Types of Heat Exchangers

Heat exchangers are devices used for efficient heat transfer between two separate substances. There are many types of heat exchangers, each with different applications in various sectors. Heat exchangers work by transferring heat from one medium to another. They can be used in heating, cooling, and industrial systems. Heat exchangers are integral to many industrial processes, allowing for the maintenance of optimal temperatures. With different types of heat exchangers, their design can be tailored to specific application requirements and parameters. If you want to learn about the types of heat exchangers distinguished based on heat transfer methods, construction, and the type of medium they can work with, read the article below.

Types of Heat Exchangers Based on Heat Transfer Methods

Based on the method of heat transfer between fluids, heat exchangers can be classified into contact and non-contact types. The latter is much more commonly used in industry. Below, you can find the answer to why this is the case.

Contact Heat Exchangers

Contact heat exchangers are devices where fluids have direct contact with each other. This allows for achieving high heat conduction coefficients. Moreover, such exchangers facilitate easy heat exchange between more than two streams of fluids. However, it's worth noting that in most industrial applications, heat exchange without mixing the fluids is necessary. This is achievable only through the use of non-contact heat exchangers, which will be described below.

Non-contact Heat Exchangers

Non-contact heat exchangers are devices that enable the transfer of thermal energy between two fluids without direct contact. Recuperators, which are the most commonly used heat exchangers in the industry, fall into this category. Plate and shell-and-tube exchangers belong to non-contact heat exchangers as well.

Non-contact heat exchangers are prevalent in the industry for a simple reason - fluids participating in many processes have different physicochemical properties and should not be mixed (e.g., oil and water).

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Types of Heat Exchangers Based on Construction

Types of heat exchangers based on construction can be divided into plate heat exchangers and tubular heat exchangers. They differ not only in construction but also in application. Below is their characterization.

Plate Heat Exchangers

Plate heat exchangers are devices composed of metal plates whose task is to efficiently exchange heat between fluids at different temperatures without mixing them. Thanks to their construction, they allow for quick and effective heat transfer using various mechanisms such as convection. The plates inside the exchanger create channels through which fluids flow. This provides a large contact surface of the plates with the fluids, enabling efficient transfer of thermal energy. Plate heat exchangers are widely used in the industry, including cooling and heating processes, helping to save energy and increase the efficiency of heating and cooling systems. The following types of plate heat exchangers are distinguished based on their construction:

• Lutowane: These are heat exchangers with a compact construction; the copper soldered connection ensures high tightness, hence high heat exchange efficiency, due to low thermal losses.
• Screwed: Plate heat exchangers with lower tightness compared to soldered ones but allowing easier servicing and cleaning of the device.

Tubular Heat Exchangers

Tubular heat exchangers, also known as shell-and-tube heat exchangers, are commonly used devices for efficient heat exchange between two fluids. Their construction is based on a cylindrical shell with tubes inside. The main purpose of such a configuration is to allow one fluid to flow around the tubes while the other fluid flows through the tubes. This facilitates heat transfer between fluids. Shell-and-tube heat exchangers find applications in various industries, including chemical, food, and power generation. Thanks to their effectiveness and ease of operation, they are an integral part of heat exchange processes in different sectors.

Types of Heat Exchangers Based on the Medium

Heat exchangers are commonly associated with systems where both media are liquids (e.g., water or glycol). However, it's worth noting that heat exchangers can transfer heat between gases or between gases and liquids. The following pairs of fluids, handled by heat exchangers, are distinguished:

• Liquid-liquid,
• Gas-gas,
• Liquid-gas.

Below are descriptions of the individual pairs of media that can cooperate with various heat exchangers.

Liquid-Liquid Heat Exchangers

Liquid-liquid heat exchangers are devices used for efficient heat exchange between two liquids with different physicochemical parameters (e.g., operating temperature, freezing temperature, density). Examples of such systems include water-water, water-oil, and water-glycol. These exchangers find applications in various fields such as the chemical industry and power generation. They enable effective and energy-efficient heat transfer between different media, contributing to the optimal utilization of available energy.

Gas-Gas Heat Exchangers

Gas-gas heat exchangers are used to transfer heat between two gas streams. One example of such an exchanger is the air-air system, where heat is transferred between two air streams. Another example is the flue gas-air exchanger, where heat from the flue gases is recovered and further utilized in heating systems, such as heating air in combustion chambers of furnaces and drying solid fuels, e.g., wood or coal. Gas-gas heat exchangers are used in various industries, including the chemical industry, power generation, and the food industry.

Liquid-Gas Heat Exchangers

Liquid-gas heat exchangers are devices that enable efficient heat exchange between a liquid and a gas. These exchangers operate with the following pairs of fluids:

• Water-air,
• Glycol-air.

The water-air heat exchanger is commonly used in heating and air conditioning systems, where water heated in boilers transfers heat to the air, which is then distributed in buildings. On the other hand, glycol-air heat exchangers are used in various industries and residential buildings. For example, the glycol-air exchanger (GWO) aims to increase the efficiency of ventilation devices used to heat air in winter and cool it in summer.

Types of Heat Exchangers Based on Fluid Flow Direction

• Co-current: These are devices where heat exchange occurs between two fluid streams flowing in the same direction. This is the least efficient way of heat exchange (in terms of flow direction).
• Counter-current: Heat exchangers with much greater efficiency compared to co-current systems. They allow achieving similar temperatures of fluids at the inlet and outlet of the exchanger.
• Cross-flow: These are exchangers where one stream flows relative to the other at a right angle. A 100% cross-flow arrangement is rare - it occurs as a component of flow in a tubular exchanger.

Types of Heat Exchangers Based on the Material They Are Made Of

Heat exchangers differ from each other in terms of the materials they are made of. One of the popular materials used for heat exchangers is stainless steel (316L). This material has high strength and excellent thermal properties. Another commonly used material is titanium, which is characterized by high corrosion resistance even in salty environments (e.g., seawater) while being lightweight and durable. Heat exchangers made of titanium are often used in the chemical and petrochemical industries, as well as in applications such as pool heat exchangers.