THERMAL POWER PLANT.........

THERMAL POWER STATION
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fossil fuel resources generally used to heat the water. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy. Certain thermal power plants also are designed to produce heat energy for industrial purposes of district heating, or desalination of water, in addition to generating electrical power. Globally, fossil fueled thermal power plants produce a large part of man-made CO₂ emissions to the atmosphere, and efforts to reduce these are many, varied and widespread.

       



 Typical  thermal  power plant:

Typical diagram of a coal-fired thermal power station

1. Cooling tower	10. Steam Control valve	19. Superheater
2. Cooling water pump	11. High pressure steam turbine	20. Forced draught (draft) fan
3. transmission line (3-phase)	12. Deaerator	21. Reheater
4. Step-up transformer (3-phase)	13. Feedwater heater	22. Combustion air intake
5. Electrical generator (3-phase)	14. Coal conveyor	23. Economiser
6. Low pressure steam turbine	15. Coal hopper	24. Air preheater
7. Condensate pump	16. Coal pulverizer	25. Precipitator
8. Surface condenser	17. Boiler steam drum	26. Induced draught (draft) fan
9. Intermediate pressure steam turbine	18. Bottom ash hopper	27. Flue gas stack

source:www.youtube.com
http://en.wikipedia.org/wiki/Thermal_power_station

SOURCES OF ENERGY

When we use energy in its usable form we convert the form of energy and get our work done during the process. Since we cannot reverse the change involved in this process so we cannot get back the original usable form of energy. Due to this, it becomes important to think about energy shortage and the related energy crisis.

Characteristics of a good source of energy:

• It should be able to do large amount of work for each unit of mass or volume.
• It should be easily accessible.
• It should be easily transported.
• It should be economical.

Conventional Sources of Energy:

The sources of energy which have been in use since a long time are called conventional sources of energy. Coal, petroleum, natural gas, hydel energy, wind energy and nuclear energy are considered to be the conventional sources of energy. Additionally, firewood is also a conventional source of energy but its usage is now limited to kitchens in the rural parts of India.

Fossil Fuels: Coal and petroleum are the fossil fuels.

Coal: Coal was formed millions of years ago. The plants got buried under swamps and due to high pressure and high temperature inside the earth; they were converted into coal. Coal is the highest used energy source in India. During the days of steam engine, coal was used in steam engines. Moreover, coal was also used as kitchen fuel; before LPG became popular. Now-a-days, coal is mainly being used in the industries.

Petroleum: Petroleum was also formed millions of years ago. The animals got buried under the ocean surface and were converted into petroleum; in due course of time. Petroleum is the third major source of energy being used today. Petroleum products are used as automobile fuel and also in the industries. Natural gas mainly comes from the oil wells and is also a major source of energy.

Non-renewable Sources of Energy:

It takes millions of years for the formation of fossil fuels. Since they cannot be replenished in the foreseeable future, they are known as non-renewable sources of energy.

Renewable Sources of Energy:

Those sources of energy which can be replenished quickly are called renewable sources of energy. Hydel energy, wind energy and solar energy are examples of renewable sources of energy.

Non-conventional Sources of Energy: Energy sources which are relatively new are called non-conventional sources of energy, e.g. nuclear power and solar energy.

REFLEX ACTION AND REFLEX ARC

REFLEX ACTION

The involuntary functioning or movement of any organ or body part in response to a particular stimulus which occurs in very short duration of time(within a second usually) and does not involve will or any thinking of brain is called reflex action.

ex-

REFLEX ARC

Reflex arc is the path followed by nerve impulses to produce the reflex action. It usually includes receptor organ, afferent nerve, nerve center, efferent nerve, effector organ or a muscle.

ex-

DO REFLEX ACTIONS INVOLVE BRAIN???

 Reflex actions are sudden responses, which do not involve any thinking. For example, 

when we touch a hot object, we withdraw our hand immediately without thinking as 

thinking may take time which would be enough to get us burnt. The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves (input) and responding to it quickly (output) is called a reflex arc. The reflex arcs−connections present between the input and output nerves − meet in a bundle in the spinal cord. Reflex arcs are formed in the spinal cord and the information (input) reaches the brain. 

he brain is only aware of the signal and the response that has taken place. However, 

the brain has no role to play in the creation of the response.

DOES REFLEX ARC INVOLVE THE BRAIN???

 No,the brain  is only made aware of your reflex travels after the incident has occured, as the the thinking process would slow down  impulse and increase the risk of danger.The incident is stored surrounded by the brain afterwards for memory purposes and to prevent happening within the future.Reflex arcs materialize at the spinal column level, so don't involve the brain. 

