A small calculation
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The pump outlet parameters and conditions remain constant. The flow rate when pumped through the long pipe of length L to point A is 22 t/h, (with point A directly connected to the atmosphere). The flow rate when pumped to point A through the long L+M pipeline is 7 t/h, (with point A directly connected to the atmosphere). So, what is the flow rate when it is pumped to point A through a long pipe of length L+M (with the relative pressure at A being –4 KPa)? (The pipe is a cast iron pipe with DN50 diameter, and the liquid density is 1.81)
The flow rate when pumped to point A through the long L+M pipeline is 7 t/h, (with point A directly connected to the atmosphere). Was it written wrong?
Your conditions are not complete; what is the height difference, and what are the properties of the medium?
Let the original pressure drop be PkPa. From Q~u2 P~Re~u, d, ρ, we have: P~L(22)1/2 P~(L+M)*(7)1/2. Find: P+4~(L+M)*?1/2. Solve for ? =( )L Watch the expert take action!
The characteristic curve of the pump is a more important factor; it is essentially impossible for a centrifugal pump to maintain a constant outlet pressure when the flow rate changes significantly. Assuming that the pipes are straight (otherwise, the resistance caused by elbows, valves, etc. should be converted into an equivalent pipe length), the pressure drops in pipelines with lengths L+M and L can be used to determine the relationship between the pipeline resistance coefficient and flow rate. Since only two data points are available, only a linear relationship can be determined, which serves as a rough estimate within a certain range. Last edited by RainWolf on 2009-2-7 12:05.]
Thank you all for your participation. To add more details: 6 elbows at 90 degrees, 4 elbows at 45 degrees; the pipe length is 100 meters, the height difference is 0, and the medium is sulfuric acid
Strictly speaking, this problem has no solution; based on the given conditions, it is possible to calculate the frictional loss along the flow path as well as the total head. But the flow rate requires knowing the head and resistance by referring to the pump’s performance curve; without knowing the pump’s performance curve, how can the flow rate be calculated? :lol