The present invention relates generally to refrigeration systems and more specifically relates to refrigeration systems with one or more Stirling coolers mounted therein so as to reduce internal vibrations.
In the beverage industry and elsewhere, refrigeration systems are found in vending machines, glass door merchandisers (xe2x80x9cGDM""sxe2x80x9d), and other types of dispensers and coolers. These systems generally have used a conventional vapor compression (Rankine cycle) refrigeration apparatus to chill beverages or other products therein. In the Rankine cycle apparatus, the refrigerant in the vapor phase is compressed in a compressor so as to cause an increase in temperature. The hot, high-pressure refrigerant is then circulated through a heat exchanger, called a condenser, where it is cooled by heat transfer to the surrounding environment. As a result, the refrigerant condenses from a gas back to a liquid. After leaving the condenser, the refrigerant passes through a throttling device where the pressure and the temperature of the refrigerant are reduced. The cold refrigerant leaves the throttling device and enters a second heat exchanger, called an evaporator, located in or near the refrigerated space. Heat transfer with the evaporator and the refrigerated space causes the refrigerant to evaporate or to change state from a saturated mixture of liquid and vapor into a superheated vapor. The vapor then leaves the evaporator and is drawn back into the compressor so as to repeat the cycle.
Although the Rankine cycle systems adequately chill the products therein and are in widespread use, there are several known disadvantages involved. First, the systems are generally large and heavy. Second, the systems may be noisy to operate. Third, the systems may have a significant power draw. Further, conventional Rankine systems generally use refrigerants for their working medium. These refrigerants are known to be harmful to the environment. The refrigerants may in some cases be noxious. The commonly used HFC refrigerant (134a) is generally assumed not to be noxious (though there have been claims to the contrary). It is known to be a powerful xe2x80x9cgreenhousexe2x80x9d gas to which there is no scientific doubt.
One alternative to the use of a Rankine cycle system is a Stirling cycle cooler. The Stirling cycle cooler is also a wellknown heat transfer mechanism. Briefly described, a Stirling cycle cooler compresses and expands a gas (typically helium) to produce cooling. This gas shuttles back and forth through a regenerator bed to develop much greater temperature differentials than may be produced through the normal Rankine compression and expansion process. Specifically, a Stirling cooler may use a displacer to force the gas back and forth through the regenerator bed and a piston to compress and expand the gas. The regenerator bed may be a porous element with significant thermal inertia. During operation, the regenerator bed develops a temperature gradient. One end of the device thus becomes hot and the other end becomes cold. See David Bergeron, Heat Pump Technology Recommendation for a Terrestrial Battery-Free Solar Refrigerator, September 1998. Patents relating to Stirling coolers include U.S. Pat. Nos. 5,678,409; 5,647,217; 5,638,684; 5,596,875 and 4,922,722, all incorporated herein by reference.
Stirling cooler units are desirable because they are nonpolluting, efficient, and have very few moving parts. The use of Stirling coolers units has been proposed for conventional refrigerators. See U.S. Pat. No. 5,438,848, incorporated herein by reference. The integration of a free-piston Stirling cooler into a conventional refrigerated cabinet, however, requires different manufacturing, installation, and operational techniques than those used for conventional compressor systems. See D. M. Berchowitz et al., Test Results for Stirling Cycle Cooler Domestic Refrigerators, Second International Conference. As a result, the use of the Stirling coolers in, for example, beverage vending machines, GDM""s, and other types of dispensers, coolers, or refrigerators is not well known.
One difficulty in the use of a Stirling cooler is the constant vibration produced by the operation of the internal free piston. In order to avoid transmitting the vibrations to the products or to the other components of the refrigeration unit, it is desirable to isolate these vibrations from the refrigeration unit as a whole. If not isolated, such constant vibrations may cause an unwanted noise or even reduce the life of the refrigeration unit or the components therein.
A need exists therefore for adapting Stirling cooler technology to conventional beverage vending machines, GDM""s, dispensers, and similar types of refrigeration units. Likewise, there is a need for isolating the Stirling coolers within these units so as to extend the life of the units and make the units more attractive to consumers.
