Class of heat exchanger designs

A shell-and-tube heat exchanger is a class of heat exchanger designs.[1][2] It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc.

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Theory and application

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Two fluids, of different starting temperatures, flow through the heat exchanger. One flows through all the tubes in parallel and the other flows outside the tubes, but inside the shell, typically in counterflow. Heat is transferred from one fluid to the other through the tube walls, either from tube side to shell side or vice versa. Cross-baffles can be used to force the shell fluid to flow perpendicularly across the tubes to develop a more turbulent flow, increasing the heat-transfer coefficient. The fluids can be either liquids or gases on either the shell or the tube side. [3]

In order to transfer heat efficiently, a large heat transfer area should be used, leading to the use of many tubes. In this way, waste heat can be put to use. This is an efficient way to conserve energy.

Heat exchangers with only one phase (liquid or gas) on each side can be called one-phase or single-phase heat exchangers. Two-phase heat exchangers can be used to heat a liquid to boil it into a gas (vapor), sometimes called boilers, or to cool the vapors and condense it into a liquid (called condensers), with the phase change usually occurring on the shell side. Boilers in steam engine locomotives are typically large, usually cylindrically-shaped shell-and-tube heat exchangers. In large power plants with steam-driven turbines, shell-and-tube surface condensers are used to condense the exhaust steam exiting the turbine into condensate water which is recycled back to be turned into steam in the steam generator.

They are also used in liquid-cooled chillers for transferring heat between the refrigerant and the water in both the evaporator and condenser, and in air-cooled chillers for only the evaporator.

Shell and tube heat exchanger design

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There can be many variations on the shell-and tube-design. Typically, the ends of each tube are connected to plenums (sometimes called water boxes) through holes in tubesheets. The tubes may be straight or bent in the shape of a U, called U-tubes.

In nuclear power plants called pressurized water reactors, large heat exchangers called steam generators are two-phase, shell-and-tube heat exchangers which typically have U-tubes. They are used to boil water recycled from a surface condenser into steam to drive a turbine to produce power. Most shell-and-tube heat exchangers are either 1, 2, or 4 pass designs on the tube side. This refers to the number of times the fluid in the tubes passes through the fluid in the shell. In a single pass heat exchanger, the fluid goes in one end of each tube and out the other.

Surface condensers in power plants are often 1-pass straight-tube heat exchangers (see surface condenser for diagram). Two and four pass designs are common because the fluid can enter and exit on the same side. This makes construction much simpler.

There are often baffles directing flow through the shell side so the fluid does not take a short cut through the shell side leaving ineffective low flow volumes. These are generally attached to the tube bundle rather than the shell in order that the bundle is still removable for maintenance.

Countercurrent heat exchangers are most efficient because they allow the highest log mean temperature difference between the hot and cold streams. Many companies however do not use two pass heat exchangers with a u-tube because they can break easily in addition to being more expensive to build. Often multiple heat exchangers can be used to simulate the countercurrent flow of a single large exchanger.

Selection of tube material

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To be able to transfer heat well, the tube material should have good thermal conductivity. Because heat is transferred from a hot to a cold side through the tubes, there is a temperature difference through the width of the tubes. Because of the tendency of the tube material to thermally expand differently at various temperatures, thermal stresses occur during operation. This is in addition to any stress from high pressures from the fluids themselves. The tube material also should be compatible with both the shell-and-tube side fluids for long periods under the operating conditions (temperatures, pressures, pH, etc.) to minimize deterioration such as corrosion. All of these requirements call for careful selection of strong, thermally-conductive, corrosion-resistant, high quality tube materials, typically metals, including aluminium, copper alloy, stainless steel, carbon steel, non-ferrous copper alloy, Inconel, nickel, Hastelloy and titanium.[4] Fluoropolymers such as Perfluoroalkoxy alkane (PFA) and Fluorinated ethylene propylene (FEP) are also used to produce the tubing material due to their high resistance to extreme temperatures.[5] Poor choice of tube material could result in a leak through a tube between the shell-and-tube sides causing fluid cross-contamination and possibly loss of pressure.

