Background Art Hot air generated by using electric heating or by appropriate means rises upwards through a duct and enters into the drying chamber through the openings provided. In the chamber wet clothes (dresses) are hanged through hangers, clips etc. When the hot air comes into contact with the wet clothes, the air temperature drops, air density increases and-is pushed down and leaves as cold saturated air at the bottom (which is open) to the atmosphere. In the process the cloth gets dried.

The age-old method of drying of clothes after soap washing and rinsing with water is by exposing the clothes to sunshine in the open. Due to the combined action of radiation from sun and air (wind) the clothes dry and the time of drying varies depending upon the climatic conditions, type of cloth, thickness etc. The sun drying quite often brings in problems for housewives during rainy season and also for people living in small living areas, flats etc. In order to overcome the drudgery to housewives modern washing machines equipped with spinners (centrifuges) were introduced. Even after spinning the residual moisture content which ranges from 20 to 25% of the weight of the cloth has to be removed by sun drying.

For convenient and faster drying forced flow cloth dryer was developed and is being marketed. The drier is essentially a rectangular box with front opening for keeping the wet cloth after spinning in a washing machine (centrifuge). A motorized central shaft gives a slow rotating motion to the cloth. A blower kept inside the rectangular box passes air heated by an electrical heater through the chamber. Hot air is contacted with the clothes continuously and leaves the chamber through an outlet port. The process is repeated till the clothes are dry. Due to the lumping of clothes inside the chamber, quite often folding and inadequate drying occur. Due to the presence of moving parts, the cost of the equipment also is relatively higher.

Further modified version of forced flow with rotating shaft and suction arrangement is invented by Huang E. J. Mijuel, Chao Suyueh, Yu Chin-Ching and Hsu Chi-Chu as

presented in the American Patent No. 4,811,495 dated 14-3-1989. Again due to the presence of moving parts the cost of the equipment is higher relatively.

An extensive literature search on cloth and laundry-drying equipment's revealed that the drier as envisaged in the present invention with reverse airflow natural convection drier are not reported.

The apparatus as per the U. S. Patent No: 4471537 entitled"Dryer apparatus having an improved air circulation"is working on the principle of natural convection with provision to speed-up the convective air circulation effect using the auxiliary blower provided. The system collects partially cooled air (by the drying process) and by the chilling unit cooling the air and thereby condensing the humidity. The dehumidified and cooled air is again heated and the procedure is continued. The drying system comprising of compressor unit for chilling and cooling of air and interconnecting connections becomes complicated and costly. In the system, circulation of air is achieved by the cooling provided by the refrigeration compressor unit. The system as a whole is complicated, cumbersome and costly.

To overcome the disadvantages of the conventionally used sun drying, spin drying in a washing machine followed by forced air flow drying with tumbling of cloth research work was carried out by us for further development of an improved natural convection drier.

Objects of the invention The main objective of the present invention is to provide a convection drier, which obviates the drudgery, associated with the sun drying and the drawbacks associated with forced flow drying of clothes.

Another objective of the present invention is to make the heated air to flow downward after contacting the wet clothes hanged vertically in the drying chamber.

Brief description of the accompanying drawings Figure 1 represents the front elevation of the drier, Figure 2 represents the sectional top view at XX and Figure 3 represents the sectional side view at YY.

Detailed description of the invention Accordingly, the present invention provides a convection drier useful for drying wet materials, which comprises a drying chamber (1) having closed top and open bottom, means for holding or hanging material (2) and (3) to be dried and provided with a closing means (11), the hot air needed for drying is produced by a heat source (5) located at the lower portion of the drier and heated air is directed to upper zone of the dryer through a duct (7), the said hot air from upper zone flows downwards contacting the wet materials (4) and escapes at the bottom (9) and in the process the wet material gets dried up.

In an embodiment of the invention, insulating materials selected from cotton, glass wool, wood, PU foam and thermocol insulates the chamber at the outer surface.

In another embodiment of the invention, the means for controlling the temperature are switch and thermostat.

In still another embodiment of the invention, the means for closing the chamber is a door or shutter.

In yet another embodiment of the invention, the desired amount of exit air can be recycled with the aid of control dampers (valves) to result in higher humidity and higher temperatures inside the drying chamber whenever needed for specific requirements.

In yet another embodiment of the invention, the drier is used for drying different types of clothes from different materials with controlled conditions of temperature as desired.

