Final answer:
Refrigerant 134a expands in a piston cylinder assembly due to an increase in volume.
Step-by-step explanation:
In a piston cylinder assembly, when refrigerant 134a expands, it means that the volume of the gas increases. This expansion can occur due to various factors such as an increase in temperature or a decrease in pressure.
During expansion, the gas molecules move apart, leading to an increase in volume. This can be visualized by imagining a piston inside a cylinder, where the cylinder represents the system and the piston is pushed outward due to the expanding gas.
Overall, the expansion of refrigerant 134a in a piston cylinder assembly is a fundamental concept in thermodynamics and is studied in the field of Physics.