I work with small thermocouples and Hot-Wire/Hot-Film devices in my lab. To test and calibrate these devices requires some crazy equipment sometimes.
Try to imagine blowing air on a thermocouple that's in a chain of thermocouples 1mm apart without disturbing the ones on either side.
Hot-films are very sensitive to the air flow direction, and it's difficult to move a big fan around keeping the air flow at accurate angles.
So, after trying straws taped to little fans and other sometimes successful ideas, I designed a small hand-held air jet for this purpose.
The case was designed using AutoCAD, and printed on a SeeMeCNC H2 Delta 3D printer.
I designed it to use a small 30mm fan , and power it with a 9V battery.
Here's the finished unit:
Here's a video of the jet in operation with a hot-film.