Abstract:
A chiller for fresh fruit and other perishable food products is cooled with a thermoelectric device and includes a cool air recirculating system that minimizes air flow path lengths and provides uniform cool air distribution throughout a fruit container removably supported above the thermoelectric module. The cooling air flow duct system is formed in part by the bottom wall of the container, thereby enhancing direct cooling air flow contact in minimizing the lengths of the flow paths.

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 known 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, where the temperature rises. Reversing the current causes the direction of heat flow to be reversed. The efficiency of the thermoelectric device may be enhanced by attaching a heat sink and a cold sink to the respective hot and cold sides. 
     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, such prior art modules have typically been quite fragile, exhibiting low mechanical strength. 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. Long air circulation flow paths also result in heat loss and pressure drop, both of which decrease the efficiency or add to the cost by requiring larger thermoelectric modules. 
     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 and improved mechanical strength, such as disclosed in U.S. Pat. No. 5,448,109, are 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 supporting base that includes a housing for mounting a Peltier effect thermoelectric module sandwiched between a cold sink and an opposite heat sink. The housing also defines an upwardly opening cooling 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 is supported on an upper peripheral edge of the housing, the container having an upper enclosing side wall above the peripheral edge of the housing and a lower bottom wall within said peripheral edge, the bottom wall forming an enclosing top wall for the duct system. The bottom wall has formed therein a plurality of inlet holes that communicate with the cool air supply duct and a plurality of outlet holes that communicate with the return air duct. 
     In one embodiment of the invention, one of the cooling system ducts is positioned to extend along an outer peripheral wall of the housing that includes the housing peripheral edge. The other of the ducts is centrally disposed within the first duct and separated from it by a generally vertically extending common dividing wall. The duct system also includes a cool air duct inlet, a return air duct outlet, and a recirculation passage that includes a circulation fan and the cold sink. The recirculation passage interconnects the cool air duct inlet and return air duct outlet. Preferably, the first outer duct comprises the cool air supply duct and has a generally horizontal lower enclosing wall that forms a common separating wall with the recirculation passage which is disposed below the separating wall. The cool air duct inlet is formed in the common separating wall adjacent the outer peripheral wall of the housing. The return air duct outlet is preferably also formed in the common separating wall. In a preferred embodiment, the common separating wall is generally horizontally disposed and generally parallel to the lower bottom wall of the container (also forming the top wall of the duct system and spaced vertically above the common separating wall). 
     In one alternate embodiment of the invention, the food container bottom wall includes a hollow central tower that extends vertically upwardly within the interior of the container. The central tower is provided with a plurality of holes which may comprise either the inlet holes for the cool air supply duct or the outlet holes for the return air duct. In this embodiment, the holes preferably comprise a hole pattern of increasing hole size in an upward direction along the tower. 
     In a presently preferred embodiment, the cooling duct system has a lower enclosing wall that forms a common separating wall with the recirculation passage disposed below the separating wall. Either of the cool air duct inlet or the return air duct outlet may be formed in the common separating wall immediately adjacent the outer peripheral wall of the housing. The plurality of inlet holes or outlet holes formed in the enclosing top wall of the duct that extends along the outer peripheral wall of the housing comprises a hole pattern of increasing hole size with increasing distance from the respective duct inlet or duct outlet. Preferably, the cool air supply duct is positioned along the outer peripheral wall of the housing. 
     The food container is removable from the housing and is provided with an annular outer edge seal between the upper peripheral edge of the housing and the lower edge of the enclosing side wall of the container. An annular inner seal is disposed between the upper edge of the common dividing wall and the underside of the container bottom wall. The outer seal may be attached to the upper peripheral edge of the housing and the inner seal to the underside of the bottom wall. Alternately, both outer and inner seals may be secured to the container bottom wall. 
     In the embodiment in which either the cold air duct inlet or the return air duct outlet is formed in the common horizontal separating wall adjacent the outer peripheral wall of the housing, the other outlet or inlet is also formed in the common separating wall in approximately the center thereof. The respective pluralities of inlet holes and outlet holes, in another embodiment, are interrupted to define solid wall portions that overlie the cool air duct inlet and the return air duct outlet to cover and protect the same from the ingress of debris. 
     The container is normally closed with a removable cover such that cooling air is continuously recirculated. In one embodiment, however, an outside ambient air supply conduit communicates with the recirculation passage 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 recirculation passage upstream of the fan. 
     In the embodiment of the invention in which the food container includes a central tower, an auxiliary food tray may be demountably supported on the tower above the container bottom wall. The central tower is preferably tapered to decrease in diameter in the upward direction, and an auxiliary food tray provided with a center through hole is adapted to be placed over the central tower for demountable support thereon. 
     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 container side wall. 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 side wall. 
