WO2013062512A1

WO2013062512A1 - Cross-flow spiral heat transfer apparatus with solid belt

Info

Publication number: WO2013062512A1
Application number: PCT/US2011/057480
Authority: WO
Inventors: Stephen A. Mccormick; Michael D. Newman
Original assignee: Linde Aktiengesellschaft
Priority date: 2011-10-24
Filing date: 2011-10-24
Publication date: 2013-05-02
Also published as: US20120273165A1

Abstract

A heat transfer apparatus for a product includes a housing having an internal chamber; a solid conveyor belt disposed within the internal chamber and arranged in a spiral configuration having upper and lower portions, the spiral configuration including an upper pathway within the upper portion, a lower pathway within the lower portion; a gas flow having an upper gas flow across the upper pathway, a lower gas flow across the lower pathway and in counter-flow to the upper gas flow, wherein the upper gas flow and the lower gas flow define a circulation loop; and a gas circulation device to induce the upper and lower gas flows along the circulation loop.

Description

SPECIFICATION

CROSS-FLOW SPIRAL HEAT TRANSFER APPARATUS WITH SOLID BELT

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of prior Application No. 12/184,386, filed August 1 , 2008, which claims the benefit of U.S. Provisional Application No. 60/964,458, filed August 13, 2007. The disclosures of the parent Application No. 12/184,386, filed August 1 , 2008, and the Provisional Application No. 60/964,458, filed August 13, 2007 are hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to a heat transfer system for cooling, chilling heating or otherwise removing heat from or supplying heat to products, such as for example food products.

BACKGROUND

[0003] In some refrigeration systems, a line of products to be for example refrigerated is moved through the refrigeration system, along a spiral or helical pathway through the cold or chilling region. Systems in which products to be refrigerated follow a spiral or helical pathway through the cold region are conventionally termed spiral refrigeration systems. Related systems may be used to heat products.

[0004] One type of refrigeration system used in the industry to remove heat from products is a spiral refrigeration system. Unless otherwise noted, as used herein, "spiral" refers to both spiral and helix forms. [0005] A single pass configuration spiral refrigeration system is one in which a gas such as cryogen is directed by fans to flow among the products to be cooled. The gas is then returned from the products to the fans through return gas conveyances in the - - system. In existing single pass systems, the return gas conveyances may consist of ductwork which do not contain products from which it is desirable to remove heat. Since there are no products to be cooled along the return ductwork path, single pass systems lose cooling capacity due to less efficient use of process volume along with the inefficiencies associated with maintaining the environment in this ductwork space. In addition, the large external return gas conveyors and ductwork add bulk and footprint area to known systems; further reducing cost-effectiveness of such systems.

[0006] It therefore remains desirable to provide for a more efficient system to cool and/or chill products, and heat and/or cook products in a spiral heat transfer system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments of the subject matter are disclosed with reference to the accompanying drawings and are for illustrative purposes only. The subject matter is not limited in its application to the details of construction or the arrangement of the components illustrated in the drawings. Like reference numerals are used to indicate like components, unless otherwise indicated.

[0008] FIG. 1 shows a cross-section elevation view of an embodiment of a cross- flow spiral heat transfer apparatus.

[0009] FIG. 2 shows a top cross-section plan view of the embodiment of FIG.1.

[00010] FIG. 3 shows a cross-section elevation view of another embodiment of a cross-flow spiral heat transfer apparatus.

[00011] FIG. 4 shows a cross-section elevation view of another embodiment of a cross-flow spiral heat transfer apparatus. DETAILED DESCRIPTION

[00012] Discussion of the heat transfer system or apparatus embodiments is with respect to cooling and heating a product, and reference to or refrigeration system could similarly include references to a heating system.

[00013] Variables defining a spiral pathway include, but are not limited to, diameter, height and pitch. As used herein, a "tier" is the part of a helix corresponding to one full thread of the spiral.

[00014] In all the embodiments herein, return of the gas flow occurs within the product processing zone of the system, not at an exterior of the system.

[00015] In all embodiments, the present system can also be used in a manner of heat transfer to also heat or cook products, such as food products. The higher the velocity of the gas being employed to pass over the products, the greater the increase in heat transfer at the products.

