Abstract:
A food chiller including an enclosed container supported on a base receives a flow of cooling air from a Peltier effect thermoelectric module in the base through cool air inlet openings into the container. Air is returned from the container to the base by a fan mounted in the air duct system in communication with the cold sink of the thermoelectric device. In each of the disclosed embodiments, duct length is minimized and air flow into the container is optimized by air hole placement and orientation.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for chilling fresh fruit and other fresh food products and, more particularly, to an improved countertop fruit chiller utilizing a Peltier effect thermoelectric device. 
     Thermoelectric devices operating in accordance with the well know Peltier effect have been used as cooling/heating devices for many years. Such a thermoelectric device comprises an array of semiconductor couples connected electrically in series and thermally in parallel. The semiconductor couples are sandwiched between metalized ceramic substrates. When DC electric current is applied in series to the thermoelectric device, it acts as a heat pump with heat being absorbed on the cold side, thereby cooling it, while heat is dissipated at the other side. Reversing the current causes the direction of heat flow to be reversed. Attaching a heat sink and a cold sink to the respective hot and cold sides may enhance the efficiency of the thermoelectric device. 
     Peltier effect devices have long been used to provide coolers and/or heaters for keeping foods fresh or for warming foods for serving. It has also been found and is well known to use forced-air convection to aid in heat transfer. A small electric fan is typically used to circulate air past the cold sink and into and through a container for the food, while another fan moves ambient outside air across the heat sink to dissipate heat from it. 
     Although chillers for fresh fruit and other perishable food products are well known in the art, the market success of such devices has been limited. There appear to be a number of reasons for this lack of market success. One is the cost and heat transfer efficiency of the solid state thermoelectric modules. In addition, the need to provide circulation of cool air to attain the greatest cooling efficiency has led to complex duct systems which add substantially to the cost of the containers, typically made of molded plastic materials. A long air circulation duct system also results in heat loss and pressure drop, both of which decrease the efficiency or add to the product cost. Another issue with prior chillers is the distribution of the cool air amongst the food to be chilled. It is important to optimize the distribution pattern of the cool air and to optimize the time that the cool air remains within the food container area. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a chiller for fresh fruit or other perishable food products utilizes a construction which optimizes a cooling air flow and thus heat transfer efficiency with a container construction that is less expensive to manufacture and permitting the use of a relatively smaller thermoelectric module. Thermoelectric modules of increased efficiency, such as disclosed in U.S. Pat. No. 5,448,109 is particularly suitable for use in the fruit chiller of the subject invention. 
     In its broadest aspect, the food chiller of the present invention comprises a base housing for mounting a Peltier effect thermoelectric module sandwiched between a cold sink and an opposite heat sink. The housing also defines a duct system that includes a cool air supply duct in heat transfer communication with the cold sink, a return air duct, and a cool air circulation fan in the cooling duct system to circulate air therethrough. 
     A food container portion is adjacent the base housing and contains an enclosing sidewall and a removable or openable cover for retrieval of the food. The food container portion has therein a plurality of inlet and outlet holes that communicate with the duct system. The inlet and outlet holes are designed to optimize the air flow. 
     In one embodiment these holes are oriented such that the cold airflow is induced into a circular swirling pattern. The swirling movement of the airflow helps maximize the time that cold air is in contact with the enclosed food thus improving the cooling efficiency. 
     In another embodiment, the cold air openings are oriented to direct the airflow away from the return air duct thus increasing the length of time the air is circulated within the food container area. The design is not restricted to these configurations as other airflow optimization patterns are also possible. The object of this invention is optimization of the airflow while minimizing manufacturing costs. 
     In one overall embodiment, the housing containing the thermoelectric device and duct system is separable from the food-containing portion. This embodiment allows for easy removal of the food container portion for cleaning, but requires a redundant wall at the interface of the housing and food container. 
     The top of the base may have holes that line up with holes in the bottom of the food container. To control the airflow rate into the food container, the food container may be rotated relative to the base thereby partially blocking the food container airflow holes. 
     In another overall embodiment, the housing containing the thermoelectric device and duct system is integrated with the food-containing portion thus requiring a single wall separating the two compartments. This approach minimizes manufacturing costs by minimizing the required number of components. 
     The food container portion is normally closed with a removable or openable cover such that cooling air is continuously recirculated. In one embodiment, however, an outside ambient air supply conduit communicates with the cooling duct system and includes a metering device to admit a controlled flow of outside air to assist in purging the cooling duct system of ethylene gas and other ripening by-products of fruit. The metering device may comprise a small diameter tube connected to the duct system upstream of the fan. 
     In another overall embodiment the housing containing the thermoelectric device also contains a tower comprising a portion of the duct system. Inlet air holes in the top of the tower help assure that the recirculated cold air flows to the top of the food container. To maintain a short duct length, the air out-flow holes are located near the base of the tower. The air out-flow holes are oriented such that the out-flowing air is directed toward the periphery of the food container. 
