FIELD

The invention relates to coolers used to maintain items within a certain temperature range. The items may include high value products such as vaccines, biological samples, soil samples, and/or water samples. The invention also relates to coolers that use an endothermic reaction to maintain a cool interior temperature.

BACKGROUND

Various implementations for cooling products are known. Fridges, freezers, ice, ice packs and coolers are commonly used to maintain the temperature of goods to prevent them from spoiling. Copper coils are commonly used to conduct refrigerant in fridges, freezers, air conditioning units and many other applications. Copper is the optimal material for heat transfer between substances due to its low specific heat capacity.

Various chemical cooling solutions have been proposed to cool products. For example,

International Patent Application Publication No. WO 95/32656 describes a device that uses an endothermic reaction to cool a liquid. Reactants are contained in a sealed cylinder that is housed inside a compartment in which the liquid is stored. The user must press on an area of the surface of an inner module to break a barrier between the two reactants, thus effectively cooling the liquid. Once the reaction has been completed the inner module can be disposed of.

Another example of an endothermic reaction used for cooling product is described in International Patent Application Publication No. WO 2006/127522, which is designed for cooling beverages. It is a container that has an inner coil of tubing surrounded by two reactants. The user must push a button, which breaks a membrane that separates two reactants and initiates an endothermic reaction. The beverage can then be poured through the inner coil of tubing thereby cooling the beverage.

Additionally, U.S. Patent Application Publication No. US 2008/0271476 uses an endothermic reaction to cool multiple beverage containers at once, through a user activated push button. In these prior designs, the reaction is user activated and the designs are single-use; that is, the user must either replace the module, thereby refreshing the reactants, or replace the reactants within the module.

SUMMARY

In one aspect, the invention provides a cooler that includes an insulated enclosure, a sample storage compartment 98, a waste container 114, at least two containers for holding at least two endothermic reaction reactants; and a controller that maintains internal temperature of the sample storage compartment within a selected temperature range by intermittently providing a mixture of the endothermic reaction reactants and circulating the mixture into a coil 100. In one embodiment, the at least two endothermic reaction reactants are (1) water, and (2) urea, ammonium nitrate, or a combination thereof. In one embodiment, the urea, ammonium nitrate, or a combination thereof is in solid form. In one embodiment, the mixture is further circulated into the waste container. In one embodiment, the waste container comprises a drain.

In one embodiment, the cooler further comprises a mixing tank 110 and an agitator, a solids handling apparatus 120 that deposits a predetermined amount of reactant into the mixing tank. In one embodiment, the cooler includes a mechanical stirrer, or a rotary stirrer 109. In one embodiment, the cooler further comprises a pump 111. In one embodiment, the temperature range is about 0 to about l0°C. In one embodiment, the solids handling apparatus 120 comprises a rotor 106 housed in a cylindrical container 107 such that when the rotor rotates, a

predetermined amount of reactant is deposited into the mixing tank. In one embodiment, the coil 100 is a copper coil. In one embodiment, the coil is helical and the sample storage compartment is inside or substantially surrounded by the helix. In one embodiment, the enclosure comprises panels of phase change material. In one embodiment, the controller generates a signal when user intervention is needed.

In one aspect, the invention provides a method of storing an item within a selected temperature range in a container including placing the item for storage within a sample storage compartment of the active cooler of the above aspect or its embodiments, using a controller to monitor the temperature range in the sample storage compartment and intermittently mix and circulate an endothermic reaction solution into a coil 100 that cools the stored item when the temperature in the sample storage compartment is close to or above a high temperature of the selected temperature range.

In another aspect, the invention provides a cooler, comprising: a storage compartment; a heat exchanger associated with the storage compartment; at least first and second containers that respectively contain at least first and second endothermic reaction reactants; apparatus that dispenses and mixes the at least first and second reactants and conducts an endothermic reaction mixture to the heat exchanger; a controller that monitors the internal temperature of the storage compartment and maintains the temperature at or below a selected temperature by intermittently providing the endothermic reaction mixture to the heat exchanger.

In one embodiment, the at least first and second endothermic reaction reactants are (1) water, and (2) urea, ammonium nitrate, or a combination thereof.

In one embodiment, the urea, ammonium nitrate, or a combination thereof is in solid form.

In one embodiment, the cooler further comprises a waste container; wherein spent endothermic reaction mixture is directed into the waste container.

In one embodiment, the waste container comprises a drain.

