--%>
Assignment Help - homework help

Problem on mechanical efficiency of the pump

The oil pump is drawing 25 kW of electric power while pumping oil with ρ = 860 kg/m3 at a rate of 0.1 m3/s. The inlet and outlet diameters of the pipe are of 8 cm and 12 cm, respectively. When the pressure rise of oil in the pump is measured to be 250 kPa and the motor efficiency is 90%, then find out the mechanical efficiency of the pump. Taking kinetic energy correction factor to be 1.05.

598_mechanical eff.jpg

E

Expert

Verified

Given:

Inlet Dia, Di = 8 cm = 8 x 10-2 m
Outlet Dia, Do = 12cm = 12 x10-2m

Density of oil,  δ = 80Kg /m3

Flow rate Q = 0.1 m3/s

Pressure rise = 250KPa = 250 x10-3 Pa

Power supplied to the pump = 25Kw = 25 x 10-3 w

Motor efficiency = .90

Kinetic energy correction factor, α= 1.05

Inlet area Ai= Π/4 x D12=-Π/4 x (8 x 10-2)2 = 0.0804 m2
Outlet area A0= Π/4 x D02 = Π/4 x (12 x10-2)2= 0.1809 m2

Average evolution 
Vi = Q/Ai = 0.1/ 0.804 = 1.1235 m/s
V0 = Q/A0 = 0.1/ 0.1809 = 0.5526 m/s

A note of kinetic energy correction factor

K. E correction factor, α = (K. E /See based on actual velocity) / (K. E / See based on average velocity)

The factor α is used when the flow is viscous.

Applying Bernoulli’s equation at the inlet (i) i outlet (0) of the pump.

Pi/ δg + α1 Vi2/ 2g +zi + HP= P0 /δg +α2 Vo2/2g + Z0 + Hf .

Given  αi= α2= α= 1.05     (Z0 –Zi is considered negligible)
HP = head added by the pump
Hf = head loss due to friction

H= HP – Hf = P0–Pi / δg + α ( V02-V12)/ 2g
    = 250 x 103 / 1000 x 9.81 + 1.05 / 2 x 9.81 (0.55262  - 1.2435)
    = 25.42 m

Power of the pump PP= δg QH
            = 1000 x9.81x 0.1 25.42
            = 24934.85 w
            = 24.934Kw

Mechanical efficiency of the pump:

Case (1)  ηm = power output/power input = 24.934/ 25 = 99%
Case (2)  if the  motor is to get 25Kw  considering its efficiency  the supply should be of 25/ 0.9 KW

ηm = 24.934/ (25/0.9) = 89.67%

   Related Questions in Mechanical Engineering

  • Q : Difference between PLC and Logic Card

    Difference between PLC and Logic Card: There is technically no difference. Both are logic controller utilized for several applications and in PLC has it's own internal memory (compared to Logic card).

  • Q : MECHANICAL ENGINEERING DESIGN KINDLY

    KINDLY SEND ME MATERIAL ON "MULTISTAGE SPUR GEAR DESIGN OPTIMISATION USING RAY DIAGRAMS"

    		•
  • Q : Excitation of Modes in Fiber A

    A multimode fiber is used to couple light into a single mode fiber. Both fibers have the same total diameter. Explain the coupling. Use equations, MATLAB, etc. if necessary. If an LED is used to excite a single mode fiber, explain the coupling of light to the fiber? U

    		•
  • Q : Solar Thermal systems Explain the two

    Explain the two Solar thermal DHW and Solar DHW Solar thermal systems n brief?

    		•
  • Q : Problem on magnitude of force A

    A horizontal pipe of dimension 540 mm diameter carrying 0.6 m3/s splits into two horizontal pipes of 300 mm diameter with 60% of the flow and another of 150 mm diameter with 40% of the flow. Find out the magnitude and direction of the force

  • Q : Difference between projectile motion

    Difference between projectile motion and rocket motion:A projectile has no motor or rocket on it, therefore all of its momentum is provided to it as it is launched. An illustration of a projectile would be pen which you throw across a room.

    		•
  • Q : Synchronous generator & Generating units

    Question 1: Three generating units operating in parallel at 60 Hz have rating of 300, 500, and 600    MW and have speed-droop characteristics of 5, 4, and 3%, respectively. Due to a change in load, a

    		•
  • Q : Undamped single degree of freedom (a)

    (a) The response for an undamped single degree of freedom system under free vibration is given as where ωn is the natural frequency and A and B are unknown that can be determined from the initial conditions. The response 

    		•
  • Q : Explain steam turbine diaphragm Steam

    Steam turbine diaphragm: Steam turbine includes of phases, number and size of the phases depends on the break horse-power of the turbine. The phase has set of moving and fixed blades. Moving blades are joined to th

    		•
  • Q : Change of power in flow of kinetic

    Air at 20 m/s, 260 K, 75 kPa with 5 kg/s flows into a jet engine and it flows out at 500 m/s, 800 K, 75 kPa. What is the change (power) in flow of kinetic energy?

    		•