air /water

[chimera]

Hullo
The Thomson double-vortex water turbine (1870) operated with a short head and long inner-radial vortex gravity-outflow. Out of idle curiosity I'm asking about efficiency of a long water-head compared with long drain producing negative air pressure. For the same mass x height.G , is it better to have high-speed water-flow at the bottom of the long water-head or low-speed near the top of the head under added air-pressure from the semi-vacuum by the drain?

[JAlberts]

From my review, either arrangement will work; but, the long discharge is limited to less than 30 feet of water discharge pipe height. As far as the flow velocity in the inlet vs. the flow velocity in the outlet, when the unit is operating the flow rate entering the inlet will always equal that of the outlet.


When considering the flow of a fluid through a system it is the differential pressure across the system that determines its throughput and for a required given total operating head the total height from the source to the discharge is what is important. One limiting factor for the outlet is that is height must be less than 30 ft but there is no limit as to how much head pressure can be applied to the inlet.

For example, if a total head of 40 ft is required then the total pipng distance and, assuming equal pipe sizes, the flow friction loss is going to be same, so as long as the outlet pipe height is less than 30 feet you are free to split the 40 feet between between the inlet and outlet piping lengths it best fit the installation location.

[chimera]

Excellent thank you. I guessed the 2 flow dynamics would be equal but the rapid acceleration at the top is unexpected. It suggests the compression in a jet engine inflow-outflow, and internal combustion injector-extractor.
Are you meaning that after 30ft the water is disintegrating with speed , allowing air back-pressure from below to limit further acceleration? Then would a tapering pipe at optimal size give continued increase until pipe-friction stops that?

[JAlberts]

You are confusing water with air. As long a there is a sufficient supply of water to the unit there will not be any air in the pump or system. Increasing the water velocity at any point in the piping will only serve to increase the flow friction loss through the system, slow the water flow rate and degrade the performance of the turbine pump.