[00016] In ail embodiments, a drum which moves the spiral conveyor belt cooperates with the spiral belt to create a bifurcated pathway for the gas, which pathway has a width equal to the width of the conveyor belt upon which the products are transported so that maximum heat transfer can be achieved from the gas flows.

[00017] In the refrigeration system embodiments herein in which heat is transferred from a product to be refrigerated to a flowing refrigeration fluid, one mode of cooling the product to be refrigerated is forced convection. In forced convection, the heat transfer coefficient is a function of the flow velocity of the refrigeration fluid. Heat transfer for cooling objects also includes a factor that the higher the velocity of gas used to effect heat transfer, the greater the heat transfer rate. [00018] A refrigeration fluid may also be called a "cryogen". One such cryogen, nitrogen gas, can be as cold at -320° F, or as dictated by the minimum temperature at which the gas exists in its gaseous state.

[00019] In addition to the efficiency benefits achieved by reducing disused regions, the size of the freezing system may be made significantly smaller because the refrigeration medium, such as a gas, is returned to the main blowers along the product pathway or in the product processing zone. Dedicated external return chambers and related ductwork are not necessary. This results in a savings in overall system cost. In addition, a lower amount of structural material is required to be cooled down which results in a secondary efficiency improvement.

[00020] Referring to FIGS. 1 and 2, FIG. 1 shows a two-pass or dual-pass cross flow spiral heat transfer system 10. The system 10 is used to cool or freeze, or heat or bake products (not shown) such as food products. The system 10 includes a housing 12 with an internal cavity or chamber 14. The housing 12 is constructed of any suitable material for freezing or heating applications. By way of example, cryogenic gas from a blower chamber 20, is pressurized and passed around an exterior of a top half of a drum 40 and along and through spiral belt 50 to contact the products. A top portion of the belt 50 includes tiers 51. Gas flow is indicated by arrows 25. A baffle 30 separates upper 16 and lower 18 portions of the chamber 14 and prevents the gas from entering into bottom tiers 53 of the belt 50. The baffle 30 may be made from various materials that are substantially impervious to prevent the flow of gas. The gas 25 flows to a return chamber 60, where it turns and is diverted back through the lower portion 18 of the freezer (bottom tiers 53 of belt) and into an inlet of the blower chamber 20, where the gas 25 is recirculated by blower or fan 22.

[00021] The spiral belt 50 provides for a spiral pathway. The spiral pathway includes an upper pathway 52 of the tiers 51 within the upper portion 16; and a lower pathway 54 of the tiers 53 within the lower portion 18. The product is transported upon the tiers 51 , 53 of the belt 50. The drum 40 drives the belt 50 along the spiral or helical path. [00022] The baffle 30 separates the upper pathway 52 from the lower pathway 54. The baffle 30 works in conjunction with the drum 40 to create the upper pathway 52 and the lower pathway 54 to each have a width equal to a width of the belt 50. This is because gas flow 25 does not flow through the drum 40, but rather is bifurcated by the drum 40 as shown in FiG. 2 into two separate streams (discussed below) flowing about and exterior to the drum 40 and then into the return chamber 60. The baffle 30 is continuous around the drum 40, as shown more clearly in FIG. 2, and extends into the blower chamber 20 and the return chamber 60. In this manner of construction, the gas flow 25 is directed from the blower chamber 20 across and onto the product being transported on the tiers 51 of the belt 50 in the upper pathway 52, through the return chamber 60 and then back in counter flow to the lower pathway 54 for further contact with the product on the conveyor belt 50, whereupon the gas 25 flows to the blower chamber 20 for continuous circulation. Replenishment of fresh cryogen to the system 10 is provided to the blower chamber 20 via conduit 24. The conduit 24 is in communication with a source of cryogen (not shown) such as for example carbon dioxide (C0₂), nitrogen (N₂), etc. The conduit 24 may be disposed at other locations of the system 10 for introduction of cryogen (or heating fluid) thereto.

[00023] FIG. 1 shows the upper pathway 52 to be a helical path comprising a plurality of tiers such as for example three tiers 51 of the belt 50, and the lower pathway 56 to be a helical path comprising a plurality of tiers such as for example three tiers 53 of the belt 50, although the number of tiers is merely illustrative and not intended as a limitation. The upper pathway 52, the return chamber 60, the lower pathway 54, and the blower chamber 20 define a circulation loop for the gas 25. Blower means 22 to induce gas flow is provided, and such can be a fan, blower, compressor or any other suitable means. The blower means 22 is constructed and arranged for operation in or communication with the blower chamber 20.

