FIELD OF INVENTION
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
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.
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.
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.
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.
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.
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.
It is an object of the present invention to provide a miniature thermoelectric cooler that can be carried with a person at all time.
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
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.
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.
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.
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.
A belt for wearing a cooler in accord with the present invention at a person's waist may be provided.
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.