Zonestar P802Q Fan Duct

This repository includes a number of parts which are designed to improve the hotend cooling duct of the [Zonestar P802Q/P802QA](http://www.aliexpress.com/item/full-Metal-Reprap-Prusa-i3-3d-Printer-DIY-kit-Stainless-Steel-Easy-Installation-2-Roll-Filament/32586716087.html?spm=2114.40010308.4.2.iW3265) 3D printer.

The design is based on the [Francis turbine](https://en.wikipedia.org/wiki/Francis_turbine) and the geometry has been [tested using OpenFOAM](https://www.youtube.com/watch?v=vOTOZOcnM