[00024] In operation, and referring to FIGS. 1 and 2, a cryogen is provided to the blower chamber via conduit 24 and upon sufficient "charging" of the system 12 with the cryogen, the conduit is closed. Blower means, which as shown in FIG. 2 can be a pair of blowers or fans 20A and 20B, provide the necessary force to initiate and sustain a flow of the gas 25 into and along the upper pathway 52 such that the gas fiow 25 contacts the tiers 51 of the conveyor belt 50 upon which the product is being transported. The conveyor belt 50 is porous, i.e. can be of mesh construction or grid-like construction, to thereby facilitate the gas 25 flowing between and among the tiers 51 of the conveyor belt 50 in the upper pathway 52. The gas flow in the upper pathway 52 is prevented from communicating with the lower pathway 54 by virtue of the disposition of the baffle 30 in the chamber 14 of the housing 12. The gas flow 25 in the upper pathway 52 is in counter-flow to the gas flow 25 in the tower pathway 54.

[00025] As shown in FIG. 2, the drum 40 is disposed substantially at the center of the chamber 14 with the baffle 30 extending in the chamber 14 around the drum 40. The drum can be hollow or solid, but an exterior wall 57 of the drum 40 is impervious to the gas flow 25. The gas under force exerted by the blowers 20A, 20B is directed in the return chamber 60 downward away from the upper pathway 52 into the lower pathway 54 to subsequently contact food product on the tiers 53 of the conveyor belt 50. It should be noted that the baffle 30, in an embodiment where the blowers 20A and 20B are disposed at the same side of the housing 12, may be angled slightly downward toward the bottom of the housing 12, as shown in FIG. 1 , to facilitate movement of the gas flow to the return chamber 60 and back through the lower pathway 54 to the blower chamber 20.

[00026] In effect, the product is subjected to a two-pass or dual-pass flow of the gas 25. The cryogen gas flow 25 is restricted for flow across a width of the tiers 51 , 53 of the conveyor beit 50, such that none of the cryogen gas is wasted on heat transfer at unnecessary portions of the freezer system 0.

[00027] The construction and operation of the embodiment shown in FIGS. 1 and 2 uses only approximately 50 % of the amount of cryogen flow as a single pass refrigeration system would require, due to the arrangement of the baffle 30 and its cooperation with the drum 40, segregation of the upper pathway 52 and lower pathway 54, and the recirculation of the gas flow 25 between and among the blower chamber 20 and the return chamber 60. This dual-pass configuration of the spiral refrigeration system 10 also requires less power, whereby the reduced power leads to additional operating efficiencies. Initial testing has shown a 35% reduction in overall power necessary in order to drive the system 10, with a cryogen efficiency improvement of at least 15% less use in the gas 25 as compared to single pass systems.

[00028] In the cross-flow spiral refrigeration system 10 of FIG. 1 , the refrigeration medium makes two passes through the product pathway, once in the upper pathway 52, and once in the lower pathway 54. In the system 10 shown, the amount of refrigeration medium that flows through the upper pathway 52 is the same as the amount that flows through the lower pathway 54. The present system 10 provides for an even constant gas flow and velocity in the upper and lower pathways 52, 54. The system 10 is constructed and arranged to provide for continuous, uniform passes of the cooling medium over the product on the belt 50. Alternatively, system 10 as a heat transfer system provides for the continuous, uniform passing of a heating or cooking gas over the product on the belt 50.

[00029] Thus, the two-pass configuration of the present system 10 may require only about 50% of the conventional airflow used in conventional airflow schemes, such as one-pass flow configurations.

[00030] In addition to the operational efficiency benefits achieved by the system 10, the size of the freezing system 10 may be made significantly smaller because the gas is returned to the blowers 20A, 20B through the upper and lower pathways. Separate gas return chambers and ductwork are not necessary, thereby providing for a smaller "footprint" for the system 10. This results in a significant savings in overall system cost.

[00031] FIG. 2 illustrates a cross-sectional plan view of the embodiment of a cross- flow spiral refrigeration system 10 in FIG. 1.

