GB1600007A - Refrigerated container - Google Patents

Description

(54) REFRIGERATED CONTAINER (71) We, Boc LIMffED, of Hammersmith House, London W6 9DX, England, an English company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to refrigerated containers and particularly, although not exclusively, to mobile refrigerated containers.

One known method of maintaining a desired sub-ambient temperature within the cargo space of a refrigerated vehicle is by spraying with a cryogenic medium, usually liquid nitrogen, or liquid carbon dioxide to form 'snow'. Operation of the sprays is controlled in response to a temperature sensor located within the cargo space so that the sprays are brought into operation when the heat inleak through the insulated walls of the cargo space raises the prevailing temperature, as sensed by the sensor, to a preselected value. The temperature sensor may itself be exposed to a spray of the cryogenic medium so that the sensor is actuated to shut off the supply shortly after spraying commences, whereby the medium is introduced into the cargo space in short sharp blasts.It will be understood that the volume of cryogenic medium which can be carried by such a vehicle in practice is limited, and, whilst being sufficient to maintain the cargo space at the required low temperature for many hours when goods already at the requisite temperature are loaded into it, systems as described above are not designed to achieve any substantial reduction of the temperature of loaded goods.

Problems can arise with such systems, therefore, in the event that goods which are not already at the requisite temperature are loaded into the cargo space (termed herein 'hot loading'). When hot loading occurs the tendency is for the temperature sensor to respond to convected heat from the goods so that the cryogenic sprays are operated repeatedly in a vain attempt to lower the temperature of the goods. The result is that the entire cryogenic supply is rapidly consumed and once this has occurred the temperature of the loaded goods will, of course, begin to rise so that the goods may eventually reach an unacceptable condition.

Furthermore, in such a circumstance it might be concluded on arrival of the vehicle at its destination that there had been a malfunction of the refrigeration system leading to the exhaustion of the cryogenic supply, as at that point the occurrence of hot loading could not be detected.

By way of example, in the case of refrigerated vehicles such as are used for the transportation of frozen or chilled foodstuffs and have cryogenic spray systems adapted to maintain a cargo space temperature in the region of, say, -15 C to -250C, loaded goods which are as little as 50C above the desired operating temperature can be regarded as 'hot' and may cause rapid exhaustion of the cryogenic supply as indicated above. In practice, goods which are as much as 10 C over temperature might be loaded with their 'hot' condition going unnoticed.

According to the present invention there is provided a thermally-insulated container having refrigeration apparatus comprising means for spraying a cryogenic medium into the interior of the container, means for controlling the operation of such spray means in response to a temperature sensor, the temperature sensor being located in a cavity in the ceiling or one of the walls of the container, and the temperature sensor being separated by thermal insulation both from the external environment and the useful volume of the container.

The thermal insulation separating the temperature sensor from the useful volume of the container shields the sensor from any convection current rising from any local 'hot spot' in the useful volume of the container.

The ratio of the thickness of the thermal insulation which separates the temperature sensor from the external environment to the thickness of the thermal insulation which separates the temperature sensor from the useful volume of the container is preferably in the range of 2:1 to 3:1. A refrigerated container according to the invention may therefore be arranged so that, in the event of hot loading, the overall rate at which cryogenic medium is sprayed into the container is sufficient just to maintain the goods at the temperature at which they are loaded.The consumption of cryogenic medium is thereby not excessive and it is considered that to operate in this manner, whereby the goods will be delivered more or less in the condition in which they are loaded, is prefer able to the above described manner of operation of known refrigerated containers whereby the risk is run of exhausting the cryogenic supply in an attempt to lower the temperature of 'hot' goods, and subsequently having the goods deteriorate.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic cross section through the upper portion of a container according to the invention such as may form part of a refrigerated road vehicle; and Figure 2 shows a detail of Figure 1 to an enlarged scale.

