Automatic clothes dryers consist of a motor driven revolving basket, an galvanic heating element or gas flame, thermostats, and a timer. Some models also have a selector switch. Air, heated by the galvanic element or gas flame, is forced straight through the tumbling clothes by a fan. The fan is driven by the drive motor. The temperature of the heated air, entering and leaving the basket, is controlled by thermostats which claim a balance between the air velocity, air volume, and air temperature. The temperature of the exhaust air is a measure of the dryness of the clothes.
After the dryer is started and loaded with damp articles, the temperature inside the basket will rise rapidly. When the temperature reaches approximately 130F, the evaporation of the moisture in the load will suck up the heat as rapidly as the heat is generated by the heater. The temperature will not rise appreciably above 130F until the load is nearly dry.
When the load is nearly dry, there will not be enough moisture in the clothes to suck up the heat, and the basket and clothing temperatures will rise. This heat rise will continue until the removal air reaches approximately 160F. At this point the heater circuit is disconnected by a thermostat. The dryer basket will continue to revolve in what is called the overrun period, and cool, fresh air will enter the basket to cool the clothes for handling. The overrun time may last from 3 to 10 min and is controlled by either the timer or an overrun thermostat which will stop the dryer.
Modern dryers of today, Maytag, Kenmore, Ge, Whirlpool, Frigidaire, have a moisture sensor which relays moisture conditions inside the dryer to a control board which controls the cycle time and cool-down modes. The moisture sensor consists of two conductive metallic wires placed inside the dryer and mounted to the plastic lint filter housing. One wire has a very low-current Ac voltage applied to it and the other one is grounded. When moisture is gift a conduction path exists intermittently between the two wires. When the clothes are dry, there is no conduction path. When the dryer is in the automatic dry cycle, the control board will then expand to the cool-down mode.
Appliances - Dryer execution