In one embodiment, the cooler further comprises a mixing tank and an agitator, mechanical stirrer, or a rotary stirrer.

In one embodiment, the cooler further comprises at least one pump.

In one embodiment, the selected temperature is about l0°C.

In one embodiment, the apparatus that dispenses the at least first and second reactants dispenses predetermined amounts of the at least first and second reactants into the mixing tank.

In one embodiment, the heat exchanger comprises a copper helical coil.

In one embodiment, an insulated enclosure encloses the cooler.

In one embodiment, the cooler further comprises panels of phase change material.

In one embodiment, the controller generates an indication when user intervention is needed.

Another aspect of the invention provides a method for storing an item at or below a selected temperature, comprising: placing the item within a storage compartment of a cooler, wherein the cooler comprises: a heat exchanger associated with the storage compartment; at least first and second containers that respectively contain at least first and second endothermic reaction reactants; apparatus that dispenses and mixes the at least first and second reactants and conducts an endothermic reaction mixture to the heat exchanger; and a controller; the method comprising using the controller to monitor the temperature in the storage compartment and intermittently dispense and mix the reactants and conduct the endothermic reaction mixture to the heat exchanger; wherein the reaction mixture in the heat exchanger cools the item in the storage compartment; wherein the item is automatically maintained at or below the selected temperature in the storage compartment. The method may include the controller generating an indication when user intervention is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, wherein:

Figs. 1 A and 1B are schematic diagrams of active coolers according to embodiments of the invention.

Fig. 2 is a schematic diagram of an embodiment of the invention.

Fig. 3 is a 3-D diagram of an active cooler that includes a sample stored within a sample storage compartment and a helical copper coil that surrounds the sample, according to one embodiment.

Figs. 4A-4C are diagrams of an active cooler according to another embodiment.

Fig. 5 is a diagram of an active cooler according to another embodiment.

Fig. 6 is a plot of internal temperature (°C) vs. time (h) for a traditional passive cooler that is cooled using ice packs, and for an active cooler according to a prototype of an

embodiment as described herein.

DETAILED DESCRIPTION

Traditional portable coolers are insulated containers that are cooled with ice, or ice packs. Users are required to monitor the internal temperature and replace the ice or ice packs as necessary to keep the interior cool. Such passive coolers are effective at keeping contents cool for several hours, but the internal temperature rises quickly once the ice or ice packs are melted, and items stored inside can spoil. Described herein is an active cooler with a controller that is capable sustaining cool internal temperatures continuously for multiple days without user intervention. Embodiments employ an endothermic reaction to provide cooling, and automatically“recharge” the cooling by maintaining or controlling the reaction, in a manner that is hands-off for the user. The controller, which may include a microprocessor, monitors the internal temperature and controls the internal temperature within a selected range, or with respect to a temperature set point, by controlling the reaction. The controller may control the reaction by performing one or more functions such as pumping and controlling release of reactants, pumping the reaction mixture to cooling coils/heat exchanger, and removing/purging spent reaction mixture from the cooling coils. Thus, according to various embodiments described herein, the controller is operatively connected to a

temperature sensor in the storage compartment, and optionally to other temperature sensors, flow sensors, as well as components such as electrically-operated (e.g., solenoid) valves, motors, pumps, and the like. Since the embodiments do not use electricity as the cooling mechanism (i.e., as an energy source for cooling, such as to operate a compressor or a solid state cooling device), they are energy efficient. Embodiments may use battery-powered components such as a controller, microprocessor, fan, solenoid valve, rotor, agitator, pump, etc., but do not use electricity to cool the interior space, and therefore have low energy consumption. The cooling source is provided by sustained and repeated injections of an endothermic liquid into a heat exchanger that absorbs heat from the interior space of the cooler, thereby cooling the interior.

The cooling effect of the heat absorbing liquid is facilitated by circulating it through the heat exchanger, such as tubing in an effective arrangement for cooling the interior of the storage compartment (e.g., arranged in an undulating manner, or as a coil or helix), and optionally by having a fan that circulates air inside the cooler. Multiple aliquots of endothermic reaction mixture can be provided over time by the control system automatically, in the absence of user intervention.

