THERMAL ACCUMULATOR CONTAINING A PCM, AND REFRIGERATED CONTAINER EQUIPED WITH SAID THERMAL ACCUMULATOR

Abstract

Thermal accumulator (1) comprising external walls (2) delimiting a closed storage space (3) that contains a PCM (4) and a heat exchanger (5) formed by a conduit for fluids having a section (12) inside said storage space (3). Two of said external walls (2) are facing one another and are connected between them by internal walls (10a) located inside the storage space (3) and arranged so that cells (11) containing the PCM (4) are formed in said storage space (3) by said internal walls (10a) and said external walls (2). The external walls (2) and the internal walls (10a, 10b) are flat copper sheets. The section of the heat exchanger (5) that goes inside the storage space (3) is joined to a face of one of said external walls (2) and internal walls (10a). The invention also relates to a refrigerated container for transporting goods comprising the thermal accumulator (1).

Claims

1. Thermal accumulator containing a PCM (phase change material), said thermal accumulator comprising external walls delimiting a closed storage space, a PCM contained in said storage space and at least a heat exchanger formed by a conduit for fluids which has an inlet port and an outlet port, said heat exchanger having a section that goes inside said storage space and which is in contact with said PCM, and wherein said external walls have an inner surface in contact with said PCM and an outer surface in contact with an external environment surrounding said thermal accumulator, wherein: at least two of said external walls are facing one another and are connected between them by internal walls, said internal walls being located inside said storage space and being arranged so that cells containing said PCM are formed in said storage space by said internal walls and said external walls; said external walls and said internal walls are flat copper sheets; said section of said heat exchanger that goes inside said storage space is joined to a face of at least one of said external walls and internal walls that form said cells.

2. Thermal accumulator according to claim 1, wherein said external walls and said internal walls are flat copper sheets having a thickness not greater than 1.016 mm (0.04 inch).

3. Thermal accumulator according to claim 2, wherein said external walls and said internal walls are flat copper sheets having a thickness in the range between 0.4 mm and 0.8 mm.

4. Thermal accumulator according to claim 1, wherein said section of the heat exchanger is a coil tube comprising at least a planar section which is parallel to one of said two facing external walls and which is joined to this external wall.

5. Thermal accumulator according to claim 1, wherein said coil tube comprises two planar sections, which are parallel to one and the other of said two facing external walls and which are joined to one and the other of said two facing external walls, respectively.

6. Thermal accumulator according to claim 4, wherein in said planar section of said coil tube comprises a succession of straight tubes connected to one another by tube elbows, said straight tubes being positioned so that at the corners formed between said one of the two facing external walls and said internal walls one of said straight tubes is joined to a face of at least one of the external wall and the internal wall.

7. Thermal accumulator according to claim 1, wherein said section of the heat exchanger is a coil tube comprising at least an inner section which is separated from said two facing external walls and which is joined to at least one of said internal walls.

8. Thermal accumulator according to claim 7, wherein said coil tube comprises at least an inner planar section which is parallel to one of said internal walls and which is joined to this internal wall.

9. Thermal accumulator according to claim 1, wherein said internal walls are separated from a bottom wall that delimitates said storage space, so that a lower band of said storage space is defined between said bottom wall and a lower edge of said internal walls, said cells being in fluid communication with one another through said lower band, and in that said internal walls are separated from an upper wall that delimitates said storage space, so that an upper band of said storage space is defined between said upper wall and an upper edge of said internal walls, said cells being in fluid communication with one another through said upper band, and wherein the level of said PCM in said storage space is in said upper band.

10. Thermal accumulator according to claim 1, wherein said internal walls have folded ends that form a planar flange, and said planar flange rests against the inner surface of one of said two facing external walls and is joined to said inner surface.

11. Thermal accumulator according to claim 1, wherein said PCM is an aqueous salt solution comprising as a solute a salt selected from the group consisting in sodium formate, potassium formate, calcium formate and magnesium formate.

12. Thermal accumulator according to claim 11, wherein said PCM is an aqueous salt solution in which the solute is sodium formate, wherein the mass fraction of sodium formate in the solution is comprised between 0.05 and 0.25.

