Types of turbines include steam, gas, water, axial, radial-flow, impulse, blade-less, transonic, ceramic, mixed flow, and wind turbines. These types are distinguished into categories based on various factors and attributes.
In this article, the types of turbines are discussed, as ordered in the following outline;
Types of Turbines : Factors used in Classification
Various factors are used to classify and distinguish the types of turbines. They include energy source, design, and mode of operation.
Each of these factors is used to categorize the types of turbines in this article.
-Types of Turbines based on Energy Source
1). Wind Turbine as one of the Types of Turbines
Because wind energy is kinetic, the overall energy conversion process in a wind turbine is relatively simple. The use of wind turbines is a means by which renewable energy can be harnessed with minimal risk of global warming or other forms of environmental degradation.
Structurally, a wind turbine has simple design, including parts like the nacelle, rotor, blades, electric generator, tower and foundation . These components work together to extract kinetic energy from wind and use this energy to generate electricity.
It is important to clarify that a wind turbine functions in a similar manner to the basic functional mechanism of turbines. Based on operational configuration, wind turbines are of two types; horizontal axis wind turbine and vertical axis wind turbine .
Horizontal axis wind turbine (HAWT) is designed such that the rotational axis (or shaft) of the turbine is horizontal with respect to the ground.
Vertical axis wind turbine (VAWT) has its rotational axis at a vertical position relative to the ground.
The horizontal axis wind turbine is more common due to its higher effectiveness and energy efficiency compared to the vertical axis type.
There are typically three rotor blades in a wind turbine. This number is optimal to ensure less torque and to reduce frictional stress and other causes of inefficiency.
The radius of the turbine blades is proportional to the output capacity, although an extremely large size can also reduce the efficiency of the turbine.
2). Gas Turbine as one of the Types of Turbines
A gas turbine is often a component of an internal combustion engine .
It derives its energy primarily from a fuel, which may include fossil fuel-derivatives like diesel and natural gas.
Gas turbine is one of the most important and widely used types of turbines, whose applications include power plants and aviation systems . It derives its name from the presence of a conductive gas which acts the hydrodynamic fluid that is mobilized by heat energy, and helps convert this heat to mechanical energy by inducing motion in the turbine.
Based on the dynamics of this fluid, three different types of turbines can be distinguished; open cycle, closed cycle and semi-closed cycle gas turbines.
The fluid circulates continuously with no outlet in a closed-cycle gas turbines, whereas there are outlets for the fluid in other types of turbines.
Based on the physical state of the fluid as it absorbs heat energy, gas turbines can also be categorized as constant-volume and constant-pressure turbines.
3). Geothermal Turbine as one of the Types of Turbines
A geothermal turbine is renewable, and depends on geothermal heat as its primary source of energy.
Like many other types of turbines, geothermal turbines work based on a mechanism of heat transfer and kineto-mechanics, whereby a heated fluid is used to drive a moveable component to produce mechanical energy, which can be used for electricity generation.
For geothermal turbines, energy can be derived using a heat pump apparatus, which extracts geothermal energy from the subsurface by means of a hydrodynamic mechanism. The energy extracted is often used for domestic heating purposes, although it may also be used to drive a turbine.
4). Gravity Turbine
Gravity turbines include all types of turbines that are designed to run on gravitational or potential energy.
Many of these gravity turbines are based on perpetual motion concepts, and are not practically sustainable.
However, a practical example of a turbine that runs on potential energy is the ‘Archimedes Screw’ or Screw Turbine . This device is designed to convert kinetic energy from gravity-induced streams of water, to mechanical energy, as the water falls upon a mechanical wheel.
The concept of the screw (gravity) turbine is similar to overshot waterwheel and reverse pump systems.
This turbine represents one of the types of turbines that converts energy in adherence to the principles of sustainable development, by being environment-friendly. It is however not as powerful as turbines driven by fossil fuels, and may not be effective for electricity generation.
-Types of Turbines based on Mode of Operation
5). Axial Flow Turbine as one of the Types of Turbines
Axial flow turbines include all types of turbines in which the working fluid flows in a direction parallel to the rotational axis or shaft of the turbine .
The axial flow turbine is fairly common, and used with many working fluids like water and various gases. It is especially effective with compressible fluids and can produce significant mechanical energy output. However, the output may decrease with increase in the radius of the rotor, and decrease in fluid velocity (or kinetic energy).
