🔍 Key Concepts

• Flash gas formation in a liquid refrigerant line • How expansion valves are designed to work with subcooled liquid refrigerant • Effect of vapor bubbles on flow, pressure, and erosion in valves

💭 Think About

• Think about what should normally be entering the expansion valve in a properly designed system: is it all liquid, all vapor, or a mix? • If vapor bubbles are present in the liquid line, how does that affect the actual mass of liquid reaching the valve and the way the valve meters flow? • Would the presence of flash gas tend to increase or decrease the effective pressure drop and flow of liquid through the valve?

✅ Before You Answer

• Confirm what flash gas is: liquid refrigerant that has boiled off into vapor before the expansion valve • Consider whether vapor in the liquid line would cause erosion of metal parts, or is erosion more associated with high velocity liquid/solid impacts and cavitation? • Carefully compare each choice against what happens to pressure at the valve inlet, actual liquid flow, and valve metering capacity when some of the liquid has already turned to vapor.