急冷処理用冷却材としてのナノ流体の有効性評価

Synopsis: Nanofluid is a liquid in which nanometer-sized particles are dispersed in base liquid. It is known that the critical heat flux and the wall superheat at the minimum heat flux in pool boiling are improved in nanofluids. In this research, performance of silica-water nanofluid as quenching coolant is explored experimentally since the above-mentioned parameters play important roles in this application. First, we investigated the immersion cooling of high-temperature test piece in the nanofluid; here, the test piece was cylindrical in shape and made of Inconel 718 or SUS304. It was confirmed that the test piece is cooled faster in the nanofluid than in distilled water. It was also found that non-uniformity of temperature in the test piece during quenching is mitigated in the nanofluid. This indicates that the silica nanofluid is considered a promising coolant to avoid the occurrence of hardening crack during quenching. Finally, Vickers hardness test was done for the Inconel 718 test piece. It was shown that the hardness tends to increase with an increase in the cooling rate even under the high cooling rate of about 1000 K/min although the difference of hardness was not noticeable between the experiments using the distilled water and the silica nanofluid as the quenching coolant.