-Problem Set up

Introduction

Abbott Power Plant had a new cooling tower built in 2003, but a design flaw caused flow disturbances in the pipeline and possible air entrained in the high point of the pipe. An investigation at the power plant was conducted and the theories learned in class was used to analyze the piping system of the power plant.

Problematic pipeline with entrained air at high point

To fully understand this problem, we looked into the blueprints of the cooling system of the power plant, visited the Abbott Power Plant to view the problematic pipeline firsthand, and consulted Mr. Mike Brewer, mechanical engineer at the power plant, about how did the problem happen and possible solution. From the blueprints provided by Mr. Brewer, a simplified engineering drawing was created. Gabe Braboy, one of our classmates in TAM335, was willing to share his drawing with the entire class.

One of the blueprints provided by Abbott showing the pipe connecting from the sump to the plant across the street.
Simplified engineering drawing of the problematic pipeline (Braboy, 2019)

With this simple drawing in hand, the full extent of the problem was able to be understood and analyzed.

Energy grade line (EGL) and hydraulic grade line (HGL)

Using the dimension from the simplified drawing and spreadsheet, a graph of energy grade line and hydraulic grade line was created to identify the problematic section of the pipeline. The flowrate in pipe is 10000 gpm (0.631 m^3/s). The diameter of the pipe is 36 in (0.9 m), and 20 in (0.5 m) at the inlet of the pump. The pump head is 75 ft (22.9 m). Bernoulli’s equation was used to calculate the pressure in the pipe, and continuity equation gave the velocity of the flow. The frictional head loss per unit length was calculated to be 0.0029 ft/ft (0.00088 m/m) using moody diagram, and assumed constant throughout the pipe, ignoring the loss caused by the bends. The height of the pipe relative to the datum level was also drawn to better visualize the pressure head in the system. Detailed calculation can be found in the Energy Analysis tab.

The spreadsheet can be found in the following link:

Energy grade line and hydraulic grade line before the pump in SI units
Energy grade line and hydraulic grade line with the pump in SI units
Energy grade line and hydraulic grade line before the pump in Imperial units
Energy grade line and hydraulic grade line with the pump in Imperial units

From these graphs, it is observed that the high point of the pipeline is higher than the water level of the reservoir, which indicates a negative gage pressure would develop at this section of the pipe. Air bubbles can generate at this section of the pipe due to the negative pressure and disrupt the flow in the pipe. Energy analysis was then performed to calculate the pressure drop and the amount of air entrained in the pipe.

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