Strut-tube coolers

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Types of Coolers

Engineman 3 - Basic Engine Mechanics

Plate-tube coolers

STRUT-TUBE COOLERS.-Another design of cooler used in the cooling systems of marine engines is the strut-tube type. The strut-tube cooler has an advantage over the shell-and-tube cooler in that it provides considerable heat transfer in a smaller and more compact unit. On the other hand, the shell-and-tube cooler, while larger for an equivalent amount of heat transfer, has an advantage over the strut-tube cooler in that it is able to withstand a higher degree of scaling and larger foreign particles before the cooling system becomes clogged. Strut-tube coolers are commonly referred to as Harrison-type coolers; however, manufacturers other than Harrison produce coolers of the strut-tube type. Sometimes, the term radiator is used for coolers with strut-tube construction.

There are many different designs of strut-tube coolers. The tube assemblies of two of these coolers, and the type of tube construction in each, are illustrated in figures 7-6 and 7-7.

Strut-tube coolers are used for the cooling of water and lubricating oil. Water coolers and oil coolers differ principally in design and in the size of the tubes. (See figs. 7-6 and 7-7.) Each of the tubes in both the oil cooler and the water cooler is composed of two sections, or strips. In the strut-tube water cooler, both sections of each tube

Figure 7-6.-Tube assembly of a strut-type water cooler.

Figure 7-7.-Tube assembly of a strut-type lubricating oil cooler.

contain either a series of formed dimples or cross tubes brazed into the tubes. These struts (sometimes referred to as baffles) increase the in-side and outside contact surfaces of each tube and create turbulence in the liquid flowing through the tube; thus, the heat transfer from the liquid being cooled to the cooling liquid is increased. The struts also increase the structural strength of the tube. In the oil cooler, the tubes are from one-half to one-third as large as the tubes of water coolers, and the sections of the tubes do not contain either dimples or cross tubes. Instead, a distributor strip, which serves the same purpose as the struts in the tubes of the water cooler, is enclosed in each tube.

The tubes of a strut-tube cooler are fastened in place with a header plate at each end and are fur-ther secured with an intermediate reinforcement plate. These plates are electroplated with tin to protect the iron parts of the cooler. The tube-and-plate assembly (sometimes called the tube bundle or the core assembly) is mounted in a bronze frame. The frame and the core assembly fit in the cast metal casing, or housing, and are held in place by the two end covers. The casing, core assembly, frame, covers, and other parts of one model of a strut-tube cooler are shown in figure 7-8.

The header plates, at the ends of the tubes, separate the cooling-liquid space in the casing from the cooled-liquid ports in the end covers. The cooled liquid flows through the tubes in a straight path from the cover inlet port to the cover discharge port at the opposite end of the cooler. The intermediate tube plate acts as a baffle to create a U-shaped path for the cooling liquid, which flows around the outside of the tubes from the inlet opening of the casing to the discharge opening.