passes your raw water makes in your oil cooler, but if there are any places where air can "pocket" then add brass fittings and run small diameter hoses from them to tee into the main outflow. That will make sure nothing in the cooler is sitting in an air pocket. Orienting the coolers on an angle will aid in shifting the air to one area where it can be better extracted. You can also "cheat" the internal dividers to purge air from early chambers to the outbound chamber - there is a slight pressure differential from high to low as you move from the inlet to the outlet, so any bleed passage you cut will move air towards the outlet side...
you might be chasing the wrong demon.
post your water flow and let's go from there.
MC
mkay. yeah, you can be getting air thru the cooler and losing efficiency, but you're still getting decent total water volume else your closed cooling loop would be showing an overheat tendency as well.
Are you splitting after the strainers and sending water one way thru the oil coolers and another way thru the engine H/E ? Or are you running thru the oil cooler and THEN into the engine h/e?
Describe your raw water path, including any splits and dumps and restrictors, etc.
Normal strainers will pass air pretty easily since the in and out are both located at the top of the strainers. Industrial air/water separators use a cyclonic action to sling the water to the outside, and they extract from the center in order to purge/separate the air. I think your top purge idea for your strainers will ASSIST in removing air, but I think a lot of it will still go thru the system. BUT some air is probably okay as long as you aren't getting pockets trapped. I'm not sure how many passes your raw water makes in your oil cooler, but if there are any places where air can "pocket" then add brass fittings and run small diameter hoses from them to tee into the main outflow. That will make sure nothing in the cooler is sitting in an air pocket. Orienting the coolers on an angle will aid in shifting the air to one area where it can be better extracted. You can also "cheat" the internal dividers to purge air from early chambers to the outbound chamber - there is a slight pressure differential from high to low as you move from the inlet to the outlet, so any bleed passage you cut will move air towards the outlet side...
you might be chasing the wrong demon.
post your water flow and let's go from there.
MC
08-12-2009, 09:39 AM
#6
Platinum Member
Platinum Member
on your motors, is it possible that the places on the block you are taking and returning oil from the cooler could possibly be on the same circuit, and thus allowing oil to partially bypass the cooler? Some BBCs need to add a restrictor in the main supply to keep this from happening.
I'm not looking at an oil flow diagram of your motors, and I don't know where you are taking and returning the oil, but this is something that has bitten people before..
bypass springs can also play a role...
I'm not looking at an oil flow diagram of your motors, and I don't know where you are taking and returning the oil, but this is something that has bitten people before..
bypass springs can also play a role...
08-12-2009, 01:13 PM
#7
Registered
Thread Starter
OK here goes;
Oil is run through Eickert/Hardin filter(HP6)/thermostat mounts. I run an external Aivaid oil pump and plum it directly into the old Filter mount with the Aiviad supplied adapter. It is the only way in. Even though it is a 14 qt. wet sump pan, everything is external.
Water; in from the sportmaster shorties, Into the MM strainers through a 6" PS cooler then into the the teague oil cooler. Then to the Eickert/hardin raw water pump then on to the coolant heat exchanger then out to the Stellings headers. I essentially followed the layout from Cigarette but with everything very upsized. I got rid of a lot of extraneous hose in the process.
All raw water is 1 1/4" ID. All oil is 12AN and all coolant is 16AN.
Oil runs 220-230 at cruise and moderate speeds, RPM from 3500 to 4500. Going up in rpm gradually brings oil temps up to 270 sometimes 280 on long hard runs (5500-6200rpm). I run Mobil V-twin oil.
When oil gets that hot, I back off to 3500 to 4000 rpm and it rapidly drops back down to 220 to 230.
Hope I got all the variables you asked for.
Oil is run through Eickert/Hardin filter(HP6)/thermostat mounts. I run an external Aivaid oil pump and plum it directly into the old Filter mount with the Aiviad supplied adapter. It is the only way in. Even though it is a 14 qt. wet sump pan, everything is external.
Water; in from the sportmaster shorties, Into the MM strainers through a 6" PS cooler then into the the teague oil cooler. Then to the Eickert/hardin raw water pump then on to the coolant heat exchanger then out to the Stellings headers. I essentially followed the layout from Cigarette but with everything very upsized. I got rid of a lot of extraneous hose in the process.
All raw water is 1 1/4" ID. All oil is 12AN and all coolant is 16AN.
Oil runs 220-230 at cruise and moderate speeds, RPM from 3500 to 4500. Going up in rpm gradually brings oil temps up to 270 sometimes 280 on long hard runs (5500-6200rpm). I run Mobil V-twin oil.
When oil gets that hot, I back off to 3500 to 4000 rpm and it rapidly drops back down to 220 to 230.
Hope I got all the variables you asked for.
08-12-2009, 01:28 PM
#8
Registered
Thread Starter
Oh yeah,
Strainers load from the top, exit from the bottom.
Both heat exchangers are what I believe are called a double pass. In and out on the same end, making a 180 turn on the other end.
.
Strainers load from the top, exit from the bottom.
