A/C style heat exchanger instead of intercooler

[dbeck]

I have supercharged my Toyota 4runner. The downside is the type of supercharger that I have bolted on (almost the only you can bolt on) replaces the intake plenum and has no way of cooling the air prior entering the combustion chamber. I read a little bit about how much heat is produced in the roots style 3 lobe supercharger. From what I can gather at max boost (about 10psi) the air has been heated almost 250 degrees F.

Is there a way to place a heat an A/C style heat exchanger between the supercharger and intake plenum to cool the air prior to entering the combustion chamber. If I did the math correctly I am looking at 660 CFM that I would like to drop at least 100 degrees. This just an idea and wanting to know if it is theoretical to cool that volume of air that much?

 

[jrmichler]

It is very practical to cool that volume of air that much, it's only 70,000 BTUH. It needs a heat exchanger specifically designed to exchange that amount of heat and survive in that environment. The correct term is intercooler. Search supercharger intercooler to learn more and find an intercooler for your specific application.

 

[dbeck]

Thank you for the BTUH conversion. In this case I am thinking something like a mini a/c unit with refrigerant rather than an air to air system.

 

[jrmichler]

Some things to think about:

1) HVAC heat exchangers are not designed for a high vibration environment. You would have to design a mounting that would support the heat exchanger all the way around its perimeter and seal against air leaks. Don't forget to allow for thermal expansion.

2) Heat transfer to a refrigerant is a very efficient process IF you have a way to distribute the liquid refrigerant over the entire heat exchange surface. This heat exchanger is called the evaporator.

3) How will you get the heat out of the refrigerant to condense it back to liquid? With a refrigerant to air heat exchanger (condenser)? You will need to calculate the liquid and gas flow rates for your selected refrigerant. then calculate line sizes so the required flow rates will be achieved.

4) How will you get the liquid refrigerant to flow back to the intercooler? If gravity, the condenser will need to be located high enough above the evaporator that the gravity head will be greater than the line loss. Will you have liquid and vapor refrigerant flowing opposite directions in the same line? This is possible, but you need to carefully calculate velocities and line losses. If you pump it back, you will be reinventing an air conditioner. And it will be a big one - six tons.

5) Since you are moving six tons of heat (AC term - one ton is 12,000 BTUH), the heat exchangers need to be sized for the air flow rate and the desired delta T between the refrigerant and the air. Larger delta T is a smaller heat exchanger. You specify what temperature the air comes out of the supercharger, the temperature into the engine, and the ambient temperature.

6) Don't forget to calculate the necessary air flow through the condenser, and figure out how to make that amount of air actually flow through the condenser.

 

[russ_watters]

For reference, 70,000 BTU is about equal to the largest residential air conditioning system you typically see. It's not a small air conditioner.

 

[cjl]

It's not a reasonable amount to handle with refrigeration. However, you're right that especially with many supercharger setups, an air to air intercooler would be difficult to plumb properly, and likely involve a large pressurized volume that would harm throttle response (and provide a lot of opportunities for boost leaks). The best solution to this is an air to water intercooler - basically an additional water cooling loop that exchanges heat between your charge air and water, then pumps that water down to the front bumper (or wherever it is convenient) to flow through an additional radiator to cool it back to ambient.

 

[Dullard]

The one (possible) un-tugged string here is 'duty cycle.' It seems improbable that any engine with an after-market supercharger 'bolted on' can be (successfully) operated at high boost levels more than briefly/intermittently - nor would it typically need to be. The average cooling requirement is much lower than 6T - probably much, much lower. An approach where cooling capacity can be 'stored up' could work, depending on how often/long that capacity needed to be available.

 

[dbeck]

I did not think of the vibration aspect. I know how an a/c unit works but I don't know all the math behind it. This could be a pipe dream. The other issue I have is space. I would need to machine or cast a new intake to allow for the exchanger. The space I have at the max is 20inx5inx5in. Don't think a/c would be the way to go. I don't have enough space to to take the compressed air, route it through an air to air exchanger and pipe it back to the intake.

Thanks for your additional things to consider.

The one (possible) un-tugged string here is 'duty cycle.' It seems improbable that any engine with an after-market supercharger 'bolted on' can be (successfully) operated at high boost levels more than briefly/intermittently - nor would it typically need to be. The average cooling requirement is much lower than 6T - probably much, much lower. An approach where cooling capacity can be 'stored up' could work, depending on how often/long that capacity needed to be available.

Thanks for bringing this up.

 

[dbeck]

My first thoughts were to base it on max RPM. That however is not where the max boost is for the supercharger. The max boost I have is between 2000 and 4000 RPM with a volume of air I need to cool of 240 to 480CFM. My initial thought of the increase of temperature gain was wrong. After reading this http://www.progl.com/General/Boost&heat.htm was off. This is based off a ambient temp of 70f. Where I live I see temperatures up to 110f. Although I do not have the same type of supercharger that these numbers are based on I have been able to match the efficiency of 75% and can use this as a base for the heat generated.

The main drive for this project is to eliminate spark knock or detonation. Currently I have a piggy back control module that I have wired into retard timing to eliminate detonation. This is not the ideal situation.

 

[dbeck]

For reference, 70,000 BTU is about equal to the largest residential air conditioning system you typically see. It's not a small air conditioner.

That is quite a bit. I don't think I could fit that under the hood...lol. My main goal is to extract some of the heat. I know I will not be able to get it all out. I would take 50% efficiency

 

[dbeck]

Some things to think about:

1) HVAC heat exchangers are not designed for a high vibration environment. You would have to design a mounting that would support the heat exchanger all the way around its perimeter and seal against air leaks. Don't forget to allow for thermal expansion.

2) Heat transfer to a refrigerant is a very efficient process IF you have a way to distribute the liquid refrigerant over the entire heat exchange surface. This heat exchanger is called the evaporator.

3) How will you get the heat out of the refrigerant to condense it back to liquid? With a refrigerant to air heat exchanger (condenser)? You will need to calculate the liquid and gas flow rates for your selected refrigerant. then calculate line sizes so the required flow rates will be achieved.

4) How will you get the liquid refrigerant to flow back to the intercooler? If gravity, the condenser will need to be located high enough above the evaporator that the gravity head will be greater than the line loss. Will you have liquid and vapor refrigerant flowing opposite directions in the same line? This is possible, but you need to carefully calculate velocities and line losses. If you pump it back, you will be reinventing an air conditioner. And it will be a big one - six tons.

5) Since you are moving six tons of heat (AC term - one ton is 12,000 BTUH), the heat exchangers need to be sized for the air flow rate and the desired delta T between the refrigerant and the air. Larger delta T is a smaller heat exchanger. You specify what temperature the air comes out of the supercharger, the temperature into the engine, and the ambient temperature.

6) Don't forget to calculate the necessary air flow through the condenser, and figure out how to make that amount of air actually flow through the condenser.

I got my idea after watching this video from Adam Savage's Tested . I was thinking I could do a system like this. Rather than cool water I would just use a heat exchanger to cool the air. Granted this would need to be a little bit bigger in scale.

 

[cjl]

As I said, this is a fairly well-understood problem, and the existing common solution is a water to air intercooler. It will remove far more heat than a reasonably sized AC unit will, and can do so basically continuously (as long as your radiator is sized appropriately).