Question:
The following operation is NOT advisable for Vapour Compression Refrigeration using Ammonia as refrigerant
The following operation is NOT advisable for Vapour Compression Refrigeration using Ammonia as refrigerant
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Ammonia (R-717) Refrigeration Rules: Suction line HEAT EXCHANGE BETWEEN VAPOR AND LIQUID IS NOT ADVISABLE because ammonia's high adiabatic index ($k=1.31$) causes dangerous overheating at discharge.
Updated On: Sep 15, 2026
- Flash vapour bypass
- Sub-cooling of liquid refrigerant
- Super heating of liquid refrigerant
- Heat exchange between vapours and liquid refrigerant
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Thermodynamic properties of ammonia (R-717) in industrial refrigeration: Ammonia possesses a very high isentropic exponent adiabatic index ($k = C_p/C_v = 1.31$); implementing a liquid-suction heat exchanger (superheating suction vapor before compression) causes dangerously high compressor discharge temperatures exceeding $150^\circ ext{C}$, breaking down compressor lubricating oils.
Key Formula or Approach:
\[ T_{\text{discharge}} = T_{\text{suction}} \left( \frac{P_{\text{cond}}}{P_{\text{evap}}} \right)^{\frac{k - 1}{k}} \quad \xrightarrow{k = 1.31, \; T_{\text{suction}} \uparrow} \quad \mathbf{T_{\text{discharge}} > 150^\circ\text{C (Oil Carbonization Danger)}} \]
Step 2: Detailed Explanation:
In industrial dairy refrigeration engineering using Ammonia (R-717 $\text{NH}_3$):
1. Liquid-Suction Heat Exchangers (Heat exchange between vapours and liquid refrigerant) (D):
- In halocarbon Freon systems (R-134a, R-22), suction line heat exchangers are used to subcool liquid while superheating suction vapor.
- In Ammonia systems, this is strictly NOT advisable:
- Ammonia has a very high specific heat ratio ($k = 1.31$). Superheating the suction vapor entering the compressor drastically drives up the compressor discharge temperature ($T_{\text{discharge}} > 140^\circ - 160^\circ ext{C}$).
- High discharge temperatures cause rapid thermal breakdown, carbonization of compressor lubricating oils, valve plate warping, and cylinder head cracking.
2. (Sub-cooling via external cooling water and flash vapor economizers are standard practices).
Step 3: Final Answer:
Hence, Heat exchange between vapours and liquid refrigerant is NOT advisable for Ammonia systems, matching option (D).
Thermodynamic properties of ammonia (R-717) in industrial refrigeration: Ammonia possesses a very high isentropic exponent adiabatic index ($k = C_p/C_v = 1.31$); implementing a liquid-suction heat exchanger (superheating suction vapor before compression) causes dangerously high compressor discharge temperatures exceeding $150^\circ ext{C}$, breaking down compressor lubricating oils.
Key Formula or Approach:
\[ T_{\text{discharge}} = T_{\text{suction}} \left( \frac{P_{\text{cond}}}{P_{\text{evap}}} \right)^{\frac{k - 1}{k}} \quad \xrightarrow{k = 1.31, \; T_{\text{suction}} \uparrow} \quad \mathbf{T_{\text{discharge}} > 150^\circ\text{C (Oil Carbonization Danger)}} \]
Step 2: Detailed Explanation:
In industrial dairy refrigeration engineering using Ammonia (R-717 $\text{NH}_3$):
1. Liquid-Suction Heat Exchangers (Heat exchange between vapours and liquid refrigerant) (D):
- In halocarbon Freon systems (R-134a, R-22), suction line heat exchangers are used to subcool liquid while superheating suction vapor.
- In Ammonia systems, this is strictly NOT advisable:
- Ammonia has a very high specific heat ratio ($k = 1.31$). Superheating the suction vapor entering the compressor drastically drives up the compressor discharge temperature ($T_{\text{discharge}} > 140^\circ - 160^\circ ext{C}$).
- High discharge temperatures cause rapid thermal breakdown, carbonization of compressor lubricating oils, valve plate warping, and cylinder head cracking.
2. (Sub-cooling via external cooling water and flash vapor economizers are standard practices).
Step 3: Final Answer:
Hence, Heat exchange between vapours and liquid refrigerant is NOT advisable for Ammonia systems, matching option (D).
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