Post AukjIIJsAoTSSnUv44 by azonenberg@ioc.exchange
 (DIR) More posts by azonenberg@ioc.exchange
 (DIR) Post #AukirbeuA8vSclbqZk by azonenberg@ioc.exchange
       0 likes, 0 repeats
       
       What are the pros and cons of pinned vs finned heatsinks? I'm thinking specifically about rectangular pins like seen in my previous post (Wakefield-Vette 960 series).Initial thoughts:* Fins absolutely have to have airflow down their long axis. Square/round pins don't care, rectangular pins degrade but not horribly if you're oriented wrong* Pins weigh less* Fins have more surface area (at least, in the direction of airflow) in the same footprint* Fins have smooth unbroken channels while pins have interrupted channels. This probably Does Things to boundary layers and eddies and such but I'm not a fluid dynamics person.I'm sure somebody has spent years CFDing heatsink designs and can accurately comment on why both are in common use still. But not me.
       
 (DIR) Post #Aukirc92M71q8DhuXg by mntmn@mastodon.social
       0 likes, 0 repeats
       
       @azonenberg subscribing to this :D
       
 (DIR) Post #AukirfbVUiaIrO3Bpo by azonenberg@ioc.exchange
       0 likes, 0 repeats
       
       My gut feeling is that surface roughness is also super important for boundary layer behavior, but I can't put any numbers to it.
       
 (DIR) Post #Aukj4FalW9SBwxhbyC by mntmn@mastodon.social
       0 likes, 0 repeats
       
       @azonenberg we currently have a large copper heatsink inside of reform with rk3588 that has milled fins and some geometry on the back side. it's expensive to mill. there's no fan in the case, so i'm thinking these fins shouldn't really matter, and currently they press against the acrylic bottom plate. i'm thinking to redesign this as a pure 2.5d cube/slab of copper and my feeling is that this should be fine under the circumstances. (no fan)
       
 (DIR) Post #AukjE7be3znU4uoxJA by jaseg@chaos.social
       0 likes, 0 repeats
       
       @azonenberg I think another point for fins is that they have more thermally conductive material overall. I think that when you have air flowing across a pin heatsink, the volume in the "shade" of these pins contributes little, and might as well be filled with thermally conductive material to transport heat to the top.Another consideration is mechanical stability. Pins have to be pretty chonky to not bend, and to be machineable or moldable, whereas you can make fins much thinner.
       
 (DIR) Post #AukjE86qC0kbdfPrvs by jaseg@chaos.social
       0 likes, 0 repeats
       
       @azonenberg In cost-sensitive applicatoins, in aluminium, fins are easier to make since you can extrude them. Pins require either casting, or milling.
       
 (DIR) Post #AukjE8SStc32ijX8dc by mntmn@mastodon.social
       0 likes, 0 repeats
       
       @jaseg @azonenberg i wonder if ideally one would want kind of a sponge like structure (from metal) instead, if this wasn't mega expensive
       
 (DIR) Post #AukjIIJsAoTSSnUv44 by azonenberg@ioc.exchange
       0 likes, 0 repeats
       
       @mntmn @jaseg If it was sufficiently open to get good airflow through it maybe? But you would also need enough material to get heat to flow from the chip into the area being cooled.
       
 (DIR) Post #Aukjdu0jEXMhRSqYGO by jaseg@chaos.social
       0 likes, 0 repeats
       
       @mntmn @azonenberg I think that might be a good thing, if you can guarantee a sufficient amount of material conducting heat. I think a regular structure would be preferrable to avoid some units having non-deterministic hot spots. On the geometry, as far as I understand, turbulence is a good thing in heatsinks, as laminar flow results in the boundary layer receiving most of the heat, and air further away from the surface not receiving much heat.
       
 (DIR) Post #AukjrrAYawC8gR67Au by jaseg@chaos.social
       0 likes, 0 repeats
       
       @mntmn @azonenberg For thin-finned copper or aluminium heat sinks, they also make them via "skiving", i.e. shaving off each fin from the surface of the copper slab, then leaving it to stand up. I think that's a cool process and that those are more economical compared to milling.
       
 (DIR) Post #AukpUPHqh6JNGwi4lE by mntmn@mastodon.social
       0 likes, 0 repeats
       
       @jaseg @azonenberg ah that's interesting, thanks
       
 (DIR) Post #AukvZ3YxUTLb4MJTV2 by gsuberland@chaos.social
       0 likes, 0 repeats
       
       @mntmn @jaseg @azonenberg this is a lesson the liquid cooling folks learned a while back too. for a while they were all trying to pitch the most laminar fluid flow possible, but it turns out that vorticity around the fin block is extremely important, especially when you go down to ultra-fine skived fin pitch for the large surface area. with purely laminar flow you end up losing all that surface area to the boundary layer, and the viscosity / surface tension functionally "block" the channels.
       
 (DIR) Post #Aukzisf1HNCdy95Wim by owiecc@en.osm.town
       0 likes, 0 repeats
       
       @mntmn @jaseg @azonenberg you can actually buy copper sponge heatsinks.
       
 (DIR) Post #AulDeMQYZvmwCQ3uq0 by mntmn@mastodon.social
       0 likes, 0 repeats
       
       @owiecc @jaseg @azonenberg wow indeed, thx :D
       
 (DIR) Post #AulDxKIOjC1L5fI0OG by mntmn@mastodon.social
       0 likes, 0 repeats
       
       @owiecc @jaseg @azonenberg heh, "The reality is that this copper foam is a more effective insulator than a conductor of heat" https://hackaday.com/2014/08/03/behold-the-most-insane-crowdfunding-campaign-ever/ also interesting about the color
       
 (DIR) Post #AulSLWcByXeZbdyt1s by owiecc@en.osm.town
       0 likes, 0 repeats
       
       @mntmn @jaseg @azonenberg This is the product: https://www.mouser.dk/pdfDocs/VTL-LowProfileHeatsink-DATASHEET-MARCH2015fv.pdf
       
 (DIR) Post #Aum1ydnEiZh5YfXBFg by poleguy@mastodon.social
       0 likes, 0 repeats
       
       @mntmn @jaseg @azonenberg I'm not a ME, but imagine a sponge like structure would cause turbulent flow, which maybe wouldn't be best?