In yet another embodiment of the invention, the chamber is provided with fixtures and perforated trays inside the drying chamber, instead of hanger for clothes for drying granular materials.

In one more embodiment of the invention, the principle on which the development of the improved natural convection drier modified for the drying of clothes of the present invention is as follows.

Hot air generated by appropriate means rises through a duct and enters the drying chamber.

Wet clothes to be dried are hanged in the chamber using hangers, clips etc so as to fill the volume of the drying chamber from top to bottom. The hot air occupies the top most zone of the drier. As it comes into contact with the wet clothes the temperature drops and the cold air descends down and finally escapes into the atmosphere through the bottom. At the bottom wire mesh is provided to partially regulate and balance the out flow of cold air.

The present invention provides a natural convection drier useful for the drying of wet clothes which comprises a drying chamber (1) in which rods (2) are provided for hooking or fixing hangers (3) clips etc for fixing of clothes (4) to be kept in hanging position. The

hot air needed for the drying is generated, as the case may be depending upon the mode of heating, by electrical heating element (5). Fresh air enters through the opening (6), gets heated up, rises through the duct (7), and enters the drying chamber (1) at inlet port (8). As the hot air at (8) comes into contact with the clothes (4) the air gets cooled, density of air increases and flows down and finally escapes through the wire mesh (9) to the atmosphere.

Thus, fresh air from atmosphere enters at (6) and cold humid air leaves at the bottom (9) and in the process the clothes get dried up. Regulating the surface temperature of the heating system (5) or thermostat in the case of electric heaters controls the temperature of air. To minimize the heat loss to the surroundings the dryer body is insulated on the outside with insulating materials (10). The drier can dry clothes made of different materials and the drying conditions can be suitably selected.

Instead of allowing the escape of complete humid air to the atmosphere at (9) part of the air recycled by simply partially closing the section (9) and also the fresh air inlet at (6). A damper control valve fitted at the bottom of the common separation wall of air inlet chamber and air exit allowed proper control of the air recirculation. The air got circulated automatically. As hot air rises through the duct (7), suction is automatically created at (6) by which a portion of humid air is sucked in and depending upon the opening area at (6) fresh air was sucked in. Partial recycling carried out with the help of control valves (dampers) allowed higher humidity conditions inside the drier and higher temperatures throughout the drying chamber.

By providing supporting fixtures in the drying chamber for keeping perforated trays granular materials were dried instead of the laundry clothes.

The use of the improved drier of the present invention is described in detail in the following examples, which are provided by way of illustrations only and therefore should not be construed to limit the scope of the invention.

Example 1 Drying of clothes after washing and hand squeezing: Different types of dresses (3.8 kg) made out of synthetic fabric, cotton and cotton-synthetic mix were soaked in water, taken out, hand squeezed to remove part of the water and placed

in the drier using hangers. The hot air was generated using electrical heaters and the maximum temperature at the top layer in the drier was controlled at 70°C. There was a moisture pick up of 4 kg and it took 5 hours for the complete drying. Initially, for the first one hour, about 500 grams of condensed water was collected in a collection tray kept at the bottom of the drier.

Example 2 Drying of clothes after washing and spin drying in a washing machine: The clothes as mentioned under example 1 were washed in a washing machine after soaking in water and partially dried using the spinner. 3.8 kg of dry cloth had the adhering water content of 2 kg. It took 3 hours for the complete drying. There was no dripping of condensed water.

Example 3 Drying of clothes after washing and hand squeezing, 50 % of exit air recirculated Different types of dresses (3.76 kg) made out of synthetic fabric, cotton and cotton- synthetic mix were soaked in water, taken out, hand squeezed to remove part of the water and placed in the drier using hangers. Controlling the damper valves fifty percent of exit air is re-circulated. The moisture pick-up was 4.91 kg, and it took five hrs for the complete drying. The total quantity of condensed water was 1000 gms.

Example 4 Drying of Granular materials Removable perforated trays were incorporated inside the drying chamber. Freshly harvested materials like coconut (cut into two halves), chillies, ginger, and garcinia cambogia were dried. The time of drying varied from 20 to 48 hrs. The time of drying depended upon the temperature, initial moisture content, final moisture content desired and quantity of material kept for drying.

Advantages of the invention The main advantages of the convection drier of the present invention are (1) The design is simple, easy to operate, compact and cost of fabrication of the drier comparatively less.

(2) The drier can dry different types of clothes made of different materials.

(3) There is no lumping of cloth and consequently no folding marks on the cloth due to drying.