US3553971A

US3553971A - Refrigeration of mobile containers

Info

Publication number: US3553971A
Application number: US784303A
Authority: US
Inventors: Terence Fursdon Crang
Original assignee: VORTAIR ENGINEERING Ltd
Current assignee: VORTAIR ENGINEERING Ltd
Priority date: 1967-12-19
Filing date: 1968-12-17
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12
Also published as: CH483347A; GB1182660A; FR1595410A; DE1815578A1

Abstract

A TRANSPORTABLE CARGO-REFRIGERATING APPARATUS IN WHICH THE CONTAINER OF THE APPARATUS IS REFRIGERATED WITH COLD AIR PRODUCED BY COLD AIR GENERATORS OF THE VORTEX TUBE TYPE. THE HOT AIR OUTLET PIPES OF THE VORTEX TUBE MAY BE CONNECTED TO HEAT THE CONTAINER SO THAT THE APPARATUS CAN BE USED TO TRANSPORT BOTH FROZEN GOODS AND GOODS THAT NEED TO BE KEPT AT A TEMPERATURE ABOVE THAT OF THE AMBIENT ATMOSPHERE.

Description

.'r. 1;'.cRANG REFRIGERATION 0F MOBILE CONTAINERS med neo. 17. 196e mill- UnitedStates Patent REFRIGERATION oF ronn CONTAINERS Terence Fursdon Crang, Wootton, Isle of Wight, England,

assignor to Vortair Engineering Limited, London, England Filed Dec. 17, 1968, Ser. No. 784,303 Claims priority, application Great Britain, Dec. 19, 1967,

v 57,602/ 67 Int. Cl. Fb 9-/02 U.S. Cl. 62-5 8 Claims ABSTRACT 0F THE DISCLOSURE The invention relates to the cooling of mobile heatinsulated containers of the type used for the transport of refrigerated cargo by road, rail or sea. These containers, which are usually from 20 to 35 feet long and 8 to 10 feet in breadth andheight and insulated with 4 to 6 inches of heat-insulating material, are packed with frozen produce at the despatch point and are then placed upon specially constructed road vehicles or railway trucks from which they are off-loaded at the destination. Alternatively, the containers may be semi-permanently attached to a road or rail vehicle and loaded and unloaded in situ. For sea transport, either the containers mounted on the vehicle are loaded complete into a sea-going vessel, for example a cross-channel car ferry, or the containers are oit-loaded on to the decks or into the holds of special container ships. This last-mentioned type of refrigerated container is coming into increasing use as time goes on.

At present such containers are refrigerated in two ways. The rst 'Way is by means of eutectic hold-over plates, which are hollow plate-like boxes lled with an eutectic freezing solution which is frozen before departure by connecting the eutectic plates to stationary refrigerating machines. The frozen eutectic solution then gradually thaws during the journey by absorbing heat from the container more or less at a constant temperature. Such eutectic plate systems are only useful for short journeys.

The second method of refrigeration is by means of a portable refrigerating machine mounted on the container or on its chassis or on the carrying vehicle. This is the system most Widely used for longer journeys. Experience of operators has shown that the normal vapour compression refrigerating machine suffers from the vibration and rough handling associated with road and rail transport, with consequent high replacement and maintenance costs. To provide electrical power for the vapour compression refrigerating machine, it is necessary to carry on the vehicle or chassis an -engine driven generator, the engine usually being a separate auxiliary unit.

The present invention is based on an appreciation of the possibility of substituting for the somewhat unreliable vapour compression refrigerating machinery at present used for cooling transport containers, a simple, reliable and maintenance-free system of refrigerating the containers 'with cold air produced by cold air generators of the vortex tube type. Y

The vortex tube is a known means of producing cold air and also hotl air from inlet air at ambient temperature. The vortex tube consists basically of a circular chamber into which pressurised air is introduced by means of tan- 3,553,971 Patented Jan. 12, 1971 gential nozzles to form a high energy vortex. In a vortex of this type, cold air is found at the centre of the vortex and hot air at the outside. By means of suitable orifices, cold air is bled-off through a tube at one side of the vortex chamber and hot air through a tube on the other side. With a pressure of 100 p.s.i. for example it is possible to obtain temperatures below 32 F. from the cold outlet and temperatures of albove 200 F. from the hot outlet.

