Cooling system design

[Eureka]

Hi guys,
I am presently working on cooling system. I want to know that is electrical thermostat beneficial or the mechanical thermostat.. and should we make it at home ??

Also, please tell me that if we want to control the coolant flow rate in the engine(acc. to the RPM), should we use a pump in the 'outlet' or the 'inlet' of the engine ??

[Adambomb]

According to some, a well-engineered cooling system doesn't need a thermostat at all. Most dirtbikes don't have them. I have absolutely zero knowledge of electric thermostats, and frankly they don't even sound interesting. Adding unnecessary electrical control to a component is a great way to ensure poor reliability (or at least give old Murphy another chance to wreck your day).

Could you make a thermostat at home? I suppose, just like you could make bolts at home, make tires at home, etc.

Why would you want to control the coolant flow rate to the engine?

[moose]

Well you may want an electric temperature sensor, but probably a mechanical thermostat since if you're asking its probably not worth the additional complexity.

[Eureka]

Actually , What I was asking is since in Mechanical Thermostat we have wax which melts (thus opening the valve) when required temp. of coolant is reached but I have read somewhere that :
Wax melting is not reliable and thus It may result in overheating of engine.. And in Electrical, Its purely based on the circuit completion..
So which should we opt for ????

@ Adambomb : Now since at different RPMs we have different HP , hence the heat load therefore suppose if the HP is high and we have set our coolant flow rate according to the average HP then this will definitely move towards overheating.. won't it ??
So, if we could increase the coolant flow rate by using a pump either in the Inlet/outlet, it will do the job..

Please share your views.. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[ZAMR]

Originally posted by Eureka:
Actually , What I was asking is since in Mechanical Thermostat we have wax which melts (thus opening the valve) when required temp. of coolant is reached but I have read somewhere that :
Wax melting is not reliable and thus It may result in overheating of engine.. And in Electrical, Its purely based on the circuit completion..
So which should we opt for ????

@ Adambomb : Now since at different RPMs we have different HP , hence the heat load therefore suppose if the HP is high and we have set our coolant flow rate according to the average HP then this will definitely move towards overheating.. won't it ??
So, if we could increase the coolant flow rate by using a pump either in the Inlet/outlet, it will do the job..

Please share your views.. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Your engine has a mechanically driven water pump inside it already.

You don't need a thermostat.

[Adambomb]

Originally posted by ZAMR:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Eureka:
Actually , What I was asking is since in Mechanical Thermostat we have wax which melts (thus opening the valve) when required temp. of coolant is reached but I have read somewhere that :
Wax melting is not reliable and thus It may result in overheating of engine.. And in Electrical, Its purely based on the circuit completion..
So which should we opt for ????

@ Adambomb : Now since at different RPMs we have different HP , hence the heat load therefore suppose if the HP is high and we have set our coolant flow rate according to the average HP then this will definitely move towards overheating.. won't it ??
So, if we could increase the coolant flow rate by using a pump either in the Inlet/outlet, it will do the job..

Please share your views.. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Your engine has a mechanically driven water pump inside it already.

You don't need a thermostat. </div></BLOCKQUOTE>

+1

[Ockham]

Grape Ape Racing has a white paper which nicely explains the issues with modifying cooling systems. The short version is that they're pretty easy to make if you just want a working cooling system, but getting ideal performance out of one is tricky.

http://www.grapeaperacing.com/tech/coolingsystems.pdf

If you want electronic cooling control, I'd suggest running an electric coolant pump (such as a Davies Craig) and fan switched by programmed logic reacting to coolant temperature sensor values. Most ECUs can do this.

Be careful with deleting the thermostat. On some engines (mainly old iron-block, high-displacement types) the thermostat's flow restriction is a critical system component. When using electric cooling, blocking open the stock mechanical thermostat is a common practice. That maintains the stock restriction, but allows the electric pump to work just fine.

[Eureka]

@ Ockham : Thank you very much for ur views and the link. Since we r using ECU therefore we will surely use a temperature sensor.

[Wesley]

Considering that "unreliable wax" is used in basically every production car since 1940, I wouldn't worry about it causing too many problems.

I don't know which iron block high displacement engines Ockham is talking about, but a thermostat isn't a critical piece in a racing engine. It's useful for a daily driver that is driven while the engine is cold.

[Adambomb]

True...if you need a thermostat to get your engine to temp, then your cooling system is too big!

