Heat Transfer and Reflectivity?

[wchowe]

Hi All,
I have an application, with mostly aluminum parts. I have a central block that is water cooled. I have exterior parts that are bolted to the central block. I do not want to impede the heat transfer from the outside block to the inside cooling block. However, I would like to plate the parts so that I can increase reflectivity. I want to reflect as much heat as possible. This is a welding head, so close proximity to the heat source. I was going to use an electroles Nickel coating for reflectivity but I haven't been able to find any info on thermal conductivity? I want to make sure I don't insulate the mating surfaces. I would have to mask the plating if the plating hurts the transfer. Any suggestions or comments appreciated.

Thanks
Bill

 

[davefitz]

regular run of the mill aluminum has a 90% reflectivity. If you anodize the aluminum, the reflectivity drops to only 10%

 

[wchowe]

The EN coating is not an anodize. I realize that anodize acts as an insulator and wouldn't be good for this application. EN coatings I believe are good at electrical conduction, and I believe heat transfer. I know some companies use EN on heat sinks and radiators (coils). I would like to find specific numbers on the heat transfer.

Thanks
Bill

 

[wchowe]

Thermal Conductivity
The thermal conductivity of an electroless nickel deposit containing 8 to 9 percent phosphorus is 0.0105 to 0.0135 cal/cm/sec/°C. Electrodeposited nickel has a value of 0.19 to 0.26 cal/cm/sec/°C.

I found the above on a website, converting 7954 W/mk = 0.19 cal/cm/sec/C. That must be wrong, higher than silver?

Thanks
Bill

 

[IRstuff]

Your conversion is off by a factor of 100: 79.55 W/m-K, which is consistent with 90.5 W/m-K for pure nickel.

However, when you look at the thermal conductance of a 5 micron thick layer of nickel, you get 16 MW/m^2-K, i.e., its conductance is absurdly large relative to the more pithy problem of contact resistance.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[IRstuff]

The converse is that if you are that concerned about radiation, you might want to be looking for reflection barriers, coupled with some sort of maze to minimize convection. Or, encase everything in vacuum insulated panels, ala:

http://www.glacierbay.com/ultra-r.asp

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize