COOLING CONTAINER USING PHASE CHANGE MATERIAL AND METHOD FOR OPERATING

Abstract

A cooling container having a coolant chamber and a product chamber. Cooling gases from the coolant chamber circulate between the coolant chamber and the product chamber to retain the latter at a desired low temperature. In one embodiment the cooling gases flow through a radiator disposed in the product chamber. In another embodiment a heat exchanger is provided on a divider wall between the coolant chamber and the product chamber. When a temperature sensor detects that the temperature in the product chamber exceeds a temperature set point, a controller opens valves that allow cool gases in the coolant chamber to circulate through the radiator or across the heat exchanger to lower the temperature in the product chamber.

Description

BACKGROUND

Technical Field

The present invention relates generally to cooling containers and more particularly to portable cooling containers that keep the contents of the container at low temperatures using a phase change material and a method for operating such cooling containers.

Background

Many commodities in the modern world need to be stored and shipped at specific temperatures to maintain their quality. In response to this requirement, suppliers have developed Phase Change Materials (PCM) for more than 100 different temperatures. The effectiveness of these PCM materials at cooling varies wildly depending on the desired temperature. There is as much as a 500% difference between the best and worst PCM in terms of ability to absorb heat energy. Generally, PCM is used commercially much the same as using cold packs (which are PCM) in a cooler. There is no active control of temperature to make sure the temperature is accurate and uniform nor is there air movement to avoid stratification.

Other solutions have been proposed based on thermal electric (TE), e.g., a Peltier device, or compressor technology. Compressor technology is bulky, expensive and not physically robust. TE is inexpensive and robust but is inefficient. TE conversion efficiencies for electrical power to cooling is typically 5 to 10% over a temperature difference of 25° C. Efficiency drops dramatically as the temperature difference increases. As a comparison of TE to the invention; good Li-Ion batteries have an energy density of around 200 WH/Kg which is the same 720 KJ/Kg. Considering the conversion efficiency of TE, this results in 36 KJ/Kg to 72 KJ/Kg of cooling capacity. In comparison dry ice with a cooling capability of 571 KJ/Kg, or water ice at 334 KJ/Kg, have roughly ten times more cooling capability per Kg.

SUMMARY OF THE INVENTION

A cooling container using PCM according to the invention overcomes many of these issues by separating the coolant (PCM) from the product. Now the PCM does not need to be well matched to the desired temperature. With this change, the most efficient PCM material can be used, and there is no longer a need for more than 100 different PCM materials; just a few, perhaps two to four, of the most efficient PCM are adequate.

In the most basic version of the invention there are two chambers, one housing the PCM, the other containing the product. PCM will typically consist of dry ice, water ice or commercial PCM. Water Ice is used for modest temperature reductions. Cooling fluid (gas or liquid) from the PCM circulate between the PCM chamber and the product chamber to retain the latter at a desired low temperature. Heat flow between the two chambers is controlled by measuring the temperature in the product chamber and adjusting the movement of fluid (gas or liquid) that transfers the heat between the chambers. In this way the product chamber can be maintained at a user-determined temperature that is independent of the PCM phase change temperature.

In one embodiment the cooling gases flow through a radiator disposed in the product chamber. In another embodiment a heat exchanger is provided on a divider wall between the PCM chamber and the product chamber.

In another embodiment the cooling fluid passes from the PCM chamber into the product chamber. When a temperature sensor in the product chamber senses that the temperature in the product chamber exceeds a temperature set point, a controller opens valves and/or powers a blower or pump that allows fluid derived from or cooled by the PCM in the PCM chamber to circulate through the radiator, or across the heat exchanger, or pass into the product chamber to lower the temperature in the product chamber.

In another embodiment the temperature control uses more sophisticated Fuzzy logic to better stabilize the temperature and minimize the power requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of a cooling container according to the invention.

FIG. 2 is a graphical representation of another embodiment of a cooling container according to the invention.

FIG. 3 is a graphical representation of third embodiment thereof.

FIG. 4 a graphical representation of fourth embodiment thereof.

FIG. 5 a graphical representation of fifth embodiment thereof.

FIG. 6 is a high level logic diagram of a method for operating a cooling container according to the invention.

