Heat exchange – Conduit within – or conforming to – panel or wall structure – Opposed plates or shells
Patent
1997-01-13
1999-01-19
Flanigan, Allen
Heat exchange
Conduit within, or conforming to, panel or wall structure
Opposed plates or shells
62349, F25B 3902, F28F 314
Patent
active
058604715
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device, notably to a heat exchanger plate for a plate freezer.
BACKGROUND TO THE INVENTION
Many foodstuffs are heated, cooled, frozen or otherwise treated thermally by holding them in, or passing them through, the parallel gaps between adjacent horizontal plates of an horizontal plate heat exchanger, for example an horizontal plate freezer; or by holding the foodstuff in the vertical gap between adjacent vertical heat exchanger plates, for example of a vertical plate freezer. In the case of a horizontal plate freezer, the foodstuff can be loaded and unloaded manually or automatically and this form of freezer is of primary use in the treatment of discrete individual units of the foodstuff, for example containers of prepared meals and the like. In the vertical plate freezer, the foodstuff is usually loaded into the vertical chamber between adjacent plates manually and as a fluent mass of the foodstuff, for example as a slurry, as with a fruit juice or puree, or as a mass of small units of the foodstuff which are not kept discrete, as with a mass of loose fish or meat which is to form a frozen block. For convenience, the invention will be described hereinafter in terms of vertical heat exchange plates, notably a vertical plate freezer, although it can equally be applied to a horizontal plate freezer or other heat exchanger.
Heat exchange fluid flows through bores or conduits within the structure of the heat exchange plate to supply heat to or remove heat from the foodstuff. Such plates are usually large, typically ranging from 0.5 to 2.5 meters by from 1 to 4 meters and are made by extruding the plate from one or more blocks of solid metal. Initially, such plates were made from mild steel, but this was replaced by the use of aluminium as aluminium extrusion techniques became accepted in the metal fabrication industry.
However, despite the advantageous thermal properties of aluminium, its use gives rise to problems. Due to the ease with which aluminium forms a food-soluble oxide/hydroxide on its surface when left in contact with food for prolonged periods, care has to be taken during the use and cleaning of aluminium freezer plates between uses to minimizes the risk of such corrosion and contamination occurring. In some countries, for example the USA, the use of bare aluminium in contact with foodstuffs under conditions where contamination of the foodstuff could occur presents particular health problems. In some applications, for example in the canning of food or beverages, it is possible to apply a protective plastic or other coating to the exposed aluminium surface. However, where solids are being handled, as with blocks of foodstuff or meal portions in metallic containers, abrasion and erosion of surface coatings will occur, notably on load-bearing surfaces as present in a plate freezer. Such coatings are not therefore practical in such applications.
Stainless steel is corrosion resistant and finds widespread use in the food processing industry. Stainless steel cannot be cast or extruded and must therefore be machined or pressed where complex shapes are required. However, stainless steel is difficult to machine and its large scale use has been restricted to applications where the metal can be formed into the desired shape by pressing, for example in heat exchanger plates which are pressed out from sheet metal. It has been considered impractical and uneconomic to manufacture a freezer plate wholly from solid stainless steel.
It has been proposed to fabricate a freezer plate from a serpentine tube, which is to carry the heat exchange fluid, sandwiched between galvanised steel or stainless steel sheets. However, since the tube contacts the adjacent sheets along only a narrow line of contact, such plates give poor and uneven heat transfer from the tube to the sheet. This results in high energy input requirements to operate the plate freezer effectively, and in localised areas of excessive and/or insufficient freezing of the foodstuff in contact with the sheets. In general,
REFERENCES:
patent: 2190280 (1940-02-01), Banigan et al.
patent: 2805557 (1957-09-01), Hilger
patent: 3126215 (1964-03-01), Raskin
patent: 3322190 (1967-05-01), Johnson, Jr.
patent: 3423952 (1969-01-01), Pugh
Perryment Alan John
Stanley Colin Michael
Flanigan Allen
Gunter Jr. Charles D.
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