This article covers everything you need to know about shell and tube heat exchangers.
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The shell and tube heat exchanger (STHE) is a highly utilized device engineered for thermal energy exchange. It comprises a sizable cylindrical shell housing numerous parallel tubes. These tubes are strategically organized within the shell to enable heat transfer between two different fluids. Appreciated for their efficiency and versatility, shell and tube heat exchangers come in multiple designs tailored to specific applications, tube configurations, and various attributes.
These heat exchangers are favored for their straightforward and efficient design in transferring heat. They operate by circulating a fluid or steam through the shell, which subsequently warms the tubes within. Achieving optimal performance often involves passing the fluid through the tubes four times, generally considered an effective tactic for heat transfer efficiency.
Shell and tube heat exchangers are among the most widely used types of heat exchangers in industrial process engineering due to their reliability, versatility, and adaptability to a broad range of heat transfer applications. The comprehensive design process for a shell and tube heat exchanger requires advanced computational techniques and precise engineering parameters to maximize thermal efficiency, mechanical integrity, and operational safety. Key components of these industrial heat exchangers include the shell, shell cover, tubes, channel, channel cover, tube sheet, baffles, and nozzles. For quality assurance and industry compliance, the design and manufacturing standards for shell and tube heat exchangers are regulated by the Tubular Exchanger Manufacturers Association (TEMA) and often align with ASME (American Society of Mechanical Engineers) codes.
Before manufacturing a shell and tube heat exchanger, several critical data points and process requirements must be gathered from end-users or system designers. These include volumetric or mass flow rates, inlet and outlet temperatures for both hot and cold fluids, pressure ratings, maximum pressure drops, resistance factors, as well as the physical and chemical properties (such as viscosity, density, and thermal conductivity) of the fluids being processed. Additionally, essential fabrication details like tube count, pipe dimensions, and overall shell diameter play significant roles in determining heat exchanger performance and lifecycle. In addition to these technical requirements, detailed thermal calculations and mechanical specifications help ensure the production of a custom shell and tube heat exchanger that aligns precisely with the system's operating conditions and the specific needs of the application. Correct engineering at this stage helps achieve optimal heat transfer rates, minimize energy loss, and maintain safe operation over long periods.
The shell of a shell and tube heat exchanger is typically constructed from high-grade pipes or welded metal plates, selected based on their ability to withstand high operating pressures, extreme temperatures, and resist corrosion from aggressive fluids. Shell materials commonly include carbon steel, stainless steel, and special alloys designed for process environments such as chemical processing plants, oil refineries, and power generation facilities. The internal diameter of the cylindrical shell is carefully engineered to minimize bypass and the gap between the baffles' perimeter and the shell wall, maximizing overall thermal efficiency and preventing dead zones that can decrease performance or cause fouling.
The choice of channel or head type for a shell and tube heat exchanger varies according to service duty, maintenance needs, and the cleaning regime anticipated throughout the equipment lifecycle. Bonnet-type heads—permanently attached and non-removable—are typically used when the head does not require frequent maintenance or cleaning. For applications that require periodic inspection or mechanical cleaning of the tube bundle, channels with removable covers (either flanged or welded) are selected. When regular access to the channel and tubes is necessary, especially for services prone to fouling, a removable cover for the channel is essential. These considerations are crucial in food processing, pharmaceutical, and petrochemical industries where operational uptime and sanitary conditions are paramount.
Tubes are the primary surface where heat exchange takes place in a shell and tube heat exchanger. Tube bundles are typically welded or extruded and made from carbon steel, stainless steel, titanium, Inconel, copper, or specialized alloys for high performance and corrosion resistance. Standard tube diameters of 0.625 inch (16mm), 0.75 inch (19mm), or one inch (25mm) are most common in compact shell and tube heat exchangers, while custom diameters can be used for process optimization. The tube wall thickness is selected based on required pressure ratings, temperature limits, mechanical stresses, and resistance to internal and external corrosion, with standard tube lengths ranging from 6 to 24 feet (2 to 7 meters). Longer tubes reduce the required shell diameter but may cause higher shell-side pressure drop, influencing system pump selection and energy efficiency.
Tube arrangement (spacing and pattern) significantly affects heat transfer performance, ease of cleaning, and fouling rates. Specialized tube enhancements, such as finned or corrugated tubes, may be utilized in applications demanding higher heat transfer coefficients or when processing viscous or fouling-prone fluids. Selecting proper tube material and surface enhancements is key for improving energy recovery, reducing maintenance costs, and extending equipment lifespan in demanding heat exchanger service environments.