Embodiments include a storage compartment that is cooled and various working parts for maintaining the internal temperature of the storage compartment within a selected range. The storage compartment has an internal volume available for storage of an item or sample to be kept cool. Examples of such samples or items include vaccines, pharmaceuticals, food or beverage items, a biological sample such as a tissue or blood sample, an organ, plant matter, small animals (e.g., insects, fish), microorganisms, a soil sample, and/or a water sample. In one embodiment, a heat exchanger, which may comprise tubing (e.g., copper), is arranged adjacent and/or surrounding the storage compartment. The heat exchanger conducts endothermic reaction fluid to the storage compartment, thereby cooling the storage compartment. According to embodiments described herein, the endothermic reaction may be provided by mixing endothermic reactants.

For example, one reactant may be water, and another reactant may be urea or ammonium nitrate, or a combination thereof.

A generalized embodiment is shown schematically in Fig. 1 A. Referring to the embodiment of Fig. 1 A, the cooler 99 includes insulated walls 103, a base 117, a lid 102 that is removable or hinged, a heat exchanger 100 comprising a copper coil that at least partially surrounds a storage compartment 98, optional panels 101 containing a phase change material (e.g., an ice pack such as Phase 5™ (Cryopak Canada) that melts at about 5° C) at least partially surrounding the storage compartment 98, a tank 104 for holding a reactant (e.g., water), a container or hopper 105 that holds a reactant such as urea and/or ammonium nitrate in a solid form such as a powder, pellets, grains, etc., a solids handling apparatus 120 that dispenses the solid reactant, a mixing tank 110 that receives the reactants, an agitator 109 that mixes contents of mixing tank 110, a pump 111, tubing 112, valves 113, a waste container 114, a drain to outside 115, a base 117, and optionally a fan 116. For example, as shown in Fig. 1 A, the lid 102 may include a fan 116 to circulate air within the interior of the cooler (i.e., storage compartment).

In the embodiments of Figs. 1 A and 1B, the heat exchanger 100 comprises a helical coil of copper tubing surrounding the storage compartment. One end of the coil 100 is operably connected to components within the working parts as detailed below and the other end is connected to a compartment located at the bottom of the cooler that is referred to herein as a waste container 114. The waste container receives spent reaction fluid (i.e., the combined reactants substantially after the endothermic reaction is exhausted) and includes a drain 115 to remove the waste. In one embodiment, the coil 100 is housed inside interior walls so it is not readily visible to the user. The working parts include a control system that may include a microprocessor, a battery holder, and a user interface to be operably engaged with the control system. The working parts may include a solids handling apparatus 120 including a rotor 106, a cylindrical housing 107 for the rotor, and a motor 108 for driving rotor 106, as shown in the embodiment of Fig. 1B. The solids handling apparatus dispenses the solid reactant into the mixing tank 110. Referring to the schematic diagram of Fig. 2, an embodiment includes the features of Fig. 1A as well as a temperature sensor 119, and a control system 118. In this embodiment, the temperature sensor is located within the storage compartment. The control system 118 may be located anywhere, for example, within the cooler’s working parts area, the lid, or the base. In Fig. 2, it is located in a hinged lid, and power is fed from the battery to the optional fan 116, valves 113a, 113b, and 113c, agitator 109, and pump 111. The control system 118 may include a user interface, and may conveniently be disposed in the lid 102, for ease of access. One or more display components of the user interface, if included, may be disposed upwardly facing on the lid, or through a window in the lid, or below the lid so as to be readily viewed upon opening the lid. Non-limiting examples of displays components include lights and/or digital readouts and/or a display screen. The one or more display components may display or indicate, e.g., one or more of on/off status of the cooler, internal temperature of the storage compartment, battery status, status/remaining level of one or more reactants, level of waste container, temperature set point, an indication of whether the temperature of the storage compartment has exceed the temperature set point, a mechanical/electrical fault, etc.

Referring to Fig. 3, a 3-D image is shown of an embodiment of the active cooler that includes a sample 88 in the storage compartment 98 located within the interior of a helical copper coil 100.

