Direct Cool And Frost Free Refrigerator
Direct Cool Refrigerator
In this refrigerator circulation of air inside the refrigerator is due to the Buoyancy effect, i.e. heavy cold air from the topside freezer moves down whereas lighter hot air from the refrigerator goes up to the freezer.
Here no fan is used to circulate the air. This type of air circulation is called natural convection.
Frost Free Refrigerator
In this refrigerator circulation of air inside the refrigerator is done forcibly by using a fan. This type of air circulation is called forced convection.
Also, the refrigerator is called frost free because, in the case of forced convection, the frosting of the condensate in the freezer will not form.