Therefore, if the cold air outlet of a vortex tube or each of the cold air outlets of a plurality of vortex tubes is connected to the interior of an insulated container of the type being considered and the tube or tubes are fed with air under pressure from a compressor driven by an engine mounted on the container or chassis, it will be possible to displace the relatively warm air initially in the container by cold air from the vortex tube or tubes. The hot air from the other outlet of the vortex tube Will be rejected to atmosphere or can be utilised for some other purpose, as for example heating the cab of a road vehicle carrying the container.

Means must also be provided for venting the warmer air displaced from the container and preventing any pressurisation of the container except for an extremely slight one as described fbelow.

According to the present invention, therefore, there is provided a transportable cargo-refrigerating apparatus, comprising a heat-insulated container having an apertured cargo-supporting floor mounted therein in closely spaced relationship above its base; at least one vortex tube having an inlet for compressed air, a hot air outlet arranged to discharge hot air outside the container and a cold air outlet connected to cold delivery means arranged to distribute the cold air received from the vortex tube throughout the space between the apertured iloor and the base of the container; and at least one outlet vent in the top of the container for the discharge therefrom of air displaced by the cold air entering the container through the said cold air delivery means.

The apertured cargo-supporting iioor may be composed of slats or a grid and be located between 4 and 6 inches above the interior surface of the base of the container.

The outlet vent or each of the outlet vents, if there is more than one, may be provided with a goose-necked vent pipe or with a cowl and may have a diameter of l to 6 inches, depending on the size of the container.

A motor, e.g. a diesel engine or other internal combustion engine, which is mounted either on the container or on the vehicle or chassis carrying the container, may be arranged to drive a compressor to produce air under pressure. In the case of road or rail vehicles, the compressed air supplied by the compressor may then be passed through a heat exchanger which may be of the tubular extended-surface type, in which the compressed air is cooled by the flow of atmospheric air through the heat exchanger due to the motion of the vehicle. The heat exchanger is preferably therefore attached to the outside of the container or to the chassis or vehicle in such a position as to take maximum advantage of the atmospheric air ow caused by the vehicles motion.

Leaving the air-cooled heat exchanger the compressed air may be fed into one or more vortex tubes, the cold end or ends of which discharge cold air into the space between the inner skin of the container and the slatted floor or grid on which the cargo stands. The vortex tubes, if there is more than one, are fitted to the container so as to obtain the most even distribution of cold air over the bottom of the inside of the container that is possible.

When the apparatus is in use, the cold air will gradually build up from the bottom of the container, being more dense than the air already in the container which will be displaced through the vent or vents in the roof until the container is completely full of cold air.

To obtain as even as possible a distribution of cold air in the lbottom space under the slatted l'loor or grid, the cold discharge pipes of the vortex tubes may be fed into distribution ducts having holes or slots distributed over their length. The temperature of the air leaving the tubes will be equal to or less than the temperature at which it is desired to keep the contents of the container.

When the air in the container reaches the required predetermined temperature, a thermostat situated in a suitable position in the container may be arranged to operate to shut off or reduce the compressed air supply to the vortex tubes. Preferably this thermostat will be of the mechanical expansion type, not requiring the supply of electricity. This thermostat, acting through a mechanical or pneumatic linkage may either reduce the engine and compressor speed to. idling or by-pass the compressor or act in some other appropriate way to cut oi the supply of air to the vortex tube or tubes or to reduce it.

When the thermostat operates in the manner just described, the cold air will have iilled the container completely and the top level of the cold air will stand at the top of the bend of the goose-necked vent or cowl, which will prevent warm air from finding its way back from atmosphere into the container and at the same time will exclude rain or moisture. The pressure in the container may be kept just above the atmospheric to an extent of a small fraction of an inch of water gauge pressure by keeping a small yflow into the container from the vortex tubes at all times, this slight positive pressure acting to seal the door of the container and to prevent any warm air entering, although this is not essential.

An economy of operating power and also a means of reaching lower temperatures than would otherwise be possible may be achieved by recirculating the cold air exhausted from the top of the container to the compressor inlet. It will be necessary to dilute this cold air with a charge of atmospheric air at ambient temperature, equal in volume to the hot fraction discharged to atmosphere, to make up the total inlet air requirement for the vortex tube or tubes. Nevertheless, the bulk inlet air temperature will be lower than that of the ambient air which, in turn, will lead to a progressive decrease of temperature in the container.

