Vertical Pumps: What Are They, Where Are They Used and How To Design Them?

Introduction

Vertical pump designs are similar to conventional pumps, with some unique differences in their applications.  Pumps use centrifugal force to convert mechanical energy into kinetic energy and increase the pressure of the liquid. Vertical pumps move liquids in the vertical direction upwards through a pipe. All pumps pressurize liquids, which are mostly incompressible. Unlike compressible gases, it is impossible to compress liquids, therefore the volumetric flow rate can not be reduced. Therefore liquids are transported by pumping and the inlet volume flow rate is equal to the exit volume flow rate.

Vertical centrifugal pumps are simply designed machines, and have similarities to their horizontal counterparts. A casing called a volute contains an impeller mounted perpendicularly on an upright (vertical) rotating shaft. The electric drive motor uses its mechanical energy to turn the pump impeller with blades, and imparts kinetic energy to the liquid as it begins to rotate. These pumps can be single stage or multistage with several in-line stages mounted in series.

The centrifugal force through the impeller rotor causes the liquid and any particulates within the liquid to move radially outward, away from the impeller center of rotation at high tangential velocity. The swirling flow at the exit of the impeller is then channeled into a diffusion system which can be a volute or collector, which diffuses the high velocity flow and converts the velocity into high pressure. In vertical pumps, the high exit pressure enables the liquid to be pumped to high vertical locations. Thus the pump exit pressure force is utilized to lift the liquid to high levels, and usually at high residual pressure even at the pipe discharge.

Applications of Vertical Pumps

An “in line” vertical pump is illustrated in Figure 1 (Reference 1), where the flow enters horizontally and exits horizontally and can be mounted such that the center line of the inlet and discharge pipes are in line with each other.  This is a centrifugal pump with a tangential scroll at the inlet that redirects the flow by 90 degrees and distributes it circumferentially and in the axial direction into the impeller eye. The discharge is a simple volute that collects the tangential flow from the impeller exit, and redirects it into the radial direction.

in line Pump - Figure 1
An “in line” Vertical Pump. Source

Figure 2 shows a vertical pump that has a vertical intake that directs the flow straight into the eye of the pump rotor. At the impeller exit, the tangential flow is collected by a volute and diffused in an exit cone. An elbow after the exit cone redirects the flow into the vertical direction to lift the liquid to the desired altitude. (Reference 2). Read More

Pump Rotor Dynamics – from Residential Pools and Human Hearts to Heavy Duty Industry Applications

You rarely find a rotary machine with a wider range of applications than pumps. These machines acting in a single role can be installed both to supply the water to a garden pool and move the crude oil in pipelines.

And even more, the same simple pump can substitute the functions of the human heart by moving the blood through it.

Fig. 1 - Left ventricular assist device - a tiny pump moving the blood in the human body
Fig. 1 – Left ventricular assist device – a tiny pump moving the blood in the human body [1]
Although the heavy duty industry applications of pumps are less delicate at first sight, they can still generate similar effects of this unique nature which is inherent only to this type of machine and should be studied carefully when executing rotor dynamics calculations. Read More

The Lovable Underdog of Turbomachinery

Everyone knows that APUs need love too…..

For Valentine’s Day, we want to look at an underdog of turbomachinery. A machine that is often overlooked, and not really in the limelight the way some of its larger cousins are, nor is it given the trendy position of being the “technology of the future” like its smaller cousins. Without this technology, airplanes would be entirely reliant on external power plants to maintain an electric power supply on the ground, and to start the main engines. So, what is this underappreciated machine?

APU plane
Okay one last hint – you can see its exhaust port.

If you haven’t been able to guess it, our Valentine this year is the aircraft auxiliary power unit, or APU for short. Although these are not present on all aircraft, they are typically used in larger airplanes such as commercial airliners. This allows aircraft to rely less on ground services when the main engines are not running. As a result, less equipment, manpower, and time are required to keep the plane in standby mode, and the aircraft can also service airports with less available resources in remote locations.

Where this Underdog Started

The aircraft auxiliary power unit can be traced back to the First World War, as they were used to provide electric power onboard airships and zeppelins. In the Second World War, American bombers and cargo aircraft had these systems as well. APUs were small piston engines, as the gas turbine had yet to be developed. These engines were typically V-twin or flat configuration engines, similar to what you might find on a motorcycle, and they were called putt-putts. These two-stroke engines usually put out less than 10-horsepower, but that was all that was required to provide DC power during low-level flight.

