Calculating pump pressures and power (Bernouilli)

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SUMMARY

The discussion focuses on calculating pump pressures and power using Bernoulli's equation in a fluid dynamics context. The flow rate is specified as 0.057 m³/s, with frictional losses of 1.83 m for the inlet pipe and 3.66 m for the outlet pipe. The calculated pressures at the inlet and outlet are 47.87 kPa and 107.71 kPa, respectively, while the necessary pumping power is determined to be 8.53 kW. The participants highlight confusion regarding the exact locations of the pump inlet and outlet, which affects the accuracy of the pressure calculations.

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  • Understanding of Bernoulli's equation
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  • Familiarity with calculating frictional losses in pipes
  • Ability to perform unit conversions and dimensional analysis
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Homework Statement


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

Homework 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

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 I am 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 :)
 
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Xengine said:

Homework Statement


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

Asked:
pressure at inlet
pressure at outlet
necessary pumping power

Homework 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

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?)

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.
 
SteamKing said:
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.

But there isn't 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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