Operation of an embodiment will now be described with reference to Figs. 1A, 2, and 3. The temperature sensor 119 senses the internal temperature of the storage compartment and sends a sensor signal to the battery-powered controller 118. The controller may be implemented with suitable circuitry, including control logic, a microprocessor, etc., as known in the art. The controller operates according to a temperature set point, or a temperature set point range, which may be internally programmed or may be set by the user. For example, the controller may have user interface comprising a keypad, touch screen, or rotary dial, etc., that allows the user to enter a desired temperature set point or temperature set point range. If the controller determines that the internal temperature of the storage compartment is too high, the controller initiates a valve 1 l3a below the water tank 104 to open, allowing a specified amount of water to flow into the mixing tank 110. Next, the controller operates the solids handling apparatus 120, which deposits a specified amount of urea into the mixing tank. In a specific example according to the embodiment of Fig. 1B, the controller operates the motor 108, which turns the rotor 106 within the cylindrical housing 107. Through rotation of the rotor, urea from the hopper 105 falls into compartments of the rotor. As the rotor turns, urea is deposited into the mixing tank 110. The controller then operates the agitator 109 which mixes the urea and the water in the mixing tank, thus initiating the endothermic reaction. After a specified time, the pump 111, a valve 1 l3b located between the mixing tank and the copper coil 100, and a valve 1 l3c located between the end of the copper coil and the waste container 114 are opened, thus allowing the endothermic mixture to be pumped into the copper coil 100. Once the coil is full of the endothermic mixture, the pump is shut off by the control system and the valves 1 l3b and 113c are closed thereby containing the mixture within the copper coil 100. The fan 116, if included, may then be turned on by the controller to circulate air around the coil to facilitate heat transfer, thereby cooling the interior of the storage compartment.

Non-limiting examples of dimensions for one embodiment according to Fig. 1B include a copper coil with about 450 mL interior volume, a rotor 106 or rotary component that is approximately 10 cm long and 5 cm radius, a hopper 105 for holding approximately 1.5 kg of urea and/or ammonium nitrate, a tank 104 for holding water with an internal volume of 4 L, a mixing tank 110 with an approximate volume of 800 mL, and a volume of the sample storage compartment of 10 L.

According to embodiments described herein, the water tank 104 and the hopper 105 can easily be filled and refilled by a user. The battery can be replaced or recharged by the user. The outer walls 103 of the cooler are insulated. In one embodiment, removable phase change material panels 101 (e.g., freezer packs or ice packs) may be disposed adjacent the insides of the outer walls 103. For example, phase change material that melts at about 5° C may be used.

The internal temperature of the storage compartment may be monitored continuously, or according to a schedule. In some embodiments the temperature is monitored according to a schedule, and the controller is allowed to enter a“sleep” mode between measurements, to conserve battery power. For example, the schedule may include measuring the temperature of the storage compartment once every hour, or every 30 minutes, or every 15 minutes, etc. When the temperature rises above the set point, or above the set point range, the control system initiates another run of the endothermic reaction. When a new reaction mixture is pumped into the coil 100, it will push out or purge the old, warmed mixture into the waste container 114. The user can use the drain 115 to drain the waste container. In one embodiment, waste is contained in a removable cartridge that can be disposed of easily.

In various embodiments, additional sensors may be employed with the controller to sense/monitor other parameters of the system. For example, an additional temperature sensor may sense ambient temperature outside the cooler. Further sensors may be disposed to sense levels of one or more of the reactants, e.g., to sense when the amount of water in the tank 104 reaches a selected level, when the amount of reactant in the a hopper 105 reaches a selected level, when the amount of waste in the waste container 114 reaches a selected level, etc. The selected level may be a critical level, e.g., a level associated with a certain minimum remaining time that the cooler can maintain the storage compartment at a set temperature. In some embodiments the controller may provide an indication of a low battery condition. The controller may provide an indication that one or more such parameters has reached a critical level, for example, an audible indication such as an alarm and/or a visible indication such as a warning light, flashing light, etc., located, for example, on the exterior of the cooler. In such

embodiments, the provided indications or warning signals indicate that user intervention is needed soon (e.g., the storage compartment is approaching or has reached a critical temperature, the reactants are low or used up, the waste compartment needs to be emptied, or when the battery needs changing or recharging). Such signals may be implemented using an alarm or a light located, for example, on the exterior of the cooler, or via wireless communications as described below.

The controller may provide the ability for a user to interact with the cooler for purposes such as turning the unit on or off, or configuring one or more parameters such as a temperature set point. In some embodiments the controller may include wireless communications technology for one or more of tracking location and one or two way communication with the cooler. For example, location of the cooler may be tracked via a suitable technology such as the global positioning system (GPS). The communications may include relaying sensed parameters and alarms as described above to a user’s device such as a smartphone, tablet, or computer, and/or a remote server.

An example of a microprocessor that may be used in embodiments described herein is an ESP8266 (Espressif Systems, Shanghai, China), however any suitable microprocessor will do. This microprocessor advantageously includes a WiFi interface, low overall power consumption, sufficient GPIO (general purpose input/output pins), ability to measure battery voltage, and the ability to go into a low power sleep mode when the unit is not active.