6). Radial Flow Turbine
Radial flow turbines include all types of turbines in which the working fluid flows radially with respect to the rotational axis or shaft .
This is similar in operation to the centrifugal pump, and can be considered a reverse version of it. A centrifugal compressor is usually responsible for controlling fluid flow in the radial direction.
Radial flow turbines can be distinguished into inward flow (or inflow) and outward flow (or outflow) types, which differ based on the flow path of the working fluid. Radial flow turbines have a generally lower output than axial turbines, and are therefore used for less energy-intensive applications.
7). Tangential Flow Turbine as one of the Types of Turbines
Also known as the ‘peripheral flow turbine’, tangential flow turbines are turbines in which the working fluid flows in a tangential direction relative to the rotational axis or shaft.
In order to function effectively, the working fluid in a tangential flow turbine should be introduced at high pressure. Water is commonly used as the working fluid in this type of turbine.
8). Mixed Flow Turbine as one of the Types of Turbines
Mixed flow turbine differs from other types of turbines by combining multiple flow patterns in its operation.
Generally, mixed flow turbines combine axial and radial flow mechanisms . The working fluid may enter the turbine in a radial direction, and may exit in an axial direction relative to the rotational axis.
In order to achieve this, the turbine may have an elaborate, multidimensional design which may include variable-pitch, flexible turbine blades. The goal of having a flexible design is mainly to achieve energy efficiency.
Mixed flow turbines can be used in water-driven applications, as well as in automotive turbochargers .
9). High Head Turbine as one of the Types of Turbines
High head turbine is a turbine which operates with heads that exceed 250 meters.
In turbines, the head is simply the height difference between the entry (inlet) and exit (outlet) levels of the working fluid. High head turbines are usually conservative in their operation, and have a high flow velocity compared to other types of turbines.
This in turn implies a greater magnitude of kinetic energy input, and an equally large magnitude of mechanical energy output, with relatively-low torque.
While a head of above 250 meters is the most widely-accepted criteria for distinguishing high-head turbines, some assessments may place this threshold value at 100 or 150 meters.
10). Medium Head Turbine as one of the Types of Turbines
Medium head turbine is a type of turbine which operates with heads between 45 and 250 meters .
In some assessments, the head range for this type of turbine may be placed between 30 and 150 meters. Medium turbines use more working fluid (which is usually water) than high head turbines, and may be used effectively in applications that require a moderate amount of mechanical energy.
11). Low Head Turbine as one of the Types of Turbines
Low head turbines are turbines which operate with head levels that fall below 45 meters.
This type of turbine is ideal in scenarios where there is need to achieve operational sustainability within the context of kineto-mechanical conversion.
According to some assessments, low head turbines are turbines which operate at heads below 30 or 20 meters.
Based on capacity, different minor types of turbines can be distinguished within this category, including low, very-low, and ultra-low head turbines. Low head turbines are useful for small-scale hydro-power schemes .
Peculiarities in the design of this type of turbine mostly affect the radius of the rotor wheel and geometry of the runners.
12). High Specific-Speed Turbine
High specific-speed turbine is a type of turbine which operates at above 250 rotations per minute (rpm).
This threshold is set at 100 or 255 rpm in some assessments. However, the basic criteria which qualifies a turbine to fall within this category is an operational speed of rotation that exceeds that of conventional types of turbines.
It is important to note that the specific speed of a turbine is the rotational speed which is capable of producing useful mechanical energy output that can be applied in electricity generation, among other purposes. This is an index quantity that can be used to assess the turbine’s performance .
13). Medium Specific-Speed Turbine
Medium specific-speed turbine is a type of turbine which operates at rotations-per-minute (rpm) of 50 to 250.
The energy output and conservation characteristics of this type is intermediate with respect to other types of turbines (such as high and low specific-speed turbines).
14). Low Specific-Speed Turbine
Low specific-speed turbine has operational speed of less than 50 rpm.
The specific speeds for individual turbines of this type, depend on the design of the turbine, especially in terms of the working fluid mechanism. Applications of low specific-speed turbine include systems where residual energy is conserved, such as cogeneration systems and hydraulic cooling towers .
15). Steam Turbine as one of the Types of Turbines
As the name implies, a steam turbine is a turbine which derives kinetic energy from steam, and converts this to mechanical energy through kineto-mechanical process.
It is one of the most common types of turbines and depends on various sources such as fossil fuels, for its initial heat energy input.
