I made a volute shaped blower where the housing for the fan is volute shaped, that is to say a widening spiral to test the effectiveness of a one way spinning impeller. The previous blower design is tear drop shaped so that the direction that the fan spins is un important. Also with the previous design the impeller spins one way and then the other as it is powered by a simple string mechanism.
source.image: Primitive Technology
In the new design, a weight was employed in the form of a heavy log attached to the rotor. The top of the rotor is held and the weight spun to create rotation. This method produces less rpm than the original but allows the fan to be spun continuously in one direction only. To compensate for the lower rpm, the fan was doubled in size (from 25 cm to 50 cm) to increase blade tip speed and so air speed.
Now with a fan that spins in one direction only, a housing could be used to take advantage of this fact. A volute is an expanding spiral and housing for fans that are volute shaped help guide the air from the center to the outlet more efficiently than a tear drop shaped one. This was made using mud on the ground as opposed to a clay portable one as it was starting to get too big to transport.
The fan was tested in an iron smelt. Disappointingly, it only produced a bit of iron in the form of much smaller prills than usual due to the low rpm and hence air pressure than the original blower. After some rough calculations from research, this design might become competitive with the original blower if the fan diameter was scaled up to 1m diameter from the original 25 cm diameter fan.