In various embodiments, the microprocessor may execute code to perform at least some of the following operations:

• Configuration and communication via a WiFi or Blue Tooth™ network. For example, configuration may be performed via a smartphone, computer, tablet, or other device.

• Configuration and communication via a cellular communications network (e.g., Code Division Multiple Access (CDMA), Global System for Mobile communications (GSM), Long Term Evolution (LTE), High Speed Packet Access (HSPA), etc.). Communication may include messaging to a user’s device such as a smartphone (e.g., an email message, a SMS message, etc.).

• Read one or more sensors and communicate the data to a remote server and/or a user’s device.

• Store/maintain a log of the temperatures within the storage compartment. For example, the log may be reviewed to confirm that the temperature never exceeded a critical temperature.

• Combine data from multiple sensors to compute useful information (for example, use data from ambient and storage compartment temperature sensors together with sensed levels of reactants to project a time when the reactants are expected to be depleted).

• Send location and diagnostic information (e.g., battery voltage, model, location, wireless connection quality and signal strength, etc.) to the user and/or server.

• Power management, including, e.g., adjusting sleep time if needed to provide extra power savings if battery power is getting critically low.

The controller may also communicate the data collected from the one or more sensors to a remote server. The communication may use standard wireless communication capabilities such as WiFi, cellular data, long range data communications (LoRa), and the like. In some embodiments, multiple communication interfaces may be used to maximize the probability of communication success in the event that one communication mechanism is not functioning.

In one embodiment, two reactants of an endothermic chemical reaction, (1) water (in liquid form) and (2) urea, ammonium nitrate, or a combination thereof (in solid form) are mixed and the resulting endothermic mixture is circulated through and held in a copper coil to effectively cool the contents of the storage compartment. The controller uses the temperature sensor in the storage compartment to determine when the endothermic liquid is no longer adequately cooling the interior. When the controller receives a signal from the temperature sensor 119 and determines that the internal temperature is at a certain level (e.g., ,the internal temperature of the storage compartment is less than but close to, or has reached the set point temperature), the control system directs fresh aliquots of water and urea and/or ammonium nitrate be deposited in the mixing tank 110, mixed, and pumped into the copper coil, and the spent mixture is deposited in the waste container 114. With a fresh batch of endothermic reaction mixture, the internal temperature of the storage compartment will be cooled and maintained within the selected temperature range or below the set point. Optionally, panels of phase change material 101 can be inserted into the active cooler in a frozen state. It will be appreciated that use of optional phase change materials such as Phase 5™ ice packs

advantageously extend the duration that embodiments can maintain the internal temperature below the a set point temperature, and/or reduce the amount of reactants required for a selected duration.

According to embodiments described herein, the control system (i.e., the controller and one or more sensors, including the temperature sensor 119 in the storage compartment) optimizes the internal temperature of the storage compartment of the active cooler. The system is controlled by a microprocessor which operates the components of the control system (e.g., motors, valves, fan, and pump) to achieve sustained and repeated injections of the reactants.

It is estimated that an active cooler as described herein will sustain cold temperatures to allow for transportation of a sample or item (e.g., a week or longer) before user intervention is required. Once the active cooler’s stock of reactants has run out, the user can prepare it for re-use by emptying the waste container, recharging the battery, and refilling the reactant supplies by adding water to the water tank, and adding urea and/or ammonium nitrate to the hopper. In one embodiment, removing waste would entail removing a full cartridge of waste material, placing in an empty waste cartridge, recharging the battery, and adding full cartridges of the reactants.

Once set up, the controller can resume cooling the interior storage compartment. In this way, only minimal user intervention is required and samples can be kept cool for longer periods than possible with portable passive coolers that are currently available.

To prepare the cooler for operation, a user ensures that the battery is charged, and loads urea and/or ammonium nitrate, and water into the appropriate containers for each component. If necessary, the user also empties the waste container. In one embodiment, the urea and/or ammonium nitrate and water are provided in cartridges that can be placed into a cartridgereceiving compartment within the active cooler. In one embodiment, the waste material is also contained in a cartridge that can be easily removed by the user. Once the urea and/or ammonium nitrate container and the water container are filled, the waste area is empty, and a charged battery is in place, the controller monitors and controls the temperature within the storage compartment. For some applications, embodiments may be configured so that once activated, no further user intervention is required until the endothermic reactants have been consumed. In such an embodiment, the temperature set point is pre-programmed, such that no user input is needed.

