Publish Time: 2023-05-26 Origin: Site
Industrial exhaust ducts are ductwork that connect range hoods to industrial chimneys through other components of the exhaust system such as fans, collectors, etc.Ducts are low pressure pneumatic conveyors used to convey dust, particles, shavings, fumes or chemically hazardous components in the air close to a workshop or any other specific location such as a water tank, sander or laboratory fume hood.Piping can be made from a variety of materials, including carbon steel, stainless steel, PVC, and fiberglass.They can be manufactured by rolling (for pipe 12" diameter or larger) or extrusion (for pipe up to 18").HVAC systems do not include such industrial applications, namely exhaust systems.The difference with HVAC system ducting is that the fluid (air) being transported through the ductwork may not be uniform.Industrial exhaust piping systems are primarily pneumatic conveying systems, essentially governed by the laws of fluid flow.
Fluid flow
The conveying fluid flowing through the piping system is air.Air transports material from the hood to its destination.It also helps to capture material into the flow system.Air is a compressible fluid, but in engineering calculations, as a simplification, air is considered incompressible without any significant error.
Design
The process design of the exhaust system will include
Identify contaminants, their density and size.
Determine airflow.
Dimensions of the piping system.
Resistance calculation.
Determining the capacity of blowers, etc.
The goal is to keep pollutants out using minimal airflow.It is estimated that each additional inch of wgin static pressure increases operating costs by several thousand dollars per year.
Darcy coefficient of friction
The coefficient of friction fD is not a constant:it depends on the properties of the pipe (diameter D and roughness ε), the properties of the fluid (its kinematic viscosity ν [nu]) and the velocity flow ⟨v⟩ of the fluid. It has been measured with high accuracy over certain flow ranges and can be evaluated by using various empirical relationships, or it can be read from published charts.These charts are often called Moody's charts, named after L. F.Moody's, so the factor itself is sometimes incorrectly called the Moody's friction factor.It is also sometimes called the Blasius coefficient of friction, after the approximate formula he proposed.