FIELD OF THE INVENTION

The present invention relates generally to an encapsulated phase change substance and relates particularly, though not exclusively, to a granular phase change substance coated in one or more epoxy resin sealing layers. The present invention further relates to a method and an apparatus for producing an encapsulated phase change substance.

BACKGROUND TO THE INVENTION It is generally understood that phase change substances can be encapsulated and thereafter used to store latent heat for use in heating or cooling. One technique used for encapsulating a phase change substance to form one or more phase change capsules involves the following steps: i) forming indents within a plastic sheet using a thermo-forming head; ii) dosing or filling each indent with a phase change substance in a liquid state; iii) covering each indent with a laminated aluminium cover which is heat sealed to the plastic sheet; and iv) cutting the plastic sheet and aluminium cover to form one or more of the phase change capsules .

Although this encapsulation technique is well suited to production thermo-forming equipment it suffers from at least the following drawbacks: i) the rate of production of capsules is low and thus the unit cost of the capsules is relatively high; ii) the phase change capsules by nature of their construction and design are not robust and thus are limited in their application; and iii) the phase change capsules, primarily because of their size, are only effective in storing latent heat for a limited number of phase change cycles.

SUMMARY OF THE INVENTION

An intention of the present invention is to provide an encapsulated phase change substance which is relatively inexpensive to produce.

According to a first aspect of the present invention there is provided a method for producing an encapsulated phase change substance, said method comprising the steps of: forming a plurality of granules each including a phase change substance having a relatively high latent heat of fusion, said plurality of granules being of a predetermined size distribution; and coating each of said plurality of granules with one or more sealing layers being substantially impermeable to said phase change substance so that the encapsulated phase change substance can, for a relatively large number of cycles, change between the solid and liquid phases thereby effectively releasing and storing latent heat, respectively.

Typically, the step of forming a plurality of granules involves forming said granules within a granulator drϋm rotationally mounted about its axis at a predetermined angle, the granulator drum being adapted to receive a quantity of said phase change substance so that the predetermined size distribution of the granules is controlled by the predetermined angle at which the granulator drum is inclined.

Typically, the step of coating said plurality of granules involves spraying said one or more sealing layers onto each of said granules.

Preferably, the step of coating said granules involves: feeding the granules to a coating drum which is rotationally mounted about its longitudinal axis; and

applying said one or more sealing layers onto each of said granules via a plurality of spray nozzles operatively communicating with the coating drum.

In one example, the plurality of spray nozzles reciprocate longitudinally along the coating drum.

Typically, the step of coating said plurality of granules involves controlling the rotational speed of the coating drum so the thickness of said one or more sealing layers is controlled. Preferably, the step of coating said plurality of capsules involves applying between approximately 1 to 12 coats of said sealing layer to each of the granules.

According to a second aspect of the present invention there is provided an apparatus for producing an encapsulated phase change substance, said apparatus comprising: a granulator adapted to receive a phase change substance having a relatively high latent heat of fusion, said granulator designed to form a plurality of granules each of a predetermined size and each including at least a portion of said phase change substance; and coating means operatively communicating with the granulator, said coating means capable of applying one or more sealing layers being substantially impermeable to the phase change substance to each of said granules so that the encapsulated phase change substance can, for a relatively large number of cycles, change between the solid and liquid phases thereby effectively releasing and storing latent heat, respectively.

Typically, the granulator comprises a granulator drum rotationally mounted about its axis at a predetermined angle, the granulator drum being adapted to receive said phase change substance such that the predetermined size distribution of the granules is controlled by the predetermined angle at which the granulator drum is

inclined. In one example, the predetermined angle of inclination is between approximately 5° to 35° measured from the vertical.

Preferably, the coating means comprises: a coating drum rotationally mounted about its longitudinal axis, the coating drum being adapted to receive a flow of said plurality of granules from the granulator; and one or more spray nozzles operatively communicating with the coating drum and designed to spray each of the granules with said one or more sealing layers.

In one example the coating means further comprises a carriage connected to said one or more spray nozzles, the carriage movably cooperating with the coating drum so that, in use, the spray nozzles can reciprocate longitudinally along the coating drum.

