【Daily Question】Utilities - Water Supply and Drainage - 20190221

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A certain water supply system consists of two parallel gravity-fed pipelines with the same diameter and friction coefficient; several connecting pipes are installed between them to divide each pipeline into several sections. If it is required that 75% of the water supply volume can be maintained in the event of damage to a section of one of the water pipelines, then the water pipeline must be divided into at least ( ). a、70% b、75% c、80% d、85% Answer: c. The two water pipes are divided into n=6 sections by connecting pipes, and assume that the friction loss in each section of the water pipe is S. Then, during normal water conveyance, the head loss H1 in the water conveyance pipe is equal to 6S( )2 ； When a certain section is damaged, the head loss H2 = 5S( )2 + SQ2a ； Since H1 = H2, it follows that the value is 81.6%; therefore, when a section of one of the water pipes is damaged, 81.6% of the designed flow rate can still be maintained, so option c is correct.