Important Stages of the Production Process - Introduction to Polymeric Composites with Rice Hulls - page 85

that sublimation occurs and materials become so cold that all moisture freezes. The
solid moisture (ice) is then given just enough heat that it becomes a vapour, bypassing
the liquid stage altogether and leaving the material dry.
IR dryers do not use air to dry materials. Instead they harness heat energy from certain
wavelengths of electromagnetic radiation. IR radiation is absorbed by solid matter
and so dries from the inside out. By matching the absorption characteristics of the
material, the drying process is efficient in terms of time and resources.
Demand for the latest and most cost-effective dryers in all aspects of their functions
have led to innovations and new technologies. Improvements in material management,
manufacturing techniques, and new technologies have impacted the constant demand
for more efficient and cost-saving machines.
7.2.2 Summary
• Air dryers are the most common type of industrial dryers. The material to be dried
comes into direct contact with heated air dispensed by the machine.
• Continuous dryers remove moisture from a constant flow of material that enter
the dryer, are dried and then exit, all without stopping.
• Conveyor dryers use a belt to move materials through a dryer at a continuous feed
rate. Agricultural materials are often dried on a belt or similar conveyor dryer system.
• Compressed air dryers remove water and other contaminants from compressed
air and the lines that carry it. This is done via refrigerant or desiccant processes.
• Desiccant dryers remove water and moisture from a material by absorption of
grainy materials such as silica gel or activated alumina.
• Flash dryers are industrial dryers that dry a material during exposure to a short
burst of intense heat. Water sludge is often dried this way at water-treatment
plants for easy removal of contaminants.
• Fluid bed dryers force heated gas through a permeable surface, where it comes
into direct contact with a bed of solid materials, causing the moisture inside them
to evaporate.
• Food dryers remove moisture from fruits, vegetables, meats and other edible
products. Dried foods preserve nutrients, colour and flavour while reducing weight
and volume, making them easy to pack and transport.