The u.2 form factor is slightly larger than a 2.5" drive. I can imagine the entire space in it taken by Flash chips. I can't imagine what cooling scheme do they employ for the chips in the middle.

Apparently TDP is 30 watts¹, according to the product brief. I would imagine it's a single PCB with flash chips on both sides then thermally bonded to the aluminum chassis. That should keep all chips at approximately the same temperature. On its own it could be easily air cooled, but with 24 in a 2U chassis you'll be having some decently hefty forced air over the drives.

1. For comparison, an HDD usually comes in around ~10 watts

The transfer rates limit how much each chip can be active at any given time, so a heat-aware writing allocator can pick the least active blocks for the next writes and distribute the heat accordingly. Even if it’s not heat-aware, the tendency will be that the writes will be distributed over as many chips as there are, and so will be the heat generated.

Now, I would LOVE to see this much SLC flash on a direct to bus attachment setting.