What is the production process of brazed plate heat exchangers?

Brazed Plate Heat Exchanger in a Vacuum Furnace

A brazed plate heat exchanger is a type of device that is brazed in a special modern vacuum furnace, where the temperature often reaches up to 450 degrees Celsius. As most may know, it consists of metal sheets, usually steel ones. They are simply called exchanger plates. They are corrugated. There is a small space between them creating regular channels that allow the flow of media that exchange heat. Heat exchange occurs through these plates.

Production of heat exchangers and its impact on durability

✅ Heat exchangers are subjected to different brazing processes during production, depending on the pressure resistance parameters that need to be achieved. As a result, some heat exchangers are approved for standard pressures of 10, 20, or 30 bar.

✅ There are also models subjected to a slightly different and longer treatment process. This process is more time-consuming and energy-intensive, but it allows for the creation of high-pressure heat exchangers capable of withstanding pressures of up to 40 or 45 bar. This enables the market to offer devices that can handle high-pressure gas systems, such as Freon used in heat pumps.

The entire process and outcome are legally regulated by the so-called Pressure Equipment Directive (also known as the PED), which introduces uniform requirements in this regard for all heat exchangers approved for sale within the EU.

The plates of a BPHE and their efficiency

The heat exchange coefficient in a brazed plate heat exchanger is greater than in conventional exchangers (shell-and-tube, which are becoming increasingly rare today), if we compare performances at comparable flows. Thanks to the fact that the plate is only 0.3-0.4mm thick (in the case of Nordic Tec exchangers), heat transfer is practically perfect - especially since the amount of material needed to make a plate model is relatively small.
✅ Plate heat exchangers, of this type, sometimes called BPHE (Brazed Plate Heat Exchanger), thus create a compact structure but with a large heat transfer area. Therefore - there is an obvious trend to replace old types of exchangers with plate models.

The Process of Joining Steel Plates - How is a Plate Exchanger Made?

The soldering process can only be carried out properly on modern, highly technologically advanced production lines - specifically in vacuum furnaces. Otherwise, we would have no guarantee that the device will be durable and leak-proof. Nordic Tec exchangers are widely recognized as one of the most durable soldered devices.

The bond of plates in heat exchangers - that is, solder

During processing in vacuum furnaces, the solder material (usually copper, less frequently nickel) is heated to enormous temperatures, where it becomes plastic. In this way, the desired physical shapes and properties can be obtained - and then the material is rapidly cooled. The smoother this process, the more durable the exchanger will be in any installation. By the way, the material cooling also takes place through a heat exchanger - but that's another story, it is a different type of exchanger, always an important element of the vacuum furnace.

This process, if carried out in an advanced and modern production line, creates solders that are resistant to various media and pressures. This is the key to creating a device that can work in different applications, with different types of installations and parameters. This makes the exchanger universal.

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Rust-like copper traces on the surface plates of the heat exchanger

Interestingly, the production process of plate heat exchangers, particularly the use of copper brazing, results in the sides of the exchanger having a characteristic rusty-copper color. Additionally, copper traces can sometimes be found on the front or back plates, often near the connections. These appear as dots or sometimes lines, which some interpret as cracks or rust marks on the exchanger.

Of course, this is nonsense; heat exchangers cannot rust before being exposed to water (even if made from very low-quality steel). Similarly, these "cracks" cannot actually be cracks. Imagine steel that cracks under normal conditions—it’s nearly inconceivable.

Corrugated Plates for Exchangers - Why and How Does It Work?

If the exchanger plates were flat, the flow of media through the device would be simple. There would be almost no pressure drops at the water (or other medium) inlet, which would rather be beneficial. However, years of research and work on improving heat exchange technology, carried out by various companies, mainly in Scandinavia, Germany, and the USA, have unequivocally shown that a corrugated plate induces turbulent flow (in simpler terms, more agitated), which gives better results in heat exchange. Heat exchange performance in terms of temperature is better, despite using a plate of the same surface area.

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Actaulisation: 11-2024