The way I read it, you are both saying the same thing. If your heat-exhange element is hotter than the incoming charge, it will heat the charge (afterheater/interheater) and if it is cooler than the charge it will cool it (aftercooler/intercooler).

Cheers,
Hymee.

 

I keep saying this: You can only heat the charge at part throttle and this has no effect on performance. At full throttle it is impossible to heat the charge air. Full throttle is what affects power potential.

Man I wish I knew how to post one of those smileys bashing my head against a wall. Obviously a few other people wish I would bash my head.:D

I do agree that we have beat this topic to death.

Peace,
Babylou

 

I respectfully disagree.

The air molecules don't say "Hey was that butterfly fully open - if it was, I'm not gunna swap some of heat energy with this hot bit of radiator fin I just bumped into."

If there is a temperature difference between the air and the heat-exchanger, one will give up it's heat and cool down a bit, and the other will warm up a bit.

Cheers,
Hymee.

 

Okay last try here. I can't handle fighting this two front war.

1. In your first paragraph you speak of the butterfly being fully open which is the same as full throttle. Agreed?

2. Since you are talking about full throttle here the charge air will be at the maximum exit temp of the compressor. Agreed?

3. The maximum exit temp for automotive compressors is ~200 F. Agreed?

4. The air temp underhood is ~140 F. Agreed?

5. The intercooler is surrounded in underhood air on the exterior and compressor outlet air on the interior. Agreed?

6. An object that is heated by its' surroundings cannot exceed the temperature of the surroundings just like my TV dinner example. Agreed?

7. The highest temp, ever, of the intercoolers surroundings is the 200 F of the compressor outlet air. Agreed?

8. Since the maximum temp of the surroundings can be 200 F the intercooler temp cannot exceed 200 F. Agreed?

9. Let's assume the intercooler is very inefficient and actually reaches the theoretical maximum temp of 200 F. Agreed?

10. Now go back to my statement #3 and connect to statement #8. The 200 F compressor air is passing through a 200 F intercooler. Agreed?

11. Same temp = no heat transfer.

Please tell me, by number, which of my statements you disagree with.

 

Cool it!!

All I was saying was that in the case of the intercooler temp being higher than the air, the air will heat up, regardless of throttle position.

You seem to say that case can't happen. I'm not going to argue that point. Maybe it can, maybe it cannot. Maybe it is just highly unlikely.

Cheers,
Hymee.

 

Disagree. There is the possibility that the compressor is producing little to no boost meaning little heat. You're assuming that boost is instant as is not the case in any application. So if you mash the gas there could be a nice rush of outside air (sealed element) but the compressor hasn't spun up yet, the warmer intercooler would heat your initial air charge in fact hurting low end power. Once the air charge and intercooler both reach the same temp, then heat transfer would stop in one direction and then begin in the other direction as the air charge keeps increasing in heat.

 

Well put!

 

Summary....

In a poorly designed Intercooler (poor airflow, easily heatsoaked) the following occurs.
1)Once Heatsoaked, it hurts performance at partial throttle. Agree/Disagree?
2)Once Heatsoaked, it no longer helps (actual HP Gains) at full thottle , a good design could by not being heatsoaked as easily, therfore still providing some cooling. Agree/Disagree ?
3)If it no longer is providding cooling, then it to some level is causing some backpressure in the intake that could cause a performance penalty. Agree/Disagree?

I think everyone is saying the same thing. A poorly designed heat exchanger while providing some benefit until heatsoaked, becomes zero benefit once heatsoaked and can actually reduce power (slightly) if it inhibits airflow.

The goal then should be to optimise the heat exchanger so that it cools quickly.

Also.
Even if not completely heatsoaked, an intercooler that is running cooler will add more power than one running at a higher temp . The cooling of the aircharge is proportional to the delta between the air and the cooler. A colder running intercooler will obviously provide more charge cooling even at partial throttle positions.

 

Congratulations! You are correct. I was neglecting boost response of the compressor. However, I keep pointing out that this entire discussion has been simplified from the start so we have eliminated drag effects of the plumbing and transient responses (boost rise, thermal lag).

If we want to nitpick I can find other phenomena in the other direction too. The effects of thermal radiation and convection have been ignored. Or that there is delay in heat transfer from one object to another. Or the effect that a cooler intake charge leads to a cooler exhaust charge which will be less efficient at driving a turbocharger which will lead to less power. Of course these effects are small so for simplicity it is best to look at the problem in a macro sense.

