Abstract
M.Tech. (Mechanical Engineering Technology)
This project researched the feasibility of using an existing mitre bend on the main condenser crossover ducting as an on-line flow measuring system. This flow measurement is based on the principle of an elbow type of flow meter. There are no detailed published standards or specifications available for Elbow flow meters.
The knowledge of the cooling water flow rate through the individual condensers would allow turbine heat rate calculations to be performed. In addition condenser, cooling tower and cooling water pump performance can be evaluated. An on-line system would also highlight potential problems sooner, thus eliminating costly unplanned shutdowns. The majority of the straight length of condenser cooling water piping is under concrete, thus making access very difficult. The exposed condenser piping
geometry is not ideal, with very distorted flow profiles expected, due to bends, valves, reducers, etc. Conventional flow measuring systems can therefore not be used, as ideal flow conditions (profiles) before and after the measuring instrument are required to er.sure the specified accuracy. The mitre bend being part of the piping geometry does not introduce additional head loss to the system and coupled to the low cost factor of an elbow type meter was the principal reason for the choice of this type of
measuring system. Part of the innovative aspect of this research is that a conventional elbow is not used but an existing mitre bend is utilised as the fundamental flow
measuring device. The Elbow/Bend differential pressure method to measure the condenser cooling water flow rate was investigated in the Flow laboratory at Eskom
(Technology Research and Investigations). A geometrically similar mitre bend was purchased and installed onto the 700 mm NB pipeline at the laboratory. The diametrical differential pressure was measured at the 22.5° and 45°axes of the 0.8 D mitre bend. The differential pressure was related to the fluid flow rate, and a calibration constant C was determined. The velocity profiles under the test conditions were verified. A Computational Fluid Dynamics model of the laboratory mitre bend was also produced. The model provided a clearer understanding of the internal flow patterns and the exact pressures on the inside and outside of the bend. The tests that were conducted in the laboratory confirmed the suitability of converting the main condenser crossover ducting mitre bends into an on-line cooling water flow measuring systems.