traydrying

Tray drying is a batch drying process in which product is spread in a thin layer on perforated trays and heated by circulating heated air in a drying chamber. It is commonly used in food processing, pharmaceuticals, and materials engineering. The method relies on hot air to remove moisture from the product as it passes through a drying chamber or cabinet dryer, with trays arranged to maximize contact with the circulating air.

Equipment typically consists of a drying chamber, a heat source (electric coils, gas burner, or hot air heater), a fan or blower to create forced convection, and control systems for temperature, humidity, and airflow. Trays are usually made of stainless steel or food-grade materials and are selected to fit the chamber; the product is spread or loaded in a thin layer, typically 5–20 mm thick, to permit uniform drying. The process is performed at moderate temperatures (often in the 40–90 °C range for foods) and varies with product type and moisture content.

Key variables include drying air temperature, velocity, humidity, product thickness, loading density, and initial moisture content. Drying kinetics show an initial fast surface evaporation, then a slower falling-rate period governed by internal moisture diffusion. The moisture ratio MR = (M_t - M_e)/(M_0 - M_e) is a common descriptor.

Advantages include simplicity, low capital cost, and suitability for batch processing and thermally stable materials. Limitations include long drying times for large volumes, potential nonuniform drying, nutrient or color loss, and energy intensity. Variants such as tunnel or solar-assisted tray dryers exist, and improvements focus on airflow design and multi-stage or dehumidified drying.