[00032] As shown in FIG. 2, the gas flow 25 enters the upper pathway 52 and is bifurcated by the drum 40 into separate branches 56, 58 of gas flow to flow around the drum 40. Subsequently, the branches 56, 58 reunite and flow into the return chamber 60. This also occurs in the lower pathway 54 as weil. That is, the returning gas flow 25 from the return chamber 60 is prevented from returning to the upper pathway 54 by the baffle 30. The gas flow 25 is similarly bifurcated by the drum 40 into separate branches in the lower pathway 54 (which would correspond to the branches 56, 58 in the upper pathway 52) as it is returned to the blower chamber 20. The cross-sectional width of branch 56 is equal to the width of the branch 58, and the sum of the cross-sectional volumes of branch 56 and 58 is equal to the cross-sectional volume of the original upper pathway 52. The width of the branch 56 is equal to the width of the tier 51 of the belt 50, and the width of the branch 58 is equal to the width of the tier 51 of the belt. Similar dimensions exist between and among the tiers 53 of the belt 50 and the related branches in the lower pathway 54.

[00033] FIG. 3 shows another embodiment, wherein a two-pass configuration of the present spiral refrigeration system is shown generally at 110 and includes two blower chambers 120, 170. In this configuration, higher velocities as well along the belt result in higher heat transfer coefficients for the product, whether the product is being heated or cooled.

[00034] The system 110 shown in FIG. 3 includes a housing 112 having an internal space or chamber 114 therein. The system 110 has many features similar to the system 10 and operates in a similar manner.

[00035] Disposed within the space 114 is a drum 140 about which a spiral conveyor belt 150 is constructed and arranged for operation, the belt 150 being driven along the spiral or helical path by the drum 140. The drum 140 is impervious to fluid flow and bifurcates the gas flow 125 similarly to that which occurs with respect to the embodiment of FIGS. 1 and 2. The conveyor belt 150 transports products {not shown), such as food products along the internal chamber 114 for cooling and/or freezing by the system 110. Similar to the embodiment discussed above with respect to FIGS. 1 and 2, the embodiment in FIG. 3 is also a heat transfer system and can be used to heat and cook products, as well as freeze products.

[00036] The internal chamber 114 consists of an upper portion 116 and a lower portion 118. The upper portion 116 and lower portion 118 are segregated from each other by a baffle 130 which extends along the internal chamber 114 of the housing 112. The upper portion 116 of the internal chamber 114 contains the upper pathway 152, while the lower portion 118 of the internal chamber 114 contains the lower pathway 154. The conveyor belt and its tiers 151 , 53 move between the upper and lower pathways 152, 154.

[00037] Disposed in the upper portion 16 of the internal chamber 114 is a blower or fan 122A, while disposed at the lower portion 118 of the internal chamber 114 is another blower or fan 122B. Fans 1 2A, 122B may be arranged at different sides of the housing 112, such as at opposed sides of the housing 112. In addition, one of the fans, such as the fan 122A, is disposed in the upper portion 116, while the other blower such as the fan 122B is disposed in the lower portion 118. The baffle 130 surrounds the drum 140 and prevents fluid flow 125 between and among the upper portion 116 and the lower portion 118, except for areas of the baffle 130 shown generally at 131 and 132. The areas 131 , 132 are those areas permitting gas flow 125 to occur between the lower portion 118 and the upper portion 116. This can be as a result of the construction of the baffle 130 extending up to only that point in the interior space 14 where the baffle meets the fans 122A, 122B, or apertures (not shown) may be provided in the baffle 130 to enable the gas flow 125 to be drawn from the lower portion into the upper portion via the fan 122A, and from the upper portion 1 6 into the lower portion 118 via the fan 122B. In either arrangement there is provided the continuous circulatory effect between and among the upper and lower portions 16, 118.

[00038] The conveyor belt 150 is arranged to extend between the iower portion 118 and the upper portion 116. At least one and preferably a plurality of the tiers 151 of the belt 150 are disposed at any given time in the upper portion 116. At least one and preferably a plurality of the tiers 153 of the belt 150 are disposed in the Iower portion 1 8 at any given time.

[00039] As shown in F!G. 3, movement of the belt 150 causes the tiers 151 , 153 to transport the product between the upper portion 116 and the Iower portion 118, but in any event the gas flow 125 assures that the products receive a continuous, uniform dual pass flow of the cryogen gas as the products are transported by the belt 150 between and among the portions 116, 118. [00040] Although the perspective of FIG. 3 shows a pair of fans 122A, 122B, it should be understood that owing to said perspective there could be a pair of fans at each opposed side of the housing 1 2.