While recirculation is in operation, it may be necessary to by-pass the air cooler at the compressor outlet as the compressed air temperature may drop below that of the ambient air used for cooling the heat exchanger. Means for by-passing the heat exchanger must therefore be provided.

The fraction of hot air from the other end of the vortex tube will normally be rejected to atmosphere Ibut it may be used for some ancillary purpose, such as heating the driving cab of a road vehicle carrying the container. The hot air can also be used for defrosting purposes: in the case of the cold air distribution ducts becoming frozen up, hot air can be discharged into the cold air ducts by means of a by-pass valve for short periods.

One embodiment of the transport container cooling system according to this invention will now be described with reference to the accompanying diagrammatic drawing.

Referring to the dra-wing, an insulated container 1 has has tted into it a slatted iioor 2 at a level of between 4 and 6 inches above the base of the container. The slatted floor 2 serves for supporting the cargo (not shown) which is to be transported. Fixed to the container 1, or mounted on the Vehicle or chassis (not shown) carrying the same, is a motor 3 driving an air compressor 4. Compressed air from the compressor 4 passes through an air-cooled heat exchanger 5 which is cooled by the air iiow due to the motion of the vehicle. From the heat exchanger 5, the air is distributed by pipes 6 to vortex tubes 7. The cold ends of the vortex tubes 7 extend through the insulation of the container 1 into ducts 8 located in that part of the interior of the container which is located between the slatted floor Z and the bottom wall of the container. The ducts 8 are formed with slots 8' which are arranged so as to distribute the cold air as evenly as possible over the floor area of the container 1.

The hot ends of the vortex tubes 7 are vented to atmosphere through outlet pipes 7. In the embodiment illustrated, by-pass pipes 9 fitted with valves 10 are also connected between the hot air outlet pipes 7 and the cold ends of the vortex tubes 7, for temporarily diverting hot air back to the ducts 8 for defrosting purposes.

At the top of the container 1 are fitted goose-necked exhaust vents 11. A thermocouple 12 fitted within the container 1 is connected by a linkage 13 to the motor 3 driving the compressor 4. This linkage 13, which may be a mechanical linkage is so arranged that, when the temperature within the container 1 is reduced below a predetermined value, the compressor Will be stopped or driven at a reduced speed and, when the temperature is subsequently raised above this predetermined value, the compressor will be restarted or driven once more at its normal speed. Preferably, the thermocouple has adjustable control means for varying the temperature at which it is set to suit cargoes requiring dierent storage temperatures.

Connected between the exhaust vents 11 and the compressor is a recirculation duct 14 through which cold air can be returned from the upper part of the container 1 to the compressor. While recirculation is in progress through this duct 14, the vents 11 may be closed by valves (not shown) and the heat exchanger 5 may be by-passed by closing a valve 16 and opening a valve 17 so that the compressed air from the compressor 4 is delivered through a by-pass pipe 15 directly to the pipes 6 leading to the vortex tubes 7.

For containers intended to travel aboard ship, the compressed air required to operate the vortex tubes may be obtained, already cooled, from the ships compressed air ring main. For this purpose, the pipes 6 may have their inlet ends connected through a shut-off valve (not shown) to a quick coupling connection suitable for coupling to the said ring main.

It will be appreciated that, while it is preferred to provide two vortex tubes 7 with two cold air delivery ducts 8 and two exhaust vents 11, only one of each of these components is essential.

It may sometimes be desirable to make provision for enabling such mobile containers to be either refrigerated or heated as and when required, so that, for example, a frozen cargo can be carried on one journey and a cargo that needs to be kept at a temperature above that of the atmosphere on a subsequent journey. For this purpose, additional distribution ducts (not shown), similar to the ducts 8, may be provided in the bottom space under the slatted floor or grid 2, which additional distribution ducts are arranged to be supplied with hot air from the hot air outlet pipes of vortex tubes. The latter may be the vortex tubes 7, in which case changeover valves (not shOwn) are needed to disconnect their cold ends from the cold air distribution ducts 8, while simultaneously connecting their hot ends to the additional distribution ducts. Alternatively, additional vortex tubes may be provided for the supply of hot air to the additional distribution ducts, in which case a changeover valve may be provided for connecting the air supply from the heat-exchanger 5 to the vortex tubes that are in use and disconnecting them from the vortex tubes that are not in use.

