Abstract:
A fruit chiller has a semispherical bowl-like container for holding fruit or other food products with the bowl forming with the supporting base a cooling air supply passage. Cooling air flows into the bowl over the upper edge and variations in the cross section of the cooling air supply passage induces a turbulence in the cooling air that enhances air distribution and cooling efficiency.

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. Another issue with prior chillers is the distribution of the cool air amongst the food to be chilled. It is well known that the mixing of various velocity airflows produces a turbulence that leads to improved overall distribution of the cold air thus improving the overall cooling efficiency. 
     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, together with a baffle plate and an inner bowl or food container, 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 outlet holes and an inlet slot that communicate with the duct system. 
     The airflow inlet slot allows air to enter the food container around the upper periphery of the food container. Generally centrally located outlet holes in the lower portion of the food container return the air to the cooling duct and cold sink. The cross sectional area of the airflow inlet slot varies in size. This variation of cross sectional area produces variations of the velocity of the inlet airflow. When the airflows of various velocities mix, turbulence results and improves the mixing of the air within the food container. 
     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. 
     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 perspective view of the fruit chiller of FIG. 1 cut in half for viewing of the interior components. 
     FIG. 3 is a vertical section through the fruit chiller shown in FIG.  1 . 
     FIG. 4 is a perspective if the food container portion of the fruit chiller of FIG.  1 . 
     FIG. 5 is a vertical section through the fruit chiller shown in FIG.  4 . 
    
    
     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 food container  2  is seated within base  1 . Base  1  surrounds the sides and bottom of food container  2 . A removable cover  3  provides access to the food to be preserved. Inside of container  2  is an inlet slot  4  for distributed flow of the cold air into the container. Centrally located holes  5  in the bottom of container  2  provide a return path for the air. Air flow is provided by a motor driven fan, as will be described below. Upon passing through holes  5 , the air is again cooled and discharged through slot  4  and into the container. While this is a preferred embodiment it is also possible to reverse the airflow thus using holes  5  as discharge ports and slot  4  as a return air port. The base  1 , container  2  and removable cover  3  may all be made of injection molded plastic materials. The base  1  and the container  2  are preferably opaque and the cover  3  transparent. 
     Referring also to FIGS. 2 and 3, the base  1  is suitably supported on feet  15  to provide an open space beneath the base for the entry of ambient cooling air through slots  35 . 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  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  13  and positioned generally horizontally in the plane of baffle  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 is attached to the upper face and a heat sink  1  I is attached to the lower face of the module. The cold sink  10  is typically made of aluminum and includes a base plate and a series of closely spaced fins. Similarly, the heat sink  11  includes an aluminum base plate and integral closely spaced fins. 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  via slots  35 . 
     An inside upper wall  7  of base  1  surrounds the outer wall  6  of the container  2 . The inside upper base wall  7  and the outer food container wall  6  define an annular air flow passage  4   a  forming part of a duct system for the transport of the cooling air. The upper edge of flow passage  4   a  forms the inlet slot  4 . The base plate  13  represents a bottom floor of a cool air chamber  8  forming another part of the duct system and separating it from the heat in chamber  16 . The outside of the container wall  6  forms the top of the duct system. The duct system is in fluid communication with the container interior  24  via slot  4  and holes  5 . A fan  9  draws air from the container  2  in through holes  5 . As the air is exhausted from the lower portion of fan  9  it passes over cold sink  10 , into the cool air chamber  8  of the duct system and reenters the container interior  24  via slot  4 . Slot  4 , like the passage  4 a, is generally annular. Thus the air within container interior  24  is recirculated and cooled. 
     The sidewall  6  of food container  2  has several indentions  36 . These indentions are best seen in FIG.  4 . The cross section area of the passage  4   a  and slot  4  increases at the indentions  36 . The resulting airflow velocity through slot  4  in the area of indentions  36  will be decreased compared to the airflow velocity through the rest of slot  4 . This variation in the cross section area of inlet slot  4  causes variations in the airflow velocity into interior  24  of food container  2 . Alternately, the indentation  36  could be formed in the upper base wall  7 . 
     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. 5, 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  inside of 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 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 in the cover  3 , however, a manually adjustable vent slot may also be used. The slot could be located in either the container wall 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 semiripe 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.