Tumble dryers
Tumble dryers continuously draw in the ambient air around them and heat it before passing it through the tumbler. The resulting hot, humid air is usually vented outside to make room for more air to continue the drying process. It is simple and reliable, and therefore has been widely used. Improvised methods of salvaging this heat for in-home heating, by use of inline vent boxes equipped with Air Damper to redirect moist heated air to indoor areas, will also increase humidity within a dwelling. Although this may be beneficial in dry winter conditions, excess humidity from these devices increases likelihood of mold, mildew, and bacterial growth inside a home. Indoor venting may also be against local regulations. Gas dryers, unlike electric dryers, must always be vented outdoors, as the products of combustion are mixed with the moist air. Building codes and manufacturers' instructions usually recommended that dryers vent outdoors. An indoor lint trap kit poses a similar concern of increased humidity within the dwelling. "Long run" dryers might have an additional external exhaust fan to boost the exiting moist air through longer sections of vent pipe, as in apartments or dwellings where the vent cannot make a short direct connection from the dryer to the outside. Beyond issues with venting exhaust, other improvised efficiency efforts with conventional dryers attempt to harvest an input source of pre-heated air rather than using the conditioned air of the living space. One notable source of heat to pre-heat dryer air is to install ductwork allowing the device to suck hot air from a dwelling's attic. Tumble dryers are sometimes integrated with a washing machine, in the form of washer-dryer combos, which are essentially a front loading washing machine with an integrated dryer or (In the United States only) laundry centers, which stacks the dryer on top of the washer and integrates the controls for both machines in a single control panel. Often the washer and dryer functions will have a different capacity, with the dryer usually having a lower capacity than the washer. Tumble dryers can also be top loading, in which the drum is loaded from the top of the machine and the drum's ends are in the left and right sides, instead of the more conventional front and rear. They can be as thin as 40 cm in width, and may include detachable racks for drying items like plush toys andVentless dryers
Spin dryers
Condenser dryers
Just as in a tumble dryer, condenser or condensation dryers pass heated air through the load. However, instead of exhausting this air, the dryer uses a heat exchanger to cool the air and condense the water vapor into either a drain pipe or a collection tank. The drier air is run through the loop again. The heat exchanger typically uses ambient air as its coolant, therefore the heat produced by the dryer will go into the immediate surroundings instead of the outside, increasing the room temperature. In some designs, cold water is used in the heat exchanger, eliminating this heating, but requiring increased water usage. In terms of energy use, condenser dryers typically require around 2 kilowatt hours (kW⋅h) of energy per average load. Because the heat exchange process simply cools the internal air using ambient air (or cold water in some cases), it will not dry the air in the internal loop to as low a level of humidity as typical fresh, ambient air. As a consequence of the increased humidity of the air used to dry the load, this type of dryer requires somewhat more time than a tumble dryer. Condenser dryers are a particularly attractive option where long, intricate ducting would be required to vent the dryer.Heat pump dryers
A closed-cycle heat pump clothes dryer uses a heat pump to dehumidify the processing air. Such dryers typically use under half the energy per load of a condenser dryer. Whereas condensation dryers use a passive heat exchanger cooled by ambient air, these dryers use a heat pump. The hot, humid air from the tumbler is passed through a heat pump where the cold side condenses the water vapor into either a drain pipe or a collection tank and the hot side reheats the air afterward for re-use. In this way not only does the dryer avoid the need for ducting, but it also conserves much of its heat within the dryer instead of exhausting it into the surroundings. Heat pump dryers can, therefore, use up to 50% less energy required by either condensation or conventional electric dryers. Heat pump dryers use about 1 kW⋅h of energy to dry an average load instead of 2 kW⋅h for a condenser dryer, or from 3 to 9 kW⋅h, for a conventional electric dryer. Domestic heat pump dryers are designed to work in typical ambient temperatures from 5 to 30 °C. Below 5 °C, drying times significantly increase. As with condensation dryers, the heat exchanger will not dry the internal air to as low a level of humidity as the typical ambient air. With respect to ambient air, the higher humidity of the air used to dry the clothes has the effect of increasing drying times; however, because heat pump dryers conserve much of the heat of the air they use, the already-hot air can be cycled more quickly, possibly leading to shorter drying times than tumble dryers, depending on the model.Mechanical steam compression dryers
A new type of dryer in development, these machines are a more advanced version of heat pump dryers. Instead of using hot air to dry the clothing, mechanical steam compression dryers use water recovered from the clothing in the form of steam. First, the tumbler and its contents are heated to 100 °C. The wet steam that results purges the system of air and is the only remaining atmosphere in the tumbler. As wet steam exits the tumbler, it is mechanically compressed (hence the name) to extract water vapor and transfer theConvectant drying
