PASSIVE REFRIGERATION SYSTEM FOR THE COLD CHAIN INDUSTRY

Abstract

A passive refrigeration box for controlled refrigeration of a product comprising: an outer box including an outer insulation layer; an inner box including an inner insulation layer, and a thermal shield on an outside of the inner insulation layer, the inner box and the outer box defining a vapour channel therebetween; and a thermal link including a thermal layer and a plurality of heat pipes or thermosyphons, the thermal layer and a top section of the inner box defining a coolant chamber, the coolant chamber including a coolant chamber access, and in communication with the vapour channel, and the thermal layer and a bottom section of the inner box defining a load chamber, the load chamber including a load chamber access, each heat pipe or thermosyphon having a condenser section disposed in the coolant chamber and an evaporator section disposed in the load chamber and extending through the thermal layer.

Claims

1. A passive refrigeration box for controlled refrigeration of a product, the refrigeration box comprising: an outer box, the outer box including an outer insulation layer; an inner box, the inner box including an inner insulation layer, and a thermal shield on an outside of the inner insulation layer, the inner box and the outer box defining a vapour channel therebetween; and a thermal link, the thermal link including a thermal layer and a plurality of heat pipes or a plurality of thermosyphons, the thermal layer and a top section of the inner box defining a coolant chamber, the coolant chamber including a coolant chamber access, and the coolant chamber in communication with the vapour channel, and the thermal layer and a bottom section of the inner box defining a load chamber, the load chamber including a load chamber access, each heat pipe or thermosyphon having a condenser section disposed in the coolant chamber and an evaporator section disposed in the load chamber and extending through the thermal layer.

2. The passive refrigeration box of claim 1, further comprising a mesh header below the plurality of heat pipes or the plurality of thermosyphons.

3. The passive refrigeration box of claim 1, further comprising an outer skin on the outer insulation and an inner liner on the inner insulation.

4. The passive refrigeration system of claim 1, wherein the thermal link includes the plurality of heat pipes.

5. The passive refrigeration box of claim 1, wherein the thermal shield is an aluminum shield.

6. The passive refrigeration box of claim 1, wherein the coolant chamber access includes an outer lid and an inner lid.

7. The passive refrigeration box of claim 6, wherein the inner lid is seated on a step in the inner box.

8. The passive refrigeration box of claim 1, further comprising a gasket between an inner lid and a step in the inner box.

9. The passive refrigeration box of claim 1, wherein the plurality of heat pipes are weld-free heat pipes.

10. The passive refrigeration box of claim 9, wherein the plurality of heat pipes include a working fluid, the working fluid selected from a group consisting of acetone, methanol, pentane, and propylene.

11. The passive refrigeration box of claim 1, wherein the thermal link is a reconfigurable thermal link.

12. The passive refrigeration box of claim 6, further comprising a check valve in the outer lid, wherein the check valve is in communication with the vapour channel.

13. A passive refrigeration system for the cold-chain industry, the system including: a box and a solid coolant, the box comprising: an outer box, the outer box including an outer insulation layer, an inner box, the inner box including an inner insulation layer, and a thermal shield on an outside of the inner insulation layer, the inner box and the outer box defining a vapour channel therebetween; and a thermal link, the thermal link including a thermal layer and a plurality of heat pipes or a plurality of thermosyphons, the thermal layer and a top of the inner box defining a coolant chamber, the coolant chamber including a coolant chamber access, and the coolant chamber in communication with the vapour channel, and the thermal layer and a bottom of the inner box defining a load chamber, the load chamber including a load chamber access, each heat pipe of the plurality of heat pipes or thermosyphon of the plurality of thermosyphons having a condenser section disposed in the coolant chamber and an evaporator section disposed in the load chamber and extending through the thermal layer, and where the solid coolant is solid carbon dioxide.

14. The system of claim 13, wherein the thermal link is a reconfigurable thermal link.

15. The system of claim 13, wherein the thermal link includes the plurality of heat pipes.

16. The system of claim 13, wherein the heat pipes are weld-free heat pipes.

17. The system of claim 16, wherein the heat pipes include a working fluid, the working fluid selected from a group consisting of acetone, methanol, pentane, and propylene.

