1. Overview

1.1  Technical Definition and Microscopic Features

Printed Circuit Heat Exchanger (PCHE) represents a paradigm shift in heat exchange technology from macroscopic structures to micro-scale precision manufacturing. Unlike conventional shell-and-tube or plate heat exchangers, PCHE does not rely on tube bundles or rubber gaskets for fluid isolation. Instead, it is fabricated based on manufacturing principles analogous to printed circuit boards (PCBs) in the electronics industry, through two core processes: photochemical etching and vacuum diffusion bonding.

Structurally, the fluid channel diameters of PCHEs typically range from 0.1 mm to 2.5 mm, with channel widths between 0.2 mm and 5 mm. This micron-to-millimeter scale channel design significantly increases the heat transfer area per unit volume, delivering a heat transfer surface area density of up to 2,500 m²/m³, whereas conventional shell-and-tube heat exchangers achieve only approximately 100 m²/m³. This 25-fold higher compactness enables PCHEs to achieve the same heat transfer capacity with only 1/4 to 1/6 the volume of shell-and-tube units, and a significant reduction in weight.

1.2 Historical Evolution

The conceptual prototype of PCHE technology emerged in the early 1980s at the University of Sydney in Australia. Researchers sought to resolve the inherent contradiction between heat transfer coefficients and pressure-bearing capabilities in conventional heat exchangers, proposing the concept of fabricating fluid channels on metal plates via chemical etching. In 1985, Heatric was founded in Australia, marking the technology’s formal entry into commercialization. Although initially applied in industrial refrigeration, its “compact and high-pressure resistant” attributes were quickly embraced by the offshore industry. On the premium “deck space” of offshore platforms, every ton of weight saved by a PCHE translates to a substantial reduction in capital expenditure (CAPEX).

In 1990, Meggitt PLC, the British aerospace and defense conglomerate, acquired Heatric and relocated its operations to Poole, UK. Backed by Meggitt’s capital and technological resources, PCHE technology rapidly established itself as the standard configuration for offshore natural gas processing, significantly raising the industry’s technology threshold.

1.3 Global Market Landscape

For a long time, the global PCHE market has been characterized by an oligopolistic structure. Besides Heatric, a handful of players including Sweden’s Alfa Laval, U.S.-based Vacuum Process Engineering (VPE), and Kelvion command the lion’s share of the market.

2. Core Manufacturing Processes and Mechanical Design Principles

The PCHE manufacturing process combines subtractive manufacturing (i.e., etching) and solid-state joining (i.e., diffusion bonding). This section outlines these two core processes and their associated mechanical design principles.

2.1 Photochemical Etching (PCE): Fabricating Microscopic Flow Channels

The fabrication of PCHE flow channels via this process introduces negligible mechanical stress and no Heat-Affected Zones (HAZ) – a key differentiator from stamping or mechanical machining.

Process Flow Analysis

First, Computer-Aided Design (CAD) is utilized to draw complex flow channel geometries (such as zigzag, serpentine, or sinusoidal patterns). Next, a photosensitive photoresist is coated onto the surface of the metal plates (e.g., 316L stainless steel, 2205 duplex steel, nickel-based alloys). Following exposure and development, the flow channel pattern is transferred onto the plate surface. Finally, the unprotected bare metal areas are chemically etched away, forming channels with semi-circular or semi-elliptical cross-sections.

Design Advantages

Chemical etching removes material in both depth and lateral directions (undercut), resulting in a rounded, near-semicircular channel cross-section, which reduces stress concentration and improves tolerance to ultra-high pressures. Furthermore, the etching process is not constrained by flow channel complexity. Engineers can design zigzag channels with high Nusselt numbers to enhance fluid turbulence, breaking the boundary layer, thereby enhancing convective heat transfer even at low Reynolds numbers.

2.2 Vacuum Diffusion Bonding: Atomic-Level Solid-State Joining 

Diffusion bonding is the core process that imparts high-pressure and extreme temperature resistance to PCHEs, and it represents the fundamental differentiator from brazed plate heat exchangers.

Mechanism and Process

The etched plates are stacked alternately based on hot and cold process fluid paths, then placed into a vacuum furnace. Under high temperatures below the melting point of the parent material (typically at a fraction of the melting temperature, material- and process-dependent) and high mechanical pressure, atoms on the plate contact surfaces gain sufficient energy to migrate and diffuse across grain boundaries. This process is generally divided into four stages: surface micro-contact, grain boundary migration, pore elimination (volume diffusion), and full metallurgical bonding.

Technical Advantages

• Parent Metal Strength Retention: Diffusion bonding requires no intermediate brazing filler metal and involves no melting, so the microstructure at the bond line is virtually identical to that of the parent material. This means the PCHE functions essentially as a ”solid block”, with its pressure-bearing capability dependent solely on the thickness of the flow channel ligaments and side walls—unrestricted by bond line strength limitations.
• Gasket-Free Structure: This design completely eliminates the rubber gaskets—the weakest link in conventional heat exchangers—enabling PCHE to withstand an extreme temperature range of -196°C to 850°C without the risk of leakage caused by gasket aging.