Figure it this way: You most likely have an electric cooling fan, giving you some level of thermostatic control over the engine. Given the fact that formula cars generally don't get driven in the winter (unless you're Helsinki...I'd link the video but it would take too long to get approved, I highly recommend it though), you have a relatively small range of temperatures to run in. Therefore your engine should be able to get to temperature without a thermostat.

Some sportbike engines have thermostats built in, in which case it really wouldn't hurt to leave it in place. Yes, it's mechanical, but it's probably the single most reliable component on the car. That would be the simplest, most reliable solution, and would allow you to be safe from overheating with a slightly oversized radiator. Just like Wesley said, "old design" mechanical thermostats are good enough for basically every production car since 1940. Just because a certain design has been around for a long time doesn't mean it's bad. OHC engines have been around since about 1920 (I'm almost thinking longer than pushrod engines? Pretty much everything else in those days were flatheads), and that's still the dominant configuration in IC engines today.

So with not only an electric fan, but also (possibly) a thermostat, it makes no sense to try to get an additional level of control by controlling water pump flow. If nothing else you'll surely get hot spots in the head if coolant isn't constantly flowing. I have never heard of any application that used an external control system for the water pump (even the electric systems are generally just switched on when running), nor can I really imagine any need for such added complexity.

I guess it all depends on what you consider "better engineered:" something that works adequately with a minimum number of components, or a complex system with "lots of innovation," that addresses a lot of problems that either don't exist, shouldn't exist, or don't have a large impact in the grand scheme of things.

~~~~~~~~~~~

I think I know somewhat of what Ockham is talking about with the thermostats, a lot of demolition derby guys will just yank the "guts" out of a thermostat before running. But that's generally just with old school low-output stock engines.

[Ockham]

I'm mainly talking about irrelevant engines, as far as this discussion goes. Part of the reason carb tuning can be such a pain is that an old, massive iron engine (think Dodge 440ci, BBC's above 500ci, etc.) takes an age to heat up, so you don't want to delete the thermostat, even with electric cooling. Unfortunately, most of my experience is with big American motors; FSAE engines have total displacements roughly equal to my evolving definition of a cylinder, so pardon me if I confused the issue.

[Adambomb]

Sort of reminds me of the setup I've got in my '87 Firebird. I plugged the internal coolant bypass at the water pump and drilled bypass holes in the thermostat. That way instead of always bypassing a certain amount of coolant back through the engine, it always bypasses that small amount through the radiator.

It no longer gets above 200 deg., but also doesn't stay warm on the highway if it's below freezing (even with a 185 deg. thermostat). Of course that's not a big deal since I refuse to drive it in salt (which is pretty much constantly present around here if it's below freezing), and if there's the slightest bit of snow on the ground it tends to get stuck anyway.

[Wesley]

Adambomb: On my '67 Mustang (302ci) I just found a thermostat housing with a bypass on it. I thought most cars had those to keep the pump from cavitating. I also got a high-flow thermostat.

Ockham - I cut my engine teeth on Ford smallblocks, so I know what you mean about iron taking a lot to heat up. I've got an electric fan on my current one, and it barely cools in traffic but overcools on the highway, even with a thermostat. However on a race car I'd size the components a little more appropriately instead of playing darts with the Summit catalog like I did in high school.

But if I were racing one I wouldn't have a thermostat. I've argued with a lot of the guys on a Ford forum I'm on about restrictors (just replace the thermostat with a washer basically) and that the extra block pressure can easily be achieved with a higher radiator cap, but those old-school guys don't like to hear things to the contrary.

Adambomb - the crossover in the intake is more to preheat your manifold is to improve fuel atomization so it runs better in cold weather. At least it is on the Fords. Most performance intakes delete this part, along with the exhaust heat riser that accomplishes the same task.

[Adambomb]

Intake crossover? I don't need no stinking intake crossover! And true, they're mainly used on wet-flow manifolds to prevent fuel puddling. A lot of them also run their EGR passages under the plenum to make it even more toasty. But then again most of those engines don't even have 8:1 compression... I'm about to order an Edelbrock RPM air gap manifold for the 360 Magnum in my Dakota, pretty stoked about it, it even goes so far as to separate the plenum from the lifter valley.