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Aircraft Fuel Systems

The airplane is a complex technical object. Like a human or other organisms, it consists of numerous vital systems; with one of the more critical ones being the fuel system. It is important part of any vehicle, let alone aircraft, aside from  the newest electric powered vehicles.

An aircraft’s fuel system provides fuel that is loaded, stored, managed and transported to the propulsion system of the vehicle[1, 2]. As aviation fuel is liquid, this system can be considered as hydraulic. Therefore, it’s able to be mapped out and modeled for analysis in a program like AxSTREAM NET™.

The Typical Fuel System of a Narrow-body Passenger Plane

For an example of a conventional aviation fuel system, consider a typical narrow-body airliner with two engines. Some of the popular planes in this category include the Boeing 737, the Tupolev Tu-204, Airbus A320, Comac C919, Sukhoi Superjet 100, Bombardier CRJ, Embraer E-Jet and Mitsubishi Regional Jet[3].

The storage fuel system is shown in figure 1 is for the Boeing 737-300. The fuel is kept in an integral tank that is divided to five separate subdivisions. They are the central, wing (main) and surge tanks[4].

Storage fuel system of a Boeing 737
Figure 1 – Storage Fuel System of a Boeing 737-300 [4]
The hydraulic scheme of the Boeing 737’s fuel system is shown in Figure 2. For fueling and defueling the storage system there are ports on the starboard wing. The system does not have pumps to onboard fuel, so fuel is pumped into the plane via a fuel truck. The other critical part of the fuel system is the line which delivers fuel to the two engines and the auxiliary power unit. In this line there are two boost centrifugal pumps by each engine.
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Evolution of Reverse Engineering

Introduction

In today’s intensely competitive global market, product enterprises are constantly seeking new ways to shorten lead times for new product developments that meet all customer expectations. In general, product enterprise has invested in CAD/CAM, rapid prototyping, and a range of new technologies that provide business benefits. Nowadays, reverse engineering (RE) is considered one of the technologies that provide business benefits by shortening the product development cycle [1]. Figure 1, shows how reverse engineering can close the gap between what is “as designed” and what is “actually manufactured” [1].

Product Development
Figure 1. Product Development Cycle. SOURCE: : [1]
Reverse engineering (RE) is now recognized as an important factor in the product design process which highlights inverse methods, deduction and discovery in design. In mechanical engineering, RE has evolved from capturing technical product data, and initiating the manual redesign procedure while enabling efficient concurrency benchmarking into a more elaborated process based on advanced computational models and modern digitizing technologies [2]. Today the application of RE is used to produce 3D digital models of various mechanical worn or broken parts. The main steps in any reverse engineering procedure are: sensing the geometry of the existing object; creating a 3D model; and manufacturing by using an appropriate CAD/CAM system [2]. Read More

Modern Challenges in Aviation Propulsion Systems

Introduction

Aviation is coming into a new age of carbon free energy, similar to what is being explored with ground transportation. Currently, aviation transportation generates about 2.5% of the global CO2 emission [1]. Several countries have introduced targets to achieve net-zero emissions by 2050 [2].

Many aerospace teams have joined the great engineering challenge to change the future of aviation.  With this, a number of different types of aircraft with different types of propulsion systems have been proposed.

Hybrid Propulsion System

The first step to a carbon-free propulsion system is hybrid technology. This kind of power plant increases efficiency, decreases emission of greenhouse gases and uses a traditional engine to produce electricity and electric motors to drive the fans or propellers [3].

The chemical engines operate at optimal conditions at any mode of a route. On the other hand, the electric motor is able to work in generator mode, using the kinetic energy of the vehicle during deceleration.

