Heat exchanger

A heat exchanger is a specialized system designed to transfer thermal energy between a source and a working fluid.

These systems are essential for both heating and cooling processes in modern industry. They can function by having fluids in direct contact or by separating them with a solid wall to prevent mixing. Because of this versatility, heat exchangers are used in diverse settings. You will find them in power stations, chemical plants, and petroleum refineries. They are also vital for natural-gas processing, sewage treatment, and residential air conditioning.

The efficiency of heat transfer depends heavily on the flow arrangement of the fluids. In a parallel-flow arrangement, both fluids enter the exchanger at the same end and travel in the same direction. This setup is useful when the goal is for both fluids to reach the same temperature. In a counter-flow arrangement, the fluids enter from opposite ends and move in opposite directions.

This counter-current design is the most efficient method. It maximizes heat transfer because the average temperature difference remains higher along the length of the device. The third primary type is cross-flow, where the fluids travel roughly perpendicular to one another.

Engineers categorize heat exchangers by their maximum operating temperature. Low-temperature models typically function up to 500–650°C. These generally do not require highly specialized materials or complex design considerations. In contrast, high-temperature heat exchangers can operate at 1000°C or even 1400°C.

To maximize performance, these devices are designed to increase the surface area of the wall between fluids. They also aim to minimize resistance to fluid flow. Features like fins or corrugations can be added to increase this surface area and induce turbulence.

The double-pipe heat exchanger is the simplest industrial model. It consists of one pipe placed inside another, with one fluid in the inner pipe and the second in the annular gap between them. While these are inexpensive to design and maintain, they have low efficiency. Because they occupy significant space at large scales, modern industries often replace them with more advanced models. However, their simplicity makes them excellent tools for teaching the fundamental rules of heat exchanger design to students.

A shell-and-tube heat exchanger is a robust design often used for high-pressure applications.

These units can handle pressures greater than 30 bar and temperatures exceeding 260°C. In this system, one fluid flows through a bundle of tubes, while a second fluid flows outside the tubes within a large shell. Baffles are installed inside the shell to support the tubes and prevent them from sagging. Baffles also direct the fluid flow and increase turbulence, which enhances heat transfer.

Engineers must carefully choose tube diameter and thickness to manage costs, fouling, and internal pressure.

Plate heat exchangers offer a compact alternative using multiple thin metal plates stacked in a bundle.

Gaskets are placed between the plates to create independent channels, allowing different fluids to flow without mixing. The surfaces of these plates are often corrugated. These patterns increase the available surface area and create turbulent flow to improve thermal performance. These exchangers are manufactured in various styles, such as plate and frame or spiral designs, to meet specific industrial needs.

Some heat exchangers are designed to manage phase changes in a fluid. A condenser is a device that cools hot gas or vapor until it reaches the point of condensation. This process transforms the gas into a liquid form.

Conversely, a boiler or evaporator facilitates vaporization, where a liquid transforms into a gas. In a surface condenser, cooling water typically runs through tubes while steam moves through the unit. These two-phase systems are critical components in large-scale energy production and chemical processing.