C. Patnaik, Stratview Research, Raipur, India
The laws of thermodynamics include: energy can neither be created nor destroyed, it can only be converted from one form to another; and heat always moves downhill, from hotter objects to the colder objects, unless the direction of heat flow is reversed using external energy.
When it comes to heat exchangers and their workings, these—along with the Zeroth law of thermodynamics—are the most important principles. Heat exchangers have been well-known since the later part of the 1870s, the first time they were made and used in the food and beverages industry.
As the years passed, heat exchangers were employed in several industries, such as refrigeration, space heating and power stations with advanced modifications. They became an important technology and helped modern equipment in transferring heat from gas-to-gas, liquid-to-liquid or liquid-to-gas in an efficient manner.
What are heat exchangers, and why are they so significant to successful operations?
UNDERSTANDING THE TECHNOLOGY: HEAT EXCHANGER TYPES
Simply put, a heat exchanger is a system that is used to transfer heat from one medium to another, mainly through conduction and convection, and occasionally through radiation. This gives heat exchangers a unique utility in cooling and heating processes; therefore, they are often used in space heating, refrigeration, petroleum refineries, natural gas processing, power stations, petrochemical plants and sewage treatment plants, among others.
Heat exchangers come in several types, and are differentiated mainly based on two factors: the working mechanism and flow type.
Based on the working mechanism, three main types of heat exchangers prevail: shell-and-tube heat exchangers, plate heat exchangers and air-cooled heat exchangers. The workings and differences between these variants of heat exchangers are discussed in the following sections.
Shell-and-tube heat exchangers. The name says it all: a shell-and-tube heat exchanger consists of multiple tubes fitted inside a pressured vessel, known as a shell (FIG. 1). One fluid flows through the tubes and the other flows over them in the vessel to aid the transfer of heat between them.
Some new technological advancements in shell-and-tube heat exchangers include finned tubes, single- or two-phased heat transfer, and single-, two- or multiple-pass configurations, among others. Shell-and-tube heat exchangers are undergoing advancements in their selection technology, as well. For example, in 2022, Bell & Gossett, an XYLEM brand, announced that it has integrated ESP-Thermal, an online plate and shell-and-tube heat exchanger selection program, into its ESP-Systemwize selection tool. This addition will help engineers select and optimize the best heat exchanger to meet their goals and requirements.
Double-pipe heat exchangers are another form of shell-and-tube heat exchangers that employ a simple design utilizing two concentric, cylindrical pipes. One fluid flows through a smaller tube and another one passes through the larger tube, helping facilitate the exchange of heat between the two fluids.
Air-cooled heat exchangers. Air-cooled heat exchangers, like the general schematic shown in FIG. 2, work on the principles of convection and conduction to dissipate heat from the fluid to the outer atmosphere. In the process, the fluid is passed through the tubes and the air stream is passed over the tube, helping dissipate the heat. The air streams are produced from the fans mounted on the unit. These exchangers are efficient in cooling or condensing water, chemicals or any other fluid. Continuous efforts and investments by market players are being put into improving the technology.
Plate heat exchangers. Plate heat exchangers (PHEs)—or plate-type heat exchangers—consist of multiple thin, corrugated metal plates bundled together (FIG. 3). They are either bolted or welded together, and two passages are created between the plates: one for cold fluid and another for the hot fluid. Various modifications in the PHE provide plate-fin heat exchangers, plate-and-frame heat exchangers, plate-and-shell heat exchangers and spiral-plate heat exchangers, among others.
PHEs are a mature technology: the first patent for a PHE was awarded to Albrecht Dracke of Germany in 1878, and they gained popularity in the 1990s. According to research by the author’s company, among these three types, PHEs have a greater market presence. Reasons for this include:
Additionally, development and innovations continue in the segment to make PHEs more environment-friendly. For example, in July 2022, Alfa Laval signed an agreement with SSAB to co-develop the world's first PHE to be made using fossil-free steel. The goal is to have the first unit made with hydrogen (H2)-reduced steel ready for 2023.
Flow configurations. Heat exchangers can be categorized depending on their flow configuration—the direction of flow of the fluids with respect to each other within the heat exchangers. Four types of flow arrangements are prevalent and detailed in TABLE 1:
MARKET TRENDS
Impact of COVID-19. The heat exchanger market was adversely affected by the global pandemic in 2020 (and after). The end-user industries of heat exchangers (e.g., oil and gas, petrochemicals, refining) suffered heavily due to a decline in demands, manufacturing restrictions, supply chain disintegration and shortage of labor, among other factors. These conditions lead to a significant decline in the heat exchangers market of 11.9% in 2020, which caused the market value of heat exchangers to fall below $13 B that year.
However, in 2021, after many restrictions were lifted, the resumption of operations in the petrochemical, chemical, oil and gas, and energy sectors buoyed the demand for heat exchangers. This helped the market grow at a CAGR of 5.2%—with this resurgent growth rate, the market is expected to reach a value of $18.3 B by 2027.
Asia-Pacific region leading the way. Countries like China, India and Japan are maintaining record-breaking growth rates in industries like oil and gas, petrochemical, carbon capture, etc. The heat exchanger segment is also strong in the Asia-Pacific region with a share of 33.9% in 2021. Factors include:
The Asia-Pacific region is also investing heavily to develop sustainable technologies, which is proving to be a boon for the heat exchangers market.
Sustainability. At the 26th Conference of Parties (COP 26) organized in Glasgow, Scotland, 197 countries negotiated and agreed on the Glasgow Climate Pact, which reaffirms the target of holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursue efforts to limit it at 1.5°C above pre-industrial levels. This has had a major effect on manufacturing companies, which are now impelled to pursue efforts to manufacture products while considering the environment.
Several companies are focusing on developing environmentally-friendly steel for their heat exchangers, as well as using environmentally-friendly cooling fluids, such as water, to absorb and transfer waste heat.
Takeaways. The heat exchangers market is emerging from a pandemic-caused growth slump and is poised to rebound due to renewed demand as restrictions continue to be lifted. Major market players are now investing heavily in environmentally-friendly new technologies.
With the re-establishment of supply chains, a surge in required skilled labor and a rise in demand from end-use industries, the future of heat exchangers is bright. HP
CHANDANA PATNAIK is a Senior Content Writer at Stratview Research and an experienced technical writer with a passion for exploring and explaining the latest technology developments in the heat and refrigeration industry and their applications across other major segments, including the oil and gas, petrochemicals and chemical industries. She is a regular contributor to various magazines and blogs, and creates insightful and engaging content that informs readers of the latest trends and developments in her areas of expertise.