Metering expansion nozzle for CO.sub.2

Details Metering expansion nozzle for CO.sub.2 Metering expansion nozzle for CO.sub.2

1998-05-11

2000-06-13

Morris, Lesley D.

Fluid sprinkling, spraying, and diffusing

Including valve means in flow line

And fluid to gas expansion effecting means

239583, 239596, 239597, 62521, B05B 132

Patent

active

060738642

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an expansion nozzle and a method for making carbon-dioxide snow for spraying refrigerated or frozen items.
It is known from U.S. Pat. No. 3,815,377 to cool or shock-freeze refrigerated or frozen items, for example food items, by spraying them with carbon-dioxide snow produced through the expansion of liquid carbon dioxide in an expansion nozzle. For this purpose, the refrigerated or frozen items are typically located in a refrigeration or froster chamber, into which a supply line for liquid carbon dioxide leads; the expansion nozzle is disposed at the end of this line in the refrigeration or froster chamber. A throttle valve that regulates the flow-through is usually provided in the supply line. The CO.sub.2 is held, normally in liquid form, in a storage tank, where it is maintained in equilibrium with the CO.sub.2 gas phase above the liquid in the tank. The pressure in the tank is usually maintained at about 18 bar, and the temperature is maintained at about -23.degree. C. In the systems known up to now, usually two pipelines lead from the tank to the refrigeration or froster chamber. In one line, the liquid CO.sub.2 flows to the refrigeration or froster chamber, where it makes available the necessary cooling capacity. The second pipeline leads from the upper gas region of the tank to the refrigeration or froster chamber, and is connected to the first line by way of a stop valve shortly before it enters the refrigeration or froster chamber. The tank and the first line are insulated with a thick insulating layer, for example comprising PU foam, against the penetration of heat or loss of cold. Gaseous CO.sub.2 flows to the refrigeration or froster chamber through the second pipeline, which is not insulated. This serves to rinse the part of the liquid pipeline disposed behind the metering valve, as well as the expansion elements. To attain and maintain the desired operating temperature in the refrigeration or froster chamber, CO.sub.2 is usually sprayed into the refrigeration or froster chamber in cycles. To this end, a temperature measurement is performed in the refrigeration or froster chamber. If the temperature exceeds a set limit value, the supply of cooling medium is initiated, that is, the valves for liquid CO.sub.2 in the supply line are opened. If the temperature is below a set limit value, the supply of cooling medium is cut off, that is, the valves are re-closed. The initiation and cutoff of cooling medium supply is typically effected with magnet valves disposed in the supply line, outside of the refrigeration or froster chamber. After the supply of cooling medium has been cut off, the pressure in the adjoining pipe and the expansion elements drops to an ambient pressure of about 1 bar. If the pressure drops below the triple-point pressure of 5.18 bar while liquid CO.sub.2 is still in the supply line, a phase conversion into solid CO.sub.2 snow occurs. This solid CO.sub.2 snow can no longer exit the expansion elements, thereby clogging the system. In an unfavorable case, this can lead to a blockage of the valves and, in an extreme case, large portions of the entire pipeline. The pipelines must then be closed at the tank and thawed over a period of several hours. Furthermore, in an extreme case of blockage, the danger of a line rupture exists, because pressures of up to 60 bar can be present in the pipelines. To prevent such clogs, the liquid line behind the valve and the expansion element are re-rinsed by means of the gaseous CO.sub.2 from the second line. The CO.sub.2 gas flowing in forces the liquid out of the line system, and prevents a pressure drop below the triple point as long as CO.sub.2 liquid is in the pipeline.
A disadvantage of this apparatus is that additional cooling medium is required for rinsing the liquid line and maintaining the pressure in the liquid line with the CO.sub.2 gas. This CO.sub.2 gas does not contribute to the cooling capacity of the froster. To the contrary, the CO.sub.2 gas used in the re-rinsing process additionally warms the atmosphere in

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patent: 5611491 (1997-03-01), Bowers

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