It typically consists of a cast iron heavy jacketed vessel. It is so strong that it can withstand the vacuum within the oven and stream pressure in the jacket.
The inner space is divided into a number of portions (shelves), which are part of this package
This shelves provide larger surface area for conduction of heat.
Over the shelves, metal trays are kept for keeping the material.
The oven is connected to vacuum pump by placing condenser in between. Pressure is usually decreased to 30-60 kPa.
Steam or heat air is passed through the hollow space of jacket and shelves. As a result, evaporation of water take place at 25-30 C.