Phase-change material for down-sizing cooling system

[Air-Hybrid]

Old article from Autospeed:
http://autospeed.com/A_110772/cms/article.html


The article describes the device as an intercooler although it is really a temporary heat-sink.
The idea is a phase-change material -or PCM- (in this case a petroleum wax) absorbs heat from the charge when on-boost and 'gives it back' to the charge when off-boost.

This only works because when the charge air is turbo'd the temperature (due to compression) raises passed the wax's fusion temperature (ie. when it turns to liquid).

Since many of the solutions today in tackling fuel economy are about evening out the peaks of a cycle (whether it be hybrids, or fly-by-wire lean-burn), then it occurred to me that the same ought to be true for cooling.

I think I read somewhere that the Prius already uses PCMs to store coolant heat for quick-up-to-temp restarting. So I was wondering, if this idea is true for intercoolers on turbo'd road cars (not race as they are on-boost over 50% of the time) then could a similar advantage be gained by employing a small tank of PCM in-line with the coolant circuit?

[Air-Hybrid]

Unlike the example in the article the use of PCM for block cooling would not be a simple heat-sink, but would be an intermediary, with the wax itself in liquid-state pumped into a specially designed radiator. On current liquid-cooled engines the mass of the fluid has the effect to even-out the temperature load across the driving cycle (ie. it is sinking variations in heat, not only at local hot-spots on the head, but from a moment of hard-driving) - This is why it is not an immediate effect for an electric rad-fan to switch on if you start pushing it.

The intermediate-PCM stage would allow several effects.
1. It could mean a much smaller mass of coolant in the system (although what there was would need to circulate quicker or have higher heat-transfer characteristics).
2. Because the specific heat of the PCM is equivalent to many times that of the same mass of water, the length of time that the engine would be able to be pushed hard for without overheating would be much longer. Looked at another way, if a driver is driving more-or-less normally then the size of the radiator (and it's aero impact) gets smaller.

So, I'm not saying this idea is workable for a mass-produced car of today (unless it's hybrid) due to it having limitations for continued heavy driving. But for the eco-minded driver it is, I believe, a realistic proposition - Remember, just like in the intercooler example in the article the driver is borrowing heat-capacity now to be paid-back later.

[bwilson4web]

Originally Posted by Air-Hybrid

. . .
I think I read somewhere that the Prius already uses PCMs to store coolant heat for quick-up-to-temp restarting. . . .

The North American, NHW20 model (2004-09) has a thermos that holds hot coolant. No phase-change heat storage.

The current ZVW30 model has a heat exchanger behind the catalytic converter to tap exhaust heat and rapidly heat up the block.

Bob Wilson

[Air-Hybrid]

Thanks Bob.

Any other opinions (or ridicule) on my idea for using PCMs - by anyone?

[ConnClark]

IMHO, downsizing a cooling system is not a good idea in general. Current cooling systems do have a phase change temperature regulation. If you look at a modern coolant recovery tank cap they are designed to vent at a given pressure. As your car engine over heats water turns to steam and builds pressure. When the cap vents it allows more steam to be generated. Provided your coolant doesn't drop below a certain level your engine cooling system will not exceed boiling point.

[Piwoslaw]

Using PCMs to store engine heat has been researched. It's called a Schatz heat battery.

[slowmover]

Good thread.

" . . many of the solutions today in tackling fuel economy are about evening out the peaks of a cycle"

is always worthy of consideration.

[Air-Hybrid]

Originally Posted by Piwoslaw

Using PCMs to store engine heat has been researched Schatz heat battery.

Thanks for the link to the previous EM discussion on these materials.
From the way I see it the simple way get the engine up to normal temp quickly is to use an exhaust heat-exchanger. I don;t suppose it takes much longer that using a thermos or a PCM, but it's got to be more simple and less bulky/lighter.

What can't be done any other way is allow for a smaller radiator opening (ignoring adjustable grill blocks). Using a PCM as an intermediate heat-sink should, under all but the most extreme driving-cycle situations, result in the need for a substantially smaller radiator and its aero penalty.

[meelis11]

Anyone has good examples to show how to set up exhaust heat exchanger?
Basically you need to wrap copper pipe around exhaust and coolant flows through that spiral? How many wraps around exhaust?
How much is it possible to make warmup time quicker?

That autospeed idea seems really good to use it as heat battery - to preserve waste heat that in the morning you get engine warm sooner.

[meelis11]

UP!
Nobody has not done exhaust heat exchanger?
What about phase-change heat-battery?