In a domestic refrigerator, a capillary tube controls the flow of refrigerant from the

Solution (By Examveda Team)

Correct Answer: Option D — Condenser to the evaporator

Key Idea: In domestic refrigerators, the capillary tube itself is the expansion device. It directly connects the condenser outlet (high-pressure liquid) to the evaporator inlet (low-pressure region) and creates the required pressure drop to enable refrigeration.

Cycle Overview (Flow Path): Compressor → Condenser → Capillary Tube → Evaporator → back to Compressor

What Happens Physically:

After compression, the refrigerant is a hot, high-pressure gas.

In the condenser, it rejects heat to surroundings and becomes a high-pressure liquid.

This liquid enters the capillary tube (a long, narrow tube). Due to its small internal diameter and length, it imposes a flow resistance, causing a substantial pressure drop from condenser pressure to evaporator pressure.

Because of the pressure drop, a portion of the liquid flashes (evaporates) and its temperature falls close to the saturation temperature corresponding to the low evaporator pressure.

The low-pressure mixture then enters the evaporator, where it absorbs heat from the refrigerator compartment and fully evaporates, producing the desired cooling.

Why Capillary Tube Is Used in Domestic Refrigerators:

• It is simple, inexpensive, and reliable (no moving parts).

• It provides automatic flow regulation to some extent: when load decreases, evaporator pressure drops, mass flow reduces through the restriction, helping maintain stable operation.

• It suits the small, steady loads typical of household refrigerators and works well with on–off (cycling) control of the compressor by a thermostat.

Why the Other Options Are Incorrect:

• Option A (Expansion valve to the evaporator): An expansion valve is a different device. Most domestic units do not use a thermostatic expansion valve; they use a capillary tube. Hence, this connection description does not apply to capillary-tube systems.

• Option B (Evaporator to the thermostat): The thermostat is a control/sensing device, not part of the refrigerant piping. Refrigerant does not flow to the thermostat; it merely senses temperature and switches the compressor.

• Option C (Condenser to the expansion valve): Again assumes the presence of a separate expansion valve. In a domestic refrigerator, the capillary tube itself performs the expansion, so the correct connection is directly to the evaporator.

Conclusion: The capillary tube controls the flow of refrigerant from the condenser to the evaporator by creating the necessary pressure drop, making Option D the correct choice.