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Publication Date: 2004-Jan-21

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A heat transfer tube for use in a heat exchanger where heat is transferred between a fluid flowing through the tube and a fluid flowing around the exterior of the tube during the heat exchange process. The tube has a plurality of fins extending around a major portion of its external surface. The tube has a heat conductive insert, such as a metal mixing element, inside the tube with the outside diameter of the cylindrical section the insert occupies essentially equal to the inside diameter of the tube after the finning process.

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The present invention relates generally to heat transfer tubes. In particular, the invention relates to the internal configuration of a heat exchanger tube that is used to increase heat transfer during laminar flow. Note that there is a pending patent application as of the date of this publication.

Many designs have been disclosed in the literature, including mechanical methods for connecting inserts to tube walls, such as USP 2,895,508 (Drake), USP 2,929,408 (Weatherwax), GB 865,983 (Dingley), GB 1,028,000, USP 3,394,736 (Pearson), USP 3,636,982 (Drake), USP 3,871,407 (Bykov), USP 4,190,105 (Dankowski), USP 4,265,275 (Heller), USP 4,296,539 (Asami), USP 4,724,899 (Frates), USP 4,865,689 (Hon), USP 6,508,983 (McBurney), USP 6,533,030 (Mitrovic) and WO 02/26370. Brazing methods include those described in USP 4,466,567 (Garrison), USP 4,688,311 (Saperstein), USP 6,206,089 (Uchikawa), and USP 6,470,570 (Prater). Mechanical methods for tube wall forming include USP 5,781,996 (Spencer), USP 5,803,165 (Shikazono) and EP 0 865 838 (Gupte). Examples of heat exchanger tube inserts include USP 4,534,409 (Cadars), USP 4,700,749 (Cadars) and USP 3,800,985. Other systems include those described in USP 6,192,583 (Roffelsen), USP 6,467,949 (Reeder et al.), USP 5,597,236 (Fasano), USP 3,775,063 (Grout et al.), USP 3,800,985 (Grout et al.), and USP 3,806,097 (Devellian et al.). All of the patents in this paragraph are incorporated herein by reference in their entirety.

Many types of internal inserts are used to enhance heat transfer rates in shell and tube heat exchangers. The internal inserts are used to modify the flow characteristics of the fluid to enhance the heat transfer rate. Heat transfer is dependant upon the surface area of the tube where the transfer of heat takes place. In laminar flow fluid tends to move slowly at the wall creating a layer that limits the rate of transfer of heat to that approaching a pure conduction mechanism which is a lower rate than convective heat transfer. It is desirable to periodically break up any tendency of the fluid to form a significantly thick layer close to the wall.

When a gap exists between the tube wall and the insert (in the region which is designed to modify the flow to prevent the development of a slow moving layer), some of the slow moving or stagnant material is not removed from the wall, thus limiting the transfer of heat. In addition, it is known that such a gap, which is filled with the fluid, prevents the conduction of heat directly from the metal tube wall to the metal insert. The heat transfer rate through the metal tube wall in contact with the surface of the metal insert is much greater than if the heat must pass through fluids. The direct contact of the metal insert and tube wall increases the heat transfer surface area exposed to the moving fluid, thus increasing further the rate of heat transfer. This is effective in both coo...