The capillary is an expansion device and, as such, has two
purposes: reduce the pressure of the liquid refrigerant and regulate the quantity (flow) of the liquid / gas mixture that will enter the evaporator, based on the principle that a liquid refrigerant mass will pass more easily through a capillary than the
same mass of refrigerant in the gaseous state.
Consequently, if the vapor from the non-condensing refrigerant enters the capillary, the mass flow will be reduced, allowing the refrigerant more cooling time in the condenser.
On the other hand, if liquid refrigerant tends to accumulate in the condenser, the pressure and temperature will increase, resulting in an increase in the mass flow of refrigerant.
The pressure reduction is due to the friction of the gas inside the capillary. The desired pressure difference can be obtained by combining the values of the internal diameter and length of the capillary, in addition to the pressure, the flow rate will also be changed. Note that the greater the friction, the greater the difference in condensation and evaporation pressures.
An increase in friction can be obtained by increasing the length and / or decreasing the capillary internal diameter. Excessive capillary restriction will cause reductions in refrigerant flow to the evaporator and compressor performance.
