Exchangers are easily one of the most important and widely used pieces of process equipment found in industrial sites. Regardless of the particular industry in question, it will likely require some type of temperature regulation, and for that exchangers are likely to come into play. Exchangers may be used for either heating or cooling, however, in the industrial sector, particularly within plants and refineries, they are overwhelmingly used for cooling. Let’s dive a little deeper into what they are, why they are needed, how they work, and how they are classified.
What Are Industrial Heat Exchangers?
As their name implies industrial heat exchangers are pieces of industrial equipment which are designed to exchange or transfer heat from one medium to another. The heat exchange may be for the primary purpose of heating up elements or cooling it down. Within the industrial sector, cooling tends to be the more prevalent function in order to prevent equipment or volatile substances from overheating. There are many different types of heat exchangers, each with their own advantages and drawbacks, yet tailored to best suit different purposes and industries.
Why Are Heat Exchangers Needed?
Heat exchangers have a very broad range of industrial applications. They are used as components of air conditioning and cooling systems or of heating systems. Many industrial processes call for a certain degree of heat to function; however, typically great care must be taken to keep these processes from getting too hot. Within industrial plants and factories heat exchangers are required to keep machinery, chemicals, water, gas, and other substances within a safe operating temperature. Heat exchangers may also be used to capture and transfer steam or heat exhaust that is released as a byproduct of a process or operation so that the steam or heat can be put to better use elsewhere, thereby increasing efficiency and saving the plant money.
How Do Heat Exchangers Work?
Different types of heat exchangers work in different ways, use different flow arrangements, equipment, and design features. One thing that all heat exchangers have in common is that they all function to directly or indirectly expose a warmer medium to a cooler medium, hence, exchanging heat. This is usually accomplished by using a set of tubes housed within some type of casing. Heat exchanger fans, condensers, belts, coolants, additional tubes and lines, along with other components and equipment work to increase heating and cooling efficiency or improve flow.
Classification of Heat Exchangers
Heat Exchangers are generally classified by one of the following four metrics:
- The nature of the heat exchange process
- The physical state of the fluids
- The heat exchanger’s flow arrangement
- The design and construction of the heat exchanger
The Nature of the Heat Exchange Process
This first heat exchanger classification method refers to whether or not the substances between which the heat is being exchanged come into direct contact with each other or not, or whether they are separated by a physical barrier, such as the walls of their tubes.
Direct Contact Heat Exchangers – Direct contact heat exchangers bring the hot and cold fluids into direct contact with each other within the tubes rather than relying on radiant heat or convection. Direct contact is an extremely effective means of transferring heating since the contact is direct, but naturally for direct contact to be used it must be safe, or even desired to have the fluids come in contact with each other. Direct contact heat exchangers may be a good choice if the hot and cold fluid are merely different temperature variations of the same fluid, or if the fluid mixture is a desired or irrelevant part of the industrial process.
Indirect Contact Heat Exchangers – Indirect contact heat exchangers keep the hot and cold fluids physically separated from each other. Typically indirect contact heat exchangers will keep the hot and cold fluids in different sets of pipes and instead rely on radiant energy and convection to exchange the heat. This is commonly done to prevent contamination or pollution of one fluid by the other.
The Physical State of the Fluids
Heat Exchangers may also be classified based on the physical state of the hot and cold fluids. For instance:
- Liquid – Gas
- Liquid – Solid
- Gas – Solid
If the heat exchanger uses direct contact then the classification “immiscible liquid – liquid” may also exist to refer to liquids that will not blend together. For example oil and water are immiscible.
The Heat Exchanger’s Flow Arrangement
The arrangement of the hot and cold fluid’s flow within the heat exchanger is another major way of categorizing them. The three major categories based on flow arrangement are: parallel-flow, countercurrent-flow, and cross-flow.
Parallel-Flow – In parallel-flow heat exchangers the hot and cold fluids enter the heat exchanger from the same end and flow parallel to each other.
Countercurrent-Flow – In countercurrent-flow heat exchangers the hot and cold fluids enter the heat exchanger from opposite sides and flow toward each other.
Cross-Flow – In cross-flow heat exchangers the hot and cold fluids enter the heat exchanger at different points and as they travel through the heat exchanger they cross paths with each other, often at right angles.
It is important to keep in mind heat exchanger maintenance and servicing. Maintenance and servicing will vary based on the particular type of heat exchangers in question and their design and construction. Keeping heat exchangers well-maintained is critical for optimal performance.