    
    
     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 vertical section taken on line  3 — 3  of FIG.  2 . 
     FIG. 4 is a top plan sectional view of the fruit chiller container taken on line  4 — 4  of FIG.  2 . 
     FIG. 5 is a sectional side elevational detail taken on line  5 — 5  of FIG.  2  and showing another embodiment of the invention. 
     FIG. 6 is a sectional detail of FIG. 5 showing the interface between the container and the cover. 
     FIG. 7 is a perspective view of another embodiment of a fruit chiller in accordance with the subject invention. 
     FIG. 8 is a vertical section taken on line  8 — 8  of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, there is shown a fruit chiller  10  in accordance with one embodiment of the present invention. The fruit chiller includes a supporting base  11  for supporting the chiller on a horizontal surface, with the base including a housing  12  for various components of the cooling system which will be described in detail hereinafter. A removable container  13  is seated on the upper peripheral edge  14  of the housing  12 . The container has an upper enclosing side wall  15  extending above the peripheral edge  14  of the housing and a lower bottom wall  16  that is generally horizontal and lies within the peripheral edge  14  of the housing. The container  13  is closed by a removable cover  17 . The base  11 , including the housing  12 , and the container  13  and cover  17  may all be made of injection molded plastic materials. The base  11  is preferably opaque and the container  13  and cover  17  transparent. 
     Referring also to FIGS. 2-4, the base  11  is suitably supported on legs  18  to provide an open space beneath the base for the entry of ambient cooling air. The lower interior portion of the base  11  defines a substantially open ambient air chamber  20  defined generally by a base bottom wall  21 , a base upper wall  22  and an enclosing base side wall  23 . The container  13  and food products contained therein are cooled with a thermoelectric module  24  utilizing the well known Peltier effect. Referring particularly to FIG. 3, the thermoelectric module  24  is mounted in the base upper wall  22  and positioned generally horizontally in the plane of the upper wall. In accordance with generally conventional construction, the module  24  includes an array of semiconductor couples  25  sandwiched between upper and lower ceramic substrates  26  and  27  with layers of metalization interposed therebetween. By applying a DC current to the module, heat will be absorbed at one ceramic substrate (in this case the upper substrate  26 ), thereby cooling it, and heat will be dissipated at the other substrate (in this case lower ceramic substrate  27 ), thereby heating it. As is also well known in the prior art, a cold sink  28  is attached to the upper substrate  26  and a heat sink  30  is attached to the lower substrate  27 . The cold sink  28  is typically made of aluminum and includes a base plate  31  and a series of parallel, closely spaced fins  32 . Similarly, the heat sink  30  includes an aluminum base plate  33  and integral closely spaced parallel fins  34 . 
     The heat rejected by the operating thermoelectric module  24  at the heat sink  30  is dissipated by a flow of ambient air through the ambient air chamber  20 . To promote the heat dissipating flow of ambient air, a heat sink fan  35  is mounted on the base bottom wall  21  where it draws ambient air in through an ambient air inlet  36  directly below the fan. Ambient air from the fan  35  passes over the heat sink fins  34  and exits the air chamber  20  via ambient air outlets  37  formed in the side wall  23  of the base. An electronic control module  40  for controlling the supply of power to the thermoelectric module  24 , the heat sink fan  35 , and a cooling air fan (to be described) is also mounted in the ambient air chamber  20 . 
     The side wall  23  of the base extends upwardly to an upper peripheral edge  41  which is joined by an annular horizontal shoulder  43  to the upper edge  14  of a vertically extending annular wall  42  that also forms the outer wall of a cooling air chamber  38 . The cooling air chamber generally comprises the housing  12  for the system providing cooling air to the container  13 . The container  13  is supported on the upper peripheral edge of the housing  12  on the recessed horizontal shoulder  43 . The container  13  includes an upper enclosing side wall  15  which terminates in a lower edge  46  that seats on an annular foam rubber seal  47  on the horizontal shoulder  43 . The container bottom wall  16  is formed integrally with and within the side wall  15 , but spaced slightly above the side wall lower edge  46 . The cooling air chamber  38 , defined peripherally by the outer wall  42 , is closed at the top by the bottom wall  16  of the container and the lower edge  46  of the container side wall. The container bottom wall  16  forms the top wall for a cooling duct system  50 . The cooling duct system includes an outer cool air supply duct  51  extending along the outer peripheral wall  42  of the housing and enclosed radially inwardly by a continuous vertically disposed dividing wall  52  which also forms a common outer wall for an interior return air duct  53 . The cooling duct system  50  (comprising the cool air supply air duct  51  and the return air duct  53 ) is generally enclosed at the bottom by a lower enclosing wall  54  that extends horizontally within the annular outer wall  42 . The lower enclosing wall  54  of the cooling duct system  50  is also the upper wall of a recirculation passage  56  formed above and enclosed at the bottom by the upper wall  22  of the base. 
