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Shell and tube heat exchangers use bundles of tubes to transfer heat between fluids. Two types of tube bundles, straight and U-shaped, are used. The U-tube layout is easier to disassemble for maintenance and copes well with high temperature differentials.
A shell and tube is a dense collection of tubes used as a radiating core in heat exchangers. These tube assemblies are typically housed in a tubular shell or outer housing with a constant flow of water flowing through it. When hot liquids or gases are circulated through the shell and tube, the large combined surface area of the tubes allows for efficient heat transfer into the shell water and cooling of the fluids in the tubes. There are two distinct types of tube bundles: straight tube and U tube. The tubes in these bundles are usually made of steel or copper depending on the specific application.
Most heat transfer methods become increasingly efficient as the combined irradiation and receiving surface areas increase. This principle underlies the operation of the tube heat exchanger; the large number of tubes in the bundles provides large contact surfaces that facilitate fast and efficient heat transfer. The arrangement of the tubes in a tube bundle is carefully calculated and typically pass through several baffles or bulkheads which maintain the spacing relationship throughout the length of the bundle. The configuration of the beam’s water inlet and outlet is dictated by which of the two common types of beam is used.
The first of the most common shell and tube configurations is the straight line type. This layout consists of straight tubes opening at both ends of the beam into inlet and outlet chambers which form the end caps of the shell. The hot material is then pumped through the bundle in a straight line from one end of the shell to the other. This arrangement is efficient, but requires considerable effort to open the case and remove the bundle should cleaning or repair be required. Straight pipe arrangements, however, have lower initial installation costs.
The second common shell and tube configuration is the U-tube layout. This variation of the shell features inlet and outlet points on the same side of the shell on a tubular shell cap divided into two sealed chambers. The tubes leave the inlet chamber and travel to the opposite end of the shell where they make a U-bend and return in the opposite direction to the outlet chamber. This type of layout is easier to disassemble for maintenance with the pack typically being pulled out as a modular unit. U-configurations also cope well with high temperature differentials and relieve most of the thermal expansion and contraction stresses in the beam.
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