In heat exchanger terminology, what term describes a configuration where the working fluid remains entirely in a single phase?

• A. Single Phase
• B. Two-Phase
• C. Condensing
• D. Evaporating

Answer: (A)

Single-phase operation means the working fluid stays in one phase (either all liquid or all gas) as it passes through the exchanger, so only sensible heat transfer occurs and no phase change happens. This is different from condensing (vapor turning to liquid) or evaporating (liquid turning to vapor), both of which involve latent heat and a mixture of phases. When the fluid remains single phase, it never crosses the boiling point inside the exchanger, simplifying the heat transfer and pressure-drop behavior. So the term that describes this configuration is single phase.