The present invention relates to a thermal storage device, and especially a thermal storage device for refrigerating foodstuffs and other perishables. The invention also relates to a container such as a bulk transportation container including such a storage device, and to a thermal transfer system including such a storage device.

Large amounts of foodstuffs are transported in bulk transportation containers, both by road, rail, sea and airfreight. It is well known that for correct and optimal conservation of a foodstuff during transportation and storage, it is important that the temperature and relative humidity of the ambient medium in which the foodstuff is stored is maintained as closely as possible at a precise predetermined level. This level depends on the type of foodstuff to be conserved.

Commonly, refrigeration units are utilised for the conservation of foodstuffs being transported in bulk transportation containers. Both electrically and diesel powered units are known. Whilst such units permit control of the temperature at which a foodstuff is maintained, they suffer from the disadvantages of high operating and maintenance costs, temperature and relative humidity fluctuations that may cause withering or blemishing of the foodstuff, and of the foodstuff perishing when they fail. Failure is common. Since such units are continuously subject to vibration and impact, loss of small quantities of freon gas or CFC mixtures harmful to the environment may be common.

It is also known to utilise ice for the refrigeration of foodstuffs in bulk transportation containers. This has several disadvantages. Firstly, rapid deterioration of the foodstuff may occur if it comes into contact with the ice,

especially when the ice melts, when rotting may occur. Secondly, this technique is not capable of quickly lowering the temperature of the foodstuff, particularly when it has been loaded directly into the container at ambient temperature without prior refrigeration. Thirdly, conservation of foodstuffs at a temperature different from that of melting ice is impossible.

Further, it is known to store water or some similar substance in a so-called "freezer-pack", as a type of thermal storage device. Such a pack is cooled in a domestic freezer and then used in conserving small quantities of foodstuffs in picnic boxes or the like. Whilst such a pack solves some of the problems encountered when using just ice to conserve foodstuffs, it would be expected to be inconvenient and impractical if used on a much larger scale with bulk transportation containers.

The present invention seeks to solve these problems.

According to the present invention, there is provided a thermal storage device comprising a thermal storage medium and a coupling arrangement for permitting thermal transfer between the medium and a thermal source at a location separate from that of the bulk of the medium, so as to change the temperature of the medium, the coupling arrangement being arranged to permit releasabie coupling between the medium and the source.

By means of a coupling arrangement which is arranged to permit releasabie coupling between the medium and the source, the thermal storage medium can be cooled or heated ("charged") in situ in the container by being coupled to a remote, or at least separate, thermal source. Once the storage medium has been charged thus, the thermal storage device can be uncoupled from the thermal source and the container transported away.

This arrangement can have the advantages of being economical to instal and maintain, convenient to use, and also highly reliable. In particular, once the medium has been charged, it need not be re-charged or attended to in any way whilst the container is being transported, until the storage medium finally "runs out". Further, the device need have no mechanical moving parts. Operating costs would be incurred only by the charging of the container by the thermal source, which would typically be an entirely conventional refrigeration unit kept at a depot. Hence the refrigeration unit would also be relatively easy to operate and maintain by comparison with a mobile refrigeration unit carried with the container, which is continuously subject to vibration, loss of small quantities of freon gas or CFC mixtures harmful to the environment, impact, and consequent necessity for repair.

An important practical advantage of the thermal storage device of the present invention is that, because it may completely obviate the need for refrigeration machinery using freon gas or "CFC" mixtures, the device may conform to international standards which in the future might completely ban the use of such polluting and ozone layer depleting substances.

Preferably, the device further includes a sealed container in which the thermal storage medium is kept. This can prevent contamination of the foodstuff by the medium.