According to a third aspect of the present invention there is provided an encapsulated phase change substance comprising: a granule including a phase change substance having a relatively high latent heat of fusion, said granule being of a predetermined size; and one or more sealing layers formed on the granule, said one or more layers being substantially impermeable to said phase change substance whereby the encapsulated phase change substance can, for a relatively large number of cycles, change between the solid and liquid phases thereby effectively releasing and storing latent heat, respectively.

Typically, each of said plurality of granules is substantially spherical in shape. More typically, the predetermined size distribution of said spherical granules ranges from a diameter of between approximately 5 to 30 mm.

Preferably, the volume of said phase change substance within each of said plurality of granules is less than approximately 14 millilitres (ml) .

Typically, said one or more sealing layers comprise a synthetic thermosetting material. More typically, the synthetic thermosetting material is an epoxy resin. In one example, the epoxy resin is a phenolic epoxy resin.

Typically, the phase change substance is a hydrate salt or a derivative thereof. According to various examples of the present invention the hydrate salt is calcium chloride, sodium phosphate, or sodium acetate having melting points of approximately 29°C, 36°C, or 58°C respectively. However, it should be appreciated that the invention is not restricted to any one particular phase change substance, the phase change substance being selected according to the application in which the encapsulated phase change substance is to be used.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a better understanding of the present invention a preferred method and apparatus for producing an encapsulated phase change substance will now be described in some detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic of an apparatus for producing an encapsulated phase change substance; and

Figure 2 is an exploded view of an encapsulated phase change substance partly cut away.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in Figure 1 there is an apparatus shown generally as 10 for producing an encapsulated phase change substance 12 (see Figure 2).

The apparatus 10 comprises one or more load-in storage vessels 14 designed to contain a phase change substance. It is envisaged that the phase change substance will be delivered to the storage vessels 14 in bags for small quantities, or sealed truck-mounted containers for relatively large quantities. Typical phase change substances processed in the apparatus 10 include but are not limited to the hydrate salts calcium chloride dihydrate (22°C) , calcium chloride hexahydrate (29°C) , sodium phosphate heptahydrate (36°C) , sodium phosphate dodecahydrate (48°C) , sodium acetate trihydrate (58°C) , and magnesium nitrate hexahydrate (90°C) . The majority of the hydrate salts are hydrophilic and thus require specific handling procedures and controlled environment storage. For example, it is recommended that storage is maintained at a constant dry temperature suited to the particular hydrate salt.

The storage vessel 14 operatively communicates with a granulator 16 via a screw conveyor 18. Rotational speed of the screw conveyor 18 is controlled so that an accurate flow rate of the phase change substance can be maintained into the granulator 16.

The granulator 16 comprises a granulator drum rotatably mounted about its longitudinal axis. The granulator drum, in this example, is approximately 2.5 metres in diameter and 0.5 metres high, and is designed to rotate at a controlled speed and a variable inclination of between approximately 5° to 35° measured from the vertical. The degree of inclination of the granulated drum controls the diameter of granules produced from the granulator 16. The granulator 16 includes an electronically controlled hydration system (not illustrated) used to add demineralised water to the phase change substance granulated within the granulator 16. For example, a granule containing the phase change substance calcium

- 7 - chloride may comprise approximately two thirds by weight calcium chloride and approximately one third by weight demineralised water. The granulator also comprises a dust extraction system (not shown) located in the vicinity of the granulator drum. Typically, phase change granules produced from the granulator 16 will be from between 5 to 30 mm in diameter.

The granulator 16 operatively communicates with coating means shown generally as 20 via a conveyor belt system 22. The coating means 20 includes a coating drum of approximately 1.2 metres in diameter and 8 metres in length set at an angle of declination of approximately 2° to 3° toward its output. The coating drum is rotated at a controlled speed about its longitudinal axis. The conveyor belt system 22 is set at a speed which will handle the quantity of phase change granules discharged from the granulator 16. The rate of granules discharged onto the conveyor 22 will depend largely on the size of the granules. Dust extraction is also provided in the vicinity of the coating drum.