Referring to the drawings, a refrigerated road vehicle includes a thermally insulated container 10 having a refrigeration system comprising a plurality of elongate tubular headers 11 formed with spray orifices at spaced locations along their length. The orifices are provided along one or both sides of the headers to direct sprays of liquid nitrogen in directions slightly downwards of the horizontal as indicated for one of the headers in Figure 2. The liquid nitrogen is supplied to the headers from a tank, preferably vacuum insulated, located in a separate compartment of the vehicle, under the pressure of nitrogen vapour in the headspace of the tank. The flow of nitrogen to the headers is controlled by a valve which is actuated by a control system in response to a temperature sensor 12.

The temperature sensor may be of the well known type consisting of an elongate bulb containing alcohol, the thermal expansion and contraction of which triggers the opening and closing of the liquid nitrogen control valve. As shown in the drawings, the sensor 12 is located within a cavity 1 3A in the thermally insulated ceiling 13 of the container, with the effectiveness of the thermal insulation 13B separating the sensor 12 from the external environment being less than that of the thermal insulation which separates the cargo space 1 0A of the container from the external environment. In addition, the sensor 12 is separated from the cargo space 1 0A by a section of thermally insulating material 14. The ratio of the thickness of insulation 1 3B to the thickness of insulation 14 may be in the range of 2:1 to 3:1.The section 14 shields and insulates the sensor 12 from any convection currents arising from any local 'hot-spots' within the cargo space 10A. The sensor 12 thus indicates a temperative dependent on the heat inleak to the container through portion 1 3B (which will represent approximately the general level of heat inleak through all the walls of the container) rather than on local variations in the temperature of the atmosphere within the cargo space 1 0A in the immediate vicinity of the insulation 14 (which, if hot loading occurs, will be determined largely by heat rising from the goods in the cargo space). Such an arrangement permits a more economical and effective usage of the liquid nitrogen than in the case of existing refrigerated containers of the same general kind.

In practice, the temperature sensor 12 is to a certain extent exposed to the atmosphere in cargo space 10A through the illustrated apertures in the intervening thermal insulation so that the sensor can respond to some degree to the actual air temperature prevailing within the container. This is of importance, for example, in triggering the refrigeration system to reduce the air temperature within the container immediately after a loading operation, when the interior of the container has been directly exposed to the external atmosphere.

As illustrated one of the headers 11 may be provided with an auxillaryjet 1 1A which directs a spray of cold liquid or gaseous nitrogen onto the temperature sensor 12 on each occasion when the spray system is operated, in order to switch off the nitrogen supply to the headers.

In this way the nitrogen will be sprayed into the container in the form of short, sharp blasts.

WHAT WE CLAIM IS: 1. A thermally-insulated container having refrigeration apparatus comprising means for spraying a cryogenic medium into the interior of the container, means for controlling the operation of such spray means in response to a temperature sensor, the temperature sensor being located in a cavity in the ceiling or one of the walls of the container, and the temperature sensor being separated by thermal insulation both from the extemal environment and the useful volume of the container.

2.A container as claimed in Claim 1, wherein the ratio of the thickness of the thermal insulation which separates the temperature sensor from the external environment to the thickness of the thermal insulation which separates the temperature sensor from the useful volume of the container is in the range of 2:1 to 3:1.

3. A container as claimed in Claim 1 or Claim 2, wherein there are at least two apertures placing the interior of the cavity in communication with the useful volume of the container.

4. Apparatus as claimed in Claim 3, in which there is means for directing cryogenic medium into said cavity so as, in use, to expose the temperature sensor to a stream of the cryogenic medium upon operation of said spray means.