13. Thermal accumulator according to claim 11, wherein said PCM is an aqueous salt solution in which the solute is sodium formate, wherein the mass fraction of sodium formate in the solution is comprised between 0.45 and 0.55.

14. Thermal accumulator according to claim 11, wherein said PCM is an aqueous salt solution in which the solute is a mixture of sodium formate and potassium formate, wherein the mass fraction of sodium formate in the solution is 0.25 and the mass fraction of potassium formate in the solution is comprised between 0.03 and 0.20, more preferably between 0.05 and 0.10.

15. Refrigerated container for transporting goods, comprising a thermally insulated main chamber for storing goods and a thermal accumulator according to claim 1, said thermal accumulator being arranged in said refrigerated container so that the indoor environment of said main chamber is in air communication with the external walls of said thermal accumulator.

16. Refrigerated container according to claim 15, wherein the refrigerated container comprises: a thermally insulated auxiliary chamber in which said thermal accumulator is located, the outer surface of the external walls of the thermal accumulator being in contact with the indoor environment of said auxiliary chamber, said auxiliary chamber being separated from said main chamber; conduits that put in air communication said indoor environment of the main chamber with said indoor environment of the auxiliary chamber; an air impeller arranged for establishing a forced circulation of air between said indoor environment of the main chamber and said indoor environment of the auxiliary chamber through said conduits; a temperature sensor arranged for measuring a temperature in said indoor environment of the main chamber; a control device configured to control the air flow rate provided by said air impeller depending on a deviation of the temperature measured by said temperature sensor with respect to a set-point value.

17. Refrigerated container according to claim 16, wherein the refrigerated container comprises one or several electric batteries arranged to autonomously power said air impeller and said control device.

18. Refrigerated container according to claim 15, wherein the refrigerated container comprises a refrigeration unit having a compressor, a condenser and an expansion valve forming a cooling circuit connected to said heat exchanger of the thermal accumulator, so that said heat exchanger is the evaporator of said refrigeration unit, and wherein at least the compressor and the condenser of said refrigeration unit are located outside said main chamber and outside said auxiliary chamber.

19. Thermal accumulator according to claim 5, wherein in said planar section of said coil tube comprises a succession of straight tubes connected to one another by tube elbows, said straight tubes being positioned so that at the corners formed between said one of the two facing external walls and said internal walls one of said straight tubes is joined to a face of at least one of the external wall and the internal wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The advantages and features of the invention will be understood from the following description in which preferred embodiments of the invention are described with reference to the drawings without limiting the scope of the invention defined in the claims.

[0044] FIG. 1 is a perspective view of a first embodiment of the thermal accumulator, in which the frontal external wall and partially the upper external wall have been cropped in order to show the inner parts of the thermal accumulator.

[0045] FIG. 2 is a sectional frontal view of the thermal accumulator of FIG. 1.

[0046] FIG. 3 is a sectional top view of the thermal accumulator of FIG. 1.

[0047] FIG. 4 is a zoomed view of an area of FIG. 3 showing a straight tube of the heat exchanger at the corner between an external wall and an internal wall.

[0048] FIG. 5 is a sectional top view of a second embodiment of the thermal accumulator.

[0049] FIG. 6 is a sectional top view of a third embodiment of the thermal accumulator.

[0050] FIG. 7 is a front perspective view of an embodiment of a refrigerated container comprising a thermal accumulator according to the invention.

[0051] FIG. 8 is a partial sectional lateral view of the refrigerated container.

[0052] FIG. 9 is a rear perspective view of the refrigerated container.

[0053] FIG. 10 is a front sectional view of another embodiment of the refrigerated container that only differs in the conduits communicating the main chamber and the auxiliary chamber.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0054] FIGS. 1 to 4 show a first embodiment of the thermal accumulator 1.

[0055] The thermal accumulator 1 is constituted by six external walls 2 forming a rectangular parallelepiped which delimitate a storage space 3, several internal walls 10a that connect between them two facing of said external walls 2, and a heat exchanger 5 having a section 12 that goes inside the storage space 3. The storage space 3 contains a PCM (phase change material) 4 which is in contact with said section 12 of the heat exchanger 5 and with the inner surface 8 of the external walls 2. The outer surface 9 of the external walls 2 are in contact with the external environment surrounding the thermal accumulator 1, so that the PCM 4 exchanges heat with the external environment through said external walls 2.

