The process
Withering troughs blow a large volume of ambient or warmed air through green leaf for hours. The trough fan is an axial fan at low pressure, often with a hot air mixer, run for long hours and cleaned often.
The gas
Warm, humid air through withering troughs and dryers with light leaf dust. Large volume at low pressure; the fan is cleaned often, so access matters.
Selection for this process
| Impeller | Coated aluminium or stainless steel impeller, stainless or coated casing |
| Form | Tube axial for low pressure; vane axial where the pressure or the downstream distribution calls for it; bifurcated where the motor must be out of hot or contaminated air |
| Density at the fan | At about 60°C the gas density is close to 1.06 kg/m³, 88% of standard air. Pressure developed and power drawn fall in the same ratio, so the selection is made at this density and the motor is checked at cold start. |
Types, construction and performance of the axial fans.
Industries
Fans in tea withering troughs
Axial Fans in other processes
Information needed to select or quote
- Gas volume and temperature. Actual flow at the inlet, normal and upset temperature, moisture.
- Dust or pollutant. Inlet loading, particle size distribution, whether it is abrasive, sticky, hygroscopic or combustible; for gases, the species and concentration.
- Required outlet. The emission limit or clean gas concentration the unit must meet.
- Site. Available space and height, material of construction preferences, and how the collected material is to be discharged.