what is refrigeration in engineering ( refrigeration and equipment engineering)

Introduction to Thermodynamics

Key Concepts

Force: Strength or energy as an attribute of physical action or movement.

Work: Activity involving mental or physical effort done to achieve a result.

Power: The ability or capacity to do something or act in a particular way.

Energy: The ability to do work.

Volume:

• Definition: Occupied space by a substance.
• Effect of Temperature: Change in temperature affects the volume of solids and liquids.

Pressure

• Definition: Scientifically, pressure is a force per unit area.

• Types of Pressure:

1. Atmospheric Pressure: Pressure exerted by the atmosphere.
2. Gauge Pressure: Difference between actual pressure and atmospheric pressure.
3. Absolute Pressure: Sum of atmospheric pressure and gauge pressure.
4. Vacuum Pressure: Pressure below atmospheric pressure.

Temperature

• Definition: The degree of hotness or coldness of a body.
• Measurement: Measured using a thermometer, which works on the principle of change in volume with temperature.
• Common Thermometers: Mercury and alcohol thermometers.

Temperature Scales:

Heat

• Definition: A form of energy that gives the sensation of warmth or hotness.
• Effects of Heat:

1. Increase in temperature.
2. Change of state (melting or vaporizing).

Modes of Heat Transfer

1. Conduction: Transfer of heat from molecule to molecule.
2. Convection: Transfer of heat by upward currents caused by heat.
3. Radiation: Transfer of heat by waves.

Sensible and Latent Heat

• Sensible Heat: Causes a change in temperature.For solids, liquids, and vapors.
• Latent Heat: Causes a change of state without a change in temperature.

1. Latent Heat of Fusion: Heat needed to change 1 kg of solid to liquid.
2. Latent Heat of Vaporization: Heat needed to change 1 kg of liquid to vapor.
3. Latent Heat of Sublimation: Heat needed to change 1 kg of solid to gas.

Comparison of Heat and Work

• Heat: Random motion of molecules.

• Work: Ordered motion in one direction.

• Conversion: Work can be converted to heat, but not vice versa (Second Law of Thermodynamics).

Laws of Thermodynamics

Overview

• Thermodynamics deals with the relations between heat, work, and properties of systems.

• It is based on empirical laws formed by experimentation.

The Four Laws of Thermodynamics

1. Zeroth Law: If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
2. First Law: Energy cannot be created or destroyed, only transformed.

3.Second Law: Heat flows from high to low temperatures spontaneously.

4.Third Law: Absolute zero is a state of zero motion and cannot be reached.

Thermodynamic Processes

• Adiabatic: No heat transferred ($Q = 0$).
• Isothermal: Constant temperature.
• Isobaric: Constant pressure.
• Isochoric: Constant volume.

Process Equations

Applications

• Refrigeration and Heat Pumps: Based on the principle of reversed Carnot cycle.

• Heat Transfer: Heat can flow from low to high temperature only with external work supplied.

Carnot Cycle and Thermodynamic Principles

Carnot Cycle

• The Carnot cycle is a theoretical model for heat engines.
• It involves:

1. Absorbing heat from a high-temperature reservoir.
2. Releasing heat to a low-temperature reservoir.
3. Producing work in the process.

Reversed Carnot Cycle. 

• In the reversed Carnot cycle:

1. Work is supplied to the system.
2. Heat is transferred from a low-temperature reservoir to a high-temperature reservoir. 

• This process is explained by the second law of thermodynamics.

Applications

Refrigerators:

• Freezers maintain low temperatures by removing heat and releasing it to the atmosphere. 
• Requires electricity to run the compressor.

Air Conditioners:

• Cool rooms by removing heat from the indoor air.

Heat Pumps:

• Heat rooms by absorbing heat from the outside atmosphere.

Thermodynamic Cycles

A thermodynamic cycle consists of processes that transfer heat and work, changing pressure and temperature, and returning to the initial state.

Types of Thermodynamic Cycles

Reversible Cycle:

1. Processes can be reversed without loss of energy.
2. No heat loss due to friction or other factors.
3. Initial conditions are restored at the end of the cycle.

Irreversible Cycle:

1. Processes cannot be reversed completely.
2. Energy loss occurs due to friction, conduction, or radiation.
3. Initial conditions are not restored.

