The Supermicro SC847 chassis of yours only allows 2U heatsinks. I use the Supermicro socket 3647 2U active heatsink (
SNK-P0068APS4) myself in a SC826 2U chassis, but have replaced the stock fan with a quieter Noctua 60mm fan - with great results. Others have had good results with the
Dynatron B5 cooler. That's basically the two choices you have when it comes to active 2U socket 3647 coolers, at least as far as I am aware of.
I also purchased the Supermicro 4U socket 3647 (
SNK-P0070APS4) heatsink for an upcoming project of mine, but that one won't fit into your SC847 chassis.