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What is Plate Fin Heat Exchanger?

What is a Plate Fin Heat Exchanger (PFHE)?

A Plate Fin Heat Exchanger (PFHE), also known as a Aluminium Brazed Heat Exchanger, is a type of compact heat exchanger characterized by its very high heat transfer surface area to volume ratio. It consists of corrugated fins sandwiched between parallel flat plates (called parting sheets) to create individual flow passages. These layers are then stacked together and brazed into a single, solid block.

Core Principle: Multiple fluids (often two or more) flow through alternating layers of fins. Heat is transferred from the hotter fluid(s) to the colder fluid(s) through the parting sheets. The fins dramatically increase the surface area and create turbulence, leading to extremely efficient heat transfer in a very small volume.

Key Components and Their Functions

The PFHE is a “built-up” structure, much more complex than a simple tube or plate:

1. Parting Sheets: These are the flat plates that separate the different fluid streams. They form the primary pressure boundary between fluids.
2. Fins: Corrugated sheets (typically in a wave, offset, or perforated pattern) that are sandwiched between the parting sheets. Fins are the most critical component and serve two main functions:
   1. Increase Surface Area: They provide the primary secondary surface for heat transfer.
   1. Enhance Heat Transfer: Their design creates turbulence and disrupts the boundary layer, improving thermal efficiency.
   1. Provide Mechanical Support: They act as stiffeners between the parting sheets, allowing the core to withstand pressure.
3. Headers/Manifolds: The inlet and outlet chambers attached to the core block. They distribute the incoming fluid into the many fin layers and collect the outgoing fluid. Their design is crucial for ensuring even flow distribution.
4. Bars/Side Bars: Metal bars that close off the edges of the fin layers, sealing the sides of the passages and forcing the fluid to flow through the finned channels.
5. Brazing: The manufacturing process. The entire stack of parting sheets, fins, and bars is assembled in a vacuum furnace with a brazing material (e.g., aluminium-silicon alloy). When heated, the brazing material melts and flows, creating a strong, leak-tight monolithic core.

Common Applications

PFHEs are the undisputed champion in applications where compactness, weight, and multi-stream capability are paramount:

1. Aerospace: Environmental Control Systems (ECS) and avionics cooling on aircraft. Their light weight is critical.
2. Cryogenic & Gas Liquefaction: The most common application. Used in:
   1. Air Separation Units (ASUs) to produce liquid nitrogen, oxygen, and argon.
   1. Liquefied Natural Gas (LNG) plants.
   1. Helium and Hydrogen liquefaction.
3. Automotive: As intercoolers and charge air coolers in turbocharged engines.
4. Chemical & Process Industries: For heat recovery between multiple clean process streams.
5. Nuclear: Cooling of inert gases.