Methods of achieving undercooling (subcooling) Which practical method can be used to obtain liquid undercooling in a vapour-compression system?

Introduction / Context:
Subcooling the liquid leaving the condenser reduces flash gas after expansion, boosting the net refrigerating effect and often improving COP. There are several practical ways to achieve subcooling.

Given Data / Assumptions:

• Liquid at condenser outlet is at or near saturation temperature.
• Goal: reduce its temperature below saturation at the condensing pressure.

Concept / Approach:
Undercooling can be achieved by enhancing heat rejection at the condenser (more or colder cooling water) or by internal heat exchange where cold suction vapour cools the liquid line. All these methods remove sensible heat from high-pressure liquid to move it into the subcooled region on the p–h chart.

Step-by-Step Solution:
Option (a): more cooling water → greater heat transfer → lower liquid-line temperature.Option (b): colder cooling water → increased temperature difference → more subcooling.Option (c): liquid–suction heat exchanger → sensible heat transfer from liquid to suction vapour, providing subcooling while superheating suction slightly.Hence, any of the above methods can achieve undercooling.

Verification / Alternative check:
System logs show lower liquid-line temperature than saturation temperature at condensing pressure when subcooling is present.

Why Other Options Are Wrong:
Each of (a)–(c) is valid; rejecting them individually would be incorrect. Two-stage throttling does not inherently subcool the high-pressure liquid; it primarily reduces pressure in stages.

Common Pitfalls:
Over-subcooling can raise compressor discharge superheat via liquid–suction exchange and may reduce evaporator capacity if not balanced.

Final Answer:
Any one of the above