PLANT MANAGEMENT
GROWING MARKETS Due to the inherent advantages of diffusion bonded PCHEs, many industries are adopting this evolving technology to improve heat transfer in various applications.
OIL AND GAS
Te compact, efficient heat transfer capabilities of PCHEs are ideal for many oil and gas applications, including preheaters, superheaters, gas compression coolers, high- temperature recuperators, and liquified natural gas (LNG) exchangers.
ALUMINIUM HEAT SINK APPLICATIONS Aluminium heat sinks are popular for the thermal management of many critical devices where weight is a factor, including automotive and aerospace. Aluminium heat sinks are also commonly used with electric batteries.
Te most common aluminium alloys used in heat sinks and exchangers are the 6000 series alloys. However, magnesium and silicon are the primary alloying elements and are difficult to join with methods such as brazing. “In many heat sink applications, brazing flux is often prohibited. Terefore, vacuum brazing remains a joining technology using filler metals based on an aluminium-silicon eutectic alloy. However, these alloys have a melting point of 580°C, very close to the melting point of the base material, thus providing only a tiny process window to achieve high-quality bonds,” says Broich. He notes that PVA TePla has developed a diffusion bonding process to successfully join high alloyed aluminium materials such as 6061 over the years.
OPTIMISING FURNACE DESIGN FOR DIFFUSION BONDING Tere are various approaches to furnace design and process implementation for diffusion bonding of PCHEs. Advances in high vacuum furnace hot presses allow superior pressure control and rapid cooling systems that improve bonding, increase yields, and significantly decrease cycle time. Manufacturers such as PVA TePla offer multi-cylinder systems with large pressing plates that accommodate various parts. Te largest, the company’s MOV 843 HP, can process substrates as large as 950mm x 1,300mm, which is quite a large area for diffusion bonding. Te pressing force is
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8,000kN. Research is underway to increase this geometrical limitation as well. Te integrated press provides remarkably consistent pressure across the entire surface by controlling and synchronising each cylinder. Te MOV also comes with built- in pressure transducers along the bottom of the pressing plate. Te individual hydraulic cylinders can be adjusted in the software to achieve uniformity even over large areas based on sensor feedback. Broich points out that high-bonding
strength is critical for applications involving PCHEs in extreme settings. “It requires a high-strength design [when a high vacuum hot press is needed] of the pressing unit [pressing rams and platens) to transfer 800 or 1000 tons at 1,000°C or even higher temperatures.” In addition, the pressing unit should
have a design that minimises the mass within the hot zone while achieving uniform force distribution throughout the working space and pressing plate. “Te design of a diffusion bonding machine should enable the shortest cycle times possible while saving energy by reducing its thermal mass; this is very important to productivity and cost- effectiveness,” he points out.
To produce a high-quality diffusion bonded PCHE, working with an expert partner can be essential for manufacturers that require process and technology support. “Most of our customers are not familiar with this technology. We support them with basic process technical knowledge so they can correctly use the machine to produce a high-quality diffusion bonded PCHE,” explains Broich. Due to the rapidly expanding need
for this precision technology in the USA, PVA TePla is opening a diffusion bonding technology centre in California. A full- scale industrial furnace that matches the capabilities offered by the firm in Germany will be available. PVA TePla will be able to demonstrate the machine’s bonding capabilities, run R&D samples, and provide processing services. “In both the USA and Germany, we can demonstrate the quality of the bonds before a customer decides to invest in a machine. We handle most of the elements of process development to prove the technology and assist in scaling up to production volumes. Alternatively, we can provide full-scale contract processing for customers if they outsource production,” concludes Broich.
PCHEs are well suited for a wide range of demanding applications
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