Heat exchange – Structural installation – Heating and cooling
Reexamination Certificate
1999-12-03
2001-04-24
Lazarus, Ira S. (Department: 3743)
Heat exchange
Structural installation
Heating and cooling
C165S919000, C312S236000
Reexamination Certificate
active
06220338
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an installation for the cold storage of food in receptacles carried on meal trays with localized reheating of certain foods.
Cabinets and trolleys performing these functions in the catering field, in hospital environments, in aircraft, in trains and in boats, are already known.
DESCRIPTION OF THE RELATED ART
In current systems, cold storage is either accomplished by means of mechanical ventilated chilling, that is to say, using a stream of cold air generated by passing a stream of air over the evaporator of a refrigerating unit, or by means of carbon dioxide in the gaseous phase resulting from the sublimation of dry ice contained in a cold reservoir located in the upper part of a cabinet, or by means of heat pipe evaporators arranged around the sides of the trays while their condensers are in a cold reservoir.
Whichever of the above techniques is used, the heat is extracted from the receptacles that are to be cooled by the air contained in the storage compartment. This means that the entire volume of air in this compartment must be cooled and the result is a large refrigeration load, especially given the fact that overall efficiency is low owing to the various transfer of heat by conduction or convection.
To this is added the difficulty of keeping the temperature the same at each level in the compartment.
The food is reheated either by means of electrical resistors arranged in a support on which the dishes to be reheated are placed, or by a stream of hot air directed at the receptacles to be reheated, in which case the receptacles are placed in a division of the storage compartment.
Resistance heating produces too fierce a heat which can spoil the taste of the food and cause them to stick to the bottom of the dish. Heating with a stream of hot air is rarely even throughout the storage compartment and necessitates the creation, in this compartment, of the separation between the area of receptacles to be kept cold and the area of receptacles to be reheated.
Added to these drawbacks which affect the evenness of the cold storage and of the reheating are drawbacks inherent in the use of dry ice, namely the difficulty of precise release to achieve the desired cold storage by limiting the emission of carbon dioxide, difficulties in achieving an even and constant temperature at the different levels at which the meal trays in the storage compartment are disposed and, above all, the emission of carbon dioxide. This last drawback is particularly serious when it comes to cabinets or trolleys used in closed spaces having a limited volume, such as aircraft and passenger trains because, on journeys lasting several hours, the amount of carbon dioxide emitted reaches thresholds close to those dangerous to humans.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to overcome these drawbacks by providing a cabinet in which the refrigeration circuit keeps the food by reducing the intermediate transfers from the cold reservoir and limits the refrigeration demand, and hence the volume of the reservoir and the emission of carbon dioxide, if dry ice is used, and in which the reheating means provide a gentle temperature rise, sufficient to reheat the food without spoiling its taste.
The invention relates more particularly to an installation composed of, on the one hand, a cabinet comprising two superimposed compartments thermally insulated from the exterior, namely an upper compartment forming a cold reservoir, and a storage compartment fitted with shelves to hold the meal trays, and, on the other hand, with meal trays made of an insulating material with vertical through wells in which the receptacles containing the food can be positioned, each tray optionally having at least one insulating lid.
In the installation according to the invention, each shelf is thermally insulating and comprises, in each of its areas that support the base of the receptacles carried by the meal tray or trays which it supports a heat pipe tubular beat exchanger each heat exchanger being connected, by intermediate pipes, to the supply and return branches, respectively, of a refrigerating heat pipe circuit, while at least one of the heat exchangers in each shelf is provided with electrical heating means, and the cold reservoir consists of a leaktight box made up of tubular heat exchangers and/or heat exchangers containing tubular heat pipe heat exchangers whose tubular networks are interconnected and are connected, respectively, directly to the return branches of the refrigerating heat pipe circuit and, via a buffer tank that thermally homogenizes the cold working flow circulating around the heat pipe network, to the supply branches of this refrigerating circuit.
By means of this arrangement, the refrigerating power of the cold reservoir is taken by heat pipe heat exchangers and conducted very rapidly by the supply branches to the heat pipe heat exchangers located in the shelves, in contact with the bases of the receptacles. It is clear therefore that heat is transferred only via the heat pipe network and by direct conduction between this network and the bases of the receptacles, thus making it unnecessary for heat to be transferred by air which reduces heat transfer efficiency. The result is that the refrigeration load that has to be charged is reduced, which makes it possible to reduce the size of the reservoir and, if using dry ice, to reduce the emission of carbon dioxide by reducing the amount of dry ice taken on board and the refrigeration capacity required.
The reheating of the dishes also benefits from an improvement in the efficiency of the thermal transfer, as it is effected by a heat pipe heat exchanger in contact with the receptacle.
In one embodiment of the invention, the heat pipe heat exchangers contained in the leaktight box of the cold reservoir are composed of vertical tube bundles projecting up from manifolds radiating out around the buffer tank and descending toward this tank.
The tube bundles improve the exchanges with the cold working fluid or the dry ice placed in the cold reservoir.
As a preference, cold bodies each consisting of a hollow body, made of a leaktight material that is a good heat conductor, having a capacity of between 2 and 30 cm
3
and containing a eutectic liquid whose freezing point is below 0° C., are in suspension in a fluid having a freezing point lower than the liquid contained by the cold bodies, fill the cold reservoir so as to be in direct contact with the tube bundles which secure them and contain them.
In this application, which uses cold bodies capable of storing the maximum amount of latent heat in the minimum of space, the volume of the cold reservoir can be still further reduced, especially as the transfer of heat between the heat pipe tube bundles and the cold bodies occurs either directly or via the fluid in which they are suspended.
Advantageously, the walls of the upper compartment and of the leaktight box of the cold reservoir are traversed by two pipes that can be connected externally to the supply and return branches, respectively, of an installation for recharging the installation with refrigerating fluid cooled to a temperature below the freezing point of the fluid contained in the cold bodies, while the walls of the box support a number of approximately vertical internal plates projecting between the bundles so as to form baffles which define, with these bundles, a preferred circuit that forces the refrigerating fluid to circulate throughout the entire reservoir when the refrigerating capacity is being renewed.
Other features and advantages will be found in the description which follows with reference to the attached schematic drawing showing, by way of examples, several embodiments of this installation.
REFERENCES:
patent: 2 391 687 (1978-12-01), None
patent: 2 594 942 (1987-08-01), None
patent: 2 594 317 (1987-08-01), None
patent: 90/02509 (1990-03-01), None
Ciric Ljiljana V.
Italinnova S.A.S.
Lazarus Ira S.
Oliff & Berridg,e PLC
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