Both heat exchangers are what I believe are called a double pass. In and out on the same end, making a 180 turn on the other end.
.
Last edited by 2112; 08-12-2009 at 02:38 PM. Reason: More info
08-12-2009, 06:10 PM
#9
Platinum Member
Platinum Member
good config on the strainers. if you do put an air bleed on the top of the strainer, be sure to put a spring loaded checkvalve in line with it so you don't suck any air into the cooling system at idle.
With the cooling water layout you describe, i'm gonna say that air in the cooler is not going to be a huge part of the problem. If you CAN, it would be a little helpful to angle the cooler so that the in/out end is higher than the closed end at running speeds, and you may still want to drill an air bleed hole (1/8" diam) between the in/out divider beneath the cap. This will ensure any air passes straight from the inlet side to the outlet side without collecting in the cooler anywhere.
Now, I'm still fixated on your oil system.
See if this is right:
Oil is pulled thru a "normal" pickup in a wetsump pan.
It passes thru the old oil pump housing, and to the factory oil filter boss on the block? (is the original oil pump there, does it have rotors in it? is it replaced by an adapter and long pickup?)
Okay, then you have an aviaid adapter screwed onto the oil filter boss and it sends oil OUT to the external pump.
It goes from the external pump to the Hardin filter/thermostat mount.
It loops out thru the cooler and back to the mount.
It leaves the mount and goes back to the aviaid adapter on the filter boss on the block.
Is this correct?
Where is your oil pressure regulator? Are you using the one in the engine block filter boss or are you using an external one?
I'm still wondering if excess pressure is being diverted somewhere that keeps some of it from flowing thru the cooler.
WHERE are you taking your oil temp reading? Where is your sender? I'd love to see what the outlet temp is of the oil right when it leaves the cooler, in comparison to the pan temp.
With the cooling water layout you describe, i'm gonna say that air in the cooler is not going to be a huge part of the problem. If you CAN, it would be a little helpful to angle the cooler so that the in/out end is higher than the closed end at running speeds, and you may still want to drill an air bleed hole (1/8" diam) between the in/out divider beneath the cap. This will ensure any air passes straight from the inlet side to the outlet side without collecting in the cooler anywhere.
Now, I'm still fixated on your oil system.
See if this is right:
Oil is pulled thru a "normal" pickup in a wetsump pan.
It passes thru the old oil pump housing, and to the factory oil filter boss on the block? (is the original oil pump there, does it have rotors in it? is it replaced by an adapter and long pickup?)
Okay, then you have an aviaid adapter screwed onto the oil filter boss and it sends oil OUT to the external pump.
It goes from the external pump to the Hardin filter/thermostat mount.
It loops out thru the cooler and back to the mount.
It leaves the mount and goes back to the aviaid adapter on the filter boss on the block.
Is this correct?
Where is your oil pressure regulator? Are you using the one in the engine block filter boss or are you using an external one?
I'm still wondering if excess pressure is being diverted somewhere that keeps some of it from flowing thru the cooler.
WHERE are you taking your oil temp reading? Where is your sender? I'd love to see what the outlet temp is of the oil right when it leaves the cooler, in comparison to the pan temp.
08-12-2009, 06:25 PM
#10
Platinum Member
Platinum Member
IF all of the oil is coming directly from the pan, through the pump, through the filter/tstat, and looping thru the cooler, then back into the block gallery, then we go back to looking at a larger cooler.
Right now, I want to completely rule out that oil is being diverted somewhere before the cooler. I'm wondering it either a bypass in the filter/tstat is diverting oil from the cooler, or something between the pump and the filter/tstat is diverting oil and keeping it from going thru the cooler.
In a perfect world, you would run pickup directly to pump. Pump directly to filter. Filter directly to tstat. The tstat would direct oil either thru the cooler or to a bypass line that tees back on the other side of the cooler. Then you go from the junction (tee) directly to the pressure regulator. 65psi oil is fed to the block gallery, and any excess oil is dumped back into the pan. The block has all of the pressure reliefs or bypass springs plugged closed.
I'm not sure your system is functioning like this. Places for oil to be diverted: in the block, either at the filter boss or in a gallery. at the aviaid adapter. at the remote filter mount.
Right now, I want to completely rule out that oil is being diverted somewhere before the cooler. I'm wondering it either a bypass in the filter/tstat is diverting oil from the cooler, or something between the pump and the filter/tstat is diverting oil and keeping it from going thru the cooler.
In a perfect world, you would run pickup directly to pump. Pump directly to filter. Filter directly to tstat. The tstat would direct oil either thru the cooler or to a bypass line that tees back on the other side of the cooler. Then you go from the junction (tee) directly to the pressure regulator. 65psi oil is fed to the block gallery, and any excess oil is dumped back into the pan. The block has all of the pressure reliefs or bypass springs plugged closed.
I'm not sure your system is functioning like this. Places for oil to be diverted: in the block, either at the filter boss or in a gallery. at the aviaid adapter. at the remote filter mount.
