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UDC 628.311
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
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UDC 697.317.2
Petrov D. Yu.
Investigating the dynamic mode of a heating system operation
Summary
Main specifications of the hydraulic mode of the advanced heating systems are given. The standard hydraulic calculation does not provide for the complete amount of information on the heating system operation. Accordingly a mathematic instrument (software-model) was developed to calculate a hydraulic circuit of an advanced heating system in a transit mode of operation. Hydraulic calculations of the two heating systems of similar structure, however, equipped with different balancing fittings were carried out. Typical tendencies of the system active elements operation were analyzed. Recommendations on specific use of the control valves were formulated.
Key words
flow rate , pressure drop , hydraulic condition , heating system , resistance characteristic , thermostatic control valve , balancing valve
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DOI 10.35776/MNP.2020.02.08
UDC 628.144:614.842.62:006.015.7
Primin Oleg
Optimization of the choice of diameters of the pipelines
in the water distribution network considering the fire safety
Summary
With the arrangement of combined drinking water and fire water supply systems, the importance of the distribution network increases even more, since additional functions are assigned to provide for the transportation of large amounts of water for firefighting. Meeting the firefighting requirements in conditions of a significant reduction in water consumption in most cities of Russia leads to negative consequences associated with low (0.1–0.3 m/s and less) flow rates and stagnation of water in some sections of the distribution network. Thereby, the organoleptic properties of water may deteriorate expressed in the appearance of flavors, unpleasant odors, increased turbidity and color, etc. In this regard, measures are required to optimize the choice of pipe diameters, to ensure and maintain the required quality of transported water in outdoor urban and distribution networks, and to guarantee meeting the required fire extinguishing standards. The research results and hydraulic calculations for assessing the minimum permissible water flow rates and minimum pipe diameters of submain networks are given taking into account the provision of external and internal firefighting. The tests were carried out in real conditions of the municipal water supply ring main in high- and low-pressure zones.
Key words
water consumption , flow rate , water supply network , head , water supply system , firefighting , velocity , nodal abstraction
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UDC 621.65:62-531.3
Economic efficiency of using pumping units with variable-speed drives at low water supply
Summary
In the process of operating pumps with variable-speed drive at low water flow rates the reduction of the pumping unit efficiency factor is observed. It is suggested to determine the amount of energy lost during the operation of such pumping units with actual efficiency factor differing from the rated one. In some instances operating with low water flow rate results in power consumption increase. In this context experimental studies on determining the pumping unit efficiency factor at different impeller speeds were carried out. The results of the studies provided for identifying the optimal operation zone where the pumping unit efficiency factor was reduced by less than 2% of the maximum value, and the less economic zone where the efficiency factor was reduced to 35% of the maximum value. To evaluate the economic efficiency and determine the optimal operation area of pumping units with variable-speed drives at low water flow rate the efficiency curves for different pump impeller speeds are required. It is appropriate to include this data in pump catalogues.
Key words
adjustable electric drive , water supply , flow rate , head , frequency of pump impeller rotation , pump , water disposal , lifting efficiency , electric motor power
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