[0056] The external walls 2 and the internal walls 10a are copper sheets. For instance, they are 0.0197 inch (0.5 mm) thick sheets of soft annealed Copper Alloy 110 (containing at least 99.9% of copper). The internal walls 10a have folded ends that form planar flanges 34 which rest against the inner surface 8 of said two facing external walls 2 and which are joined to said inner surface 8 preferably by brazing. The internal walls 10a are parallel between them and transversal to the two facing external walls 2, so that these walls 10a, 2 form cells 11 that contain PCM 4 in the storage space 3. As can be appreciated in FIG. 2, the internal walls 10a are separated from a bottom wall 18 and from an upper wall 20 which delimitate the storage space 3. In this exemplary embodiment the bottom wall 18 and the upper wall 20 are also external walls 2. A lower band 19 and an upper band 21 of the storage space 3 are thus defined between the bottom wall 18 and a lower edge of the internal walls 10a, and between the upper wall 20 and an upper edge of said internal walls 10a, respectively. The storage space 3 is filled with PCM 4 so that the level of PCM 4 in said storage space 3 is in the upper band 21. The cells 11 are thus in fluid communication with one another through the lower band 19 and the upper band 21. Therefore, the fraction of PCM 4 which is in liquid state can circulate between the cells 11 through these bands 19, 21. As it can also be appreciated from FIG. 2, an air gap 41 is provided between the level of PCM 4 and the upper wall 20. This air gap 41 acts as an expansion chamber to absorb the variations of volume of the PCM 4 at the phase change. The upper wall 20 is provided with a cap 35 than can be removed to fill the storage space 3 with PCM 4. At least a temperature probe 36 is inserted in the storage space 3 for measuring the temperature of the PCM 4 in order to control the process of charging the thermal accumulator 1 with a thermal load and also for monitoring the state of the PCM 4 during the phase of delivering the thermal load to the environment.

[0057] The section 12 of the heat exchanger 5 that goes inside the storage space 3 is a coil tube comprising two planar sections 13 which are parallel to one and the other of the two facing external walls 2 and which are joined to one and the other of said two facing external walls 2. This coil tube is also made of Copper Alloy 110. Each planar section 13 of the coil tube comprises a succession of straight tubes 14 connected to one another by tube elbows 15. The straight tubes 14 are positioned so that, at the corners formed between one of the two facing external walls 2 and the internal wall 10a connected to it, one of said straight tubes 14 is joined to a face of at least one of the external wall 2 and the internal wall 10a. Preferably, they are joined to both walls 2, 10a as shown in FIG. 4. In the exemplary embodiment, the straight tubes 14 are joined to the walls 2, 10a by brazing. Each of said planar sections 13 of the heat exchanger 5 is thus joined to a face of one of the two facing external walls 2. As can be seen in FIGS. 1 and 2, the tube elbows 15 pass from one cell 11 to another through the lower band 19 and the upper band 21.

[0058] The heat exchanger 5 is formed by a conduit for fluids, in this case in form of a coil tube, and has an inlet port 6 and an outlet port 7, so that a heat transfer fluid can enter the thermal accumulator 1 through the inlet port 6, flow inside said heat exchanger 5 while exchanging heat with the PCM 4 and exit the thermal accumulator 1 through the outlet port 7. This heat transfer fluid circulating in the heat exchanger 5 provides a thermal load to charge the thermal accumulator 1.

[0059] Preferably the PCM is an aqueous salt solution comprising as a solute a salt selected from the group consisting in sodium formate, potassium formate, calcium formate and magnesium formate.

[0060] The following examples are some possible preferred choices for the PCM.

Example 1 (Solute: Sodium Formate)

[0061] The PCM 4 is an aqueous salt solution in which the solute is sodium formate. The mass fraction of sodium formate in the solution is selected in the range between 0.05 and 0.25. The crystallization temperature of the brine in this range of mass fraction is the following:

TABLE-US-00001 Mas fraction of sodium formate Crystallization temperature 0.05 −4° C. 0.10 −9° C. 0.25 −16° C. 

