Refrigeration Principles and Coefficient of Performance

Questions and Answers

What is defined as the refrigerating effect produced by melting 1 ton of ice at 0°C in 24 hours?

Refrigerant efficiency

Coefficient of performance

Ton of refrigeration (correct)

Heat transfer rate

Which of the following is the formula for Coefficient of Performance (COP)?

COP = Work of compressor / Refrigerating effect

COP = Refrigerating effect + Work of compressor

COP = Refrigerating effect / Work of compressor (correct)

COP = Work of compressor + Heat loss

Which component in the Vapour Compression Refrigeration System (VCRS) is responsible for evaporating the refrigerant?

Evaporator (correct)

Expansion device

Compressor

Condenser

What is the typical cooling medium used in the condensation process of VCRS?

Air or water Signup and view all the answers

During which process does the refrigerant absorb latent heat from the space to be cooled?

Evaporation Signup and view all the answers

At which point does low pressure and low temperature vapor enter the compressor?

Point 1 Signup and view all the answers

What is the result of the refrigeration process in terms of energy efficiency represented by COP?

Greater than unity Signup and view all the answers

Which process occurs when the high pressure, high temperature vapor condenses in the condenser?

It rejects heat Signup and view all the answers

What is the condition of refrigerant at the exit to the condenser?

Low temperature saturated liquid Signup and view all the answers

What occurs during process (3-4) in the refrigeration cycle?

Pressure of saturated liquid decreases Signup and view all the answers

Which components make up the Vapour Absorption Refrigeration System (VARS)?

Evaporator, condenser, generator, absorber, pump, and expansion device Signup and view all the answers

What replaces the compressor in the Vapour Absorption Refrigeration System?

Absorber Signup and view all the answers

What characteristic does ammonia have when it comes to absorption in water?

Easily absorbed at low pressure and temperature Signup and view all the answers

What happens to ammonia vapour in the generator of the VARS?

It is separated from water Signup and view all the answers

After passing through the expansion device, what is the state of the refrigerant?

Low temperature and low-pressure liquid Signup and view all the answers

During the evaporator process, what does the liquid refrigerant absorb?

Latent heat of evaporation Signup and view all the answers

What is the primary function of a spring loaded safety valve?

To protect the boiler from high pressure Signup and view all the answers

How does a fusible plug protect the boiler?

By preventing overheating due to low water levels Signup and view all the answers

What is the purpose of a blow off cock in a boiler?

To remove accumulated mud and sediments Signup and view all the answers

What role does the feed check valve play in a boiler system?

It allows water flow only when pressure is adequate Signup and view all the answers

Where is the steam stop valve located in relation to the boiler?

Above the boiler, between steam space and steam supply line Signup and view all the answers

Which of the following is NOT considered a boiler accessory?

Blow off cock Signup and view all the answers

What is a key function of the economizer in a boiler system?

To utilize waste heat to preheat the feed water Signup and view all the answers

What is the main purpose of the air preheater in a boiler?

To heat the air before it enters the combustion chamber Signup and view all the answers

What is the main function of a feed pump?

To feed water to the boiler at a high pressure Signup and view all the answers

How does an economizer improve boiler efficiency?

By harnessing heat from outgoing flue gases Signup and view all the answers

What is the primary role of an air preheater?

To preheat the air used in the furnace Signup and view all the answers

What is refrigeration primarily used for?

To remove heat and lower temperature Signup and view all the answers

What property is essential for a good refrigerant's thermal conductivity?

Good thermal conductivity for rapid heat transfer Signup and view all the answers

Which characteristic is NOT desirable in a good refrigerant?

High saturation pressure Signup and view all the answers

According to the second law of thermodynamics, what is required to move heat from a cold body to a hot body?

External work Signup and view all the answers

What is the function of a refrigerant?

To absorb heat from the desired space and reject it outdoors Signup and view all the answers

What characterizes a strong solution of NH3 in water?

Amount of NH3 is more than the water Signup and view all the answers

What process occurs in the generator of a Vapour Absorption Refrigeration System?

NH3 vapour is separated and heated Signup and view all the answers

Which component is responsible for the circulation of air in an air conditioning system?

