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Heat Transfer vs. coolant mass flow - Induction/Turbo/Chargecooler/Manifold/Exhaust - The Lotus Forums Jump to content
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MrDangerUS

Heat Transfer vs. coolant mass flow

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There some individuals, who insist, that if we use a higher volume pump resulting in higher coolant velocity , the heat transfer in the HE/radiator is lower, because "the heat does not have enough time to convect out of the coolant, due to flow being too fast".
IMO: incorrect!
 
FYI:
The equations cited in this paper
http://jullio.pe.kr/fluent6.1/help/html/ug/node245.htm
show the only time dependent element, which is m, (fluid mass flow rate, kg/s), is in the numerator, hence the heat flux q (W/m^2) shall increase proportionally to the fluid mass flow rate, (eq. 6.21-6). In another words, larger the pump trough-put - the higher heat transfer and efficiency of the heat exchanger.

The same is true for the heat transfer coefficient, h, in eq. 6.21-7.

Some individuals are probably thinking in terms of the coolant temperature change (delta t), which is different. Higher flow will certainly result in a lower coolant temperature change, but that is actually desirable, as it's associated with a lower thermal resistance of that heat exchanger. At a system level, that is what you want to achieve. The lower coolant temperature change is compensated by the higher coolant flow rate, and the reduction in the latter is greater than the decrease in the former.
 
Hence, conclusion:  a high pressure/high volume pump improves heat extraction in the air to water intercooling system.
                                    Careful with upgrading the pump though, you can't simply buy a pump with a higher flow figure. High pressure is more likely to increase cooling than high flow.
 
For example: Bosch 0 392 022 010 pump delivers 20 lpm at the pressure of 40 kPa.
Jabsco Cyclone 50840-0012 pump, at the same 20 lpm flow bumps it to 54 kPa !
Edited by MrDangerUS

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There are a lot of variables determining the heat transfer coefficient h, especially at higher flow rates and in a real (= non-ideal) radiator. So I'd be careful with generalizing that the lower temperature difference is (always) compensated by the higher flow. For a small increase in flow this should be the case, provided the system is operating well within it's design limits to start with.

As for pumps, pressure and flow are of course dependent, with the actual pressure (for a given flow) determined by the design of the system (bends, cross section, length, ...). It is not the higher pressure that increases cooling, because the heat flux is independent of pressure. The flow does increase if the pump is able to deliver higher pressure, there is a (non-lineair) relation between pressure and flow in a system. With the higher pressure pump, flow will increase until the pressure in the system equals what the pump can deliver at that specific flow. A better way to compare pumps (for this exercise) would be the flow for a given pressure. The result being the same obviously, the Jabsco will outperform the Bosch (at least around 50kPa, it could well be the other way 'round for higher or lower pressure, depending on the design of both pumps).

In short, I agree better flow will give better cooling, but it's not quite as simple as it might seem.

Filip 

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Hi Philip, good to hear from you!

Here is a chart, which may help in the future design/projects.

IMG_3610.JPG

Edited by MrDangerUS

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True that some people think that a pump could pump too much coolant, and "not give it enough time to absorb the heat", but I think the last time we had this discussion around here was in 2009...

 

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OK you guy's. Let me know when you have come to an agreement as this is way way over my head. I am but a simple mechie.

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You ain’t alone @johnpwalsh just leave them to debate the issue. I reckon some more confusing graphs would help

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Do you have to take the velocity of the medium being cooled into account when making such calculations?

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Do you mean its velocity relative to the coolant, or relative to a given point in space/time?

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2 minutes ago, Sparky said:

Do you mean its velocity relative to the coolant, or relative to a given point in space/time?

I’m thinking relative to the coolant, because the point in space/time is always moving, and depends on where the car is at the time, so it would surely provide differing results.

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Would you be so kind as to elucidate by way of an attractive and informative graphic?

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I think the jist here is that if the coolant doesn’t go between being quite hot to quite cold (with a slow pump) but rather from warm to cool (with a faster pump) the lower change in heat doesn’t shock the components as much.. but as there is higher flow of this water, the same effect on the actual air temperature is gained in the actual charge cooler. A bit like a fast flowing narrow stream versus a slow flowing wide stream. The same amount of water passes through them per second (heat) but the slower wider stream is a less likely to erode its banks.

Is that right? Or is it just too late at night. :)

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I demand a graphic.

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33 minutes ago, Sparky said:

I demand a graphic.

Just researching flow dynamics now.....

E770A5B5-2585-497F-9BB2-A3C4A76C0A1C.jpeg.0e62a236fa2da25441fc4d37508e41c6.jpeg

  • Haha 1

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Yes, that is similar to my calculation, but in my case the peak is considerably greater.

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The size at the peak is indirectly proportional to the knowledge of this subject...

  • Thanks 1

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I have no idea what you mean.

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I gave up trying to spell dinamicks and looked at a manifold picture. That had a direct affect on the peak ?

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This is all well and good, but you've failed to take into account the angle of dangle vs the mass of the ass, the lube in the tube, and the fool with the tool.

Not to mention the wally with the brolly, and the prat in the hat.

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