In this paper, a novel Multi-loop Moving Coil Linear Compressor (M-MC-LC) is studied, in which the piston is driven by the Co-core Bilateral Reverse Coil (CBRC) in a reciprocating motion within the magnetic array. The DC excitation technique is introduced to address the phenomenon that the piston is axially offset under the influence of gas force. In order to clarify the effect of DC excitation on the performance of the moving-coil linear compressor, the compressor prototype is developed, and the dynamic performance testing test-bed and the refrigeration performance test-bed are built to qualitatively and quantitatively analyze the relevant performance parameters of the compressor from theoretical and experimental aspects. The results show that when the DC excitation accounts for less than 20% of the total input voltage, the pressure ratio increases with the increase of DC excitation; when the percentage is at 22.9%, a sudden drop in the volumetric efficiency of compressor occurs. Mass flow and COP increases first and then decreases with the increase of DC voltage excitation. The study results provide a guideline for the stable and reliable operation of the system and provide a valuable reference for the linear compressor piston offset adjustment.

This study examines the impact of aging at 600 °C on the tensile properties of 0.3NbFeCrAl alloy at various temperatures, including room temperature (RT), 300 °C, 350 °C, and 400 °C, as well as the corresponding changes in microstructure. Results demonstrate that as aging time increases, the grain size remains relatively stable, while the amount of precipitate gradually increases and becomes uniformly distributed. The tensile strength (R_m) also increases steadily with aging time, reaching its maximum after 1000 h of aging. This can be attributed to the precipitation strengthening effect of the Laves phase after 1000 h of aging. The yield strength (R_p0.2) remains constant when the specimen is stretched at room temperature, but gradually increases with both the stretching temperature and aging time. Additionally, the section shrinkage ratio (Z) exhibits a decreasing trend with aging time, except for stretching at room temperature. Nevertheless, Z remains above 50% in all other cases, indicating that the toughness of the aged specimens is maintained well. While fracture shrinkage is significant for tensile tests at RT, it exhibits minimal change with increasing aging time. Furthermore, a notable increase in the number of dimples and a decrease in their size is observed on the tensile fracture surface with aging.

The fir-tree blade tenon is an important connection part of the turbine blade; its machining quality directly affects the life and power of the aeroengine. At present, the machining of the blade tenon requires multiple profile grinding processes. This study highlights the whole profile of the grinding processes of K4002 nickel-based superalloy blade tenons in ultrasonic vibration-assisted grinding (UVG). A probability superposition method was utilized to calculate the undeformed chip thickness and contact rate considering the random distribution of the abrasive grains and the overlap of the grinding trajectories. Subsequently, the grinding force, grinding temperature and surface integrity of the blade tenons in conventional grinding (CG) and UVG were investigated. The results indicate that the ultrasonic vibration causes intermittent cutting behavior which can reduce the contact rate to 0.6 at most. The grinding force, grinding temperature and surface integrity are deeply affected by the fir-tree shape of the blade tenon. The maximum grinding force occurs at the start of the full contact stage; surface burnout easily occurs in the middle top area of the blade tenon. Compared to CG, the use of UVG leads to an average reduction in the grinding force and temperature by 20% and 23%, respectively, improving the surface burnout of the K4002 superalloy.