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September 4th, 2010 at 3:38 pm

Compact heat exchangers classification

Compact elements usually fall into some classes including:

1. Array or matrix surfaces. These are the surfaces that are used in regenerative equipment rotation, such as the burning flue gas – air pre heaters for fossil conventional ovens. In this application, the metal is distributed to its capacity to absorb heat with minimal friction hot fluid while exposed to smoke and to dispense with this cold combustion heat incoming air when it is rotated in the flow of incoming cold air. No designation is used.

2. flattened and circular tubes. These are the simplest form of compact heat exchanger surface. The designation ST indicates flow inside pipes straight (example: ST-1), FRANCE TÉLÉCOM indicates flow inside pipes flattened straight (example: FT-1) and FTD indicates flow inside straight tubes dimpled flattened. Dimple stops the boundary layer, which tends to increase the heat transfer coefficient without increasing the speed of the stream.

3. Plate fin surfaces.

4. Finned-tube surfaces. Circular Tubes with radial spiral fins are designated with the letters CF followed by one or two numbers. The first digit indicates the number offins per inch and the second (ifone is used) refers to the nominal pipe size. With circular tubes with fins continuous, is not used any prefix letter and two numbers have the same meaning as for circular tubes with radial ins spiral. For finned tubes of dishes, do not use any prefix letter; the first digit indicates the fins per inch and the second digit indicates the largest dimension of the tube. When CF don’t appear in the designation of the circular tube with fins radial spiral, the surface shall be presumed to have fins continuous.

5. Surfaces with normal flow smooth tube banks. Unlike low radial fin tubes, smooth ducts are expanded in fins that can accept a number oftube rows, as shown in fig. 11.16a. Holes can be applied in the fin with a hub designed or foot to improve contact resistance or as a spacer between successive fins, as shown, or soldered directly to the pinna with or without a hub. Other types of reduce the resistance to flow out of the tubes through flattened tubes and brazing, as shown in Figure b and c below. Tube plate is done by strips similar to manufacture of circular welded pipes, but is much more subtle and is joined by welding or brazing, rather than welding. The designation considers staggered (S) and in-line (I) agreements oftubes and identifies relationships cross-sectional and longitudinal pitch. The suffix (s) indicates data correlation from steady-state test. All other data were related by a temporary technique. Examples include the surface S1.50-1.25 (s), which is a staggered arrangement with the data obtained via stationary test with of1.50 ratio pitch-a-transversal and longitudinal pitch diameter-to-diameter ratio of1.25. The surface I1.25-1.25 has a provision in line with the data obtained from the transient tests with both of1.25 reports of pitch-a-longitudinal and transverse diameter.

6. Tubular surfaces. These are arrays oftubes ofsmall diameter, from ” 0.9535 down to 0.635 cm, used in service where robustness and cleanup of conventional shell-and-tube heat exchanger are not required. Usually, tubesheets are relatively thin and welding or brazing a tube for a tubesheet provides a suitable seal against interleakage and differential thermal expansion.

Tags: heat, heat exchanger
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