A STUDY ON BOILING HEAT TRANSFER OF NON-METALLIC NANOPARTICLES IN WATER-BASED NANOFLUID BOILING

• Material Type: 博士論文
• Title: A STUDY ON BOILING HEAT TRANSFER OF NON-METALLIC NANOPARTICLES IN WATER-BASED NANOFLUID BOILING
• Author/Editor: MUHAMAD ZUHAIRI, BIN SULAIMAN
• Author Heading: MUHAMAD ZUHAIRI, BIN SULAIMAN
• Publication Date: 2018-06-30
• Publication Date (W3CDTF): 2018-06-30
• Alternative Title: 非金属粒子を縣濁させた水ベースナノ流体のプール沸騰熱伝達に関する研究
• Degree grantor/type: 電気通信大学
• Date Granted: 2018-06-30
• Date Granted (W3CDTF): 2018-06-30
• Dissertation Number: 甲第943号
• Degree Type: 博士（工学）
• Conferring No. (Dissertation): 甲第943号
• Text Language Code: eng
• Target Audience: 一般
• Note (General): Heat transfer characteristics in boiling systems are significantly important, especially in high-density cooling, for instance, the application of In-Vessel Retention (IVR) during the Loss of Coolant Accident (LOCA) in a Nuclear Reactor. In the present study, the performance of nanofluids in a boiling system, namely, non-metallic water-based nano fluids has been explored. The parametric effects of the nanofluids in nucleate pool boiling with various configurations have been tested. Three main experimental setups were prepared separately to investigate the effect of heater orientations:material, concentration, and dispersion as well as heat flux density, respectively. Additional research was performed by using a separate experimental apparatus in order to elucidate a possible nucleate boiling mechanism occurring in nanofluids. Conclusively, the Critical Heat Flux(CHF) was improved significantly in the nanofluid nucleate boiling, compared to pure water. The orientation effects showed similar magnitudes of enhancement, up to 200 percent in both upward-facing and downward-facing heaters. Several parameters related to the CHF enhancement rate, such as concentration and boiling time in nanofluids, were simultaneously investigated. The CHF enhancement rates are considerably high in a higher concentration of TiO2 nanofluid and vice versa. In addition, the CHF enhancement for the downward-facing heater orientation is only half of that for the upward-ward facing heater. Surface wettability measurements were also being conducted to explore the relationship between surface properties and the CHF enhancement. Separately, the effects of nanoparticle materials, concentrations and dispersion conditions on the heat transfer coefficient and CHF were elucidated. The boiling heat transfer characteristics observed were significantly different depending on the nanoparticles’material as well as on the difference in the concentration. The higher concentration of TiO2 and Al2O3 showed higher heat transfer enhancements (except for the low concentration of TiO2), whereas for SiO2 the heat transfer deteriorated for all concentrations in the time-variation of wall superheat. However, no noticeable effects of the dispersion condition was observed. Some peculiar boiling curves (BCs) were observed in TiO2and SiO2 at the high heat flux compared to the simple BCs in Al2O3. The CHF enhancement was found to be within the range of 1.7 up to 2.1 MW/m2 for all materials. The effects of different heat flux density on the