/* propeller's airfoil creates a pressure imbalance due to the Bernoulli effect */
Rather than nozzle try to think about EMDrive in terms of this device - the pipe, which separates the stream of gas to hot and cold part with vortex. The hot gas is more lightweight and it has lower momentum.
The nozzle for vacuum also reportedly exist as so-called Nassikass' drive. Nassikass thruster is even wilder stuff, as it reportedly doesn't require any external energy for its working, thus behaving like true perpetuum mobile in this way.