Key Concepts

Enthalpy (H)

• A measure of energy in a thermodynamic system.
• Defined as: H = U + PV  where U is internal energy, P is pressure, and V is volume.

Entropy (S)

• A measure of disorder in a system.
• Increases with added heat and decreases with heat removal.
• Important for understanding heat transfer in thermodynamics.

Principle of Refrigeration

• Lowers the temperature of a space below the surrounding atmosphere.
• Requires extracting heat to maintain the desired temperature.

Classification of Refrigeration Systems

Direct Expansion (DX) Systems

Centrifugal Chillers

Screw Chillers

Absorption Systems

Heat Pumps

Types of Refrigeration Systems

• Vapor Compression Refrigeration Systems
• Vapor Absorption Refrigeration Systems
• Gas Cycle Refrigeration Systems
• Steam Jet Refrigeration Systems
• Solar Energy-Based Refrigeration Systems
• Thermoelectric Refrigeration Systems

Vapor Compression Refrigeration System

• Also known as mechanical refrigeration.
• Involves a compressor to produce mechanical energy.
• Working of Vapor Compression Refrigeration System
• Refrigerant is stored at high pressure in the receiver.
• High-pressure liquid refrigerant is released to evaporator coils.
• Liquid refrigerant expands and absorbs heat, turning into vapor.
• Vapor enters the compressor, where it is compressed to high pressure and temperature.
• Hot vapor passes to the condenser, where it cools and condenses into liquid.
• Liquid refrigerant returns to the receiver, completing the cycle.

Parts of the Vapor Compression Refrigeration System

Receiver: Storage tank for refrigerant.

Flow Control Devices: Regulate refrigerant flow to the evaporator.

Evaporator: Where refrigerant absorbs heat and changes to vapor.

Suction Line: Connects evaporator to compressor.

Compressor: Pumps refrigerant through the system.

Discharge Line: Connects compressor to condenser.

Condenser: Cools and condenses refrigerant vapor.

Advantages and Disadvantages

Advantages:

1. Smaller size for given capacity.
2. Lower running costs.
3. High coefficient of performance.

Disadvantages:

1. High initial cost.
2. Leakage prevention is a major concern.
3. Vapor Absorption Refrigeration System
4. Uses heat energy instead of mechanical energy.

Components:

• Boiler/Generator: Similar to the compressor in vapor compression systems.
• Condenser and Evaporator: Serve the same purpose as in vapor compression systems.
• Absorber: Absorbs low-pressure refrigerant vapor.

Functioning

• Ammonia vapor is absorbed in the absorber by a weak solution.
• The strong solution is heated in the generator to expel ammonia gas.
• The cycle continues as the weak solution is pumped back to the absorber

This summary provides a concise overview of the Carnot cycle, thermodynamic principles, refrigeration systems, and their components.

Refrigeration Systems

Vapor Compression System

Main Components:

• Compressor
• Condenser
• Receiver
• Refrigerant control device
• Evaporator                       

Operation:

1. The system operates by compressing refrigerant gas, which increases its pressure and temperature.
2. Heat is removed from the refrigerant in the condenser, turning it back into a liquid.
3. The liquid refrigerant then passes through an expansion valve, reducing its pressure before entering the evaporator

Characteristics:

• Noisy in operation.
• Contains many moving parts, leading to potential wear and tear.
• Requires mechanical energy input, typically from electric motors, diesel, or petrol engines.
• Uses steel or copper tubes for connections.
• More efficient but occupies more space.
• Charging of refrigerant is quite simple.

Vapor Absorption System

Main Components:

• Generator
• Rectifier
• Condenser
• Absorber
• Evaporator

Operation:

• Heat is added to the generator from a heating source (e.g., gas burner or steam).
• A strong solution is created in the generator and then condensed into a liquid in the condenser.
• The liquid is passed to the receiver and then to the absorber after ammonia is expelled.

Characteristics:

• Quiet in operation.
• No moving parts, minimizing wear and tear or sticking.
• Energy input is mainly heat (from gas, kerosene, or electric heaters).
• Steel tubes are used for connections.
• Pressure is reduced using hydrogen gas.
• The flow of gas depends on gravity and the operation of the generator.
• Charging of refrigerant to the system is difficult.
• Generally less efficient compared to vapor compression systems.