SIGNIFICANCE OF SYNAPSE B/W THE NEURONS..

Synapse- A specialized junction where transmission of information takes place between a nerve fibre and another nerve cell, or between a nerve fibre and a muscle or gland cell. The term was introduced at the end of the nineteenth century by the British neurophysiologist Charles Sherrington, who argued, on the basis of his own observations of reflex responses and the studies of the great Spanish anatomist, Ramón y Cajal, that a special form of transmission takes place at the contact between one cell and the next.

Synapses serve as one-way communication devices, transmitting information in one direction only, from the fibre ending to the next cell. They come in two varieties, known as chemical and electrical, according to the mechanism by which the signal is transmitted from the presynaptic to the postsynaptic cell. 

At electrical synapses, which are relatively rare in vertebrates, the membranes of the two cells are in tight contact, producing electrical coupling, which enables a nerve impulse arriving at the presynaptic nerve ending to pass swiftly and reliably to the next cell. 

                                                 

Chemical synapses are more complex, because the presynaptic and postsynaptic cells are physically separated by a minute gap (the synaptic cleft), which prevents simple electrical 

transmission of the action potential to the postsynaptic cell. Instead, transmission is accomplished by the release of a chemical neurotransmitter substance from the presynaptic fibre.

IN A CHEMICAL SYNAPSE-

The cytoplasm of the presynaptic nerve terminal  is packed full of small vesicles, each containing a few thousand molecules of neurotransmitter. When an action potential arrives in the terminal it stimulates the opening of calcium channels in the nerve ending. As a consequence, calcium ions flood into the cell and cause the synaptic vesicles to release their contents into the synaptic cleft. The neurotransmitter molecules that are liberated diffuse across the cleft or gap  and interact with specialized protein receptor molecules in the postsynaptic neuron. The molecular structure of the neurotransmitter and its receptor are matched, so that they fit one another like a lock and key. At nerve–muscle synapses, and in many nerve–nerve synapses, the receptors have a double function, since they also serve as ion channels. Binding of a neurotransmitter molecule produces a change in the three-dimensional shape of the receptor that opens a tiny intrinsic pore in the protein.

spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain (the medulla oblongata specifically). The brain and spinal cord together make up the central nervous system (CNS). The spinal cord begins at the occipital bone and extends down to the space between the first and second lumbar vertebrae; it does not extend the entire length of the vertebral column. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women.

The enclosing bony vertebral column protects the relatively shorter spinal cord. The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body but also contains neural circuits that can independently control numerous reflexes and central pattern generators. The spinal cord has three major functions: as a conduit for motor information, which travels down the spinal cord, as a conduit for sensory information in the reverse direction, and finally as a center for coordinating certain reflexes. 

 The spinal cord is protected by three layers of tissue, called spinal meninges, that surround the canal. The dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of the vertebrae is a space called the epidural space. The epidural space is filled with adipose tissue, and it contains a network of blood vessels. The arachnoid mater is the middle protective layer. Its name comes from the fact that the tissue has a spiderweb-like appearance. The space between the arachnoid and the underlying pia mater is called the subarachnoid space. The subarachnoid space contains cerebrospinal fluid (CSF).

Blood supply

The spinal cord is supplied with blood by three arteries that run along its length starting in the brain, and many arteries that approach it through the sides of the spinal column. The three longitudinal arteries are called the anterior spinal artery, and the right and left posterior spinal arteries. These travel in the subarachnoid space and send branches into the spinal cord. They form anastamoses (connections) via the anterior and posterior segmental medullary arteries, which enter the spinal cord at various points along its length. The actual blood flow caudally through these arteries, derived from the posterior cerebral circulation, is inadequate to maintain the spinal cord beyond the cervical segments.
The major contribution to the arterial blood supply of the spinal cord below the cervical region comes from the radially arranged posterior and anterior radicular arteries, which run into the spinal cord alongside the dorsal and ventral nerve roots, but with one exception do not connect directly with any of the three longitudinal arteries. These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses and supplement the blood flow to the spinal cord. In humans the largest of the anterior radicular arteries is known as the artery of Adamkiewicz, or anterior radicularis magna (ARM) artery, which usually arises between L1 and L2, but can arise anywhere from T9 to L5. Impaired blood flow through these critical radicular arteries, especially during surgical procedures that involve abrupt disruption of blood flow through the aorta for example during aortic aneursym repair, can result in spinal cord infarction and paraplegia.

