Lesson 7 - Refrigeration Theory and Cycle SAQ
This lesson allows you to test yourself on the material covered in the Refrigeration Cycle and Theory lesson and determine the level to which you have met the learning outcomes.
Suggested Response - Q1
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a) Describe what a refrigerant is.
b) Differentiate between primary, secondary, and tertiary refrigerants.
c) You have a household fridge in your kitchen that uses isobutane to cool the beer in your fridge. Describe the refrigerants that are used in the refrigeration system, and determine whether they are primary, secondary, or tertiary.
Response:
a) A refrigerant is a fluid that undergoes phase changes within a refrigeration cycle in order to transfer heat from the heating source to the heat sink or destination. A good refrigerant possesses ideal thermodynamic properties for the refrigeration process, such as a high heat of vaporisation and a high critical point.
b) A primary refrigerant is the fluid that goes through the phase change in the OVC cycle. It removes heat from the sink by evaporation, and releases heat to the source by condensation.
A secondary refrigerant is the fluid that receives the cooling from the primary refrigerant. They are usually aqueous solutions that have a low freezing point so that they can harness the cooling effect and pass it on to a process.
A tertiary refrigerant is the fluid that receives the cooling from the secondary refrigerant.
c) The primary refrigerant is the isobutane that absorbs heat from the air in the fridge. The secondary refrigerant is the air that passes the cooling action to the receiver and the beer, and also transfers heat from the beer to the primary refrigerant.