Miniature thermoelectric cooler

Abstract

A miniature thermoelectric cooling device for storing small amounts of thermally unstable substances, like drug vials with insulin for diabetic patients or protein based drugs for thrombolytic therapy, is disclosed. A solar energy collector coupled with a rechargeable battery is provided as the energy source. The miniature cooler is small enough to be belt-carried at all time by a person, whose life or health depends on the drugs. When switched to a heating mode, the thermoelectric device can temporarily elevate the temperature of the drug to a body temperature thus providing comfortable conditions for the injection. A combined solar-and-battery power supply allows keeping an article in the cooler at low temperatures around o'clock at all times during substantially long travels in hot or tropical conditions where even short term exposure to surrounding temperatures can destroy the potency of the drug.

Description

FIELD OF INVENTION

[0001] This invention relates to thermoelectric temperature control devices, used for creating a zone of lowered temperatures for storing articles with low thermal stability. The invention is most suitable for storing small articles, mainly drug vials with protein based drugs, primarily insulin for the diabetic patients or drugs for out-of-hospital thrombolytic therapy.

DESCRIPTION OF THE PRIOR ART

[0002] Portable coolers that can be comfortably carried by a person are well known. Typically, such coolers comprise a storage compartment with thick walls, fabricated of a polystyrene foam with closed cells and provided with a lid and a carrying handle. For a limited time this thermally isolated compartment can maintain constant temperature. To compensate for the heat transfer that does occur through the walls of the compartment and to maintain a low temperature in the compartment for longer period of time, a thermoelectric, or Peltier, device is often employed.

[0003] According to the Peltier effect, an electric current passing through the junction of two dissimilar materials causes generation or absorption of heat, with the direction of heat flow depending upon the direction of the current. The rate of the thermal effect—the heat flow—is proportional to the magnitude of the current. By positioning a multitude of such junctions thermally parallel and electrically in series in a small space a significant thermal effect can be achieved. Such devices are now commercially available with junctions of n-type and p-type semiconductors materials. These devices are operable in a range of DC voltages. A fan, generally associated with the device, is used to circulate air from the p-n junctions to the region where the thermal effect is desirable.

[0004] About 16 million of people in the United States and 120 million people worldwide suffer from diabetes. Life and health of a significant number of these patients often depends on daily injections of insulin. Insulin, like many other protein based drugs, has relatively low thermal stability. The storage of insulin solution in vials requires low temperature environment, preferably a temperature range 4-10 degrees Centigrade. At room temperature an insulin solution can preserve its potency only for a limited period of time, at most several weeks. When traveling, people with diabetes experience additional inconvenience associated with lack of low temperature environment required for the storage of insulin. In a tropical climate or during a hot day at the beach even short term exposure of the insulin to elevated temperatures can destroy its potency and thus jeopardize the health or even life of a diabetes patient. This is especially true for long vacations during summer time in the United States or in other countries with hot climate.

[0005] In U.S. Pat. No. 5,379,594 a portable, hand-held, solar energy thermoelectric device for the use, storage and transportation of substances requiring a temperature controlled environment in a wide ambient temperature range is disclosed. The storage chest described in the patent has at least 1 cubic foot of usable volume and consumes about 70 watts of electric power from generated by a solar energy collector. This thermoelectric chest is too large to meet the requirements for a drug storing cooler capable of being carried at all the time with a person.

[0006] In U.S. Pat. No. 4,981,019 a portable food container is disclosed. It is cooled by a solar powered refrigeration unit and includes a thermoelectric power unit and heat pipes so that the container will be cooled even when there is no solar radiation and will have an even temperature distribution. The intended use of the cooler is a picnic food container. Once again, this device is too large to be conveniently carried by a person at all times.

[0007] It is desirable to develop a miniature temperature controlled device, which could be carried with a person at all time and would guarantee stability of the insulin or other drug during several months in hot or tropical climate.

[0008] It is an object of the present invention to provide a miniature thermoelectric cooler that can be carried with a person at all time.

[0009] It is another object of the present invention to provide a cooler with a power supply comprising a solar energy collector coupled with an electrical rechargeable battery, with an overall capacity of large enough to power the cooler around the clock during days and nights at all times.

