Tue, 16 July, 2024
TWI has recently completed a programme of work, which aimed to develop the diffusion bonding parameters for aluminium-alloys. Aluminium-alloys are of particular interest in the transport sectors, but are typically difficult to join due to fast growing oxides hindering the joining processes.
Industry’s need to drive towards Net Zero in the transport sectors, has meant that printed circuit heat exchanger (PCHE) technology is required to realise increases in efficiency and become more lightweight and compact in size. By manufacturing lightweight shims via photochemical etching, intricate channel geometries can be achieved, enhancing convective heat transfer intensity together with high heat transfer area density, thus decreasing the footprint of the heat exchanger unit. An example of a demonstrator photo chemically etched Al-alloy shim containing micro channels and integrated headers is shown in Figure 1.
Figure 1. Photochemically etched Al-alloy shim containing zig-zag microchannels (semicircular in shape with a diameter of 500 microns per channel) and integrated headers
The design of the demonstrator works on a cross-flow principle, with each shim layer alternating between hot and cold working fluids, and the microchannels stacked directly in line with one another. There are a total of 60 shims present in the PHCE core, 30 ‘hot’ and 30 ‘cold’. By developing the diffusion bonding parameters for aluminium alloys, these features can be sealed during the joining process with minimal distortion to the internal complex network of channels.
TWI has now manufactured a demonstrator PCHE as shown in Figure 2.
Figure 2. Al-alloy PCHE diffusion bonded demonstrator
In addition to Al-alloys, TWI also explored the diffusion bonding of other low-density alloys such as commercially pure Ti and Ti6Al4V. TWI developed suitable bonding parameters in this study, ready to apply to real-world components when the need arises, including PCHE applications.
In summary, TWI was able to design and manufacture a PCHE made using a low density alloy, aluminium alloy in this case, thus demonstrating the feasibility of such a concept, which could help realise industrial targets and requirements.
This work was completed as part of TWI’s exploratory programme, and more information on the exploratory programme and its projects can be found by clicking the link above.
More information on thermal processing technologies, such as diffusion bonding, can be found here.