Liquid addition is a mass-transfer problem
Uniform results depend on exposing fresh powder surface to the spray while preventing local over-wetting. The correct mixer, spray pattern and addition rate work as one system.
Control droplet size and spray location
Large droplets can create wet agglomerates; extremely fine droplets may drift or evaporate. Nozzles should be located where material circulation is active and where the spray will not strike the wall or agitator directly.
Match the mixer to the objective
Ribbon mixers can handle modest additions, paddles can protect fragile products and plough mixers can provide more intensive distribution with optional choppers. Higher liquid loading may require a different process route.
Define the finished state
Coating, binding, flavor addition, moisture adjustment and granulation are different objectives. Each requires its own spray rate, mixing intensity and endpoint.