     The container bottom wall  16 , which as indicated previously also provides the upper wall of the cooling duct system  50 , includes a plurality of inlet holes  57  by which cool air in the cool air supply duct  51  is supplied to the interior of the container  13 . The laterally interior portion of the container bottom wall  16  is provided with a plurality of outlet holes  58  allowing cooling air in the container interior to be returned for re-cooling. The top of the vertical dividing wall  52  is provided with an annular foam rubber seal  49  to prevent the short circuiting of cooling air from the cool air supply duct  51  to the return air duct  53 . The center of the lower enclosing wall  54  is provided with an upwardly opening cylindrical sleeve  60  centered in the return air duct  53 . The cylindrical sleeve  60  defines a return air duct outlet  61  through which air is drawn by a cold sink fan  62  to move the air through the recirculation passage  56 . The bottom of the recirculation passage  56  is closed by the upper wall  22  of the base and the thermoelectric module  24  mounted therein. The cold sink fins  32  extend into the recirculation passage  56  where recirculating air, propelled by the cold sink fan  62 , is cooled for return to the cool air supply duct  51 . Cooled air is returned via a cool air duct inlet  63  formed in the lower wall  50  of the cooling duct system adjacent the outer wall of the housing. 
     To summarize the path of cooling air flow thus described, air within the container  13  is drawn into the return air duct through the outlet holes  58 , exits the return air duct  53  via the return air duct outlet  61 , passes through the cold sink fan  62  in the recirculation passage  56 , past the cold sink fins  32  where the air is cooled, exits the recirculation passage and returns to the cool air supply duct  51  via the cool air duct inlet  63 , and finally is returned into the container  13  via the inlet holes  57  in the outer peripheral surface of the container bottom wall  16 . The entire cooling duct system  50  is characterized by a simple construction and short flow paths, and is further characterized by unique flow equalizing features as will be described below. 
     Referring particularly to FIG. 4, because the return air duct outlet  61  bringing cooled air into the cool air supply duct  51  is located near the outer wall at one end of the housing  12 , cooling air might preferentially remain nearer that end and not adequately cool the opposite end of the container. To more equally and efficiently distribute the cool air, the inlet holes  57  in the outer peripheral portion of the container bottom wall  16  are formed to progressively increase in size as their distance from the return air duct outlet  61  increases. Alternately, the inlet holes  57  may be of equal size, but disbursed in an array that increases in hole density as the distance from the return air duct outlet increases. In this manner, the air flow from the cool air supply duct  51  upwardly through the holes  57  in the container bottom wall is more uniform, resulting in more uniform cooling temperature throughout the container. 
     It should be noted that by reversing the direction of the air flow, cooling air recirculation through the cooling duct system  50  may be reversed. Similarly, reversal of the contacts supplying DC current to the thermoelectric module  24  will reverse the heat pump function of the module so that the interior of the container may be heated. However, this is not a preferred function and a unit intended primarily for heating or warning would preferably include a number of structural changes. 
     To prevent the ingress of fruit juices, debris and other contaminants into the lower portion of the cooling duct system, a few practical expedients are utilized. In the container bottom wall  16  the pattern of inlet holes  57  is interrupted directly above the return air duct outlet  61  to define a solid wall portion  64 . Similarly, the pattern of outlet holes  58  in the bottom wall is interrupted immediately above the cool air duct inlet  63  formed in the cylindrical sleeve  60  to define another solid wall portion  65 . Any juices, debris or the like finding their way into the cool air supply duct  51  or the return air duct  53  are restricted from movement downwardly into the recirculation passage  56  by an upstanding lip forming the return air duct outlet  61  and the upwardly extending cylindrical sleeve  60 . 
     Ripening fruit is known to emit ethylene gas and other by-products of organic decomposition. It may be desirable to exhaust these gases by regular or periodic replacement of the cooling air recirculating within the container  13 . Referring particularly to FIG. 5, an ambient air conduit  66  comprising a small diameter metering tube extends from the side wall  23  of the base into the recirculation passage  56  where a small volume flow of ambient outside air is drawn in by the cold sink fan  62  and mixed with the recirculated cooling air. As shown, the ambient air conduit  66  opens into the recirculation passage  56  just upstream of the inlet to the fan  62 . It is believed, however, that the conduit could connect to the recirculation passage at another location therein. The inflow of ambient air may be regulated with the use of an optional pinch valve  59  at the inlet end of the conduit  66 . To provide for the corresponding exhaust of ethylene and other gaseous by-products, it is preferred to provide a small leak between the container  13  and the cover  17 . As shown in the FIG. 6 detail, such a controlled leak may be provided by a small annular space  67  between the outer rim  70  of the cover and the top edge  69  of the container side wall  15 . A horizontal supporting rim  68  on the cover seats on the upper edge of the container side wall, but is lifted by internal container pressure, thereby allowing small amounts of air to escape which are replenished with ambient air via the conduit  66 . 
