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Old 09-16-2015, 05:35 PM   #1
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Default Heat Transfer Question

I'm working on building a heat shield for my header, and I have a question regarding heat transfer. The header is wrapped in DEI Titanium header wrap.

The goal is to minimize heat coming out of the header so my SC doesn't get very hot since it's literally right next to the header. I have confirmed enough heat will kill a really expensive supercharger.

I'm building the shield out of stainless sheet metal. One side is bare stainless (emissivity ~0.55) the other side is #8 mirror polished (emissivity ~0.07)

Now the shield will be very close to the header tubes. The question is, which way should I orient the sheet metal? Shiny side towards the header, or away?

Either way you orient it, the sheet metal is going to get really hot since it will be very close to the primaries.

In theory, shiny side towards the primaries will reflect more radiant heat, so the sheet metal will be cooler, but then that cooler surface has a much higher emissivity.

On the flip side, I could do shiny side out. Now sheet metal will be hotter, but shiny side emissivity is out so it won't radiate as much heat out.

My guess is shiny side facing the heat source, since radiant heat increases with temperature to the 4th order, having the sheet metal surface on the outside be cooler would ultimately result in less radiant heat hitting the SC.

Which would work better?
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Old 09-16-2015, 05:36 PM   #2
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<p>Why not both sidez shiny?</p>
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Old 09-16-2015, 05:38 PM   #3
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<p>Why not both sidez shiny?</p>
Could not find material that was #8 polished on both sides, already ordered material that has only one side polished. So just looking for a definitive "which way would work better" at this point.
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Old 09-16-2015, 05:39 PM   #4
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<p>Give to Jeffbucc for polishing?</p><p>I would tend to say that its going to get heat soaked over time no matter what side is facing the header. So put the shiny side out so that less of it radiates out.</p>
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Old 09-16-2015, 06:02 PM   #5
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Polished side down facing headers, raw facing out towards sc.

Heat reflection away from the sc is what you want. Sure the raw side will emit heat but with the other side being reflective it should be 'better'.

If you want the raw side to dissipate heat more efficiently & hold less, paint it black.
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Old 09-16-2015, 06:03 PM   #6
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<p>What about when it all becomes heat soaked and the shield is the same temp as the headers?</p>
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Old 09-16-2015, 06:04 PM   #7
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Not a heat transfer expert by any means but if I were you, I would build a 3 layer heat shield with two skins of metal and a fiberglass layer in between like the OEM heat shields.
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Old 09-16-2015, 06:07 PM   #8
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Quote:
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<p>What about when it all becomes heat soaked and the shield is the same temp as the headers?</p>
This is going to happen regardless
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Old 09-16-2015, 06:14 PM   #9
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<p>So when it is heatsoaked don't you want it to not radiate at the supercharger?</p>
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Old 09-16-2015, 06:17 PM   #10
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Quote:
Originally Posted by Girz0r View Post
Polished side down facing headers, raw facing out towards sc.

Heat reflection away from the sc is what you want. Sure the raw side will emit heat but with the other side being reflective it should be 'better'.


If you want the raw side to dissipate heat more efficiently & hold less, paint it black.
Thanks, that's the way I thought would work best too.

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Originally Posted by aidandj View Post
<p>What about when it all becomes heat soaked and the shield is the same temp as the headers?</p>
Quote:
Originally Posted by Girz0r View Post
This is going to happen regardless
Yes either way you orient the metal, with it being 1/2" away from the header primaries it's going to get really really hot, no doubt. Still, one way is probably better than the other, thus this thread.


leboeuf- I don't know 100% yet how it's going to get built. I'm going to test some things to see what seems to work better. But you are right, and I am in fact going to try to build a double layer heat shield. In fact, if it's possible, I'm going to try to build a stainless heat shield that fits underneath the factory heat shield. Then install the factory heat shield over that. If that works, I would have an air gap between the header and stainless, and another air gap between the stainless and stock heat shield. And an air gap between the stock heat shield and the SC. But I don't know if I can actually make that work yet, my sheet metal equipment includes a pair of shears and rivets and the packaging in this area sucks big time.
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Old 09-16-2015, 06:18 PM   #11
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Quote:
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<p>So when it is heatsoaked don't you want it to not radiate at the supercharger?</p>
Correct. The perfect heat shield for me would result in the supercharger not receiving any heat from the exhaust header at all. Goal is to keep the SC as cool as possible for reliability.
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Old 09-16-2015, 06:28 PM   #12
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The mirrored finish isn't going to hold in the heat, just mostly reflect.

If you had both sides polished it would just reflect both ways and the sc would be affected by it's own heat. But in his case with only 1 side polished, you want to reflect as much heat as possible away from the SC. Heat radiation is going to happen no matter what but the metal itself will still do most of the job. The reflection is just a bonus.

Painting the side towards the sc black would have it dissipate the heat much faster.







The reflective gold keeps heat radiation 'out', while the black parts emits heat out.

https://en.wikipedia.org/wiki/Emissi...esliesCube.png
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Heat Transfer Question-vid-206.jpg   Heat Transfer Question-setrab%2520oil%2520cooler.jpg   Heat Transfer Question-current_install.jpg  
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Old 09-16-2015, 06:34 PM   #13
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Quote:
Originally Posted by Girz0r View Post
The mirrored finish isn't going to hold in the heat, just mostly reflect.

If you had both sides polished it would just reflect both ways and the sc would be affected by it's own heat. But in his case with only 1 side polished, you want to reflect as much heat as possible away from the SC. Heat radiation is going to happen no matter what but the metal itself will still do most of the job. The reflection is just a bonus.

