In the improved natural convection driers named RRLT-NC drier, the hot air is generated separately outside the drier chamber and is conveyed upwards through a separate duct by natural convection. At the top of the duct an opening is provided for the entry of the hot air to the drying chamber. Performed trays are arranged one above the other in the drying chamber. All the sides of drier chamber, except the bottom side are covered with heat insulating materials. The hot air after entering into the drying chamber tends to occupy the topmost layer just below the top-covering sheet. As the hot air comes into contact with the wet material on the top tray, the temperature of air drops, consequently the density increase & has a tendency to flow down by percolating through the trays and the wet material placed on the trays. The cooled air by the process of heat transfer finally leaves at the bottom of the drier to the drier to the atmosphere. Thus the hot air is made to flow in a downward direction after overcoming the frictional resistance offered by the perforated trays and the wet material contained in the trays without the help of any blower or fan. Thus the wet material gets dried. The driers are simple in design, easy to operate, energy utilization is maximum. It’s cheap and affordable. It comes in various models.

RRLT-NC Drier Model no. 101: It is also called 'Domestic trays are provided in drying chamber. An electrical heater of 500/600 watts is provided water-evaporating capacity is 500gms per hour. A thermostat is also provided to control the temperature.

RRLT-NC Drier model no. 151: It is called 'small farmer model'. Its capacity is double than model 101. An electrical heater of 1000 watts powers it. Here the heater and the duct housing the heater are placed at the center.

RRLT-NC Drier model no. 201: This model is also called 'small farmer's model' with agricultural waste burning system. The capacity & construction is same as that of model 151.

Hot air is generated by the burning of agricultural waste materials like coconut shell, husk etc.

By the usage of these driers granular materials can be dried e.g., coconut into copra, grapes into raising, chilies, stems of medicinal plants etc.