The shell-and-tube type is a general classification that includes all coolers in which the two liquids are prevented from mixing by the thin walls of the tubes of the element. Modifications of the shell-and-tube cooler have resulted in two other types of coolers: the strut-tube cooler and the plate-tube cooler. These coolers are of the shell-and-tube type in that the fluids are prevented from mixing. Because of design features, however, the coolers used in engines are commonly identified as being either strut or plate-tube types.

SHELL-AND-TUBE COOLERS. -The cool-ing systems of many engines are equipped with coolers of the shell-and-tube type. Shell-and-tube coolers serve to cool lubricating oil and fresh water. Coolers that are used for the cooling of lubricating oil are somewhat smaller than those that are used for the cooling of water. One model of a shell-and-tube cooler is shown in figure 7-5. The shell-and-tube cooler consists principally of a bundle (also called a bank or nest) of tubes encased in a shell. The cooling liquid generally flows through the tubes. The liquid to be cooled enters the shell at one end, is directed to pass over the tubes by baffles, and is discharged at the opposite end of the shell. In other coolers of this type, the cooling liquid flows through the shell and around the tubes; the liquid to be cooled passes through the tubes.

The tubes of the cooler are attached to the tube sheets at each end of the shell. This arrangement forms a tube bundle that can be removed as a unit from the shell. The ends of the tubes are expanded to fit tightly into the holes in the tube sheets; they are flared at their outer edges to prevent leakage. One tube sheet and a bonnet are bolted to the flange of the shell. This sheet is referred to as the stationary-end tube sheet. The tube sheet at the opposite end floats in the shell, a design that allows for expansion of the tube bundle. Packing rings, which prevent leakage past the floating-end tube sheet, are fitted at the floating end between the shell flange and the bonnet. The packing joint allows for expansion and prevents the mixing of

Figure 7-5.-Jacket-water shell-and-tube cooler.

the cooling liquid with the liquid to be cooled in-side the shell by means of a leak-off, or lantern, gland that is vented to the atmosphere. Transverse baffles are arranged around the tube bundle in such a manner that the liquid is directed from side to side as it flows around the tubes and through the shell. The deflection of the liquid ensures the maximum cooling effect. Several of the baffles serve as supports for the bank of tubes. These baffles are of heavier construction than those that only deflect the liquid.

The flow of the liquid in the tubes is opposite the liquid flow in the shell. (See the directional arrows.) On this basis, the cooler could be classified as the counterflow type. Since heat transfer is through the walls of the tubes, the cooling liquid enters one end of the cooler, flows directly through the tubes, and leaves at the opposite end. The cooler, however, could be more precisely classified as a single-pass, indirect-type cooler.