Preferably, the coupling arrangement includes a heat exchange device for exchanging heat between thermal transfer fluid carried from the thermal source by the coupling arrangement and the thermal storage medium. This arrangement has the advantages firstly that the thermal storage medium need not be bodily moved during the charging process (for instance, by being pumped from the thermal source to the thermal storage device). Hence it can easily be kept in a sealed container. Secondly, this arrangement allows the thermal transfer fluid and thermal storage medium to be different substances. Thus,

for example, the thermal transfer fluid is still able to be in the liquid phase whilst it is being pumped from the thermal source through the heat exchange device, whilst the medium may be changing phase from liquid to solid.

For optimum efficiency, the heat exchange device is in direct contact with the medium.

Preferably, the thermal storage medium consists of a substance which changes phase at a selected temperature. By using a phase change substance, the thermal storage device can accurately maintain the selected temperature (and hence also a selected relative humidity) for a considerable period of time. Since the device is advantageously used for refrigeration, the selected temperature is preferably less than 50°C, more preferably less than 20 or 30°C, even more preferably less than 5 or 10°C. In many circumstances the temperature is preferably 0°C or lower than 0°C.

The invention extends to a container (suitably a bulk storage container or the container on a panel body vehicle) including a thermal storage device as aforesaid, and further including a body defining a load space and means for affording access to the load space, the coupling arrangement of the thermal storage device being arranged to permit releasabie coupling of the container and a thermal source external to the container. Thus, once the thermal storage device has been charged, the container can be uncoupled from the source and used completely autonomously.

For an even distribution of heat or cold within the container, preferably a plurality of thermal storage devices are provided, disposed about the container. In this event, the coupling arrangements of the thermal storage devices preferably share a common coupling arrangement at their ends remote from their respective thermal storage media. This facilitates charging of the thermal storage device, since the

thermal source can be coupled to a single commop coupling arrangement.

For ease of coupling to the thermal source, the or each coupling arrangement suitably terminates at its end remote from its thermal storage medium at the exterior of the container.

The container may further include an insulating arrangement for insulating the load space.

The invention extends to a thermal transfer system including a thermal storage device or a container as aforesaid, and a thermal source at a location separate from that of the bulk of the thermal storage medium.

Preferred features of the invention are now described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a part sectional perspective view of a container incorporating a number of thermal storage devices,

Figure 2 is a similar view showing one particular thermal storage device at an enlarged scale; and

Figure 3 is a schematic representation of a fluid circuit incorporating the thermal storage devices.

Referring to Figures 1 and 2, a container 10 according to the present invention has the dimensions of a standard bulk transportation container. The container comprises five panels 12 (namely two side panels, a floor panel, a roof panel and one end panel) defining a load space, and an aluminium or steel framework supporting the panels (not shown) . One end of the container is provided with access doors (also not shown). Each of the five panels 12 is of a sandwich construction, and comprises inner and outer thin metal sheets 14 and 16 (shown for clarity as having no thickness) between which is sandwiched a thick layer of high density polyurethane

insulation 18 (shown by the cross-hatching in Figure 1 and by the dots in Figure 2) and thermal storage devices 20.

As shown in Figures 1 and 2, each thermal storage device 20 includes a rectangular cross-section container 22 containing thermal storage medium 24 and a heat exchange device 26.

In more detail, each rectangular cross-section container 22 is located immediately below the inner sheet 14 of the relevant panel 12, and contiguous with its neighbouring containers 22. This ensures an efficient release of thermal energy from the thermal storage devices 20 which is continuous over the load space (apart from the access doors, which are not provided with thermal storage devices) . The container is made by an extrusion process from aluminium alloy (although other materials may also be suitable). It will be understood that the cross-sectional shape of the rectangular cross-section container 22 need not be perfectly rectangular; considerations of low specific weight and high mechanical strength may dictate somewhat different profiles.

The thermal storage medium 24 in each container 22 is a ternary or quaternary aqueous solution, for example, a brine solution having a freezing/melting point of -20°C, and hence in this embodiment functions with container 22 as a thermal cold storage device.

