Need some reference on centrifugal pump design

• ecfedele
In summary: From what you've written, it sounds like you want help with understanding the engineering flow for a centrifugal pump. A centrifugal pump is a device that uses the centrifugal force to move fluid. The centrifugal force is created by the spinning of the pump impeller. The centrifugal force causes the fluid to move outward. This is used to move liquid or gas from one place to another. The centrifugal force is also used to create power.The engineering flow for a centrifugal pump is similar to the engineering flow for a rocket pump. For a given density and gravitational field strength, head and pressure are interchangeable terms. You can use whichever you like, just convert as required. The head is what is throwing you.
ecfedele
Little bit of a disclaimer: if you take a look at my first (introductory) post, you'll see that I'm working towards aerospace engineering; therefore, this is leaning towards turbopump design, but for the time being I'll start out slow.

Basically, I'd like it if anyone could help me get a sense of the engineering flow for a centrifugal pump. I've already examined multiple books on the subject and consulted any number of web PDFs about it, so I have some exposure to many of the fundamental concepts (impeller velocity triangles, head, NPSH considerations, cavitation), but in a really disparate manner that doesn't amount to anything enabling me to start sitting down and working on a trial or first design.

I'm not asking for anyone to walk me through the calculations in a textbook, cookie-cutter or formulaic manner, but I'd like some explanation of the design flow in a way that helps me put all the formulas and concepts I've read about together into a way that would actually enable me to feel like I could go and crank out a design, however inefficient or idealistic.

Now, let me approach this from my desired angle, which is a rocket turbopump, so you can see the way I'm seeing the design and the conundrums I'm looking at. I know that a turbopump is (usually) a large centrifugal pump with an emphasis on light weight and high efficiency that is driven by a turbine, but from looking at the basic pump equations it appears that since density is a primary consideration, the theoretical, basic design shouldn't be all that different. The fundamentals are similar.

My main issue is the idea of the head from source and to exit of the pump and with the pressure requirement. Rocket engines don't usually bother with stating their flow requirements as a unit of head. They require that the pump can develop the designed chamber pressure with the required flow rate. Obviously, flow rate, Q, is a direct parameter of pump design, but not pressure. I asked around on Engineering Stack Exchange and found that the pressure is usually a related concept to the head (via the Bernoulli equation), but the head is what is throwing me.

In a rocket, the fuel tanks mount above the pumps which mount above the motor. This almost implies that the head requirements would be negative. The design of a pump that would function in that manner is the hardest thing I'm trying to wrap my head around.

For anyone who can help me work through all this, many thanks. It feels here like I simultaneously have a good grasp of the basic concepts but still know nothing to the point of having to be walked through those basics.

For a given density and gravitational field strength head and pressure are interchangeable terms. You can use whichever you like, just convert as required.

billy_joule said:
For a given density and gravitational field strength head and pressure are interchangeable terms. You can use whichever you like, just convert as required.

Which, as I said, I understand that element of it. But pressure generated from head and the head as the computed requirement don't appear to be the same thing. So let me know if what I've got so far is correct or even in the right ballpark.

According to Wikipedia, hydraulic head appears to be the combination of pressure head and elevation head, so:

## h = \psi + z = \frac{P}{\rho g_0} + z##

Now, for computation's sake I'll make an example where water needs to be supplied to a nozzle at 1MPa where the nozzle is situated one meter below the pump inlet. So, if my ideas are right, the elevation head (##z##) is -1m. If this is the case, is this head calculation correct? Or if I'm missing something, what would it be?

## h = \frac{1000000}{9806.65} - 1 = 100.972m##

What I'm much more worried about though, is how to translate the head and flow-rate requirements into an actual pump design. I know about some of the impeller geometry and velocity triangles, but most books on the subject are more pump selection guides than design texts, so I have no idea what the link is between the input requirements and the actual pump/impeller/volute design process. Can you shed any light on that?

1. What are the main components of a centrifugal pump?

The main components of a centrifugal pump include an impeller, casing, volute, shaft, bearings, and a drive mechanism. The impeller is responsible for creating the centrifugal force that moves the fluid through the pump, while the casing and volute help direct and control the flow. The shaft connects the impeller to the drive mechanism, which can be a motor or other power source. Bearings support the rotating parts and help reduce friction.

2. How does a centrifugal pump work?

A centrifugal pump works by converting mechanical energy from a motor or other power source into kinetic energy in the form of rotational motion. This rotational motion is then used to create centrifugal force, which propels the fluid through the pump and out the discharge port. The fluid enters the pump through the suction port and is directed towards the center of the impeller, where it is then pushed outward by the spinning blades.

3. What considerations should be made when designing a centrifugal pump?

When designing a centrifugal pump, several considerations should be made, such as the type of fluid being pumped, the desired flow rate and pressure, and the operating conditions (temperature, pressure, etc.). Other factors may include the material of the pump components, the size and shape of the impeller, and the efficiency and cost of the pump design.

4. How is the efficiency of a centrifugal pump determined?

The efficiency of a centrifugal pump is typically calculated by dividing the pump's hydraulic power output by its mechanical power input. This is known as the pump's total efficiency, which takes into account both the efficiency of the impeller and the power losses due to friction and other factors. Other methods for determining efficiency include using pump curves and efficiency equations specific to centrifugal pumps.

5. What are some common applications of centrifugal pumps?

Centrifugal pumps have a wide range of applications, including irrigation, water supply and distribution, wastewater treatment, chemical processing, and petroleum refining. They are also commonly used in heating and cooling systems, power generation, and mining operations. The versatility and efficiency of centrifugal pumps make them a popular choice for many different industries and processes.

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