Patent ID: 8272231

Claim:
A direct expansion evaporator for making frozen product from raw material, comprising: a feeding channel having a feeding end and a dispensing end for said raw material feeding through said feeding channel; a heat exchange channel thermally communicating with said feeding channel, wherein said heat exchange channel has a pre-cooling portion defining from said feeding end of said feeding channel and a freezing portion to said dispensing end to thermally communicate with said feeding channel in a two-stage evaporation manner; wherein said heat exchange channel is guided for refrigerant passing therethrough in order to heat exchange with said raw material within said feeding channel, wherein when said refrigerant flows at said pre-cooling portion of said heat exchange channel, said raw material fed from said feeding end of said feeding channel is initially pre-cooled at a pre-cooling temperature, and when said refrigerant flows at said freezing portion of said heat exchange channel, said raw material is then substantially frozen to form said frozen product before said frozen product is dispensed at said dispensing end of said feeding channel while being energy efficient; an outer guiding duct and an inner guiding duct coaxially enclosed within said outer guiding duct to define said feeding channel within said inner guiding duct and said heat exchange channel between said outer and inner guiding ducts in an air-sealed manner, wherein when said raw material is fed along said inner guiding duct, said refrigerant is thermally communicating with said raw material through said inner guiding duct; and a guiding wall extending between said outer and inner guiding ducts at said pre-cooling portion of said heat exchange channel in a spiral manner, wherein said freezing portion of said heat exchange channel has a cylindrical shape for maximizing an expansion area of said refrigerant between said feeding channel and said heat exchange channel, while said pre-cooling portion of said heat exchange channel has a helix shape for prolonging a traveling time at said pre-cooling portion so as to ensure said refrigerant being completely evaporated; wherein said guiding wall has a trapezoidal cross section that a width of said guiding wall is gradually reducing from said outer guiding duct to said inner guiding duct.