Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1981-11-23
1984-12-04
Schwartz, Larry I.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 48, 34 55, F26B 2110
Patent
active
044855664
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a tumble dryer for the drying of laundry, comprising a drum arranged in a housing and driven by a motor, heating means for heating the air entering the dryer and being guided through the drum, first and second temperature sensing means for sensing the temperatures of the air led into the drum and being discharged from the drum, and control means connected to the temperature sensing means for energizing and de-energizing the heating means and the drum motor.
Such a tumble dryer is known for example from the British Pat. No. 1,470,163. The temperature sensing means of this tumble dryer sense the temperatures of the air supplied to the drum and the air discharged from the drum and de-energize the heating means when a pre-determinated temperature difference has been reached. The temperature of the air supplied to the drum is sensed after passing the heating means. This temperature neither varies with room temperature nor with room humidity. After de-energizing the heating means the drum motor remains energized for a pre-determinated period of time or is de-energized when a certain temperature of the discharged air is reached. A dependence of the further running period on the contents of the drum or the remaining humidity of the drum contents is not provided.
From the Austrian Pat. No. 190 024 there is further known a tumble dryer with heating means being provided above the drum and the air entering the dryer being guided twice along these heating means and entering the drum from above after having been heated solely by the heating means. No temperature difference control means are provided.
The object of the invention is to provide a tumble dryer of the type described at the beginning, which on the one hand permits a precise de-energizing of the heating means with the lowest possible circuit complexity, and on the other hand ensures a cooling down period dependent on the drum content and humidity with further energizing drum motor after the de-energizing of the heating means until the desired remaining humidity of the drum content is achieved.
According to the invention, this object is solved in that the air led to the drum is guided for preheating before passing the heating means over and around the drum, that the first temperature sensing means is arranged for sensing the temperature of the preheated air upstream of the heating means and that the control means de-energizes the heating means upon reaching a first presettable temperature difference of the preheated and the discharged air and de-energizes the drum motor upon reaching a second temperature difference of the preheated and the discharged air.
With this arrangement, it is achieved that on the one hand the temperature difference between the preheated and discharged air is kept relatively low during the entire drying cycle and the de-energizing of the heating means can take place with a relatively small temperature difference. On the other hand, the cooling period after de-energizing the heating means and with still energizing drum motor is not restricted to a pre-determined period of time or determinated merely dependent on the temperature of the discharged air, but is automatically adapted to the drum filling and also to its humidity. After termination of the drying cycle, the humidity of the dried laundry lies within the range desired for the further handling, namely independent of the filling degree of the drum.
The first temperature sensing means is expediently disposed directly in front of the heating means and protected against heat radiation therefrom.
The second temperature sensing means is advantageously disposed at the end of an outlet duct for air discharged from the dryer.
The temperature sensing means are expediently thermistors and the control means is an electronic control means.
Alternatively the temperature sensing means may be vapor or liquid filled sensors and the control means mechanical control means.
In accordance with the desired remaining humidity of the laundry upon termination of the drying cycle of
REFERENCES:
patent: 2933823 (1960-04-01), Cramer et al.
patent: 3513566 (1970-05-01), Shacklock et al.
Ranco Incorporated
Schwartz Larry I.
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