Final answer:
A diffuser is designed to slow down the flow of air, increasing its pressure and decreasing its velocity, applying principles from fluid dynamics such as the continuity equation.
Step-by-step explanation:
The purpose of a diffuser in an engineering context, specifically when air enters a diffuser operating at steady state, is to increase the pressure of the air while simultaneously decreasing its velocity. A diffuser is a device that slows down the speed of the flowing fluid; in this case, air, which causes a corresponding increase in pressure according to the principles of the conservation of energy and fluid dynamics such as the continuity equation. This effect is leveraged in various applications to ensure the desired air flow and pressure within systems like air conditioning, ventilation, and engines.