source: http://en.wikipedia.org/wiki/Spinal_cord

HUMAN BRAIN

BRAIN STRUCTURE

1)This image shows the major lobes of the brain. You need to know where the major lobes are located and      what each lobe does in terms of function




2)Here we see the interior of the brain. Again you need to know the locations and functions of these labeled      parts of the brain.




source-http://cognitrn.psych.indiana.edu/busey/Q301/BrainStructure.html

Amazing 10 signs of a spiritual awaking!!

  source: http://www.youtube.com/watch?v=txTsbeuY5gM

ELECTRIC MOTORS AND GENERATORS

                               DIFF. b/w ELECTRIC MOTORS AND GENERATORS

    Motors and generators are electromagnetic devices. They have current-carrying loops that rotate in magnetic fields. This rapidly changing magnetic field produces electromotive forces, called emfs or voltages. Electric motors and generators are the opposite of each other. Electric motors convert electrical energy into mechanical energy, while electric generators convert mechanical energy into electrical energy.


                                           DIFF. b/w AC AND DC GENERATORS
A DC generator produces an electrical current that flows in only one direction, hence the term "direct current." The current produced by an AC generator, also called an alternator, constantly switches directions.

DC

• Each terminal of a DC generator's armature connects to a different segment of the commutator, which is a two-segmented metal ring. As the armature spins, so does the commutator, which transmits the electrical current to two graphite connectors called brushes. Each brush touches a different segment of the commutator every half rotation of the armature, thereby keeping the polarity of the electrical current positive and the current flowing in the same direction.

  
  
  
  
  

  AC

  • Instead of a two-segmented commutator, an AC generator has two metal slip rings which spin with the armature. Each terminal of the armature connects to a different slip ring. However, unlike a commutator, each slip ring transmits electrical current to just one brush, rather than a different brush every half rotation. A slip ring's polarity changes when the armature turns from one pole of the generator's magnet to the other, causing the electrical current to reverse directions.

    
    

  
  
  

  
  

METALLURGY (STEP 3 AND 4)

   Last week we studied first two steps involved in metallurgy.Let's continue that topic and learn about the next two steps.
Starting with -

STEP 3-Conversion of metal oxide into metal

This step is divided into two parts-
(i)Conversion of concentrated ore into metal oxide

It can be done by two methods-
CALCINATION and ROASTING which is explained in the given video.



(ii)Conversion of metal oxide to metal

Generally the 3 methods used are:

Reduction by heating the oxide  Chemical reduction  Electrolytic reduction.                                                                                                                                                                                                                                                                                                  Reduction by heating alone (Heating process)  The oxides of metals that are low in the reactivity series can be reduced to obtain the metals by heating their ore.  For example, mercuric oxide (HgO), obtained from its ore mercuric sulphide (HgS), when heated to about 3000 C forms mercury metal.     2HgS + 3O2 Roasting  -------> 2HgO + 2SO2 Mercuric sulphide (from air) Mercuric  oxide 2HgO Heat  ---------> 2Hg + O2 (Reduction) (Mercury) Roasting and reduction processes are carried out simultaneously. Chemical reduction process Under this process the oxides of metals that are in the middle of the reactivity series are reduced to free metals using chemical reducing agents such as carbon, aluminium, sodium or calcium. 1. Reduction by carbon process  Oxides of metals like zinc, iron, copper, nickel, tin and lead are reduced using carbon as the reducing agent. Carbon can be used only if it has greater affinity for oxygen than the metal. For example, carbon can reduce copper oxide to copper, but it cannot reduce calcium oxide. It can reduce zinc oxide. ZnO + C -----> Zn + CO Zinc metal Carbon  monooxide 2. Reduction with aluminium by thermite process Metals which are too active to be obtained by reduction of their oxides with carbon are reduced using aluminium, which is a more powerful reducing agent. Chromium and manganese oxides are reduced using aluminum. This reaction is highly exothermic. Cr2O3 + 2Al -----> 2Cr + Al2O3 Chromium metal 3MnO2 + 4Al -----> 3Mn + 2Al2O3 Manganese metal Electrolytic reduction process The oxides (or chlorides) of highly reactive metals like sodium, magnesium, aluminium and calcium cannot be reduced by using carbon or aluminium. Electrolytic reduction is the process used to extract the above metals. Molten oxides (or chlorides) are electrolysed . The cathode acts as a powerful reducing agent by supplying electrons to reduce the metal ions into metal. Fused alumina (molten aluminium oxide) is electolysed in a carbon lined iron box. The box itself is the cathode. The aluminium ions are reduced by the cathode. At the cathode  Al3+ + 3e-  electrolysis ------------------> Al Aluminium Ion Aluminium  Atom MgCl2 electrolysis  ----------------> Mg + Cl2

STEP 4-Refining of metal

This process ensures the separation of even the residual impurities from the extracted metals. Refining methods are different for different metals. The methods depend upon the purpose for which the metal is to be used. Refining can also be used to recover some valuable by-products such as silver or gold. 

