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Cooling intake air below ambient air temp

Cooling intake air below ambient air temp

(OP)


I have been contemplating an air to water intercooler system for my car (2010 Subaru WRX for anyone interested) and I want to cool the air below ambient temperature without having to use ice. Ideally, the intake air temp would be around 45-50*F or lower and relatively constant. I've thought about using the existing air conditioning system and a second evaporator in the water reservoir, but if I were to do that, I would have to use coolant to prevent freezing and I'm not sure that dropping the thermal conductivity would allow the heat transfer I want. The other issue is that the power loss from running an A/C pump constantly may negate the effects of cooler intake air. This led me to think about Peltier cooling modules. Once again though, the potential power loss from having to use a larger alternator may negate the effects. I'm looking for a little guidance on this.

About the system:
Water Reservoir- I'm considering two different water reservoir ideas, one using a single reservoir with Peltier modules around it and a grid pattern within to provide a path for the water to flow and give it more time to cool. The other idea I've been considering is an additional reservoir (smaller) to hold ice in the event that I want even colder IAT's (intake air temperatures). Depending on the Peltier efficiency and amperage requirements, it may not be needed. The water reservoir(s) will be located in the trunk of my car.

Water Pump- I'm not sure of what kind of flow will be required for a system like this, but the one recommended to me was 500GPH. I really have no idea if this will be too much flow or too little.

Water Lines- I'll be using insulated lines for everything.

Intercooler- I'll be using the intercooler in the link below. It will be covered in heat reflective tape or coated in a thermal dispersant coating from SwainTech. (Intercooler link: http://www.frozenboost.com/product_info.php?cPath=... )

Heat Exchanger- I'll have a primary heat exchanger to remove as much heat from the water before going to the reservoir. This will go in front of my radiator. I anticipate that the heat exchanger will get the water to within 10*F of ambient air temp (in my area, we see highs of 85-90*F in the summer) Link to heat exchanger: http://www.frozenboost.com/product_info.php?cPath=...

My questions:
Will I gain power from this? (will the power gained be greater than the additional power loss from a larger alternator?)
How much flow will I need from a water pump?
How many and what wattage of Peltier modules should I get to get the water temp below 40*F?

This is a repost from the thermodynamics forum.

RE: Cooling intake air below ambient air temp

The analysis is easier for a normally aspirated car

Your intake air is probably around 100F at the moment at the plenum

So if you can get it down to 50F, the incoming charge will be roughly 10% denser.

So you'll make about 10% more power, less the power to drive the cooler.

Note that you aren't breaking any laws of thermodynamics yet, because the system is an open system..

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Cooling intake air below ambient air temp

You need a low voltage high current power supply for Peltier modules. A supply like that can be heavy. The wiring alone can be heavy.

For how long a duration in time will you need the cooling?
E.g. a bucket of dry ice could be effective for a few minutes. When it's gone, you need to stop at a supermarket and buy more.

If you want something that doesn't need frequent stops to top up something, e.g. Peltier cells ulimately driven by the alternator, that power comes out of the fuel tank, through the engine. Or maybe it comes out of a separate fuel tank through a separate engine, at considerable cost in weight and space.

Are you racing in a class with defined rules, or just screwing around on the street?



Mike Halloran
Pembroke Pines, FL, USA

RE: Cooling intake air below ambient air temp

The next question is how much power does it take to cool the air, and how much air is needed

Assume a 2 litre engine making 100 kW at 6000 rpm, air required is 0.002m^3 per cycle, 50 cycles per second =>0.1 m^3/s, air has a density of 1.2 kg m-3 so we need to cool 0.12 kg/s of air by 50 F, or 28 deg C

SHC of air is 1 kJ/kg/C, so we need 0.12*1000*28 W of cooling, or 3.3 kW. Not too bad, as we gained 10 kW from the denser charge.

That is with a 100% efficient cooling system, which is where this comes unstuck. A peltier is only 15% efficient typically, so we'd need to use 20kW of electricity to run it, for a net loss of 10 kW.

BUT, you only need max power for short bursts so you could use the battery to supply that rather than the alternator. But you'd need a big battery, an automotive battery will struggle to supply that sort of juice.

So another alternative would be to use a conventional air conditioner. I'm not usre how efficient they are but random googling suggests 50% for this sort of job, ie you'd need about 1.7 kW supplied to the a/c.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: Cooling intake air below ambient air temp

I do think the only practical way is to either do it through storage.
This could be the alternator charging the battery while not under heavy load to use for cooling while under load or it could be Peltier cooling a very small amount over a long period of time or something like AC cooling more over a shorter period of time.
Either way you would need a big enough insulated reservoir to absorb as much heat as you could dump into it before it has time to recharge.
This all depends on what kind of driving you do. If you just want it for drag racing you might as well just use ice.
If you use it for the occasional freeway onramp or passing a semi is it really worth all the effort?
If you use it for something like extended spirited driving you will need to work out duty cycle. Something like the Peltier will take a considerable amount of time to cool the system if you don't use a lot. You could run them all the time as the load wouldn't be significant but it would take a lot of time to cool back down unless you are running a lot of them. In which case you would want to disable them during high load otherwise they will negate most or all of the gains.
Same thing with AC. It will definitely use more power to run the AC than it will absorb from the intake charge so you would want it switched off under load.

Any way you cut it I don't see a system like this paying off in any sort of performance driving other than drag racing because otherwise there won't be enough time to recharge unless the system is big, complex, bulky and uses a lot of power.
Maybe if you could figure out a way to take the energy from braking and convert it to rapid cooling or something but again it would be big, expensive, complex and bulky.

RE: Cooling intake air below ambient air temp

If you live in a climate with low enough humidity, you could just mist the intercooler with water for an evaporative swamp cooler effect.

RE: Cooling intake air below ambient air temp

Using a Peltier is not viable. Not only are these devices not efficient, but they are heavy for the heat flow capacity and they require heatsinks.
I think the easiest way to get high flow capacity atmospheric pressure cooling of air is with a supercharger with evaporative water cooled intercooler followed by air cooling by pressure release (compressed air refrigeration).

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