Applications and uses

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The simple design of a shell-and-tube heat exchanger makes it an ideal cooling solution for a wide variety of applications. One of the most common applications is the cooling of hydraulic fluid and oil in engines, transmissions and hydraulic power packs. With the right choice of materials they can also be used to cool or heat other mediums, such as swimming pool water or charge air.[6] There are many advantages to shell-and-tube technology over plates

• One of the big advantages of using a shell-and-tube heat exchanger is that they are often easy to service, particularly with models where a floating tube bundle is available.[7](where the tube plates are not welded to the outer shell).
• The cylindrical design of the housing is extremely resistant to pressure and allows all ranges of pressure applications

Overpressure protection

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In shell-and-tube heat exchangers there is a potential for a tube to rupture and for high pressure (HP) fluid to enter and over-pressurise the low pressure (LP) side of the heat exchanger.[8] The usual configuration of exchangers is for the HP fluid to be in the tubes and for LP water, cooling or heating media to be on the shell side. There is a risk that a tube rupture could compromise the integrity of the shell and the release flammable gas or liquid, with a risk to people and financial loss. The shell of an exchanger must be protected against over-pressure by rupture discs or relief valves. The opening time of protection devices has been found to be critical for exchanger protection.[9] Such devices are fitted directly on the shell of the exchanger and discharge into a relief system.

Tubes

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Overview

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Shell-and-tube heat exchangers are integral components in thermal engineering, primarily used for efficient heat transfer. The design and arrangement of the tubes within these exchangers are fundamental to their operation and effectiveness.[10] The precise design and specification of tubes in shell and tube heat exchangers underscore the complexities of thermal engineering. Each design aspect, from material selection to tube arrangement and fluid flow, plays a vital role in the exchanger's performance, showcasing the intricacies and precision required in this field.[10]

Specification and Standards

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Tubes in these exchangers, often termed as condenser tubes, are distinct from typical water tubing. They adhere to the Birmingham Wire Gage (BWG) standard, which dictates specific dimensions such as the outside diameter. For example, a 1-inch tube according to BWG will have an exact outside diameter of 1 inch.[11] Detailed specifications are available in specialized references.

Materials

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The tubes in shell and tube heat exchanger[1]s are constructed from a range of materials, selected based on factors such as thermal conductivity, mechanical strength, corrosion resistance, and compatibility with the process fluids. The selection of tube material is crucial for optimizing heat exchanger performance, ensuring durability, and preventing issues such as corrosion and fouling.

Common materials used for the tubes include:

Stainless Steel (e.g., 304, 316L, 904L): Stainless steel is commonly used in shell and tube heat exchangers due to its favorable combination of thermal conductivity, corrosion resistance, and mechanical strength. These alloys are suitable for a wide range of industries, including chemical, petrochemical, and food processing. Stainless steel's resistance to corrosion in both high and low temperatures makes it a popular choice.

Titanium and Titanium Alloys: Titanium is highly resistant to corrosion, particularly in harsh environments such as seawater and acidic conditions. Its excellent strength-to-weight ratio and resistance to chloride stress corrosion cracking make it ideal for applications in the chemical and marine industries, where corrosion resistance is critical.

Nickel Alloys (e.g., Inconel, Hastelloy): Nickel alloys are often used in high-temperature and highly corrosive environments. These materials, such as Inconel and Hastelloy, provide excellent resistance to oxidation and corrosion, making them ideal for power generation, aerospace, and chemical processing industries.

Copper and Copper Alloys (e.g., CuNi, Brass): Copper and copper alloys are chosen primarily for their high thermal conductivity, which enhances heat transfer. These materials are often used in applications such as HVAC systems, refrigeration, and desalination processes, where efficient heat exchange is essential.

Carbon Steel: Carbon steel is a cost-effective material commonly used in less corrosive environments. It is often selected for applications where cost is a major consideration, but protective coatings or internal linings are usually required to reduce the risk of corrosion.

Aluminum: Aluminum offers good thermal conductivity and is lightweight, making it suitable for applications that require both high heat transfer rates and reduced weight, such as in certain heat recovery and aerospace applications.