Hey, I also congratulate you for scientifically responding to a specific point I have made instead of just saying "you need to quit reading books or whatever."

 

I hate to dig up a dead horse but I want to clarify a mistake I made here.

After re-reading this entire thread I see that my statement above insinuates I took the above classes with Corky Bell. This is not true. I meant that I took the same classes at the same university while we were getting the same Mechanical Engineering degrees. I'm actually a bit younger than he is. I apologize for misleading anyone.

I will now go an edit the original text.

Peace,
Babylou

 

Thank you!!! This is what I've said the whole time (and EVERYONE except one person agreed with me!) and was being told I was wrong about. There are CERTAIN times things can occur. Once again someone who isn't ignoring "scientific point" in one area to prove otherwise in another area. Way to go! We're probably still wrong though! Oh well. Unlike many others out there, I actually own a turbocharged car so I can go outside and prove everything I have been saying easily.

Remember education doesn't necessarily imply intelligence. Shhh... Don't tell my engineering professors I said that. Yes, I went to school for mechanical engineering too! So what. That doesn't mean anything whatsoever.

I'm enjoying reading others responses so from now on I'll just read and laugh and maybe comment about the way things are going. This is fun! Comedy Central online.

 

Bullshit! You never talked of pressure losses. Never, ever, ever. I was the one that mentioned profile and skin drag effects which lead to pressure losses and that was a loss we were neglecting. Much like we were neglecting gains like thermal radiation.

QUOTE]Originally posted by rotarygod
Remember education doesn't necessarily imply intelligence. Shhh... Don't tell my engineering professors I said that. Yes, I went to school for mechanical engineering too! So what. That doesn't mean anything whatsoever.[/QUOTE]

I suppose by once again saying I'm dumb makes you feel that your point is more valid. Good for you. I can do the same: It is obvious you have a rudimentary knowledge of heat transfer and thermodynamics. I noticed you "went to school for mechanical engineering too". Nothing about graduating. I'm thinking that first calculus class and first statics class washed you out.

 

Can I get in on this???
I know I should keep out of it, but!!!
You are all very brite people, no one can deny you that.
Everyone is right but you just can't comunicate. I should talk, I'm the worst.
You guys are saying the same thing. I THINK. You all agree that the intercooler can work but it has to be in the right place at the right time.
It has problems, everything does. It's big problem is that there is so much hype out there. If you can run without one do so. If you are going to melt down then figue out how to do it right. My objection to them is running them for no reason.
On a street engine an air to air system does not get the air going fast enough to work like it does on a race car.

Try a liquid to air cooler and it may prove more practical. Of course it too has problems like it takes more time to recharge. Or to get the coolent radiator back down. It's all a matter of heat storage. Oh ****! I just started another long thinking thread.

Wait guys, I too have been to school and make my living with fluid dynamics. Like I said better not to open my mouth. I only wanted to comment so as to sooth thing down.

This reminds me of friday nights at school with beer and pizza flying around. All the smart *** know it all engineerg students yelling at each other. Trouble here is no beer.
Thing is that now I know why we did that. Because it was the art students who were out with the girls. We were stupid, girls didn't take engineering courses.


I've said it before all you get is what the compressor puts out. BUT, every drop of heat you put in goes all the way throgh. If it is cooler it will not reach the thermal limit of the internal parts. It will be more resistant to detonation. You may tune more out of it. BUT ignition advance is not an end to itself. you don't want it unless you have to have it. The more you advance it the more pressure the engine is pushing against on the compression stroke.

Will someone please take this keyboard away from me.
Forget I said anything. Because to explain myself to the degree that is required in this forum is impossable. You guys are just to demanding. I'm going with Rotorygod, I'll just read.

 

FFS - the argument is over. We all basically agreed. We don't need to get personal.

Lets get the topic back on track to blowers for the Renisis!

Cheers,
Hymee.

 

hymee the peacemaker. Always to the rescue :D

 

Damn, I have to break my vow of silence so soon. I just opened Turbines spreadsheets. John, we have talked in the past and I love your plots and speadsheets, nice work. Now I'm an engineer and love math as much as the other guy. With all do respect, I must side with RotoryGod on one thing.
There comes a time when we must leave the math in the office and go out into the shop.
You said it yourself, ther are two pumps working here.

