Diffuser (engineering)
An engineering diffuser is a component that decelerates a flowing fluid, converting kinetic energy back into pressure energy, thereby increasing the static pressure. Diffusers are used in compressors, wind tunnels, aircraft intakes, and HVAC systems to recover pressure with minimal losses. The performance of a diffuser is characterised by the pressure recovery coefficient, which compares actual pressure rise to the ideal isentropic value.
Key Formula
C_p = (P2 - P1) / (0.5 × ρ × V1²)
LaTeX: C_p = \frac{P_2 - P_1}{\frac{1}{2} \rho V_1^2}
| Symbol | Meaning | Unit |
|---|---|---|
| C_p | Pressure recovery coefficient | dimensionless |
| P_1 | Inlet static pressure | Pa |
| P_2 | Outlet static pressure | Pa |
| \rho | Fluid density | kg/m³ |
| V_1 | Inlet velocity | m/s |
Worked Example
Problem
Air enters a diffuser at 80 m/s with a static pressure of 100 kPa and density 1.2 kg/m³. The outlet static pressure is 103.84 kPa. Calculate the pressure recovery coefficient.
Solution
Step 1: ΔP = P2 − P1 = 103,840 − 100,000 = 3,840 Pa. Step 2: Dynamic pressure = 0.5 × 1.2 × 80² = 0.5 × 1.2 × 6400 = 3,840 Pa. Step 3: C_p = 3,840 / 3,840 = 1.0 (ideal diffuser in this case).
Answer
C_p = 1.0 (ideal recovery; real diffusers achieve 0.6–0.9)
Diffuser Types and Performance Characteristics
| Type | Geometry | Typical C_p | Application |
|---|---|---|---|
| Straight-walled | Linear diverging | 0.6–0.75 | Wind tunnels |
| Curved | Curved diverging walls | 0.7–0.85 | Compressor stages |
| Annular | Radial expanding | 0.75–0.90 | Centrifugal compressors |
| Vaned | With guide vanes | 0.80–0.88 | Turbomachinery |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Engineering Nozzle
An engineering nozzle is a shaped duct or orifice designed to accelerate a fluid by converting pressure energy into kinetic energy, thereby increasing the fluid's velocity. Nozzles are critical components in rocket engines, gas turbines, steam turbines, and fluid spray systems. In a converging nozzle, the cross-sectional area decreases in the flow direction, while a converging-diverging (de Laval) nozzle is used to achieve supersonic flow.
Compressor (engineering)
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume, thereby increasing its energy content. Compressors are fundamental components in refrigeration systems, gas turbines, pneumatic tools, and industrial processes where pressurised gas is required. The work input to a compressor is governed by thermodynamic principles, and the efficiency of the compression process determines overall system performance.
Heat Exchanger
A heat exchanger is a device designed to transfer thermal energy between two or more fluids at different temperatures, without the fluids mixing. Heat exchangers are ubiquitous in engineering applications including power generation, chemical processing, HVAC systems, and automotive radiators. The rate of heat transfer depends on the temperature difference, the overall heat transfer coefficient, and the heat transfer area.
From Latin "diffundere" meaning "to pour in different directions", from "dis-" (apart) and "fundere" (to pour). In engineering, the term was applied in the 19th century to describe devices that spread or slow a fluid flow.