The Definitive Guide to Heat Exchangers: Everything You Need to Know
When it comes to heat exchangers, there are a lot of things to consider. What type is best for your needs? What are the basic principles underlying heat exchangers? How do you choose the right one for your application? In this definitive guide, we will answer all of these questions and more. We’ll start by discussing the fundamental principles underlying heat exchangers. Then we’ll take a look at the different types of heat exchangers and their characteristics. Finally, we’ll provide some tips on how to select the right heat exchanger in Canada for your needs.
Heat Exchangers Explained
Heat exchangers transfer heat between two or more fluids that are at different temperatures. Essentially, heat exchangers allow heat energy to flow from a hotter fluid to a cooler one, all without the two fluids touching. This is important because it avoids cross-contamination while allowing heat to be transferred efficiently.
Heat Exchanger Thermodynamics
All heat exchangers, regardless of type or design, operate under the same fundamental principles—namely the, First, and Second Laws of Thermodynamics.
The First Law of Thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. In the context of heat exchangers, this means that in a closed system, the combined heat energy of both process streams is the same before and after the heat exchanger (ignoring losses).
The Second Law of Thermodynamics states that heat always flows from hot objects to cold objects, and never the reverse. This is because it is thermodynamically impossible for heat to flow from a colder object to a hotter one. In other words, heat energy will always flow from the hotter fluid to the cooler fluid in a heat exchanger.
Heat Exchanger Design Characteristics
There are many different types of heat exchangers, each with its own unique design characteristics. Some of the most important design characteristics to consider include:
How the fluids flow through the heat exchanger. The three most common flow configurations are concurrent, countercurrent, and crossflow.
Cocurrent flow: Both fluids flow in the same direction. This is the simplest and most efficient type of heat exchanger but does not allow for temperature cross (the outlet of cold fluid to be hotter than the outlet of hot fluid, or vice-versa).
Countercurrent flow: The fluids flow in opposite directions. This type of heat exchanger allows for temperature crosses and is the most desirable configuration for maximum heat transfer.
Crossflow: The fluids flow perpendicular to each other. This type of exchanger is typically used in HVAC and other processes when the low-pressure drop is required on the air side.
Method of Construction
Heat exchangers can be made from a variety of materials (glass, plastics, metal, etc.), but the most common materials in petrochemical processes use metals for most applications.
Carbon and stainless steel heat exchangers typically utilize a welded construction of various components that have been forged, formed, machined, and drilled.
Brass and copper-nickel exchangers may use similar components as steel exchangers but are typically brazed instead of welded.
Static vs. Dynamic
In a static heat exchanger, the fluid is stationary. In a dynamic heat exchanger, the fluid is in motion. Dynamic heat exchangers are more efficient than static heat exchangers as they have higher heat transfer coefficients due to forced convection.
Components and Materials
The type of heat exchanger you choose is highly dependent upon the type of fluids, the inlet and outlet temperatures, flow rates, and maintenance access requirements.. Typical exchanger components include shells, tubes, plates, forgings, flanges, pipes, bolting, and gaskets.
Shells are the primary pressure component that encases the heat exchanger and contains the process fluids. They can be made of materials such as stainless steel, carbon steel, or nickel alloys.
Tubes are the heat transfer medium between fluids and are placed inside the heat exchanger in a bundle. They are often made of materials such as stainless steel, carbon steel, nickel alloys, or cupronickel. Low-fin tubes can be used in place of regular tubes to increase surface area and heat transfer.
Heat Transfer Mechanisms
How heat is transferred is called the heat transfer mechanism. There are two key types of heat transfer mechanisms used in heat exchangers – single-phase and two-phase transfers.
Single-phase heat transfer: The heat is transferred between the two fluids by heat energy conduction through a shared medium (eg, tube wall). This type of heat transfer does not involve any phase change, liquids stay liquids, and gases remain gases.
Two-phase heat transfer: The primary mode of heat transfer is via latent heat during a phase change – a gas condensing to liquid or a liquid evaporating to gas. A tremendous amount of heat is transferred during phase change, so these types of heat exchangers can be relatively small given the amount of heat transferred.
Types of Heat Exchangers
two important types of heat exchangers are shell and tube heat exchangers, and air-cooled heat exchangers.