[00041] Conduits 124, 126 are in communication with the blower chambers 120, 170 to "charge" the system 110 with a cooling or heating fluid as necessary. The conduits 124, 126 are connected to a source (not shown) of cooling or heating fluid and may be in

communication with other areas of the chamber 114.

[00042] The system 10 shown in FIG. 3, due to the blower arrangement 122A, 122B, does not necessitate a grade or angle of the conveyor belt 150 to be other than at the horizontal with respect to the housing 112, aithough such a grade or angle can be employed if required for a particular processing application.

[00043] in the embodiments of F!GS. 1 -3, the fans 22, 20A, 20B, 122A, 122B exert a sufficient force of the fluid flow 25, 125 such that same does not displace the products from the tiers 51 , 53, 151 , 153.

[00044] In the embodiments shown in FIGS. 1-3, the systems 10, 110 function as heat transfer systems. That is, in effect, these heat transfer systems 10, 1 10 can be employed to heat or cook products, such as food objects, just as the systems 10, 110 can be employed to cool and/or freeze products as discussed above. In other words, instead of the gas flow 25 being a cryogen for example, said gas flow 25 could consist of high temperature air or other gases to warm, heat or cook products, such as food products being transported for processing in the system 10, 110. Accordingly, the subject matter of the present invention is not limited to cooling and freezing, but rather can be employed to heat or cook products such as food products.

[00045] Referring to another embodiment of the invention at FIG. 4, a solid belt conveyor is used, which eliminates the need for the internal baffles, since no gas will pass through the belt, i.e. the solid belt is impenetrable by the gas. In addition, gas is directed on!y where needed for heat transfer and therefore, a bypass airflow above and below the drum is eliminated, which results in the efficiency of the apparatus being improved. Elimination of the baffles also increases the cleanliness of the apparatus and improves access to an interior of same.

[00046] FIG. 4 shows the cross-flow spiral heat transfer apparatus with a solid belt generally at 210. In contrast, the airflow path in the embodiments of FIGS. 1-3 has that the airflow pass over fifty percent (50%) of the tiers from the blower discharge and the remaining fifty percent (50%) of tiers in a return path to the blower. This requires the solid baffle 30 to extend through a center of the freezer which uses an open mesh belt. With a solid belt of the embodiment 210 of FIG. 4, the baffle 30 is no longer necessary. The pathways between the tiers of the belt are individually isolated in the apparatus 210, so that there is no cryogen flow through the belt from tier to tier or directly between and among the tiers. In addition, on!y minimal airflow is diverted above and below the drum. All of the airflow is directed only where it is needed. As a result, the apparatus 210 of FIG. 4 uses less overall energy, but will stil! be able to achieve increased overall heat transfer coefficients similar to the coefficients of the embodiments of FIGS. 1-3.

[00047] Referring to FIG. 4, the spiral heat transfer apparatus 210 can be used to cool and freeze, or heat and bake products (not shown), such as food products. The apparatus 210 includes a housing 212 with an internal cavity or chamber 214. The housing 212 is constructed of any suitable material for freezing or heating applications. By way of example, cryogenic gas from a blower chamber 220, is pressurized and passed around an exterior of the drum and along a spiral belt 250 to contact the products. The drum 240 rotates the spiral belt 250. The belt 250 includes tiers 251 of the belt. Gas flow is indicated by arrows 225. The gas flow moves along a spiral pathway 226 between the tiers 51. The chamber 214 includes upper 216 and lower 218 portions. The gas 225 flows to return back through the lower portion 218 of the freezer (bottom tiers 253 of belt) and into an inlet 221 at the blower chamber 220, where the gas

225 is recirculated by the blower 222 or fan.

[00048] The spiral belt 250 provides for the spiral pathway 226. The spiral pathway

226 includes an upper pathway 252 of the tiers 251 within the upper portion 216; and a lower pathway 254 of the tiers 253 within the lower portion 218. The product is transported upon the tiers 251 , 253 of the belt 250. The drum 240 drives the belt 250 along the pathway which resembles a spiral or helical pathway.

