In this study, infrared thermometry techniques were used to conduct surface wetting performance tests (wicking tests) on micropillar structures with good fluid supply capabilities to enhance the critical heat flux. Wicking tests were conducted based on various micropillar shapes (i.e., diameter and spacing) to investigate the surface wetting performance near the boiling point of the fluid(~100°C). The surface temperature was increased from 20°C to 95°C, to examine the wicking performance The shape of the micropillars were quantified by the roughness and the effect of the roughness and temperature on the wicking performance was analyzed. As a result, we confirmed that the roughness of the micropillars increases the capillary pressure, improving the wicking performance. The sample D04 G10 with the highest roughness coefficient at room temperature (r=2.51) exhibited the highest wicking coefficient, showing a 170% improvement in wicking performance compared to D04G20 with the smallest roughness coefficient at room temperature(r=1.51). Additionally, the D04 G10 sample (r=2.51) recorded a 50% improvement in the wicking coefficient at the highest temperature(95°C) compared to room temperature(20°C). The wicking coefficient data will be utilized as a database for developing a new correlation for critical heat flux.

Highly safe lithium-ion batteries (LIBs) are required for large-scale applications such as electrical vehicles and energy storage systems. A highly stable cathode is essential for the development of safe LIBs. LiFePO4 is one of the most stable cathodes because of its stable structure and strong bonding between P and O. However, it has a lower energy density than lithium transition metal oxides. To investigate the high energy density of phosphate materials, vanadium phosphates were investigated. Vanadium enables multiple redox reactions as well as high redox potentials. LiVPO4O has two redox reactions (V5+/V4+/V3+) but low electrochemical activity. In this study, LiVPO4O is doped with fluorine to improve its electrochemical activity and increase its operational redox potential. With increasing fluorine content in LiVPO4O1-xFx, the local vanadium structure changed as the vanadium oxidation state changed. In addition, the operating potential increased with increasing fluorine content. Thus, it was confirmed that fluorine doping leads to a strong inductive effect and high operating voltage, which helps improve the energy density of the cathode materials.

This paper studies an effect of vibration on twisted string actuation inside conduit at high curvature angles. In our previous work. we have mentioned that twisted string actuators can be used to transmit power even at significant curvature angles of the conduit. However, several undesirable effects, namely pull-back, hysteresis, and chattering, were present during actuation due to friction between strings and the internal sheath of the conduit. This paper reports the results of experimental study on effects of vibration on twisted string actuation inside curved conduits. We have demonstrated that applying vibration generated near natural frequency of the system during the stages of twisting and untwisting cycles helped reduce pull-back and hysteresis and increase string contraction. In case when sheath was deflected by 180° under a constant load of 3 kg, we were able to achieve over 40% decrease in pull-back and 30% decrease in hysteresis, compared with no vibration case.