The methods are-

(a)Liquation method 
Readily fusible metals (low melting points) like tin, lead and bismuth are purified by liquation.  
The impurities do not fuse and are left behind. 
 In this process, the block of impure metal is kept on the sloping floor of a hearth and heated slowly. The pure metal liquifies (melts) and flows down the furnace. The non-volatile impurities are infusible and remain behind. 

(b)Distillation method
In this process, metals with low boiling point, such as zinc,calcium and mercury are vaporized in a vessel. The pure vapours are condensed into pure metal in a different vessel. The non-volatile impurities are not vaporised and so are left behind. 

(c)Oxidation method
In this process, the impurities are oxidised instead of the metal itself. Air is passed through the molten metal. The impurities like phosphorus, sulphur, silicon and manganese get oxidised and rise to the surface of the molten metal, which are then removed. 

(d)Electrolytic refining method
The process of electrolysis is used to obtain very highly purified metals. It is very widely used to obtain refined copper, zinc, tin, lead, chromium, nickel, silver and gold metals. 
  

In this process,

The impure slab of the metals is made the anode  A pure thin sheet of metal is made the cathode  A salt solution of the metal is used as the electrolyte.

On passing current, pure metal from the electrolyte is deposited on the cathode.  
The impure metal dissolves from the anode and goes into the electrolyte. The impurities collect as the anode mud below the anode. 


source- www.nedians.8m.com

                                                                                                                                             

what is corrosion??

In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.  

Corrosion removal

Often it is possible to chemically remove the products of corrosion. For example [phosphoric acid] in the form of [naval jelly] is often applied to ferrous tools or surfaces to remove rust. Corrosion removal should not be confused with electropolishing, which removes some layers of the underlying metal to make a smooth surface. For example, phosphoric acid may also be used to electropolish copper but it does this by removing copper, not the products of copper corrosion.

Resistance to corrosion

Some metals are more intrinsically resistant to corrosion than others (for some examples, see galvanic series). There are various ways of protecting metals from corrosion including painting, hot dip galvanizing, and combinations of these.

Protection from corrosion

US Army shrink wraps equipment such as helicopters to protect it from corrosion and thus save millions of dollars.

Surface treatments

Applied coatings

Main article: Galvanization

Galvanized surface

Plating, painting, and the application of enamel are the most common anti-corrosion treatments. They work by providing a barrier of corrosion-resistant material between the damaging environment and the structural material. Aside from cosmetic and manufacturing issues, there are tradeoffs in mechanical flexibility versus resistance to abrasion and high temperature. Platings usually fail only in small sections, and if the plating is more noble than the substrate (for example, chromium on steel), a galvanic couple will cause any exposed area to corrode much more rapidly than an unplated surface would. For this reason, it is often wise to plate with active metal such as zinc or cadmium. Painting either by roller or brush is more desirable for tight spaces; spray would be better for larger coating areas such as steel decks and waterfront applications. Flexible polyurethane coatings, like Durabak-M26 for example, can provide an anti-corrosive seal with a highly durable slip resistant membrane. Painted coatings are relatively easy to apply and have fast drying times although temperature and humidity may cause dry times to vary.

Reactive coatings

If the environment is controlled (especially in recirculating systems), corrosion inhibitors can often be added to it. These form an electrically insulating or chemically impermeable coating on exposed metal surfaces, to suppress electrochemical reactions. Such methods obviously make the system less sensitive to scratches or defects in the coating, since extra inhibitors can be made available wherever metal becomes exposed. Chemicals that inhibit corrosion include some of the salts in hard water (Roman water systems are famous for their mineral deposits), chromates, phosphates, polyaniline, other conducting polymers and a wide range of specially-designed chemicals that resemble surfactants (i.e. long-chain organic molecules with ionic end groups).

Anodization

Main article: Anodizing

This climbing descender is anodized with a yellow finish.

