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.
