A capillary copper tube is a very thin copper tube commonly used in refrigeration and air conditioning systems as a throttling (expansion) device. Its main functions are:
- Pressure Reduction
- It connects the condenser outlet (high pressure side) to the evaporator inlet (low pressure side).
- The small inner diameter and long length of the tube create resistance to refrigerant flow, which causes a drop in pressure.
- Metering of Refrigerant Flow
- The tube controls how much refrigerant enters the evaporator by restricting flow.
- The flow rate depends on the tube’s length, inner diameter, and refrigerant pressure difference.
- Maintaining System Balance
- It ensures the refrigerant entering the evaporator matches the system load.
- When load increases, more refrigerant flows due to higher pressure difference; when load decreases, the flow reduces.
- Simple, Reliable, Low-Cost Device
- Unlike expansion valves, it has no moving parts, so it’s reliable and cheap.
- Commonly used in small refrigeration systems (like refrigerators, window AC units, water coolers).
⚠️ Limitation:
- Not suitable for large or variable-load systems because it cannot adjust flow as precisely as a thermostatic expansion valve (TXV) or electronic expansion valve (EEV).