Refrigeration – Processes – Treating an article
Patent
1987-04-20
1988-06-14
Capossela, Ronald C.
Refrigeration
Processes
Treating an article
62388, F25D 2500
Patent
active
047503319
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the surface cooling of food products, of the type in which said products are subjected, in a confined zone thermally insulated from the surroundings, to the cryogenic action of particles formed by the expansion of carbon dioxide under pressure and in the liquid state through nozzles oriented toward the mean surface offered by the products in the course of the surface cooling, and of the type employing spraying under pressure. This surface cooling, or crusting, permits the subsequent treatment of all food products including the most fragile such as broccoli and mushrooms. As the case may be, after this "crusting", a deep freezing is carried out. According to the technique recalled above, the expansion of carbon dioxide is usually accompanied by an intense ventilation so that it is not possible to produce the cryogenic effect of the solid particles of the carbon dioxide snow directly on the surface of the product to be cooled. Moreover, the carbon dioxide snow is constituted by large particles which, in accumulating, form a layer of snow which hardly promotes a good thermal transfer.
An object of the present invention is to provide a process of this type whereby it is possible to obtain remarkable performances in respect of the thermal transfer of the carbon dioxide snow to the surface of the product; further, the cooling process and the equipment are particularly simple and reliable, with no risk of breakdown due to a clogging of the conduits by the solid particles of carbon dioxide; in addition, there is the benefit of very high precision owing to a correct determination of temperature in the cooling tunnel. These results are obtained, according to the invention, in that there is ensured a quasi-instantaneous sublimation of the solid particles of carbon dioxide in contact with the products by choosing nozzles of the type providing a spraying under pressure having an ejection section of between 0.2 sq mm and 1.13 sq mm and an ejection pressure of between 6 and 30 bars, producing a composite jet of fine solid particles whose sizes are between 20 microns. The fine solid particles are and 300 microns rapidly carried along in a gaseous current exclusively composed of carbon dioxide resulting from said expansion, the flow rate and the pressure of carbon dioxide being so regulated as to produce a flow rate of fine solid particles which is lower than 0.5 kg/hr per sq cm of the surface area of the product, the duration of the treatment being between 0.5 minute and 5 minutes (min).
All of these measures permit the obtainment of the mentioned results. the fineness of the particles carried along with the minimum of ventilation, i.e. with no accompanying stirring means, permit the deposit of a fine layer of micronic particles on the products to be cooled which is immediately sublimated to form a layer of snow, which ipso-facto ensures the best thermal transfer effect. Moreover, the random dispersion of the particles outside said surfaces is avoided. Further, by an ingenious regulation of the flow rate and the pressure of the carbon dioxide, the surface cooling is ensured under conditions of short duration with a minimum flow of solid particles.
The invention also concerns a surface cooling tunnel of the type comprising an elongated insulating body with an inlet and an outlet at the two longitudinal ends, a flat conveyor, a plurality of nozzles distributed in said elongated body, connected by a conduit and valves to a tank containing carbon dioxide under pressure, and this tunnel is characterised in that said nozzles are all oriented toward the flat conveyor and have ejection sections of between 0.2 and 1.13 sq mm.
The invention is now described with reference to the accompanying drawings in which the single figure is a perspective view, with a part cut away, of a refrigeration tunnel.
With reference to the drawings, a tunnel comprises an elongated insulation case 1 having a rectangular parallelepipedic shape with an inlet 2 and an outlet 3 for the products to be cooled. For example, the length
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Barthelmes Patrice
Dubreuil Thierry
Ottinger Claude
Capossela Ronald C.
L'Air Liquide
Robinson, Jr. Lee C.
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