Fluid systems centrifugal pumps

In summary: For the hydraulic efficiency, you need to calculate the actual head developed by the pump using the equation, Hactual = P2/ρ + V2^2/2g + z2 - P1/ρ - V1^2/2g - z1 where, P1,P2 are pressures at inlet and outlet, V1,V2 are velocities at inlet and outlet, ρ is density of the liquid, g is acceleration due to gravity and z1,z2 are the elevations of the inlet and outlet. Then, you can use the equation for hydraulic efficiency, Hactual/Hideal = Actual Head Developed/Theoretical Head Developed by Impeller. In summary, the conversation discusses the configuration of an impeller in a centrifugal
  • #1
bluffreggie
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Homework Statement


Hi guys, I've been working on some problems at uni to try and get to know this subject better and i have been unable to answer a question.

the impellar of a centrifugel pump has the following configaration,
diameter 254 (hence r2=127) blade exit angle (Beta) 32degrees, effective outlet area=0.017m^2, Speed (N)=1450 rpm (hence omega =151.84 rad/s). the diameter of the suction and delivery openings are 150mm and 125mm. delivery rate is 30.8l/s, pressure heads at suction and delivery are 4.5m and 13.5 m below and above respectively(atmospheric), pump motor is 8.28Kw. Alpha 1 is 90 degrees due to shockless entry and the actual tangential velocity at impeller outlet is 0.7 of the ideal. Determine
1. the overall efficency
2. the hydraulic efficency based on the actual tangentail velocity at blade outlet.


Homework Equations


I have used for the hydraulic efficency
actual head developed by pump/theoretical head developed by impleller.

vbar^2/2g energy loss in impeller
(u2*vbart2)/g ideal head
ideal head-energy loss = actual


The Attempt at a Solution


i have for my values
u2=19.28
vbarn2=2.27
vbart2=15.64 15.64x0.7=10.95
vbar2=15.77

when i calculate for the hydraulic efficency i get 71% when the answer is 80% and i can't seem to get far enough in the first part to get an answer for it, but the correct answer for part one is 66%.
 
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  • #2
so i was just wondering if anyone could help me out.For overall efficiency, You need to calculate the power input of the pump using the equation, P =Q*H/Eta where, P is power, Q is flow rate, H is total head and Eta is efficiency. You can calculate the total head using Bernoulli's equation. Htotal = P1/ρ + V1^2/2g + z1 - P2/ρ - V2^2/2g - z2 where, P1,P2 are pressures at inlet and outlet, V1,V2 are velocities at inlet and outlet, ρ is density of the liquid, g is acceleration due to gravity and z1,z2 are the elevations of the inlet and outlet. Using the above equation, you can calculate the power input. Power Input = Q*Htotal/Eta Now, calculate the power output of the pump. Power Output = Q*H/Eta Efficiency = Power Output/Power Input This should give you the overall efficiency.
 
  • #3


Hello! It seems like you are working on some interesting problems in your university course. Centrifugal pumps are an important component in fluid systems and understanding their efficiency is crucial for their proper functioning. I will try to provide some guidance on the questions you are struggling with.

Firstly, for the overall efficiency, you need to use the equation:

Overall efficiency = (Power output/Power input) x 100%

The power output can be calculated using the delivery rate, pressure heads, and density of the fluid. The power input is given as 8.28 kW in the problem statement.

Secondly, for the hydraulic efficiency, you are correct in using the equation:

Hydraulic efficiency = Actual head developed by pump/Theoretical head developed by impeller

However, you need to use the actual tangential velocity at the blade outlet, which is 10.95 m/s in this case, instead of 15.64 m/s. This will give you the correct answer of 80%.

I hope this helps you in solving the problem. Remember to always double check your calculations and units. Good luck with your studies!
 

1. What is a centrifugal pump?

A centrifugal pump is a type of fluid system that uses centrifugal force to move fluids through a system. It works by converting rotational energy from a motor into kinetic energy, which is then used to move the fluid through the pump and into the system.

2. How do centrifugal pumps work?

Centrifugal pumps work by using an impeller, which is a rotating component that creates the centrifugal force necessary to move the fluid. As the impeller rotates, it creates a low-pressure area at the center, causing the fluid to be pulled in. The fluid then moves outward, gaining speed and pressure as it is pushed through the pump and into the system.

3. What are the advantages of using a centrifugal pump?

There are several advantages to using a centrifugal pump. These include their ability to handle high flow rates, their simplicity and ease of maintenance, and their ability to operate without the need for valves or other complex control systems.

4. What are some common applications of centrifugal pumps?

Centrifugal pumps are used in a wide variety of industries and applications, including water and wastewater treatment, oil and gas, chemical processing, and HVAC systems. They are also commonly used in irrigation, mining, and power generation.

5. What factors should be considered when selecting a centrifugal pump?

When choosing a centrifugal pump, factors such as flow rate, pressure, fluid viscosity, and the type of fluid being pumped should be taken into account. Other considerations include the pump's size and power requirements, as well as its compatibility with the system and any specific industry regulations or standards.

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