Plate fin heat exchanger

A plate-fin heat exchanger is one of the most efficient and compact heat exchangers.

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History

During World War II, the American aircraft industry was in need of light, compact and efficient heat exchangers for its large transport aircraft. Some companies were able to develop the necessary technology to make the Brazed Aluminium Plate-Fin Heat Exchangers (PFHE). Due to their exceptional thermal efficiency they quickly found a place in the cryogenics process.

Parts are still used today in aircraft applications, however, aluminum PFHEs are typically used with liquids due to their operating temperature limitations and stainless steel, inconel, or titanium are used for hot gases, such as engine bleed air.

Description

Plate fin heat exhangers are made by the stacking of corrugated sheets (fins) separated by planar sheets (or separation sheet that usually has a clad alloy that will melt at a lower temperature than the parent aluminum during brazing to bond the various components) and closed on the sides by lateral bars. The gaps between constitute a fluid layer. A core is made of a great number of layers. The exchanger can be made of one or more cores. The number of plate and fin layers, the size of the plates and fin, the height of the fin and the type of fin are engineered for optimum performance. The core is assembled (stacked) and typically held together by tack welding a weld rod to the top and bottom layer of the core. The stacked core is then placed within a fixture that exerts force on the individual pieces to keep them in contact. The part is then vacuum brazed in an environmentally-controlled room to ensure high quality and reliability. After brazing the core is typically heat treated or aged in order to increase its strength. Manifold ducting and mounting brackets are then welded in place as required, and any required paint or coating can be added.

Plate-fin heat exchangers can be designed for use with any combination of gas, liquid, and two-phase fluids.

Heat exchange Area

Fins

• Plain fins
• Perforated fins
• Serrated fins
• Lanced and offset fins
• Louvered fins
• Herringbone or wavy
• Characteristic dimensions

Advantage

As mentioned in the history of PFHEs, they are extremely efficient and lightweight. Making them an ideal solution for applications where weight (and therefore performance) is critical, such as aircraft applications. They are also very reliable parts under uniform operating pressures. A quality braze joint is often stronger than the parent material being brazed. Failures (other than those due to fatigue) often occur within the headering of the part.

PRHEs are also highly customizable by being able to use different fin geometries and circuiting.

Drawback

The biggest drawback of PFHEs is the price. Due to the enormous amount of labor that is involved in stacking the layers of the core, and the various processes (fin manufacturing, brazing, heat treating, and welding) a small part (12"W x 12"H x 4"D) can cost thousands of dollars.

Area of application

The fin type heat exchangers have wide range of applications such as:

• Radiators
• Economisers for Boilers

Flow arrangement

Layout

Stacking

Cost

Although the estimated price range is unknown, it is very expensive.

See also

• Plate heat exchanger
• Shell and tube heat exchanger
• Heat transfer
• LMTD