FIG. 7 is a flow chart showing one embodiment of a method therefor.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

A cooling container 10 that uses a phase change material (PCM) such as dry ice 12 (solid CO₂) as a cooling medium according to the invention is shown in FIG. 1. The container includes a coolant chamber 14 and a product chamber 16 and may have more than two chambers. The coolant chamber contains PCM 12, the product chamber 16 is sized for carrying goods that need refrigeration such as medicines or biological samples. Applicants have determined that pellet dry ice is a suitable PCM for use in the cooling chamber.

The container 10 comprises an insulated bottom 18, side walls 20, and a removable lid 22. Cooling gas 24 (which may include cold CO₂ gas such as created from sublimation of dry ice) in the PCM chamber 14 is circulated within the container 10 to control the amount of cooling that occurs in the product chamber 16. In the embodiment illustrated in FIG. 1 the cooling gas 24 passes through a radiator 26 to keep the CO₂ gas out of the product chamber 16.

A temperature sensor 28 monitors the temperature in the product chamber 16 and is connected to a controller 30 to which power is supplied by a battery 32. In one embodiment, the battery may be rechargeable. The battery 32 in turn is connected to a power port 33 so that it can be charged.

When the product chamber 16 warms above a predetermined temperature set point, valves 34, 36 are opened that allow the cooling gas 24 to be circulated by a blower or fan 38 through the radiator 26 to cool the product chamber 16 but prevent CO₂ from being introduced into the atmosphere of the product chamber. In one embodiment, the fan motor is located outside the coolant chamber 14. In another embodiment valves 34, 36 may be mechanically driven by, for instance, a solenoid, to allow passive cooling by gas flow due to temperature differences. In yet another embodiment valves 34, 36 are passive and spring loaded such that forced air opens them to increase the amount of cooling gas 24 moved through the product chamber 16. Circulation of cooling gas 24 is regulated by controller 30 to minimize self-induced movement of cooling gas due to temperature differences when it is not needed to cool the product chamber 16.

Cooling gas 24 circulating through the radiator 26 once returned to the coolant chamber 14 is directed through and around the PCM 12 to maintain the gas 24 at a low temperature. The PCM chamber 14 may contain baffles to route the circulating gas 24 through the PCM 12 as seen, for example, in FIG. 4 discussed below. The PCM chamber 14 also may contain a valve 40 that vents excess cooling gas from the container.

An insulating air gap or slot 42 in a center wall 44 may be provided to reduce unintended heat transfer from the product chamber 16 to the PCM chamber 14. Tubing or conduit of low thermal conductivity may also be used for that portion of the radiator that passes through the wall 44 to minimize unintended cooling of the product chamber 16.

In one embodiment of the cooling container, lid 22 may be divided, as seen in FIGS. 4 and 5, so that replacing the PCM 12 in the PCM chamber 14 can be done without opening the product chamber 16 and so that the product chamber 16 can be opened without opening the PCM chamber 14. Alternatively, the PCM 12 can be replenished through a side or bottom opening (not illustrated).

The embodiment 200 shown in FIG. 2 is similar to that shown in FIG. 1 and described above, except that the cooling gas 24 passes directly from the PCM chamber 14 into the product chamber 16.

In the embodiment 300 shown in FIG. 3, the cooling gas 324 may pass into a dedicated circulation chamber 302 located between the center insulation wall 344 and a heat exchanger 304 disposed on a divider wall 306 separating the cooling chamber 314 from the product chamber 316. A cold-side 308 of the heat exchanger 304 is disposed in the circulation chamber 302 and the corresponding hot-side 310 of the heat exchanger is disposed in the product chamber 316. Intake tube 312 draws cooling gas 24 in from the PCM chamber 314 and directs it into the circulation chamber 302 and across the cold-side 308 of the heat exchanger. An exhaust tube 315 accepts cooling gas 324 from the circulation chamber 302 and directs it back into the PCM chamber 314.

Another embodiment 400 of a cooling container according to the invention, shown in FIG. 4, has an insulated bottom and side walls 418, 420. A center wall 422 divides the interior of the container into a cooling chamber 414 and a product chamber 416. PCM 412 is held in the cooling chamber 414 in a rack of baffles 415. An air slot 424 in center wall 422 reduces heat transfer from the product chamber 416 to the cooling chamber 414. Cooling gas 426 circulates between the cooling chamber 414 and the product chamber 416 through inlet and outlet channels 428, 430, each of which includes a valve 432 to control flow direction. A fan 434 disposed in one of the channels 428, 430 circulates gas 426 through the channels and between the cooling and product chambers 414, 416.

