GB2475478A

GB2475478A - Method of manufacturing a temperature-control packaging

Info

Publication number: GB2475478A
Application number: GB0920141A
Authority: GB
Inventors: Alex Roskoss
Original assignee: DGP
Current assignee: DGP
Priority date: 2009-11-18
Filing date: 2009-11-18
Publication date: 2011-05-25
Also published as: GB0920141D0

Abstract

A method of manufacturing a temperature-control package 10 comprises the steps of selecting a mass and volume for the temperature-control package 10, selecting an insulation material 14 and a thermally driven physical change material 16, and calculating a wall thickness for walls formed of the insulation material 14. The calculation being based on values of density, heat flow and thermal conductivity of the insulation material 14 and on values of density and latent heat of the physical change material 16. The final step of the method involves forming the walls of a temperature-control package 10 having dimensions substantially defined by the selected volume of the temperature-control package 10 and the calculated wall thickness.

Description

Temperature-Control Packaging This invention relates to a temperature-control packaging and to a method of producing a temperature-control packaging.

Substances exhibit changes in physical properties at specific temperatures and pressures. These changes are associated with latent heat energy intake or output by the substance. These heat energy intakes or outputs have been used extensively to control the temperature of other materials thermally associated with the thermally driven physical change materials. Many of the uses made of these physical principles are in the field of packaging production.

Materials are chosen that seek to keep an article inside the packaging either above or below a certain temperature. The materials chosen relate to the temperature range required for the article, the size of the article and also the cost of the value of the article.

Calculating the parameters for a given packaging to ensure the required temperature range is maintained is typically done by trial and error, which can lead to disadvantageously ineffective or costly packaging designs.

It is an object of the present invention to address the 2bovementioned disadvantages.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to an aspect of the present invention there is provided a method of manufacturing a temperature-control package comprises: selecting a mass and volume for the temperature-control package; selecting an insulation material and a thermally driven physical change material; calculating a wall thickness for walls formed of the insulation material said calculation being based on values of density, heat flow and thermal conductivity of the insulation material and on values of density and latent heat of the physical change material; and forming walls of a temperature-control package having dimensions substantially defined by the selected volume of the temperature-control package and the calculated wall thickness.

The method may also include calculating a volume of an internal space for an article to be placed in the temperature-control package, in which case the formed walls also define the calculated internal space.

The method may also include locating the phase change material inside the walls to control the temperature inside the temperature-control package.

Preferably, the package is a substantially cubic package.

Preferably the mass of the temperature-control package excludes a mass of an article to be place in the package.

Preferably the mass of the temperature-control package includes the mass of the insulation material and the thermally driven physical change material.

Preferably the thermally driven physical change material is chosen based on a target temperature range for the interior of the temperature-control package, preferably a target temperature range within the insulation of the temperature-control package.

The invention extends to a method of designing a temperature control package.

The invention extends to a temperature-control package designed and/or manufactured according to one of the above methods.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a schematic cross-sectional view of a temperature-control packaging.

Figure 1 shows a temperature-controlled packaging 10 comprising an outer protective layer 12, an insulation section 14, a phase-change material 16, an inner box 18 and an article to be transported 20.

The article 20 is separated from the phase-change material 16 by the inner box 18 in order to protect the article from condensation for example.

When it is required to keep the article 20 below ambient temperatures, then a phase change material is chosen that absorbs heat from its surroundings to achieve the phase change and thereby prevents heating of the article 20.

Different phase change materials can be used, depending on the temperature range required for the article and also the cost constraints for the package.

The temperature control performance characteristics of the temperature-control packaging 10 can be constrained by limits in both mass and volume of the article 20. To balance these mass and volume properties with the thermal control of the article 20 to be shipped it is possible to optimise the design parameters of insulation wall thickness and space available for the thermally driven physical change material 16 to produce a temperature-control packaging design. The design should optimise the duration the article thermally associated with the phase-change materials 16 remains within a given temperature range for a known external temperature exposure.

By determining the thermal energy flow through a given insulation material 14 as a function of its thickness and then using this thickness to simultaneously determine the space available for a specific thermally driven physical change material 16 the packaging wall thickness can be defined to provide the maximum duration of temperature control of the product.

Under different physical volume and mass restraints the optimum thickness will vary.

Different thermally driven physical change materials and different thermal insulation materials will vary the optimum thermal insulation material thickness.

Examples of phase-change materials that are used include dry ice (frozen carbon dioxide), wet ice (frozen water) and brine for packaging intended to keep an article below ambient temperature. Paraffin is an example of a phase-change material that is used to keep an article in a temperature range above ambient. These materials are simply examples and others could be used, based primarily on the latent heat capacity, cost and chemical stability.

Examples of insulation material used are expanded polystyrene, expanded polylactic acid, vacuum insulation panels, polyurethane foam, extruded polystyrene and expanded polypropylene. These materials are simply examples and others could be used, based primarily on the insulative properties, cost and chemical stability.

Examples of temperature ranges that are frequently required are as follows. <18°C (hard frozen) , 5°C+I-3°C, 2-10°C, 2-12°C, 2-15°C and "do not freeze". For a hard frozen product brines or dry ice may be used as the phase-change material.