[00049] The blower 222 is provided with a sidewall 228 which forms an entrance cone in communication with a return airflow at the lower portion 218. As shown in FIG. 4, the sidewall 228 of the entrance cone coacts with one of the solid tiers "X" of the conveyor belt 250 to in effect provide generally the upper pathway 252 and the lower pathway 254 for the solid tiers of the conveyor belt. That is, the tiers 251 of the solid belt 250 above the tier X show the airflow being directed from the blower 222 away from same between each one of the tiers 251 of the conveyor belt 250. The tiers 253 of the conveyor belt below the tier X provide the pathway for the airflow returning to the entrance cone 221 of the blower. This sort of arrangement and coaction between the entrance cone and the tier X of the conveyor belt overcomes the need for a baffle or baffles to be used with the freezer.

[00050] The tier X separates the upper pathway 252 from the lower pathway 254. The tier X coacts with the entrance cone to create the upper pathway 252 and the lower pathways 254 to each have a width equal to a width of the belt 250. This is because gas flow 225 does not flow through the drum 240 or the belt 250, but rather is bifurcated by the drum into separate streams (discussed below) flowing about and exterior to the drum and then into the return chamber 260. The tier X is continuous around the drum 240, and extends into the blower chamber 220 and the return chamber 260. In this manner of construction, the gas flow 225 is directed from the blower chamber 220 across and onto the product being transported on the tiers 251 of the belt 250 in the upper pathway 252, through the return chamber 260 and then back in counter flow along the lower pathway 254 for further contact with the product on the conveyor belt 250, whereupon the gas 225 flows to the blower chamber 220 for continuous circulation. Replenishment of fresh cryogen to the system 210 is provided to the blower chamber 220 via conduit 224. The conduit 224 is in communication with a source of cryogen (not shown) such as for example liquid or gaseous carbon dioxide (C0₂), or liquid nitrogen (N₂). The conduit 224 may be disposed at other locations of the apparatus 210 for introduction of the cryogen (or heating fluid) thereto. [00051] The upper pathway 252 is a helical path comprising a plurality of tiers such as for example three tiers 251 of the belt 250, while the lower pathway 256 is a helical path comprising a plurality of tiers such as for example three tiers 253 of the belt 250, although the number of tiers is merely illustrative and not intended as a limitation. The upper pathway 252, the return chamber 260, the lower pathway 254, and the blower chamber 220 define a circulation loop for the gas 225. The blower 222 to induce gas flow can be a fan, blower, compressor or any other suitable means. The blower 222 is constructed and arranged for operation in or communication with the blower chamber 220.

[00052] In operation, and referring to FIG. 4, a cryogen is provided to the blower chamber 220 via conduit 224 and upon sufficient "charging" of the system 212 with the cryogen, the conduit 224 flow is controlled via a modulating valve which is typically never fully closed during production. Flow of cryogen is continuously supplied to the freezer to maintain a desired set point temperature. The blower 222 provides the necessary force to initiate and sustain a flow of the gas 225 into and along the upper pathway 252 such that the gas flow 225 contacts the tiers 251 of the conveyor belt 250 and food product upon which the product is being transported. The conveyor belt 250 is solid to thereby facilitate the gas 225 flowing between adjacent ones of the tiers 251 of the conveyor belt 250 in the upper pathway 252. The gas flow in the upper pathway 252 is prevented from communicating with the lower pathway 254 by virtue of the solid tiers of the belt in the chamber 214 of the housing 212. The gas flow 225 in the upper pathway 252 is in counter-flow to the gas flow 225 in the lower pathway 254.

[00053] As shown in FIG. 4, the drum 240 is disposed substantially at the center of the chamber 214, and an exterior wall 257 of the drum 240 is impervious to the gas flow 225. The gas under force exerted by the blower 220 is directed in the return chamber 260 downward away from the upper pathway 252 into the lower pathway 254 to subsequently contact food product on the tiers 253 of the conveyor belt 250. It should be noted that the tiers may be angled slightly downward toward the bottom of the housing 212 as shown to facilitate movement of the gas flow to the return chamber 260 and back through the lower pathway 254 to the blower chamber 220.

[00054] In effect, the product is subjected to a two-pass or dual-pass flow of the cryogen. The flow 225 is restricted for flow across a width of the tiers 251 , 253 of the conveyor belt 250, such that none of the cryogen gas is wasted on heat transfer at unnecessary portions of the freezer system 210.

