Class: Senior Secondary School 1 (SS1 / SSS1)
Term: 3rd Term
Week: 4
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Compressor: Types of Compressor.
Topic: Compressors Construction of compressors
Subject Matter: Reciprocating compressor construction, centrifugal compressor construction, component identification

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Describe the construction of a reciprocating compressor.
Describe the construction of a centrifugal compressor.
Identify the main components of both types of compressors.

Affective Domain:

Appreciate the importance of correct compressor construction in refrigeration.
Show interest in the working principles of different compressors.

Psychomotor Domain:

Draw a simple labeled diagram of a reciprocating or centrifugal compressor.
Correctly identify physical components of compressors.

Participate actively in class discussions and practical identification tasks.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary School.
State Unified Scheme of Work for Refrigeration and Air Conditioning (SSS 1).
Dossat, R. J. (2009). Principles of Refrigeration. Pearson Prentice Hall.
Althouse, A. D., Turnquist, C. H., Bracciano, A. F., & Wigginton, D. A. (2012). Modern Refrigeration and Air Conditioning. Goodheart-Willcox Co.

Instructional Materials

The teacher will teach this lesson with the aid of:

Actual compressor parts (e.g., piston, cylinder head, impeller).
Labeled diagrams of reciprocating and centrifugal compressors.
Spanner set (for demonstration of component assembly/disassembly).
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils understand how different types of compressors are built, which is important for diagnosing faults and performing maintenance in refrigeration and air conditioning systems. Knowing the construction also enables pupils to properly identify components in real-world applications.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of the refrigeration cycle and the general function of a compressor in a refrigeration system.

Lesson Content/Board Summary

Compressor Construction

Reciprocating Compressor Construction

A reciprocating compressor is a positive displacement compressor that uses pistons driven by a crankshaft to compress refrigerant vapour. It works by reducing the volume of a fixed amount of gas.

The following are the key components of a reciprocating compressor:

Cylinder: The chamber where the piston moves.
Piston: A cylindrical component that moves up and down within the cylinder to compress the gas.
Connecting Rod: Links the piston to the crankshaft.
Crankshaft: Converts the rotary motion of the motor into the reciprocating motion of the piston.
Suction Valve: Allows low-pressure refrigerant vapour to enter the cylinder.
Discharge Valve: Allows high-pressure compressed refrigerant vapour to exit the cylinder.
Motor: Provides the power to drive the crankshaft.
Crankcase: Encloses the crankshaft and connecting rods, often containing lubricating oil.

Centrifugal Compressor Construction

A centrifugal compressor is a dynamic compressor that uses a rotating impeller to accelerate refrigerant vapour and convert its velocity energy into pressure energy. It operates on the principle of kinetic energy conversion.

The following are the key components of a centrifugal compressor:

Impeller: A rotating disc with blades that centrifugally accelerates the refrigerant vapour.
Diffuser: A stationary component that converts the high-velocity, low-pressure gas from the impeller into low-velocity, high-pressure gas.
Volute Casing: A spiral-shaped casing that collects the high-pressure gas from the diffuser and directs it to the discharge outlet.
Shaft: The rotating component that holds the impeller and is connected to the motor.
Bearings: Support the rotating shaft and impeller.
Motor: Provides the power to rotate the shaft and impeller.

Component Identification

Pupils should be able to identify the individual parts of both reciprocating and centrifugal compressors, understanding their specific roles in the compression process. This includes distinguishing between parts unique to each type (e.g., piston vs. impeller, valves vs. diffuser).

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and reviews the previous lesson on types of compressors. The teacher then introduces the topic of compressor construction by asking pupils what they think is inside a compressor.
Pupils’ Activity: Pupils respond to the teacher’s questions and share their ideas about the internal components of a compressor.
Learning Point: Pupils recall previous knowledge and are prepared for the new topic.

Step 2: Reciprocating Compressor Construction

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the construction of a reciprocating compressor, using labeled diagrams and, if available, actual parts. The teacher describes the function of each major component (piston, cylinder, valves, crankshaft).
Pupils’ Activity: Pupils listen attentively, observe the diagrams and parts, and ask questions for clarification. They may take notes.
Learning Point: Pupils understand the basic construction and function of a reciprocating compressor.

Step 3: Identification of Reciprocating Compressor Components

Time: 5 minutes
Teaching Skill: Identification/Practical
Teacher’s Activity: The teacher points to specific parts on a diagram or actual reciprocating compressor components and asks pupils to identify them and state their function. The teacher corrects any misconceptions.
Pupils’ Activity: Pupils identify the components orally, practicing their knowledge of the parts.
Learning Point: Pupils can correctly identify the components of a reciprocating compressor.

Step 4: Centrifugal Compressor Construction

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the construction of a centrifugal compressor, highlighting the differences from a reciprocating compressor. Labeled diagrams and actual parts (if available, e.g., an impeller) are used to illustrate components like the impeller, diffuser, and volute casing.
Pupils’ Activity: Pupils observe the diagrams and parts, listen to the explanation, and note down key differences in construction.
Learning Point: Pupils understand the basic construction and function of a centrifugal compressor.

Step 5: Identification of Centrifugal Compressor Components

Time: 5 minutes
Teaching Skill: Identification/Practical
Teacher’s Activity: The teacher points to specific parts on a diagram or actual centrifugal compressor components and asks pupils to identify them and state their function. The teacher emphasizes how these parts contribute to the compression process.
Pupils’ Activity: Pupils identify the components orally, reinforcing their understanding of centrifugal compressor parts.
Learning Point: Pupils can correctly identify the components of a centrifugal compressor.

Step 6: Practical Demonstration/Drawing

Time: 5 minutes
Teaching Skill: Demonstration/Drawing
Teacher’s Activity: The teacher quickly draws a simple, labeled diagram of one of the compressor types on the board, emphasizing key components. The teacher can also briefly demonstrate how a spanner set might be used for assembly/disassembly of parts (without actual disassembly if time is short).
Pupils’ Activity: Pupils observe the drawing and demonstration. Some may attempt to draw their own simple diagrams in their notebooks.
Learning Point: Pupils visualize the internal structure and understand the practical aspect of component handling.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define a reciprocating compressor.
List three main components of a reciprocating compressor.
Describe the primary function of an impeller in a centrifugal compressor.
Mention two key differences in construction between a reciprocating and a centrifugal compressor.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the main points of the lesson, reiterating the construction and key components of both reciprocating and centrifugal compressors. The teacher assigns homework for pupils to draw and label a diagram of both types of compressors.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for independent practice.

Lesson Keywords

Reciprocating Compressor – A compressor that uses a piston to compress gas.
Centrifugal Compressor – A compressor that uses a rotating impeller to accelerate and compress gas.
Piston – A moving component in a reciprocating compressor that compresses gas.
Impeller – A rotating component in a centrifugal compressor that accelerates gas.
Crankshaft – Converts rotary motion to reciprocating motion in a reciprocating compressor.
Volute Casing – A spiral casing in a centrifugal compressor that collects and directs compressed gas.
Diffuser – Converts high-velocity gas to high-pressure gas in a centrifugal compressor.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to explain the working principles of each compressor type in detail or research specific applications where each type is preferred. For pupils needing more support, the teacher can provide simpler, pre-labeled diagrams and give additional one-on-one guidance during component identification.

Note for teachers using this lesson plan

It is highly recommended to have actual compressor components or detailed 3D models available for this lesson to enhance practical understanding. If actual parts are not available, clear, large, labeled diagrams are essential. Encourage pupils to draw and label as part of their learning process. Ensure safety precautions are observed if handling real compressor parts.