Abstract:
A unitary thermoelectric heating and cooling device for foodstuffs is described. In one embodiment, the device includes at least one detachable container to place food stuffs and a sturdy platform which holds the detachable container, comprising at least one thermoelectric module, wherein said module selectively heats or cools food stuffs in the detachable container depending upon desired temperature set, independent to ambient temperature. Further, the device includes a temperature adjusting slider, wherein desired temperature is set and depending on the set temperature, the direction of flow of current in the module is automated through DPDT switch. In another embodiment, a method for heating and cooling food stuffs using said device includes setting the desired temperature using a temperature adjusting slider, automating the flow of current in a thermoelectric module depending on the set temperature and selectively heating or cooling food stuffs in a detachable container depending on the desired temperature.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a device for conditioning the temperature of food stuffs. Particularly, the present invention relates to a unitary thermoelectric heating and cooling device, which provides both heating and cooling options to bring food stuffs to a desired temperature. 
       DESCRIPTION OF PRIOR ART 
       [0002]    The conventional coolers typically use ice chests for cooling food stuffs. Such ice chests have number of disadvantages. For example, as the ice melts, container gets filled with the water which needs to be removed periodically. Often, outlet ports are provided in such coolers to allow the melted ice to be drained. However, in conventional coolers, only sealed containers can be placed within the container if water damage is to be avoided. Further, to keep the contents cool for an extended period, ice must be repeatedly added. Furthermore, only a relatively small amount of food stuffs can actually be stored within a cooler of a given size because required ice occupies more space and also the weight of the cooler is significantly increased due to the presence of the ice. 
         [0003]    Further, systems exist, wherein a cooling system is incorporated within a cooler type container, so that when the container is coupled to power source the food stuffs inside the cooler is automatically cooled. With such automatic cooling, there is no need for ice and the container can hold more food stuffs than conventional ice chests of comparable size. The thermoelectric technology which allows a cooling system to be incorporated in a cooler was developed by NASA and eliminates the need for bulky compressors and piping. However, the existing devices for cooling food stuffs which utilize said thermoelectric technology fail to utilize the advantages provided by the thermoelectric chip effectively. Also, there is no unitary device which provides heating option along with cooling proficiently to bring the temperature of the food stuffs to a desired temperature. 
         [0004]    The existing devices which utilize the thermoelectric chips for heating or cooling have various drawbacks such as: inability to cool adequately when the ambient temperature exceeds certain temperature such as 85 degree F. The assembly of thermoelectric chip with heat sink and cold plate are mostly done with the ordinary heat sink compound past and silicon grease, which has low thermal conductivity, which creates an inefficient thermal junction between the hot side of the chip and the heat sink&#39;s base plate. The standard configured fins do not adequately dissipate the heat whatever absorbed from base plate to the surrounding which limits the exposed total fin surface area. Also, the air flow due to the standard fans and the positioning of the fan do not get rid of all the heat from fin surface. In addition, there exists no portable device which provides both heating and cooling option for food stuff efficiently which can be achieved by the thermoelectric chips. 
         [0005]    Therefore, it is desirable to utilize the maximum efficiency of the thermoelectric chips, such as, when used in heating and cooling device to take advantages provided by these chips by overcoming the drawbacks as mentioned above. 
       SUMMARY OF THE INVENTION 
       [0006]    The primary objective of the present invention is to provide a thermoelectric cooler and warmer which overcomes the short comings of conventional thermoelectric units as set forth above. 
         [0007]    In one aspect, a unitary thermoelectric heating and cooling device for food stuffs is described. The device includes at least one detachable container to place food stuffs and a sturdy platform which holds at least one detachable container, comprising at least one thermoelectric module, wherein the thermoelectric module selectively heats or cools the food stuffs in the detachable container depending upon a desired temperature set, independent to the ambient temperature. 
         [0008]    Accordingly, the present invention relates to the device, wherein the detachable container is made up of metallic material with high thermal conductivity, and a base of the detachable container is braced with metallic fins such as aluminum fins and forged with metallic plate such as copper plate, thereby increasing the efficiency of dissipating heat from surface of the sturdy platform. 