[00055] The construction and operation of the embodiment shown in FIG. 4 uses only approximately 65% of the amount of cryogen flow as a single pass refrigeration system would require, due to the arrangement of the solid belt and its cooperation with the drum 240, segregation of the upper pathway 252 and lower pathway 254, and the recirculation of the gas flow 225 between and among the blower chamber 220 and the return chamber 260. This dual-pass configuration of the spiral refrigeration system 210 also requires less power, whereby the reduced power leads to additional operating efficiencies. Initial testing has shown a 45% reduction in overall power necessary in order to power the system 210, with a cryogen efficiency improvement of at least 20% less use in the gas 225 as compared to the embodiments of FIGS. 1-3. The overall gas flow is the embodiment of FIG. 4 is reduced by 30% as compared to the mesh belt arrangement, while power used is reduced by 20%, with a 5 - 10% cryogen efficiency improvement.

[00056] In the cross-flow spiral heat transfer apparatus 210 of FIG. 4, the refrigeration medium makes two passes through the product pathway, once in the upper pathway 252, and once in the lower pathway 254. In the apparatus 210 shown, the amount of refrigeration medium that flows through the upper pathway 252 is the same as the amount that flows through the lower pathway 254. The present apparatus 210 provides for an even, constant gas flow and velocity in the upper and lower pathways 252,254. The apparatus 210 is constructed and arranged to provide for continuous, uniform passes of the cooling cryogen medium over the product on the belt 250. [00057] Alternatively, the apparatus 210 as a heat transfer apparatus provides for the continuous, uniform passing of a heating or cooking gas over the product on the belt 250.

[00058] Thus, the two-pass configuration of the present system 210 may require only about 65% of the airflow used in conventional airflow arrangements, such as one-pass flow configurations.

[00059] In addition to the operational efficiency benefits achieved by the apparatus 210, the size of the freezing apparatus 210 may be made significantly smaller because the gas is returned to the blowers 220 through the upper and lower pathways. Separate gas return chambers and ductwork are not necessary, thereby providing for a smaller "footprint" for the apparatus 210. This results in a significant savings in overall system cost.

[00060] While the present subject matter has been described above in connection with illustrative embodiments as shown in the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function without deviating therefrom. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments may be combined to provide the desired characteristics. Variations can be made without departing from the spirit and scope of the invention. Therefore, the cross-flow spiral heat transfer system should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the attached claims.

Claims

CLAIMS What is claimed is:

1. A heat transfer apparatus for a product, comprising:

a housing having an internal chamber; a solid conveyor belt disposed within the internal chamber and arranged in a spiral configuration having upper and lower portions, the spiral configuration, comprising: an upper pathway within the upper portion,

a lower pathway within the lower portion; a gas flow, comprising:

an upper gas flow across the upper pathway,

a lower gas flow across the lower pathway and in counter-flow to the upper gas flow, wherein the upper gas flow and the lower gas flow define a circulation loop; and a gas circulation device to induce the upper and lower gas flows along the circulation loop.

2. The apparatus of claim 1 , wherein the upper gas flow and the lower gas flow are of substantially uniform velocity.

3. The apparatus of claim 1 , wherein the upper portion and the upper pathway have a similar width, and the lower portion and the lower pathway have a similar width.

4. The apparatus of claim 1 , wherein the the gas circulation device comprises at least one fan disposed in at least one of the upper and lower portions.

5. The apparatus of claim 1 , further comprising a drum disposed in the internal chamber and extending between the upper and lower portions, and about which is arranged the solid conveyor belt in the spiral configuration.

6. The apparatus of claim 5, wherein the drum comprises an outer sidewall adjacent the solid conveyor belt and impervious to the upper and lower gas flows.

7. The apparatus of claim 1 , wherein the upper and lower gas flows comprise gas selected to reduce a temperature of the product.

8. The apparatus of claim 7, wherein the gas comprises a cryogenic gas selected from the group consisting of carbon dioxide, nitrogen and combinations thereof.

9. The apparatus of claim 1 , wherein the upper and lower gas flows comprise a gas selected to heat the product.

10. The apparatus of claim 1 , wherein the circulation loop is arranged in the internal chamber.

11. The apparatus of claim 1 , wherein the product comprises a food product.