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

Back to Basics: What Makes a Good Pump?

Everyone is familiar with pumps, but how many people really think about how much depends on this ubiquitous invention? The scope of pump applications is wide: distribution and circulation of water in water supply and heat supply systems, irrigation in agriculture, in the oil industry, in fire extinguishing systems, etc.

A pump is a hydraulic machine designed to move fluid and impart energy to it. A schematic diagram of a simple pumping unit is presented below.

Figure 1 Pumping Unit Diagram
Figure 1: Pumping Unit Diagram
1 – intake valve; 2 – suction pipeline; 3 – vacuum gauge; 4 – pump; 5 – manometer; 6 – check valve; 7 – gate valve; 8 – pressure pipeline

Positive Displacement and Dynamic Pumps

According to the principle of operation, pumps can be divided into two main groups: positive displacement and dynamic. In positive displacement pumps, a certain volume of the pumped liquid is cut off and moved from the inlet to the pressure head, where additional energy is supplied to it. In pumps with dynamic action, the increase in energy occurs due to the interaction of the liquid with a rotating working body.

The most widely used pumps are centrifugal pumps which are of the dynamic type. The principle of centrifugal pumps uses a rotating impeller to create a vacuum in order to move the fluid. The impeller rotates within the housing and reduces pressure at the inlet. This motion then drives fluid to the outside of the pump’s housing, which increases the pressure.

These pumps benefit from a simple design and lower maintenance requirements and costs. This makes them suited to applications where the pump is used often or continuously run.

Figure 2 Centrifugal Pump
Figure 2a: Centrifugal Pump
Centrifugal Pump Designed using AxSTREAM
Figure 2b: Centrifugal Pump Designed using AxSTREAM

In most cases, the pumps are electrically driven, but if the pump is of high power and high speed, then these pumps are driven by steam turbines. 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

Centrifugal Compressors for Fuel Cells

The development of fuel cell technologies and improvements in fuel cells power densities combine to make the use of fuel cells possible in different power sectors as primary or secondary power sources for commercial purpose, residential power requirements, and automobiles, etc. The fuel cell harnesses the chemical energy of a fuel along with an oxidizing agent by converting it into electrical energy through a pair of reactions. For example, in a hydrogen fuel cell, as shown in Figure 1, the hydrogen combines with oxygen from the air to produce electricity and releases water.

Fuel Cell System
Figure 1 Fuel Cell System [1]
The design of a fuel cell system is quite complex and depends on fuel cell types and their applications. With so many possible combinations of fuel cells, this article will not focus on different type of fuel cells, but on Air Management Systems which may significantly affect the overall performance of a fuel cell system.

Air Management Systems

Key sub-systems of any fuel cell system are the fuel processor, fuel cell stack, air management and power management systems. The air management system strongly affects the fuel cell stack efficiency and the power loss of the fuel cells. Therefore, it is necessary to develop a clean, reliable, cost-effective oil-free air system [2].

Major tasks in air management system are Air Supply, Air Cleaning, Pressurization and Humidification.
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A Century of Chiller Technology

A convergence of technologies had to occur to make the modern, high-efficiency centrifugal chiller a reality. To appreciate the technology fully, we must go back in history and understand the origins of the air conditioning and refrigeration industry. Along the way, we will find an important diversion in aerospace and the critically important centrifugal compressor. Ultimately, we will find that the modern chiller is a testament to advanced technology that was developed in multiple fields.

Some of the first advances in and applications of modern industrial refrigeration were in the United States. In May 1922, Willis Carrier revealed the “Centrifugal Refrigeration Machine” – a very early incarnation of what we now call a chiller [1]. The first installation went to a Philadelphia candy manufacturer; it’s interesting to know that the birth of modern refrigeration and air conditioning started on a large scale. Back in those days, economy of scale enabled the technology to be developed. It was not until a decade later that the core technology began to be adopted into compact units that could be used in smaller businesses such as boutique shops. It took several more decades for smaller residential air conditioners to take off commercially.

Shown in the photograph below is Carrier’s first centrifugal chiller in his New Jersey factory [1].

