classic | mobile
 

Search...

SA Instrumentation & Control Buyers' Guide

Technews Industry Guide - IIoT 2018

Technews Industry Guide - Maintenance, Reliability & Asset Optimisation

 

Open channel flow
October 2018, Flow Measurement & Control


Open channel flow is defined as flow in any channel in which the liquid flows with a free surface: examples include rivers and irrigation channels. Certain closed channels such as sewers, when flowing partially full and not under pressure, are also classified as open channels, which are used to conduct liquids in most sewer systems, sewage treatment plants, industrial waste applications and irrigation systems.

A flume is a specially shaped open channel flow section providing a restriction in channel area (Figure 1). The flow rate in the channel is determined by measuring the liquid depth at a specified point in the flume. The design of the flume is determined by the width of the throat: the bigger the throat the more flow through the flume. Common materials of construction are stainless steel, fibreglass and concrete. Similar measurements can be made with other flow restricting devices such as rectangular or vee-shaped weirs. However, flumes result in a lower head loss and are inherently self-cleaning, thus requiring less maintenance.

Figure 1. Schematic layout of a flume in a river channel.
Figure 1. Schematic layout of a flume in a river channel.

A secondary measuring device is used in conjunction with the flume to measure the rate of flow in the open channel. The ‘flowmeter’ measures the liquid level at one point in the channel and then converts this measurement into flow rate based on the known level-to-flow rate relationship of the flume.

There are a number of technologies for measuring the level in the channel. The most common is the non-contact method utilising ultrasonic and radar sensors. The open channel flow meter uses software to convert the nonlinear level measurement into a flow rate.

WIKA recently received an order to supply 3-inch and 9-inch Parshall flumes constructed from 2 mm 316L stainless steel. The flumes will be installed at the NCP Chlorchem site to measure exit effluent flow into the Jukskei River.

As mentioned previously, the level probe must be positioned at a special point in the throat of the flume. A frame has been attached to the walls of the flume positioning the level probe in the correct position. This will simplify the installation, as there will be no confusion as to where the level sensor must be positioned. The frame serves two purposes: one is to position the level sensor correctly; the second is to provide the capability to check the zero and range calibration of the flow meter while there is flow through the flume.

As can be seen in the image above, there are tabs attached to the side of the flume. This is for securing it into a concrete structure and to prevent the sides from caving in. The straps across the top are for structural support during installation only, once the concrete has cured they will be removed.

Parshall Flumes can be favourably installed in the following applications:

• Sewage works: because of the self-cleaning effect, no debris is collected on the side walls.

• Factory-treated effluent discharge into rivers.

• Measurement of irrigation water in open channels to predefined areas.

• Discharge water from purification plants.


Credit(s)
Supplied By: WIKA Instruments
Tel: +27 11 621 0000
Fax: +27 11 621 0060/59
Email: sales@wika.co.za
www: www.wika.co.za
Share via email     Share via LinkedIn   Print this page

Further reading:

  • Flow control problems in a pulp mill
    January 2019, Valve & Automation, Flow Measurement & Control
    NAF’s advanced process valves solve pulp, paper and cellulose applications.
  • Pressure calibrator with electric pump
    January 2019, WIKA Instruments, Maintenance, Test & Measurement, Calibration
    WIKA has expanded its range of portable calibrators to include an instrument with integrated electric pressure pump. The new model CPH7650 pressure calibrator – supplied in a robust case – is multi-functional ...
  • Hygienic diaphragm pressure gauges
    December 2018, WIKA Instruments, Pressure Measurement & Control
    WIKA has expanded the application range of its hygienic diaphragm pressure gauges with the model PG43SA-S, which is now also available in a version with ATEX approval. The pressure gauge can thus be used ...
  • Picomag for utility measurement
    December 2018, Endress+Hauser, Flow Measurement & Control
    In industrial process measurement and automation, demand is steadily rising for simple, reliable and maintenance-free measuring instruments in a pocket-sized format. The new Picomag from Endress+Hauser ...
  • Optisonic biogas flowmeter
    December 2018, KROHNE, Flow Measurement & Control
    The new Optisonic 7300 Biogas ultrasonic flowmeter from Krohne has been specially designed to measure dry and wet biogas with variable composition. The meter provides additional functions like calculation ...
  • Environmental challenges in the mining industry
    November 2018, Endress+Hauser, Flow Measurement & Control
    Endress+Hauser’s water quality measurement instruments.
  • Improved fuel management for mine fleets
    November 2018, Endress+Hauser, Flow Measurement & Control
    In the current economic climate, most companies are looking to make their Rands go further. This is especially the case when it comes to fuel, as modern industries cannot operate without it and diesel ...
  • Steam turbine control
    November 2018, WIKA Instruments, Sensors & Transducers
    In coal-fired power plants, steam is produced by pumping highly purified water through boiler tubes. The water is heated to a high temperature and pressure, and then flows through several orifices into ...
  • Clearly visible flow measurement
    November 2018, Instrotech, Flow Measurement & Control
    To check the flow processes in pipeline systems and for insight into the interior of process pipes, many flow indicators are used in which the flowing medium sets a rotor turning and thus, to a large ...
  • Electromagnetic flowmeter
    October 2018, Instrotech, Flow Measurement & Control
    Kobold’s new model EPS electromagnetic flowmeter has a standard accuracy of ±0,3% of reading stability of zero. The new developed, microprocessor-controlled UMF2 converter guarantees highest accuracy ...
  • Innovative compact orifice plate
    October 2018, WIKA Instruments, Pressure Measurement & Control
    Compact orifice plates can be used without difficulty for the measurement of liquids, gases and vapours. WIKA’s new compact orifice plate Model FLC-CO enables direct mounting of differential transmitters. Differential ...
  • Foxboro’s top performing intelligent vortex flowmeters
    September 2018, EOH Process Automation Solutions, Flow Measurement & Control
    The 84 series measures volumetric and mass flow of saturated and super-heated steam.

 
 
         
Contact:
Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Other
Terms & conditions of use, including privacy policy
PAIA Manual





 

         
    classic | mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.