Each heat exchange device 26 comprises a portion of a meandrine conduit 28, the same conduit being shared by a number of contiguous thermal storage devices 20. The conduit extends through the rectangular cross-section containers 22 and hence is in direct contact with the thermal storage medium 24.

Referring now to Figure 3, the heat exchange devices 26 form part of a fluid circuit 30 carrying thermal transfer fluid. The thermal transfer fluid is typically of the same

composition as the thermal storage medium, although having a lower freezing/melting point. The fluid circuit functions as a coupling arranged to be coupled to a cold source such as a refrigeration unit (not shown) and to effect thermal transfer between the source and the individual thermal storage media 24.

In more detail, the fluid circuit 30 comprises a number of individual circuits 32, each individual circuit itself including a number of heat exchange devices 26. For illustration purposes, four individual circuits 32 are shown in Figure 3; normally, five would be employed, one for each panel of the container. The heat exchange devices 26 within each individual circuit 32 are connected in series, although a parallel connection is possible. The individual circuits 32 are connected together in parallel, although a series connection is possible. Finally, the common flow and return conduits 34 and 36 for all the individual thermal storage devices terminate at inlet and outlet valves 38 and 40 respectively. As is clear from Figure 1, these valves are positioned on the exterior of the container 10. The valves are designed to permit easy and rapid releasabie coupling of the container to the thermal cold source (not shown) .

The operation of the container 10 including the thermal storage devices 20 is as follows. Before the container is used for transporting foodstuff (or perishables) the thermal storage devices 20 are charged. An external thermal cold source in the form of a refrigeration unit located at a depot is connected via a flexible conduit to the inlet and outlet valves 38 and 40.

The thermal cold storage media 24 are charged by pumping refrigerated thermal transfer fluid from the refrigeration unit via the inlet valve 38 through the fluid circuit 30 to the individual heat exchange devices 26 in the individual circuits 32. Charging is complete when the thermal storage

media 24 have completely changed phase from liquid to solid. It will be appreciated that the refrigerated fluid needs to remain in the fluid state at temperatures at and below the freezing point of the thermal storage media 24.

It will be understood that, for efficient charging, the flow rate of refrigeration fluid to the individual heat exchange devices 26 needs to be carefully controlled to ensure that all the thermal storage devices 20 are cooled at the appropriate rate. Such control can be pre-established during the design stage. Factors which influence the flow rate are the lengths of the conduits 28 in the panels 12, the cross-sectional areas of the inlet and outlet circuit branches to each panel (loss of head of the fluid circuit), and so on. In particular, by arranging the individual heat exchange devices 26 in series, and the individual circuits 32 in parallel, relatively uniform flow rates can be achieved in the individual heat exchange devices.

Once the thermal storage devices 20 have been charged so that the _. thermal storage media 24 have changed phase from liquid to solid, the valves 38 and 40 are closed to prevent loss of refrigeration fluid, and the external refrigeration unit is uncoupled. The container 10 is now ready to be transported.

Once the refrigeration unit has been uncoupled the thermal storage devices act completely autonomously, in that they do not require any further attention. They act to cool the contents of the container by natural convection and radiation from the internal walls, floor and ceiling of the container. They continue to act thus until near the time when the thermal storage media 24 have completely changed phase from solid to liquid. This time is dependent on many factors, such as the quantity of thermal storage medium, the degree of insulation of the container 10, and the external temperature to which the container is subjected. These factors would be taken into consideration at the design stage, to produce a container

having the requisite capabilities.

It will be understood that, since the thermal storage medium 24 is a phase change substance, once charged, the thermal storage devices 20 can maintain foodstuffs or other items such as perishables at a relatively constant temperature (the temperature at which the phase changes) for a relatively prolonged period due to the significant latent heat of fusion of the phase change substance. Hence also the foodstuffs can be maintained at a relatively constant humidity.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. For example, it will be appreciated that modifications can be made to the shapes and dimensions in the drawings.