CHF enhancements were also investigated. The enhancement rate of CHF greatly depended on the heat flux density; the heat flux at the higher densities had shown considerably higher CHF enhancements rate to compare to lower heat flux density. The CHF enhancement still did not reach the asymptotic CHF value after boiling for 1 hour at the lowest heat flux in the present experimental investigation. Both the dimensionless CHF enhancement value respective to the dimensionless heat flux, concentration and boiling time were correlated. The trend showed a linearity in the high heat flux, especially for 450 and 600 kW/m2. Nevertheless, for lower heat flux, non-linear trends were observed especially at heat flux densities of 300 kW/m2 and more obvious at 150 kW/m2.In conclusion, nanofluids showed an enhanced CHF both for upward-facing and downward-facing conditions. However, the heat transfer characteristic (HTC) performances was stochastic depending on materials and concentration of nanofluids, and nearly no noticeable dispersion condition was observed. The heat flux density affected the rate of CHF enhancements, where the high heat flux resulted in high enhancement rates, but nominal enhancements in the lowest heat flux. 非金属ナノ粒子を縣濁させた水ベースのナノ流体中における沸騰伝熱特性を系統的に調べた。3種類の実験装置を用いて、伝熱面姿勢、ナノ粒子材料、ナノ粒子濃度、ナノ粒子分散状態、ナノ粒子層形成時の熱流束の影響を検討した。伝熱面姿勢としては、上向き面と下向き面で実験を実施し、限界熱流束(CHF)の絶対値は伝熱面姿勢によって異なるが、いずれの条件においてもナノ流体中のCHFは純水中の値の約2倍となることを示した。次に、ナノ流体中の沸騰熱伝達率は、ナノ粒子の材質および濃度により大きく異なり得ることを示した。ナノ粒子の材質として、本研究ではTiO2、Al2O3、SiO2を使用したが、Al2O3では伝熱促進、SiO2では伝熱劣化が生じるのに対して、TiO2では低粒子濃度で劣化、高粒子濃度で向上する結果となった。一方、ナノ流体中における粒子の分散状況は、本実験で調べた範囲内において、沸騰熱伝達に及ぼす影響は顕著ではなかった。また、各実験条件で沸騰曲線を描いたところ、Al2O3ナノ流体では水の場合と類似の沸騰曲線が得られたのに対して、TiO2とSiO2では、高熱流束条件で壁面過熱度が大きく増加するという独特の振る舞いを呈する場合があった。ただし、計測されたCHF値は1.7～2.1MW/m2の範囲にあり、純水中のCHFよりも顕著に増大するものの、ナノ粒子の材質、濃度、分散状態による明確な影響は認められなかった。これに対して、伝熱面上にナノ粒子層を形成する際の熱流束は、CHF値に多大な影響を及ぼした。すなわち、高熱流束条件では、ナノ粒子層を形成する際の沸騰時間が短くても顕著なCHF増大を実現できるのに対して、低熱流束条件では十分なCHF向上を達成する伝熱面状態とするのにきわめて長いナノ粒子層形成時間を要した。特に、本研究で用いた最低熱流束条件では、ナノ流体中で沸騰状態を1時間継続した場合でも、十分なCHF向上効果を発現するには至らなかった。本研究では、純水中にナノ粒子を添加した後の熱伝達率の時間変化を様々な条件で調べたが、ナノ粒子の添加直後では、熱伝達率が向上する場合が多かった。そこで、ナノ流体中における熱伝達率変化のメカニズムについて知見を得るため、透明容器を用いた可視化実験を実施して、ナノ粒子天下の前後における沸騰気泡の生成状況の差異を検討した。この結果、ナノ粒子を加えた直後、より多数の発泡核で気泡生成が生じることが観察された。これより、伝熱面上にナノ粒子層が形成される際に、そのいくつかの部分が気泡生成核となり、核沸騰熱伝達の促進に寄与することを示した。; 2018
• DOI: 10.18952/00008705; https://doi.org/10.18952/00008705
• Persistent ID (NDL): info:ndljp/pid/11123717; https://dl.ndl.go.jp/pid/11123717
• Collection: 障害者向け資料
• Collection (Materials For Handicapped People:1): テキストデータ
• Collection (particular): 国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文; https://dl.ndl.go.jp/collections/A00014
• Acquisition Basis: 博士論文（自動収集）
• Date Accepted (W3CDTF): 2018-08-03T23:36:01+09:00
• Date Created (W3CDTF): 2018-06-25
• Format (IMT): application/pdf
• Access Restrictions: 国立国会図書館内限定公開
• Service for the Digitized Contents Transmission Service: 図書館・個人送信対象外
• Availability of remote photoduplication service: 可
• Periodical Title (URI): http://dx.doi.org/10.18952/00008705; http://id.nii.ac.jp/1438/00008705/
• Data Provider (Database): 国立国会図書館 : 国立国会図書館デジタルコレクション; https://dl.ndl.go.jp

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2023-09-05 再収集