Actually on the Firebird I wasn't referring to the intake crossover, but the little port underneath one of the water pump ports (don't remember if it was inlet or outlet, I'm a bit tired now so I'm sure my dyslexia would prevent me from giving a correct answer now) on a small block Chevy. That one's an internal bypass. Although I have seen the ones in the water neck; in fact, right now I have a small block Ford water neck on a Buick V6 in my Busan (Buick powered Nissan pickup). For some reason the TPI (MPFI) system has coolant lines running through the throttle body; those have also long since been disconnected. Seems a bit less detonation happy now, gee I wonder why? http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Ockham]

A point, gentlemen; all of these issues and oddities can be neatly sidestepped with modern aluminum blocks and multi-port fuel injection. http://fsae.com/groupee_common/emoticons/icon_wink.gif No weird mechanical solutions (advance weights, coolant crossovers, etc.) to tuning problems - just programming.

[Eureka]

Hi thanks for all your views guys

I need to ask one thing that what different positions of mounting of radiator on the car do we have and out of them which one is best to place upon the radiator ??

Waiting for your replies http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Ockham]

Strictly speaking, you can mount the radiator anywhere it receives enough air flow. You should know what "enough" means from your mass flow calculations. If you felt like fourteen feet of coolant hoses, you could mount the radiator at the front, but the judges (and any sane engineer) would tear you a new one. Typical mounting locations are alongside the main roll hoop or at the rear, but the right answer depends on your packaging situation.

[TorqueWrench]

AS Ockham said, radiator location has a lot to do with compromising mass flow rate for other things.

Sticking the radiators in sidepods is the standard answer because it keeps them low to the ground and keeps the polar moment of inertia of the car to a minimum. You just have to make sure you size the radiators correctly, but I have heard a lot of people just use the stock bike radiators if all else fails. They are normally over-sized from what I know in our application after ducting.

I have also seen people mount them to the back of the car with a duct from behind the drivers head. I always thought it would be slick to take advantage of how leaned back our drivers are and run a radiator right under the seat fed by NACA ducts.

[Eureka]

I have seen many universities mounting their radiator on the side pot. Now I have two questions arising from this:

1) There are two possibilities to put the radiator... Either at an acute angle or an obtuse angle. The obtuse angle will have less drag while in acute angle the drag will be more.
Also mass flow rate will also be different in the twos. Please suggest which of the two angles would be more efficient ??

2) The radiators mounting affects the center of gravity position. And we want it to have as low as possible so for finding the C.O.G. how much wieght should we consider of the radiators. I know it varies with the radiator but wat I am asking is how much weight of the coolant and of all that extra stuff should we consider ??

[Jersey Tom]

I have also seen people mount them to the back of the car with a duct from behind the drivers head. I always thought it would be slick to take advantage of how leaned back our drivers are and run a radiator right under the seat fed by NACA ducts.

Some of the Colorado cars had something like this. Radiator right behind the seat, fed by a duct on the side of the car. Air exits the rad then flows over the headers and engine. Mixed results, but it's doable.

Your sig... did the UB team get canned?

[Ockham]

Personally, I wouldn't use dual radiators. Radiators are less efficient near the edges of the fin matrix, and dual radiators just increase the edge length with no core area improvement. As far as I can tell, the only reasons for dual side-mounted radiators is "that's how F1 does it," and aesthetics. Poor reasons for increasing the system's weight, cost, and complexity.

I like the idea of a single radiator mounted low on one side at an obtuse angle to the vehicle's longitudinal axis, with the fan pulling air toward the frame. The radiator gets the coolest possible air, the fan nestles nicely behind it, and the acute angle makes the mount shorter, lighter, and stronger. I saw one team mount a long, narrow radiator at an acute angle to the ground, which was a neat way to get a little ground effect vacuum and keep the mass close to the CG.

[TorqueWrench]

Originally posted by Jersey Tom:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I have also seen people mount them to the back of the car with a duct from behind the drivers head. I always thought it would be slick to take advantage of how leaned back our drivers are and run a radiator right under the seat fed by NACA ducts.

Some of the Colorado cars had something like this. Radiator right behind the seat, fed by a duct on the side of the car. Air exits the rad then flows over the headers and engine. Mixed results, but it's doable.

Your sig... did the UB team get canned? </div></BLOCKQUOTE>

UB always ran an air cooled engine, so I thought it would be cool to stick the oil cooler there and duct the cooling that way. The design judges last time asked us if we had cooling problems and we said no. This last year....lets just say there was a reason the oil cooler was off a pickup.

Jersey Tom, you have a PM about the other question. Don't feel like de-railing a perfectly good thread.

[Adambomb]

