Explanations of liquid-to-liquid heat exchangers with a list of manufacturers
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Liquid-to-liquid heat exchangers (LLHE) are heat exchangers that heat or cool liquids by transferring heat from one liquid to another without the liquids making contact. The exchange of heat is accomplished by the liquids coming into close contact through conductive metal barriers, such as plates, tubes, or pipes. Liquid-to-liquid heat exchangers are an energy efficient solution for heating and cooling liquids to dissipate or eliminate heat from a process.
Heat transfer refers to a process by which the flow of heat or thermal energy moves from one place to another place due to differences in temperature. It is achieved by advection, conduction, convection, or radiation. The method of heat transfer used by liquid-to-liquid heat exchangers is convection or conduction.
The most common design of liquid-to-liquid heat exchangers has fluids of different temperatures separated by a conducting medium with one fluid flowing through metal tubes as the other fluid flows around the tubes. Transfer of heat by convection takes place by conduction through the tube walls. This method of liquid-to-liquid heat exchangers is referred to as ordinary or common heat exchange, which is unlike regenerative and cooling tower types.
The applications of liquid-to-liquid heat exchangers are classified as regenerative or non-regenerative where non-regenerative involves two fluids flowing together while regenerative has fluids flow at different times. The effectiveness of heat transfer by a liquid-to-liquid heat exchanger is measured by the heat transfer coefficient or U-factor, which is a measure of the heat transfer rate per unit area and temperature difference. A high coefficient indicates a better heat transfer performance.
All types of liquid-to-liquid heat exchangers work by passing heat from a hot fluid to a cold fluid across the surfaces of metals where the heat from one fluid passes into another fluid without making contact. Fluid velocity, turbulence, surface area, and temperature differential determine the efficiency of the transfer process. Although the function of all types of liquid-to-liquid heat exchangers is the same, the different designs of each type determine their effectiveness and efficiency.
Liquid-to-liquid heat exchangers are effective at transferring heat with the level of efficiency, cost, and space being factors that determine the type of liquid-to-liquid heat exchanger that will be used. There are certain dynamics of liquid-to-liquid heat exchangers that need to be considered when determining which liquid-to-liquid heat exchanger is the best choice for an application.
The factors that engineers consider during the selection process are:
| Features of Liquid-to-Liquid Heat Exchanger Types | ||||||
|---|---|---|---|---|---|---|
| Brazed Plate | Gasketed Plate | Shell & Tube | Spiral Plate | Plate & Shell | Finned Tubes | |
| Max Temperature | 200°°ä | 200°°ä | >200°°ä | 450°°ä | 600°°ä | 300°°ä |
| Max Pressure | 45 bar | 25 bar | 60 bar | 60 bar | 200 bar | 15 bar |
| Materials of Construction | Cu, 304, 316L | 304, 316L, Ti, C276 etc | 304, 316L, Ti, C276 etc | 304, 316L, Ti, C276 etc | 304, 316L, Ti, C276 etc | GI, MS, CS, 304, 316, Cu, Ni |
| Application | Liquid/Liquid, Gas/Gas | Liquid/Liquid, Condensation | Liquid/Liquid, Condensation Evaporation | Liquid/Liquid, Condensation Evaporation | Liquid/Liquid, Condensation, Evaporation and More | Liquid/Liquid, Condensation Evaporation |
| Access for Mechanical Cleaning | No | Yes | Tube Side Only | Openable Only | Openable Only | Surface Tubes Only |
| Fouling Particle Size Allowed | Very Small | Small | Large | Large | Small | Small |
| Max Viscosity | 1000 cp | 1000 cp | 2000 cp | 5000 cp | 1000 cp | 500 cp |
| LMTD | >1°°ä | >1°°ä | >3°°ä | >5°°ä | >1°°ä | >3°°ä |
Shell and tube liquid-to-liquid heat exchangers consist of a series of tubes encompassed in a cylindrical shell. One fluid flows through the tubes while the second fluid flows around the tubes inside the shell. The conduction between the fluids cools one while heating the other as the temperatures of the two try to equalize. Shell and tube liquid-to-liquid heat exchangers are the most widely used type of liquid-to-liquid heat exchanger due to their ability to endure high pressure and high temperature applications.