The choice of material for the tubes in a shell and tube heat exchanger is influenced by the operating conditions, including temperature, pressure, and the chemical nature of the fluids involved. Proper material selection helps prevent premature failure, corrosion, and inefficiency, thus ensuring the heat exchanger operates effectively throughout its service life.

Tube Arrangement

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The arrangement of tubes is a crucial design aspect. They are positioned in holes drilled in tube sheets, with the spacing between holes - known as tube pitch - being a key factor for both structural integrity and efficiency.[10] Tubes are typically organized in square or triangular patterns, and specific layouts are detailed in engineering references.

Tube Counts

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Tube count refers to the maximum number of tubes that can fit within a shell of a specific diameter without weakening the tube sheet.[10] This aspect is crucial for ensuring the structural integrity and efficiency of the heat exchanger. Information on tube counts for various shell sizes can be found in specialized literature.

Shell and tube===Fluid Flow=== In shell and tube heat exchangers, there are two distinct fluid streams for heat transfer. The tube fluid circulates inside the tubes, while the shell fluid flows around them, guided by various types of baffles (e.g., segmental, helical, or disc-and-doughnut). The movement of the shell fluid, designed to enhance turbulence and heat transfer, can be arranged in different flow configurations, such as counter-current, co-current, or cross-flow. The number of passes, whether single or multiple, made by the shell and tube fluids over the heat exchange surfaces plays a key role in optimizing the exchanger's overall performance. These aspects are detailed in specialized references.

Design and construction standards

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• Standards of the Tubular Exchanger Manufacturers Association (TEMA), 10th edition,
• EN -3 "Unfired Pressure Vessels - Part 3: Design", Section 13 ()
• ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, Part UHX

See also

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• Boiler or Reboiler
• EJMA
• Fired heater
• Fouling or scaling
• Heat exchanger
• NTU method as an alternative to finding the LMTD
• Plate and frame heat exchanger
• Plate fin heat exchanger
• Pressure vessel
• Surface condenser

References

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Shell and Tube Heat Exchangers: Types and Applications

Chapter One: What is a Shell and Tube Heat Exchanger?

A shell and tube heat exchanger (STHE) is a widely used apparatus designed for heat transfer. It features a large cylindrical shell encasing a series of parallel tubes. These tubes are arranged within the shell to facilitate the transfer of heat between two fluids. Shell and tube heat exchangers are popular due to their efficiency and adaptability, and they come in various configurations depending on the specific application, tube design, and other attributes.

Shell and tube heat exchangers are favored for their straightforward design and high heat transfer efficiency. This type of heat exchanger works by circulating a fluid or steam through the shell, which heats the tubes inside. For optimal performance, passing the fluid through the tubes four times is typically regarded as the most effective method for heat transfer.

Chapter Two: What are the key considerations in shell and tube heat exchanger design?

Shell and tube heat exchangers are designed using advanced computational techniques and precise engineering parameters. Key components of these devices include the shell, shell cover, tubes, channel, channel cover, tube sheet, baffles, and nozzles. The design and manufacturing standards for shell and tube heat exchangers are regulated by the Tubular Exchanger Manufacturers Association (TEMA).

Before manufacturing a shell and tube heat exchanger, several critical data points are required from the manufacturers. These include flow rates, inlet and outlet temperatures, pressure levels, pressure drops, resistance factors, the physical properties of the substances being processed, pipe dimensions, and the shell diameter. In addition to these fundamental aspects, detailed technical specifications are necessary to ensure the production of a heat exchanger that meets the specific needs of the application.

Shell

The shell of a shell and tube heat exchanger is constructed from pipes or welded metal plates, selected for their ability to endure high temperatures and resist corrosion. The interior of the shell is designed to be cylindrical with a uniform diameter to reduce the gap between the baffled perimeter and the shell itself.

Channels or Heads

The choice of channel or head type for a shell and tube heat exchanger varies based on its application. Bonnet-type heads are typically used when the head does not need frequent removal. For maintenance purposes, channels with removable covers are either flanged or welded. When regular access to the channel and tubes is required, a removable cover for the channel is essential.

