Multi-wall heat exchanger for a water heater

A heat exchange tube assembly comprising:

• a metallic outer tube having a wall with an inner surface;
• and
• a metallic inner tube positioned within said outer tube, said inner tube having a wall with an outer surface;
• wherein a portion of said outer surface of said inner tube contacts a portion of said inner surface of said outer tube, thereby facilitating the transfer of heat between said inner tube and said outer tube;
• wherein an elongated passageway is defined between a portion of said outer surface of said inner tube and a portion of said inner surface of said outer tube, thereby facilitating the flow of fluid along a length of said heat exchange tube assembly;
• and
• wherein said wall of said outer tube is thicker than said wall of said inner tube.

A heat exchange tube assembly comprising:

• a metallic outer tube having a wall with an inner surface;
• and
• a metallic inner tube positioned within said outer tube, said inner tube having a wall with an outer surface;
• wherein a portion of said outer surface of said inner tube contacts a portion of said inner surface of said outer tube, thereby facilitating the transfer of heat between said inner tube and said outer tube;
• wherein an elongated passageway is defined between a portion of said outer surface of said inner tube and a portion of said inner surface of said outer tube, thereby facilitating the flow of fluid along a length of said heat exchange tube assembly;
• and
• wherein said passageway is at least partially defined by at least one spiral groove formed by said outer surface of said inner tube or by said inner surface of said outer tube.

A method of forming a heat exchange tube assembly comprising the steps of:

• inserting a metallic inner tube within a metallic outer tube;
• urging a portion of an outer surface of the inner tube and a portion of an inner surface of the outer tube into contact with one another, thereby facilitating the transfer of heat between the inner tube and the outer tube;
• and
• maintaining an elongated passageway between a portion of the outer surface of the inner tube and a portion of the inner surface of the outer tube , thereby facilitating the flow of fluid along a length of the heat exchange tube assembly.

A water heater comprising:

• a tank having a wall defining an interior for holding water to be heated;
• and
• a heat exchange tube assembly extending in said interior of said tank and having:
• a metallic outer tube having a wall with an inner surface;
• a metallic inner tube positioned within said outer tube, said inner tube having a wall with an outer surface and defining an interior for containing fluid, wherein an elongated passageway is defined between said outer surface of said inner tube and said inner surface of said outer tube, thereby facilitating the flow of fluid along a length of said heat exchange tube assembly;
• and
• a fitting extending into the interior of said tank, said fitting being sealingly coupled to said outer tube and to said wall of said tank, thereby preventing the mixing of fluid in said elongated passageway and water in said tank, said fitting at least partially defining a fluid flow passageway extending between said elongated passageway and an exterior of said tank, thereby facilitating the flow of fluid from said elongated passageway to said exterior of said tank.