Choosing the method of gravity flow measurement in public sewers

Summary

The aspects of choosing the method of measuring the flow rate and volume of wastewater gravity flow, particularly in case when the measurement results are used in accounting procedures (commercial accounting) are considered. It is shown that before studying the methods of measurement possible replacing gravity flow with pressure flow shall be considered because pressure flow rate can be measured more accurately. This measurement option is optimal from the technical point of view; however, in case the pressure section in the gravity pipeline is not available additional expenses are required for the water main reconstruction. In case this option is unacceptable the following methods of gravity flow measurement shall be considered (in the order of application priority): «level-flow rate» with the use of standard orifices (weirs and flumes) according to MI 2406-97 regulatory document; «level-flow rate» without any orifices with preliminary calibration of the measuring section according to MI 2220-13; «velocity-surface area» with the use of ultrasound flow meters; studying the velocity profile of the cross-section of the water main; calculation-instrumental (balance). By the specific example of an ultrasound flow meter it is shown that the flow rate error subscribed by the technical documentation can be several times lower than the actual one.

Key words

flow rate , measurement error , wastewater , ultrasonic flowmeter , gravity flow , flow measuring flume , calibration of measuring section

Methods of determining flow velocity in open channels at turbulent regime

Summary

The turbulent flow structure and velocity distribution at turbulent liquid flow is considered. The methods of determining flow velocity in open channels based on keeping records of the speed of helix blade rotation, of the floating object speed, of the dynamic pressure, of the flow force impact; on the heat exchange principle; on measuring water amount entering the meter for the observation period; on the use of ultrasound; on the use of laser are presented. The error of measuring velocity by different methods is indicated. The profile of liquid velocity in a complete-mix activated sludge model system is specified.

Key words

turbulent flow , hydrodynamics , Reynolds number , actual velocity , Bernoulli equation , Pitot tube , ultrasonic flowmeter , laser method , complete-mix activated sludge system

Metrological support for measuring water flow rate
in non-pressure large-diameter pipes

Summary

Possible verification of operating flow meters in large pipes of circular cross section with free flow of water is considered. Using a portable device placed in the pipeline through an inspection hatch is proposed as a working standard. The principles of installing and fixing the device are stated. Measuring instruments are pigmy meters mounted on a rotating rod. The experimental results are expressed by the average flow velocities on the selected circles. While processing the data, the Gaussian quadrature formula is used. The error in determining the flow rate is estimated using a model of pressure turbulent flow in a round pipe.

Key words

ultrasonic flowmeter , non-pressure large-diameter pipes , flow meter station , fluid flow rate , mobile standard