Mechanical Engineering

Since you want bearings on the outer tube 1/3 from the ends, lubrication, wear on the tube, and the type of bearings may be a problem. Also since those bearings will be further from the centerline, you will need a larger drive because of the increased torque. A rack and pinion drive will be difficult to keep clean and lubricated. That will also increase the torque requirements.

Bearings on a center shaft, even with one below the waterline, will have many benefits. Same with a center drive. The Dutch have been using screws like this for many years and have perfected the technology. You should study what they have done.

Composite bearings without rolling elements are typically used on the lower bearing. Water intrusion on this type of bearing isn’t a problem and can actually be used as the lubricant. A closed tube that rotates with the flights will minimize or even eliminate gap flow but it’s subject to fouling that will be difficult to clean. Having the screw located in a fixed half shell (trough) is much easier to construct and maintain. Gap flow really isn’t much of a problem because of the low head between the flights.

Thanks for your response. This is for a pilot project I want to see if it is possible to support a rotating Archimedes screw pump so part from this rack and pinion drive don't you think there is any kind of support for a hand driven one.

Whether motor or hand driven, the principals are the same. Furthermore, being hand driven, you want to keep the efficiency as high as possible. Center bearing support and no rack and pinion would be even more important.

However, a closed rotating tube may be more desirable on a hand driven pump. The slow hand drive speed may require gap flow to be kept to an absolute minimum.

Noted. I am wondering if it would work to put on a center bearing support for closed rotating tube at angle of 38 degree?