For forced-convective flow in a resistive-heated cylindrical channel, the heat transfer coefficients and friction factor of the nanofluids composed of ethylene glycol aqueous solution (50 wt%) and oxide-ceramic nanoparticles, with particle diameter of 200 nm or 300 nm and particle volume concentration of 3.6%, were evaluated under constant heat-flux boundary conditions. The experiments were conducted under turbulent conditions, where the temperature at the entrance of the heated section was 353.15 K. The experimentally measured heat-transfer coefficients of all nanofluids were higher than those of the estimated coefficients obtained from their thermophysical properties. The difference between the experimental and estimated heat transfer coefficients followed the order of the absolute zeta potential value (i.e., the electrostatic repulsive force on the surface of particles) of the nanofluids, which may be owing to the dispersibility of the particles. At the same pumping power, the order of the heat exchange output in the nanofluids was, from largest to smallest, SiO₂, ZrO₂, Al₂O₃, and TiO₂, which agreed well with the order of the absolute value of their zeta potential.

The effective utilization of carbon fibers recovered during the thermal decomposition recycling of carbon-fiber-reinforced plastic (CFRP) was investigated. Carbon fibers have a uniform diameter and a suitable size for the use as a combustion catalyst for particulate matter (PM). Thus, in this study, carbon fibers were used as a template to synthesize hollow-form LaNiO₃ perovskite-type oxide via the precursor accumulation method. The calcination temperature was lowered by the internal heat supply from the combustion of the carbon template. Hollow-form LaNiO₃ exhibited the same chemical properties as LaNiO₃ prepared via the common sol–gel method. The morphology of the hollow form decreased the bulk density of the catalyst, resulting in enhanced contact with PM and, consequently, high PM combustion efficiency.

In the transformation reaction of alkanes in alkenes via catalytic dehydrogenation, it is generally accepted that catalytic deactivation will occur. This phenomenon causes a drastic reduction in the catalytic activity with time-on-stream. It is understood that carbon deposits generated during the reaction then covers the surface of the catalyst, leading to a drastic decrease in activity. However, in contradiction, our laboratory reported that the dehydrogenation of isobutane to isobutene on NiO/γ-Al₂O₃ within a specific range of NiO loading with CO₂ improved the yield of isobutene with time-on-stream. Since few such cases have been reported, in this study, isobutane was dehydrogenated with CO₂ over the NiO/α-Al₂O₃ catalyst, with 20% NiO loading, and an improvement was again observed. To investigate the cause of the improvement, both NiO/γ-Al₂O₃ and NiO/α-Al₂O₃ with 20% NiO loading were examined in detail following the reaction. According to transmission electron microscopy (TEM) analysis, both catalysts were covered with a large amount of carbon deposit after the reaction; however, there was a difference in the types. The carbon deposit on NiO/γ-Al₂O₃ exhibited a fibrous nature, while that on NiO/α-Al₂O₃ appeared to be a type of nanowire. Raman spectroscopy revealed that the carbonaceous crystal-growth properties of the two forms differed depending on the support. In particular, a catalytically active species of metallic nickel was formed in a high degree of dispersion in and on the above two forms of carbon deposits during the reaction, and this resulted in a high catalytic activity even when the catalyst was covered with a carbon deposit.