First Centrifugal Chiller
Photo from [1]
The size of this machine is evident, as is the fact that its design, at the time, necessitated components be spread out in space for assembly and maintenance. By modern standards, the same footprint space could be used to accommodate a modern chiller with over 500 refrigeration tons in capacity. By comparison the original design has less than 100 refrigeration tons of capacity.

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Modeling a Ground Source Heat Pump

Ground source heat pumps (GSHP) are one of the fastest growing applications of renewable energy in the world, with annual increase of 10% in about 30 countries over the past 15 years.  Its main advantage is that it uses normal ground or ground water temperatures to provide heating, cooling and domestic hot water for residential and commercial buildings. GSHP’s are proving to be one of the most reliable and cost-effective heating/cooling systems that are currently available on the market and have the potential of becoming the heating system of choice to many future consumers, because of its capacity for providing a variety of services such as heat generation, hot water, humidity control, and air cooling. Additionally,  they have the potential to reduce primary energy consumption, and subsequently provide lower carbon emissions, as well as operate more quietly and have a longer life span than traditional HVAC systems. The costs associated with GSHP systems are gradually decreasing every year due to successive technological improvements, which makes them more appealing to new consumers.

The basic purpose of a GSHP is to transfer heat from the ground (or a body of water) to the inside of a building. The heat pump’s process can be reversed, in which case it will extract heat from the building and release it into the ground. Thus, the ground is the main heat source and sink. During winter, the ground will provide the heat whereas in the summer it will absorb the heat.

A GSHP comes in two basic configurations: ground-coupled (closed-loop) and groundwater (open loop) systems, which are installed horizontally and vertically, or in wells and lakes. The type chosen depends upon various factors such as the soil and rock type at the installation, the heating and cooling load required, the land available as well as the availability of a water well, or the feasibility of creating one. Figure 1 shows the diagrams of these systems.

Two Basic Configurations
Figure 1. Two Basic Configurations of GSHP Systems. SOURCE: [1]
In the ground-coupled system (Figure 1a), a closed loop of pipe, placed either horizontally (1 to 2 m deep) or vertically (50 to 100 m deep), is placed in the ground and a water-antifreeze solution is circulated through the plastic pipes to either collect heat from the ground in the winter or reject heat to the ground in the summer. The open loop system (Figure 1b), runs groundwater or lake water directly in the heat exchanger and then discharges it into another well, stream, lake, or on the ground depending upon local laws. Between the two, ground-coupled (closed loop) GSHP’s are more popular because they are very adaptable.
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Vapor-Compression Refrigeration Systems

Present day refrigeration is viewed as a necessity to keep our popsicles cold and our perishables fresh. But have you ever wondered what people did to keep their food from spoiling hundreds or even thousands of years ago? Or just what goes into a refrigerator system today? In this blog, we’ll take a look at how refrigeration works; the history behind it; and examine the cycle, working fluids, and components.

Schematic of Refridgeration System in AxSTREAM NET
Figure 1. Modern-day Refrigeration System in AxSTREAM NET
Introduction

Refrigeration is based on the two basic principles of evaporation and condensation. When liquid evaporates it absorbs heat and when liquid condenses, it releases heat. Once you have these principles in mind, understanding how a refrigerator works becomes much more digestible (pun intended). A modern-day refrigerator consists of components such as a condenser, compressor, evaporator and expansion valve, as well as a working fluid (refrigerant). The refrigerant is a liquid which as enters the expansion valve the rapid drop in pressure makes it expand, cool, and turn into a gas. As the refrigerant flows in the evaporator, it absorbs and removes heat from the surrounding. The compressor then compresses (as the name suggests) the fluid, raising its temperature and pressure. From here, the refrigerant flows through the condenser, releasing the heat into the air and cooling the gas back down to a liquid. Finally, the refrigerant enters the expansion valve and the cycle repeats. But what did we do before this technology was available to us?

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Unsteady Flow Simulation in Hydraulic Systems

An unsteady flow is one where the parameters change with respect to time. In general, any liquid flow is unsteady. But if a hydraulic system is working at constant boundary conditions, then the parameters of the fluid flow change slowly; thus this flow is considered steady. At the same time, if the parameters of the fluid flow oscillate over time relative to some constant value, then it called quasi-steady flow 1.

