When topping off a refrigeration system containing a blended refrigerant, how should the refrigerant be introduced?

Introducing the refrigerant as a liquid into the low side using a throttling valve is the correct approach when topping off a refrigeration system that uses a blended refrigerant. This method ensures that both components of the blended refrigerant are introduced into the system in the correct proportions to maintain the designed performance and efficiency of the refrigeration cycle.

When blended refrigerants are used, they are often composed of different substances with varying boiling points. If the refrigerant is added as a gas, particularly in a high-pressure area like the high side of the system, there is a risk of fractionation; this occurs when one component of the refrigerant mixture boils off and separates from the others. As a result, the balance of the blend can be altered, leading to reduced efficiency and potential system issues.

Using a throttling valve when introducing the refrigerant in liquid form into the low side allows the refrigerant to vaporize appropriately as it moves through the system. This method not only maintains the mixture's integrity but also optimizes the system's performance criteria, ensuring that it operates as designed without risking unwanted refrigerant behavior.