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> push rod tube, to paint or not
jacksun
post Jul 1 2014, 11:43 AM
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Hi,

got my first push rod tube cleaned up and would like to paint it with

hi-temp paint? any problems doing so?

tks

randal
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Highland
post Jul 8 2014, 05:39 PM
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I just watched both u-tube videos and it seems like no one talks about natural convection versus forced convection. I could see how the black paint leads to a higher surface temperature resulting in greater natural convection and significantly lower air output temperature. Of course with a fan or a car driving forward natural convection would be insignificant. The guy in the engineering video says 3 degrees is significant, but my guess is 3 degrees is within their measurement accuracy of not only their thermocouples, but the hair dryer’s ability to provide constant flow and temperature.

So my understanding is that you want air flow with no separation for good heat transfer. The fins have to be spaced far enough from each other so the adjacent boundary layers don't interfere with each other while maximizing the number of fins. I assume the VW engineers spaced the fins based on “design for manufacturing” so the range of surface roughness, flash, etc. would not affect the flow patterns and boundary layer thickness around the fins.

So back to the push rod tubes. The tubes measure a bit less than an inch. I could use some input here, but from what I can find a Reynolds number greater than 10 results in the start of air flow separation for a cylinder shape. If 60 mph air (either from forward travel or the fan) is passing around the tubes, that’ll give us a Reynolds number of about 700. I assume if you have the warm air guides installed most of the airflow whether standing still or moving is from the fan. Does anyone the air flow velocity of the fan? In any case there appears to be very little convection heat transfer occurring especially since the downstream tubes are getting turbulent air. If there is any heat transfer in radiation I’d rather have hot tubes than the tubes radiating toward the cylinders. I’m assuming the tubes are hot because they have so little mass compared to cylinder, shielding, and other parts.

So maybe black is not so good, but bare metal or a light color is okay? Although I agree with everyone else that it probably makes no real difference.
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jacksun   push rod tube   Jul 1 2014, 11:43 AM
914Sixer   Paint holds heat. They were plated gold or clear ...   Jul 1 2014, 02:13 PM
jacksun   hmm ..... now I have four painted.............. f...   Jul 1 2014, 04:59 PM
Mike Bellis   Has anyone really done a study to find out how muc...   Jul 1 2014, 05:24 PM
Mike Bellis   BTW, Kirchoff's Law of Thermodynamics basicall...   Jul 1 2014, 05:34 PM
jacksun   just kidding about the purple....... they are blac...   Jul 1 2014, 05:37 PM
Mike Bellis   just kidding about the purple....... they are bla...   Jul 1 2014, 06:07 PM
swooshdave   Some of you are worried that a little paint on the...   Jul 1 2014, 06:08 PM
Mike Bellis   Some of you are worried that a little paint on th...   Jul 1 2014, 06:12 PM
r_towle   Some of you are worried that a little paint on th...   Jul 1 2014, 07:20 PM
swooshdave   What happens if I paint my jackstands? (oops, I h...   Jul 1 2014, 07:25 PM
PlantMan   What happens if I paint my jackstands? (oops, I ...   Jul 1 2014, 07:59 PM
malcolm2   I painted mine..... But masked off the o-ring sea...   Jul 1 2014, 08:04 PM
PanelBilly   It it looks good then do it. Are you going to race...   Jul 1 2014, 08:18 PM
malcolm2   It it looks good then do it. Are you going to rac...   Jul 1 2014, 08:21 PM
Keyser Sose   All the oil that goes to the rocker assemblies, wh...   Jul 1 2014, 08:49 PM
jacksun   http://www.vw-resource.com/cooling_qa.html ...   Jul 2 2014, 04:56 AM
Keyser Sose   Oil 'dribbles' back? Sure, at idle. Fift...   Jul 2 2014, 12:23 PM
stugray   The old wive's tale of "Black gets hott...   Jul 2 2014, 01:19 PM
Java2570   And we all know what happened to Dr. Malcolm in Ju...   Jul 2 2014, 01:47 PM
WLD419   I went ahead and painted mine :) , I ended up us...   Jul 3 2014, 04:01 AM
stugray   What's with the plug wires? Must be dual plug...   Jul 3 2014, 08:03 AM
WLD419   What's with the plug wires? Must be dual plu...   Jul 3 2014, 08:23 PM
barefoot   Sorry, slight thread hijack, but an order of magni...   Jul 3 2014, 08:36 AM
barefoot   xx   Jul 3 2014, 04:06 PM
stugray   Funny that I stumbled across this after this discu...   Jul 6 2014, 10:49 PM
jacksun   thanks for the link   Jul 7 2014, 06:08 AM
Keyser Sose   Sorry, can't believe that, no way. Bare metal...   Jul 7 2014, 06:53 AM
stugray   I think that the point was: "Black painted ...   Jul 7 2014, 07:14 AM
Keyser Sose   You're talking about the point in that video, ...   Jul 7 2014, 12:32 PM
stugray   Yes, and it also applies to this discussion. 1 ...   Jul 7 2014, 01:06 PM
Keyser Sose   In the video you posted the black paint really imp...   Jul 7 2014, 04:16 PM
stugray   That's exactly what I have been saying as wel...   Jul 7 2014, 06:07 PM
Keyser Sose   OK, reality check. Stu, we're talking about p...   Jul 7 2014, 07:54 PM
stugray   OK, reality check. Keyser - First I said it doesnt...   Jul 7 2014, 10:09 PM
Highland   I just watched both u-tube videos and it seems lik...   Jul 8 2014, 05:39 PM
Mike Bellis   I knew this would turn into a good debate... :evil...   Jul 8 2014, 06:04 PM


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