Cold, clean and green: improving the efficiency and environmental impact of a cryogenic expander

摘要

The Dearman Engine is a cryogenic expander, utilised in the case of combined power and cooling, currently applied in truck refrigeration units. As the temperatures involved (~30°C) are significantly lower than those experienced in an internal combustion engine, there is scope for material replacement. These operating conditions open up the opportunity to employ polymers and exploit their tribological properties. A composite is often used to combine preferable properties of each material. It has been hypothesised that a composite could be replaced by a cheaper alternative: a laminate. Five materials were tested for friction and wear: PEEK, PTFE, PTFE-PTFE laminate, PEEK-PTFE composite and PEEK-PTFE laminate. The surfaces were also examined under an SEM/EDS post test in order to determine any defects and to detect any transfer layers. The results showed that the friction and wear for the PTFE-PTFE laminate were similar to that of pure PTFE and so the bonding of the material had no impact on the overall result. This was also the case in the PEEK-PTFE composite and laminate. The major difference was the presence of a transfer layer in the PEEK-PTFE laminate that was not present in the composite. These results suggest that lamination is a suitable alternative that warrants further investigation.