Hybrid propulsion energy system
Figure 1 – Hybrid propulsion energy system

The hybrid aircraft is classified by several attributes. Using thrust devices, we will consider the two base types of propellers and fans. Read More

Modeling and Simulating Bearings/Bearing Leakages

Bearings are very important machinery components since they dominate machine performance. Almost all machines and mechanisms with a rotating part, from the smallest motor to the largest power plants, from turbomachinery to reciprocating engines, and other industrial equipment our modern society relies upon, could not function without the use of bearings in some form. If one of the bearings fail, not only do the machines stop, but the assembly line also stops, and the resulting costs may be extremely high. For this reason, every bearing manufacturer makes every effort to ensure the highest quality for each bearing and that the end user subjects the bearing to careful use and properly maintains this component.

A bearing can be defined as a machine element which supports another moving machine element (known as a journal). It permits a relative motion between the contact surfaces of the members, while carrying the loads (static and dynamic). Some consideration will show that due to the relative motion between the contact surfaces, a certain amount of power is wasted in overcoming frictional resistance. If the rubbing surfaces are in direct contact, there will be rapid wear. In order to reduce frictional resistance, wear, and in some cases to carry away the heat generated, a layer of fluid (known as lubricant) may be provided. This lubricant is used to separate the journal and bearing, which allows the moving parts to move smoothly and helps to achieve more efficient machine operation. Some of the common bearing types are shown in Figure 1.

Figure 1. Common Types of Bearing Examples. SOURCE: [1]
Figure 1. Common Types of Bearing Examples. SOURCE: [1]
The main purpose of bearings is to prevent direct metal to metal contact between two elements that are in relative motion. This prevents friction, heat generation and ultimately, the wear and tear of parts. It also reduces the energy consumption required for moving parts. Additionally, they also transmit the load of the rotating element to the housing. This load may be axial, radial or a combination of both. Bearings also restrict the freedom of movement of moving parts to a predefined direction. With all these aspects, bearings are clearly important for the operations and the reliability of mechanical products. The right bearing can increase useful life of the machine, and enhance the machine’s overall performance. The wrong bearing can lead to premature failure, increased downtime, and increased wear and fatigue among all components of the machine. Read More

Considerations in Industrial Pump Selection

Pumps are machines that transfer liquids from suction to discharge by converting mechanical energy from a rotating impeller into what is known as head. The pressure applied to the liquid forces the fluid to flow at the required rate and to overcome frictional losses in piping, valves, fittings, and process equipment.

When it comes to pump selection, reliability and efficiency go hand-in-hand. Generally, a pump that has been selected and controlled properly for its normal operating points will operate near its best efficiency point (BEP) flow, with low forces exerted on the mechanical components and low vibration — all of which result in optimal reliability.

There are several factors like process fluid properties, end use requirements, environmental conditions, pump material, inlet conditions, and others which should be considered while selecting pumps for industrial applications. Selecting the right pump type and sizing it correctly are critical to the success of any pump application. Pumping applications include constant or variable flow rate requirements, serving single or networked loads, and consisting of open loops (nonreturn or liquid delivery) or closed loops (return systems).

Some crucial factors considered while pump selections include:

Fluid Properties: The pumping fluid properties can significantly affect the choice of pump. Key considerations include:

  • Acidity/alkalinity and chemical composition. Corrosive and acidic fluids can degrade pumps and should be considered when selecting pump materials.
  • Operating temperature: Pump materials and expansion, mechanical seal components, and packing materials need to be considered with pumped fluids that are hotter than 200°F.
  • Solids concentrations/particle sizes: When pumping abrasive liquids such as industrial slurries, selecting a pump that will not clog or fail prematurely depends on particle size, hardness, and the volumetric percentage of solids.
  • Specific gravity: It affects the energy required to lift and move the fluid and must be considered when determining pump power requirements.
  • Vapor pressure and Viscosity: Proper consideration of the fluid’s vapor pressure will help to minimize the risk of cavitation. High viscosity fluids result in reduced centrifugal pump performance and increased power requirements. It is particularly important to consider pump suction-side line losses when pumping viscous fluids.

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Materials of Construction: It is always required to check the compatibility of materials of construction with the process liquid or any other liquids the pump might encounter. The initial cost of these materials is normally the first consideration. The operational costs, replacement costs and longevity of service and repair costs will, however, determine the actual cost of the pump during its lifetime. Charts are available to check the chemical compatibility and identify the most appropriate materials of construction for the pump.

