Tube & Shell Heat Exchanger
Heat Exchangers (Shell& Tube Type) –
Application of Tube Heat exchanger – Shell Heat exchanger , shell and tube heat exchangers :
heat exchangers include chemical, petrochemical, oil & gas, power generation, refrigeration, pharmaceuticals, HVAC, food & beverage processing and pulp & paper industries.
Transfer of heat from one fluid to another is an important operation for most of the processing industries. Heat transfer equipment for transferring heat from one fluid to another fluid are generally called heat exchanger.
are normally classified depending on the transfer process occurring in them, Among st of all type of exchangers, shell and tube exchangers are most commonly used heat exchange equipment. The common types of shell and tube exchangers are Fixed tube-sheet exchanger (non-removable tube bundle): The simplest and cheapest type of shell and tube exchanger is with fixed tube sheet design. In this type of exchangers the tube sheet is welded to the shell and no relative movement between the shell and tube bundle is possible.
Removable tube bundle: Tube bundle may be removed for ease of cleaning and replacement. Removable tube bundle exchanger further can be categorized in floang head and U-tube exchanger.
Floating head exchanger :
It consists of a staonery tube sheet which is clamped with the shell flange. At the opposite end of the bundle, the tubes may expand into a freely riding floang-head or floang tube sheet. A floang head cover is bolted to the tube sheet and the enre bundle can be removed for cleaning and inspecon the interior.
This type of exchanger consists of tubes which are bent in the form of and rolled back into the tube sheet. This means that it will omit some tubes at the center of the tube bundle..
Thermal Design Consideration :
The flow rates of both hot and cold streams, their terminal temperatures and fluid properer are the primary inputs of thermal design of heat exchanger. Thermal design of a shell and tube heat exchanger typically includes the determination of heat transfer area, number of tubes, tube length and diameter, tube layout, number of shell and tube passes, type of heat exchanger (fixed tube sheet, removable tube bundle etc), tube pitch, number of baffles, its type and size, shell and tube side pressure drop etc.
Shell is the container for the shell fluid and the tube bundle is placed inside the shell. Shell diameter should be selected in such a way to give a close fit of the tube bundle. The clearance between the tube bundle and inner shell wall depends on the type of exchanger Shells are usually fabricated from standard steel pipe with satisfactory corrosion allowance.
Tube OD of ¾ and 1” are very common to design a compact heat exchanger. The most efficient condition for heat transfer is to have the maximum number of tubes in the shell to increase turbulence.
The tube thickness should be enough to withstand the internal pressure along with the adequate corrosion allowance. The tube thickness is expressed in terms of BWG (Birmingham Wire Gauge) and true outside diameter (OD). Longer tube reduces shell diameter at the expense of higher shell pressure drop. Finned tubes are also used when fluid with low heat transfer coefficient flows in the shell side. Stainless steel, admiralty brass, copper, bronze and alloys of copper-nickel are the commonly used tube materials.
Tube pitch, tube-layout and tube-count :Tube pitch is the shortest center to center distance between the adjacent tubes. The tubes are generally placed in square or triangular paerns, The number of tubes that can be accommodated in a given shell ID is called tube count. The tube count depends on the factors like shell ID, OD of tube, tube pitch, tube layout, number of tube passes, type of heat exchanger and design pressure.
Tube passes: The number of passes is chosen to get the required tube side fluid velocity to obtain greater heat transfer co-efficient and also to reduce scale formaon. The tube passes vary from 1 to 16. The tube passes of 1, 2 and 4 are common in application.
The paron built into exchanger head known as paron plate (also called pass paron) is used to direct the tube side flow.
The tubes are fixed with tube sheet that form the barrier between the tube and shell fluids. The tubes can be fixed with the tube sheet using ferrule and a so metal packing ring. The tubes are aached , to tube sheet with two or more grooves in the tube sheet wall by tube rolling. The tube metal is forced to move into the grooves forming an excellent ght seal. This is the most common type of fixing arrangement , in large industrial exchanger. The tube sheet thickness should be greater than the tube outside diameter to make a good seal. The recommended
standards (IS:4503 or TEMA) is followed to select the minimum tube sheet thickness, Selection of fluids for tube and the shell side: The roung of the shell side and tube side fluids has considerable effects on the heat exchanger design.