Concept Notes
Refrigerant is a working fluid used in Refrigeration & Air Conditioning (RAC) systems. It undergoes phase changes (liquid ↔ vapor) to absorb heat at a low temperature region (evaporator) and reject it at a higher temperature region (condenser).
🔹 Ideal Properties of a Refrigerant
A good refrigerant should have:
- Thermodynamic Properties
- Low boiling point → to absorb heat at low temp.
- High latent heat of vaporization → more cooling per kg.
- Moderate critical temperature & pressure.
- Low specific volume → smaller compressor size.
- Chemical Properties
- Non-corrosive to system parts.
- Non-flammable, non-explosive.
- Chemically stable.
- Environmental Properties
- Low Ozone Depletion Potential (ODP).
- Low Global Warming Potential (GWP).
- Non-toxic & eco-friendly.
🔹 Common Refrigerants & Codes
- R-12 (CCl₂F₂) → Chlorofluorocarbon (CFC), older domestic refrigerators, banned (high ODP).
- R-22 (CHClF₂) → Hydrochlorofluorocarbon (HCFC), air-conditioners, being phased out.
- R-134a (C₂H₂F₄) → Hydrofluorocarbon (HFC), eco-friendlier replacement for R-12.
- Ammonia (R-717) → Excellent refrigerant, high latent heat, used in large industrial plants (but toxic).
- Carbon dioxide (R-744) → Non-toxic, non-flammable, eco-friendly, used in transport refrigeration.
- Water (R-718) → Used in absorption systems.
- R-290 (Propane) → Hydrocarbon refrigerant, eco-friendly, but flammable.
🔹 Desirable vs. Undesirable Properties
✅ Desirable:
- High latent heat, low viscosity, high thermal conductivity.
- Environment friendly.
- Easily detectable in case of leakage.
❌ Undesirable:
- High toxicity (Ammonia).
- High flammability (Hydrocarbons).
- High ODP/GWP (R-12, R-22).
⚙️ Formulas
- Refrigerating Effect (per kg):
(where h1h_1h1 = enthalpy at evaporator outlet, h4h_4h4 = enthalpy at evaporator inlet) - Coefficient of Performance (COP):
Ton of Refrigeration (TR):
🔟 10 MCQs
Q1. Which of the following refrigerants is toxic but widely used in industry?
a) R-12
b) R-22
c) R-717
d) R-134a
Q2. The refrigerant with the highest ozone depletion potential (ODP) is:
a) R-12
b) R-134a
c) R-717
d) R-290
Q3. Which property is most desirable for a refrigerant?
a) High specific volume
b) High latent heat of vaporization
c) High ODP
d) High viscosity
Q4. COP of a refrigerator is given by:
a) QHQL\frac{Q_H}{Q_L}QLQH
b) QLWcomp\frac{Q_L}{W_{comp}}WcompQL
c) WcompQL\frac{W_{comp}}{Q_L}QLWcomp
d) QHWcomp\frac{Q_H}{W_{comp}}WcompQH
Q5. R-134a belongs to which group?
a) CFC
b) HCFC
c) HFC
d) Hydrocarbon
Q6. Which refrigerant is most eco-friendly?
a) R-12
b) R-22
c) R-290
d) R-717
Q7. 1 Ton of Refrigeration is equal to:
a) 1.5 kW
b) 3.517 kW
c) 5.2 kW
d) 2.1 kW
Q8. Which refrigerant is flammable?
a) R-717
b) R-134a
c) R-290
d) R-22
Q9. Which refrigerant is most commonly used in domestic refrigerators now (eco-friendly)?
a) R-22
b) R-12
c) R-134a
d) R-744
Q10. The COP of a refrigerator is always:
a) Less than 1
b) Greater than 1
c) Equal to 1
d) Infinity
✅ Answer Key
| Q | Ans |
|---|---|
| 1 | c |
| 2 | a |
| 3 | b |
| 4 | b |
| 5 | c |
| 6 | c |
| 7 | b |
| 8 | c |
| 9 | c |
| 10 | b |
🧠 Explanations
- Q1: Ammonia (R-717) → toxic but efficient → (c).
- Q2: R-12 has very high ODP → (a).
- Q3: Good refrigerant must have high latent heat → (b).
- Q4: COP = Refrigerating Effect / Work → (b).
- Q5: R-134a = Hydrofluorocarbon (HFC) → (c).
- Q6: R-290 (Propane) has low ODP, eco-friendly → (c).
- Q7: 1 TR = 3.517 kW → (b).
- Q8: R-290 (Propane) → flammable → (c).
- Q9: R-134a → widely used in fridges → (c).
- Q10: Refrigerator COP > 1 always → (b).
🎯 Motivation / Why Practice Matters
Refrigerants are a favorite topic in ECET RAC questions. One question almost always comes on R-12, R-22, R-134a, or COP/ton of refrigeration.
If you practice MCQs daily, you’ll easily grab 2–4 marks directly in the exam.
Remember → small topics, big impact on rank. 🚀
📲 CTA
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