Chapter One: Understanding Shell and Tube Heat Exchangers
A shell and tube heat exchanger (STHE) is a common device. It has a big round shell that holds tube bundles. A heat exchanger transfers heat between two similar substances or mediums. Shell and tube heat exchangers are noticeable for their simple design and efficient heat exchange rates.
Shell and Tube Heat Exchanger
Shell and tube heat exchangers are popular because they are simple and effective at moving heat. The basic process involves the flow of liquid or steam into the shell, and heating the tubes. For optimal heat transfer, a configuration of four passes through the tubes is considered the most effective method.
Chapter Two: Designing Shell and Tube Heat Exchangers
Shell and tube heat exchangers undergo sophisticated computer-aided design processes. Key components include the shell, shell cover, tubes, channel, channel cover, tube sheet, baffles, and nozzles. The Tubular Exchanger Manufacturers Association (TEMA) establishes specifications and standards for STHEs.
Shell
The shell is made from pipe or welded metal plates. It needs to endure extreme temperatures and not corrode. To reduce space, make sure the diameter is consistent and round, with no gaps between the edge and baffles.
Channels or Heads
The type of channel or head depends on the specific application. Bonnet-type heads are often used when they don’t need to be removed often. Removable cover channels are used for maintenance.
Tubes
Tubes are made from different materials like steel, titanium, or copper. They are welded or extruded. We select tube sizes and thicknesses based on pressure, temperature, stress, and corrosion.
Tube Sheet
The tube sheet is a plate with holes. It supports tubes on both ends of the shell. It also extends beyond the tubes, creating a chamber covered by heads.
Expansion Joint
An expansion joint is important for temperature changes. It prevents stress-related problems in the heat exchanger’s parts.
Tube Pitch
The distance between tubes affects how easy it is to clean and how turbulent it is. Square pitch arrangements, allowing vapor to rise between tubes, are advantageous.
Baffles
Baffles direct flow in the shell and tube sides, increasing fluid velocity and minimizing fouling. In horizontal heat exchangers, baffles support tubes and prevent sagging or vibration damage.
Tie Rods and Spacers
Tie rods and spacers support baffles and maintain spacing, preventing sagging. The number is determined by the shell’s diameter and the number of baffles.
Leading Shell and Tube Heat Exchanger Manufacturers and Companies
- Enerquip Thermal Solutions
- Mason Manufacturing LLC
- Xylem
- Delta T Heat Exchangers
- Exact Exchanger, Inc.
Chapter Three: Operation of Shell and Tube Heat Exchangers
A shell and tube heat exchanger facilitates the exchange of temperature between two fluids. In this process, one fluid flows through the tubes, and the other flows through the shell. The decision on which fluid enters which side is termed fluid allocation. The decision is influenced by factors such as pressure differences. Lower-pressure fluids enter the shell side.
Shell Side
The shell side, more expensive and harder to clean than the tubes, has baffles directing fluid flow across tube bundles. It is suitable for processing viscous fluids and those with high flow rates.
Tube Side
The tube side requires turbulent flow achieved by installing turbulators inside the tubes. Turbulence helps transfer heat and keeps the flow smooth with less pressure.
Passes
Shell and tube heat exchangers can have one to eight passes, influencing heat transfer efficiency. As the number of passes increases, so does the heat transfer coefficient.
Operating Shell and Tube Heat Exchanger
During the heat exchange process, fluids in the shell and tubes come into thermal contact. As a result, one fluid becomes cooler while the other becomes warmer.
Chapter Four: Varieties of Shell and Tube Heat Exchangers
Shell and tube heat exchangers are classified by TEMA into Class B, Class C, and Class R, based on construction and service type.
Flow Types
Flow types include parallel, counter, and cross. Fluids enter and exit at the same ends in parallel flow. Counterflow has opposite directions. Crossflow involves fluids flowing perpendicular to each other.
Fixed Tube Sheet TEMA Type M
This design has straight tubes secured at both ends to stationary tube sheets welded to the shell. It is cost-effective, easy to clean, and maintain.
U Tube Heat Exchanger
U-tube heat exchangers have tubes configured like a ‘U,’ with inlet and outlet valves located at one end. They can handle high-temperature variances.
Floating Head Heat Exchanger TEMA Type S
Similar to U U-tube design, the floating head can withstand high temperature variances. The floating end allows for easy cleaning and inspection.
TEMA Type T or Type AKT
This design allows pulling out the tube bundle for maintenance and has an abnormal clearance between the baffle and shell.
Scraped Surface Heat Exchanger
Scraped surface heat exchangers are made for thick substances. They have blades to remove buildup and transfer heat efficiently.
Chapter Five: Advantages of Shell and Tube Heat Exchangers
Shell and tube heat exchangers have many advantages, so they can be used in different industries and applications.
Cost
They are cost-effective compared to plate-type coolers.
Heat Capacity
Capable of handling a wide temperature range, ensuring consistent production.
Pressure
Built to withstand high pressures, adhering to industry codes.
Pressure Loss
Designed to minimize pressure loss, enhancing overall performance.
Adjustments
Adaptable design allows for adjustments to fit specific production processes.
Thermal Expansion
Multi-tube design accommodates thermal expansion, suitable for handling flammable and toxic fluids.
Chapter Six: Standards and Regulations for Shell and Tube Heat Exchangers
The food, drink, dairy, and medicine industries have rules to ensure their products are safe and consistent.
3-A Sanitary Standards (3-ASSI)
Focuses on keeping equipment clean in place (CIP) for dairy, food, and pharmaceutical industries.
American Petroleum Industry Standard 660 (API660)
These rules govern the creation of heat exchangers in the petroleum and petrochemical industries.
Tubular Exchangers Manufacturers Association (TEMA)
Sets widely used standards for the design and categorization of shell and tube heat exchangers.
American Society of Mechanical Engineers (ASME)
ASME Code VIII applies to the pressurized parts of shell and tube heat exchangers.
Pressure Equipment Directive (PED)
International standard for products manufactured in the U.S. but used globally, ensuring safety.
Canadian Registration Number (CRN)
A provincial approval system based on size, fluids, pressure, and temperature range, varying by province.
Conclusion
Shell and tube heat exchangers are widely used in various industries. They are popular due to their straightforward design and efficient heat transfer. By following rules and guidelines, they can be used safely, reliably, and for various purposes.