R-Theta Group Buy Anyone?

[Coulomb]

The company for which I head up the procurement team is a Customer of R-Theta. Using my new influence, I have some special pricing, the likes of which I do not beleive were available to our community before now.

This particular profile has been around the block here at about $55 US plus taxes and shipping for very large Qty buys a few years ago before metals started climbing in price.


How about $47.50 CAD plus taxes and shipping for Clear Anodized 11" sections if I buy 50 pecies?

A) Quote is based on providing R-Theta extrusion 65340 cut to 11.0+/- 0.020'' length.
B) Quote is based on clear anodize finish per MIL-A-8625, TYPE II, CLASS 1, CLEAR.

Regards

Anthony

[Ed LaFontaine]

....so using the thermal resistance given for a 3" section of 0.6, the thermal resistance of an 11" section would be...0.163?

[Coulomb]

Here is a thermal convection plot of 6 x 30Watt devices on a 12" section of this heatsink.

Anthony

[Coulomb]

oops a little confusion here on the Thermal plots.

The first one is a 12" section of 9012 profile.

[Coulomb]

Here is a thermal plot of an 11" section of the 9019 profile.

Same criteria, 6 devices dissipating 30 watts ea.

Anthony

[GRollins]

Originally posted by Ed LaFontaine


....so using the thermal resistance given for a 3" section of 0.6, the thermal resistance of an 11" section would be...0.163?

Unfortunately, no. The relationship is not linear because the heatsink depends on "room temperature" air to meet those specs. By the time the air conducts heat away from the lower portion of the heatsink and rises to the upper portion, it's warmer than room temperature and the efficiency of the heat transfer decreases rather quickly.
Heatsinks much taller than 6 or 8" may look nifty, but they really aren't all that much better at getting rid of heat than something 6-8" or shorter. If your goal is how it looks, go for it. If it's heat transfer, you'll waste money.
There's an easy-to-use calculator at Aavid-Thermalloy that can give you a gut feeling for these things even if the heatsink isn't exactly the same profile. Since a lot of the heatsink manufacturers have pretty similar profiles you can probably find something close to the one Coulomb is offering.

Grey

[Coulomb]

Well actually I am not offering anything. The extrusion can be cut to any length. The graphs I have posted are from the Calcultor on the R-Theta site. As is clearly demonstrated by the plot on the 9012 profile the Heat sink has wicked away the heat between the two rows of devices as demonstated by the much cooler blue centre.

Anthony

[Coulomb]

Here is the same plot from the R-Theta site on an 8" section with the same 6 x 30Watt heat sources.

You will note how much hotter the overall Heatsink is and how the average temperature of the Heatsink is also up.

Anthony

[GRollins]

Hmmm, the thumbnails disappear when you hit reply. I think I can do this from memory without having to open a bunch of windows or print the images.
Note that the 8" section is more consistent in temperature when comparing top to bottom. The taller section shows a distinct difference between top and bottom rows. Not only are the top devices running hotter than the bottom ones, but you'll find that the top and bottom rows won't bias quite the same due to the temperature differences.
Is it the end of life as we know it? Of course not. And it's nothing specific to R-Theta--just simple thermodynamics that applies to every manufacturer of heatsinks.
A twice-as-tall heatsink will dissipate somewhat more heat than a shorter one, but not twice as much. If you compare a 12" section to two 6" sections of the exact same profile, you'll find that two shorter sections beat one taller one every time, even though the surface area is the same, the profile is the same, the ambient temperature is the same, same number of active devices dissipating the same number of watts of heat, etc. I don't think of it as degrees C/inches of heatsink. I think of it as Pd/$. The math works out a little differently that way.

Grey

[cwujek]

Originally posted by Coulomb
The company for which I head up the procurement team is a Customer of R-Theta. Using my new influence, I have some special pricing, the likes of which I do not beleive were available to our community before now.

This particular profile has been around the block here at about $55 US plus taxes and shipping for very large Qty buys a few years ago before metals started climbing in price.


How about $47.50 CAD plus taxes and shipping for Clear Anodized 11" sections if I buy 50 pecies?

A) Quote is based on providing R-Theta extrusion 65340 cut to 11.0+/- 0.020'' length.
B) Quote is based on clear anodize finish per MIL-A-8625, TYPE II, CLASS 1, CLEAR.

Regards

Anthony

This was actually the exact profile I was thinking of switching to instead of going with Conrad. They quoted me at pretty much the same rate ($46USD) for 12" sections, which at first was significantly cheaper than Conrad. The problem was that they charge a ridiculous amount for milling, drilling, and/or tapping. The Conrad heat sinks are also already finished in black enamel, which provides a better thermal rating. All in all, looks like a good heat sink though.