Difference Between Nozzle and Diffuser
In fluid mechanics and thermodynamics, nozzles and diffusers are fundamental devices used to control the velocity and pressure of fluids. Though they look similar in design, their functions are opposite. Understanding their differences is essential for students, engineers, and professionals working with turbines, compressors, jet engines, and HVAC systems.
🔍 Basic Definitions
- Nozzle: A device that accelerates fluid flow, resulting in higher velocity and lower pressure.
- Diffuser: A device that decelerates fluid flow, resulting in lower velocity and higher pressure.
📊 Key Differences Between Nozzle and Diffuser
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📊 Comparison of Nozzle and Diffuser
🧩 Working Principle
1. Nozzle
- In incompressible flow:
- Static pressure decreases.
- Velocity increases.
- In compressible flow (supersonic nozzle):
- Typically has three sections: convergent, throat, divergent.
- At the throat, Mach number = 1 (sonic condition).
- In the divergent section, velocity increases further to supersonic speeds (Mach > 1).
2. Diffuser
- In incompressible flow:
- Static pressure increases.
- Velocity decreases.
- In compressible flow:
- Diffuser slows down the fluid, converting kinetic energy into pressure energy.
✈️ Real‑World Examples
Nozzle:
- Jet engines accelerate exhaust gases to produce thrust.
- Garden hose nozzle increases water jet speed.
Diffuser:
- Gas turbine diffusers slow down air before entering the combustion chamber.
- HVAC duct diffusers distribute air evenly at lower velocity.
🎯 Key Takeaways
- Nozzle = Speed Up, Pressure Down
- Diffuser = Slow Down, Pressure Up
- Both conserve mass flow rate but manipulate velocity and pressure differently.
- Their design depends on whether the flow is subsonic or supersonic.