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Calculating pump pressures and power (Bernouilli)

  1. Mar 14, 2015 #1
    1. The problem statement, all variables and given/known data
    http://imgur.com/ktfgCAL

    flow rate: 0.057 m^3/s
    cross sectional area of all pipes: 1.864*10^-2 m²
    frictional losses inlet pipe: 1.83m
    frictional losses outlet pipe: 3.66m
    density: 1000 kg/m^3
    g= 9.81 N/kg

    Asked:
    pressure at inlet
    pressure at outlet
    necessary pumping power


    2. Relevant equations
    Bernouilli: http://imgur.com/EEptkNX where h_A is the energy added by the pump and h_r and h_l are the losses
    pumping power= q*rho*g*h

    3. The attempt at a solution
    first of all, i am not sure what location they actually mean exactly by pump inlet and outlet (is it in the tank or really at the pump?)

    inlet: I assumed p1 to be 0, v1=v2 and z1=0 and z2=3.05m which results in a p2 of 47.87kPa (i assumed h_A to be equal to 0, not sure if this is correct)
    outlet: using the previous value as p1 now, assuming v1=v2 and z1=0 and z2=12.2m i found a p2 of 107.71 kPa
    power: 0.057*1000*9.81*15.25 = 8.53kW

    Apparentely, all my answers seem to be wrong. I'm fairly sure that im making a critical mistake for the pressure calculations, but I really don't understand what could be wrong in my power calculation.

    Thanks in advance :)
     
    Last edited: Mar 14, 2015
  2. jcsd
  3. Mar 14, 2015 #2

    SteamKing

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    The pump inlet and outlet seem to be indicated pretty clearly on the system diagram. The pump outlet is located further away from the pump itself apparently to accommodate the shut-off valve.
     
  4. Mar 14, 2015 #3
    But there isnt any data given about the exact height of the outlet point for example, i think the arrow just indicates the inlet and outlet pipe rather than the specific point that the pressure needs to be calculated on, or am I missing something?
     
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