Short answers, pulled from the story.
The first patented automatic clothes dryer was invented by African American inventor George T. Sampson in 1892, earning U.S. Patent 476,416. A hand-cranked predecessor was built by M. Pochon of France as early as 1800, and Henry W. Altorfer patented the first electric clothes dryer in 1937.
A conventional electric dryer uses 3-9 kilowatt-hours per load. A condenser dryer uses around 2 kilowatt-hours, while a heat pump dryer cuts that to roughly 1 kilowatt-hour. Mechanical steam compression dryers operate in a similar efficiency range as heat pump dryers.
Failure to clean the dryer is the leading cause, accounting for 34% of residential dryer fires according to the US Fire Administration. From 2008 to 2010, fire departments responded to an estimated 2,900 clothes dryer fires per year in the United States, resulting in an annual average of 5 deaths, 100 injuries, and 35 million dollars in property loss.
A heat pump clothes dryer uses a heat pump to condense moisture from the drum air and reheat that air for re-use, rather than exhausting it outside. This closed loop allows heat pump dryers to use up to 50% less energy than conventional electric or condenser dryers, consuming about 1 kilowatt-hour per load versus 2 kilowatt-hours for a condenser dryer.
Over 80% of US and Canadian homes have a clothes dryer, and dryers rank as the second largest residential electricity consumers in America after refrigerators and freezers. The US Environmental Protection Agency estimates that widespread adoption of energy-efficient dryers would prevent more than 10 billion kilograms of greenhouse gas emissions and save over 1.5 billion dollars in utility costs annually.
Ultrasonic dryers use high-frequency signals to drive piezoelectric actuators that physically shake fabric, releasing water as a mist that is then removed from the drum. They can dry a load in about one-third the time of a conventional electric dryer while consuming significantly less energy, and they avoid lint buildup issues common in other dryer types.