Principles of a Steam Turbine

A steam turbine is a mechanical device whose purpose is to convert thermal (or heat) energy into work. Thermal energy is the type of energy that manifests itself as an increase in temperature. The steam turbine uses thermal energy from steam under pressure and converts it into rotary motion, or mechanical work. The original version of the steam turbine was the steam engine, which was powered by reciprocating pistons (pumps that travel up and down in order to convert pressure into motion).

Introduction

The steam turbine is highly thermodynamically efficient, meaning that it acts at a high level of performance without losing much energy in the process, and has a low power-to-weight ratio. This is a ratio of actual performance used to compare devices across their respective weights. These qualities make the steam turbine ideal for power stations, according to roymech.co.uk. Its thermodynamical efficiency comes from the fact that it has multiple stages for steam expansion. Steam turbines come in a variety of sizes, from small 0.75 kW units that are used in pumps and compressors, to 1.5 million kW units that are used to generated electricity.

The Process

Energy from steam is converted into mechanical work via expansion. Expansion occurs through a series of nozzles (or fixed blades) and moving blades within the turbine. The nozzles are arranged with the circular turbine casing that is specifically designed to withstand steam pressure.The moving blades rotate around the central turbine motor, according to roymech.co.uk. If the energy output is too great, then additional turbine rotor units are attached to the primary turbine, around a common center. The design of turbine blades is based on two fundamental principles: impulse blading and reaction blading.

Impulse Blading

An impulse in physics refers to the change in momentum that results from a force acting over a period of time. The impulse blading principle states that when steam is directed, the impact drives the blades around. In other words, steam at a high velocity operates on the concave surfaces of the blade, resulting in energy.

Impulse Blading Features

The steam is directed at the blades at an angle of between 45 and 85 degrees, and the power is transferred through impulse, according to phoenixnavigation.com. As a result, the velocity of the steam decreases when it exits the blades, but the pressure remains constant. Therefore, energy is transferred by the change in velocity of the steam and not by pressure.

Reaction Blading

The reaction blading principle depends on the blade diverting the flow of steam and gaining kinetic energy in the process. Reaction turbines have a different blade cross section than impulse turbines. The reaction blades act like the wings of a plane, while the impulse blades act like an engine piston, according to phoenixavigation.com. Just like the wing of an airplane, the kinetic energy is converted to power by decreasing the steam's velocity and lowering pressure. When the steam enters the blade and travels across it, there is a decrease in pressure on the upper surface and an increase in pressure on the lower surface. As a result, the force that drives the turbine is a reaction force.

References

• Roymech.co.uk
• PhoenixNavigation.com