Marketed by some manufacturers as a "static clothes drying technique", convectant dryers simply consist of a heating unit at the bottom, a vertical chamber, and a vent at top. The unit heats air at the bottom, reducing its relative humidity, and the natural tendency of hot air to rise brings this low-humidity air into contact with the clothes. This design is slower than conventional tumble dryers, but relatively energy-efficient if well-implemented. It works particularly well in cold and humid environments, where it dries clothes substantially faster than line-drying. In hot and dry weather, the performance delta over line-drying is negligible. Given that this is a relatively simple and cheap technique to materialize, most consumer products showcase the added benefit of portability and/or modularity. Newer designs implement a fan heater at the bottom to pump hot air into the vertical drying rack chamber. Temperatures in excess of 60 ºC can be reached inside these "hot air balloons," yet lint, static cling and shrinkage are minimal. Upfront cost is significantly lower than tumble, condenser and heat pump designs. If used in combination with washing machines featuring fast spin cycles (800+ rpm) or spin dryers, the cost-effectiveness of this technique has the potential to render tumble dryer-like designs obsolete in single-person and small family households. One disadvantage is that the moisture from the clothes is released into the immediate surroundings. Proper ventilation or a complementary dehumidifier is recommended for indoor use. It also cannot compete with the tumble dryer's capacity to dry multiple loads of wet clothing in a single day.Solar clothes dryer
The solar dryer is a box-shaped stationary construction which encloses a second compartment where the clothes are held. It uses the sun's heat without direct sunlight reaching the clothes. Alternatively, a solar heating box may be used to heat air that is driven through a conventional tumbler dryer.Microwave dryers
Japanese manufacturers have developed highly efficient clothes dryers that use microwave radiation to dry the clothes (though a vast majority of Japanese air dry their laundry). Most of the drying is done using microwaves to evaporate the water, but the final drying is done by convection heating, to avoid problems of arcing with metal pieces in the laundry. There are a number of advantages: shorter drying times (25% less), energy savings (17–25% less), and lower drying temperatures. Some analysts think that the arcing and fabric damage is a factor preventing microwave dryers from being developed for the US market.Ultrasonic dryers
Ultrasonic dryers use high-frequency signals to drive piezoelectric actuators in order to mechanically shake the clothes, releasing water in the form of a mist which is then removed from the drum. They have the potential to significantly cut energy consumption while needing only one-third of the time needed by a conventional electric dryer for a given load. They also do not have the same issues related with lint in most other types of dryers.Hybrid dryers
Some manufacturers, like LG Electronics and Whirlpool, have introduced hybrid dryers, that offer the user the option of using either a heat pump or a traditional electric heating element for drying the user's clothes. Hybrid dryers can also use a heat pump and a heating element at the same time to dry clothes faster.Static electricity
Clothes dryers can cause static cling, through the triboelectric effect. This can be a minor nuisance and is often a symptom of over-drying textiles to an extremely low humidity level. Fabric conditioners and dryer sheets are marketed to correct this condition.History
A hand-cranked clothes dryer was created in 1800 by M. Pochon from France. Henry W. Altorfer invented and patented an electric clothes dryer in 1937. J. Ross Moore, an inventor from North Dakota, developed designs for automatic clothes dryers and published his design for an electrically operated dryer in 1938.Lint build-up (tumble dryers)
Safety
Dryers expose flammable materials to heat. Underwriters Laboratories recommends cleaning the lint filter after every cycle for safety and energy efficiency, provision of adequate ventilation, and cleaning of the duct at regular intervals. UL also recommends that dryers not be used for glass fiber, rubber, foam or plastic items, or any item that has had a flammable substance spilled on it.Environmental impact
The environmental impact of clothes dryers is especially severe in the US and Canada, where over 80% of all homes have a clothes dryer. According to the US Environmental Protection Agency, if all residential clothes dryers sold in the U.S. were energy efficient, "the utility cost savings would grow to more than $1.5 billion each year and more than 22 billion pounds 0 billion kilogramsof annual greenhouse gas emissions would be prevented”. Clothes dryers are second only to refrigerators and freezers as the largest residential electrical energy consumers in America.See also
* Laundry-folding machine * List of home appliances *References
External links
* /books.google.com/books?id=yt0DAAAAMBAJ&pg=PA170&dq=1954+Popular+Mechanics+January&hl=en&sa=X&ei=pboPT5H_K8TuggfN7KDUAw&ved=0CDQQ6AEwAQ#v=onepage&q&f=true "What You Should Know About Clothes Dryers."''Popular Mechanics'', December 1954, pp. 170–175, basic principles of dryers even today. {{Authority control 19th-century inventions Dryers Home appliances Laundry drying equipment Products introduced in 1937