Patent attributes
A conveyor belt (36) is arranged in at least one spiral conveyor unit (32) or (34) is arranged in tiers forming at ascending spiral stack (38) and/or a descending spiral stack (40). A ceiling or top sheet (58) is positioned over the spiral stack. A circulation fan (60, 62) draws spent thermal processing medium laterally from the tiers of the spiral stack, up the exterior of the stack and across the top of the stack above the ceiling or top sheet and through a heat exchanger (64) located above the ceiling. The treated thermal processing medium is then routed across the remainder of the diameter of the spiral stack and then down the side of the spiral stack diametrically opposite to the circulating fan thereby to enter the spiral stack in a lateral direction diametrically toward the circulating fan. At least one opening (70, 100, 200) is formed in the ceiling between the heat exchanger and the diametrically distal end of the spiral stack from the circulating fan thereby to provide an alternative flow path for a portion of the thermal processing medium to enter the spiral stack from above, thereby resulting in more uniform treatment of the work product being carried by the conveyor of the spiral stack.