SUMMARY OF THE INVENTION

[0010] The present invention is a miniature belt-carried cooler intended for long term storage of small articles, particularly drugs, at lowered temperatures. The present invention comprises a thermally isolated storage compartment, a solar power collector coupled with a rechargeable electric battery and a thermoelectric unit. The solar energy collector and rechargeable batteries are secured to the side walls of the storage compartment and serve as a power supply for the thermoelectric system providing control of the temperature inside the storage compartment. The thermoelectric system includes a block of Peltier elements, a programmable control unit, mounted on the top wall of the storage compartment, and a temperature sensor placed inside the storage compartment.

[0011] The storage compartment is made of thermally insulating materials, with its top wall openably connected to the side wall of the compartment. The storage compartment may include a Dewar flask for additional thermal insulation of the stored article.

[0012] A solar energy collector generates enough power to cool the compartment and to recharge the battery at the same time. The capacitance of the fully charged electric battery is sufficient to power the thermoelectric system during nights, when solar energy is not available.

[0013] The hot end of the Peltier unit extends up from the top wall of the storage compartment, whereas the cold end of the unit extends down from the top wall inside the storage compartment. The hot end of the Peltier unit is provided with a radiator, which serves as a heat sink, dissipating heat to the surrounding air.

[0014] A belt for wearing a cooler in accord with the present invention at a person's waist may be provided.

[0015] The foregoing objects of the invention will become apparent to those skilled in the art when the following detailed description of the invention is read in conjunction with the accompanying drawings and claims. Throughout the drawings, like numerals refer to similar or identical parts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a perspective view of a miniature thermoelectric cooler in accord with the present invention.

[0017] FIG. 2 is a schematic view of the miniature thermoelectric cooler shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention comprising a miniature thermoelectric cooler 10 will be described with reference to FIGS. 1 and 2. Cooler 10 comprises a thermally insulated compartment 12 adapted for storage of the drug vials or other small articles 14 at lowered temperatures. The compartment 12 has a bottom wall 16 and side walls 18 made of a thermally insulating material, such as a closed cell foam material. A top wall or lid 20 of the compartment is openably-connected to its side wall 18. Compartment 12 may include a Dewar or double wall flask 22, made of glass or stainless steel.

[0019] A thermoelectric unit 24 is shown attached to the lid 20. A heat sink 26 is attached to the hot or upper end 28 of the thermoelectric unit 24. Heat sink or radiator 26 protrudes through an appropriately configured opening 30 in the top wall 12 so as to be exposed to the ambient environment. That is, the heat 26 sink serves for cooling of the hot end 28 of the thermoelectric device by the surrounding air.

[0020] Preferably, the cooler 10 is powered by a renewable energy resource. By way of example, cooler 10 may include a photovoltaic collector panel 32 for collecting the solar energy during day time hours. Panel 32 will provide electric power to charge one or more electric batteries 34, which provide power to the thermoelectric cooling system during nights, when the solar energy is unavailable. Advantageously, the power output of the solar battery 34 may be less than 10 watts. A programmable control unit 36 may be mounted on the top wall 20 to provide control of the temperature inside the storage compartment 12. The temperature inside the storage compartment may be measured by a temperature sensor 38. The whole cooler assembly is secured on a waist belt 40, which allows to comfortably carry the cooler at all time.

[0021] FIG. 2 schematically shows a cross section and electric circuits of a cooler in accord with the present invention. The miniature cooler may comprises a compartment 12 having a volume of 100-250 cubic centimeters with the top wall 20 and side walls 18 fabricated of a closed cell polymeric foam, such as polystyrene. Located interior to the side walls 18 is the Dewar flask 22. The flask 22 includes a space 42 between the two walls 44 and 46 thereof, which is evacuated to a high level of vacuum. The vacuum between the walls 44 and 46 reduces the transfer of heat to or from the cooler 10. Dewar flasks provide excellent thermal insulation from environment and often are used for storing liquid gases.