Example 2 (Solute: Sodium Formate)

[0062] The PCM is an aqueous salt solution in which the solute is sodium formate. The mass fraction of sodium formate in the solution is selected in the range between 0.45 and 0.55. The crystallization temperature of the brine in this range of mass fraction is the following:

TABLE-US-00002 Mas fraction of sodium formate Crystallization temperature 0.45 +6° C. 0.55 +15° C. 

Example 3 (Solute: Sodium Formate+Potassium Formate)

[0063] The PCM is an aqueous salt solution in which the solute is a mixture of sodium formate and potassium formate. The mass fraction of sodium formate in the solution is 0.25, which corresponds to the eutectic point for a sodium formate brine. The mass fraction of potassium formate in the solution is selected in the range between 0.03 and 0.20, more preferably between 0.05 and 0.10. The crystallization temperature of the brine in this range of mass fraction of potassium formate, for a mass fraction of sodium formate of 0.25, is the following:

TABLE-US-00003 Mas fraction of Mas fraction of Crystallization sodium formate potassium formate temperature 0.25 0.03 −21° C. 0.25 0.05 −25° C. 0.25 0.10 −33° C. 0.25 0.20 −48° C.

Example 4 (Solute: Potassium Formate)

[0064] The PCM 4 is an aqueous salt solution in which the solute is potassium formate. The mass fraction of potassium formate in the solution is selected in the range between 0.17 and 0.38. The crystallization temperature of the brine in this range of mass fraction is the following:

TABLE-US-00004 Mas fraction of potassium formate Crystallization temperature 0.17 −9° C. 0.24 −16° C.  0.38 −34° C. 

Example 5 (Solute: Calcium Formate)

[0065] The PCM 4 is an aqueous salt solution in which the solute is calcium formate. The mass fraction of potassium formate in the solution is 0.14, which corresponds to the maximum solubility of potassium formate in water. The crystallization temperature of the brine is −12° C.

Example 6 (Solute: Magnesium Formate)

[0066] The PCM 4 is an aqueous salt solution in which the solute is magnesium formate. The mass fraction of magnesium formate in the solution is 0.12, which corresponds to the maximum solubility of magnesium formate in water. The crystallization temperature of the brine is −10° C.

Example 7 (Solute: Sodium Formate+Calcium Formate)

[0067] The PCM 4 is an aqueous salt solution in which the solute is a mixture of sodium formate and calcium formate. The mass fraction of sodium formate in the solution is 0.25, which corresponds to the eutectic point for a sodium formate brine. The mass fraction of calcium formate in the solution is 0.14, which corresponds to the maximum solubility of calcium formate in water. The crystallization temperature of the brine is −35° C.

Example 8 (Solute: Sodium Formate+Magnesium Formate)

[0068] The PCM 4 is an aqueous salt solution in which the solute is a mixture of sodium formate and magnesium formate. The mass fraction of sodium formate in the solution is 0.25, which corresponds to the eutectic point for a sodium formate brine. The mass fraction of magnesium formate in the solution is 0.12, which corresponds to the maximum solubility of magnesium formate in water. The crystallization temperature of the brine is −30° C.

[0069] Besides these examples, the PCM can be an aqueous salt solution in which the solute is formed by other mixtures of the above mentioned formate salts. It can also include suitable additives in addition to said formate salts.

[0070] FIG. 5 shows a second embodiment which only differs from the first embodiment in that the section 12 of the heat exchanger 5 that goes inside the storage space 3 is a coil tube that comprises inner sections 16 which are separated from the two facing external walls 2 and which are joined to at least one of the internal walls 10a.

[0071] FIG. 6 shows a third embodiment which only differs from the second embodiment in that it comprises longitudinal internal walls 10b which are orthogonal to the transversal internal walls 10a and which connect between them two facing external walls 2, and in that the inner sections 16 of the coil tube are inner planar sections 17 which are parallel to said longitudinal internal walls 10b and which are joined to them. In this embodiment, the transversal internal walls 10a that connect between them the two facing external walls 2 are not continuous. In fact, they are discontinued by longitudinal internal walls 10b to which they are joined.

