| 研究実績の概要 |
1. Experimental study of boiling heat transfer on a biphilic surface
We have designed and fabricated a heterogeneous boiling surface with spatially varying wettability, which exhibits exceptional heat transfer performance at various pressures. Specifically, at atmospheric pressure, the onset of nucleate boiling is lowered significantly (to negative levels) on a superhydrophilic (CA<10°) TiO2 surface coated with an array of hydrophobic PTFE (Polytetrafluoroethylene, CA>120°) spots of 6-mm diameter and 7-mm pitch. The facilitated boiling incipience extends boiling to low-heat-flux applications as an effective means of heat transfer. At reduced pressures, on the other hand, technical limitations on boiling, such as large incipience temperature overshoots, have been greatly mitigated by using a copper boiling surface sputter-coated with 5-micron Ni/TFEO (Tetrafluoroethylene oligomer) particles of various designs. Additionally, we have used a laser Mach-Zehnder interferometer to observe thermocapillary convection above the biphilic surface, which contributes to enhanced heat transfer with high concentrations of dissolved gas.
2. Numerical simulation of bubble dynamics on a biphilic surface
We have performed a numerical study of phase transition of a two-component system by using a diffuse-interface method. The results show contrasting bubble behaviors, from firm attachment under dynamic equilibrium to partial departure (pinch-off) from the biphilic surface, as the concentration of dissolved gas increases.
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