Tubes

Tubes of a shell and tube heat exchanger are welded or extruded and made from carbon steel, stainless steel, titanium, Inconel, or copper. Tube diameters of 0.625 inch (16mm), 0.75 inch (19mm), or one inch (25mm) are used in compact heat exchangers. The thickness of the tubes is chosen for pressure, temperature, thermal stress, and resistance to corrosion at lengths of 6 to 24 feet or 2 meters to 7 meters. Tubes that are longer reduce shell diameter and result in high shell pressure drop.

Tube Sheet

The tube sheet is a plate or sheet that is perforated with holes for the insertion of pipes or tubes and designed to support the tubes on either end of the cylindrical shell. The shell extends beyond the tube sheets and is sealed on both ends to form the enclosed chamber that is covered by the heads.

Expansion Joint

The main function of a heat exchanger is to transfer heat between a hot fluid on one side and a cold fluid on the other. As a result, these units frequently experience a wide range of temperatures.

Materials expand when heated and contract when cooled. Without proper allowances for these changes, the materials in the heat exchanger could become overstressed and fail. This can lead to issues such as tube buckling, tubes being dislodged from the tube sheets, shell deformation, or distortion of nozzle connections. Such problems compromise the heat exchanger's structural integrity and could render it unsafe for operation.

To address this, an expansion joint is used. This flexible component is designed to absorb the stresses caused by temperature and pressure variations.

Tube Pitch

Tube pitch refers to the measurement from the center of one tube to the center of the neighboring tube. Tubes can be arranged in either a triangular or square configuration. The square pattern is generally preferred for its ease of cleaning and minimal turbulence. This arrangement also facilitates the ascent of vapors between the tubes, offering a benefit compared to the triangular and rotated square pitch layouts.

Baffles

Baffles are installed to control the fluid flow within the shell side of a heat exchanger. Their purpose is to enhance the velocity of the fluid, which improves the heat transfer efficiency and helps reduce fouling. Fouling refers to the buildup of unwanted materials on the heat transfer surfaces, which impedes heat transfer and degrades the performance of the heat exchanger. In horizontal shell and tube heat exchangers, baffles also play a crucial role in supporting the tubes, preventing them from sagging or experiencing damage due to vibrations.

Tie Rods and Spacers

Tie rods and spacers serve as structural supports for the baffles within a heat exchanger, ensuring they stay securely in position and maintaining the proper spacing between them. The quantity of rods and spacers required is based on the number of baffles and the diameter of the shell. Tie rods are attached to the tube sheet and span the length of the tube bundle, extending to the final baffle to provide necessary support.

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Chapter Three: How Do Shell and Tube Heat Exchangers Work?

The concept and operation of a shell and tube heat exchanger are rather simple and are based on the flow and thermal contact of two liquids. The name of a shell and tube heat exchanger serves as an explanation of the process, which is the exchanging of temperature between two fluids. In a heat exchanger, a heated or hot fluid will flow around a cold fluid and transfer heat in the direction of the flow of the cold fluid.

Whenever two materials come into contact, heat will be transferred through the conductive surfaces between them. Shell and tube heat exchangers are designed to facilitate this heat transfer, allowing two different fluids to exchange heat through metal surfaces.

In a shell and tube heat exchanger, one fluid moves through the tubes while the other flows around the tubes within the shell. For instance, in a straight tube shell and tube heat exchanger, the shell fluid enters through the top inlet, while the tube fluid enters from the bottom right inlet.

These heat exchangers consist of two main sections: the shell side and the tube side. Proper fluid allocation is essential, determining which side will handle the hot fluid and which will handle the cold fluid.

In cases where there is a pressure differential between the fluids, the lower pressure fluid is directed through the shell inlet, as the tubes are built to withstand higher pressures.

Shell Side

When configuring fluid flow on the shell side, it's crucial to remember that the shell is costlier to manufacture compared to the tubes and is also more challenging to clean. Baffles inside the shell help manage the fluid flow, directing it across the tube bundles.