Electronic controls 436 are disposed atop the center wall 422 as seen and are connected to the fan 434 and a temperature sensor 438 disposed in the product chamber 416. Electronic controls 436 may include a battery, power connections, a display, and a controller. Each of the coolant and product chambers 414, 416 has a lid 440, 442, equipped with a handle. Excess coolant gas 426 may be released from the coolant chamber 414 via valve 444 provided in the side wall 420 thereof.

In operation, when the temperature in the product chamber 416 rises above a set level, a controller in the electrical controls 436 activates the fan 434 causing cooling gas 426 from the cooling chamber 414 to circulate through the product chamber 416 until a desired low temperature is reached. The PCM is arranged on baffles 415 so that the cooling gas 426 is more effectively cooled as it circulates through and around the PCM.

With reference now to FIG. 5, another embodiment 500 of a cooling container according to the invention is shown. Cooling container 500 is similar to embodiment 400 shown in FIG. 4, having bottom and side walls 518, 520, center wall 522, air gap 524, circulating cooling gas 526, inlet and outlet channels 528, 530, electrical controls 536, temperature sensor 538, lids 540, 542, and release valve 544. However, circulation of the cooling gas 526 is achieved using circulation tubes similar to those shown in FIGS. 2 and 3. Intake tube 512 draws cooling gas 526 in using fan 546, whence it is directed into intake channel 528 and into product chamber 516 where it cools the product chamber and its contents. Cooling gas 526 is returned to the coolant chamber 514 via outlet channel 530 where it is routed into outlet tube 548.

In another aspect of the invention which could be implemented in connection with any of the embodiments discussed above, a heat sink could be provided in the coolant chamber upon which the PCM could be disposed. In such an implementation, heat is absorbed by the heat sink from the air in the coolant chamber and the PCM absorbs heat from the heat sink for more efficient heat transfer. An aluminum heat sink would be suitable in such an embodiment.

In one aspect of the invention fuzzy logic is used in a method to determine when and how much to open the fan or fans in the device and how much to open the valves. For example, considering again the embodiment shown in FIG. 1, when the sensor 28 detects the temperature in the product chamber 16, depending on how close the temperature is to a selected high temperature set point, the controller will instruct the valve 36 to open partially or all the way and the fan 38 run for a shorter or longer period. If the temperature is not close to the high temperature set point, the controller 30 may instruct the valve 36 to open only slightly and the fan 38 to run for a short time. If the temperature close to the high temperature set point, the controller 30 may instruct the valve to open wide and the fan to run for a longer time. Selection of how wide to open the valve 36 and how long to run the fan 38 is determined as a function of how close the temperature is to the high temperature set point. Such determinations can be implemented using fuzzy logic or by entering static values into a logic program that operates the controller.

A high level method for operating the cooling container is shown in FIG. 6 wherein a deviation or error 602 of the temperature sensed by a temperature sensor 604 in the product chamber from a set point 606 is determined. Fuzzy logic 608 then calculates how much to open the upper valve 610 and the lower valve 612, and how long to operate the fan 614 and the optional fan 616. This calculation is continually repeated as long as temperature regulation of the product chamber is required.

In another embodiment of a cooling container according to the invention, the product chamber is maintained at a desired temperature by proportionally controlling the fans and valves which govern the amount of cooling gas that circulates between the cooling chamber and the product chamber. Thus, with reference now to FIG. 7, a temperature in the product chamber is determined at 702. If the temperature is determined at 704 not to be above a set point S1, e.g., 6° C., it is determined at 706 if the temperature is below set point S0, e.g., 4° C., which could be the lowest temperature in a range. If the temperature is below set point S0, the controller instructs the valve to close at 708 and to deactivate the fan at 710. If the temperature is above set point S1, it is next determined if the temperature is above set point S2 at 712. If the temperature is below set point S2 (but above set point S1), the controller instructs the valve to open a small percent such as 20% at 714 until the temperature is below set point S0 at 706. If it is determined that the temperature is above set point S2 it is next determined if the temperature is above set point S3 at 716. If the temperature is not above set point S3 (but is above set point S2), the controller instructs the valve to open 40% at 718 and the fan to run for time T1 at 720 until the temperature is determined to be below set point S0 at 706. A similar iterative process repeats at 722 where it is determined if the temperature is above the next set point (e.g., S4, S5). If not, the controller instructs the valve to open at 724 to a preset degree and the fan to operate for a time (e.g., T1, T2, T3) according to the temperature, until it is determined that the temperature is below set point S0 at 706 when it instruct the valve to close and the fan to turn off. Regardless of the temperature, if it is determined that the fan has not operated for more than a predetermined time period at 728, the controller instructs the fan to operate for a set time at 730 to circulate cooling air in the product chamber and avoid unwanted stratification, and then turn off at 710. It will be understood that many variations on the embodiment shown in FIG. 7 are possible, the operative principle being to repeatedly check the temperature in the product chamber and adjust the valve and fan to optimally maintain the temperature within a desired range.