[0022] As noted, a thermoelectric unit 24 is secured in the middle of the top wall 12 with its cold end 48 facing the interior of the Dewar flask 22 and the hot end 28 attached to the heat sink 26. The thermoelectric unit 24 consists of two or more elements 50 of semiconductor material (such as bismuth telluride) that are connected electrically in series and thermally in parallel. These thermoelectric elements 50 and their electrical interconnects are mounted between two ceramic substrates 52 and 54 at their top and bottom ends 28 and 48 respectively. The substrates 52 and 54 serve to hold the overall structure together mechanically and to insulate the individual elements 50 electrically from one another and from external mounting surfaces. Preferably, the various components of the cooling elements 50 are integrated in a cylindrical plug (not shown for purposes of clarity) that fills the neck of the Dewar flask 22. During operation of the cooler the semiconductor elements 50 actually are moving the heat from the colder end of the compartment 12 to the upper hotter end 28 and heat sink 26. The thermoelectric unit 24 is powered by a low voltage direct current from rechargeable batteries 32 located outside the storage compartment. A thermocouple 38 or other temperature sensor, placed inside the storage compartment, measures the temperature to which stored articles 14 are exposed.

[0023] A signal from the thermocouple 38 comes to the controller 36 and is used for stabilization of the temperature inside the storage compartment at a preprogrammed level. The controller 36 turns on and off the thermoelectric unit 24 depending on the temperature inside the compartment. During the “off” state, the heat exchange between the inside volume of the container and the environment outside is minimal. In part this is due the fact that the thermal convection inside the container 12 is very low, because the articles 14 at the bottom of the container 12 are colder than the ceramic substrate 54 above them. When the thermoelectric unit 24 is on, the plate 54 becomes colder then the bottom of the compartment and convection heat flow starts pumping heat from the bottom to the flask to the cold end 48 of the thermoelectric unit 24. The overall device thus is very efficient in keeping the internal part of the Dewar flask cold, with very low energy being spent. The operational state of the cooler is vertical with the heat sink and the hot end of the thermoelectric unit positioned above the storage compartment.

[0024] The present invention having thus been described, other modifications, alterations, or substitutions may now suggest themselves to those skilled in the art, all of which are within the spirit and scope of the present invention. For example a miniature cooler in accord with the present invention may include a universal electrical adapter which allows the operator to use power from electric current sources of other direct current voltages or 120 and 220 volts alternating current. In addition, the present invention could further include a heating mode of operation of the thermoelectric unit 24 during which the temperature of the insulin or another drug can be elevated to the body level thus making injections more comfortable for the patient. It is therefore intended that the present invention be limited only by the scope of the attached claims below.

Claims

1. A miniature cooler comprising:

a storage compartment made of thermally insulating materials and having top and side walls with said top wall openably-connected to said side wall such that said top wall closes the compartment or allows access to the compartment;

a power supply including a photovoltaic collector panel and a rechargeable battery, said panel being externally attached to said compartment sidewall and electrically connected to said rechargeable battery, said photovoltaic collector being provided for generating to cool said compartment and to recharge said battery; and

a temperature control system comprising:

a thermoelectric unit imbedded in said top wall of the compartment, said unit having a hot end and a bottom end, said hot end of said unit facing upwardly and said cold end of said unit facing downwardly from said top wall, respectively;

a control unit operationally connected to the thermoelectric unit and the power supply, said control unit being provided for selectively turning said thermoelectric unit on and off; and

a temperature sensor placed inside the storage compartment and operatively connected to said control unit.

2. The miniature cooler of claim 1 wherein:

the storage compartment further additionally includes a Dewar flask, in which the articles to be stored are placed.

3. The miniature cooler of claim 1 wherein:

the volume of the storage compartment is less than 250 cc.

4. The miniature cooler of claim 1 wherein:

the power output of the solar battery is less than 10 W.

5. The miniature cooler of claim 1 wherein said thermoelectric unit comprises semiconductors connected electrically in series and thermally in parallel.

6. The miniature cooler of claim 5 wherein said semiconductors are made of bismuth telluride.

7. The miniature cooler of claim 5 wherein:

the storage compartment further additionally includes a Dewar flask, in which the articles to be stored are placed.

8. The miniature cooler of claim 5 wherein:

the volume of the storage compartment is less than 250 cc.

9. The miniature cooler of claim 5 wherein:

the power output of the solar battery is less than 10 W.

10. The miniature cooler of claim 5 and further comprising a belt for attachment of said cooler, said belt for wearing around the waist of a person.

11. The miniature cooler of claim 1 and further comprising a belt for attachment of said cooler, said belt for wearing around the waist of a person.