You are pumping from one into another so the resistance changes because even if the pumps are both positive displacment they cannot match all along the rev range.

Next if you are talking dynamic compressor things get more complex as you also noted. So far we agree. The problem comes when you state that there will be more air going into the engine. If you are using a positive displacment pump then no more air can come out. That is a given.

If you are talking a turbo or centrifugal compressor you can get more. that is because it will give up more flow for less resistance. The problem is that you can't plot it that easy. I think you said that also. But this thread is about roots blowers, right?

You mentioned that you were ploting an axial compressor, if that is so then I know something about that. Since I'm the only one who has worked on this problem and even I don't know enough about it. One thing is for sure, the axial is 100% adiabatic and all internal compression. It doesn't like a lot of external compression.

In the case of the axial I think it would have to be resized if you were to get the most out of it. Someday I want to build a Bonniville engine with one of my blowers at about 2.5 Pr. and intercool it with ice water. That can take a bunch of BTU'S off the charge. In that set up you would have control over all the delta's.


Turbine, you and I are going to talk about this and maybe you can help me understand a few things. I have to say that some of it baffles even my old professor of turbo machinery. And He is a smart guy, ex NASA and the like. Overachiver.

Hope I mixed up the thread some more. I am not the final judge, only your dyno knows for sure

Just one more thing and this goes back in the thread a ways. The reworking of the ports on the Eaton hurt efficency. If it comes in the top and out the bottom that is better then working it around the place. Also they did not invent the helix rotor, GM has been using that design since WWll or before. The dragster blowers started out with the 6-71 back in the early '50's. They still use that rotor only streched to 19". In fact untill recently they used actual GM rotors spliced to get the 19".



Good night,
Richard

 

Hey Richard,

Thanks for the input. I'd like to include twin-screws in this discussion as well, if people agree. They are different than roots, but many people assume they are the same.

Cheers,
Hymee.

 

Hymee,

Yes, I think we can all agree on the fact that the screw is a positive displacment blower. Therefore it should be taken in the same light. However the twin-screw is more efficiant.

Richard

 

Completly agree. The twin-screw positive displacement blower is what needs to be on the RX-8 IMO. After all this discoussion about temps and what not I'll point out that the twin-screw puts out lower air charge temps and more volume per psi of boost than the roots style blower. It also has a more instant boost response than centrifugal style blowers which will fatten up the curve on the 8 nicely. With no other change, I went from 380rwhp to 450rwhp in my lightning just by swapping blowers from roots to twin screw. They were both at 15psi as well. That's a 70hp gain in just blower to blower comparisons and the gains get exponentially larger as boost increases.

 

Mmmmm.... Sounds nice

I think the main mechanical concern with the rotary is lunching the apex seals due to detonation. Something to be concerned about with high temps, and possible the injectors not being able to deliver enough fuel need for the mass of air - i.e. too lean.

Cheers,
Hymee.

 

Ok guys great topic on which SC is best and I agree that twin Screw would work out to be the best for the RX-8. Now how do we go about and who do we put presure on to come out with this SC.. I would hate to wait a year but I could if if means having the best SC for my RX-8...

 

Wait, wait, wait. I didn't say the screw was the best blower, I just said it was better then the roots. It of course is only my opinion but I'm betting a lot on the axial flow being the best. That means I am putting my money where my big mouth is.

In fact I'm so sure of it that you'll notice on my thread I have built the Rx8 blower already. That in addition to that gamble we are so sure of it that we actually built 7 of them and bought the matirial for 25 more.

Truth is that they are machined, only 2 are assembled for bench tests next week. That's comitment, that's progress. We've only been on this for about 30 days.

Richard

 

Richard,

Is an "Axial Flow" the same as a centrifugal compressor in this contect??

Cheers,
Hymee.

 

No. Axial flow means the charge air moves along the axis of rotation of the compressor. Like a modern jet engine or a series of fans placed one after another. Centrifugal means the charge air enters in the center of the compressor and is flung out radially. Picture kids on one of those spinning discs on the playground. The faster the disc spins the stronger the force that is trying to fling the kids off.

 

That is what I thought, but I have not seen much (any??) of this in terms of automotive apps.

Cheers,
Hymee.