18. The system of claim 13, wherein the thermal shield is an aluminum shield.

19. A passive refrigeration box for controlled refrigeration of a product, the refrigeration box comprising: a bottom; four sides attached to the bottom; an inner lid; and an outer lid, the sides including an outer insulation layer and an inner insulation layer, the layers and the inner and outer lids defining a vapour channel therebetween, an aluminum shield adjacent the vapour channel and abutting an outer side of the inner insulation layer and a top of the inner lid; a thermal layer, the thermal layer disposed below the inner lid and between the inner insulation layers to define a coolant chamber, the coolant chamber for retaining a coolant and in communication with the vapour channel; and a load chamber, the load chamber defined by the inner insulation layer and the thermal layer; and a plurality of heat pipes, each heat pipe of the plurality of heat pipes having a condenser section disposed in the coolant chamber and an evaporator section disposed in the load chamber and extending through the thermal layer.

20. A method of refrigerating a load passively, using the refrigeration box of claim 1, the method comprising loading the load into the load chamber and charging the coolant chamber with a solid coolant.

21. The method of claim 20, further comprising configuring the thermal link to regulate the temperature of the load.

22. The method of claim 20, wherein the solid coolant is solid carbon dioxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the present invention are described below with reference to the accompanying drawings in which:

[0024] FIG. 1 is a longitudinal sectional view of a heat pipe in accordance with an aspect of the present invention.

[0025] FIG. 2 is a longitudinal sectional view of an end cap and tube end of the heat pipe of FIG. 1.

[0026] FIG. 3 is a perspective sectional view of the passive refrigeration box in accordance with an aspect of the present invention.

[0027] FIG. 4 is a longitudinal sectional view of passive refrigeration box of FIG. 3.

[0028] FIG. 5 is a longitudinal sectional view an alternative embodiment of a passive refrigeration box.

[0029] FIG. 6 is a longitudinal sectional view of an alternative embodiment of a passive refrigeration box.

[0030] FIG. 7A illustrates the operation of a reconfigurable thermal link in accordance with an aspect of the present invention.

[0031] FIG. 7B illustrates the operation of a reconfigurable thermal link in accordance with an aspect of the present invention.

DESCRIPTION

[0032] The present invention now will be described more fully hereinafter with reference to the accompanying drawing(s), which form a part hereof, and which show, by way of illustration, exemplary embodiments by which the invention may be practiced. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense.

[0033] Except as otherwise expressly provided, the following rules of interpretation apply to this specification (written description, claims and drawings): (a) all words used herein shall be construed to be of such gender or number (singular or plural) as the circumstances require; (b) the singular terms a, an, and the, as used in the specification and the appended claims include plural references unless the context clearly dictates otherwise; (c) the antecedent term about applied to a recited range or value denotes an approximation within the deviation in the range or value known or expected in the art from the measurements method; (d) the words herein, hereby, hereof, hereto, herein before, and hereinafter, and words of similar import, refer to this specification in its entirety and not to any particular paragraph, claim or other subdivision, unless otherwise specified; (e) descriptive headings are for convenience only and shall not control or affect the meaning or construction of any part of the specification; and (f) or and any are not exclusive and include and including are not limiting. Further, the terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted.

[0034] To the extent necessary to provide descriptive support, the subject matter and/or text of the appended claims is incorporated herein by reference in their entirety.

[0035] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Where a specific range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is included therein. All smaller sub ranges are also included. The upper and lower limits of these smaller ranges are also included therein, subject to any specifically excluded limit in the stated range.

[0036] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the relevant art. Although any methods and materials similar or equivalent to those described herein can also be used, the acceptable methods and materials are now described.

Definitions

[0037] Heat pipein the context of the present invention, a heat pipe consists of a sealed pipe that un-releasably retains a working fluid. A wick is present in the bore of the pipe. (In essence, a heat pipe is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to effectively transfer heat between two solid interfaces. At the hot interface of a heat pipe a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor then travels along the heat pipe to the cold interface and condenses back into a liquidreleasing the latent heat. The liquid then returns to the hot interface through capillary action (wicking), and the cycle repeats. Due to the very high heat transfer coefficients for boiling and condensation, heat pipes are generally highly effective as heat transfer devices.)

[0038] Thermosyphonin the context of the present invention, a thermosyphon is similar in components and construction to a heat pipe, except it contains a larger amount of working fluid and it does not contain a wick structure. It unreleasably retains a working fluid.

[0039] Weld-free heat pipein the context of the present invention, a weld-free heat pipe is one that has barbed end caps and barbs on the inside of the tube of the heat pipe proximate the ends. The end caps and tube are press fit together.

