Refrigerants – Which has the highest critical pressure among the following? Select the refrigerant with the highest critical pressure from this list: R-11, R-12, R-22, and ammonia.

Introduction / Context:
Critical properties (critical temperature and pressure) are essential when comparing refrigerants for high-side operating limits, compressor discharge pressures, and component ratings. The question asks which listed refrigerant has the highest critical pressure.

Given Data / Assumptions:

• Standard refrigerant identifiers: R-11 (trichlorofluoromethane), R-12 (dichlorodifluoromethane), R-22 (chlorodifluoromethane), and ammonia (R-717).
• Typical published critical pressures under standard references.

Concept / Approach:
Ammonia (R-717) has a comparatively high critical pressure and moderate critical temperature, which drives higher allowable pressure ranges and compact heat exchangers but requires robust, rated components.

Step-by-Step Solution:
Recall approximate critical pressures: ammonia ≈ 11 MPa (110+ bar), R-22 ≈ 5 MPa, R-12 ≈ 4 MPa, R-11 ≈ 4–5 MPa.Compare the values across the options.Identify the maximum: ammonia.

Verification / Alternative check:
Check manufacturer or handbook tables; all corroborate ammonia’s critical pressure being significantly higher than common halocarbons listed.

Why Other Options Are Wrong:

• R-22, R-12, and R-11 have substantially lower critical pressures than ammonia.
• R-134a (extra distractor) also has lower critical pressure than ammonia.

Common Pitfalls:
Confusing critical temperature with critical pressure; assuming modern HFCs necessarily have higher critical pressure than natural refrigerants—this is not generally true.

Final Answer:
Ammonia