The shell side is typically used for handling viscous fluids and those with high flow rates, as it provides enhanced turbulence and a higher heat transfer coefficient. This setup is particularly effective for managing large temperature differences.

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Tube Side

To ensure turbulent flow on the tube side, turbulators are installed inside the tubes through the openings in the tube sheet. This turbulence enhances the heat transfer efficiency, similar to the effect in the shell side. Additionally, turbulators help maintain the cleanliness of the tubes by preventing fouling. While the tubes generally have lower turbulence and pressure drop, they facilitate a smoother flow of the fluid.

Passes

Shell and tube heat exchangers are categorized by the number of passes, which can range from one to eight or more. This is denoted as 1-1, 1-2, 1-4, etc., where the first number represents the number of shells and the second indicates the number of passes. Each pass refers to the number of times the fluid circulates through the shell side. For instance, a single-pass heat exchanger allows the fluid to traverse the shell only once. Increasing the number of passes typically enhances the heat transfer coefficient.

An Operating Shell and Tube Heat Exchanger

The illustration demonstrates that cold fluid enters through the inlet of the tube or shell and undergoes heating via conductive methods within the tubes, then exits after being processed. The diagram below depicts a heat exchanger with a two-pass shell and tube design.

In a shell and tube heat exchanger, turbulent flow enhances the efficiency of heat transfer and reduces the risk of fouling on the tubes and shell surfaces. The consistent turbulence has a self-cleaning effect that helps maintain optimal performance. Flow baffles in the shell generate turbulence, while internal turbulators in the tubes contribute to this effect.

Heat exchange occurs through thermal contact between the fluids circulating within the shell and tubes. This process results in one fluid exiting at a lower temperature, while the other exits at a higher temperature.

Chapter Four: What are the different types of shell and tube heat exchangers?

The Tubular Exchangers Manufacturers Association (TEMA) has established guidelines for the design, manufacture, and construction of shell and tube heat exchangers. These guidelines are categorized into three classes: Class B, Class C, and Class R. The classification of a shell and tube heat exchanger is based on its construction specifics and the type of service it is intended to deliver.

TEMA Classifications:

• Class B Chemical Processing
• Class C General Commercial Applications
• Class R Petroleum and Large Scale Applications

TEMA classifies shell and tube heat exchangers based on their front end or head, rear end, and shell configurations. The chart below uses columns and rows to categorize and detail each type of shell and tube heat exchanger.

To simplify the identification of various designs and configurations, TEMA has created a three-letter identification system'BEM, AEM, or NEN'for straight tube and fixed tube sheet shell and tube heat exchangers.

The first letter indicates the type of front end stationary head, specifying how the tube sheet is attached to the shell and channel'whether by bolting or welding.

The second letter represents the shell type, detailing the arrangement of inlets and outlets as well as the presence of longitudinal baffles and distribution plates.

The third letter denotes the rear end head type, covering the connection between the shell and the second tube sheet and the channel closure method'bolted or welded.

For example, a BEM shell and tube heat exchanger features a bonnet header, a single pass shell, and a fixed tube sheet.

Flow Types

To better understand the function and operation of shell and tube heat exchangers, they are categorized based on their characteristics. One key characteristic for classification is the type of flow they utilize.

Shell and tube heat exchangers can be grouped into three main flow types: parallel, counter, and cross. Each type has distinct design, operational, and application requirements, and often these flow types are used in various combinations.

In parallel flow, both the shell and tube sides enter the heat exchanger at the same end and move directly to the opposite end. This means that the temperature change in each fluid is uniform, with each fluid heating or cooling by the same degree.

Counter flow involves fluids moving in opposite directions. They enter the heat exchanger from opposite ends and exit from the other ends. This flow arrangement is the most efficient and commonly used type of heat exchanger due to its effective heat transfer capabilities.

Cross flow heat exchangers feature fluids flowing perpendicular to each other at a 90-degree angle. In this design, one fluid changes state (as seen in steam condensers where cooling water absorbs steam), and the other fluid, which remains in its liquid form, absorbs the heat.