The shell of a shell and tube liquid-to-liquid heat exchanger is made of carbon steel, stainless steel, and various alloys in order to withstand high pressure. The tubes are the surface where the heat exchange takes place and are welded or extruded. The walls of the tubes come in different thicknesses in accordance with the required temperature rating, temperature limits, mechanical stress, and resistance to corrosion. The spacing and arrangement of the tubes affects the heat transfer process, impacts cleaning, and determines the fouling rate. Adjustments can be made to the tubes to increase the heat transfer coefficient or when processing special forms of fluids.
A critical part of the placement of tubes in a shell and tube liquid-to-liquid heat exchanger is its tube sheet. A precision formed machined metal plate, the tube sheet has a grid of holes into which the tubes for the heat exchanger are inserted. The tube sheet serves as an anchor and support for the tube bundle at both ends of the cylindrical shell, which extends beyond tube sheets and is sealed at both ends.
With a shell and tube liquid-to-liquid heat exchanger, the process fluid, with a higher temperature, moves through the tubes as the cold or utility fluid moves around the tubes and is contained within the shell. When there is a pressure difference between the fluids, the lower pressure fluid moves through the shell due to the bundled structure of the tubes being capable of withstanding the higher pressure.
A spiral liquid-to-liquid heat exchanger has two concentric spiral flow channels, one for each fluid. One fluid enters the unit at the center and flows outward while the other fluid enters at the outer edge and flows toward the center. The flow of the fluids in a separate channel creates a scrubbing effect that cleans a spiral liquid-to-liquid heat exchanger. If there is fouling in a channel, the pressure created by the blockage causes an increase in flow due to the pressure drop.
The design of spiral liquid-to-liquid heat exchangers can be helical or be two coiled flat panels. They are typically used for heating and cooling liquids that contain solids. Inside the outer casing of the heat exchanger are two long metal strips with spacer studs. The strips are coiled around a central core that forms the spiral body. The spiraling increases the surface area.
The flow of liquids in spiral liquid-to-liquid heat exchangers can take place in three ways, which are counter current, cross, and distributed vapor. With counter current flow, fluids flow in opposite directions. Heat exchangers with this type of flow are mounted vertically to condense vapor or horizontally for high levels of solid particles. In the spiral or cross flow type, one fluid is in a spiral flow while the other is in a cross flow. This type of flow requires passages welded on each side of the heat exchanger. Distributed vapor or spiral flow heat exchangers are mounted vertically for subcooling of condensate and non-condensable fluids. Coolant moves spirally and discharges out the top of the heat exchanger as hot gases are discharged out the bottom.
Plate and frame liquid-to-liquid heat exchangers use a series of stacked steel plates that are sealed with a gasket. The plates form channels through which fluids flow. The design of plate and frame liquid-to-liquid heat exchangers creates turbulence and wall shear stress that produce a high heat transfer coefficient and resistance to fouling. The fluids in the heat exchanger are in two streams in opposite directions with hot fluids moving down one plate while cold fluids flow up the other plate.
Gaskets are used to keep the fluids from mixing. The plates are placed in an alternating pattern to create the counter current flow. Heat is efficiently transferred between the fluids through the plates. The large surface area of the stacked plates and the compact design takes up less area to provide a smaller footprint.
One of the reasons for the wide use of plate and frame liquid-to-liquid heat exchangers, aside from their compact design, is the ease with which they can be cleaned. Plates can be removed and cleaned, which makes it easy to maintain and repair plate and frame liquid-to-liquid heat exchangers. In addition, plates and gaskets can be replaced and reconfigured to adjust for changes in fluid flow or types of heat transfer.