Provision may also be made for enabling waste heat from the motor 3 to be fed to the above-mentioned additional distribution ducts when the container is to be heated.

I claim:

1. In a movable vehicle having a cargo-refrigerating apparatus carried by the vehicle, the combination with the vehicle of a motor means carried by the vehicle and an air compressor connected to and driven by the motor means, the air compressor having a discharge outlet for the discharge therefrom of air under pressure, a heatinsulated container means carried by the vehicle and dening an enclosed cargo chamber therein, the container means including a base and an apertured cargo-supporting oor mounted therein in closely spaced relationship above said base, cooling means connected between said air compressor and said chamber for cooling the chamber within said container means, said cooling means including at least one vortex tube having an inlet interconnected to the compressor discharge outlet for permitting air to be supplied to said vortex tube, said -vortex tube further having a hot air outlet arranged Ito discharge hot air outside the container means and a cold air outlet, cold air delivery means connected to the cold air outlet of said vortex tube for distributing the cold air discharged from the vortex tube throughout the space between the apertured cargo-supporting iloor and the base of said container means, whereby the cooled air Hows upwardly through the apertured `cargo-supporting oor for cooling the cargo supported thereon, an air-cooled heatexchanger means mounted on said vehicle and connected between the discharge outlet of said air compressor and the inlet of said vortex tube for cooling the compressed air as it is supplied from the compressor to the vortex tube due to the flow of atmospheric air through the heatexchanger due to the motion of the vehicle, and at least one outlet vent means disposed adjacent the top of said container means for discharging from the container means air displaced by the cold air entering said container means through said cold air delivery means.

2. An apparatus according to claim 1, wherein the heat-exchanger is of the tubular extended surface type.

3. An apparatus 4according to claim -1, wherein means are provided for temporarily diverting hot air from the hot air outlet to the cold air outlet of each vortex tube for defrosting purposes.

4. An apparatus according to claim 1, wherein a connection is provided between the outlet vent and the compressor for recirculating air from the upper part of the container to the air-compressor.

l5. An apparatus according to claim 4, wherein means are provided for closing the outlet vent while recirculation is in progress.

6. An apparatus according to claim 5, wherein means are provided for by-passing lthe heat-exchanger while recirculation is in progress.

7. An apparatus according to claim 1, wherein means are provided for interrupting the supply of cold air to the cold air delivery means while at the same time causing hot air from the hot air outlet of the vortex tube, or of another vortex tube, to be distributed throughout the space between the apertured oor and the base of the container.

8. A transportable cargo-refrigerating apparatus adapted to be carried on and transported by a vehicle, comprising a heat-insulated container means defining an enclosed cargo storage chamber therein, said container means having a. base and additionally having an apertured cargo-supporting floor disposed closely adjacent to but spaced slightly upwardly from said base for dening a small space therebetween, motor means positioned externally of said container means, air compressor means positioned externally of said container means and driven by said motor means, a vortex tube disposed adjacent the container means and means connecting the discharge outlet of the compressor means to the inlet of the vortex tube for supplying pressurized air thereto, said lastmentioned means including a heat exchanger disposed eX- ternally of said container means, said vortex tube including a hot air outlet for discharging hot air externally of said container means, said vortex tube further including a cold air outlet arranged for discharging cold air into the cargo chamber for cooling the cargo stored therein, cold air delivery means connected to the cold air outlet of said vortex tube for distributing the cold air from the vortex tube throughout the cargo chamber of said container means, said cold air delivery means including an elongated distributor duct disposed within the space between said cargo-supporting floor and said base, said duct having a plurality of longitudinally spaced openings extending therethrough for permitting the cold air to be substantially uniformly distributed throughout said space, whereby said cold air then flows :through the apertured cargo-supporting oor for surrounding and cooling the cargo within said chamber, and vent means disposed adjacent the top of said container means for the discharge therefrom of air displaced by the cold air entering the container means through said cold air delivery means.

References Cited UNITED STATES PATENTS 2,123,678 7/1938 yInadden 62-418 2,166,283 7/1939 Betz 62-419 2,737,028 3/ 1956 Inachlanski 62-5 2,819,590 1/l958 Green 62-5 3,197,969 8/1965 Over 62-5 3,307,366 3/ 1967 Smith 62-5 WILLIAM J. WYE, Primary Examiner U.S. Cl. X.R. 62--419