The tello is known to get quite hot whilst idle. If you’re programming a flight, setting up a wifi extender or doing any type of development/inspection you would of experienced this.
PC case fans are cheap and the right size for a tello to sit on.
I took the power leads (black and read) from a USB cable and connected it to the black and yellow cables on the fan.
Very easy to setup and you can run it from any USB port like a power pack.
You're right, it sits flush to the ground so airflow is limited. I am going to raise it off the ground and put a mesh over the top so the tello doesn't fall into the blades.
I bought this fan and it works great for the same purpose and I also use it to cool the Tello between flights. I live in a desert area and in the summer it is the only way I can fly more than 1 battery in the heat.