The present invention thus provides a vibration isolation system for operating a Stirling cooler within an enclosure. The system may include a number of linkages for connecting the Stirling cooler to the enclosure. The system may further include a balance mass connected to the Stirling cooler by a balance mass spring.
Specific embodiments of the present invention include using the linkages to limit the movement of the Stirling cooler to a first dimension. The movement may be limited to about one or two degrees. The balance mass and the balance mass spring may be positioned adjacent to the Stirling cooler so as to vibrate in the first dimension. The Stirling cooler may vibrate with a given frequency while the balance mass spring may vibrate with substantially the same frequency out of phase by about 180 degrees. The balance mass and said balance mass spring are essentially resonant at the operating frequency of the Stirling cooler, usually about sixty (60) to about seventy-five (75) cycles per second.
The system also may include a frame to connect the Stirling cooler and the balance mass spring. Further, the system may include a first number of connectors attached to the enclosure and to the linkages and a second number of connectors attached to the Stirling cooler and to the linkages. The connectors may be pivot mounts.
The system further may include a guide attached to the enclosure. The guide may include a fixed retention device on a first end and a movable retention device on a second end. A carriage may be slidable along the guide. Pivot mounts may be attached to the carriage and the linkages and to the Stirling cooler and the linkages.
A further embodiment of the present invention may provide for a balance mass operated pump for use with a refrigeration system having a Stirling cooler. The pump may include a spring mounted in communication with the Stirling cooler and a balance mass attached to the spring for movement therewith. The balance mass may include a magnetic portion such that vibrations from the Stirling cooler are transmitted to the balance mass and the magnetic portion. The pump may further include a pump chamber positioned in communication with the magnetic portion of the balance mass. A magnetic piston may be positioned within the pump chamber such that the magnetic piston moves with the magnetic portion so as to provide a pumping action within the pump chamber.
The refrigeration system may further include an evaporator and a condenser connected by tubing such that the pump chamber is in fluid communication with the tubing. A frame may connect the Stirling cooler and the spring. The pump chamber may be mounted on the frame. The magnetic portion may include a tubular structure. The magnetic piston may include a hollow structure. The magnetic piston also may include a check valve positioned thereon.
The balance mass and the balance mass spring may be essentially resonant at about sixty (60) to about seventy-five (75) cycles per second. Specifically, the Stirling cooler may vibrate with a frequency and the balance mass spring may be resonant at a second frequency. The second frequency is chosen to reduce Stirling casing vibration to a minimum level.
A further embodiment of the present invention may provide for a vibration isolation system for mounting a Stirling cooler to a frame. The system may include a first number of mounts positioned on the frame, a second number of mounts positioned on the Stirling cooler, and a number of linkages. Each of the linkages may connect one of the first number of mounts and one of the second number of mounts.
The linkages may limit the movement of the Stirling cooler to a first dimension. The movement of the Stirling cooler may be limited to about one or two degrees in the first dimension. The system may include a guide rail attached to the frame. The guide rail may include a fixed retention device on a first end and a movable detention device on a second end. The first number of mounts may be attached to the carriage such that the carriage and the Stirling cooler can slide along the guide rail.
A further embodiment of the present invention provides for a refrigeration system powered by a Stirling cooler. The refrigeration system may include an outer frame. The outer frame may include a product area and a refrigeration deck area. A refrigeration deck may be positioned within the refrigeration deck area. The refrigeration deck may include a first section and a second section. An insulated plate may separate the first section and the second section. The Stirling cooler may be hung within the first section by a number of linkages so as to reduce the amount or the extent of the vibrations transmitted by the Stirling cooler to the insulated plate.
The first section may include a condenser positioned therein. The condenser may be in communication with the Stirling cooler. The second section may include an evaporator positioned therein. The evaporator may be in communication with the condenser via a number of lengths of tubing. The second section may include an air movement device positioned therein to circulate air through the refrigeration deck area and the product area. The system further may include a balance mass operated pump positioned in communication with the tubing so as to pump fluid from the condenser to the evaporator. The balance mass operated pump may be positioned in communication with the Stirling cooler so as to absorb the vibrations produced therefrom.
Other objects, features, and advantages of the present invention will become apparent upon review of the following specification when taken in conjunction with the drawings in the appended claims.