I'd really like to mount the radiator behind/under the seat, and I remember seeing Colorado did that. We tried to in '08, but it was too hard to package in there with the single, since the engine and exhaust ends up pretty close to the driver's back. It could be done, but when it came down to the wire we just hung it off the side of the roll hoop simply because we couldn't make it work under the seat, and it was the only other reasonable place with good airflow.

[Wesley]

Dual radiators are typically used for packaging reasons - when you need a specific core size but don't have enough room for it. They may be less efficient, but they also offer a way to centralize mass and improve packaging.

And as for using these newfangled "computers," a PE-3 is in the plans for my '67. Carburetors are cool, but not my preference.

[Eureka]

Hey ... Thanks guys

1)But I have actually seen the pics of many universities mounting their radiator at an acute angle.. So I am getting quite confused since we have to settle out between the Drag and the mass airflow rate...

2)Can anybody tell me that since we should not cool engine oil in the radiator itself, thus we use oil coolers.. So How do we choose the oil cooler, where is it mounted and is there any separate and better way to cool the oil ???

[Wesley]

Well, there are generally two types of coolers, air-oil and water-oil, one cools the oil with ambient air, the other exchanges heat with engine coolant.

Air cooling offers a higher temperature gradient, so a potential for higher heat rejection, but oil-water is typically more compact and more easily packaged.

You can mount the oil cooler in front of the radiator, or in another duct, or just put a fan on it.

Choose an oil cooler the same way you chose a radiator - how much heat do you need to reject to keep it in the right operating range?

[L B0MB]

Hint: use the oil and water radiators from a stock 600cc bike, mount them in a side pod with a fan pulling air through and you're set. Forget about calculations, time is of the essence. That way you get a working cooling system and we don't have to continually reply to your "how do I..." questions http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Eureka]

Thanks guys,
But we have come into another problem that we are trying to decide the dimensions, surface area of the fins.... and in the formulae, we need the reynolds numbers. And in reynolds no. formula we have velocity term, so what should we take the velocity since we cant know it till the time we run it practically with the help of water pump !!!!

[Ockham]

I think there's a volume flow rate chart for the CBR600RR mechanical water pump floating around the forums. If you find that, and know the radiator inlet's ID, you can figure out the mass flow rate and fluid velocity. Alternately, if you have an electric water pump, the manufacturer should be able to tell you the volume flow rate, which should be nearly constant since most electric pumps run at a constant RPM.

[Wesley]

I would suggest you ask a few teams what their average speeds are on an FSAE course, then use some worst case numbers to do your calculations (or average case with an appropriate safety factor)

You might also find with whatever design you come up with you need more air than velocity supplies, and in that case you have to consider fans.

[Eureka]

Hey guys,

Can anybody please tell me that if we are using an MPFI engine with ECU and all that stuff, can we control the speed of the fan of the radiator (since we are using a coolant temperature sensor which is used to switch on/off the fan) ???
Also, if any university is doing such thing, Please tell me how do we do this ??

[Kirk Feldkamp]

I can't think of a DC automotive fan that has speed control. They're usually just cycled based on a temperature limit. There are PWM and CAN controlled water *pumps* that are being used these days to help reduce parasitic losses, but they're not exactly cheap. Plus, you have to have a controller to run them (aka extra weight). Either way, with the high load and rapidly changing conditions you'll see with one of these cars, that's probably an unnecessary complication. Frankly, if you can get a system to adequately cool your engine under all probable conditions without having to add too much weight, you're probably ahead of most of the pack. It's not always about being the best, but not sucking as much as other teams.

-Kirk

[Adambomb]

Originally posted by Kirk Feldkamp:
It's not always about being the best, but not sucking as much as other teams.

-Kirk

+100

[Simon Dingle]

+1 to kirk

We're thinking about doing it. We have a Motec M800 and they sell a little bit of ciruitry that changes the PWM output from the ECU to a proportional voltage output. I can't remember what it's called right now but it only weighs about 10g. We're using it to regulate the fuel pressure as it's lighter than a mechanical reg and it does multiple outputs.

I suspect that if we do it we'll find out that it's on max 90% of the time anyway...

[anand paul]

how do you calculate for the heat dissipated by the radiator.it is a cross flow heat exchanger , is it done by lmtd method or ntu method ??and wht various factors should be considered

[Wesley]

That's probably a question best answered by a late night with a textbook, or consultation with a professor. Most heat transfer professors are more than willing to help you understand calculations/methods when they realize you're actually APPLYING the things they are teaching in class.