Thermal Engineering

Thermal Engineering

Thermal engineering refers to the study of e-Academic & e-Academic – FAA lifts the restrictions and allows students upward, thus increasing the duration of their stay in the US.nmagnetic waves of ultra-low frequencies, especially the conversion of latent heat into work, and the corresponding processes that are based on the law of conservation of energy. The points you mentioned are necessary in thermal engineering, especially for the engines, boilers, refrigeration, and air conditioning.

1. Boilers

Definition and Function

A boiler is a closed container designed to heat water or any other liquid to the boiling point, so as to generate steam out of it, which then is used for such purposes as heating, power generation and industrial processed. The similar to of the heat jumps from the firing of fuel to the water is described as the boiling process in a boiler. The prime mission of the boiler is to make steam by heating water that will be used for mechanical task, etc., heating systems or other industrial processes.

Classification of Boilers

Boilers can be classified in different ways according to a few independent criteria, such as:

1. Based on the Axis of Heat Flow:
   • Fire Tube Boilers: In these boilers hot gases from the gameflow material flow through the tubes while water is around the tubes. This type of boiler, like, the refineries boiler and the ship boiler that has the Combustion chamber, a boiler section, and the movable boiler part, all the tubes, is in two-thirds of the shell’s height. (e.g., Lancashire boiler, Cornish boiler).
   • Water Tube Boilers A – In these boilers water is pumped through the boiler tubes and hot gases are feed into the furnace. (e.g., Babcock & Wilcox boiler, Stirling boiler).
2. Based on the Number of Tubes:
   • Single Tube Boilers: Only one tube included in it. For example, a Cochran boiler.
   • Multi-tube Boilers: Multi tubes include in the boilers (e.g., Babcock & Wilcox, Stirling boiler).
3. Based on the Furnace Position:
   • Externally Fired Boiler: The furnace is situated out of the boiler shell.
   • Internally Fired Boiler: The furnace is located inside the boiler shell.
4. Based on the Pressure:
   • Low-Pressure Boilers: Operating below 2 MPa.
   • High-Pressure Boilers: Operating above 2 MPa.

Construction and Working of a Simple Vertical Boiler

A simplified vertical boiler is composed of a vertical cylindrical shell, with a fire-tube placed inside it. It is usually made up of the following details:

• Shell: This is the outside retaining wall in which water is deposited.
• Fire Tubes: Tubes where hot gases are discharged from fuel combustion and these, in turn, transmit heat to the nearby water.
• Furnace: Situated at the bottom of the boiler, the site at which the fuel is burned.
• Flue gases: Gases of escape produced by combustion that go through the fire tubes.
• Water: Heated in the shell by the hot gases passing through the fire tubes, in this way, becomes steam.

Principles of operation:

• The furnace consumes the fuel, and the hot gases emitted are passed through the fire tubes.
• The water around the fire tubes absorbs the heat, and thus boils, and steam is formed.
• The steam travels upwards from the boiler till it is collectable and is used for a number of applications.

Boiler Accessories

Boiler accessories are the gadgets which help in running a boiler and making it more efficient, safe, and reliable. There are such things as:

• Steam Drum: A place to keep steam and moving water from steam.
• Superheater: Raising the temperature of steam beyond its saturation point.
• Economizer: A device that rpcleats the feedwater before it enters the boiler and in doing so, it improves the energy efficiency of the boiler.
• Air Preheater: Is the equipment where the combustion air is preheated before it enters the furnace.
• Safety Valve: The valve safeguards the boiler from overpressure.

Comparison between Fire Tube and Water Tube Boilers

2. Otto Cycle

Definition and Working Principle

The Otto cycle is the thermodynamic cycle commonly employed in gasoline (spark-ignition) engines. It is constituted by two processes, each adiabatic and isochoric, respectively.

• Process 1-2 (Compression Stroke): The intake valve closes, and the piston is pushed up to compress the air-fuel mixture. This leads to an increase in pressure and temperature of the mixture.
• Process 2-3 (Power Stroke): The air-fuel mixture is compressed into a small space, which is ignited by the spark plug. The gas rapidly burns, thus, the temperature and pressure rise, which propels the piston downwards.
• Process 3-4 (Exhaust Stroke): The exhaust valve opens, and the piston is raised to dispose of the gas that formed during combustion.
• Process 4-1 (Intake Stroke): The intake valve welcomes a fresh air-fuel mixture through the cylinder.

3. Diesel Cycle

Definition and Working Principle

The Diesel cycle is a part of diesel engines with the essential action of combustion of fuel that is directly started by the compression rather than a spark plug. The motor engine does the Otto cycle close but altering the ignition process and type of fuel.

• Process 1-2 (Compression Stroke): The intake valve is closed and the air is compressed by the piston, which makes the air get increased in pressure and temperature.
• Process 2-3 (Fuel Injection and Power Stroke): At the final stage of compression, fuel is injected directly into the pre-compressed air. It auto-ignites because of the high temperature. This causes the increase of pressure, which drives the piston down.
• Process 3-4 (Exhaust Stroke): The exhaust valve is opened and the piston is moved upward to expel the exhaust gases.
• Process 4-1 (Intake Stroke): The intake valve is opened and fresh air flows into the cylinder.

4. Refrigeration and Air-conditioning Cycles

Definition and Working Principle of Refrigeration

Refrigeration is the course of extracting heat from a particular space or object to decrease its temperature. One of the most widely used refrigeration cycles, namely the Vapour Compression Refrigeration Cycle, includes the following steps:

1. Evaporation: In low-pressure condition, refrigerant absorbs heat from the environment (or space) by evaporation and gets converted into a gaseous state.
2. Compression: The refrigerant gas that has come out of the evaporator enters the compressor where it gets compressed thus, raising the pressure and temperature.
3. Condensation: This high-pressure and high-temperature gas are taken through a condenser where most of the heat gets lost to the environment and condenses back to the liquid phase.
4. Expansion: The liquid refrigerant expands through the expansion valve, releasing the pressure and the temperature, and hence, the cycle restarts.

Applications of Refrigeration Cycle

The Refrigeration Systems are Found in Various Applications Such as:

• Air conditioning: This is used for the modification of indoor temperature such as cooling and heating of buildings.
• Food preservation: This is done in refrigerators and freezers to help the food endure.
• Industrial cooling: Is used in manufacturing industries as a temperature control method, such as chemical production and oil refining.
• Medical applications: These include respiratory therapies, blood storage, and the like which need a constant temperature.

Example: In a fridge, the heat is drawn off from the inside (which is cold) and passed to the outside environment (which is warm) thus, the refrigeration cycle operates.