         [0009]    Accordingly, the present invention relates to the device, which includes a means to set the desired temperature such as temperature adjusting slider, wherein the desired temperature is set using the temperature adjusting slider and depending on the set temperature, the direction of flow of current in the thermoelectric module is automated. 
         [0010]    In another aspect, a method for heating and cooling food stuffs using a unitary thermoelectric heating and cooling device is described. The method includes setting the desired temperature using a means to set the desired temperature such as temperature adjusting slider, automating the flow of direction of current in the thermoelectric module depending on the set temperature and selectively heating or cooling food stuffs in a detachable container depending on the desired temperature, independent to the ambient temperature. 
         [0011]    Accordingly, the present invention relates to a method, wherein the flow of current in one direction through the thermoelectric module heats up the food stuffs in the detachable container and the reverse direction cools the food stuffs in the detachable container. 
         [0012]    In yet another aspect, the described method includes regulating an AC input voltage, converting the regulated AC input voltage to a DC voltage, and supplying the DC output voltage to the thermoelectric module, as the thermoelectric module work on DC voltage. The regulation of the AC power supply is achieved by a limit circuit and the AC to DC voltage conversion is achieved by a full wave diode bridge circuit. 
         [0013]    It is advantageous that the unitary device in the present invention includes not much moving parts to wear out. Further, the unitary device is portable hence it is feasible to be used in buffet set up at parties. 
         [0014]    The systems and apparatuses disclosed herein may be implemented in any means for achieving various aspects. Other features will be apparent from the accompanying drawings and from the detailed description that follows. 
     
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING FIGURES 
         [0015]    Example embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
           [0016]      FIG. 1(   a ) is a perspective view of a unitary thermoelectric heating and cooling device, in accordance with the present invention. 
           [0017]      FIG. 1(   b ) is a perspective view of a unitary thermoelectric heating and cooling device illustrating a detachable container. 
           [0018]      FIG. 2(   a ) and  FIG. 2(   b ) is a sectional view of base of a detachable container, in accordance with one embodiment of the present invention. 
           [0019]      FIG. 3  is a schematic representation of a circuit in a sturdy platform to supply power to a thermoelectric module, in accordance with one embodiment of the present invention. 
           [0020]      FIG. 4(   a ) and  FIG. 4(   b ) are schematic representations of flow of direction of current in a thermoelectric module using a double pole double throw (DPDT) switch, in accordance with one embodiment of the present invention. 
           [0021]      FIG. 4(   c ) is a cross sectional view of a thermoelectric module. 
       
    
    
       [0022]    Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows. 
       DETAILED DESCRIPTION OF INVENTION 
       [0023]    The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art about making and/or using the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. 
         [0024]    The present invention describes a unitary thermoelectric heating and cooling device for food stuffs, which provides both heating and cooling options to bring food stuffs to a desired temperature. The phrase ‘food stuffs’ used through out the document includes both food and beverages. 
         [0025]      FIG. 1(   a ) is a perspective view of a unitary thermoelectric heating and cooling device ( 100 ), in accordance with the present invention. Particularly, said unitary device ( 100 ) includes at least one container ( 102 ), which is placed on a sturdy platform ( 104 ). In one exemplary embodiment, the container ( 102 ) can be detached from the sturdy platform ( 104 ) for serving the heated or cooled food stuffs, for cleaning purpose etc. as shown in  FIG. 1(   b ). In one example embodiment, the container ( 102 ) is preferably constructed of a metallic material, such as aluminum or stainless steel, having relatively high thermal conductivity and the construction of base of the container ( 102 ) is as shown in  FIG. 2 . 