Fans Signup and view all the answers

What is the main purpose of the evaporator in the Vapour Absorption Refrigeration System?

To absorb latent heat and produce cooling Signup and view all the answers

What is considered a standard comfort condition for relative humidity (RH) in air conditioning?

30 to 70 % Signup and view all the answers

What type of air conditioning focuses on human comfort?

Comfort air conditioning Signup and view all the answers

Which of the following components collects condensed water in an air conditioning system?

Tray Signup and view all the answers

How is liquid NH3 processed before entering the evaporator?

It is throttled through an expansion device Signup and view all the answers

Study Notes

Refrigeration Concepts

Ton of Refrigeration: Refers to the cooling effect equivalent to melting 1 ton of ice at 0°C in 24 hours.
1 ton of refrigeration translates to a capacity of 3.5 kW.
Coefficient of Performance (COP): The ratio of the refrigerating effect to the work input for compression, indicating system efficiency. The COP is always greater than unity.

Vapour Compression Refrigeration System (VCRS)

Components: Comprises an evaporator, compressor, condenser, and expansion device.
Works by circulating a refrigerant that alternates between gas and liquid phases, absorbing heat during evaporation and releasing heat during condensation.
Processes:
- Process 1-2: Low pressure, low temperature vapor enters the compressor and is compressed to high temperature and pressure.
- Process 2-3: The high pressure vapor condenses in the condenser by rejecting heat to a cooling medium like air or water.
- Process 3-4: The liquid refrigerant undergoes throttling through the expansion device, dropping in pressure and temperature.
- Process 4-1: The low-pressure liquid absorbs heat in the evaporator, turning into vapor and returning to the compressor.

Vapour Absorption Refrigeration System (VARS)

Components: Includes an evaporator, condenser, generator, absorber, pump, and expansion device.
Utilizes ammonia as refrigerant, absorbed by water as the absorbent.
Working Principle:
- Low-pressure vapor from the evaporator enters the absorber where it is absorbed by a weak ammonia-water solution.
- The mixture is heated in the generator, separating ammonia vapor from water.
- The ammonia vapor then condenses in the condenser and passes back as a liquid to the evaporator.

Boiler Safety Components

Spring Loaded Safety Valve: Essential for preventing boiler explosion by relieving pressure.
Fusible Plug: Protects against overheating due to low water levels in boiler tubes.
Blow Off Cock: A valve used to remove sediments from the boiler and for complete emptying during maintenance.
Feed Check Valve: Allows water flow into the boiler at higher pressure and prevents backflow.
Steam Stop Valve: Regulates steam supply from the boiler to the supply line.

Boiler Accessories

Non-mounted components essential for boiler operation and efficiency:
- Feed Pump: Supplies water to the boiler at high pressure.
- Economizer: Captures heat from flue gases to preheat feed water, improving thermal efficiency.
- Air Preheater: Uses flue gas heat to preheat combustion air.

Refrigeration Overview

Refrigeration is the process of lowering system temperature by continuously removing heat.
External work is necessary to move heat against the natural flow (cold to hot).
Refrigerant Properties:
- High latent heat of evaporation, low specific volume, and excellent thermal conductivity.
- Non-toxic and non-corrosive with low specific heat in liquid state.
- Chemical interactions occur, e.g., ammonia absorbed by water will change solubility based on pressure/temperature.

Air Conditioning Fundamentals

Primary functions include air cooling/heating, moisture control, purification, and distribution.
Applications:
- Comfort air conditioning for human comfort with optimal temperature (17° to 25°C) and relative humidity (30% to 70%).
- Industrial air conditioning for manufacturing processes requires specific environmental conditions.
Components:
- Fans for airflow, filters for cleanliness, heating elements for warmth, and control systems for temperature regulation.
- Refrigerating plant consisting of compressor, generator, absorber, evaporator, condenser, and expansion device.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the concepts of ton of refrigeration and coefficient of performance. Participants will learn about the definitions, calculations, and significance of these terms in thermodynamics and refrigeration processes. Test your understanding of how refrigeration systems operate and their efficiency metrics.