Governors working and Classification

Governors

The function of a governor is to regulate the mean speed of an engine, when there are variations in the load. e.g.

• When the load on an engine increases, its speed decreases, therefore it becomes necessary to increase the supply of working fluid.

• When the load on the engine decreases, its speed increases and thus less working fluid is required.

• Automatically controls the supply of working fluid to the engine with the varying load conditions and keeps the mean speed within certain limits.

• When the load increases, the configuration of the governor changes and a valve is moved to increase the supply of the working fluid.

•   Conversely, When the load decreases, the engine speed increases and the governor decreases the supply of working fluid.

Applications of Governors

•  Automobile Engines

•  Steam Engines

•  Internal Combustion Engines

•  Turbines 

Types of Governors

• Centrifugal governors 

• Inertia governors

Centrifugal Governors:

The centrifugal governors are based on the balancing of centrifugal force on the rotating balls by an equal and opposite radial force, known as the controlling force.

Characteristics of Governors

1. Stability of Governors:

 A governor is said to be stable when for every speed within the working range there is a definite configuration

 For a stable governor, if the equilibrium speed increases, the radius of governor balls must also increase.

2. Sensitivity of Governors:

 The smaller the change in speed from no load to the full load, the more sensitive the governor will be.

 It is the ratio between speed range and mean speed. The smaller the ratio, the sensitive
the governor.

 3. Isochronism:

 A governor is said to be isochronous if equilibrium speed is constant for all the radii of

rotation in the working range.

 4. Hunting:

 A governor is said to be hunt if the speed of the engine fluctuates continuously above and below the mean speed.

 This is caused by a too sensitive governor which changes the fuel supply by a large amount when a small change in the speed of rotation takes place.

Types of Thermodynamics Systems

Introduction

System: 

                 A quantity of matter or a region in space under consideration

Surroundings:

                       Mass or region outside the system

Boundary :

                   The surface that separates system and surroundings  

Types of Thermodynamics Systems

There are three types of systems in thermodynamics: open, closed, and isolated.

Closed system:

A system which can exchange only energy with its surroundings, not matter. If we put a very tightly fitting lid on the pot from the previous example, it would approximate a closed system.

Open System:

A system which can exchange both energy and matter with its surroundings. The stovetop example would be an open system because heat and water vapor can be lost to the air.

Closed system:

A system which can exchange only energy with its surroundings, not matter. If we put a very tightly fitting lid on the pot from the previous example, it would approximate a closed system.

Isolated System:

                             A system that cannot exchange either matter or energy with its surroundings. A perfect isolated system is hard to come by, but an insulated drink cooler with a lid is conceptually similar to a truly isolated system. The items inside can exchange energy with each other, which is why the drinks get cold and the ice melts a little, but they exchange very little energy (heat) with the outside environment. 

Turbine and its Classification

Turbine

Turbine is a device that extracts energy from a fluid (converts the energy held by the fluid to mechanical energy)

• Pumps are devices that add energy to the fluid (e.g. pumps, fans, blowers, and compressors)  
• Hydroelectric power is the most remarkable development pertaining to the exploitation of water resources throughout the world.
• Hydroelectric power is developed by hydraulic turbines which are hydraulic machines.
• Turbines convert hydraulic energy or hydro-potential into mechanical energy.
• The mechanical energy developed by turbines is used to run electric generators coupled to the shaft of turbines.
• Hydroelectric power is the cheapest source of power generation.

  Classification of turbines

 1: On the basis of hydraulic action or type of energy at the inlet

•  Impulse Turbine (Pelton Wheel)
•  Reaction Turbine (Francis Turbine)

 2: On the basis of the direction of flow through the runner

• Tangential flow turbine (Pelton)
• Radial flow turbine (Francis )
• Axial Flow Turbine (Kaplan)
• Mixed flow turbine (Modern Francis)  

3: On the basis of the head of water

• High head turbine (Pelton, H>250m)
• Medium head turbine (modern Francis, 60-250m)
•  Low head turbine (Kaplan, <60m)

4: On the basis of specific speed Ns of the turbine

•  Low specific speed (Pelton, 10-35)
•  Medium (Francis, 60-400)
• High specific speed (Kaplan, 300-1000)  

Why Are Tires Black? The Science Behind Rubber Tires

Have you ever wondered why tires are black, even though natural rubber is white? The answer lies in the addition of an ingredient called carbon black, which transforms the color of rubber and significantly improves its performance.

