Thesis submitted in fulfilment of the requirements for the degree
Master of Technology: Civil Engineering
in the Faculty of Engineering
at the CAPE PENINSULA UNIVERSITY OF TECHNOLOGY
2014 / The current problems of orifice, nozzle and Venturi flow meters are that they are
limited to turbulent flow and the permanent pressure drop produced in the
pipeline. To improve these inadequacies, converging-diverging (C-D) tubes were
manufactured, consisting of symmetrical converging and diverging cones, where
the throat is the annular section between the two cones, with various angles and
diameter ratios to improve the permanent pressure loss and flow measurement
range.
The objective of this study was firstly to evaluate the permanent pressure loss,
secondly to determine the discharge coefficient values for various C-D tubes
and compare them with the existing differential pressure flow meter using
Newtonian and non-Newtonian fluids, and finally to assess the performance of
these differential pressure flow meters.
The tests were conducted on the multipurpose test rig in the slurry laboratory at
the Cape Peninsula University of Technology. Newtonian and non-Newtonian
fluids were used to conduct experiments in five different C-D tube flow meters
with diameter ratios (β) of 0.5, 0.6 and 0.7, and with angles of the wall to the
axis of the tube (θ) of 15°, 30° and 45°.
The results for each test are presented firstly in the form of static pressure at
different flow rates. It was observed that the permanent pressure loss decreases
with the flow rate and the length of the C-D tube. Secondly, the results are
presented in terms of discharge coefficient versus Reynolds number. It was
found that the Cd values at 15° drop earlier than at 30° and 45°; when viscous
forces become predominant, the Cd increases with increasing beta ratio. The Cd
was found to be independent of the Reynolds number for Re>2000 and also a
function of angle and beta ratio.
Preamble
Performance of a symmetrical converging-diverging tube differential pressure
flow meter
Finally, the error analyses of discharge coefficients were assessed to determine
the performance criteria. The standard variation was found to increase when the
Reynolds number decreases. The average discharge coefficient values and their
uncertainties were determined to select the most promising C-D tube geometry.
An average Cd of 0.96, with an uncertainty of ±0.5 % for a range of Reynolds
numbers greater than 2,000 was found.
The comparison between C-D tubes 0.6(15-15) and classical Venturi flow meters
reveals that C-D 0.6(15-15) performs well in turbulent range and shows only a
slight inaccuracy in laminar.
This thesis provides a simple geometrical differential pressure flow meter with a
constant Cd value over a Reynolds number range of 2000 to 150 000.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/1029 |
| Date | January 2014 |
| Creators | Ilunga, Luc Mwamba |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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