Working Principle of Cochran Boiler.

Cochran Boiler

The Cochran boiler is also called a fire tube boiler. cochran boiler workes on the principle of heat convection. In cochran boiler, the hot gases are being passed through the fire tube running in the sealed container filled with water. The locomotive boiler is self-propelled and the power is being supplied by the diesel, steam or electricity. This type of steam engine has been used in the railway for a long time. The locomotive boiler is consisting of vertical cylinder shell the top of the cylinder is of dome-shaped. This dome shape provides enough space for steam which is produced on heating. Basically, the water is being heated in a high amount at high temperatures which produce a high amount of steam which is used to do mechanical work. The hemispherically shaped furnace is provided to burn the fuel mostly coal is used. Fuel is kept on the grate to burn the fuel easily and ash is then settled in the ash pit. Fire bricks are used for lining as shown in the figure to overcome with the heat loss. On the burning of the fuel, it produces a large amount of smoke that has to be expelled outside for that chimney is provided. When the heat is generated, it heated the fire tube which is filled with flue gases. this flue gases used to heat the water surrounded by the fire tube. all they are of equal dimensions and is kept in a horizontal position. In this process the coal has to feed periodically to make the heating process continues, fire door is provided to feed the coal periodically. The safety valve is used in an emergency when the steam pressure exceeds its limit then it is being opened to release the excess amount of steam. Flue pipe is provided to heat from the furnace to the combustion chamber.

So many safety kinds of stuff are used in the boiler, a fusible plug is provided at the top of the combustion chamber. When the boiler temperature exceeded the safe working limit then it gets melted and stops the fire. Usually, the fusible plug is made up of aluminium and zinc metal. The blow of cock is used to blow of the impurity, mud and sediment from the boiler.    

To deal with any boiler safety must be the first priority because silly mistakes are enough to destroy the valuable thing even can catch the fire burn the whole plant along with human being.

Cochran boiler

   

Working:

On the burning of the fuel in the furnace, it produces a large amount of heat in the form of flue gases. This flue gases entered in the flue pipe and goes to the combustion chamber. Fire tubes are placed horizontally and it is surrounded by the water completely. Flue gases enter in the fire tube pipe and heated the water and form the steam. Formed steam is being kept in the steam chamber.

To produce the steam water has to supply uniformly to the shell and it is controlled by the feed check valve. When the flue gases supplies boiler heated up and the cold water settled down and steam flow over it between the fire tube. Produced steam is kept in the dome shape chamber on the requirement it is supplied to anti priming pipe where water droplets are filtered. 

Advantages

1. Less floor area is required.
2. Construction cost is less.
3. It can easily move to different locations, semi-portable.
4. It has a self-contained furnace.
5. Easy to operate.
6. Higher volume to areas ratios.

Disadvantage

1. The rate of steam generation is less.
2. Corrosion and scale formation takes place.
3. Overheating problem.
4. Periodic cleaning is required and it is difficult to clean all the parts.

Application

Railway and marine

Properties of Fluid Used in Fluid Power System.

Classification of fluids 

1. Ideal fluid: A fluid which is incompressible and is having no viscosity. it is an imaginary fluid, it does not exist. 
2. Real fluid: A fluid which posses viscosity is known as real fluid 
3. Newtonian fluid: In a fluid, in which shear stress is directly proportional to the rate of shear strain
4. Non- Newtonian fluid: A fluid in which the shear stress is not proportional to the rate of shear strain. 
5. Ideal plastic fluid: A fluid in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain

Properties of fluid

1. Viscosity: 

The viscosity of the fluid is its resistance to flow. The fluid of hydraulic power system is the compromise. if the viscosity of the fluid is too low then the fluid will leak by the internal seal causing a volumetric loss of the efficiency. if the viscosity of the fluid is too high then the fluid is difficult to push through the hoses, fittings and valves causing a loss of mechanical efficiency.

The dynamic viscosity is the shearing resistance of the fluid and it is measured by placing the fluid between two plates and shearing one plates with respect to other.

