Patent Application
20240376661
This invention relates to clothes and fabrics dryers in general, and tumble dryers in particular.
In a tumble dryer, a horizontal drum inside a cabinet rotates wet clothes to create air space between them. Heated air is circulated through the drum and between the clothes to evaporate and remove their moisture. The air leaves the drum through a lint screen or filter.
During this process, the clothes deform and rub consistently against each other, which causes compression, breaking, and separation of fibers from them. The wear and tear to the clothes is substantial and negatively affects their texture, color, softness, appearance, and useful life. Even the damage to new clothes is visible after the first drying. The amount of lint collected on the lint screen is evidence of the damage to the clothes.
Experiments have shown that heating of the clothes in tumble drying is not responsible for damages such as shrinking or discoloration. The mechanical agitation by tumbling and blowing air is the sole cause of all damage to the clothes including shrinkage, color change, wear, and tear. As an example, in a 30 min drying cycle, the clothing fibers are compressed and released a few thousand times.
In addition to damaging clothes, tumble drying also harms the environment. Microfibers from clothes pass through the dryer lint screens into the environment and pose a threat to human health. They have been found in ocean fish, beer, and even placentas of babies.
Worldwide, about one million ton of microfiber are blown into the air from tumble dryers annually. Besides households, tumble drying is used in businesses such as hospitality, healthcare, factories, and labs. The economic losses and environmental damages have global proportions.
The objects of this invention are:
In a tumble dryer, a horizontal drum inside a cabinet rotates and separates wet clothes to create air space between them. Hot air is blown through the drum and between the clothes to evaporate and remove their moisture.
The present invention uses intermittent rotation of the drum to reduce the time that clothes deform and rub against each other, and thus, reduce the wear to them. The hot air is continuously blown to essentially maintain the same drying time as in a regular dryer.
In a continuing cycle, The drum rotates for a given first time period to separate the clothes and let the moisture escape from them. Then, the drum stops and stays stationary for a given second time period to allow drying of clothes exposed to the hot air, outward transfer of moisture within the clothes, and heating of clothes by the hot air for further drying.
In a tumble dryer, a horizontal drum inside a cabinet rotates wet clothes to create air space between them. Hot air is blown through the drum and between the clothes to evaporate and remove their moisture.
In newer dryers, the drum has an open front end to receive wet clothes and a closed back end with a shaft for attachment and rotation via bearings to the cabinet. The cabinet has a door that covers the front end of the drum.
The drum has a few axial blades on its internal surface to lift the clothes during rotation. The clothes drop at the top of the drum by gravity and separate from each other.
The cylindrical surface of the drum is perforated. An enclosure around the drum creates a space around the drum. Hot air enters the space and flows through the perforations into the drum.
The air circulation system includes a blower, a heater, and ducts, having a first opening to receive air from outside the cabinet and blow it over the heater into the space between the drum and its enclosure. The air leaves the drum through a second opening at the open end of the drum, passes through a lint screen and leaves the cabinet through a third opening.
Some dryers use a heat pump as the heater in a closed loop air circulation system for energy efficiency. The air is heated by the heat pump condenser, enters the drum, and heats the cloths, and picks up their moisture. The moist air returning from the drum is then cooled down and dried by the heat pump evaporator and recirculated to the heat pump condenser.
The drum is rotated by a pulley-belt drive system with a first pulley fixed at the end of the drum shaft coupled to an electric motor through a second pulley and a belt.
A control system allows drying option setting by the user via an interface and controls the running time and air temperature accordingly. In advanced dryers, the control system monitors and controls the dryness of the cloths through humidity or temperature sensors.
If the difference in air temperature entering and leaving the drum is small, it indicates that either the clothes are dry, or the entering air temperature is too high. In this condition, the control system reduces the air heating level or ends the drying process.
In older versions of tumble dryers, the wall of the drum is not perforated. The back end of the drum is also open and is covered by a vertical wall. Hot air enters the drum through a perforated portion of the vertical wall. The drive system uses the drum as a pulley with a belt around it coupled to a pulley on the motor shaft.
For complete elimination of the wear to the clothes in a tumble dryer, they should be kept stationary, but the hot air cannot go through the bulk of clothes for convective heating, and clothes have low conductivity and cannot efficiently conduct the heat through them. Even if heated in any way, the vaporized moisture cannot escape easily through the layers of clothes. The rotation is also needed to prevent creasing of the clothes.
Also, the drum cannot be rotated below a certain speed to reduce the duration and severity of clothes deforming and rubbing because it cannot lift the clothes from its bottom side and drop them at the top side for separation.
The present invention uses intermittent rotation of the drum in any tumble dryer, such as those described above, to reduce the time that clothes deform and rub against each other, and thus, reduce the wear and tear to them. The hot air blows continuously so the total drying time remains essentially the same as in a regular dryer.
According to the present invention, in a repeating cycle, the control system rotates the drum for a given first time period to separate the clothes and remove moisture from them. The control system then stops and keeps the drum stationary for a given second time period to allow outward transfer of moisture within the body of the clothes, convective heating and drying of clothes exposed to the hot air, and some conductive heating of the bulk of the clothes in contact with the drum. The drying air is heated, enters into the drum, heats the clothes, removes moisture from the cloths, and leaves through the lint screen as in a standard tumble dryer.
The principle of the invention applies to all types of tumble dryers. The control system of the dryer of the invention has additional features to automatically control the intermittent rotation of the drum and the corresponding temperature or flow of the circulating air as required.
During each rotating state, the clothes are shuffled and reoriented. This helps redistribution of temperature and moisture inside and between the clothes. As a result, in the next stationary state, heat transfer and moisture removal will be more uniform and efficient.
A dryer with perforated drum is preferred for the present invention as it allows more distributed heating of the exposed clothes, higher rate of heating to the bulk of clothes in contact with drum wall through convection and conduction, and additional moisture removal at the perforations. This is especially helpful for optimized heating and drying during the stationary state of the drum.
The duty cycle of the dryer is defined as the duration of rotation of the drum to the total drying cycle time. The smaller the duty cycle, the less the deformation, rubbing and wearing of the clothes. The amount of wear and tear to the clothes as well as separated lint are proportional to the duty cycle. Therefore, if the dryer runs at a duty cycle of 25%, the wear and tear resulting from the process of the invention would be 25% that of a standard tumble dryer.
As an example, rotate the drum for 3 seconds and keep it stationary for 9 seconds for a duty cycle of 3/12 or 25%. The drum speed is about 60 rpm. So, in 3 sec the drum rotates 3 times which is quite sufficient for tumbling, shuffling, aerating, and smoothing the clothes.
The rotation duration could be as little as the time for a few turns. The goal is to minimize the stationary state duration to the extent that the drive system capabilities and the minimum required rotation allow. To the purpose of the present invention, a direct drive system is recommended for higher efficiency, lower noise and inertia, and faster response.
A higher duty cycle places less stringent conditions on the dryer and clothes but also with less reduction in wear and tear. For example, the dryer can be easily run with the drum turning for 5 sec and stopping for 5 sec resulting in a duty cycle of 5/10 or 50% which is still considerable.
During the stationary state, the amount of air flow or temperature may be reduced by the control system for optimized and distributed heating of the clothes.
During the drum rotation, higher air flow or temperature may be set by the control system to maximize heat input to the clothes. This allows maximum removal or moisture during the drum rotation and continued evaporation of moisture during the stationary state.
Cloth balls or towels have been added to the wet cloths to reduce the drying time. The present invention can even take further advantage of these tools for humidity transfer during the stationary state.
This application has priority date of provisional patent application 63/463,281 filed 1, May 2023.