Painting the side towards the sc black would have it dissipate the heat much faster.
...
The reflective gold keeps heat radiation 'out', while the black parts emits heat out.

https://en.wikipedia.org/wiki/Emissi...esliesCube.png
Ok question: So in theory, whatever is the last metal layer that faces the header: You're saying painting that black would have it dissipate the heat out faster. I agree. Problem I see is, that heat that's being dissipated would be radiated towards the SC. Right? It would make the metal surface cooler, but ultimately that would radiate more heat out of the exhaust. Your heat exchanger pics show that, they're black to maximize their effectiveness at radiating heat. I actually want to do the opposite, I want as little heat to radiate towards the SC as possible.
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Old 09-16-2015, 06:43 PM   #14
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Quote:
Originally Posted by patsmx5 View Post
Ok question: So in theory, whatever is the last metal layer that faces the header: You're saying painting that black would have it dissipate the heat out faster. I agree. Problem I see is, that heat that's being dissipated would be radiated towards the SC. Right? It would make the metal surface cooler, but ultimately that would radiate more heat out of the exhaust. Your heat exchanger pics show that, they're black to maximize their effectiveness at radiating heat. I actually want to do the opposite, I want as little heat to radiate towards the SC as possible.
The side towards the header, you want reflective always.

With it that close to the header and being near the header temp, the heat is going to build up and have nowhere to go and will radiate heat for a longer period of time. Having the raw side up towards the SC will emit heat but it with dissipate much quicker if it is black (black pieces examples).

If you want even less heat radiating towards the sc, leboeuf's idea would be perfect. The middle layer would transfer less heat absorbed from the headers. If you used 2 polished pieces facing out, and a middle layer. You would reflect any heat from the SC, back towards the SC. Heat from the header -> back to header.

Or if you're still using 1 piece, you can weld a bunch of chipset heatsinks to the top of the metal so any passing air will dissipate even more heat much quicker
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Old 09-16-2015, 06:55 PM   #15
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So ideally (if it's possible to package) I need to build a double-layer heat shield, with either an air gap, or a middle layer of fiberglass, and have both outer surfaces shiny. Have the raw surfaces facing each other. I like this idea, and I think it's awesome. Problem is, I couldn't use the stock heat shield if I did this, AND, I don't know that my fab skills with sheet metal are up to this task.

I think what I'm going to do when the metal arrives is build some small samples of each variation we've discussed, and then test each sample by mounting it near the header and idling the car for a while and see which works best. If the double-layer-both-both-shiny-sides-out approach proves to be amazing, I could then ditch the stock heat shield.
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Old 09-16-2015, 07:03 PM   #16
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You're going to be fighting a loosing battle at idle, I'd just be sure the low pressure area at the rear of the undertray circulates fresh air around the headers, if possible.

Heat goes up, and it sounds like your supercharger is up. Unless you completely close off the header heat will just wrap up and around the shield.

If you get the airflow right, hopefully the shield never fully heatsoaks.

That'd be how I went after it.
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Old 09-16-2015, 07:04 PM   #17
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<p>I would switch to a coldside supercharge. I've seen how fast you work, bet you could bust one out in a weekend</p><p>&nbsp;</p>
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Old 09-16-2015, 07:12 PM   #18
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Quote:
Originally Posted by deezums View Post
You're going to be fighting a loosing battle at idle, I'd just be sure the low pressure area at the rear of the undertray circulates fresh air around the headers, if possible.

Heat goes up, and it sounds like your supercharger is up. Unless you completely close off the header heat will just wrap up and around the shield.

If you get the airflow right, hopefully the shield never fully heatsoaks.

That'd be how I went after it.
This is the best pic I can find to show the location of the SC relative to the header. It's basically up, forward a bit, and to the drivers side some relative to the header primaries.


I know it's possible to shield this thing well. I'm not the only person running a hotside SC setup. Also OEMs shield their exhaust systems well and package stuff close to them all the time.
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Old 09-16-2015, 07:15 PM   #19
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Quote:
Originally Posted by deezums View Post
You're going to be fighting a loosing battle at idle, I'd just be sure the low pressure area at the rear of the undertray circulates fresh air around the headers, if possible.

Heat goes up, and it sounds like your supercharger is up. Unless you completely close off the header heat will just wrap up and around the shield.

If you get the airflow right, hopefully the shield never fully heatsoaks.

That'd be how I went after it.
Also, there will be airflow as you say once I'm driving. At idle with the hood shut it will only be airflow from the fans running on low. But heat load at idle is low. I suspect the supercharger will be the hottest while cruising down the highway. That seems to be when it was the hottest before.

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<p>I would switch to a coldside supercharge. I've seen how fast you work, bet you could bust one out in a weekend</p><p>&nbsp;</p>
You're funny! Yeah, that would take forever. Also would introduce a lot more problems I'd have to solve, and stuff I'd have to move. No way I'm doing that at this point. I'll build an insulated and air conditioned box around the SC before I move it to the coldside.
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Old 09-17-2015, 12:23 AM   #20
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Quote:
Originally Posted by patsmx5 View Post
So ideally (if it's possible to package) I need to build a double-layer heat shield, with either an air gap, or a middle layer of fiberglass, and have both outer surfaces shiny. Have the raw surfaces facing each other. I like this idea, and I think it's awesome.
Something like this: Insulated Heat Shield (1990-2015)

It's more fun to build something, but ...
these guys have already engineered it, it works and it's easy.
I've used them since I put my aftermarket header on.
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