The Natural Color of Rubber

Rubber, in its natural state, is actually milky white. This may come as a surprise since we're so accustomed to seeing black tires on our vehicles. So why aren't tires white?

The Role of Carbon Black

In the early 19th century, manufacturers discovered that adding carbon black to rubber produced a much stronger and longer-lasting tire. Here’s how carbon black works:

• Reinforcing Filler: Carbon black acts as a reinforcing filler in rubber, which increases the durability and strength of the tire. This means the tire can withstand more wear and tear over time.
• Heat Conduction: Tires generate a lot of heat while driving, especially in the tread and belt areas. Carbon black helps conduct heat away from these areas, reducing the likelihood of damage and extending the tire’s lifespan.

Why Are Tires Black?

In summary, tires are black because carbon black is added during the manufacturing process. This ingredient not only changes the color of the rubber but also makes the tires stronger, more durable, and longer-lasting.

So, the next time you look at your car’s tires, remember that their black color is a key part of what makes them safe and reliable on the road!

Casting and Forging difference

Casting vs Forging

Casting:

Casting is a process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity

• The term casting also applies to the part made in the process
• Steps in casting seem simple:

1. Melt the metal
2. Pour it into a mold
3. Let it freeze

Advantages of Casting:

•       Can create complex part geometries
•       Can create both external and internal shapes.
•       Some casting processes are net shape*; others are near net shape.
•       Can produce very large parts.
•       Some casting methods are suited to mass production.
•       Suitable for any metal that can be heated to a liquid.

  Disadvantages of Casting:     

•       Limitations on mechanical properties.
•       Poor dimensional accuracy and surface finish for some processes; e.g., sand casting.
•       Safety hazards to workers due to hot molten metals.
•       Environmental problems.

Forging:

                Deformation process in which work is compressed between two dies using either impact or gradual pressure to form the part.

•        Oldest of the metal forming operations, dating from about 5000 BC.
•        Components: engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts. 
•         Also, basic metals industries use forging to establish a basic form of large parts that are subsequently machined to final shape and size.  
• 
  

Classification of Forging Operations:

                 1. Hot or warm forging:

                               Most common, due to the significant deformation and the need to reduce strength and increase the ductility of work metal.

               2. Cold forging:   

                      Advantage: increased strength that results from strain hardening. Cold forging is generally preferred when the metal is already a soft metal, like aluminum.  

Advantages of Forging:

• It produces a tougher product compare to other.
• The product made by forging has high impact or tensile strength.

Heat Transfer

Difference between Heat and Temperature

• Temperature is a measure of the amount of energy possessed by the molecules of a substance. It is a measure of hotness and coldness.
• Heat, on the other hand, is energy in transit. Heat is a form of energy which transfers from one system to another due to the temperature difference. 

Modern theory of Heat transfer

The kinetic energy of molecules of a substance is directly proportional to the absolute temperature.
The kinetic energy of molecules is sum of

1. Vibrational Energy
2. Rotational Energy
3. Translational Energy

Application Areas of Heat Transfer

Basic law of Thermodynamics

1) The First Law of Thermodynamics:

         Energy can not be created nor destroyed but can be changed from one form to another. It is also known as the law of conservation of energy.

2) The Second Law of Thermodynamics:

The change in the entropy in the universe can never be negative.

3) The Third Law of Thermodynamics:

     The entropy of a system approaches zero as the temperature approaches absolute zero.

4) The Zeroth Law:

    If two systems are in thermal equilibrium with the third system, they are equilibrium with each other.

Modes of Heat Transfer

1) Conduction:

    An energy transfer across a system boundary due to a temperature difference by the mechanism of molecular interaction.

Conduction is a mode of heat transfer that occurs in solid and fluids when there is no bulk movement of fluid.  

Fourier’s law of heat conduction: 
      The law of heat conduction, also known as Fourier's law, states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to that gradient, through which the heat flows
                               q = -kAdT/dx

2) Convection: 

The transfer of heat from one place to another by the movement of fluids. Convection is usually the dominant form of heat transfer in liquids and gases

Newton’s law of cooling:

                              q = hA (Tw - T∞)

3) Radiation:

Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region.Radiation emitted by a body is a consequence of thermal agitation of its composing molecules.

Radiation required no medium for heat transfer.

Stefan-Boltzmann Law:

An ideal thermal radiator, or blackbody, will emit energy at a rate proportional to the fourth power of the absolute temperature of the body and directly proportional to its surface area

                              q emitted = σAT 4