Dryer

A clothes dryer or tumble dryer (also spelt with an i: drier) is a major household appliance that is used to remove the residual moisture from clothing or fabrics, generally shortly after being cleaned in a washing or washing/drying machine.

Most dryers consist of a rotating drum through which high-temperature air is circulated. The hot air removes the moisture from the fabric through evaporation. The drum is rotated relatively slowly in order to create a tumbling effect. In most cases, the drum is belt-driven by an induction motor.

The electric dryer generally uses a coiled wire that is heated by using electric current. The amount of electric current is varied to adjust the air temperature.

The gas dryer employs a gas burner that burns natural gas, propane or butane to form a jet of hot gases that are directed into a venturi chamber that uses Bernoulli's principle to pull in ambient air so as to raise its temperature. The air temperature can be adjusted by adjusting the size of the gas flame or more commonly by merely switching it on and off.

Condenser dryers are ventless and can be either electric or gas. There are two types: water cooled and air cooled. Condenser dryers generally have smaller capacity and longer drying times than vented dryers. Models exist which combine a washing machine and a dryer.

The air is sucked into the dryer through openings in the outside of the machine. One fan drives all of the air through the dryer, but the fan is actually the last step in the process.

In brief, this is how the air makes its way through the dryer:

It enters the body of the dryer through a large hole in the front of the dryer.

It is sucked past the heating element and into the tumbler.

It enters the door and is directed down through the lint screen.

It passes through a duct in the front of the dryer and into the fan.

The fan forces it into the duct leading out the back of the dryer, at which point it exits your house.

The first thing that the air hits is the heating element. After the air enters the body of dryer, it is sucked through the heating element, and then into the clothing tumbler.

This is a standard nichrome-wire heating element, just like the heating element in a toaster. This heating element consumes lots of power -- 4,000 to 6,000 watts on most dryers.

The air is drawn through the heating element and into the holes in the back of the tumbler.

The metal stamping on the right, with the big holes in it, makes sure that air can enter the tumbler only after it has gone through the heating element.

The hot air now makes its way through the clothes in the tumbler, and then into the holes in the door.

The air passes through the holes in the door, and out through the big slot in the bottom of the door which leads to the lint screen.

The air is drawn through the lint screen and down a duct in the front of the dryer, where it enters the fan.
The fan is a centrifugal type of device -- as it spins, it flings the air to the outside, sucking air from the center and forcing it out the duct at the back of the dryer. In the next section we'll see what makes the tumbler spin.

If you open up a dryer, one surprising thing is the lack of any gears on the tumbler. It turns out that the tumbler is one giant gear (or actually a pulley), and the motor drives a tiny pulley. Because of the ratio between the huge tumbler diameter and the tiny motor pulley diameter, no other gears are needed!

A motor drives the small silver pulley that is visible beneath the black pulley in the picture above. The belt loops through the silver pulley, through the black pulley and then around the tumbler. The black pulley provides tension -- when the belt is hooked up, the pulley is drawn off center, and the spring tries to pull it back. This gives the belt its tension.

The same electric motor drives both the fan and the tumbler. The pulley for the tumbler belt is hooked up to one output of the motor, and the fan is hooked to the other.

Another funny thing about most dryers is that the tumbler has no bearings to help it spin smoothly. So what supports the weight of the clothes?

At the back of the tumbler is a flange, connected to a simple bushing that allows the flange to spin. The back of the tumbler bolts to this flange. The front of the tumbler rides on two white plastic pads that are mounted to the top of the support structure.

The dryer also has a couple of safety features that help to prevent overheating. There are two temperature shut-off switches. When these switches reach certain preset temperatures, they break contact, which shuts the dryer off. The first switch is located near the lint screen.

The picture above shows the front of the dryer, with the front panel partially removed. The first temperature sensor is on the right. And to the left, you can see a set of six holes in the outer edge of the tumbler. These holes are only there to blow hot air on the sensor every time they go by. If the temperature in the tumbler gets too hot, this sensor cuts the power, shutting the dryer off.

But what happens if the belt breaks and the holes don't happen to be in front of the temperature sensor? Or if the fan gets clogged and no air is coming out of the tumbler? This is where the second temperature switch comes in.

The second sensor is located close to the heating elements. If airflow is shut off for any reason, the air near this sensor will quickly heat up to the temperature that triggers this sensor, and the sensor will shut off power.

Before you purchase a dryer you may want to keep this things in mind to keep your dryer running longer and in top condition:

Get a dryer with a large lint duct and capture trap and clean it out after each dryer load.
Keep the distance from the dryer to the outside vent as short as possible. You hurt the efficiency of the intake and outtake of air and can cause possible lint buildup in the ductwork that can cause fires.
Make sure your washer is up to its tasks, spinning the clothes well, so there is less moisture for the dryer to extract.
Separate lightweight from the heavier clothing for an even and faster drying.
Consider a laundry day when you can dry clothes one load after another, keeping the dryer from having to heat up between loads.
Look for a dryer that has a moisture sensor, a good reliability record, and, if possible, gas fueled.



Additional Links

Kitchen and household appliances
Appliance Parts Depot
Kitchen Appliances and Replacement Parts
Heating Ventilation and Air Conditioning
Kitchen Items