chap0070

chap0070 - Other Losses : Minor (Local) Losses In Pipes...

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Unformatted text preview: Other Losses : Minor (Local) Losses In Pipes M.S. Ghidaoui, Spring 2002 Introduction: Minor losses are localized losses which arise whenever an adverse pressure exists in the system. Adverse pressure is said to occur whenever the pressure down-stream is larger than the pressure upstream. Once adverse pressure occurs, stream-lines bend and a separation zone is created. This separation zone dissipates energy through turbulence. The mathematical form of all minor losses is as follows: g V K h ml 2 2 = where V is the average velocity at the minor loss location, K is the minor loss coefficient which is usually determined from experiments. Examples of locations in pipelines where minor losses occur include pipe bends, elbows and joints, valves, sudden pipe expansion, sudden pipe contraction. Below, qualitative explanation of why and how minor losses occur is provided. In addition, tabulated values for the minor loss coefficients k are given. However, the tabulated values given here are by no means exhaustive. Note : The total losses in a pipe (friction + minon) is: g V D fL K D fL g V K D fL g V D fL g V K h ml 2 ) 1 ( 2 ) ( 2 2 2 2 2 2 + = + = + = If K<<fL/D, minor losses can be neglected. Therefore, you should perform an order of magnitude analysis before deciding whether or not to include minor losses. For example, if a pipe has a diameter of 200 mm and a length of 1000 and this pipe is connected to an upstream reservoir. The K between reservoir and pipe is of order 1.0. The friction factor for commercial pipes is of order 0.02. The fL/D is of order 1000*0.02/0.2=100>>1.0. Therefore, the minor losses between pipe and reservoir need not be included in this case!...
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chap0070 - Other Losses : Minor (Local) Losses In Pipes...

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