Steam turbines are usually a component of thermal power plants, where they are used for electricity generation . In some elaborate electric generator systems and mechanical load carriers, the steam turbine may be used to power an electric motor which is directly linked to a mechanical load.
To ensure effectiveness, steam turbines are usually equipped with blades which provide a good contact surface for steam. Also, various types of turbines can be distinguished within this category, based on the pressure of the working fluid. These are the high-pressure, medium-pressure and low-pressure steam turbines.
16). Impulse Turbine
An impulse turbine is a type of turbine that is driven solely by the kinetic impact of high-velocity fluid .
Unlike other types of turbines, the rotor of an impulse turbine is equipped with split buckets, or hollow discs, which are designed to extract maximum kinetic energy from the working fluid .
The working fluid is often water, which is fed at high pressure through a jet so that it strikes the curved rotor blades at an oblique angle.
Due to its structural and operational configuration, impulse turbine is able to operate with high effectiveness and high-power output compared to other types of turbines. It is also conservative in its volume requirement of working fluid.
17). Reaction Turbine as one of the Types of Turbines
A reaction turbine is a turbine which derives its energy input as a combination of kinetic and potential energy that depend on velocity and pressure of the working fluid respectively.
Reaction turbines usually operate in a hydrological setting . The system is configured so as to allow water to flow in through an inlet, thereby delivering a hydrodynamic lift force that is similar to the aerodynamic lift force in aviation systems.
Factors that influence the effectiveness and performance of reaction turbines include pressure differences, water volume and water head.
-Types of Turbines based on Design
18). Propeller-Type Turbine
The propeller-type turbine, or propeller turbine, is a modified reaction turbine, equipped with fixed blades and a propeller-based runner design.
This type of turbine operates by radial, inward flow of the working fluid. They are used in large-scale energy recovery systems that operate at low to medium head, such as submarines and ships. Efficiency of this type of turbine is totally dependent on water flow patterns .
19). Bladeless Turbine as one of the Types of Turbines
Bladeless turbines operate based on the boundary layer effect and resonance, unlike other types of turbines that operate based on kineto-mechanical conversion.
As the name implies, this type of turbine does not possess rotor blades. In place of the rotor assembly, it includes components that perform translational and vibrational motion under the influence of fluid pressure.
Due to relative simplicity, the bladeless turbine is more cost efficient and requires less maintenance than bladed ones. However, less energy than conventional turbines . Bladeless turbines are most applicable in wind-based electricity generation.
20). Shrouded Turbine
Shrouded turbine is a type of turbine in which the rotor is concealed within a duct, diffuser or shroud which reduces the effect of unwanted pressure on the turbine blades.
The main purpose of the shroud in this type of turbine is to increase energy output . In shrouded turbines, all components of the system are configured to have minimal interference with the shroud-rotor assembly.
Several modifications of the turbine have been carried out, all with the purpose of achieving economical energy conversion. These modifications include adjustments of the shroud’s geometry, and addition of other components like ring brims .
21). Shroudless Turbine as one of the Types of Turbines
Shroudless turbine is a turbine which does not have any protective component for the rotor assembly.
Many types of turbines can be classified within this category. The removal of shrouding reduces the centrifugal pressure on the turbine blades, but can introduce over-tip leakage of working fluid especially under high-pressure conditions. This can be addressed by using an aerodynamic casing to control fluid flow around the turbine .
22). Statorless Turbine
A statorless turbine is a type of turbine in which there is no intermediate stator vane system that adjusts the pressure or kinetic energy of inflowing working fluid before energy conversion occurs.
Other types of turbines are equipped with a stator vane system whose role is to direct fluid flow toward the rotor conversion system. While this stator vane system can ensure sustainability and efficiency of the turbine, the statorless design enables the system to achieve a high flow rate, which can result in high energy output.
Types of turbines are;
- Wind Turbine
- Gas Turbine
- Geothermal Turbine
- Gravity Turbine
- Axial Flow Turbine
- Radial Flow Turbine
- Tangential Flow Turbine
- Mixed Flow Turbine
- High Head Turbine
- Medium Head Turbine
- Low Head Turbine
- High Specific-Speed Turbine
- Medium Specific-Speed Turbine
- Low Specific-Speed Turbine
- Steam Turbine
- Impulse Turbine
- Reaction Turbine
- Propeller-Type Turbine
- Bladeless Turbine
- Shrouded Turbine
- Shroudless Turbine
- Statorless Turbine
These types are categorized based on energy source, design, and mode of operation.
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