There have thus been described and illustrated certain embodiments of a/an cooling container that uses PCM as a cooling medium according to the invention. Although the present invention has been described and illustrated in detail, it should be clearly understood that the disclosure is illustrative only and is not to be taken as limiting, the spirit and scope of the invention being limited only by the terms of the appended claims and their legal equivalents.

Claims

1. A cooling container using phase change materials, the cooling container comprising: a container body having insulated side and bottom walls, an insulated center divider, a top opening defined by the side walls, and one or more lids, the side and bottom walls defining an interior compartment, the one or more lids for fitting over the top opening to seal off the compartment, the center divider separating the interior compartment into a coolant chamber and a product chamber, the coolant chamber sized for holding a coolant, the product chamber sized for holding products,the center divider including first and second apertures, the coolant and product chambers in communication with each other through said first and second apertures,a controller,a power source in communication with the controller, anda sensor disposed in the product chamber, the sensor in communication with the controller,a fan in communication with the controller and in operative communication with the first aperture,wherein when the sensor detects a temperature in the product chamber above a selected threshold, the controller is configured to activate the fan so that cool gases from the coolant chamber flow through the first aperture into the product chamber and gases from the product chamber are flow the second aperture back into the coolant chamber, thereby maintaining the temperature in the product chamber below said threshold.

2. The cooling container of claim 1 further comprising: the coolant including phase change materials.

3. The cooling container of claim 1 further comprising: a length of sealed conduit disposed in the product chamber extending between the first and second apertures for retaining cooling gases.

4. The cooling container of claim 3 wherein: the length of sealed conduit comprises one or more coils.

5. The cooling container of claim 1 wherein: the divider includes a sealed air gap.

6. The cooling container of claim 1 further comprising: a valve in communication with the first aperture for restricting the flow of gases from the coolant chamber to the product chamber to one direction,wherein the controller is configured to activate the valve when the sensor detects a temperature in the product chamber above a selected threshold.

7. The cooling container of claim 1 wherein: the one or more lids comprises two lids, each of the two lids closing one of the coolant and product chambers.

8. A cooling container using phase change materials, the cooling container comprising: a container body having insulated side and bottom walls, an insulated center divider, a top opening defined by the side walls, and one or more lids, the side and bottom walls defining a chamber, the one or more lids for fitting over the top opening to seal off the chamber, the center divider separating the chamber into a coolant chamber and a product chamber, the coolant chamber sized for holding a coolant, the product chamber sized for holding products,a controller,a power source in communication with the controller,a sensor in communication with the controller, the sensor disposed in the product chamber, andthe center divider including first and second partitions and first and second apertures, the first and second partitions spaced apart to define a circulation chamber, the coolant and circulation chambers in communication with each other through said first and second apertures, the first partition including a heat exchanger having a cold side and a hot side, the cold side extending into the circulation chamber and the hot side extending into the product chamber such that heat in the air in the product chamber is transferred from the hot side heat exchanger to the cold side heat exchanger into the circulation chamber,a fan for driving air from the coolant chamber to the circulation chamber through the first aperture, the fan in communication with the controller,wherein when the sensor detects a temperature in the product chamber above a selected threshold, the controller is configured to activate the fan so that cool air from the coolant chamber is driven into the circulation chamber through the first aperture, heat is extracted from the product chamber via the heat exchanger into the circulation chamber, and warmed air from the circulation chamber flows through the second aperture back into the coolant chamber, thereby maintaining the temperature in the product chamber below said threshold.

9. The cooling container of claim 8 further comprising: a valve in communication with the second aperture for preventing back flow of gases from the circulation chamber to the coolant chamber.

10. The cooling container of claim 8 further comprising: the second partition including a sealed air gap.

11. A method for controlling the temperature in a cooling container, the container using phase change materials, the method comprising: detecting the temperature in a product chamber in a cooling container,activating a fan in a cooling chamber in the cooling container to circulate cooling gases between the cooling chamber and the product chamber.