The tube sheet is a precision-machined plate or perforated sheet featuring a grid of holes for the insertion of the heat exchanger tubes, anchoring and supporting the tube bundle at both ends of the cylindrical shell. Tube sheets are manufactured from corrosion-resistant materials compatible with the process fluids to prevent galvanic corrosion and chemical attack. The shell extends beyond the tube sheets and is sealed on both ends to form an enclosed, pressurized chamber covered by the exchanger's heads, allowing for efficient heat transfer while minimizing the risk of leakage or product contamination. Proper design and material selection for tube sheets ensure the mechanical integrity of the heat exchanger, especially under high-pressure or temperature cycling conditions.
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, a process frequently subjecting these units to extreme temperature differentials and thermal expansion. Over time, repeated heating and cooling cycles can cause expansion and contraction in the metal components. Without appropriate allowances for these dimensional changes, internal stresses may develop, increasing the risk of mechanical failure such as tube buckling, tubes being dislodged from tube sheets, shell deformation, or nozzle misalignment. Such failures can significantly compromise the pressure boundary and affect both system safety and production uptime.
To absorb and compensate for thermal stresses and maintain long-term durability of the heat exchanger, an expansion joint is integrated into the shell design. This flexible component is engineered to mitigate thermal and pressure-induced movements, protecting weld seams, tube-to-tubesheet joints, and nozzle fittings from overstress. Carefully engineered expansion joints are critical in high-temperature services, such as steam condensers, reboilers, or power plant heat exchangers, where temperature fluctuations are pronounced.
Tube pitch is the distance measured from the centerline of one tube to the centerline of its adjacent tube within the tube sheet. This critical design parameter determines the arrangement of tubes—commonly in triangular or square pitch patterns—inside the tube bundle. The square pitch is generally preferred in applications requiring ease of mechanical cleaning and minimal fluid turbulence, making it suitable for fluids prone to fouling. In contrast, triangular and rotated square layouts can enhance heat transfer coefficients by promoting greater turbulence, albeit at a potential cost to ease of maintenance. The tube pitch arrangement also affects pressure drop through the shell side, channeling vapor and optimizing flow distribution for efficient heat exchange and minimal energy consumption.
Baffles are engineered plates strategically placed on the shell side of a shell and tube heat exchanger to guide and control fluid flow across the tube bundle. They serve multiple functions: enhancing fluid velocity, increasing turbulence, improving overall heat transfer coefficients, and reducing the risk of fouling by disrupting laminar flow that leads to the deposition of unwanted material. Baffle spacing, configuration, and cut (such as segmental or double segmental) directly influence the exchanger's performance, including pressure drop, heat transfer rate, and structural support for the tubes. In long, horizontal shell and tube heat exchangers, baffles also stabilize the tube bundle, mitigating vibration-related tube damage and extending the operational life of the system. Selection of proper baffle design is essential for optimizing shell-side heat transfer and minimizing maintenance needs in both new installations and heat exchanger retrofits.
Tie rods and spacers are integral structural components that secure the position of baffles and maintain the desired spacing between them within the shell. The number, diameter, and arrangement of tie rods and spacers depend on baffle count, tube bundle configuration, and shell size. Tie rods are affixed to the tube sheet and run the length of the bundle, providing stability under pressure or flow-induced vibrations. Properly installed tie rods and spacers help preserve shell side flow patterns, prevent baffle movement, and ensure the overall mechanical reliability and safety of the heat exchanger in demanding industrial applications.
When sourcing a shell and tube heat exchanger for industrial applications, it is important to evaluate factors such as thermal design, pressure and temperature ratings, construction materials, maintenance requirements, compliance with industry standards (TEMA, ASME), and lifecycle cost. Leading heat exchanger manufacturers provide engineering support to customize designs that match specific process requirements, enhance energy efficiency, and extend service intervals. Comparing quotes and equipment specifications, reviewing warranties, and investigating manufacturer experience in key industries such as chemical processing, oil & gas, food & beverage, or HVAC can help ensure the optimal choice for your heat exchange application. Regular inspection, cleaning, and adherence to manufacturer-recommended maintenance schedules further ensure long-term, reliable heat exchanger performance.
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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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:
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.
Removing the tube bundle necessitates its disassembly. This design maintains a standard clearance between the baffle diameter and the inner diameter of the shell.
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.
The fluids are sealed by O-rings separated by a lantern ring.
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.
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.
A significant advantage of shell and tube heat exchangers is their cost-effectiveness. They are considerably more affordable compared to plate-type coolers.
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.
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 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.
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.
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.
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 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:
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.
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.
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.
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:
These rules are adopted to ensure the safety of both products and workers.
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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