When I googled personal cooling I got the strange looking cooling vests. I think I got a much easier idea.
I simply took a USB deskfan and connected it to a powerbank. With this I got a descent airflow and a very long battery time.
The fan was 10cm in diameter and rated at 2.5W.
I could easily run this fan for more than 4 hours. Together with a low noise profile and long battery time this idea has some interesting uses.
Be sure not use it near water or in the rain.