Product Drying

How does it work?

• Chamber loaded with product usually on trolleys or racks
  Chamber doors closed, cycle started.
  Can be automatic programmed cycle or simple on/off.

• Initial heat input to get to operating temperature, typically 40-55°C but may be up to 70°C.  Heat encourages moisture to evaporate from product, by increasing internal vapour pressure.

• Air moving over the product takes moisture away from surface taking it to the dehumidifier, which may be assisted by fans positioned above a false ceiling.

• Dehumidifier extracts moisture from proportion of air flow that passes through the unit.  Latent heat is returned back into chamber reducing the requirement for heat input.  The lower vapour pressure of the dried air increases the rate of evaporation, and therefore rate of drying.

• The heat return from the dehumidifier can exceed the heat losses from the chamber.  A temperature balance fan allows excess heat to be exhausted from the chamber, whilst an inlet louvre allows cool air back into the chamber.

• The control of both humidity and temperature allows a drying cycle to be created that is tailored to a particular product.  Temperature is controlled by activating either the heaters or exhaust fan, whilst the humidity is controlled by activating the dehumidifier. 

• On an automatic cycle it is possible to:
  Delay the start of the dehumidification until the product has been heated up initially. 
  Provide stepped increases in temperature during the cycle to assist in getting the last few per cent of moisture out of the product.
  Progressively reduce the humidity to provide a gentle drying regime for sensitive products.

• Special case: drying timber:
  Humidity has to be increased during the heat-up phase at the start of the cycle, otherwise splitting and cracking, or warping of the timber is possible as the timber starts drying too rapidly.