The amount of cooling time will depend on a number of factors such as the temperature of the surroundings, the size of the storage compartment, and the volume of reactants available for the endothermic reaction. As described in the Working Examples, a prototype of the active cooler maintained a cool interior for approximately twenty hours with only one aliquot of endothermic mixture. However, as described above, embodiments would use multiple aliquots of endothermic mixture and would be able to maintain a cool temperature with no user intervention for multiple days.

Notably, the waste material produced by the endothermic reaction is substantially non- toxic. In some embodiments, the waste material may be regenerated by dehydrating it.

Alternatively, the waste could be added to soil as a fertilizer, or poured down the sink.

Embodiments may be constructed as“inserts” to be inserted into existing or custom coolers. Such an embodiment 400 is shown in Fig. 4A. This embodiment, which is fully- functioning, is shown inserted into a cooler 402 in Fig. 4B, where it benefits from the insulation of the cooler to enhance performance. As noted above, ice packs (not shown) comprising a phase-change material may optionally be disposed around the embodiment within the cooler to further enhance performance. An exploded view of this embodiment is shown in Fig. 4C, wherein components include a urea tank 410, a water tank 412, a storage compartment 414, a spent coolant/waste tank 416, a copper or aluminum coil for heat transfer 418, a solids handling apparatus comprising a dispenser flapper 420 and a dispenser flapper motor 422, a water pump 424, a coolant pump/spent coolant purge pump 426, a flow sensor 428, a spent coolant solenoid valve 430, a spent coolant purge solenoid valve 432, an active coolant solenoid 434, a baseplate 436, a mixing container 438, and a controller/user interface 440 (battery and wiring not shown). Fig. 5 shows an embodiment in which components are specifically designed to fit into a cooler 502. For example, the urea tank 510, a water tank 512, and spent coolant/waste tank 516, are designed to use the internal space of the cooler 502 efficiently. The figure also shows the storage compartment 514. In this embodiment, the cooler 502 is equipped with wheels 550 for ease of transport.

WORKING EXAMPLE

Comparison of Active Cooler vs. Ice-Pack Cooled Passive Cooler

A preliminary study compared performance of an embodiment and a traditional cooler with ice packs.

The embodiment was a prototype built using a commercially available 60 L Coleman™ cooler with insulated walls that was fitted with the following components: copper tubing 3/8 inch diameter configured as a helical coil with 400 mL volume, vinyl tubing, a pump, a funnel, sealant tape, water, urea, fans, and a temperature monitor. Fans were glued to the inside surface of the lid of the cooler. The copper coil was placed in the middle of the cooler. A hole was drilled in the lid of the cooler. Vinyl tubing and a power cord for the fans passed through the drilled hole. The vinyl tubing was connected to the inlet of the copper coil and the outlet of the copper coil was connected to a drain at the bottom of the cooler using vinyl tubing. The cooler was filled with 3 kg of initially frozen phase change material (i.e., ice packs) with a melting point of 5 °C. A temperature monitoring device was suspended in the middle of the coil and the temperature data were collected. The lid of the cooler was closed. A pump and funnel were attached to the inlet vinyl tubing. 550 mL of water and 250 grams of urea were mixed in a beaker and once the temperature reached 0 °C the mixture was poured in the funnel. The pump was turned on and it was allowed to fill the coil. The outlet tube was plugged and the fans were turned on for 20 minutes.

Temperature readings were collected for the traditional passive cooler using the same 60 L Coleman™ cooler with 3 kg of initially- frozen ice packs as the only cooling mechanism.

The data are shown in Fig. 6. The plot shows internal temperature vs. time for the traditional passive cooler that was cooled using ice packs, and for the prototype cooled using the endothermic reaction, over a 20 h period. Only one aliquot of urea and water was used. The data show that the duration of cooling provided by the prototype embodiment was twice as long (20 h vs 10 h) as that of the passive cooler. Of course, fresh aliquots of reactants may be automatically injected by a control system as described herein, which would substantially increase the duration of cooling of the prototype.

All publications listed and cited herein are incorporated herein by reference in their entirety. It will be understood by those skilled in the art that this description is made with reference to certain preferred embodiments and that it is possible to make other embodiments employing the principles which fall within its scope as defined by the claims.