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Unit 204Scientific Principles
Simple mechanical principles and their application in the mechanical
services industry
www.cardiffandvalecollege.ac.uk
Luke Gonzales TMInstR EngTech LCIBSE
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Class Rules / Rheolau Dosbarth
Mobile Phones on silent – In Pockets
Appropriate Language
Questions throughout
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Lesson Objectives / Amcanion Gwersi
Knowledge of Latent & Sensible Heat
Apply theoretical knowledge to vapour
compression cycle
List RAC system components within
the vapour compression cycle
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Recap – 18/04/2016
1. What is Superheat?Superheat is the term given to a vapour above the boiling point ( saturation temperature) of a substance.As the substance is above its boiling point, the term superheat can only be applied to Vapour only.
2. What is Sub-Cooled Liquid? Sub-cooling is a term given to a liquid that is below its boiling point.As the liquid is below its boiling point and above freezing point, the substance must be in its Liquid state only.
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Latent Heat - Gwres CuddLatent heat causes a change in phase but not in temperature.Example:The temperature remains constant but the substance changes its nature from solid to liquid or liquid to vapour – Boiling , melting or freezing points of a substance.
Where would you find latent heat take place on a RAC System?
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Condenser & Evaporator
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Sensible Heat - Gwres Synhwyrol
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Sensible Heat causes a change in temperature but not in phase (state).
Example:When a substance gains heat its temperature rises but does not change from a solid to liquid or from a liquid to a vapour.
Where would you find sensible Heat on a RAC system?
Compressor Suction – Compressor Discharge – Condenser Sub cooling
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Phase Diagram for 1Kg of Water
www.cardiffandvalecollege.ac.uk
100
50
0
-10
Latent Heat
Sensible Heat
Heat kJ/kg KTemp °C
Ice + Water
2.1 335 4.2 2260
Solid Liquid Water + Steam
Latent Heat
Sensible Heat
Superheated Water Vapour
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RAC Vapour Compression Cywasgu Anwedd RAC
www.cardiffandvalecollege.ac.uk
High Pressure (warm) Superheated Vapour
Condenser Rejecting
Latent Heat
High Pressure (warm) Sub-cooled Liquid
Low Pressure (cold) Superheated Vapour
Evaporator Absorbing
Latent Heat
Low Pressure (cold) Liquid / Vapour Mixture. Saturated 2 Phase Mix
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System Components Cydrannau System
www.cardiffandvalecollege.ac.uk
Compressor
Condenser
Evaporator
Expansion Device
Drier
Sight glass
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System Components - 2 Cydrannau System - 2
High & Low Pressure Switch
Suction Line Accumulator • Liquid Line Receiver
Liquid Line Solenoid Valve
Oil Separator
Vibration Eliminator• Could be used on
discharge or suction
Suction Drier
www.cardiffandvalecollege.ac.ukWorkshop & Identify the Components
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Task 1 - Tasg 1
In pairs using the laminated resources, label up the RAC Vapour Compression System.
*You have a total of 15 minutes for this task*Ask if you require any assistance
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Feedback
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Compressor Discharge
High pressure – superheated
vapour
Condenser High pressure super
heated vapour to High pressure liquid
After Condenser High pressure sub-
cooled liquid
TXV to Evaporator Low pressure
saturated 2 phase mixture
Evaporator to Compressor
Low pressure superheated
vapourHigh
PressureLow
Pressure
Sensible Heat Gain / Loss
Latent Heat Rejection
Sensible Heat Loss
Latent Heat Absorbed
Sensible Heat Gain / Loss
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Recap of Objectives
Have we achieved the following objectives?• Knowledge of Sensible &
Latent Heat• List RAC System Components• Apply theoretical knowledge
to RAC vapour compression cycle.
Any questions?
www.cardiffandvalecollege.ac.uk
Cwestiynau?