Cooling systems

[MAGP]

Think about how an electronically controlled EWP works. They work using PWM to control the amount of flow through an engine to keep the engine at a desired operating temperature. In other words the EWP is a controlled restriction. I have an EWP115, the OEM mechanical pump, and a thermostat in my 350. The EWP has never gone to full flow in the years it has been on my 350, why? because the water has to remain in the radiator long enough to actually cool down. I could have fitted the EWP80 and it would have been enough. There is an EWP150 available now and it would be complete overkill in my car.

[immortality]

I think one of the articles I linked earlier debunks the myth of coolant needing to be in the radiator a long time to shed it's heat. Some fancy stuff about thermodynamics explains it.

[MAGP]

Personal experience with my own car indicates to me it's not a myth.

EDIT: It's not just about being in the radiator long enough, the water has to be in the engine long enough to absorb heat. Heat needs to be controlled to get an engine operating at its best. If you have to much flow you have no control, thermostats are a control mechanism. No thermostat no control of flow.

[Macca97]

brought a v8 water pump this week, and it has a cast impeller,

to much flow is just as bad as not enough,

[vlad01]

I think one of the articles I linked earlier debunks the myth of coolant needing to be in the radiator a long time to shed it's heat. Some fancy stuff about thermodynamics explains it.

yeah its complete bogus urban myth. If the desired effect it absolute maximum cooling performance (not what you want in a car, but other cooling solutions where its ideal) then maximum flow allows for maximum convection and transfer of thermal energy. Having designed and built many personal and customer high end PC water cooling systems, fastest flow is desirable for best performance, when coolant volumes are large you can afford to run a bit smaller pumps and less flow due to water's specific heat capacity but its a fine line before water blocks and radiators start to saturate before the water ever does so the flow must be fast enough for effective heat rejection.

Also ever wondered what is better? copper rad or alloy? Alloy most definitely, and reasons you wouldn't otherwise think about.

[The1]

alloy for longevity?

[vlad01]

alloy for longevity?

No alloy for cooling performance. Longevity is just a bonus byproduct.

[immortality]

I linked an article a few pages back that explains it all quiet well, even the bit about radiators.

[MAGP]

PCs are very different to engines, I build my own PCs and have always upgraded the cooler but have never had to resort to water cooling.

It is no secret that alloy sheds heat more efficiently than copper. There are design considerations that help to though. I've had a PWR radiator since the early 2000s, the old copper radiator used to pop tanks off with monotonous regularity. The PWR is much stronger and more efficient in cooling.

EDIT: I think I'll bow out here, I mentioned reverse flow cooling and we ended up only concentrating on radiators I'll agree to disagree and leave it there.

[vlad01]

Aluminum isn't more efficient in cooling. Fact is copper has a transfer rate almost double that of aluminum, but the problem with copper radiators is not the copper itself.

There is a few design problems with them, one the water tubes are made from brass and brass is a more conductor of heat compared to aluminium, about half of it or 1/4 of copper as tin the component of brass has a transfer rate of about 62 (W/m K), aluminum is 204 and copper is 385ish. Brass ends up around 110. So like a weak link in the chain is blocks effective heat transfer.

But there is more! what are the copper fins joined to the crappy brass with? High lead, tin solder. Tin already mentioned but lead has a transfer of 35 (W/m K). Absolutely piss poor.

Aluminium radiators are all aluminium and even the brazing/welding (looks more like moten aluminium dipping) for the fin to tube interface is aluminium, so the entire radiaor heat exchanging part is a continuous hunk of aluminium so the transfer rate is a nice constant 200 odd (W/m K)

There is one other factor to consider is spesific heat capacity of the metals used.

In (kJ/kg K)

Aluminum 0.91

Copper 0.39
Lead 0.13
Tin 0.21

You can see aluminium has a much larger capacity for heat, so it can take a lot more thermal energy for it to rise in temp by a certain degree, so this helps dampen thermal loads and shocks a lot better provided it isn't already saturated with heat, not only but it will keep the water hot if the situation goes the other way.

So the alloy rad is far better and a good example is the 6cyl VL or probably prior models with its 50mm copper/brass core and still can be overheated easier than a bigger more powerful V6 with factory 30m core, now days 30mm core is not available and only 20-25mm cores are and they still cool just fine.

I also found the same thing with PC radiator, copper is all the rage due to marketing but I have tested and alloy trumps it as its the same construct at an automotive one.

As for PC not being the same? how do you cal that judgment if you don't run water on yours?

PC system has a heat source to be cooled > GPU/CPU same as combustion, and a water block = water jacket, pump same same, water-ethylene glycol coolant same same, a radiator and reservoir, pull through fan same same (can get fancy with fan controls too). Only difference is an engine has a stat so its a steady temp and doesn't get too cold, were a PC you want full flow and as cold as possible, therefore its a great playing field for exploring and testing every aspect of a cooling system.

I haven't run air cooling on my main PCs for over 12 years, always been water cooled. All this copper or alloy heat sinks, heat pipes, vapor chambers, massive sinks the size of a mellon...pfft in the bin!