Drying and gas or vapor contact with solids – Apparatus – Removable shelf or tray type
Patent
1998-01-30
1999-11-16
Bennett, Henry
Drying and gas or vapor contact with solids
Apparatus
Removable shelf or tray type
34238, F26B 1118
Patent
active
059835192
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a product tray for drying a product by means of contact heating by heating plates extending over the tray bottom.
Known product trays of the type mentioned consist of deep-drawn plastic materials, such as polypropylenes or polyethylene. Because of a change in their shape under the effect of heat, these trays are not always in form-fitting contact with the heating plate. Furthermore, their relatively thick walls hamper the heat transfer from the heating element to the product. However, a satisfactory and even heat transfer at the bottom of the product trays plays an essential role in the quality of drying by means of contact heating in a vacuum drying cabinet. The quality of drying is determined by the degree of drying, foaming and length of drying.
To assure even temperature distribution and an even degree of drying in the overall product, the following conditions must be met:
a. Stable shape of the product trays (in particular the bottom) during drying,
b. Good contact between the heating plate and the tray bottom over the entire surface, even small hollow spots constituting insulators hamper the heat transport,
c. An overall even wall thickness of the tray bottoms, and
d. Even heat distribution in the heating plates.
To meet these conditions better, product trays made of metal, such as stainless steel or aluminum, are known. However, damages to and unevenness in the bottom results during knocking the dry product cake out, which leads to uneven drying.
It is the object of the invention to avoid the mentioned disadvantages of known product trays.
In accordance with the invention, this object is attained in connection with a product tray of the type mentioned at the outset by a frame which constitutes or supports the lateral walls of the product tray, and by a bottom consisting of a thin, flexible, heat-resistant material with good heat conduction.
Features of preferred embodiments of the invention are recited in the dependent claims.
The following properties are among the advantages gained by means of the invention:
1. The flexible material of the bottom of the product tray allows optimal contact between the bottom and the heating plate. The material adapts to small unevennesses of the heating plate, so that no insulating air cushions are being created between the heating surface and the product to be dried.
2. The small thickness of the bottom allows a good heat passage, so that the heat is conducted into the product very quickly. Because of the resulting reduced length of drying time, the quality of drying is improved in comparison with known tray types. Comparative measurements have shown that reductions of the length of drying time of 40 to 500% can be achieved.
3. If the product is placed warm into the product trays, it is known that during the evacuation of the installation extensive cooling of the product mass takes place because of the evaporation of the volatile components. This leads to an increase in the viscosity of the product with the result of the undesired, too violent foaming of the product. Under certain conditions such foaming can lead to the soiling of radiating heating plates arranged above the product. With the product trays in accordance with the invention, the viscosity of the product remains low because of the rapid heat transfer, and foaming because of entrapped air is less marked.
4. Because of the good heat penetration, there is also faster cooling of the product at the end of the drying process, along with a further gain in time.
5. In most cases, tipping of the trays and slight knocking against the flexible bottoms for emptying the dried product cake out of the product trays is sufficient for a product removal free of losses to a large extent .
The invention will be described in detail in the following description and in the drawings, which represent exemplary embodiments. Shown are in:
FIG. 1, a vertical sectional view parallel with the lateral wall of a product tray in accordance with the invention on a heating plate,
FIG. 2, a detailed view of a ver
REFERENCES:
patent: 3807057 (1974-04-01), Noel
patent: 4190757 (1980-02-01), Turpin et al.
patent: 4455763 (1984-06-01), Elevitch
patent: 4677764 (1987-07-01), Cerny
patent: 4751368 (1988-06-01), Diafotes
patent: 4943534 (1990-07-01), Andreasen
International Search Report dated Aug. 6, 1997.
Bennett Henry
Bucher-Guyer AG
Gravini Steve
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