[0040] Weld-free, soldered heat pipein the context of the present invention, a copper heat pipe is soldered to close the end caps to the tube.

[0041] Weld-free, soldered thermosyphonin the context of the present invention, a thermosyphon is soldered to close the end caps to the tube.

[0042] Working fluidin the context of the present invention, a working fluid is one that is present as both a saturated liquid phase and a vapour phase in the heat pipe. The liquid is evaporated to a vapour at the evaporator region of the heat pipe, and the vapour is condensed to a liquid at the condenser region of the heat pipe. For present purposes, any one of pentane, propylene, acetone and methanol, are good candidates for use as the working fluid; other refrigerants that are also suitable for use as the working fluid will be apparent to a person skilled in the art.

[0043] Wickin the context of the present invention, a wick is a material that lines the bore of the heat pipe and exerts a capillary action on the liquid phase of the working fluid.

[0044] Thermal linkin the context of the present invention, a thermal link is an interface for the management of heat flow (thermal energy flow). The design and the material used determine the thermal conduction of the thermal linkage. The thermal linkage includes the heat pipes and an insulating or conducting layer (the thermal layer).

[0045] Reconfigurable thermal linkin the context of the present invention, a reconfigurable thermal link refers to a thermal link that can be altered to change or optimize the thermal conductivity for a given application (temperature requirement).

[0046] Solid coolantin the context of the present invention, charging the coolant chamber with a solid coolant means that a solid coolant is added, or a liquid coolant is injected which then changes phase from a liquid to a solid coolant.

DETAILED DESCRIPTION OF THE INVENTION

[0047] A heat pipe, generally referred to as 8 is shown in FIG. 1. It is a tube 10 that has a first end 12, with a first end cap 14, and a second end 16, with a second end cap 18. The second end cap 18 has a fill tube 20 extending therefrom. A bore 22 extends from the first end cap 14 to the second end cap 18. The fill tube 20 has a crimping end 24 distal to the second end cap 18 and a fill tube bore 26. The second end cap 18 has a central aperture 28. The wall 30 of the central aperture 28 has a step 32 upon which the proximal end 32 of the fill tube 20 is seated (as may be more clearly seen in FIG. 2). A solder bead 34 attaches the fill tube 20 to the second end cap 18. In FIG. 1, the crimping end 24 is crimped, after the working fluid has been added to the pipe. A bead of solder 40 seals the crimped end 24. The heat pipe 8 has a wick 42 in the bore 22.

[0048] As shown in FIG. 2, and using the second end cap as an example, the first end 12 and the second end 16 and the end caps 14, 18 are barbed 50, with the end cap 14, 18 preferably being the male mating member 52 and the ends 12, 16 being the female mating member 54 and also having barbs 56. An O-ring 60 is seated in the mating pair. This provides a weld-free heat pipe.

[0049] As noted above, the heat pipe or thermosyphon (as the case may be), may be weld-free and soldered closed.

[0050] A passive refrigeration box, generally referred to as 80 is shown in FIG. 3. The refrigeration box 80 provides passive cooling through the use of heat pipes 8 (for ease of illustration, only a single row of heat pipes is shown in FIG. 3, although it should be understood that additional rows of heat pipes or an array of heat pipes would preferably be used) and with no release of coolant into the load chamber 82. The outer box 81 includes a bottom 84 attached to four walls 86, and an outer lid 88. The box is preferably constructed to provide sufficient strength and support for the load and to be moved using a fork lift. An outer skin 90 of aluminum or steel or plastic is optionally supported by a metal frame 92 in the bottom 84 and four walls 86. A layer of outer insulation 94 lines the inside 96 of the skin 90 and frame 92. The outer insulation 94 is preferably closed cell, extruded or expanded polystyrene or the like and may include vacuum insulated panel insulation. The bottom 84 includes slots 97 for accepting forks of a forklift.

[0051] An inner box 98 includes four inner walls 100, an inner bottom 102, and an inner lid 104. A layer of inner insulation 110 lines the inner liner 112 of the walls 100 and the skin 114 of the inner lid 104. The inner insulation 110 is preferably closed cell, extruded or expanded polystyrene or the like (including vacuum insulated panel insulation). The inner liner 112 and skin 114 are aluminum or plastic. The inner liner 112 includes stand-offs 116 that extend a short distance into the load chamber 150 to ensure that an air gap is maintained between the inner liner 112 and the load. The outer lid 88 is preferably similarly constructed of a skin which is aluminum or plastic, and provided with insulation that is preferably closed cell, extruded or expanded polystyrene or the like (including vacuum insulated panel insulation).

