A semi-frozen product dispensing apparatus comprising a refrigeration unit including a freezing cylinder represented by an heat exchanger as an evaporator; said heat exchanger comprising a first tube extending along a central axis of the heat exchanger and defining a chamber that is foreseen to contain a first medium ; a corrugated sheath disposed radially outward from and extending circumferentially about an outer face of the first tube , wherein the corrugated sheath is a ribbon spiraled about the first tube , wherein the ribbon includes a plurality of windings that each extend around the first tube and are adhered to the outer face of the first tube via a connection at each end of the ribbon , with each winding including a plurality of corrugations that extend laterally between opposite longitudinal ribbon edges , and wherein the plurality of corrugations of a first winding of the plurality of windings are circumferentially misaligned with the plurality of corrugations of an adjacent winding of the plurality of windings , wherein a longitudinal edge of the first winding contacts a second longitudinal edge of the adjacent winding, wherein each of the plurality of corrugations extend between and are substantially normal with opposite longitudinal edges of the winding; and a second tube disposed concentrically to and radially outward from the first tube , wherein a pathway is defined between the first tube and the second tube for flowing a second medium , wherein the second medium is a refrigerant , wherein the corrugated sheath is in the pathway , and wherein the pathway is annular in shape, and wherein the pathway is oriented to direct the flowing second medium to flow generally axially through the annual pathway by passing over and around the plurality of corrugations along the annular pathway, and the first medium being a product to be cooled. heat exchanger comprising a first tube extending along a central axis of the heat exchanger and defining a chamber that is foreseen to contain a first medium ; a corrugated sheath disposed radially outward from and extending circumferentially about an outer face of the first tube , wherein the corrugated sheath is a ribbon spiraled about the first tube , wherein the ribbon includes a plurality of windings that each extend around the first tube and are adhered to the outer face of the first tube via a connection at each end of the ribbon , with each winding including a plurality of corrugations that extend laterally between opposite longitudinal ribbon edges , and wherein the plurality of corrugations of a first winding of the plurality of windings are circumferentially misaligned with the plurality of corrugations of an adjacent winding of the plurality of windings , wherein a longitudinal edge of the first winding contacts a second longitudinal edge of the adjacent winding, wherein each of the plurality of corrugations extend between and are substantially normal with opposite longitudinal edges of the winding; and a second tube disposed concentrically to and radially outward from the first tube , wherein a pathway is defined between the first tube and the second tube for flowing a second medium , wherein the second medium is a refrigerant , wherein the corrugated sheath is in the pathway , and wherein the pathway is annular in shape, and wherein the pathway is oriented to direct the flowing second medium to flow generally axially through the annual pathway by passing over and around the plurality of corrugations along the annular pathway, and the first medium being a product to be cooled. <EOS>