[0072] FIGS. 7 to 10 show a refrigerated container 22 for transporting goods, comprising a thermally insulated main chamber 23 for storing goods and a thermal accumulator 1 according to the invention. The front wall of the main chamber 23 is provided with an openable door 43 that allows a person to access the goods from the outside of the refrigerated container 22. The refrigerated container 22 also comprises a thermally insulated auxiliary chamber 25 in which the thermal accumulator 1 is located, so that the outer surface 9 of the external walls 2 of the thermal accumulator 1 are in contact with the indoor environment 26 of said auxiliary chamber 25. Both the main chamber 23 and the auxiliary chamber 25 are delimited by thermally isolating walls 38. The auxiliary chamber 25 is separated from the main chamber 23. However, the indoor environments 24, 26 of the two chambers 23, 25 are in air communication between them by conduits 27, 28. In the example shown in FIGS. 7 and 8 the conduits 27, 28 are two openings that extend through the thermally isolating wall 38 that separates the two chambers 23 and 25. At least one of these openings is provided with an air impeller 29 that drives an air flow through said opening, so that a forced circulation of air is established between the indoor environment 24 of the main chamber 23 and the indoor environment 26 of the auxiliary chamber 26 through said conduits 27, 28. This forced circulation of air puts in air communication the indoor environment 24 of the main chamber 23 with the external walls 2 of the thermal accumulator 1 located in the auxiliary chamber 25. A temperature sensor 30 is arranged for measuring a temperature in the indoor environment 24 of the main chamber 23. A control device 31 is comprised in the refrigerated container 22. The control device 31 is configured to control the air flow rate provided by the air impeller 29 depending on a deviation of the temperature measured by the temperature sensor 30 with respect to a set-point value.

[0073] The refrigerated container 22 also comprises an electric battery 32 able to autonomously power the air impeller 29 and the control device 31.

[0074] FIG. 10 shows another embodiment of the refrigerated container 22 that only differs in the conduits 27, 28 that communicate the two chambers 23, 25. In this case the conduits 27, 28 are air ducts that extend in the main chamber 23 in order to better distribute the flow of air in said chamber 23.

[0075] As shown in FIG. 9, the bottom wall of the refrigerated container 22 is optionally provided with wheels 39 and/or with guides 40 for a pallet fork. These means 39, 40 make transportation of the refrigerated container 22 easier.

[0076] The refrigerated container 22 optionally comprises a refrigeration unit 33 having a compressor, a condenser and an expansion valve forming a cooling circuit connected to the heat exchanger 5 of the thermal accumulator 1, so that the heat exchanger 5 is the evaporator of said refrigeration unit 33. At least the compressor and the condenser, preferably the expansion valve also, of the refrigeration unit 33 are located outside the main chamber 23 and outside the auxiliary chamber 25. They are preferably located in a second auxiliary chamber 37 having an opening to the external environment surrounding the refrigerated contained 22. In the embodiment shown in FIGS. 7 to 9 the second auxiliary chamber 37 is located under the auxiliary chamber 25 and it is separated from said external environment by a grid that allows air to circulate.

[0077] The refrigerated container 22 according to the invention can advantageously be applied to be loaded on a vehicle for transporting goods, such as a truck or a van, in particular for transporting food and pharmaceutical products. It is particularly suitable to this purpose because the thermal accumulator 1, in comparison to those from prior art, has a reduced weight, it accumulates less dirt and it can be cleaned more easily. In addition, when the mentioned formate brines are used as PCM, it is suitable for food contact applications and it is not harmful to the environment. Furthermore, the refrigerated container 22 is able to effectively maintain the temperature of the goods stored in the main chamber 23 at the desired value without receiving any power from the vehicle after having charged the thermal accumulator 1 with a cooling load. This is done preferably by connecting the refrigeration unit 33 to an external electricity network. When the refrigerated container 22 does not comprise a refrigeration unit 33, this is done by connecting the inlet and the outlet ports of the heat exchanger 5 to the refrigerant circuit of an external refrigeration unit by means of connection hoses, so that said heat exchanger 5 becomes the evaporator of said refrigeration unit.