The coating means 20, in addition to the coating drum, comprises the following components:

1. a compressed air vessel with a 5 kilowatt (kW) driven compressor; 2. a water tank and a 1 kW delivery pump;

3. one or more storage vessels containing coating compounds, in this example two (2) epoxy resins held at a temperature of approximately 60°C;

4. one or more pumps located between the storage vessels and the coating drum.

Dye is added to the coating compounds so that the phase change substance and its approximate melting point can be identified by the colour of the encapsulated phase change substance 12. The coating compounds are delivered to a

spray nozzle located inside the coating drum via a multi- core hose. The spray nozzle reciprocates back and forth longitudinally along the coating drum during the coating process.

Once the granulated phase change substance has been coated in the coating drum, the encapsulated phase change substance 12 is then conveyed from the coating drum to load-out storage vessels. Each phase change substance will require a separate load-out storage vessel.

A typical encapsulated phase change substance 12 produced from the apparatus 10 described above is illustrated in Figure 2. The encapsulated phase change substance 12 comprises a substantially spherical granule 24 including a phase change substance such as the hydrate salt calcium chloride dihydrate (22°C) . The granule 24 is between approximately 5 to 30 mm in diameter and includes approximately 30% by weight demineralised water. The volume of phase change substance within the granule 24 is thus relatively low, typically being less than 14 millilitres (ml) . Thus, the tendency of the phase change substance to break down into salt and water after a limited number of phase changes is minimised.

The encapsulated phase change substance 12 further comprises a multi-skin sealing layer 26 formed on the granule 24. The sealing layer 26 is constructed of a phenolic epoxy resin material being substantially impermeable to the phase change substance. In this example, the sealing layer 26 comprises from between approximately 1 to 10 layers of the epoxy resin coating material. The sealing layer 26 constitutes approximately 10% by weight of the encapsulated phase change substance 12. When the phase change substance is in a solid state the encapsulated phase change substance 12 will support a mechanical pressure of approximately 340 kilograms (kg) and

in a liquid state will support a mechanical pressure of approximately 50 kg. This robust sealing layer 26 also has relatively high heat transfer properties.

The encapsulated phase change substance 12 can be used in a variety of applications, the phase change substance being selected according to the chosen application. For example, an encapsulated phase change substance 12 comprising the hydrate salt calcium chloride dihydrate (having a melting point of approximately 22°C) can be introduced into a concrete wall or floor as part substitution for aggregate within the concrete. The hydrate salt will absorb heat when ambient temperatures are in excess of 23°C and will release energy when ambient temperatures are less than approximately 21°C. Thus, the encapsulated phase change substance 12 located within the concrete wall or floor maintains the structure at a constant temperature of approximately 22°C thereby producing a constant temperature using passive heating.

The encapsulated phase change substance 12 can also be included in other concrete structures such as a footpath, swimming pool, or road. The phase change substance is then selected in each application according to its purpose. For example, an encapsulated phase change substance 12 including a relatively low temperature phase change substance such as calcium carbonate (having a melting point of approximately 6°C) could be used for de-icing roads.

Now that a preferred embodiment of the present invention has been described in some detail it will be apparent to those skilled in the relevant arts that the encapsulated phase change substance has at least the following advantages over the admitted prior art:

1. the encapsulated phase change substance can perform a relatively large number of phase changes without a breakdown of the phase change substance;

2. the encapsulated phase change substance is relatively inexpensive to manufacture;

3. the encapsulated phase change substance is adaptable and robust thus lending itself to a variety of applications;

4. the encapsulated phase change substance by nature of its design has relatively high heat transfer properties and thus is relatively effective in use; and

5. the encapsulated phase change substance has a high latent heat storage capacity.

It will be apparent to persons skilled in the relevant arts that numerous variations and modifications can be made to the invention described above in addition to those already mentioned without departing from the basic inventive concepts. For example, the encapsulated phase change substance may not be shaped spherical but rather capsule- shaped. The encapsulated phase change substance is not restricted to any one particular phase change substance, the phase change substance being selected according to the application in which the encapsulated phase change substance is to be used. Where the phase change substance selected has a melting point below ambient temperature the granulator is refrigerated so that phase change granules are formed in the solid state. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.