         [0026]    In one exemplary embodiment, the sturdy platform ( 104 ) includes a switch ( 106 ) to turn on and turn off the device ( 100 ), a means to set a desired temperature such as temperature adjusting slider ( 108 ) to adjust to a desired temperature within maximum hot of about 100° C. ( 108 ( a )) to maximum cold of about 0° C. ( 108 ( b )) temperatures, and a liquid crystal display ( 110 ) to show the adjusted temperature. In one exemplary implementation, the top surface of said platform ( 104 ) is shaped in such a manner to fit perfectly with the container&#39;s ( 102 ) bottom in order to transfer heat for warming or removing heat for cooling purposes. Further, the sturdy platform ( 104 ) includes a fan for exhausting of heat. The device further includes a connector ( 112 ) for connection to an external power supply and/or a removable battery for cordless operation. In one exemplary embodiment, the sturdy platform ( 102 ) includes at least one thermoelectric module and electronic components. The thermoelectric module is preferably a solid state device, which is powered using a 12 volts DC supply. It is to be noted that the inclusion of one or more thermoelectric modules depends on the size of the container. The circuit diagram of power supply to the thermoelectric module is illustrated in  FIG. 3 . 
         [0027]    In operation, when the temperature in the slider ( 108 ) is raised, the thermoelectric module generates heat and thereby, warms the food stuffs in the container ( 102 ) to the set temperature. When the temperature in the slider ( 108 ) is lowered, the direction of flow of current in the thermoelectric module get reversed and hence, decreases the temperature as set in the slider ( 108 ), independent to the ambient temperature. 
         [0028]      FIG. 2(   a ) and  FIG. 2(   b ) is a sectional view of base of a container (the container ( 102 ) of  FIG. 1(   a )), in accordance with one embodiment of the present invention. Particularly, the base of the container ( 102 ) is braced with metallic fins such as aluminium fins ( 202 ), which tremendously increases the surface area of the fins and thereby, dissipating the heat more efficiently. It is to be noted that the thickness of the base plate of the container ( 102 ) can be increased or doubled, to absorb heat more efficiently. Further, the aluminium base plate is cold forged with about 3 to 5 mm thick metallic plate such as copper plate ( 204 ) to enhance spreading of heat. It is to be appreciated that by combining the forged copper plate with convoluted fins, the heat dissipation from surface of the sturdy platform ( 104 ) is increased about four folds. Furthermore, the fan in the sturdy platform ( 104 ) blows the air through said fins, length wise, which results in dissipation of heat to ambient temperature more efficiently. 
         [0029]      FIG. 3  is a schematic representation of a circuit in a sturdy platform (the sturdy platform ( 104 ) of  FIG. 1 ) to supply power to a thermoelectric module, in accordance with one embodiment of the present invention. Particularly, the circuit ( 300 ) of  FIG. 3  illustrates a typical power supply to the unitary device ( 100 ) of  FIG. 1 . The circuit ( 300 ) regulates the high AC voltage and converts AC power supply to a DC voltage necessary to operate the unitary device ( 100 ). The circuit ( 300 ) includes an AC to DC converter ( 302 ) coupled to a thermoelectric module ( 304 ) as shown in  FIG. 3 . The AC-to-DC converter ( 302 ) includes AC power supply ( 306 ) connected to a full wave diode bridge ( 308 ) at its input terminals ( 310 ) and ( 312 ) through a limit circuit ( 314 ). Further, the output terminals ( 316 ) and ( 318 ) of the bridge rectifier ( 308 ) are connected across the voltage support capacitor ( 320 ). 
         [0030]    In one exemplary embodiment, the voltage regulation is achieved using the limit circuit ( 314 ), wherein the circuit input lead ( 306 ( a )) is connected to the input of a triac ( 332 ), and to the resistor ( 334 ). The junction of diodes ( 322 ) and ( 324 ) are connected to the input of a diac ( 330 ), the output of which is connected to the input of the triac ( 332 ), i.e. the gate terminal. The output of the triac ( 332 ) is connected to the junction of diodes ( 326 ) and ( 328 ), and to a capacitor ( 336 ) and a variable resistor ( 338 ) as shown in  FIG. 3 . Further, the input of the diac ( 330 ) is also connected through parallel resistor ( 334 ), a capacitor ( 336 ) and the variable resistor ( 336 ), which provides power to the triac ( 332 ). Furthermore, the limit circuit ( 314 ) also consists of a circuit, consisting an NPN transistor ( 340 ) for generating supply voltage for use in the circuit ( 300 ), wherein a series of resistors ( 342 ) and ( 344 ) are connected to the emitter and base terminal of the NPN transistor ( 340 ) and the junction of the two resistors is connected to diodes ( 324 ) and ( 328 ). Further, a resistor ( 346 ) is connected in parallel with a capacitor ( 348 ), which in turn connected to the collector and base terminals of the NPN transistor ( 340 ). Also, the junction of the resistor ( 346 ) and the capacitor ( 348 ) is connected to diodes ( 322 ) and ( 326 ). 
