Random vibration impact and fatigue life analyses of aluminium tubes in latent heat thermal energy storage systems on refrigerated trucks

Energy storage systems are paramount in enabling progress towards a zero-emission future. The structural integrity of a latent heat thermal energy storage system for transport of refrigerated food has been investigated for the first time. Fatigue failure is a critical issue for tubes made from aluminium alloys containing phase change material at low temperatures, due to random vibration loads induced by trucks moving on rough roads. Random vibration fatigue life analysis was conducted for tubes with nominal diameters of 50 mm and 32 mm, and thicknesses of either 1.6 mm and 3 mm, using ANSYS Mechanical. The results of the modal analyses showed that the natural frequencies of the tube-PCM systems are higher than 136 Hz. This is outside the frequency domain induced by driving on rough roads, which is between 1 and 100 Hz. Tube-PCM behaves as one solid body when filled with PCM and it is bonded to tube wall resulting in balanced deformation and stress on both sides of a middle support. However, tube filled partly with PCM bonded to tube wall showed an unbalanced distribution of stress concentrated to the side with confined PCM. During cyclic melting and solidification processes, contact between tube and PCM changes where PCM can slide or form a gap. This reduces the maximum stress while still unbalanced between the two sides of tube with and without confined PCM. Tube-PCM with larger ratio of diameter to thickness (Di/t) are more sensitive to contact type, for instance tube diameter of 50 mm and 1.6 thickness compared with tube 32 mm and 3 mm thickness with no sensitivity. The minimum fatigue life was found 2.6 million hours for tube-PCM size 50 mm with 1.6 mm tube thickness. This was assuming a full cycle with minimum to maximum stress ratio equal to one. The lifetime reduced to 2.8 million hours under random vibration cycles with stress ratio equal to 0.5. These results indicate that aluminium tube sizes of 50 and 32 mm with a thickness of 1.6 mm are satisfactory for an expected life of 20 years. Aluminium is well-suited for thermal energy storage in refrigeration due to its low density, excellent corrosion resistance, and high thermal conductivity. The optimal size and thickness depend on the expected lifetime and specific design criteria.