What will happen if a uniform cross section draft tube is used instead of a conical draft tube?

Answer 1

In a Reaction turbine,the Draft Tube is used to reduce the exit velocity loss in order to minimize the exit energy loss. The conical Draft tube ensures this as the diverging area ensures a lower velocity at draft tube exit (since acc. to Q = VxA; the continuity principle,an increase in area renders a decrease in velocity) than its entry point ( at runner exit). A straight (uniform c/s draft tube) draft tube will impart no reduction in the magnitude of exit velocity and thus the employment of a draft tube at the runner exit will be futile.