with reference to fig1 - 12 , wherein like numerals refer to similar parts , the basic components of an ice cream machine 100 in accordance with the present invention include lower , back and top casing shells 14 , 13 , 12 , a power switch 1 , a refrigeration plate 3 , a heat radiator 5 , a cold container 7 , a motor 9 and a stirring shaft 10 . the refrigeration plate 3 is positioned immediately below and in direct contact with the cold container 7 within the lower shell casing 14 . a cooling fan 4 directs airflow over the heat radiator 5 in the bottom of the lower shell casing 14 . the power switch 1 is mounted to the top casing shell 12 . the refrigeration plate 3 , motor 9 and cooling fan 4 are supplied with 12vdc power by the power supply 2 . the power supply 2 includes a rectifier and transformer for converting household voltage of 120 or 220vac to 12vdc . the power switch 1 is used to selectively apply household voltage to the power supply 2 . the motor and cooling fan might alternatively be powered by household ac power . the refrigeration plate 3 is connected to a thermally conductive guiding device 6 which is positioned above and at least partially surrounding the cold container 7 , effectively providing a thermal path surrounding the cold container 7 . the cold container 7 , refrigeration plate 3 and the guiding device 6 are surrounded by expanded plastic insulating material 8 to insulate the chilled portions of the ice cream machine from the heat of the surrounding atmosphere and heat generated by other components within the ice cream machine . an ice cream mixture is poured into the cold container 7 through an opening 16 . the motor 9 drives the stirring shaft 10 to rotate a spiral agitator 17 rotatably mounted within the cold container 7 . the ice cream mixture is chilled and blended to form soft serve ice cream which may then be extruded through an outlet opening controlled by a control bar 11 . when the power switch 1 is turned on , household voltage is applied to the power supply 2 , which supplies 12vdc to the refrigeration plate 3 , motor 9 and cooling fan 4 . ( it should be noted that the motor 9 and the cooling fan 4 might alternatively be powered directly by household voltage .) application of 12vdc to the refrigeration plate 3 produces a cold face on the side of the refrigeration plate 3 in contact with the guiding device 6 and a hot face on the side of the refrigeration plate 3 in contact with the heat radiator 5 . heat is conducted from the cold container 7 to the refrigeration plate 3 by the thermally conductive guiding device 6 . within the refrigeration plate 3 , heat is moved from the cold face to the hot face by semiconductor refrigeration . heat at the hot face is conducted to the heat radiator 5 and dissipated into air forced over the heat radiator by the cooling fan 4 . use of semiconductor refrigeration permits production of an extremely compact and portable ice cream maker 100 . fig3 - 6 illustrate the appearance and size of one embodiment of an ice cream maker 100 in accordance with the present invention . as illustrated , the ice cream maker 100 has a rectangular box - like shape with a height h of approximately 30 cm , a length l of approximately 40 cm and a width of approximately 28 cm the operating principals of the semiconductor refrigerator incorporated into the refrigeration plate 3 are best described with reference to fig7 - 11 . semiconductor refrigeration is based on the peltier effect , that is , that exothermic and endothermic effects occur when current flows through junctions between dissimilar materials . fig7 illustrates the simplest unit of a semiconductor refrigerator , a single p - n semiconductor thermocouple . a p - n type semiconductor thermocouple preferably incorporates p - type semiconductor material ( bi2te3 - sb2te3 ) and n - type semiconductor material ( bi2te3 - bi2te3 ). the p - type and n - type semiconductors are connected at one end by a metallic connection . the opposing end of the p - type semiconductor material is connected to the negative pole (−) of the dc power supply and the n - type semiconductor material is connected to the positive pole (+) of the dc power supply . current flows from the n - type semiconductor material to the p - type semiconductor material , causing an endothermic effect at the metallic connection . a corresponding exothermic reaction occurs at the opposing end of the n - type and p - type semiconductor materials . fig9 illustrates that a plurality of p - n semiconductor thermocouples can be connected to form a refrigerator using the peltier effect . a seen in fig8 energy in the form of electric current forces electrons from the p - type semiconductor to combine with molecules in the n - type semiconductor . this forced combination is an exothermic reaction that causes the release of heat . fig9 illustrates that current flow forces electrons to separate from molecules in the semiconductor material and flow away from the p - n junction . this electron movement has an endothermic effect . in cumulative combination , these effects transfer heat from the upper connections 20 of fig1 to the lower connections 21 . fig1 illustrates the exothermic end ( lower connections 21 ) of the p - n semiconductor refrigerator may be connected to a heat radiator to dissipate heat removed from the endothermic end of the refrigerator . refrigeration plates of varying cooling capacity can be formed by combining differing numbers of p - n semiconductor thermocouples electrically in series as illustrated in fig9 . the exothermic face of the refrigeration plate may be air cooled , as illustrated , or water - cooled . the largest temperature differential between the endothermic face of the refrigeration plate 3 and the ambient atmosphere is preferably 75 ° c .- 78 c , that is , if the ambient temperature is 38 c endothermic face of the refrigeration plate may reach − 40 c . of course , it must be understood that the exothermic and endothermic reactions may also be used to concentrate heat in a particular location . such heat concentration may be used to heat or thaw foods , for example . it should also be noted that a reversal of current flow through the refrigeration plate will cause heat to be transferred from the heat radiator 5 to the guiding device 6 . while a preferred embodiment of the foregoing invention has been set forth for purposes of illustration , the foregoing description should not be deemed a limitation of the invention herein . accordingly , various modifications , adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention .
an ice cream machine for household use employs semiconductor refrigeration to produce an efficient , compact and non - polluting appliance . the ice cream machine includes a refrigeration plate , a heat radiator , a cold container , a motor and a stirring shaft . the refrigeration plate includes a plurality of p - n junction semiconductor refrigerators . the ice cream maker includes a power supply to provide 12vdc power to the semiconductor refrigerators . a thermal guiding device conducts heat from the cold container to the refrigeration plate .