The relationship between duration in a given temperature range and wall thickness can be described by the following equations, where t= time duration, tMAx being the maximum duration attainable T=Thickness of insulation m = mass of phase changing material e energy flow through the insulation V = Volume maximum (the external volume limit) a = a constant of a function f(T) relating to heat flow, such that f(T)= a /12 /3 = constant of a thickness function g(T) relating to the volume of insulation such that g(T) = /3 T3 The equations assume a cubic package, which shape minimises surface area for a cuboid.

V-g(T) -V-f3T3 -VT2 J3T3T2 e f(T) -a/T2 -a a at tMftJ( =-O at = 2VT J3T = [2VT -5J3T = -5J3T)= o This physical solution is further constrained by the total mass mTOT of 5 kg which can be defined as follows mIOT =m +mINS =p1(V-g(T))+p2(g(t)) where mpc is the mass of phase changing material, is the mass of the insulation material and i and p2 are the densities of both materials respectively. V is the volume limit as above, m101 must remain below the mass limit.

These formulae when used with experimentally determined values for density, heat flow, thermal conductivity and latent heat of the phase-change materiall6 can determine the optimum wall thickness within a specified mass and volume limit.

A box has been designed to regulate the temperature of an article using the solid to gas sublimation physical change exhibited by Carbon Dioxide at -78°C at standard air pressure. The physical properties of the solid to gas sublimation phase change are well documented and the specific preparation of the solid material has a known density.

The insulation material 14 is chosen to be moulded expanded polystyrene having a controlled density of 20kg m3. The realistic thermal conductivity and energy flow for this material in moulded forms are 0.037 W m1 Ic1) and 4.09 W m1 respectively.

The specific limits on mass and volume were 5kg and 281 for the total product with reductions in both of these to account for exterior and interior fittings.

For limits of mç-and V of 5kg and 281 respectively using a phase change material of density 800kg m3 and an insulation material of density 20kg m3 the expression for the mass equation above is: mioi-= 20V -20 g(T)+800 g(T).

Experimentally we can determine the heat flow with thickness of insulation to equal 0.030 W m1 K and the latent heat of sublimation of dry ice per kg at standard air pressure is 8.94 x 106 J kg'.

With an experimentally defined external temperature profile with a mean kinetic temperature of 308°K the heat flow function f mentioned above can be determined providing an experimentally defined value for a.

Similarly by evaluation of heat flow by means of duration to sublimation of known masses of dry ice a value for flcan be determined (for this material by this means of construction 73.3).

T=3/' T=3/2<28 with /3 = 67.7 the expression becomes X 67.7 = 0.0549 m This gives a thickness of 55 mm to the nearest mm This produced a thermal packaging design with a wall thickness of 55mm, which leads to an interior volume of 6.281. Thus, for a cubic package, the interior volume of 6.281 gives a cubic space measuring 184mm on each side for the article to be transported and the phase change material.

This thickness, a rounding to the nearest millimetre (precision of moulding) is the value determined to give the longest duration during which the phase changing material is at the temperature of phase change.

From the above it can be seen that given the initial values of a mass and volume of the final package, as well as values for thermal conductivity, heat flow, and latent heat of the phase-change material, that a package size can be determined. This is a significant advance on previous trial and error methods for developing a package.

The ability to provide a system and method for producing packages of optimum size is particularly advantageous.

We have described a method for the determination of the optimal thermal insulation thickness necessary for the greatest duration of thermal stability offered by combinations of specified thermal materials in systems of restricted mass and volume.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims 1. A method of manufacturing a temperature-control package comprises: selecting a mass and volume for the temperature-control package; selecting an insulation material and a thermally driven physical change material; calculating a wall thickness for walls formed of the insulation material; said calculation being based on values of density, heat flow and thermal conductivity of the insulation material and on values of density and latent heat of the physical change material; and forming walls of a temperature-control package having dimensions substantially defined by the selected volume of the temperature-control package and the calculated wall thickness.
2. The method of claim 1, also comprising calculating a volume of an internal space for an article to be placed in the temperature-control package.
3. The method of claim 2, in which the formed walls also define the calculated internal space.
4. The method of any preceding claim also comprising locating the phase change material inside the walls to control the temperature inside the temperature-control package.
5. The method of any preceding claim, wherein the package is a substantially cubic package.
6. The method of any preceding claim wherein the mass of the temperature-control package excludes a mass of an article to be place in the package.
7. The method of any preceding claim wherein the mass of the temperature-control package includes the mass of the insulation material and the thermally driven physical change material.
8. The method of any preceding claim wherein the thermally driven physical change material is chosen based on a target temperature range for the interior of the temperature-control package.
9. The method of claim 8, wherein the target temperature range for the interior of the temperature-control package is a target temperature range within the insulation of the temperature-control package.
10. A method of designing a temperature control package comprises: selecting a mass and volume for the temperature-control package; selecting an insulation material and a thermally driven physical change material; calculating a wall thickness for walls formed of the insulation material; said calculation being based on values of density, heat flow and thermal conductivity of the insulation material and on values of density and latent heat of the physical change material.
11. A temperature-control package designed and/or manufactured according to one of the methods of claims 1 to 10. Co