[0052] Abutting the upper surface 118 of the insulation 110 of the inner lid 104 and the outer surface 120 of the inner insulation 100 is a thermal shield 122 which in the preferred embodiment is an aluminum shield 122. The aluminum shield 122 and both the layer of outer insulation 94 on the walls 86 and the outer lid 88 define a space referred to as vapour channel 124. The thermal shield 122 helps to manage heat leaks and maintain the temperature of the cold space. It also decreases the time to cool a load from its initial higher temperature to steady-state while consuming less solid coolant/dry-ice.

[0053] As shown in FIG. 4, the inner lid 104 sits on a step 126 in the inner liner 112. A gasket 128 fits between the inner lid 104 and the step 126 in the inner liner 112. The vapour channel 124 may be sealed from the ambient environment and, optionally, from the coolant chamber 140. Although not expressly shown in FIG. 3, in one embodiment, the vapour channel 124 can be in communication with the coolant chamber 140, such that the vapour channel 124 also serves to circulate the sublimated or evaporated coolant from the coolant chamber 140; in this fashion, the cold sublimated or evaporated (as the case maybe, depending on the coolant used) vapour of the coolant may also be used to help cool the load chamber. Also optionally, a check valve 125 mounted in the outer lid 88 may be provided, so that a small over pressure can be maintained inside the vapour channel 124. This prevents the ingress of external moist air when the coolant/dry ice charge is depleted. Further, the check valve 125 can also serve to prevent the build-up of excess coolant (evaporated or sublimated) in the vapour channel 124. As such, the check valve 125 may simply be a one-directional valve, i.e. which allows vapour to be vented outside to the ambient environment, but prevents air from the ambient environment from entering the vapour channel 124. A coolant 142, which is preferably solid carbon dioxide, is loaded and retained in the coolant chamber 140. Once closed, the coolant chamber 140 does not communicate with the ambient environment. The coolant chamber 140 has a plurality of heat pipes 8 extending into the load chamber 150 through a base 143 of the coolant chamber 140. The base 143 and the heat pipes 8 form a reconfigurable thermal link 144. The reconfigurable thermal link 144 (as described in further detail below) may also allow for customization and optimization of thermal energy transfer between the coolant 142 in the coolant chamber 140 and the load chamber 150. The coolant chamber 140 is in a top section 146 of the inner box 98. The load chamber 150 is in a bottom section 148 of the inner box 98.

[0054] The construction of the heat pipes 8 assist in providing this customization. The portion of the heat pipes 8 extending into the coolant chamber 140 includes the condenser section 152. Below the base 143 and the inner liner 112 is the load chamber 150. The portion of the heat pipes 8 extending into the load chamber 150 includes the evaporator section 156. A mesh header 160 protects the heat pipes 8 from damage in case the load in the load chamber 150 shifts. The mesh may be made from aluminum, steel or plastic and additionally functions to ensure sufficient space for air circulation. The mesh header 160 extends across the load chamber 150 in the vicinity of the top 162 of the load chamber 150. The load chamber 150 is an enclosed space.

[0055] An inner door 170 and an outer door 172 may be constructed in the same manner and with the same materials as the lids 88, 104. These doors do not impede the vapour channel 124. At least one temperature sensor 176 may be located in the load chamber 150 and is in electronic communication with a display 178 that is remote to the refrigerator box 80 or is on an outer surface 178 of the refrigerator box 80.

[0056] In one embodiment, the refrigeration box 80 is sized to accept a pallet load of product. The load is placed in the refrigeration box and then the refrigeration box can be moved into and out of a storage facility or a truck for transport. Different refrigeration boxes operating at different temperatures can be placed side by side and can be delivered together or independently of other refrigeration boxes in the truck. This increases the flexibility in the truck load to be delivered, allows for optimization of storage conditions for product, and reduces energy consumption and the associated pollution caused by running a generator to cool a truck load.

[0057] In an alternative embodiment, a side access allows the coolant chamber 140 either to be slid out and charged/recharged with solid coolant 142, or simply accessed on the side and charged.