In practice, most fluid flows are steady or quasi-steady. Examples of the three flows are presented in Figure 1. Steady flow is presented by a simple pipe. The quasi-steady flow is represented by a sharpened edge channel. The unsteady flow is presented by an outflow from a reservoir.

Figure 1 - Different Types of Fluid Flow
Figure 1 – Different Types of Fluid Flow
Different Cases of Unsteady Flow

During operations, hydraulic systems act for long intervals at steady conditions which are called operating modes. Change between two different operating modes occurs over a short time interval (called a transient mode). If any hydraulic system works more than 95% of the time at these operating modes though, why is the unsteady flow is so important? Because the loads depend on time intervals. If the load is less, then the maximum system pressure is higher. Read More

Preventing Choke and Surge in a Compressor

Turbo Compressors are used to increase the pressure of a gas, which are required in propulsion systems like a gas turbine, as well as many production processes in the energy sectors, and various other important industries such as the oil and gas, chemical industries, and many more.

Such compressors are highly specific to the working fluid used (gas) and the specific operating conditions of the processes for which they are designed. This makes them very expensive. Thus, such turbo compressors should be designed and operate with high level of care and accuracy to avoid any failure and to extract the best performance possible from the machine.

Axial Compressor and Centrifugal Compressor in AxSTREAM
Figure 1 (A) Axial Compressor (B) Centrifugal Compressor in AxSTREAM®

Turbo Compressor Characteristic Curves

The characteristic curves of any turbo compressor define the operating zone for the compressor at different speed lines and is limited by the two phenomenon called choke and surge. These two opposing constraints can be seen in Figure 2.

Choke conditions occurs when a compressor operates at the maximum mass flow rate. Maximum flow happens as the Mach number reaches to unity at some part of the compressor, i.e. as it reaches sonic velocity, the flow is said to be choked. In other words, the maximum volume flow rate in compressor passage is limited by limited size of the throat region.  Generally, this calculation is important for applications where high molecular weight fluids are involved in the compression process.

Surge is the characteristic behavior of a turbo compressor at low flow rate conditions where a complete breakdown of steady flow occurs. Due to a surge, the outlet pressure of the compressor is reduced drastically, and results in flow reversal from discharge to suction. It is an undesirable phenomenon that can create high vibrations, damage the rotor bearings, rotor seals, compressor driver and affect the entire cycle operation.

Compressor Performance Curve
Figure 2 Compressor Performance Curve

Preventing Choke and Surge Conditions

Both choke conditions and surge conditions are undesirable for optimal operation of a turbo compressor.  Each condition must be considered during design to ensure these conditions are prevented. Read More

Industrial Refrigerator Modeling

Refrigerators are an integral part of everyday life to the point where it is almost impossible to image our day without them. As in our everyday life, refrigeration units are also widely used for industrial purposes, not only as stationary units but also for transporting cold goods over long distances. In this blog, we will focus on the simulation and modeling of such an industrial refrigeration unit.

Picture 1 - Industrial Refrigerator
Industrial Refrigerator

Like any stationary refrigeration unit, a unit used for cooled transportation includes an intermediate heat exchanger, a pump, an evaporator, a compressor, a condenser, and a throttle. The most common refrigeration scheme uses three heat fluids in the industrial refrigeration cycle. There is Water, which is used for heat removal from Refrigerant- R134A and Propylene glycol 55%. These other fluids are used as intermediate fluids between the refrigerator chamber and refrigerant loop. The working principle of all fridge systems are based on the phase transition process that occurs during the refrigerator cycle shown in Figure 1. The propylene glycol is pumped into the evaporator from the heat exchanger, in which it cools and transfers heat to the refrigerant. In the evaporator, the refrigerant boils and gasifies during the heat transfer process and takes heat from the refrigerator. The gaseous refrigerant enters the condenser due to the compressor working, where its phase transition occurs to the liquid state and cycle repeats.
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