         [0031]    In operation of the circuit of  FIG. 3 , at 110 volts AC input line voltage, the total voltage across the base of the transistor ( 340 ) is small, and thereby the transistor ( 340 ) generates a high current. This current charges the capacitor ( 336 ) fully on one half cycle of the input AC to a voltage which reaches the threshold of the diac ( 330 ), and fires the triac ( 332 ). This arrangement provides the desired internal voltage for the rest of the power supply. Further, the output of the triac ( 332 ) and the input voltage ( 306 ( b )) are fed to the bridge rectifier ( 308 ) for AC to DC conversion. In addition, the variable resistor ( 338 ) increases and/or decreases the output voltage fed to the bridge rectifier ( 308 ) as set by a slider (the slider ( 108 ) of  FIG. 1 ). Thus, increases and/or decreases the temperature on the top surface of the thermoelectric module ( 304 ). 
         [0032]    In one exemplary embodiment, the bridge rectifier circuit ( 308 ) is essentially a full wave rectifier circuit, including four diodes ( 350 ,  352 ,  354  and  356 ), forming the four arms of an electrical bridge. In operation, when the switch (the switch ( 106 ) of  FIG. 1 ) is turned on, the AC voltage is applied to the input terminals of the bridge ( 310 ,  312 ) through a circuit ( 314 ), and the rectified DC voltage is taken from the output terminals of the bridge ( 316 ,  318 ). During positive half cycle of AC input voltage, the diodes ( 350 ) and ( 352 ) are forward biased, while the diodes ( 354 ) and ( 356 ) are reverse biased. During the negative half cycle, the diodes ( 354 ) and ( 356 ) are forward biased, while the diodes ( 350 ) and ( 352 ) are reverse biased. Since, in both half cycles of AC input voltage, the load current flows in the same direction, hence a full wave rectified output is achieved. It is to be noted that the output of the bridge rectifier is not pure DC, but it contains fluctuations or ripple, which are undesired. To minimize the ripple content in the output, filter circuits are used. In one exemplary implementation, a capacitor ( 320 ) is used as the filter or voltage support capacitor, wherein the capacitor ( 320 ) opens to DC and blocks the flow of AC as the capacitance is sufficiently large enough. Thus, a pure DC current is supplied to the thermoelectric module ( 304 ). Further, the direction of flow of current in the thermoelectric module ( 304 ) is achieved by a double pole double throw (DPDT) switch as illustrated in  FIG. 4(   a ) and  FIG. 4(   b ). 
         [0033]      FIG. 4(   a ) and  FIG. 4(   b ) are schematic representations of flow of direction of current in a thermoelectric module (the thermoelectric module ( 304 ) of  FIG. 3)  through a double pole double throw (DPDT) switch ( 402 ), from point A and B (connection points as shown in  FIG. 3  and  FIG. 4(   a ) ( b )), in accordance with one embodiment of the present invention. Particularly, when the temperature is set high in a temperature adjusting slider (the temperature adjusting slider ( 108 ) of  FIG. 1) , the direction of flow of current is as shown in  FIG. 4(   a ) and when the temperature is set to low, the direction of flow of current is reversed as shown in  FIG. 4(   b ) and vice versa. It is to be appreciated that the flow of power to the thermoelectric module ( 304 ) is automated with the DPDT switch ( 402 ) based on the temperature set in the temperature adjusting slider ( 108 ) for selectively heating or cooling process. The process of heating and cooling in the thermoelectric module ( 304 ) is illustrated in  FIG. 4(   c ). 