Aluminium alloys often undergo a surface treatment. Electrochemical conditions in the bath are carefully adjusted so that uniform pores several nanometers wide appear in the metal's oxide film. These pores allow the oxide to grow much thicker than passivating conditions would allow. At the end of the treatment, the pores are allowed to seal, forming a harder-than-usual surface layer. If this coating is scratched, normal passivation processes take over to protect the damaged area.
Anodizing is very resilient to weathering and corrosion, so it is commonly used for building facades and other areas that the surface will come into regular contact with the elements. Whilst being resilient, it must be cleaned frequently. If left without cleaning, panel edge staining will naturally occur.

source:  http://en.wikipedia.org/wiki/Corrosion

What do you mean by thermite process?

                        A thermite mixture using iron (3) oxide

Thermite is a pyrotechnic composition of metal powder fuel and metal oxide. When ignited by heat, thermite undergoes an exothermic oxidation-reduction reaction. Most varieties are not explosive but can create brief bursts of high temperature in a small area. Its form of action is similar to that of other fuel-oxidizer mixtures, such as black powder.
Thermites have diverse compositions. Fuels include aluminium, magnesium, titanium, zinc, silicon, and boron. Aluminium is common because of its high boiling point. Oxidizers include boron(III) oxide, silicon(IV) oxide, chromium(III) oxide, manganese(IV) oxide, iron(III) oxide, iron(II,III) oxide, copper(II) oxide, and lead(II,IV) oxide. 
 

Chemical reactions

thermite reaction using iron(3) oxide.

A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.

The aluminium reduces the oxide of another metal, most commonly iron oxide, because aluminium forms stronger bonds with oxygen than iron:

Fe₂O₃ + 2 Al → 2 Fe + Al₂O₃

The products are aluminium oxide, free elemental iron, and a large amount of heat. The reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation.
The reaction is used for thermite welding, often used to join rail tracks. Other metal oxides can be used, such as chromium oxide, to generate the given metal in its elemental form. Copper thermite, using copper oxide, is used for creating electric joints in a process called cadwelding:

3 CuO + 2 Al → 3 Cu + Al₂O₃

Some thermite-like mixtures are used as pyrotechnic initiators such as fireworks.
Thermites with nanosized particles are described through a variety of terms, such as metastable intermolecular composites, super-thermite, nano-thermite, and nanocomposite energetic materials.

Iron thermite

The most common composition is the iron thermite. The oxidizer used is usually either iron(III) oxide or iron(II,III) oxide. The former produces more heat. The latter is easier to ignite, likely due to the crystal structure of the oxide. Addition of copper or manganese oxides can significantly improve the ease of ignition.
The original mixture, as invented, used iron oxide in the form of mill scale. The composition was very difficult to ignite.

Copper thermite

Copper thermite can be prepared using either copper(I) oxide (Cu₂O, red) or copper(II) oxide (CuO, black). The burn rate tends to be very fast and the melting point of copper is relatively low so the reaction produces a significant amount of molten copper in a very short time. Copper(II) thermite reactions can be so fast that copper thermite can be considered a type of flash powder. An explosion can occur and send a spray of copper drops to considerable distance.
Copper(I) thermite has industrial uses in e.g. welding of thick copper conductors ("cadwelding"). This kind of welding is being evaluated also for cable splicing on the US Navy fleet, for use in high-current systems, e.g. electric propulsion.

Source:   http://en.wikipedia.org/wiki/Thermite

METALLURGY (step 1 and 2)

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use.

There are four main methods of metallurgy
STEP1.Crushing of the ore into powder.
STEP2.Concentration of the ore.
         This step is done for removal of unwanted impurities from the ore.Given below are the various methods for the concentration of different ore

(a) HYDRAULLIC WASHING

(b) FROTH FLOATATION PROCESS

(c)MAGNETIC SEPARATION

(d) BAYER PROCESS(for Al)

Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. The concentration, temperature and pressure used depend on the source of the bauxite and exactly what form of aluminium oxide it contains. Temperatures are typically from 140°C to 240°C; pressures can be up to about 35 atmospheres.

High pressures are necessary to keep the water in the sodium hydroxide solution liquid at temperatures above 100°C. The higher the temperature, the higher the pressure needed.

With hot concentrated sodium hydroxide solution, aluminium oxide reacts to give a solution of sodium tetrahydroxoaluminate

.

Impurities  like iron oxide present in this ore do not react with sodium hydroxide,it is therefore separated by filtration but silica reacts to form water soluble sodium silicate.

The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously produced aluminium hydroxide. This provides something for the new aluminium hydroxide to precipitate around.

Aluminium oxide (sometimes known as alumina) is made by heating the aluminium hydroxide to a temperature of about 1100 - 1200°C.

STEP(3)Extraction of metal from the concentrated ore.

STEP(4)Refining or the purification of metal.