Product Drying: Design considerations

There are three important factors in the design of a drying chamber that affect the rate of drying.

Air Temperature
This can be limited by the product, or with a dehumidifier by the operation of the refrigerant circuit. Usually there is no need to operate at the typical 120°C of a gas fired oven. Often needed to create suitable differential in vapour pressure for drying to occur.

Air Speed
Higher the air speed, the greater the turbulence, and the higher the rate of drying. However there is a law of diminishing returns.

Moisture Extraction
The size and quantity of dehumidifiers for a chamber is dependant on the quantity of moisture to be removed from the product and the time available for the drying process. The removal of moisture is often forgotten in hot air ovens, as they are designed for curing processes not drying. It costs money to heat the air that replaces the extracted air.

Control panels
Calorex can manufacture and supply control panels to operate all the functions of a drying chamber and control both temperature and humidity in the chamber.  The control panels contain all the necessary contactors, relays, fuses and timers to operate the dehumidifier compressors and fans, heaters, and circulation and overheat fans within the chamber.  The control panels have digital displays of actual and set point humidity and temperature, and also visual display of machinery status and fault indications.  These control panels are fitted outside the chamber and are supplied in two basic types:

Simple single stage control panel
This gives the facility to control the temperature and humidity in the chamber and allows the chamber to run for any designated period of time.

Modular control panel
These have the ability to provide between 2 to 6 timed stages with individual temperature and humidity set points, allowing the operator to set up a drying schedule in steps of days, hours or minutes.  They are capable of operating 1 or 2 dehumidifiers and the modular format allows them to be configured to control multiple units.