Final answer:
The term describing a refrigerant blend's range of boiling or condensing points at constant pressure is '4. temperature glide.' It occurs because each component of the refrigerant mixture has different boiling points, affecting phase change temperature.
Step-by-step explanation:
The term used to describe the fact that a refrigerant blend has a range of boiling or condensing points at a constant pressure is temperature glide. Refrigerants that consist of a mixture of substances with different boiling points exhibit a temperature glide when they change phase from a liquid to a gas or vice versa. This occurs because each component of the mixture has its individual boiling point. During the phase change process at constant pressure, the overall temperature of the mixture will vary due to the different components transitioning at their specific temperatures, unlike a pure substance that changes phase at a singular, defined temperature.
Understanding temperature glide is crucial when designing and operating refrigeration systems as it can affect the performance and efficiency of the system. For instance, a refrigerant blend with a high temperature glide may not be ideal for certain applications where tight temperature control is necessary. Conversely, some systems can be designed to take advantage of the glide to improve heat transfer efficiency.
Furthermore, the boiling point of a pure liquid is the temperature at which it changes phase to become a gas, also known as evaporation, and is affected by the surrounding pressure. The boiling point is typically defined for standard atmospheric pressure (1 atm). Refrigerants, especially blends, will exhibit different boiling points under different pressures, and this dynamic behavior is important when considering thermodynamic processes within refrigeration cycles.