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How the Wankel engine works

Working principles of Wankel engine

4 stroke cycle on wankel engine

From our previous post, we've seen some major difference between the Wankel engine and other internal combustion engine (reciprocating piston types), this self explanatory photo shows the uniqueness of the four stroke cycle in Wankel engine.

Wankel engine

Wankel engine, also known as rotary engine is a type of internal combustion engine that converts pressure into rotary motion using an eccentric rotary design. The wankel engine operates on four stroke cycle but unlike other internal combustion engines, the combustion takes place in a moving combustion chamber in the oval-shaped housing, The rotor is triangular in shape (unlike the crankshaft used in other engine types).

The Wankel engine has the advantages of compact design and low weight over the most commonly used internal combustion engine employing reciprocating piston These advantages have given rotary engine applications in a variety of vehicles and devices, including: automobiles, motorcycles, racing cars, aircraft, chain saws, and auxiliary power units.

FLUID COUPLING: Torque converter mechanism

NUCLEAR POWER PLANT

NUCLEAR POWER PLANT

Nuclear power plants are thermal power stations, the main aim of this is to generate electrical energy from heat [to convert thermal energy to electrical energy]. Off course this conversion takes a whole lot of components to achieve but the end aim is to rotate a high performance generator with a steam turbine.

The nuclear power plant consist of numerous buildings and facilities which will be broken down as we progress. They are;

1.     The turbine building [houses the turbine, generator, and several other electrical components for power generation]

2.     The containment building [is made of meters thick reinforced concrete because it houses the nuclear reactor. In this building, nuclear reactions take place and water is heated up to generate steam]

3.     The cooling tower [Usually about 200 meters in height, here hot water is cooled]

note: Nuclear power plants may seem complex but it is not, the aim is to use nuclear rection to generate heat, use the heat to generate steam, use the steam to drive steam turbines, use the turbines to drive a generator on the same shaft and generating electricity from it.

MAJOR COMPONENTS

In the containment building, there is a pressurized water reactor [PWR], it consists of a reactor pressure vessel which is usually about 12meters tall and about 25cm tick. It contains a set of fuel assemblies, each fuel assembly contains about 150 ‘fuel rods’. A fuel rod is about 5meters long and about 23cm in diameter. Each fuel rod contains the real nuclear fuel which are the fuel ‘pellets’. The nuclear fuel pellets is made up of enriched URANIUM or PLUTONIUM which make nuclear chain reaction possible. In this chain reaction, a tremendous amount of thermal energy (heat) is released [which is the main aim of the entire assembly]. The PWR is filled with water and the set of fuel assemblies are immersed in it so this large amount of heat can be absorbed by the water and keep the chain reaction going. The water in the PWR heats up to 570°F but a pressurizer is installed to prevent the water from boiling by keeping the pressure constant [about 160bars].

note: this heated water is not the one used to drive the steam turbine, it never leaves the containment building because it has been in direct contact with the fuel rods making it radioactive.

A pump is used to pump this superheated water to a heat exchanger [for info on heat exchangers follow our posts], this heat exchanger is the STEAM GENERATOR, this heat exchanger is designed as a shell shaped tube inside a sealed container. The superheated water is pumped through the shell shaped conductive metal pipe and back to the PWR where it is reheated by the fuel rods. As the superheated water passes through the conductive pipe [the conductive pipes are immersed in water], it heats another water inside the container of the heat exchanger and this water is allowed to boil and becomes steam, the steam passes through a set of pipes to the turbine building where it is fed to the steam turbines, driving both high and low pressure turbines causing rotation. The turbines are connected via the same shaft and rotates the electrical generator [alternator] operating on the same speed and a large amount of electricity is generated. The Pressurized Water Reactor converts the thermal energy of the fuel rods to kinetic energy of the steam, the steam turbine converts kinetic energy of the steam to rotational mechanical energy, the alternator converts the rotational energy of the turbine to induced electrical energy which is stepped up and distributed.

After the steam the turbines, it is fed to a condenser where it is cooled till it condenses back to liquid form after which it returns back to the steam generator so the cycle can be repeated.

In other to achieve this cooling, another water [coolant] is needed to absorb heat from the steam so it can condense. The COOLING TOWER is used to achieve this process. The cooling tower circulates cold water through the steam causing a temperature drop and it condenses [more info on cooling towers at the-mechanist.blogspot.com].

note: The water circulation networks are of three divisions;

1.     Primary circulation system: Used to generate steam by conveying heat from the PWR to the steam generator, then it returns to the PWR to repeat the cycle. The water in this system does not leave the containment building because it is radioactive [having contacted the fuel rods].

2.     Secondary circulation system: This is the working fluid that drives the turbine, it moves from the steam generator where it absorbs heat to become steam, then travels to the turbine building where it drives the turbines in high and low pressure, then it goes through the condenser where it loses heat to become liquid again and returns to the steam generator to repeat the cycle. This water is not radioactive.

3.     Coolant circulatory system: Water in this system can be from a river or a cooling tower. This water has to be kept at a cool constant temperature because it is constantly absorbing heat from the secondary circulation system which in turn absorbs from the primary.

HEAT TRANSFER MOVERMENT

Heat is generated from the fuel rods and is absorbed by the water in the primary circulation system [this occurs in the Pressurized Water Reactor]. Water in the primary circulatory system is highly pressurized water and is a closed system.

Heat absorbed by the water in the primary circulation system is transferred to the water in the secondary circulation system via conductive metal pipes [this occurs in the steam generator], this is the heat used to generate steam and the steam coveys the heat out of the containment building through the turbines to the condenser. As the steam passes through pipes and through the turbine, some amount of heat is lost via conduction till it reaches the condenser where it undergoes a tremendous temperature drop. In the secondary circulation system, steam is conveyed out of the containment building and water is pumped in [after condensation]. water in the secondary system is a closed system.

At the condenser, the heat is further transferred from the water [now steam] in the secondary circulation system to the coolant water causing condensation. The water in the coolant system is usually in an open system and so looses almost all its heat to the environment.

HEAT EXCHANGERS

Three heat exchangers can be identified in this system. The first is the steam generator where pressurized water from the primary circulation system looses heat to that of the secondary circulation system via metallic pipes causing it to boil and become steam.

The second heat exchanger is the condenser where steam in primary circulation system looses heat to the coolant water and undergoes condensation.

The third heat exchanger is the cooling tower where hot coolant water loses heat to the environment.

 

 

STEAM TURBINE ROTOR

STEAM TURBINE ROTOR
A steam turbine converts thermal energy from fluid to mechanical energy. The steam turbine rotor is the most important component of the steam turbine, the principle is very simple, just like the pelton turbine rotor traps mechanical energy from a jet of water from a nozzle and creates rotation, so does the steam turbine traps mechanical energy from high pressure steam. The first designs of steam turbine rotors were similar to the pelton wheel having only one set of blade fins so couldn’t trap all the mechanical energy of the high pressure steam as they are immediately deflected by 90°