The different types of plate and frame liquid-to-liquid heat exchangers are designed for specific applications. The most common types are gasketed, welded, and brazed, which are differentiated by how the plates are separated and connected. Gasketed plate heat exchangers have elastomeric gaskets that seal the plates together while welded plate heat exchangers have the plates welded together. Brazed plate heat exchangers have the plates bonded with a brazing alloy.
A double tube liquid-to-liquid heat exchanger has two tubes arranged along the same axis and are ribbed inside and out to expand the heat transfer surface. Between the inner and outer tubes is a partition that is the heat transfer surface. The outer tubes are connected to each other to form a flow channel and act as a conductor. The inner tubes carry the working fluid with the transfer of heat taking place through the inner tube. As with other tube to tube types of liquid-to-liquid heat exchangers, the flow of the fluids happens in opposite directions.
The design of double tube liquid-to-liquid heat exchangers enables them to withstand high pressure and high temperatures due to their solid structure. Components are easy to modify and change. Double tube liquid-to-liquid heat exchangers have a flexible design that makes them exceptionally efficient and easy to maintain. They are the simplest form of heat liquid-to-liquid heat exchanger and are manufactured in different sizes and configurations.
The tubes on fin tubed liquid-to-liquid heat exchangers have external fins. The primary fluid flows through the tubes as air or gas flows over the fins. Heat is transferred from the hot fluid to the cold fluid through the fins, which are made of aluminum or copper. The large surface of the fins enhances and accelerates the heat transfer process.
The fins are the critical element in fin tubed liquid-to-liquid heat exchangers since gases have very low thermal conductivity. The style of the fins, with their increased surface area, allows heat to be absorbed or released in a short amount of time. This aspect of their design makes them ideal for applications with limited space but require high heat exchange efficiency.
Fin tube liquid-to-liquid heat exchangers are available in different designs that include straight, helical, and studded fins. A critical aspect of the construction of fin and tube liquid-to-liquid heat exchangers is the connection between the fins and tubes, which is completed using mechanical expansion or welding. As with double tube liquid-to-liquid heat exchangers, fin tubed liquid-to-liquid heat exchangers have a compact design requiring limited area and footprint. Their design decreases energy intake and enhances overall performance.
As hot fluids flow through the tubes, heat is transferred to the fins by convection and radiation. Air or gas flowing over the fins absorbs the heat cooling the fluid inside the tubes. The cooled fluid returns to the heat supply as part of a continuous and ongoing cycle. Fin tubed liquid-to-liquid heat exchangers come in several flexible sizes and provide exceptional heat transfer.
There are many forms of fin tubed liquid-to-liquid heat exchangers that are designed to meet the needs of an expansive number of applications. Straight finned tubes have fins attached parallel to the tubes while helical finned tubes have spiral fins for enhanced turbulence and heat exchange efficiency. Other types of fins are plate, studded, L-shaped, U-tubed, and extruded.
The six liquid-to-liquid heat exchangers described above are some of the primary forms of liquid-to-liquid heat exchangers. Other types include kettle, regenerative, twisted tube, and scraped surface. Each kind of liquid-to-liquid heat exchanger is designed to meet the requirements of an application, process, or operation.
The basic function of liquid-to-liquid heat exchangers is to move heat between fluids without allowing the fluids to mix. It is a tool that is essential for removing heat and transferring energy. The amount of energy transferred and the rate of transfer are related with heat transfer defining how and how fast distribution occurs. Convection, conduction, and radiation happen together in a system with natural convection happening when a heated fluid becomes less dense and rises relative to a cooler fluid.
Industrial processes and energy systems generate waste heat that needs to be captured for reuse. Liquid-to-liquid heat exchangers use different transfer methods to assist in the reuse process. Three areas where liquid-to-liquid heat transfer is essential are industrial applications, data centers, and residents.
