Duct (industrial exhaust)
Industrial exhaust ducts are pipe systems that connect hoods to industrial chimneys through other components of exhaust systems like fans, collectors, etc. Ducts are low-pressure pneumatic conveyors to convey dust, particles, shavings, fumes, or chemical hazardous components from air in the vicinity to a shop floor or any other specific locations like tanks, sanding machines, or laboratory hoods. Ducts can be fabricated from a variety of materials including carbon steel, stainless steel, PVC, and fiberglass. [1] They can be fabricated through rolling (preferable for ducts of 12" or more in diameter) or extruded (for ducts up to 18").[2]
HVAC systems do not include this category of industrial application, namely exhaust systems. A distinction from HVAC system ducts is that the fluid (air) conveyed through the duct system may not be homogeneous. An industrial exhaust duct system is primarily a pneumatic conveying system and is basically governed by laws of flow of fluids.[3]
Fluid flow
The conveying fluid that flows through the duct system is air. Air transports materials from the hood to a destination. It is also instrumental in capturing the material into the flow system. Air is a compressible fluid, but for engineering calculations, air is considered as incompressible as a simplification, without any significant errors.
Design
Process design of exhaust system will include
- Identification of contaminants, their density and size
- Deciding of air flow
- Sizing of the ductwork
- Calculation of resistance
- Finalizing the capacity of blower, etc.[4]
The goal is to keep contaminants out using minimum airflow. It is estimated that increase in an inch wg[clarification needed] of static pressure can add a few thousands of dollars to the operation cost per annum.
See also
- Darcy friction factor Friction factor for designing duct systems.
- Colebrook equation
- Process Duct Work
- Air quality
References
- ^ Duct Work Assembly Archived 2020-02-24 at the Wayback Machine U.S. Bellows, (retrieved May 2012)
- ^ KCH Engineered Systems
- ^ [1] Archived 2015-09-19 at the Wayback Machine ASHRAE Technical Committee 5.2 - Duct Design
- ^ [2] Archived 2017-02-20 at the Wayback Machine Industrial Duct System Design Fundamentals