Shell and Tube Heat Exchangers
This is the most common type of heat exchanger. It consists of a bundle of tubes that are placed inside a shell. One fluid flows through the tubes and heat is transferred to or from a fluid outside the tubes. Baffles support the tubes and direct the fluid streams outside the tubes. Shell and tube heat exchangers are available in a variety of sizes and designs, and heat exchanger manufacturers often custom design and fabricate them in order to maximize heat transfer efficiency while minimizing cost.
Most of the heat exchangers used in process industries are shell and tube heat exchangers as they are robust and suitable for a wide range of applications.
Air Cooled Heat Exchangers
An air-cooled heat exchanger is like a shell and tube heat exchanger without the shell. It consists of a bundle of fin tubes that are exposed to the atmosphere (air). . A hot fluid flows through the tubes and the heat is transferred to the outside air. Most air-cooled heat exchangers have a fan that blows air over the tube bundle to increase cooling – this is called forced convection (like blowing on the hot soup).
Air-cooled heat exchangers are used in various process industries, but they are a key component in HVAC systems, especially refrigeration.
Heat Exchanger Selection Considerations
When selecting a heat exchanger, there are a number of considerations that must be taken into account:
Fluids, Fluid Stream, Other Properties:
The type of fluids, their flow rates, temperatures, and their physical properties must be taken into account when selecting a heat exchanger. For example, if the fluid is a gas, then a heat exchanger with fin tubes and a large footprint may be required. If the fluid stream is a liquid, then a heat exchanger with a small heat transfer surface may be sufficient.
Depending on the desired thermal outputs, heat exchangers can be classified as heaters, coolers, or regenerative heat exchangers. Heaters transfer heat from a heat source to the fluid, coolers transfer heat from the fluid to a heat sink, and regenerative heat exchangers transfer heat between two fluids. This will influence the kind of exchanger you choose.
Purchasing a heat exchanger that is too big for the given space is a waste of money while purchasing one that is too small will limit the heat transfer capacity. It is important to take into account the size limitations when selecting and designing a heat exchanger.
The cost of the heat exchanger is an important consideration. Some heat exchanger types are more expensive up-front than others, but long-term operating costs should be considered along with the purchase price should when making a decision. The most economically efficient heat exchanger at purchase is not always the best option as it could cost more in cleaning, maintenance, and repairs down the road.
Heat Exchanger Applications
The heat exchanger you select will be determined by the application. Some common heat exchanger applications include:
Heat exchangers are used in HVAC systems to transfer heat between the air and fluid. The fluid is usually steam, water, or glycol, and the heat exchanger helps to regulate the temperature of the air in the system. The most common types of heat exchangers used in HVAC systems are shell and tube heat and air-cooled heat exchangers.
Heat exchangers are used in process industries to transfer heat between two process streams and change the temperature of each process stream without mixing. The most common types of heat exchangers used in process industries are shell and tube and air-cooled heat exchangers.
Heat exchangers are a critical component in many industries. They are used to transfer heat between two fluids, and they come in a variety of designs and sizes. When selecting a heat exchanger, it is important to take into account the type of fluid, the fluid stream, the thermal outputs, the size limitations, and the cost. Finding the perfect heat exchanger for your application may require the expertise of a heat exchanger manufacturer in Canada.
Heat Exchanger Maintenance and Troubleshooting
Heat exchangers are a critical component of many industrial processes, and they must be properly maintained to ensure optimal performance. Heat exchanger maintenance typically involves cleaning the heat exchanger and inspecting it for damage. If damage is found, it is important to repair or replace the heat exchanger as soon as possible.
Other services for heat exchangers include:
Engineering Support and Troubleshooting
If you are having problems with your heat exchanger, our engineers can help. We offer engineering support and troubleshooting services to help you identify the problem and find a solution.
Full & Partial Re-Tubes, Tube Plugging
This is the process of removing all or part of the heat exchanger tubes and replacing them with new tubes. This is typically done when the heat exchanger is damaged or corroded.
…And much more.
Contact Altex Industries for Heat Exchangers in Canada and Tier One Service
Altex is a leading heat exchanger manufacturer in Canada, and we offer a variety of heat exchangers to meet your needs. We also offer engineering support, troubleshooting, re-tubing, and repair services. Contact us today to learn more about our heat exchangers in Canada and how we can help you.