The maintenance of precision temperatures in the food and beverage industry is essential for ensuring the quality of food products. Liquid-to-liquid heat exchangers are used to heat and cool food products, including milk, juices, sauces, and soups. Key processes of the food industry are pasteurization, sterilization, and cooling that are used to ensure food safety, quality, and consistency. With beer production, liquid-to-liquid heat exchangers are used to control the temperature of the wort during boiling and cooling after fermentation.
As with the food and beverage industry, the maintenance of temperature control is an essential part of the production of pharmaceuticals. Pharmaceutical manufacturing systems require strict temperature control, including water for injection systems, mixing processes, and sterilization. Since all aspects of pharmaceutical production requires adherence to Food and Drug Administration (FDA) regulations, liquid-to-liquid heat exchangers are an essential part of ensuring the purity of the water being used. Mixing and blending of ingredients necessitates strict temperature controls in order to maintain the integrity and safety of drugs.
During the production of chemical substances, temperature control is essential to ensure the stability of products and the safety of personnel. Liquid-to-liquid heat exchangers manage the temperatures of fluids as they undergo chemical reactions, distillation, and refining processes. High-capacity liquid-to-liquid heat exchangers are used for high volume liquid production when fluids are separated into their components.
During power plant operations and process stages, it is important that fluids be kept at a constant and uniform temperature. Liquid-to-liquid heat exchangers are a critical part of the process. They are used with steam turbines, cooling towers, and equipment involved in the generation of electricity. Important aspects of power generation are efficiency and waste reduction. It is for this reason that liquid-to-liquid heat exchangers are used to cool steam from turbines, making it possible to reuse the water. Liquid-to-liquid heat exchangers help manage the heat balance in power plants to prevent overheating.
As the demand for EV cars grows, battery cooling systems have become essential and more complex. Liquid-to-liquid heat exchangers are a key part of battery systems in EV vehicles. Batteries for EVs have to be maintained at the proper temperature regardless of power demands to ensure battery stability. Liquid-to-liquid heat exchangers provide efficient heat dissipation using a compact and lightweight design, a necessity for modern vehicles.
The heat exchanger transfer works by absorbing heat from the battery coolant and releasing it into the air. This is especially important during rapid acceleration or battery charging. By maintaining a consistent temperature using a liquid-to-liquid heat exchanger, the battery remains stable, prevents thermal runaway, improves efficiency, and extends an EV’s range.
The byproduct of some industrial operations is high temperature wastewater, which can be recovered and used in other ways. Liquid-to-liquid heat exchangers are used to facilitate the process of capturing the high temperatures liquids and transferring it to other systems where it can be used for preheating feed steam and other uses. The practical use of high temperature wastewater helps reduce energy consumption, lowers costs, and prevents environmental damage.
The applications for liquid-to-liquid heat exchangers described above are a small sampling of the many ways that liquid-to-liquid heat exchangers are used for industrial operations. The careful management and control of heat and high temperature liquids is an essential part of ensuring the safe and efficient completion of industrial processing. Liquid-to-liquid heat exchanger manufacturers work with their clients to choose the best liquid-to-liquid heat exchanger for an application.
The various types of liquid-to-liquid heat exchangers take different forms but have similar components. An essential part of all liquid-to-liquid heat exchangers is the metal from which they are made that facilitates the transfer of heat from one medium to another medium. The most widely used liquid-to-liquid heat exchanger is the shell and tube version that consists of a cylindrical tube into which a set of tubes is immersed.
Although there are several factors that are relevant to all forms of liquid-to-liquid heat exchangers, the main consideration is the point where heat is transferred from one medium to another, which takes place through some form of convection material. With shell and tube liquid-to-liquid heat exchangers, the process takes place within the shell or cylindrical tube.
All forms of liquid-to-liquid heat exchangers begin with some form of tubes, which are found in most liquid-to-liquid heat exchangers. The tubes are rolled, shaped, formed, and fitted into a liquid-to-liquid heat exchanger to carry the fluids. Depending on the design of a liquid-to-liquid heat exchanger, there may be one or two sets of tubes that can be straight, twisted, spiraled, or in a customized form.
