radiator design

[danzim]

forgot to say that it is definitely all about ...

Compact Heat Exchangers by Kays & London.

Bit of headfuck at first but got all the theoretical info you need to build your models.

[jonno]

Danzim,

core size means next to nothing. My core for our '05 car is 190mm x 160mm and there is only 1.
The 1/3 thing is for standard road cars. It's for tests like the ones Aston Martin have been doing recently on the V8 Vantage ie going to the middle east and then drilling it through the desert in 40 deg heat at 150mph for hours on end. It's a worst case scenario but likely to happen since some oil sheikh will undoubtably pummel it through the desert at 150mph, and want his aston to work the next day. therefore you can go below 1/3 (I think i've mentioned either somewhere on this or another - possibly single engine arguement thread that the course only has WOT condition for 15% of a lap). Most load is produced at the WOT condition, hence most heat is created at WOT. Since you are only at WOT for 15% of the time, you can drop below the 1/3 max power bit.

Our fan pulls 4A which is fine with our CBR and a red top 8 across 4 coils. The WR has a poxy alternator (120W) and barely creates enough juice to run the coil, let alone anything else. 4A isn't to severe a draw though in the scheme of things, and i'd say a fan is essential. If nothing else it simplifies your airside calculation - if you know your core pressure drop you know exactly what your fan will pull through it (and exactly how many Amps it will draw in doing so). The fan weighs 778g, and the sh roud weighs less (it's just a thin fiberglass thing) so weight is no real issue there. By the way a well specced cooling system weighs under 6kg (including coolant and fan and shroud)
In terms of measuring bits and pieces on your dyno, a rotameter is easy enough to install to get a flow rate. Thermistors and pressure transducers are cheap as chips from RS, whack a few of those at various places (I'd strongly reccomend either side of your rad right at the inlet and outlet , and either side of the engine, again at inlet and outlet) and that is your coolant side pretty much sorted.
Most bike engines reject oil heat to the coolant,the CBR has a water jacket around the oil cooler on the front of the engine I assume most other formula student engines are a similar setup, unless you are running a dry sump I doubt any oil hoses have come into the equation, it will all be internal. Therefore if you are on a wet sump, the easiest way to monitor oil temp is to drill a thermistor into the sump, so it's sitting in the oil.

Hope that is of interest, gotta get back to studying for finals now.

[Rob Davies]

Jonno,

What fan are you running that weighs 778Kg? What is the quoted volume flow rate on that?

We have a 225 mm (largest we could fit in) SPAL suction fan that has 1100 m^3/hour air flow at 0mm H20 so it will be much less when pulling through the radiator. This fan weighs 1Kg and we reckon it was the best we could find, so just wondering if we were wrong - lol.

In my opinion fan flow rate is almost as important as size of radiator. From my rough calculations on our radiator, doubling air face velocity increases heat dissipation by 1.6.

We have the same battery problems as you guys so we went for a 240mm x 240mm x 32mm rad, actually bigger than we could fit as its angled 35 degrees. Angleing (upto a point....) has no noticable effect from our testing. Hopefully the fan wont be used much when we are moving.

See you at Bruntingthorpe....

Rob

[jonno]

If you look carefully you will see fanwas underlined in my previous post, as it is in this (it's linked to the manufacturers website: Kenlowe. We use the 8" model, which will give just over 1000 m^3/hr, although I imagine our pressure drops reduce that. No idea what it actually is off the top of my head though. Your fan sounds pretty similar to ours though, 200g is next to no difference really I wouldn't loose any sleep over it.

Increasing air flow massively increases heat rejection - validated in several physical tests I've done at Visteon over several cores. The change in heat rejection from a 2 l/sec to 10 l/sec airflow with a constant coolant flow rate is of the order of 5 times hence why I have always stressed sealing your fan shroud is critical. It really is one of the easiest ways to make your system more efficient. Switching the fan will save you loads of electricity, 4A is quite a drain on the singles! We're stuck with pretty much permanently running it, cos we get next to no ram air with the ground mount core.

