[module0000]

If you have available vertical space, I've printed a "cooling case" that works great with my pi 3b+ without heatsinks. It's shaped like a flower vase(wide top, narrow bottom). The top is open(think of it like a large, open drinking cup), and the pi sits in the very bottom. Two funnel-shaped openings(large inlet, small outlet) allow outside airflow directly onto the CPU and wifi chips.

So far it works at full load without throttling for at least the time span of a full length movie(my use-case is a plex media server). The concept is that exhaust heat leaving through the larger opening up top is heated(and expanding) air. The depressurized vase pulls cooler ambient air in through the 2 funnels, which strike the CPU and wifi module for a poor-mans "active cooling", albeit at much lower speeds than a motor-driven fan could provide.

The downside is required vertical; the case is 8 inches tall. This is several times the vertical height of the board itself, so it's a bit of a non-starter for small embedded device use-cases. If you have space to spare though, it might be worth a shot depending on your use-case.

[solstice]

Is there anything on top of it? If not, how do you deal with dust coming in from above when the pi isn't used that much (eg during the night) and the airflow lower?