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{{Short description|Thermodynamic device}} |
{{Short description|Thermodynamic device}} |
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A ”’diffuser”’ is “a device for reducing the [[velocity]] and increasing the [[static pressure]] of a fluid passing through a |
A ”’diffuser”’ is “a device for reducing the [[velocity]] and increasing the [[static pressure]] of a fluid passing through a .<ref>{{cite encyclopedia |chapter-url= http://www.merriam-webster.com/dictionary/diffuser.html |contribution=diffuser |title=Merriam–Webster Dictionary |accessdate=5 August 2016}}</ref> The fluid’s static pressure rise as it passes through a duct is commonly referred to as pressure recovery. In contrast, a [[nozzle]] is used to increase the discharge velocity and lower the pressure of a fluid passing through it. |
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Frictional effects during analysis can sometimes be important, but usually they are neglected. Ducts containing fluids flowing at low velocity can usually be analyzed using [[Bernoulli’s principle]]. |
Frictional effects during analysis can sometimes be important, but usually they are neglected. Ducts containing fluids flowing at low velocity can usually be analyzed using [[Bernoulli’s principle]]. Analyzing ducts flowing at higher velocities with [[Mach number]]s in excess of 0.3 usually require [[compressible flow]] relations.<ref>{{cite web|title=Mach Number|url=https://www.grc.nasa.gov/www/k-12/airplane/mach.html|website=NASA|publisher=National Aeronautics and Space Administration|accessdate=5 August 2016}}</ref> |
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A typical subsonic diffuser is a [[Duct (HVAC)|duct]] that increases in area in the direction of flow. As the area increases, fluid velocity decreases, and static pressure rises. |
A typical subsonic diffuser is a [[Duct (HVAC)|duct]] that increases in area in the direction of flow. As the area increases, fluid velocity decreases, and static pressure rises. |
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* Accomplish the above while producing the minimum amount of [[noise]] |
* Accomplish the above while producing the minimum amount of [[noise]] |
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, extractors, and other flow control devices not placed near diffusers’ inlets (necks) have been shown to dramatically increase noise. For as-cataloged diffuser performance, a straight section of [[duct (HVAC)|duct]] serve a diffuser. An elbow, or kinked flex duct, just before a diffuser often leads to poor air distribution and increased noise. |
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Diffusers |
Diffusers round or linear slot diffusers take the form of one or several long, narrow slots, mostly semi-concealed in a fixed or suspended ceiling with [[airfoil]]s behind the slots directing the airflow in the desired direction. |
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Occasionally, diffusers are |
Occasionally, diffusers are used in reverse as air inlets or returns linear slot diffuser and ‘perf’ diffusers commonly, [[Grille (architecture)|grille]]s are used as return or exhaust air inlets. |
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==See also== |
==See also== |
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Latest revision as of 03:10, 27 January 2026
Thermodynamic device
A diffuser is “a device for reducing the velocity and increasing the static pressure of a fluid passing through a system”.[1] The fluid’s static pressure rise as it passes through a duct is commonly referred to as pressure recovery. In contrast, a nozzle is used to increase the discharge velocity and lower the pressure of a fluid passing through it.
Frictional effects during analysis can sometimes be important, but usually they are neglected. Ducts containing fluids flowing at low velocity can usually be analyzed using Bernoulli’s principle. Analyzing ducts flowing at higher velocities with Mach numbers in excess of 0.3 usually require compressible flow relations.[2]
A typical subsonic diffuser is a duct that increases in area in the direction of flow. As the area increases, fluid velocity decreases, and static pressure rises.
Supersonic diffusers
[edit]
A supersonic diffuser is a duct that decreases in area in the direction of flow which causes the fluid temperature, pressure, and density to increase, and velocity to decrease. These changes occur because the fluid is compressible. Shock waves may also play an important role in a supersonic diffuser.
Diffusers are very common in heating, ventilating, and air-conditioning systems.[3] Diffusers are used in both all-air and air-water HVAC systems, as part of room air distribution subsystems, and serve several purposes:
- To deliver both conditioning and ventilating air
- Evenly distribute the flow of air, in the desired directions
- To enhance mixing of room air into the primary air being discharged
- Often to cause the air jet(s) to attach to a ceiling or other surface, taking advantage of the Coandă effect
- To create low-velocity air movement in the occupied portion of room
- Accomplish the above while producing the minimum amount of noise
Dampers, extractors, and other flow control devices are not typically placed near diffusers’ inlets (necks) as such devices have been shown to dramatically increase system noise. For as-cataloged diffuser performance, a straight section of duct is recommended serve a diffuser. An elbow, or kinked flex duct, just before a diffuser often leads to poor air distribution and increased noise.
Diffusers are typically round or rectangular. Narrow rectangular linear slot diffusers take the form of one or several long, narrow slots, mostly semi-concealed in a fixed or suspended ceiling with airfoils behind the slots directing the airflow in the desired direction.
Occasionally, diffusers are used in reverse as air inlets or returns, linear slot diffuser and ‘perf’ diffusers in particular. More commonly, grilles are used as return or exhaust air inlets.
- ^ “diffuser”. Merriam–Webster Dictionary. Retrieved 5 August 2016.
- ^ “Mach Number”. NASA. National Aeronautics and Space Administration. Retrieved 5 August 2016.
- ^ Designer’s Guide to Ceiling-Based Air Diffusion, ASHRAE, Inc., Atlanta, GA, USA, 2002