     To help maintain the interior temperature of the container, a removable insulating sleeve may be inserted into the container. The sleeve is shaped to conform to the interior of the enclosing sidewall. The removable cover may also be provided with an insulating liner. 
     Various arrangements of partitions may be placed within the container to divide the container into different temperature zones by varying the flow of cooling air through the zones. Such partitions may be vertically disposed to extend upwardly from the container bottom wall or may be horizontally disposed and attached, for example, to a central tower or to the container sidewall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the general arrangement of the fruit chiller of the subject invention. 
     FIG. 2 is a vertical section through the fruit chiller shown in FIG.  1 . 
     FIG. 3 is a perspective view of the fruit chiller cut in half for viewing of the interior components. 
     FIG. 4 is a perspective view of FIG. 3 with the food container and cover removed. 
     FIG. 5 is a detailed view of the section of FIG.  2 . 
     FIG. 6 is a top view of the fruit chiller with the cover removed. 
     FIG. 6A is a sectional detail taken on line  6 A— 6 A of FIG.  6 . 
     FIG. 7 is a top view of the fruit chiller with the cover removed showing an alternate embodiment of the invention. 
     FIG. 8 is a vertical sectional detail through the fruit chiller of FIG.  7 . 
     FIG. 9 is a vertical section of the fruit chiller showing an alternate embodiment of the invention. 
     FIG. 10 is a perspective view of the fruit chiller showing an alternate embodiment cut in half for viewing of the interior components. 
     FIG. 11 is a vertical section through the fruit chiller shown in FIG.  10 . 
     FIG. 12 is a vertical section of the fruit chiller showing an alternate embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, there is shown a fruit chiller  14  in accordance with one embodiment of the present invention. The fruit chiller includes a supporting base  1  for supporting the chiller on a horizontal surface. There is space inside the base for housing various components of the cooling system, which will be described in detail herein. A removable container  2  is seated on base  1 . A removable cover  3  provides access to the food to be preserved. Inside of container  2  are a plurality of inlet holes  4  for distributed flow of the cold air into the container. Centrally located outlet holes  5  provide a return path for the air. Upon passing through holes  5 , the air is again cooled and discharged through holes  4 . While this is a preferred embodiment it is also possible to reverse the airflow thus using holes  5  as inlet ports and holes  4  as outlet air ports. The base  1 , container  2  and removable cover  3  may all be made of injection molded plastic materials. The base  1  is preferably opaque and the container  2  and cover  3  transparent. 
     Referring also to FIGS. 2 and 5, the base  1  is suitably supported on legs  15  to provide an open space beneath the base for the entry of ambient cooling air. The lower interior of base  1  defines a substantially open ambient air chamber  16  defined generally by base side walls  17  and a base baffle plate  13 . 
     The container  2  and the food products contained therein are cooled with thermoelectric module  12  utilizing the well-known Peltier effect. The thermoelectric module  12  is mounted in the base baffle plate  13  and positioned generally horizontally in the plane of baffle plate  13 . By applying a DC current to the module, heat will be absorbed at one face (in this case the upper side of  12 ), thereby cooling it. Heat will be dissipated at the other face of the module (in this case the lower side of  12 ), thereby heating it. As is also well known in the prior art, a cold sink  10  is attached to the upper face and a heat sink  11  is attached to the lower face of the module. The cold sink  10  is typically made of aluminum and includes a base plate  18  and a series of closely spaced fins  19 . Similarly, the heat sink  11  includes an aluminum base plate  20  and integral closely spaced fins  21 . The heat rejected by the operating thermoelectric module  12  at the heat sink  11  is dissipated by a flow of ambient air through the ambient air chamber  16 . 
     The upper wall  7  of base  1  supports the lower wall  6  of the container  2 . Holes  4  in the container are in fluid communication with arcuate slots  22  in the base upper wall  7 , and holes  5  in the container are in fluid communication with holes  23  in the base upper wall  7 . The space  8  between the upper base wall  7  and the base baffle  13  represents a duct system that is in fluid communication with the container interior  24  via holes  4  and slots  22 , and holes  5  and  23 . A fan  9  draws air in through holes  5  and  23 . As the air is exhausted from the lower portion of fan  9  it passes over cold sink  10 , into duct system  8  and reenters the container interior  24  via slots  22  and  4 . Thus the air within container interior  24  is recirculated and cooled. 
     In another embodiment, the inflow of chilled air into the container interior  24  may be modulated. With a chiller construction in which the base upper wall  7  and the lower container wall  6  are generally circular in shape, the arcuate slots  22  in the base upper wall  7  may be replaced with a circular array of holes sized and spaced to align directly with the holes for in the lower wall  6  of the container. Full air flow into the container takes place when the holes in base upper wall  7  and the container lower wall  6  are completely aligned. However, slight rotation of the container relative to the base will partially close the alignment and result in a reduction in air flow. 
