scudderfish
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| posted on 30/6/13 at 10:06 AM |
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How much heat should a radiator remove?
If I'm feeding water into my radiator at 90+C, what sort of temperature should the water be coming out of it? How much heat should a radiator
be able to shed if it's doing a reasonable job (assuming good airflow through due to car movement or fans)?
Regards,
Dave
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PhillipM
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| posted on 30/6/13 at 10:37 AM |
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Depends entire on the speed/quality of airflow going over the rad, the rad sizing and the water flow rate through it.
However, rough rule of thumb for most cars, 20-30*c
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lewis
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| posted on 30/6/13 at 10:55 AM |
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Really? My MK (zetec 2.0l,alloy race rad) runs at about 90* in airflow & fan comes on @ 105* so 15* difference.
I am a driving god!..........sort of
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blakep82
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| posted on 30/6/13 at 11:57 AM |
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quote:
Originally posted by lewis
Really? My MK (zetec 2.0l,alloy race rad) runs at about 90* in airflow & fan comes on @ 105* so 15* difference.
Maybe, but the thermostat will close at certain temperatures to keep the temperature up to stop over cooling
Not sure what temperatures they tend to close at though.
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PhillipM
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| posted on 30/6/13 at 11:59 AM |
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quote:
Originally posted by lewis
Really? My MK (zetec 2.0l,alloy race rad) runs at about 90* in airflow & fan comes on @ 105* so 15* difference.
What does that have to do with the outlet water temps??
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Mr Whippy
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| posted on 30/6/13 at 02:11 PM |
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Bit of an odd question really, so long as the engine remains within the operating temp, what comes out is irrelevant. Why do you even want to know?
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britishtrident
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| posted on 30/6/13 at 03:08 PM |
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On the surface it seems a very simple question but really difficult to pin because of the effects of thermostat.
With a typical 88c thermostat the thermostat only starts to open at 88c and fully opens at 96c and will typically on a tintop will maintain the head
outlet temperature of 90 to 91c.
Recent engines tend to have the thermostat at the water pump inlet and have a huge amount of by-pass flow tend to maintain the temperature at water
pump inlet of about 88c
The only way to check if the rad has enough heat exchange capacity is to measure the inlet and outlet temperature with the thermostat in and then
repeat with the thermostat out. If the temperatures don't drop noticeably the then the rad is operating at close to capacity.
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matt_gsxr
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| posted on 30/6/13 at 03:42 PM |
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Interesting question. I think the water input vs output temperature approach is a tricky way of trying to estimate as it all depends on the water
flow-rate which generally we don't know.
What about the alternative approach, which is to estimate the airflow through the radiator and then use the heat capacity of air. From my measurements
the temperature increase of the air through my rad is about 35K.
Heat capacity of air is 0.0013 J/ml.K. Or 1300 J/K.cubic m
Area of polo rad is about 0.2 square meters.
So if the air flow were 5m/s (~10miles per hour).
Then that is 1cubic meter per second.
So, multiplying it all up. 35deg K* 1cubic meter/s * 1300 J/K. cubic meter = 45kJ/s = 45kW
The 5m/s figure is a guess though.
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rusty nuts
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| posted on 30/6/13 at 04:09 PM |
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Different coolants have an effect as well , tap water isn't an efficient coolant as some AF mixtures for example and Water Wetter breaks down
the surface tension of the coolant which somehow drops the coolant temperature. Been a long time since I did any calculations on cooling system
efficiencies .Also how the cooling air is ducted through the rad has a very large effect and some engines can have more efficient pumps ,ie BMC A
series ,hose bore again has a large effect, not always the way you think either
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SPYDER
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| posted on 30/6/13 at 04:26 PM |
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My initial thoughts were that matt gsxr's estimate of 45kw must be too high but think about it. if anything like equilibrium is being achieved
then the rad must be removing a similar amount of heat from the water as the engine is putting in.
Starting with a 150kw engine around 100kw is lost as heat. Maybe more. A quick google search suggests that half this will end up in the coolant and
half up the exhaust pipe.
So matt gsxr could be in the ball park if running at sustained high output.
Maybe when pootling along using 30kw of engine output you might be looking at 10kw.
The temp gradient across the rad must be similar to that across the engine too, I would have thought. I doubt that the temp drops by more than 20 or
30 degrees across the rad, otherwise one end of your engine would be running 30 degrees cooler than the other.
Somebody with a contact temp probe needs to go and measure it.
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PhillipM
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| posted on 30/6/13 at 04:46 PM |
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Like I say, most times when I've checked it it's been 20-30*c across the rad, but it depends on setup.
The 45kw estimate above is probably a touch high as only about 60-70% of the area of the rad is actually open for airflow.
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