fitting a radiator at an angle

[02GF74]

Don't even ask why .... but I am looking to fit a radiator at an angle from the vertical, i.e. sloping from its normal position.

Is there a maximum angle beyond with the radiator is no longer working efficiently?

The vertical surface area decreases so is there any data on how cooling and air flow is affected according to the radiator angle?

Or is it simply such a bad idea that I should forget consider it?

I do not know if what I plan will be possible nor what sort of angle will result, I'd be very surprised if it is more than 45 degrees, probably about closer to 20.

[white90]

is this related to the kit car?

[02GF74]

is this related to the kit car?

yep, but no prizes though. IMO the fan/radiator set up is not the best.

[Les Brock]

yep, but no prizes though. IMO the fan/radiator set up is not the best.

Anything can be done with copper pipe if you try hard enough

[pigster]

Anything can be done with copper pipe if you try hard enough

Yeah 'cos Les can make any vehicle over heat and run badly..

[02GF74]

Anything can be done with copper pipe if you try hard enough

Les, copper tube is so yesterday

Work in progress is to replace the indicator mounts on the nose cone by aluminium tubing, no guesses what material they were made from.

[Diff]

Don't even ask why .... but I am looking to fit a radiator at an angle from the vertical, i.e. sloping from its normal position.

Is there a maximum angle beyond with the radiator is no longer working efficiently?

The vertical surface area decreases so is there any data on how cooling and air flow is affected according to the radiator angle?

Or is it simply such a bad idea that I should forget consider it?

I do not know if what I plan will be possible nor what sort of angle will result, I'd be very surprised if it is more than 45 degrees, probably about closer to 20.

You can lean a rad over until it is almost flat, and it will still work.

To some extent the efficiency will fall if you lean it over a lot. There are plenty of factors which will affect how efficient it is. If you would normally be relying on cold air blowing horizontally through the rad fins as you go along to cool the rad, then this may become a problem with a leant over rad. Some simple air ducting may help here. An electrical fan will be very important when the air flow is slow.

Are you sure the current set up in the car is no good? My advice would be... 'if it ain't broke, don't fix it'.

Regards,

Diff

[02GF74]

You can lean a rad over until it is almost flat, and it will still work.

Regards,

Diff

I should have pointed out that I want to take advantage of forced air cooling rather than rely on fans.

I guess wit hte right sort of ductiing even a horizontally mounted rad would work, after all doesn't the hummer have a horizontal rad, albeit fan cooled?

Are you sure the current set up in the car is no good? My advice would be... 'if it ain't broke, don't fix it'.

where is the fun in that? idle hands etc...

[Diff]

I should have pointed out that I want to take advantage of forced air cooling rather than rely on fans.

I guess wit hte right sort of ductiing even a horizontally mounted rad would work, after all doesn't the hummer have a horizontal rad, albeit fan cooled?

where is the fun in that? idle hands etc...

You should always 'try' to keep it as upright as you can within the confines of your usable space though. This is because you want the hot inlet at the top and the cold outlet at the bottom, you want the air to flow through the rad as cleanly as possible, you need any air in the water to be able to rise to the top, and you don't want to 'trap' hot air beneath the angle of the rad when air flow is low. As I said before, you will need an electric fan to come on when air speed is low, because hot air radiating from the back/underside of the rad will be trying to rise back through the rad(thereby heating the rad up again) if there is no/little air flow to take the hot air away.

Regards,

Diff

[jeremy996]

You can place a radiator at almost any angle and it will still work. The things that can go wrong and are usually easier if the radiator is conventionally vertical are:-

Getting the airflow to strike the matrix cleanly - at 90 degrees, without too much turbulence. Turbulent air is slow and heat transfer rates suffer at most sensible speeds.

Getting any trapped air out - water is a good conducter of heat, air is rubbish, even without airlocks, air in the system will seriously compromise the cooling systems ability to get rid of heat.

If the cooling system is fully pumped, the radiator will not need convection to work OK, i.e. the radiator can be mounted horizontally, (but it will be much more sensitive to air in the system).

Most aircraft and racing cars will use rads at all kinds of silly angles, but they will always try to ensure that the airflow is ducted through the matrix as smoothly as possible. They often have very elaborate systems for purging the air from the system.

My Imp Rallye had a huge front mounted radiator from a transit van, laid back to fit under the bonnet. There was a pacet fan set to suck air through the matrix and the exhaust air went under the vehicle. This was a brute force solution as there was little positive ram air from the heater box. The most elegant solution for an Imp I saw was a custom rad in the heater box venting into the wheel arches - the car had no fan and when moving, the ram air was sufficient. However my solution was £40, scrap rad and a scrap fan - his solution was nearer £500 back in 1980!