         [0034]      FIG. 4(   c ) is a cross sectional view of a thermoelectric module (the thermoelectric module ( 304 ) of  FIG. 3) . Particularly, the thermoelectric module includes an electrical conductor consisting of thermoelectric legs ( 404 ) connected to an upper ( 406 ) and lower ( 406   a ) layers by cold soldering. The high thermal conductivity substrate such as ceramic plates ( 408 ) and ( 408   a ) are attached to the upper ( 406 ) and lower ( 406   a ) layers respectively. In one exemplary implementation, the legs ( 404 ) include a series of alternating p-doped and n-doped semiconductors electrically connected in series by the upper ( 406 ) and lower ( 406   a ) layers. Further, a thin graphite flat patch can be used as interface ceramic surface of the thermoelectric module ( 304 ) which in turn increases the junction&#39;s thermal efficiency. 
         [0035]    In operation, a DC current source ( 410 ) provides current to the lower layer ( 406   a ) of electrical conductor. Current flows from the lower layer ( 406   a ) through the thermoelectric legs ( 404 ), and into the upper layer of electrical conductor ( 406 ). In one example embodiment, the current proceeds to pass through successive p-doped and n-doped legs, finally exiting through a portion of the lower layer ( 408   a ). Further, the current passing through the legs ( 404 ) in one direction pumps heat away from the upper layer ( 408 ) of the thermal conductor. As indicated by the  FIG. 4(   c ), each p and n doped semiconductors simultaneously pumps heat from its cold side ( 412 ) and to its hot side ( 414 ). In other words, if the heat is pulled from the top junction ( 412 ), the same heat is deposited at the bottom junction ( 414 ), which is in contact with a heat sink. The heat will be distributed on large surface area of heat sink&#39;s fins and is blown away by the fan as described in  FIG. 2 . Thus, the temperature of the bottom junction ( 414 ) becomes close to ambient temperature and not hot, which increases the efficiency of the described device when compared to conventional devices. It is to be noted that the elements in the thermoelectric module ( 304 ) are electrically connected in series and thermally connected in parallel. 
         [0036]    In one example embodiment, the surface of the thermoelectric module ( 304 ) gets heated as the current flows through the module ( 304 ) in one direction through the DPDT switch ( 402 ) as shown in  FIG. 4(   a ) and becomes cold, when the current is reversed through the DPDT switch ( 402 ) as shown in  FIG. 4(   b ). Thus, the temperature set in the slider ( 108 ) controls the direction of flow of current in the thermoelectric module ( 304 ) through the DPDT switch ( 402 ). Therefore, the unitary device (the unitary device ( 100 ) of  FIG. 1(   a )) makes steam or ice within a short span of time without fire or a compressor. 
         [0037]    In summary, when the device ( 100 ) is turned on (i.e., the switch ( 301 ) of  FIG. 3  is turned on), the regulated AC voltage from the circuit ( 314 ) is fed into the bridge rectifier ( 308 ), wherein the AC to DC voltage conversion takes place. Further, the pure DC is fed to the thermoelectric module ( 304 ) through the DPDT switch ( 402 ). Consequently, the variable resistor ( 338 ) is automatically adjusted depending on the temperature set in the slider ( 108 ); thereby the direction of the current in the thermoelectric module ( 304 ) is decided for heating or cooling purpose through DPDT switch ( 402 ). Therefore, the food stuffs in the container ( 102 ) reach to the set temperature accordingly. 
         [0038]    It is advantageous that the described device includes not much moving parts to wear out. Further, the size and weight of the device is comparatively less, when compared to existing devices. The heating and cooling operations are performed in a unitary device by mere sliding the temperature setting bar, independent to the ambient temperature and also allow precise temperature control over a long period of time. It is to be appreciated that with the described device, the efficiency of the thermoelectric module is utilized to the maximum. In addition, the described device is portable hence it is feasible to be used in buffet set up at parties and more reliable. 
         [0039]    In general, it is clear that the present invention and its advantages are not limited to the above described embodiments only. With minor modifications, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the present invention as described in the claims. Accordingly, the specification and figures are to be regarded as illustrative examples of the invention, rather than in restrictive sense.