     Holes  4  in container  2  are shaped to optimize the flow of the chilled air. In one embodiment shown in FIG. 6, holes  4  are oriented such that the out-flowing chilled air will induce a counter-clockwise swirl pattern. The swirl pattern tends to increase the time the chilled air is in contact with the fruit thus improving cooling efficiency. 
     In another embodiment shown in FIG. 7, holes  25  are oriented such that the out-flowing chilled air is forced in a direction away from holes  5  thus increasing the time the chilled air remains in the container interior  24 . FIG. 8 illustrates a section through the outward oriented holes  25 . 
     The invention is not limited to the two hole orientations described above, as other optimization geometries are also possible. 
     In another cost saving embodiment, container  2  is not removable from base  1 . The bottom of container  2  is shared with the upper wall of base  1 . FIG. 9 shows a vertical section through a fruit chiller of this alternate configuration. Wall  26  is common between container interior  24  and duct system  8 . Chilled air is distributed into chamber  24  via inlet holes  27  and returned to duct system  8  via holes  28 . The orientation of holes  27  is such that the airflow into the container interior  24  is optimized. 
     In a variation of the FIG. 9 embodiment, the common wall  26  is formed as part of the container  2  which is separable from the base. Thus, when the container is lifted from the base, the duct system is opened. In one variant of this embodiment, the return outlet air flow from the container into the duct system is through the holes  28  in the center of container bottom wall  26 , or the holes  28  may be provided in a small circular plate forming part of the housing for the fan  9 . In this latter arrangement, the container bottom wall is provided with a central circular opening that surrounds the small circular plate when the container is placed on the base. 
     In another embodiment shown in FIGS. 10 and 11, tower  31  is an integral part of base housing  1 . Air inlet holes  5  are located at the top of tower  31 . Inlet holes  4  are located in the bottom wall of food container  2  and are oriented such that the outflowing cold air is directed upwardly and outwardly toward the periphery of food container  2 . This overall embodiment assures that cold air will circulate to the top of food container area  24  yet maintains a short duct length by virtue of the optimized shape and positioning of holes  4 . The return portion of the duct system  8 , receiving air via holes  5 , is preferably shortened by an intermediate barrier wall  32 . 
     Ripening fruit is known to emit ethylene gas and other by-products of organic decomposition. It may be desirable to exhaust these gasses by regular or periodic replacement of the cooling air recirculating within the container interior  24 . Referring particularly to FIG. 12, an ambient air conduit  29  comprising a small diameter metering tube extends from the side wall  17  of the base into the duct system  8  where a small volume flow of ambient outside air is drawn in by the cold sink fan  9  and mixed with the recirculated cooling air. As shown, the ambient air conduit  29  opens into the duct system  8  just upstream of the inlet to the fan  9 . It is believed, however, that the conduit could connect to the duct system at another location therein. The inflow of ambient air may be regulated with the use of an optional pinch valve or metering valve  30  at the inlet end of the conduit  29 . To provide for the corresponding exhaust of ethylene and other gaseous by-products, it is preferred to provide a small leak between the container  2  and the cover  3 , however, a manually adjustable vent slot may also be used. The slot could be located in either the container wall  2  or the cover  3 . 
     As indicated previously, the thermoelectric module  12  is normally configured so the upper face is cold while the lower face is hot. Because reversal of the polarity of the supplied current to the thermoelectric module causes the direction of heat flow to be reversed, the fruit chillers of either of the embodiments described herein may also be utilized to warm the fruit to promote or enhance ripening. In this alternate configuration the upper face of the thermoelectric module  12  is hot while the lower face is cold. 
     Certain fruits may often be purchased in a green or semi-ripe condition. One example is bananas which are often purchased in some semi-ripe condition and allowed to ripen in the open air. By reversal of the supplied current to the thermoelectric module  12 , a green or semi-ripe fruit may be ripened more quickly by warming and, when ripe, preserved for a longer time by again reversing the current to provide a cooling air supply to the container  24 . 
     In general, temperature control is an excellent, and by far the best means, of controlling ripening in fruit. As discussed above, warming may be used to enhance and promote ripening of green or semi-ripe fruit, but after the fruit has ripened, cooling is the best means available to slow the biological ripening processes and preserve the fruit for a longer period of time. 
     The direction of heat transfer of the thermoelectric module  12  can be reversed as mentioned above. The level of heating and cooling can also be controlled by control of the level of supplied current and voltage. In this manner, the user may, for example, select a set point to ripen fruits at a desirable rate or, conversely, a cooling set point to maintain ripened fruit at a temperature found to make the fruit most palatable. Other cooling or warming strategies may also be utilized, either with manual settings by the user or by using programmed microprocessor control.