Since the tubes for a liquid-to-liquid heat exchanger are its main component, they are made of highly durable materials that can withstand the stress and pressure of the heat exchange process. The list of metals includes copper, stainless steel, titanium, copper nickel, and carbon steel.
Some forms of liquid-to-liquid heat exchangers include plates through which the tubes pass. The plate design allows liquid-to-liquid heat exchangers to be more compact and efficient. The positioning of the plates in relation to the tubes varies in this form of heat exchanger in accordance with the heat exchangers design. Plate style liquid-to-liquid heat exchangers are very efficient regardless of their small footprint. The transfer of heat is accomplished quickly.
The enclosures of liquid-to-liquid heat exchangers take several forms depending on the type and design. Since much of the work of liquid-to-liquid heat exchangers takes place under high pressure, enclosures are strong, durable, and exceptionally sturdy to be able to endure the applied stress. As may be assumed, the main metal used to produce liquid-to-liquid heat exchanger enclosures is steel but also includes carbon steel, stainless steels, and various other high performance, highly durable metals. To ensure peak performance, the structure is tightly welded and sealed or bolted, a critical part of the assembly that ensures top performance.
Baffles are used in tube type liquid-to-liquid heat exchangers for higher heat transfer and to increase flow turbulence. In addition, they help support the tubes and control vibrations. Baffles prevent the tubes from shifting, direct the flow, and obstruct vanes or panels.
Liquid-to-liquid heat exchangers take many forms. The components described above are the basic parts upon which all liquid-to-liquid heat exchangers are built. Although these are the basic features of liquid-to-liquid heat exchangers, how they are arranged, configured, and placed varies from one type to another. In addition, special features and structures may be added to enhance a liquid-to-liquid heat exchanger's performance or to customize it to fit a special application. Liquid-to-liquid heat exchanger manufacturers work closely with their clients to shape, design, and assemble a liquid-to-liquid heat exchanger that perfectly fits an application.
The two fluids that exchange heat in a liquid-to-liquid heat exchanger are referred to as the process fluid and utility fluid, with the process fluid being the more valuable and costly of the two. The flow patterns of liquids in a liquid-to-liquid heat exchanger are critical to the heat exchanger's efficiency. They affect the temperature differences between the fluids and determine the speed and effectiveness of heat transfer. Each of the types of flow patterns has their advantages and disadvantages.
The fluid flow patterns of liquid-to-liquid heat exchangers is another method used to categorize them with the three main types of flow patterns being parallel, counter current, and cross flow. In essence, the operation and effectiveness of a liquid-to-liquid heat exchanger is determined by the direction of the fluid flow.
With parallel flow, hot and cold fluids enter the heat exchanger from the same end and flow parallel to each other. The process fluid and utility fluid move in the same direction. At the inlet, the temperature difference between the liquids is the highest and is known as the driving temperature. As the fluids flow through the heat exchanger, their temperatures drop radically, which limits the transfer rate. From the inlet, the hot fluid releases heat to the cold fluid, which absorbs it.
Parallel flow is used in liquid-to-liquid heat exchangers when the temperature difference between the process fluid and utility fluid is low to offer low heat exchange efficiency. Liquid-to-liquid heat exchangers with parallel flow are used for their simple structure and ease of design.
In contrast to parallel flow in a liquid-to-liquid heat exchanger, counter flow has the process fluid and utility fluid enter at opposite ends and flow toward each other. This flow pattern is regarded as the most efficient pattern and is widely used. It maximizes the temperature difference or log mean temperature difference (LMTD), which results in more effective and uniform heat transfer, increased heat recovery, and reduced thermal stress. With counter flow, the cold fluid’s outlet temperature approaches the hot fluid’s inlet temperature. The increased efficiency decreases the need for wide surface area.
