Final answer:
The devices that increase the velocity of a gas inside an axial compressor are called airfoils or blades, which function similarly to entrainment devices by converting rotational motion into linear velocity.
Step-by-step explanation:
The devices that increase the velocity of a gas inside an axial compressor are known as airfoils or blades. These components are analogous to wings of an airplane and are designed to accelerate the gas as it passes through the compressor by converting rotational motion into linear velocity. This is accomplished in a process similar to that of other entrainment devices, such as the common aspirator or the Bunsen burner, which use increased fluid speed to create low pressures, thereby entraining one fluid into another. The blades essentially act upon the gas, applying a force that results in an increase in velocity and thereby energy of the gas, which is central to the compressor's function in systems such as refrigeration cycles or jet engines.