The impact of the impeller material on the life of a pump under cavitation conditions is shown in Figure 1. As an example, changing from mild steel (reliability factor of 1.0) to stainless steel (reliability factor of 4.0) would increase the impeller life from cavitation damage by a factor of four. Hard coatings, such as certain ceramics, can also increase the impeller life under cavitating conditions.

Material Cavitation Life Factors
Figure 1 Material Cavitation life factors

Pump Sizing and Performance Specifications: The desired pump discharge is needed to accurately size the piping system, determine friction head losses, construct a system curve, and select a pump and drive motor. Process requirements can be achieved by providing a constant flow rate, or by using a throttling valve or variable speed drives. Read More

Rotor Dynamics Study of 4-Stage Compressor – from Theory to Application

Rotating machines have huge and important roles in our daily life although we may rarely think about them. Steam turbines at electrical power plants rotate the electrical generator shafts which produce electricity coming into our homes and offices. Driving to or from work, the reciprocating cycle in your vehicle’s internal combustion engine results in rotation of the transmission and the wheels of vehicles, while the electric car wheel operation is a result of induction motor rotation. If you get on an airplane, rotation of the turbo reactive gas turbine engine produces the effective thrust to sustain flight by moving, compressing and throwing the gas behind the plane. We can even find the useful effects of rotation in our kitchens when we are blending the food or washing our closes.

Although these rotating machines are different, the approaches to modelling their rotor dynamics are pretty much the same, since similar processes occur in rotating parts which differ in their vibrations from the non-rotating machines.

Do you remember the example of rotating washing machine? Have you ever seen it jumping on the floor trying to squeeze out your closet? We bet you have. This is the simplest example of the increased unbalance affecting the amplitudes of machine vibrations. Washing machines are designed to experience these noticeable vibrations during their operation without breaking. But the steam turbine or compressor rotors which have the tight clearances between the impellers and the casing can not boast of that leeway. In addition to that, the excessive vibrations significantly influence the machine’s useful life due to the increased fatigue.
This is why the rotor dynamics predictions are one of the most important parts of rotating machine analyses. And although they may seem easier than comprehensive stress-strain investigations of machine components, in some cases the rotor dynamics analysis can be trickiest part.

Usually, the rotor dynamics analyses are divided into lateral and torsional stages depending on the nature of rotor response to be used. They are discussed in different types of standards (API [1], ISO [2], etc.). Let’s consider the example of the lateral vibrations of a 4 stage compressor rotor with an operational speed of 8856 rpm.

Fig. 1 - 4 Stage Compressor Rotor
Fig. 1 – 4 Stage Compressor Rotor

This rotor rotates in the 4 pad tilting, pad oil film journal bearings. The characteristics of these bearings should be determined carefully to ensure that there will not be an excessive wear, heat generation or friction in them. Read More

When to Use 1D Vs. 3D Simulation

Today’s simulation and analysis (S&A) tools allow engineers to study and verify system/machine properties and visualize the aerodynamic, thermodynamic, structural, and other physical properties without having to build a physical prototype. We can perform cooling secondary flow systems analysis in a gas turbine; a detailed performance study for a supercritical CO2 turbine/compressor; predict cavitation for industry a water pump/rocket turbopump; and so many more. Products and machines are becoming more and more complex. Unfortunately, engineers only run a handful of designs through the S&A process, due to the cost associated with limited computer resources and the time required to run simulations and to create complex 3D models of designs. Furthermore, verification and certification of system designs are often done using actual hardware—a costly and time-consuming endeavor. Considering these aspects, 1D and 3D simulations are significantly important. However, engineers need to determine the trade-off between 1D and 3D simulation.

AxSTREAM and STAR-CCM
Figure 1 AxSTREAM Platform with Modules from 0D to 3D including seamless geometry import into STAR-CCM+

1D Simulation

Imagine what’s required to generate one 3D design for a gas turbine secondary cooling flow system, and multiply it by 1,000 design alternatives. Even if we were to only use conceptual CAD models, this project would require extraordinary computing power and data storage—not to mention simulation and design expertise.

And so, even with the movement to bring more cloud-based S&A tools to market, resources required for 3D modeling will still result in very few designs being extensively explored, thanks to their complexity. Detailed low-dimensional models of system behavior can provide valuable insights into system performance and function thus guiding the design process. Read More