Fixed Tube Sheet TEMA Type M

A fixed tube sheet heat exchanger consists of straight tubes that are attached at both ends to stationary tube sheets, which are welded directly to the shell. This type of heat exchanger is known for its straightforward design and construction, making it one of the most economical options available. However, it has a limitation in handling significant temperature differences between the fluids, though this issue can be mitigated by incorporating an expansion joint. One of the main advantages of a fixed tube sheet heat exchanger is its simplicity in cleaning and maintenance.

U Tube Heat Exchanger

The U-tube shell and tube heat exchanger derives its name from the U-shaped configuration of the tubes. The inlet and outlet valves are positioned at one end of the heat exchanger, with fluids entering through the upper portion of the tube sheet and exiting from the lower portion. The tubes are free to expand at the U-bend, enabling the U-tube heat exchanger to accommodate significant temperature differences.

The placement of inlet and outlet valves in a U-tube shell and tube heat exchanger can vary depending on the design. In the diagram below, the shell fluid enters from the top left and exits from the bottom right.

Floating Head Heat Exchanger TEMA Type S

The floating head design resembles the U-tube design but without the U-shaped tubes. In this design, one end of the tubing is fixed to a stationary tube sheet, while the other end is left unattached, allowing it to expand and float freely. This flexibility enables the floating head design to handle significant temperature differences as the tubes expand. Additionally, this type of heat exchanger is easy to clean and inspect because the tubes can be conveniently removed.

Floating head designs are categorized into four distinct types:

• TEMA P Outside Packed Stuffing Box
• TEMA W Outside Packed Lantern Ring
• TEMA S Floating Head with Backing Device
• TEMA T Pull Through

TEMA Type T or Type AKT

The tube bundle can be removed from the shell, featuring an unusual clearance between the baffle's outer diameter and the inner diameter of the main shell.

TEMA Type S or Type AES

Removing the tube bundle necessitates its disassembly. This design maintains a standard clearance between the baffle diameter and the inner diameter of the shell.

TEMA Type P or Type AEP

The shell side is sealed using packing rings that are compressed into a stuffing box, enabling the tube sheet to slide back and forth smoothly.

TEMA Type W or Type AJW

The fluids are sealed by O-rings separated by a lantern ring.

Scraped Surface Heat Exchanger

In certain applications, where heat transfer involves viscous or sticky substances, materials can build up on the internal surface of the heat exchanger. Scraped surface heat exchangers are specifically designed for these situations, featuring scraping blades that continuously remove accumulated material from the interior surface. Structurally, they resemble other heat exchangers but are equipped with rows of scraping blades inside the cylinder.

The blades in a scraped surface heat exchanger are spring-loaded and rotate, effectively scraping the surface while draining liquid from the exchanger. Typically, four blades are used, though the number can vary. However, increasing the number of blades also raises the cost of the heat exchanger. In practice, a higher blade count is often unnecessary since the intervals between scrapings are already brief.

Scraped surface heat exchangers can be installed either horizontally or vertically, with the vertical configuration being preferred as it allows liquids to flow downward naturally due to gravity.

Chapter Five: What are the benefits of shell and tube heat exchangers?

Shell and tube heat exchangers are versatile and serve various applications across multiple industries. Their diverse configurations allow them to be customized to meet the specific needs of different manufacturing and production processes.

In refineries and factories, shell and tube heat exchangers are integrated into processing equipment to facilitate efficient heat transfer. They represent about 65% of the heat exchangers available in the market.

Cost

A significant advantage of shell and tube heat exchangers is their cost-effectiveness. They are considerably more affordable compared to plate-type coolers.

Heat Capacity

Heat exchangers must accommodate a broad range of temperatures, depending on the application. Their capacity to handle extreme temperatures is crucial for maintaining production and operational efficiency. Shell and tube heat exchangers offer high-temperature resilience and can be customized to meet various conditions.

Pressure

Due to the high pressure they endure, shell and tube heat exchangers require robust materials, which can make them heavy or costly, especially if nickel alloys are used. High pressure can lead to significant issues and production delays. The shell and tubes are engineered and tested to handle pressure fluctuations while complying with ASME and PED standards.