2.3 Definition of Mechanical Structural Parameters 

In the mechanical design of PCHEs, several key geometric parameters directly dictate the pressure-bearing capacity and heat transfer efficiency:

• Channel ligaments: The unetched regions between adjacent flow channels, serving as the primary load-bearing ribs. Their width must be determined via Finite Element Analysis (FEA) based on the design pressure.
• Residual Plate Thickness: The thickness of the metal plate remaining after flow channel etching, which directly dictates the heat conduction distance between cold and hot fluids. The microchannel design of PCHEs allows for ultra-thin residual wall thicknesses, thereby minimizing thermal resistance.
• Block Ends & Margins: The unetched regions at the edges of the plates, designated for welding headers and side plates. Sufficient width must be reserved to ensure adequate welding strength.

3. Development History of PCHEs in China

• Inception Phase (2014-2016): China State Shipbuilding Corporation (CSSC) took the lead in initiating PCHE R&D efforts. In 2016, the company successfully developed the country’s first prototype, validating the feasibility of domestically engineered etching and diffusion bonding processes.
• Engineering Application Phase (2017-2020): Domestic PCHEs moved beyond laboratory validation and entered practical application, with initial deployments in Brayton cycle power systems and other high-end fields.
• Commercial Expansion Phase (2020–Present): Enterprises represented by Shanghai Plate Heat Exchange Equipment Co., Ltd. (SHPHE) have leveraged continuous technological iteration and upgrading, with their product parameters gradually extending to ultra-high pressure and ultra-high temperature domains.

4. Application Analysis of Key Industrial Scenarios

4.1 Hydrogen Energy Industry

Hydrogen exhibits extreme physical properties—it is highly difficult to compress and has an extremely low liquefaction temperature—posing a dual challenge for heat exchanger design and operation.

• Hydrogen Refuelling Station Pre-cooling Systems

To meet the 70 MPa high-pressure fast-refuelling standard, heat exchangers must withstand a design pressure of 100 MPa while adapting to frequent pressure cycling conditions. Conventional brazed plate heat exchangers are highly susceptible to cracking and failure under cyclic pressure loads. The PCHEs launched by manufacturers represented by SHPHE have a rated design pressure of up to 100 MPa, and their fully diffusion-bonded structure boasts excellent fatigue resistance, making them perfectly suited for this demanding operating condition.

• Liquid Hydrogen Supply Chain

In Liquid Hydrogen Vaporizer applications, PCHEs must endure ultra-low cryogenic temperatures. The diffusion-bonded structure eliminates the risk of gasket leakage, making it one of the few compact devices capable of stable operation in this temperature zone.

4.2 Advanced Power Systems

Supercritical Carbon Dioxide (sCO₂) Power Generation is regarded as the core of next-generation thermal power and concentrated solar power. Under the same high-temperature heat source conditions, its efficiency is 3-5 percentage points higher than that of the steam Rankine cycle. The Recuperator in this cycle operates in a high-temperature (500-700°C) and high-pressure (20-30 MPa) environment. Diffusion-bonded structures can maintain high-pressure strength above 600°C. Additionally, microchannel design can effectively cope with the drastic changes in physical properties of the supercritical fluid near the pseudo-critical point.

4.3 Nuclear Energy Engineering

In Generation IV nuclear reactors (such as High-Temperature Gas-cooled Reactors (HTGR)) and fusion reactors (ITER/CFETR), PCHEs are used as Intermediate Heat Exchangers (IHX) for cooling systems. Microchannel PCHEs have been widely studied and considered as candidates for Intermediate Heat Exchangers (IHXs) in CFETR-related power conversion systems and thermal-hydraulic validation loops. The atomic-level bonding interface formed by diffusion bonding possesses excellent sealing properties against small-molecule gases like helium, meeting the rigorous standards of nuclear-grade safety.

5. Conclusion and Outlook

PCHEs represent a generational leap in the manufacturing technology of thermal equipment. Through the integration of photochemical etching and vacuum diffusion bonding processes, precise control over fluid flow and heat transfer is achieved at the microscale, while the macrostructure maintains mechanical strength comparable to that of the base material.

Chinese enterprises represented by SHPHE have acquired the capability to manufacture products rated for ultra-high pressure of 100 MPa and ultra-high temperature of 850°C, and have realized large-scale engineering applications in natural gas, hydrogen energy, and supercritical CO₂ Brayton cycle systems. Of course, there is still room for improvement in ultra-compactness (weight reduction optimization) and anti-clogging operation and maintenance technologies. With the continuous breakthroughs in materials science (e.g., high-temperature nickel-based alloys) and flow channel optimization design, PCHEs are bound to play an irreplaceable cornerstone role in the global energy system’s transition toward low-carbonization adaptation.