Black Body Radiator vs painted surface

  • #26
Yes, this vid is all wrong....I see this kind of stuff all the time....

They are using "common sense" which often fails miserably in physics and chemistry.
A "super thick" coating of epoxy is not a good idea for heat transfer or durability...in fact, it's backwards.

A little about construction:
Pure A1100 aluminum is extremely salt water resistant, no coating is required.
If the aluminum heat sink is corroding, they are using an alloy of aluminum, not pure aluminum...but this isn't a surprise.
The likely reason for the alloy choice is CP (commercially pure) aluminum is widely available in structural shapes (extrusions) and very uncommon in sheet form. It's too weak/soft for most sheet metal applications.

To properly coat aluminum with anything, an etch must be used. There is no other method for sound bonding and protection.
Scratching with sandpaper may give the appearance of a good bond but won't pass the ASTM B117 salt spray test.
I never fails to amaze me how salt will get into the smallest micro-pores make it's way through almost anything given enough time.

Most epoxy shrinks with time and it usually develops cracks at the edges. Thin coats are used to prevent this type of cracking.
Thick epoxy is very susceptible to large amounts of shrinkage/cracking.....bad choice.
 
  • #27
906
223
fascinating thread.

I found this abstract. I think you have to pay to see the full article. is anyone a member or have access that can look at the full paper. it appears interesting and relevant to this topic. I would love to read the conclusion and results;

http://iopscience.iop.org/article/10.1088/0957-0233/17/11/012/meta;jsessionid=D01CFE890E4FDD8363148DDEF9DB0972.c1

Abstract
A scanning photo acoustic technique to determine the thermal transport parameters, thermal diffusivity, effusivity and conductivity, as well as heat capacity of paint coatings on different backings is described. These parameters are obtained by measuring the normalized photo acoustic phase values from paint coatings of varying thicknesses and then fitting the experimental data with the theoretical expression for phase. Results are reported on four different black paint coatings on a metallic backing. The values obtained for thermal diffusivity are comparable to those reported in the literature following other techniques. Measurements have also been carried out on paint coatings over backings that are good as well as poor thermal conductors. No significant changes in the values of the thermal parameters of paint coatings could be detected for different backing materials with widely differing thermal properties.
 

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