The path of the gas stream may be a single long tube, camel back, loop design or series of cyclones, and each configuration offers unique characteristics. For example, a single, long tube will require less energy to compensate for losses and can process high throughput rates. A loop design will allow for classification and additional residence time based on moisture content, or, alternatively, may reduce the particle size by milling the material in the dryer. The carrier is induced or forced into the feed throat from a hot gas generator that heats the gas to the desired operating inlet temperature. Flash dryers utilize fans to provide the motive force for transferring the product.
Process designs for dryer systems yield thermal energy and air requirements.
The energy represents the sensible and latent heat needed to elevate the product temperature to the point at which it will allow evaporation at the ensuing pressure. The air requirement represents both the volume needed to carry this energy as well as remove and hold the moisture above the mixture's dewpoint. This requires detailed and involved calculations to obtain the correct heat and mass balance requirements. The throat is composed of a carrier introduction duct, an acceleration zone to increase feed velocity and a discharge zone where the gas-entrained product is injected into the flash tube. Acceleration usually is accomplished by means of a venturi or mechanical accelerator that imparts kinetic energy into the feed stream, allowing it to reach the required conveying velocity.