Understanding Shell and Tube Heat Exchangers
Shell and tube heat exchangers are one of the most effective heat exchangers employed in various industries such as refineries and chemical industries. These process equipment are widely used in applications, which require cooling or heating a large volume of process fluids or gases. Shell and tube heat exchangers comprise a cylindrical shell with a large number of small tubes. The tubes are positioned into the cylinder using a tube bundle or "tube stack" which can either have fixed tube plates. The tubes are constructed using thermally conductive materials, which enable the exchange of heat between the hot fluids flowing outside the tubes and the coolant flowing through the tubes. These heat exchangers offer an optimal cooling solution in different fields such as Industrial, Hydraulic, Marine, Railways, etc.
Components of Shell & Tube Exchangers
The shell-and-tube heat exchanger is named for its two major components – round tubes & cylindrical shell. The shell cylinder can be fabricated from a rolled plate or from piping while the tubes are thin-walled tubing manufactured specifically to facilitate heat exchange.
● Tubes: The tubing may be seamless or welded. Tubing may consist of ‘Finns’ to provide more efficient heat transfer surface. Fins are commonly found on the outside of the tubes but are also available on the inside of the tubes. Tubes with a special surface, called high flux tubes, are used to enhance heat transfer on either or both sides of the tube wall.
● Tubesheets: Tubesheets are plates or forgings drilled to provide holes (triangular or square) for holding and inserting the tubes. Tubes are properly secured to the tube sheet to prevent the fluid on the shell side from mixing with the fluid on the tube side. The distance between the tube holes, measured from their centers, is called the tube pitch. Triangular pitch provides higher heat transfer and compactness while square pitch facilitates mechanical cleaning of the outside of the tubes.
● Baffles: Baffles are used for 3 reasons
○ To support the tubes
○ To maintain spacing between them
○ To direct the flow of fluid through the shell.
A segment, known as the baffle cut, is chipped in a way so as to permit the fluid to flow parallel to the tube axis as it flows from one baffle space to another. The spacing between segmental baffles, called as the baffle pitch, along with the baffle cut, is used to determine the cross-flow velocity and hence the rate of heat transfer and the pressure drop.
● Tie Rods and Spacers - Tie rods and spacers are used to hold baffle assembly together & maintain the selected baffle spacing. The tie rods are secured at one end to the tube sheet and at the other end, holding the assembly together.
● Front Header: Also referred to as a stationary header, is the section from where the fluid enters the tube end of the exchanger.
● Rear Header: Is a section from where the fluid from the tube end leaves the exchanger or returns to the front header.
Working of Shell and tube heat exchanger
There are two fluids of different temperatures involved in the cooling operation, one - the process and the other - the cooling medium. The process fluid to be cooled is generally run through small diameter tubes that are housed within the shell. The outer shell, on the other hand, circulates the cooling medium. Both process and cooling fluid are kept in continuous circulation for the heat exchanger to function properly.
Applications of Shell and Tube Heat Exchangers
Shell and tube heat exchanger is used in various industrial applications due to their expertise in performing tasks such as:
● Cooling of hydraulic and lube oil
● Cooling of turbine, compressor, and engine
● Condensing process vapor or steam
● Evaporating process liquid or steam
Benefits of using Shell and tube exchangers
Shell & Tube Heat Exchangers are used in a number of industries such as refineries because of their advantages on other types of heat exchangers. Their benefits include
● Increased efficiency of heat transfer
● Easy to dismantle, clean and repair
● Compact in size
● Capacity can be increased simply by adding plates in pairs
● Affordable as compared to plate type coolers
● Can be used in systems with high operating temperatures and pressures
Praj industries - one of the leading Heat Exchanger Suppliers in the country, offers Critical Process Equipment & Systems to various process industries such as Oil & Gas, Refining, Petrochemicals, Fertilizers, Chemicals, Food, Pharma and Biotech. Praj also offers a range of static equipment like pressure vessels, reactors, shell and tube heat exchangers, distillation columns and other proprietary equipment as per the client design.