[Daves]

For you metrically challenged (like me), that's about 588 CFM (1000 m^3/h).

[Rob Davies]

200g id say is quite a lot if its on an item of the car that can be reduced in weight without reducing factor of safety (too low) or performance. I would trade the 100m^3/hour for the 200 grammes but I wont lose sleep over it as I know there will be bits of our car much further from optimal than the fan (we also got a good deal on it) and it will still be an improvement over last years which is a success in its own right.

I guess im gonna sound stupid saying that as we will probably weigh in twice as much as delft but we have to start somewhere...

Catch can is such an example. We had a 150g hiking water bottle, I looked all over Iowa, USA when I was on holiday for an aluminium beer can but apparently they cant legally sell beer cans that big so I bought a steel 1 litre beer can at sainsburys weighing in at 100g then a teamate brings in a 50g shampoo bottle that gets soft at 120degrees C but still has some strength so our supervisor says to go with that. 200 grammes saved over the two catch cans there.

One of the main areas we tried to save weight on the cooling system was to reduced the tubing lengths. This decreased the volume of water in the tubes and hence weight. Could well have reduced the tube diameters somewhat but didnt want to mess with the flowrate. The fact that Jonnos rad is right next to the engine will really help this....

Here is a pic of our radiator shorud and fan:

http://pg.photos.yahoo.com/ph/ssdav9...&.dnm=a999.jpg

Can you tell im bored of exams and just want to get into building the car ( I cant get it out of my mind even though I should be concentrating on exams).

Jonno, are you going to the IMechE driver training on 16th June?? We are taking ten drivers (nearly all our team) but unfortunately we will be taking last years car as we will never be ready in time.

Laters, Rob

[kreuk]

DOes someone has any idea how to find the max. power produced from engine? will it be the same with motorcycle specs?

[Daves]

You can assume it is higher than the actual work you are outputting to the crankshaft because some parts rob power (alternator & water pump). Therefore, you could probably estimate that the stock motorcycle max power is near your maximum engine power.

[kreuk]

Compact Heat Exchangers by Kays and London.
Ntu=A*U/Cmin
Eff=[Cc*(Tc,out-Tc,in)]/[Cmin*(Th,in-Tc,in)]
where R=Cmin/Cmax
Eff=f(R,Ntu), if you can find a relation for unmixed crossflow and solve for Ntu, you should then be able to solve for the heat transfer cooeficients


I just found an SAE paper relating temperature and flowrate changes to Specific Disipation. There may be some helpful equations in there for you.here is the link

Ya..but how do u deal with the area since that what we're designing for?

[BeaverGuy]

Originally posted by kreuk:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Compact Heat Exchangers by Kays and London.
Ntu=A*U/Cmin
Eff=[Cc*(Tc,out-Tc,in)]/[Cmin*(Th,in-Tc,in)]
where R=Cmin/Cmax
Eff=f(R,Ntu), if you can find a relation for unmixed crossflow and solve for Ntu, you should then be able to solve for the heat transfer cooeficients


I just found an SAE paper relating temperature and flowrate changes to Specific Disipation. There may be some helpful equations in there for you.here is the link

Ya..but how do u deal with the area since that what we're designing for? </div></BLOCKQUOTE>

That looks like a post I originally made so I'm going to respond. The reference I was making was for a situation in which the the area and heat transfer data was allready given. They simply wanted the heat transfer coefficients.

However, if you want to find the transfer area, you start with the same equations and work backwards. A good reference for this would again be Kays and London's Compact Heat Exchangers. In the examples they make some assumptions about the overall heat transfer coefficient and log mean temperature difference. This means that to achieve good final value you may need to iterate. This makes a computer a very useful tool for this method. I did this innitially two years ago. However, I haven't been able to verify the programs I wrote with physical testing. If you would like more information feel free to PM me.