Standard design parameters used by engineers for pipeline design uses static hydraulic conditions between new pipe and old pipe by varying friction factors. Previous work has found hydraulic conditions cyclically vary during one calendar year to where energy loss ranges change from values equal to either new pipe (winter conditions) or aged pipe (summer conditions) friction factor values. Thus, there are two different types of roughness: pipe roughness and biofilm roughness. Pipe roughness is based on actual rugosity of the pipe wall. Biofilm roughness is based on the seasonal variations of friction factor, which directly quantifies energy loss, that can be attributed to biofilm growth.
Previous work on pipe roughness for large diameter pipe, or pipe that is 60-inches in diameter or larger, found that when experimental results were plotted on the traditional Moody diagram, the ratio of the roughness of the pipe to the inertial forces captured with Reynolds number does not follow the classic model used with the Moody diagram for large diameter pipe.
Biofilm is considered a viscoelastic medium in that the thickness can vary. Previous work has found velocity of the water in the conduit has an inverse relationship with the thickness of biofilm. The higher the velocity, the thinner the biofilm and visa versa. Biofilm thickness is also impacted by environmental conditions of the water within the pipe. An environmental process which can directly impact pipe roughness over time may be due to the presence of biofilm in the pipeline as evidence shows that nitrification occurs within the pipeline. This process lowers the pH of the water in the line which then can put any cementitious lining in jeopardy of increasing pipe roughness since the Langlier Saturation Index (LSI) will be negative, which indicates calcium carbonate (CaCO3) dissolves in water. In the system studied, the limestone aggregate as well as the sand contain high amounts of CaCO3 which have been eroded over time increasing the rugosity of the inner pipe wall.
This paper will try to
Establish the difference between pipe hydraulic roughness and biofilm roughness in long large diameter raw water transmission pipeline.
Establish there is a relationship between algal growth and increased friction factor values and in turn, determine the change in the hydraulic roughness of the pipe.
Establish if there is a spacial and time relationship between LSI, pipe rugosity, and biofilm growth.
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