     In FIGS. 7 and 8, there is shown another embodiment of the invention that includes a container  71  that is more bowl shaped and has a tapering side wall  72  terminating in a generally flat bottom wall  73 . The container  71  is removably supported on a base  74  which internally includes a thermoelectric module, an ambient cooling air chamber for the heat sink, and a cooling air duct system supplying recirculating cooled air to the container, all in a manner similar to the previously described embodiment. 
     In this embodiment, the container bottom wall  73  includes an integral hollow central tower  75  that extends vertically upwardly within the interior of the enclosing container side wall  72  and may extend into the space defined by a removable bowl shaped cover  76 . The tower is provided with a plurality of holes  77  communicating with the hollow interior which holes may act as inlet holes for the flow of air to be recooled or outlet holes for cooled air being returned to the container, depending on the direction of operation of a cold sink fan  78  functioning as described with respect to the previous embodiment. Preferably, the holes  77  comprise outlet holes permitting air within the container  71  to be returned via fan  78  to a recirculation passage  80 , past the fins  81  of a cold sink  82 , back out through a return air duct outlet  83 , into a cool air supply duct  84 , from which the cooled air re-enters the container via a pattern of inlet holes  85  in the bottom wall  73 . The interior of the tower  75  comprises a return air duct  86  which corresponds functionally to the return air duct  53  of the embodiment of FIGS. 1-4, but is substantially different in shape. 
     The use of a central tower  75  enhances cool air distribution throughout the container. By using a pattern of outlet holes  77  which increase in size as the distance of the holes increases from the inlet holes  85 , a more uniform flow of air and thus a more uniform cooling of the entire interior of the tower  75  and cover  76  may be attained. This embodiment is still characterized by substantially shortened air flow paths and the elimination of flow paths from exposed exterior walls, all characteristic of the prior art. In particular, the total length of the tower  75  is less than one-half the circumference of domed chillers of the prior art having an air flow path in the outer spherical wall. 
     The center tower  75  is tapered from a larger diameter at its base to a smaller diameter at its free upper end. Fruit or other food products may be stored in the container  71 , supported by the bottom wall  73  and side wall  72 . In addition, one or more trays, including a larger diameter lower tray  87  and a small diameter upper tray  88  may be removably supported on the tower  75 . Each of the trays is provided with a central through hole  90  by which the tray may be slid over the tower until it engages the tower surface of the same diameter as the through hole where it is retained in position. Preferably, the through holes  90  are defined by tapered sleeves  91  to enhance surface contact and support by the tower  75 . 
     The removable trays  87  and  88  may also function as partitions which separate the interior of the container  71  into zones of varying temperature and/or for providing a baffle effect to vary the flow of air through the zones to effect varying levels of cooling. In this manner, different types of fruit or other food products, having different optimal storage temperatures, may be kept in the same container. To effect such a partitioning, the trays  87  and  88  may be made of a solid piece having no air holes therein, may be made with outer diameters selected to restrict the flow of cooling air upwardly from the cooled air inlet holes  85 , or may be utilized with a tower having a different pattern of outlet holes  77 . The fruit chiller  10  of the previously described embodiment of FIGS. 1-4 may be similarly partitioned, as with horizontal partitioning trays suitably supported on rims (not shown) on the interior side wall  15  of the container or by vertically disposed intermediate walls (not shown) extending upwardly from the bottom wall  16  of the container. Variations of the patterns of the inlet holes  57  and outlet holes  58  may also be used in conjunction with these auxiliary interior walls. 
     Another feature that is particularly adaptable for use with the embodiments described herein is a separate removable insulating sleeve  92 , shaped to fit the interior surface of the container side wall  15  and to extend from the bottom wall  16  to the lowermost edge of the cover  17 . The interior of the cover  17  may also be provided with an interior insulating layer  93  inserted separately into the interior of the cover after molding. The insulating sleeve  92  and the insulating layer  93  are particularly useful in maintaining the cool interior of the container after the container has been lifted from the base as for transport, display, or serving. 
     As indicated previously, the electronic module  40  is used to control the supply of power to the thermoelectric module  24 , the heat sink fan  35  and the cold sink fan  62 . Because reversal of the polarity of the current supplied 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. 
     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 utilizing a controller  40  permitting the user to reverse the current and thus the heat flow, 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  13  or  71 . 
     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 electronic control module  40  may also utilize a thermostat to allow user control of the desired level of cooling and/or heating. 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.