US Patent 11585611 Duct heat exchanger

A duct comprising: an inlet; an outlet; a shell having a tubular form extending between the inlet and the outlet; a main flow path (H) within the shell for conveying a main flow between the inlet and the outlet; and a heat exchange structure, wherein the heat exchange structure comprises: an intake port provided in the shell; an output port provided in the shell; and a secondary flow path (C) within the shell for conveying a secondary flow between the intake port and the output port, wherein the secondary flow path is spirally intertwined with the main flow path for a section of the duct to provide a heat exchanger within the duct.