5. A thermally-insulated container substantially as hereinbefore described with reference to the accompanying drawings.

6. A vehicle including a container as claimed in any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. able to the above described manner of operation of known refrigerated containers whereby the risk is run of exhausting the cryogenic supply in an attempt to lower the temperature of 'hot' goods, and subsequently having the goods deteriorate. The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic cross section through the upper portion of a container according to the invention such as may form part of a refrigerated road vehicle; and Figure 2 shows a detail of Figure 1 to an enlarged scale. Referring to the drawings, a refrigerated road vehicle includes a thermally insulated container 10 having a refrigeration system comprising a plurality of elongate tubular headers 11 formed with spray orifices at spaced locations along their length. The orifices are provided along one or both sides of the headers to direct sprays of liquid nitrogen in directions slightly downwards of the horizontal as indicated for one of the headers in Figure 2. The liquid nitrogen is supplied to the headers from a tank, preferably vacuum insulated, located in a separate compartment of the vehicle, under the pressure of nitrogen vapour in the headspace of the tank. The flow of nitrogen to the headers is controlled by a valve which is actuated by a control system in response to a temperature sensor 12. The temperature sensor may be of the well known type consisting of an elongate bulb containing alcohol, the thermal expansion and contraction of which triggers the opening and closing of the liquid nitrogen control valve. As shown in the drawings, the sensor 12 is located within a cavity 1 3A in the thermally insulated ceiling 13 of the container, with the effectiveness of the thermal insulation 13B separating the sensor 12 from the external environment being less than that of the thermal insulation which separates the cargo space 1 0A of the container from the external environment. In addition, the sensor 12 is separated from the cargo space 1 0A by a section of thermally insulating material 14. The ratio of the thickness of insulation 1 3B to the thickness of insulation 14 may be in the range of 2:1 to 3:1.The section 14 shields and insulates the sensor 12 from any convection currents arising from any local 'hot-spots' within the cargo space 10A. The sensor 12 thus indicates a temperative dependent on the heat inleak to the container through portion 1 3B (which will represent approximately the general level of heat inleak through all the walls of the container) rather than on local variations in the temperature of the atmosphere within the cargo space 1 0A in the immediate vicinity of the insulation 14 (which, if hot loading occurs, will be determined largely by heat rising from the goods in the cargo space). Such an arrangement permits a more economical and effective usage of the liquid nitrogen than in the case of existing refrigerated containers of the same general kind. In practice, the temperature sensor 12 is to a certain extent exposed to the atmosphere in cargo space 10A through the illustrated apertures in the intervening thermal insulation so that the sensor can respond to some degree to the actual air temperature prevailing within the container. This is of importance, for example, in triggering the refrigeration system to reduce the air temperature within the container immediately after a loading operation, when the interior of the container has been directly exposed to the external atmosphere. As illustrated one of the headers 11 may be provided with an auxillaryjet 1 1A which directs a spray of cold liquid or gaseous nitrogen onto the temperature sensor 12 on each occasion when the spray system is operated, in order to switch off the nitrogen supply to the headers. In this way the nitrogen will be sprayed into the container in the form of short, sharp blasts. WHAT WE CLAIM IS:

1. A thermally-insulated container having refrigeration apparatus comprising means for spraying a cryogenic medium into the interior of the container, means for controlling the operation of such spray means in response to a temperature sensor, the temperature sensor being located in a cavity in the ceiling or one of the walls of the container, and the temperature sensor being separated by thermal insulation both from the extemal environment and the useful volume of the container.

2.A container as claimed in Claim 1, wherein the ratio of the thickness of the thermal insulation which separates the temperature sensor from the external environment to the thickness of the thermal insulation which separates the temperature sensor from the useful volume of the container is in the range of 2:1 to 3:1.

3. A container as claimed in Claim 1 or Claim 2, wherein there are at least two apertures placing the interior of the cavity in communication with the useful volume of the container.

4. Apparatus as claimed in Claim 3, in which there is means for directing cryogenic medium into said cavity so as, in use, to expose the temperature sensor to a stream of the cryogenic medium upon operation of said spray means.

5. A thermally-insulated container substantially as hereinbefore described with reference to the accompanying drawings.

6. A vehicle including a container as claimed in any one of the preceding claims.