In a refrigeration system, what primarily causes the temperature of remaining refrigerant to lower during the metering process?

• A. The expansion of refrigerant to a vapor
• B. The increase in pressure
• C. The decrease in pressure
• D. The addition of heat

Answer: (C)

During the metering process in a refrigeration system, the temperature of the remaining refrigerant lowers primarily due to the decrease in pressure. When the refrigerant passes through the metering device (such as an expansion valve), it experiences a significant drop in pressure. This drop in pressure leads to a phenomenon known as Joule-Thomson effect, where the refrigerant expands rapidly and its temperature decreases. As the refrigerant expands, it absorbs energy in the form of heat from the surrounding components in the system, which further contributes to the cooling effect.

In this context, the decrease in pressure is critical to the thermodynamic process that allows the refrigerant to transition from a high-pressure liquid state to a low-pressure mixture of liquid and vapor, enhancing the cooling capability of the refrigeration system. The other options, such as the expansion of refrigerant to a vapor, describe a related effect but do not directly address the primary cause of temperature lowering, while an increase in pressure would typically lead to a rise in temperature rather than a decrease. Additionally, the addition of heat is not applicable during this process, as the focus is on a cooling and expansion scenario.