Pressure Loss

Pressure loss represents a loss of energy and results in reduced downstream pressure, slowing the flow velocity. Shell and tube heat exchangers are designed to minimize pressure loss within acceptable limits. They are also equipped to manage issues like fouling of the shell and tubes, thereby preventing related problems.

Adjustments

The design of shell and tube heat exchangers is highly adaptable to various production processes. Adjustments can be made to pipe diameter, quantity, length, pitch, and arrangement to suit specific application requirements.

Thermal Expansion

The multi-tube structure of shell and tube heat exchangers accommodates thermal expansion between the tubes and shell, making them suitable for handling flammable and toxic fluids.

Chapter Six: What are the standards and regulations for shell and tube heat exchangers?

Shell and tube heat exchangers are essential in the food, beverage, dairy, and pharmaceutical industries for producing consumer products while ensuring safety, efficacy, and consistency. These sectors are regulated by the Food and Drug Administration (FDA), and the equipment used must comply with FDA guidelines and standards.

3-A Sanitary Standards (3-ASSI)

3-A Standards for the dairy industry are created through the collaboration of equipment manufacturers, professional sanitarians, and product processors. These stakeholders work together to establish the 3-A Sanitary Standards for the dairy, food, and pharmaceutical sectors, emphasizing the importance of clean-in-place (CIP) systems and ensuring equipment can be easily cleaned manually.

3-ASSI upholds 70 sanitary standards for these categories:

• Vessels
• Fillers
• Valves & Fittings
• Pumps & Mixers
• Heat Exchangers
• Conveyors & Feeders
• Instruments
• Concentrating Equipment
• Farm/Raw Milk
• Cheese & Butter Equipment

American Petroleum Industry Standard 660 (API660)

API 660 is a standard established by the API that covers the design, materials, fabrication, inspection, testing, and shipping of shell and tube heat exchangers used in the petroleum and petrochemical industries. This standard applies to various equipment, including heat exchangers, condensers, coolers, and reboilers.

Tubular Exchangers Manufacturers Association (TEMA)

TEMA has established the most commonly used standards for shell and tube heat exchangers. The organization provides specific identifications for each configuration of these heat exchangers and categorizes them into three industry types. The criteria for these categories depend on the operational demands of the industry and whether a more robust and durable heat exchanger construction is needed.

American Society of Mechanical Engineers (ASME)

ASME Code VIII addresses the pressurized components of a shell and tube heat exchanger, specifically the tubes within the shell. Section VIII is most relevant to these heat exchangers, though Sections II and V may also be applicable, covering material specifications and testing requirements.

Pressure Equipment Directive (PED)

Products manufactured in the United States for use internationally must comply with global standards. One such standard is the PED, which applies to shell and tube heat exchangers. The PED guidelines include:

• Materials
• Harmonized standards
• Essential requirements
• Market surveillance
• Conformity assessment

These rules are adopted to ensure the safety of both products and workers.

Canadian Registration Number (CRN)

The CRN (Canadian Registration Number) is issued by a Canadian province or territory to approve a boiler, pressure vessel, or fitting for use within that jurisdiction. In this context, a shell and tube heat exchanger is classified as a pressure vessel. The CRN approval process can be complex, as each province or territory has its own set of requirements.

The CRN classification of heat exchangers is based on factors such as size, fluids, and their pressure and temperature ranges. Specifications vary for lethal and non-lethal substances, with detailed charts guiding manufacturers' designs.

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Conclusion

• A shell and tube heat exchanger (STHE) is a type of heat exchanging device constructed using a large cylindrical enclosure, or shell, that has bundles of tubing compacted in its interior.
• The use and popularity of shell and tube heat exchangers is due to the simplicity of their design and efficient heat exchange rate.
• The components of a shell and tube heat exchangers include the shell, shell cover, tubes, channel, channel cover, tube sheet, baffles, and nozzles.
• In the shell and tube heat exchanger process, one fluid flows through the tubes while the other fluid flows through the shell.
• The stipulations for the manufacture, design, and construction of shell and tube heat exchangers are outlined by the Tubular Exchangers Manufacturers Association (TEMA).