Radiator Sizing? 3

[cymeryss]

I am aware that this is a very broad question, but was wondering if there is an approximate method to evaluating a needed radiator size? For example, lets take a 200hp, turbocharged engine, 1.8L, 4cyl motor. I know there are lots of variables in this problem such as the coolant flow rate, air speed, radiator heat transfer coefficient, etc, and detailed analysis would be needed to properly size the radiator. I am looking basically for a worst case scenario. First of all what would be a good assumption for how much heat is dissipated to the coolant from the IC engine. As I read, that would be about 1/3 of total power, which assuming 1/4 only goes down to the groud, that would mean almost 200kW gets transfered to the coolant. Now, at steady state, are radiators sized to cope with this condition or some precentage of that? To start would two flow conditions be sufficient, for example at idle, and at max power output, in order to size the radiator? What is a typical heat transfer coefficient, U for an automotive radiator of average size 3.0L? I found it very dificlut to find any information, data, U, effectiveness, etc on automotive radiators, if anybody can provide me with a good source, website, book for this type of data that would be great. Thanks for reading.

Best Regards,

Cymeryss

 

[Chumley]

You really don't have to reinvent/redesign the wheel. Water cooled cars with radiators have been in existance for over 100 years. Just go and look at a similar sized car with a similar sized engine. (engineers have all ready solved the problem for you) What size radiator is in there? There's your answer.

Chumley

 

[andyv8]

For a high output n/a 3.0L V6, here's a heat balance (based on dyno data). As you can see, heat to coolant is nearer 1/4 of ouput power. Radiators are normally sized to achieve steady state cooling at maximum torque, but this is not very realistic unless you are towing.
I don't have any info on heat transfer of radiators I'm afraid.

Andy


Engine Heat to Exhaust Coolant Oil Brake Other
Speed Fuel
7080 100% See Other 7% 2% 27% 64%
7019 100% See Other 7% 2% 27% 63%
6959 100% See Other 8% 4% 27% 61%
6707 100% See Other 8% 4% 27% 61%
6457 100% See Other 8% 4% 28% 60%
6205 100% See Other 8% 4% 28% 60%
5955 100% See Other 9% 4% 29% 59%
5454 100% See Other 9% 4% 29% 57%
4951 100% See Other 8% 3% 30% 58%
4649 100% See Other 9% 4% 30% 58%
4600 100% See Other 9% 4% 30% 57%
4550 100% See Other 9% 3% 30% 57%
4450 100% See Other 9% 3% 29% 59%
3949 100% See Other 9% 4% 28% 59%
3450 100% See Other 10% 4% 31% 55%
2949 100% See Other 10% 4% 30% 56%
2444 100% See Other 12% 4% 32% 51%

 

[GregLocock]

Andyv8's post is relevant and I gave it a star. The reason I thought it was relevant was that it gave real numbers for the proportion of the energy going into the coolant, which I thought was probably a handy number if you are designing a radiator.

Cheers

Greg Locock

 

[SBBlue]

Just out of curiosity. . . . . .

has anyone done any work figuring out how over designing the coolant system decreases fuel efficiency? For example -- If you design the radiator surface area for the absolute highest thermal load (towing a trailer up a hill at 85 mph) the radiator cross sectional area will cost fuel efficiency at lower loads where that much area is not needed.

The same thing could be said about the water pump; designed to pump the amount of coolant necessary for cooling at maximal loads, resulting in excess power being used to generate a coolant flow that's too high most of the time.

The only area that I can see this being addressed is in the design of cooling fans and clutches.

 

[patprimmer]

SBBlue

Davies Craig make a plastic, electrically driven water pump with a microprocessor controlled electric motor that senses water temperature, and increases pump speed according to temperature.

The air duct to the radiator could also be thermostatically controlled to adjust air flow, and if correctly designed, could significantly reduce the drag caused by the duct when the minimum airflow was required.

I don't know if this is being done, just that it must be possible.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bazeleur]

From what I understand the Davies Craig water pump has some problems. Autospeed (

http://www.autospeed.com)

tested one, and DC were so displeased with the results they threatened legal action, or something along those lines... You wouldn't happen to have any personal or anecdotal experience with them would you?

 

[patprimmer]

No, But I think I saw somewhere that they are supplied to Jaguar as OEM on at least one model. It might be a rumour, as I cannot recall the source of the info.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[andyv8]

Just thought that if cymeryss didn't really know anything about engines, then knowing % heat rejection to coolant for a modern engine may be of use. (Thanks for the star Greg !)

Andy

 

[cymeryss]

Thanks a lot Andy. When in comes to Davies Craig electric pumps, I was going to use one on my project, but the head pressure on the pump is really low, and just did not suit my application. I don't know what the problem with the pump was, but maybe because of fouling the flow rates are reduced and that is what causes them not to perform. Does anybody know what is a typical pressure drop through an average size engine, such as a 3.0L V6?

Cymeryss

 

[andyv8]

Didn't measure the pressure drops, but flow rates were as follows for the V6:
EngWatP WatinT WatoutT Wat_flo
RPM Bar(g) øC øC l/min
7080 0.69 89 94.5 142.5
7019 0.73 91.5 97.4 140.9
6959 0.78 93.6 99.7 140
6707 0.81 93.6 99.8 140.8
6457 0.75 89.2 95 144.3
6205 0.78 92.8 98.8 139
5955 0.77 90.3 96.5 140.2
5454 0.73 87.2 93.5 131.9
4951 0.77 93 98.9 120.7
4649 0.78 91.1 97.2 114.8
4600 0.78 90.3 96.3 114.1
4550 0.78 89.5 95.6 112.8
4450 0.77 88.9 95 110.7
3949 0.76 88.1 94.3 99.6
3450 0.75 89.9 95.6 86.9
2949 0.76 90.6 96.7 73.2
2444 0.77 90.6 97.3 59.3
1939 0.78 90.1 97.6 46.4
1438 0.78 89.1 97.7 34.8
1039 0.79 87.5 97.7 25.7

Based on some other data for a 2.0L I4, I've got pressure drops of ~45kPa&105L/min@5000rpm and 55kPa&135L/min@6000rpm.


Andy

 

[cymeryss]

Hey, all my thanks to you Andy. This is great info and definitely very insightful information which I was exactly looking for.