2. Chemical stability:

It is an important property of the hydraulic fluid. it is defined as the ability of the fluid to resist oxidation and deterioration for long time periods. Under the severe operating condition, the fluid undergoes unfavourable changes. a chemical reaction takes place with a hydraulic component, these reactions result in the formation of sludge, gums, carbon, etc, which clog the openings and cause valve and piston to stick.

3. Cleanliness: 

It is a very sensitive factor which received very considerable attention, especially when the hydraulic system used in the aerospace industry because it is extremely sensitive to the contamination. fluid cleanliness is of primary importance because the contaminants can cause malfunction, prevent proper valve seating, cause wear in the component.

4. Anti-wear and lubrication characteristics: 

The fluid must be capable of covering the contact surfaces of all the moving parts with a thin continuous lubricating film. the lubricating film may be destroyed as a result of high loading forces, insufficient oil delivery and low viscosity, it leads to wear due to fretting.

5.Compatibility:

In the hydraulic system, different materials are used and all the material has their own properties, so the fluid should be fully compatible with the other material used in the hydraulic system. it should not react chemically with any of these materials nor changes their physical properties.

6. Foaming: 

All the fluid contain a certain amount of dissolved air in it.  the amount of the dissolved air depends on the temperature and pressure. material based oil can contain 10 to 12 % by volume of dissolved air. as the temperature of the fluid increases or the pressure decreases the dissolved air is liberated and it forms the bubble. when the fluid contains the entrained air return to the reservoir, the air rises to the surface and cause foam. this foam can cause a severe problem. a foam-depressant additive is used to break down of the foam.

Read moreHow Fluid Power System Works.

  

       

How Fluid Power System Works.

It can be said that fluid power the backbone or muscles that make the industry move. The fluid power system is used to push, pull, rotate, regulate and drive directly or indirectly all the machines of industry.  fluid power is the technology that deals with the generation, control and transmission of power using the pressurized fluids. Almost in all the industries process required to move the body from one place to other places, some time to hold the body or object for some manufacturing process, such activities are performed by the prime mover.

whenever we talk about the fluid power system two comes into the picture-

1. Hydraulic system: Fluid based system using the liquid as a transmission medium.

this system uses the liquid such as petroleum oil, water etc. in the earliest fluid used was water hence the name was applied to the system using liquids.

2. Pneumatics system: Gase based system is called a pneumatic system.

In this system gases used are, compressed air, some time nitrogen.

Fluid power is the general term used for both hydraulic and pneumatic system. there are two type of fluid power system.

1. Fluid transport: it is used to deliver the fluid from one place to another place.
2. fluid power: it is designed specially to perform work that is accomplished by a pressurised fluid bearing on an operating fluid cylinder or fluid motor.                                   
   
                                                                                                                                                         *Fluid is a substance that can flow or continually deform under the applied shear stress.

Advantages

1. Simple and accuracy of control: using the simple lever and push button, one can operate the system easily and accurately. 
2. Multiplication and variation of forces: a fluid power system can multiply forces simply and efficiently from a kilogram to several hundreds of ton. 
3. Multiplication control: a single hydraulic pump or air compressor can provide power and control for numerous machine using a valve manifold and distribution system.
4. Constant force and torque: It is capable of providing a constant torque of force regardless of speed changes. 
5.  Low weight to power ratio: the hydraulic system has a low weight to power ratio compared to other systems.
6.  the system is Economical and compact.
7. The fluid power system is used where the safety is much more important.
8. Eliminate complicated mechanical trains of gear.

Disadvantages

1. Hydraulic lines can burst to cause serious human injuries.
2. Prolong exposure to loud noise.
3. Fire hazard
4. Systems are messy.
5. Physical injury from the high-speed particle.
6. The hydraulic system is highly corrosive to most of the aircraft material.

Applications

1. Medical : Medical equipment such as dental drives and human patient simulator, heart assist devices.
2. Aviation: landing wheel in aircraft, aircraft trolley, luggage loading and unloading system, aileron, flight simulator.  
3. Automobile: hydrostatic transmission, suspension system, power brakes