[0058] In another embodiment, shown in FIG. 5, the passive refrigeration box 80 of FIGS. 3 and 4 further includes a liquid injection port 180 and a distribution manifold 182 in the coolant chamber 140 for the addition of liquid carbon dioxide. This liquid carbon dioxide flashes into solid carbon dioxide snow (solid coolant 142), hence charging the coolant chamber with solid coolant 142. In an embodiment, such a charging supply of liquid carbon dioxide may be provided/stored with the passive refrigeration box 80 for ready convenience.

[0059] In another embodiment, shown in FIG. 6, the refrigeration box is sized to fit as a single unit in an ISO container 200, hence it is slightly smaller than the inside dimensions of an ISO container 200. The load chamber 150 has a load chamber access 202 that may comprise an inner door 204 and an outer door 206. The coolant chamber access 208 may be through lids or an access 208 on the side, as shown in FIG. 6. The construction and relationship between the doors is the same as the lidsthere is a thermal shield 206 on the outer side 208 of the inner door 202 and the vapour channel 210 has an unimpeded path between the doors 202, 204.

[0060] In another embodiment, the refrigeration box is a container for transport on a trailer or a flat bed. It again may be configured with doors and is as described and shown in FIG. 6.

[0061] In another embodiment, the refrigeration box 80 is a trailer. It again may be configured with doors and is as described and shown in FIG. 6.

[0062] In yet another embodiment, the heat pipes in the refrigeration box or system are replaced with thermosyphons.

[0063] One embodiment of a reconfigurable thermal link (mentioned above as 144) is illustrated in FIGS. 7A and 7B (and generally referenced therein as 249). The function of the reconfigurable thermal link 249 is to modulate the thermal resistance along a specific thermal conductive pathway joining a relatively warm region to a relatively cooler region. By physically adjusting the internal element(s) of the reconfigurable thermal link, the thermal resistance of the aforementioned thermally conductive path can be altered to affect a change in the rate at which heat energy is transferred from the relatively warm region to the relatively cooler region.

[0064] When the reconfigurable thermal link 249 is placed in the thermal path between the load chamber 150 (relatively warm region) and the coolant chamber 140 (relatively cooler region), the rate of heat transfer may be modulated to the point that some degree of load chamber temperature control can be achieved. In one embodiment, the reconfigurable thermal link 249 can be placed at the condenser end of the heat pipes or thermosyphon arrangement (relatively warm region) and the far colder coolant chamber 140, to affect control over the heat transfer rate achieved between the relatively warmer region and the relatively cooler region.

[0065] FIG. 7A shows a relatively warmer region 250, a relatively cooler region 251 and a heat transfer path 252. The reconfigurable thermal link is made up of a thermally conductive housing 253 that is divided into two parts by a thermally insulating housing barrier 254. Together the thermally conductive housing elements 253 and the thermally insulating housing barrier 254, make up the entire housing 258. Inside the housing 258 there is a cavity 255 that is partially occupied by a moving element 259. A portion of the moving element 259 is made up of a thermally conductive end 256 and a thermally insulating end 257. The moving element 259 is capable of be moved the entire width of the internal cavity 255.

[0066] FIG. 7A shows the moving element 259 in an internal position whereby the thermally resistive path from the relatively warm location 250 to the relatively cooler location 251 is minimized. Heat travels through the thermally conductive housing 253, through the thermally conductive portion of the internal moving element 256, through the thermally conductive housing 253 and finally out to the relatively cooler region beyond 251. At each stage of this thermal path, heat is allowed to travel through thermally conductive materials, thus making the total thermal resistance of this path low.

[0067] FIG. 7B shows a perspective view of the reconfigurable thermal link 249 with the internal moving element 259 shifted in such a way as to produce a large thermal resistance impeding heat transfer from relatively warm location 250 to relatively cooler location 251. In this configuration, the pathway for heat to transfer is substantially blocked by the dual insulating materials present in the internal moving element 257 and the housing insulated segment 254. The thermal resistance of both potential heat transfer pathways is very high as a result of the thermal insulating materials that now occupy the potential heat transfer path(s) 252.

[0068] The movable internal thermal element 259 can be motivated to change position by a number of means. Some of these means are passive in that they use no electrical energy to operate, while other motivating mechanisms may use non-passive methods.

[0069] While example embodiments have been described in connection with what is presently considered to be an example of a possible most practical and/or suitable embodiment, it is to be understood that the descriptions are not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the example embodiment. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific example embodiments specifically described herein. Such equivalents are intended to be encompassed in the scope of the claims, if appended hereto or subsequently filed.