A feed worm carries solid material from a hopper to an air stream, which helps transport and disperse it beyond the screw outlet. This calculator compares an assumed volume delivered per turn with fuel density, screw speed and a selected primary-air ratio. Its nozzle result is an equivalent flow area, not a burner specification or a combustion setting.
Feed Worm and Air Blast Interactive Calculator
Compare assumed fuel delivery and primary-air flow. The diameter represents a uniform-velocity equivalent opening; it does not size a working burner or establish safe operating conditions.
Equation Used
The entered displacement is the effective volume delivered per turn, including the assumed fill. Multiplying it by speed and bulk density gives fuel flow. Primary air is prescribed by the entered ratio, and its flow and velocity give an equivalent circular area. The output labelled Jet Momentum is air momentum flux in newtons. Combustion air demand, pressure loss, flame stability and particle transport are not calculated.
- Feed worm meters a fixed displaced volume per revolution.
- Fuel is dry pulverised solid with steady bulk density.
- Primary air density is 1.2 kg/m3.
- Nozzle is treated as a single equivalent round opening.
Screw delivery followed by air transport
Material enters the screw from the hopper. Turning flights move it toward the discharge, where an air stream receives it. Screw delivery and pneumatic transport are separate functions: a steady screw speed does not by itself establish uniform mass flow or adequate transport air.
A volumetric screw feeder depends on effective volume per revolution and bulk density. Fill, material flowability and density can vary in service. Use measured delivery data for the material and feeder when converting speed to mass flow.
The drawing shows the arrangement of hopper, screw and air outlet. It does not define a venturi profile, manufacturing clearances, combustion chamber or fuel-isolation system.
Understanding fuel and primary-air quantities
The tool illustrates a screw-fed, air-assisted fuel supply. It can compare how assumed delivery changes with screw speed or bulk density, and how a chosen primary-air ratio changes air mass flow.
Primary transport air is not automatically the total air required for combustion. Fuel composition, moisture, chamber design, secondary air and operating conditions determine a working firing arrangement. This calculation does not establish those conditions or choose a fuel for a furnace.
Mass flow and equivalent opening
For effective displacement V in litres per revolution, speed N in rpm and bulk density ρf in kg/m³, fuel flow is mf = 0.06VNρf in kg/h. The factor 0.06 converts litres per minute to cubic metres per hour.
At the selected primary air/fuel mass ratio R, air flow is ma = Rmf in kg/h. Divide by 3,600 to get kg/s. The calculator holds air density at 1.2 kg/m³ and assumes uniform velocity v, so area A = (ma/3,600)/(1.2v).
The equivalent round diameter is d = 1,000√(4A/π) in millimetres. Air momentum flux is (ma/3,600)v in newtons. That quantity is not particle momentum or a complete nozzle-thrust calculation. Pressure losses and compressibility are not included.
Example using the calculator defaults
With 1.2 L/rev, 30 rpm and 650 kg/m³, fuel flow is 0.06 × 1.2 × 30 × 650 = 1,404 kg/h. Selecting a primary-air ratio of 2 gives 2,808 kg/h of air, or 0.78 kg/s.
At 45 m/s and the assumed air density of 1.2 kg/m³, the equivalent opening is about 135.61 mm diameter. Air momentum flux is 0.78 × 45 = 35.1 N.
These values are an arithmetic example. The default air ratio and velocity are not recommended burner settings, and the result does not predict steam output or fuel burnout.
What changes with each input
Doubling speed, effective displacement or bulk density doubles calculated fuel flow. At a fixed air ratio, air flow doubles too. With unchanged blast velocity, equivalent nozzle diameter then increases by √2 rather than doubling.
Increasing blast velocity at fixed air mass flow reduces the equivalent opening and raises calculated air momentum flux. It does not establish that particles will remain suspended or that the flame will stay within the chamber.
A real fuel-handling system also needs controls for loss of airflow, fuel isolation and the particular combustible material. Obtain operating limits from the equipment design and manufacturer; the slider limits here are calculation ranges.
Frequently asked questions
Is displacement the theoretical screw volume?
Use effective delivered volume per turn, including the intended fill assumption. A geometric swept volume alone does not account for incomplete fill or material movement within the screw.
Does the air/fuel slider calculate combustion air demand?
No. It prescribes primary-air mass flow as a multiple of fuel flow. Total combustion-air demand is not calculated.
Can I fabricate a nozzle from the diameter output?
The output only equates air flow to a circular area at uniform velocity and fixed density. A working nozzle requires its pressure, geometry, solids handling and combustion conditions to be evaluated separately.
Why can mass flow change at constant screw speed?
Bulk density and effective volume delivered per turn can change. The tool holds each at the entered value; it does not predict hopper flow or feeder fill.
What does Jet Momentum mean here?
It is the calculated air momentum flux: air mass flow in kg/s multiplied by velocity in m/s, giving newtons. Solid-particle momentum and pressure thrust are omitted.
Does this establish a minimum firing rate?
No. It has no flame-stability, ignition or heat-release model. Use the operating limits of the specific burner and fuel system.
References
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
