Project Description

Bellmouth Reducer

Bellmouth reducers have a smaller opening at the end of a duct system. The shaped of bell mouth reducers looks like a bell shape. Fabric expansion joints are sometimes used in a duct system. We also provide ducting expansion joints. Bellmouth reducers help return air or extract air in building ventilation systems.

The Bellmouth reducer open area usually is double that of the duct area. Therefore, the air entering the bell mouth reducer is low. Thus, reducing noise, turbulence, and pressure drop. The bell-mouth reducer shape allows the maximum amount of air to be drawn into the duct with minimum loss.

The purpose of bellmouth reducers is to lower the pressure drop at the intake into a duct from an open space. Also, bellmouth reducers discharge from a chimney into an open space. The discharge is known as shock loss or, more generally, a fitting pressure loss.

The fitting pressure loss for a ducted intake from an area is equal to the velocity pressure. Therefore, it is equal to the square of the velocity. Thus, by increasing the area at the intake, you can drastically reduce the pressure drop of the fitting. Also, a bellmouth reducer is used to reduce shock losses at entry.

A bell-mouth reducers inlet duct is a form of convergent inlet air duct used to direct air into the inlet of a gas turbine engine. The area of a convergent duct gets smaller as the air flows into the engine.

A bell-mouth reducer inlet duct is highly efficient and helpful where there is little ram pressure available to force the air into the engine. Bell-mouth ducts are used in engine test cells and on engines installed in helicopters.

How To Choose A Bell Mouth Reducer

Know the velocity of the air used for the bellmouth reducers. Also, know the well as the size of the duct. And the CFM is being handled by the duct section. Next, know that bell mouth reducers should taper at 45 degrees for smooth entry/exit of air.

Also, learn about the equation Q=Av. Finally, using all this information, how do you find the maximum size of the bell mouth reducer?

How to Find the Maximum Size of Bellmouth Reducers?

The maximum size depends on what you want the average inlet velocity to be. But, moreover, it’s not so much about size. And it’s more about geometry.

Typically anything up 4-5m/sec is possible or as low as 0.1m/sec if you want the air to “drift” in or out. Therefore, there is an extensive range of end areas which is up to you and your particular requirements and issues.

Be aware that unless you make a significant effort, in reality, the velocity across the end area won’t be uniform and could easily be 2-3 times as much in the center as the outer edge.

If the entrance of the bellmouth reducers velocity, then Q=Av gives us the area of the bell mouth reducer entrance/exit section. The other end is, of course, sized equal to the duct.

Entry air in a bellmouth reducer is usually a lower velocity as the pressure drop is more critical than exhaust air where you are providing the motive power. Many inlets are just the same size as the duct but result in a bit of noise and some losses/turbulence as it enters the duct.