FLUID ENERGY CONVERTER

Embodiments include apparatus and methods of fluid energy conversion. One embodiment relates to a tube for a fluid energy converter. The tube may include a generally cylindrical and hollow body having an interior surface, an exterior surface, and a longitudinal axis. Another embodiment includes a fluid energy converter having a longitudinal axis and a rotatable tube coaxial about the longitudinal axis. In some embodiments, the rotatable tube converts kinetic energy in a fluid into rotating mechanical energy, or converts rotating mechanical energy into kinetic energy in a fluid.