Choosing the Right Heat Exchanger

Heat exchangers are devices that allow thermal energy to be transferred between two fluids at different temperatures through a wall that separates them, without mixing them. Heat exchangers are widely used in industry, as the transfer of thermal energy is at the heart of many industrial processes (heating or cooling a product, condensing vapors or evaporating liquids, etc.). They are also used to save energy (recovering lost energy, energy optimization), in cars, heating and air conditioning systems, etc.

There are many different types of exchangers to meet specific needs, but most industrial exchangers can be classified into two main categories: tubular exchangers and plate exchangers.

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What are the criteria for choosing a heat exchanger?

If you’re looking for a standard heat exchanger, many manufacturers offer them. If you have a specific requirement, you can ask them for an exchanger with a customized construction, according to the intended use and the environmental conditions in which the equipment will operate. Your choice should be based on the following factors:

Type of exchanger required:
- Tubular heat exchangers are the most common. One fluid circulates inside the tubes arranged inside a shell and a second fluid passes through the space between the tubes inside the shell.
- Gasketed plate heat exchangers are a more compact and less expensive alternative. In these exchangers, the fluids circulate between metal plates without mixing.
- Welded plate heat exchangers work similarly to gasketed plate heat exchangers.
- Brazed plate heat exchangers are mainly used in heating, ventilation, air conditioning, and refrigeration systems.
Operating conditions, including temperature, flow, and pressure of the fluids at the inlet and outlet of the exchanger.
Types of fluids circulating inside the exchanger and their physical and chemical properties.
Installation and maintenance constraints.

Based on these elements, manufacturers will be able to help you size the heat exchanger according to your needs, including its thermal power.

Type of Heat Exchanger	Advantages	Disadvantages
Tubular heat exchanger	Available in large dimensions Supports fluids with large temperature differences at the inlet Withstands very high pressures Minimal pressure losses of the fluids circulating both in the shell and tubes	Good heat transfer between the two fluids, but lower energy efficiency than plate heat exchangers Difficult to maintain, especially for larger exchangers
Gasketed plate heat exchanger	Compact Good energy efficiency due to the turbulence caused by the shape of the plates Self-cleaning Easy to dismantle Possibility of increasing or decreasing the number of plates	Maximum temperatures between 150°C and 200°C Maximum pressure of 25 bar High-pressure losses of both fluids due to turbulence caused by the shape of the plates
Brazed plate exchanger	Very compact Good energy efficiency due to the turbulence caused by the shape of the plates Self-cleaning Able to be dismantled High-pressure cleaning is possible Some can withstand pressures of up to 140 bar	Inlet fluid temperature limited to 200°C High-pressure losses of both fluids due to turbulence caused by the shape of the plates
Brazed plate heat exchanger	Very compact Good energy efficiency due to the turbulence caused by the shape of the plates Self-cleaning High-pressure cleaning is possible Thanks to the welded joints, large temperature differences between the fluids at the inlet are possible Can withstand temperatures between -40°C and +500°C.	Can’t be dismantled Maximum pressure of 30 bar High-pressure losses of both fluids due to turbulence caused by the shape of the plates

Why should you choose a tubular heat exchanger?

Bowman tubular heat exchanger

Tubular heat exchangers were the first to appear on the market, and are still widely used in industry for their excellent reliability, particularly with high-pressure or high-viscosity fluids. Tubular heat exchangers are made up of tubes inside which a fluid circulates. These tubes are inside a shell, which contains a second fluid.

Tubular heat exchangers can have very large dimensions and meet very high heat transfer requirements. They can be more difficult to maintain than plate heat exchangers, precisely because of their size and the possible accumulation of residue inside the tubes. In addition, the efficiency of a tubular exchanger is lower than that of a plate exchanger.

The shell’s material must be compatible with the fluid that will circulate inside it and the material of the tubes must be compatible with both fluids.

Some manufacturers offer heat exchangers with spiral tubes, which are more compact.
Why should you choose a plate heat exchanger?
FISCHER plate heat exchanger

Plate heat exchangers offer many advantages over tubular heat exchangers. They are more compact, lighter, and efficient than tubular heat exchangers of equivalent performance.

Plate heat exchangers can have different designs, but they all work according to the same principle: fluids flow between several very thin, corrugated plates (in the transverse direction of the fluid flow, to create turbulence), which ensures thermal exchange. The fluids can pass through the plates counter-currently, increasing the efficiency of the heat exchange. In certain models, more plates can be added to obtain a larger heat exchange area without significantly increasing the space occupied by the exchanger.

These exchangers are considered self-cleaning since the turbulent flow of the fluids is usually enough to clean any residue. However, this turbulence causes significant pressure losses for both fluids.

There are plate heat exchangers made of specific materials that are lighter and more corrosion-resistant, such as stainless steel heat exchangers, titanium heat exchangers, etc.

Plate heat exchangers can be divided into three main types:
- Gasketed plate heat exchangers: Each plate has a gasket around it and the plate assembly is mounted between two bolted plates. This type of exchanger is modular, as you can easily increase or decrease the number of plates to change the total exchange area and therefore the power of the exchanger. In this way, it is possible to adjust the temperatures of the fluids leaving the exchanger. Maintenance of these exchangers is relatively simple. However, they have limited resistance to high pressures and temperatures. These must not exceed 150°C to 200°C at a maximum pressure of 25 bar. You will also have to ensure that the materials of the plates and gaskets are compatible with the fluids circulating in the equipment.
- Brazed plate heat exchangers: Plates are joined by brazing copper or nickel, resulting in compact, one-piece heat exchangers. These exchangers can withstand temperatures of around 200°C and 30 bar of pressure. However, the number of plates cannot be changed to adjust the exchanger’s power to different needs. They are generally more expensive than gasketed plate heat exchangers, but they are more durable and easier to clean thanks to the possibility of high-pressure cleaning. This type of exchanger can be dismantled for maintenance.
- Welded plate heat exchangers: Plates are welded together, which makes them more resistant than brazed plate heat exchangers. They can also withstand higher temperatures and pressures than other plate heat exchangers (between -40°C and +500°C, at a maximum pressure of 30 bar). However, the number of plates cannot be changed to adjust the exchanger’s power. Although they cannot be dismantled, they are easy to clean under high pressure.