Fmic as a heat exchanger?

Just thinking out loud so forgive the silliness of this idea.

I have a large fmic  but I need two charge coolers foŕ a twincharged build.  I have room for 2 smaller water to air units but instead of a reservoir tank and heat exchanger could I cap off the air to air FMIC fill it with water and utilise this as a reservoir and heat exchanger in one? The in/out barbs would have internal piping to reach down to the lower area of the fmic. 

Again just a thought but interested in why this wouldn't work. Thanks 

I don't see why it wouldn't work to a degree. Surface area is going to play a roll in how the heat dissipates off the intercooler so you'll probably have to see if there's equal surface area with the smaller coolers. After that as long as the density remains constant the only thing that will vary is the volumetric flow rate which will be reduced as it enters the intercooler end tanks then speed up as it goes through the bars. The larger the bars are the longer the coolant will be in there. (Hopefully I'm thinking about this correctly.) So as long as the fluid is in the intercooler core long enough to sufficiently exchange the heat from the water with the air I can't see why it would be a problem, well besides potentially trying to burp the end tanks.

There might also be an issue with the end tanks evenly distributing the coolant since it's a different fluid from air.

It's been 12 years since I've had a fluid dynamics class though so a real engineer might want to chime in. All I remember is the equation of continuity states that as long as the density doesn't change the only thing that would vary is the flow rate.

Wouldn't the ratio of fluid volume to surface area in the matrix be the key determining factor? 

I have no idea if that's true, I'm just genuinely curious.

I do know air-to-air intercoolers typically have much larger veins than water-to-air radiators, but I don't know if that really means anything. 

It might work, but water-to-air intercoolers aren't exactly a new idea.  Typically, a small radiator meant for water is used.  An issue I could potentially see is air-to-air intercoolers are designed to flow air through them. Water might not flow through them as efficiently.

Air to air ic will have larger passages so the water may flow through it too quickly in the most direct path from in to out. A tube with smaller holes within the end tank will disperse the water as it comes in throughout all the passageways and work better.??

Possibly. I'm not a hydronics expert, but it seems to me the flow through the tubes would be inconsistent and may not cool the water effectively. Perhaps if there is a way to force a cross-flow where the coolant has to travel across the top of the tube assembly, then back and then out the other side.  Not sure if that is clear...

Remember you'll need some sort of pump to circulate the coolant.

I hear ya. But adding dividers to direct flow isn't an option. . That's why I was  suggesting an inner tube with smaller holes that went along the end tank to disperse the coolant on it's return.

There will be a pump in the system.

I'm no expert  either but if the coolant travels too fast through the fmic to have the heat expelled surely the same goes for the water  to air intercoolers. They will be getting a greater volume of coolant so not getting to heat it as much which should be a good thing? 

Coolant will just be travelling in a loop, faster. 

As I say this may never happen. Just thinking. 

It would probably work, but chances are, it would end up taking up far more space than a cooler designed for water (assuming equal cooling capacity for both). 

Oh for sure but I built the front end to house this air to air unit so it fits perfectly.  It will also hold a lot more coolant which is probably necessary as I'm trying to cool 2 units.  A regular heat exchanger would probably need a reservoir anyways.  

I'll wager a guess that it will work good enough probably but quite a heavy volume of water compared to a liquid cooler. The size of the tubes has something to do with the density or heat capacity of the fluid and water is quite a bit different than air. The tube volume to fin surface area ratio will be too large but what actual difference in real world performance who knows? As long as the cooler is big enough for adequate cooling.