The traditional clothes dryer heats the ambient air and transports it around the drum. The resulting hot and humid air is discharged, leaving dry air to continue the drying process. The traditional design does not recover heat, so it is very inefficient.
However, the basic design is simple, reliable, and inexpensive. Most household dryer company's washing and drying machines use this working principle and are automatically controlled by a computer. Different drying temperatures and drying times can be configured according to the drying requirements.