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A tube bundle is a densely packed collection of pipes used as a radiation core in heat exchangers. These pipe groups are typically housed in a tubular shell or outer housing with a constant flow of water moving through it. When hot liquids or gases are circulated through the tube bundle, the large combined surface area of the tubes allows for efficient transfer of heat into the shell water and cooling of the fluids in the tubes. There are two distinct types of tube bundles: straight and U tube. The pipes in these bundles are generally made of steel or copper depending on the specific application.
Most heat transfer methods become increasingly efficient as the combined radiation and recipient surface areas increase. This principle forms the basis of tube heat exchanger operation; the large number of tubes in the bundles offer extensive contact surfaces which facilitate quick and efficient thermal transfer. The layout of the pipes in a tube bundle is carefully calculated, and they typically pass through several baffles or bulkheads which maintain the spacing relationship throughout the length of the bundle. The water entry and exit configuration of the bundle are dictated by which of the two common bundle types are being used.
The first of the most common tube bundle configurations is the straight line type. This layout consists of straight tubes which open on either end of the bundle into entry and exit 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 shell and remove the bundle should cleaning or repairs be required. Straight tube arrangements do, however, feature lower initial installation costs.
The second common tube bundle configuration is the U tube layout. This bundle variant features entry and exit points on the same side of the shell on a tube shell cap divided into two sealed chambers. The tubes leave the entry chamber and travel to the opposite end of the shell where they make a U bend and return in the opposite direction to the exit chamber. This type of layout is easier to disassemble for maintenance with the bundle typically being slid out as a modular unit. U configurations also accommodate high temperature differentials well and relieve most thermal expansion and contraction stresses in the bundle.