Counter flow allows for a large amount of heat to be exchanged over a short distance, making possible for liquid-to-liquid heat exchangers with this flow pattern to be smaller and compact. Due to design requirements, counter flow liquid-to-liquid heat exchangers are more complex.
The cross flow pattern has the process fluid and utility fluid moving perpendicular to each other at an angle. As with the counter flow pattern, the two liquids enter the liquid-to-liquid heat exchanger at different points. During their movement through the heat exchanger, the fluids make contact at different points on an angle. The use of cross flow allows for flexibility in liquid-to-liquid heat exchanger design, especially when one fluid is a gas and the other is a liquid.
The pattern for cross flow liquid-to-liquid heat exchangers provides better heat transfer than parallel flow but is not as efficient as counter flow. More complex flow paths are required by the cross flow pattern but are necessary when there are space constraints for a liquid-to-liquid heat exchanger. Liquid-to-liquid heat exchangers that use the cross flow pattern are flexible, adaptable, and adjustable to fit unique challenges.
Hybrid flow patterns fall outside the typical flow patterns and are engineered with the best features of the other flow patterns. Some shell and tube liquid-to-liquid heat exchangers use counter flow and cross flow with multi-pass and split flow designs that involve the complex arrangements of tubes and plates. In many cases, hybrid flow patterns can increase heat transfer, accommodate a wider range of temperatures, reduce fouling, and be adapted to space restrictions or maintenance issues.
Some of the support regarding the hybrid flow pattern is that it provides for more tube spacing for freer, unrestricted fluid flow. There is increased contact between fluids and the exchange surfaces to maximize heat transfer efficiency.
During the selection process for a liquid-to-liquid heat exchanger, in regard to the flow pattern, the requirements of an application, target temperatures, pressure drop, maintenance, structural material, and space have to be considered. Manufacturers match data regarding an application to a flow pattern that provides the most efficient and effective treatment of fluids. A helpful aspect of working with producers is having rudimentary knowledge of the various aspects of liquid-to-liquid heat exchangers and their components.
Liquid-to-liquid heat exchangers heat or cool products during processing, including filling, drying, and concentration. They are designed to exchange heat between mediums during processing to maximize efficiency. Liquid-to-liquid heat exchangers combine precision temperature control with holding time for various production applications. Their precision and efficiency enhance production and ensure the quality of final products. The many advantages of including liquid-to-liquid heat exchangers in a process are numerous and impactful.
The first factor that producers immediately point out is the efficiency of liquid-to-liquid
heat exchangers. Their ability to quickly transfer heat from one fluid to another fluid for cooling or heating reduces energy consumption and lowers overall operational costs. Uniform temperature control is a critical aspect of modern manufacturing and requires precision and accuracy, all of which is provided by liquid-to-liquid heat exchangers.
All liquid-to-liquid heat exchangers are made of highly durable materials that ensure their longevity and reliability. Modern manufacturing places a great deal of stress on equipment, which can seriously damage the equipment. The steel, carbon steel, and stainless steel used to produce liquid-to-liquid heat exchangers guarantees their strength and long useful life.
The multiple ways that the heat transferred by liquid-to-liquid heat exchangers prevents it from being released into the atmosphere. The efficient cooling of fluids reduces the over consumption of water and eliminates the need for excess energy. All of the factors related to liquid-to-liquid heat exchangers radically reduce their environmental footprint and their effects on the atmosphere. A major selling point that manufacturers point out is the strict compliance of liquid-to-liquid heat exchangers in regard to EPA regulations.
There are many factors that liquid-to-liquid heat exchangers influence regarding cost due to their sturdy construction and exceptional efficiency. Regardless of the type of liquid-to-liquid heat exchanger, each type is constructed to avoid waste and reduce costs. Lower energy consumption and reduced downtime prevent loss of wages and the interruption of production. In addition, their long work life and low maintenance further reduces costs.
Liquid-to-liquid heat exchangers provide sustainable and cost effective cooling solutions. They are an investment in a high quality heat removal process with long term benefits.
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