I have seen some real bodges on some kit cars, but so long as there is enough volume in the system and there is clean airflow through a generous matrix, you can get away with murder. With a racing car, the designer is trying to minimise size, weight and drag, so there is where you can see how to do it correctly. Ideally, you want a small intake, leading smoothly to a larger radiator, (to reduce airspeed), leading to a larger, in cross sectonal area air exhaust, (to minimise drag). Frank Costin's treatment of the early Lotus cars shows a good solution - see how small the intake area can be, if the radiators are ducted and the exhaust is properly designed.

[Hybrid_From_Hell]

The info that nobody seems to have added here is about the airflow.

The "Angle" of the rad is almost irrelevent, providing the top ans bottom hoses are exactly that, and any blled valve or top scrw is at the higest point, the key tho is to have some cowling and to ENSURE that ALL the air goes therough the rad and not past it each side over the top and underneath.

If you blank off any route other than through the rad iteserlf then tilting it is fine, but frankly I have seen expensive whizzy ali mounted normally but with no cowling and gaps on the sises / top / bottom etc and overheating probs....

Nige

[BogMonster]

I should have pointed out that I want to take advantage of forced air cooling rather than rely on fans.

Damn

There goes the opportunity for an obvious witticism that if you have to mount the viscous fan (and therefore engine, gearbox, t-box...) at 45 degrees then 1) it'll be a bit top heavy and 2) you might have problems with propshafts binding a bit

[02GF74]

cheers; there have been some useful and helpful responses.

I am intrigued by this one though:

.... Ideally, you want a small intake, leading smoothly to a larger radiator, (to reduce airspeed), leading to a larger, in cross sectonal area air exhaust, (to minimise drag). Frank Costin's treatment of the early Lotus cars shows a good solution - see how small the intake area can be, if the radiators are ducted and the exhaust is properly designed.

especially the bit about increasing the cross sectional area followed by decreasing - something to do with fluid flow speeds and air pressure ... will need to think and read up about this. slowing the air as it passes trhough the radiator is top idea as it allows more time for the heat to be transferred to the air. Interesting, as up to know, certainly when I was playing with the sereis 3 rad for v8 in my lightweight, my ideas were to increase the frontal area (which I didn't do) by moving the cowling in front of the radiator. My solution ended up puting an additional sucker fan behind the rad to help shift the air.

The info that nobody seems to have added here is about the airflow.

The "Angle" of the rad is almost irrelevent,

Nige

I would agree but by adding the caveat that the flow of air should strike the radiator at right angles and be as smooth as possible, i.e. not go through sharp angles. A big right angle vent like those used for air con could be used to turn the air though 90 degrees and similarly after the radiator.

Will need to give the cowling in front of the radiator some more thought.

[dollythelw]

You can run high speed, low pressure air at 90 degrees to the fins (using the resultant pressure differential to draw through and exhaust low speed, high pressure air through the rad), if you want an example look at a Honda VTR.

save the ram air for the induction side of life (although setting up an injection system to make full use of it is real pain), we had a lot of fun doing this on the race bikes

[Turbocharger]

slowing the air as it passes trhough the radiator is top idea as it allows more time for the heat to be transferred to the air.

Nope, you want high airflow to increase the heat transferred - you're not trying to heat a small volume of air, you're trying to shift a lot of heat. The heat transfer coefficient will be boosted by higher flow. If you're interested, higher speeds boost the Reynolds number which means that term dominates the Nusselt number term in the HTC.

When you're ducting a radiator, the frontal area doesn't need to be large at higher speeds but remember that you will never see peak efficiency with a rad which is ducted both sides - you'll never match the flows across the full speed range. Much better to have it free-ducted or ducted-free unless you want to spend lots of time with a calculator or CFD software!

[Ex Member]

With all due respect to what has been said........this is not a race car.

For this application, the worst case cooling duty is at slow speed and high power output when off road. The air flow must come from the fan in this case. All that is important is that the fan is big enough AND is pulling/pushing as effieciently as possible through the radiator. Many high horsepower rig run the rad in the back where little or no forced airflow is available (this keeps them from plugging with mud).

Because the rads are sized for this low speed condition, they are way oversized for high power road use where much more airflow is available. If you do not believe me, compare a car rad of the same power level and you will see it is much smaller.

[Turbocharger]

Red - spot on and I agree totally (that's why there's a raging rad muff market for LRs) but I think 02's talking about a Caterham project car.

[02GF74]

Nope, you want high airflow to increase the heat transferred - you're not trying to heat a small volume of air, you're trying to shift a lot of heat. The heat transfer coefficient will be boosted by higher flow. If you're interested, higher speeds boost the Reynolds number which means that term dominates the Nusselt number term in the HTC.

I remeber nuxxelt, reynolds and prandtl numbers but that is many years ago.

I was visualising that the longer the air is in contact with the fins, the more heat is trasnfered i.e. slow air moving through the radiator is better; sounds from what you saying I want to shift as much air as quickl as is possible.

I doubt my application is that critical (lotus 7 kit car) that I need to worry too mcuh about it as long as there is air flow ducted in a sensible way.