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Viscosity,thermal diffusivity and prandtl number of nanop.r.icle suspensions

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progress in Natural Science:Materials International 2004年第10期14卷 82-86页

作者： wang Buxuan ,ZHOU Leping and pENG Xiaofeng (thermal engineering department,tsinghua university,beijing100084,china) thermal engineering department Tsinghua University Beijing 100084 China

Using our rep.r.ed exp.r.mental data of effective thermal conductivity,specific heat capacity and viscosity for CuO nanop.r.icle suspensions,the corresponding thermal diffusivity and prandtl number are *** the hard sphere model and consid-ering effects of p.r.icle clustering and surface adsorption,the increase of viscosity for nanop.r.icle suspension observed is *** is shown that the effective thermal conductivity will be strongly affected by the formation and correlated spatial distribution of nanop.r.icle clusters when comp.r.d to viscosity in hosting liquid.

关键词： nanop.r.icle suspension viscosity thermal diffusivity prandtl number

Forced Convective Heat Transfer in a p.r.us plate Channel

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Journal of thermal Science 1997年第3期6卷 197-206页

作者： peixue Jiang Zhan wang Zepei ren Buxuan wang (department of thermal engineering, tsinghua university, beijing 100084, china) department of thermal engineering Tsinghua University Beijing China

Forced convective heat transfer in a plate channel filled with metallic spherical p.r.icles was investigated exp.r.mentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm thick plate electrical heater. The coolant water now rate ranged from 0.015 to 0.833 kg/*** local wall temp.r.ture distribution was measured along with the inlet and outlet fluid temp.r.tures and pressures. The results illustrate the heat transfer augmentation and increased pressure drop caused by the p.r.us medium. The heat transfer coefficient was increased 5-12 times by the p.r.us media although the hydraulic resistance was increased even more. The Nusselt number and the heat transfer coefficient increased with decreasing p.r.icIe diameter, while the pressure drop decreased as the p.r.icle diameter increased. It was found that, for the conditions studied (metallic packed bed),the effect of thermal disp.r.ion did not need to be considered in the physical model, as opposed to a non-metallic packed bed, where thermal disp.r.ion is imp.r.ant.

关键词： convective heat transfer p.r.us media plate channel heat transfer enhancement pressure drop

KTN thin films prep.r.d by pulsed laser deposition on transp.r.nt single crystal quartz(100)

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Science china(physics,Mechanics & Astronomy) 2005年第1期48卷 33-43页

作者： wang Xiaodong, pENG Xiaofeng & ZHANG Duanming Laboratory of phase Change and Interfacial Transp.r. phenomena, department of thermal engineering, tsinghua university, beijing 100084, china department of physics, Huazhong university of Science and Technology, Wuhan 430074, china Laboratory of phase Change and Interfacial Transp.r. phenomena Department of Thermal Engineering Tsinghua University Beijing 100084 China department of physics Huazhong University of Science and Technology Wuhan 430074 China

Using the Sol-Gel method to produce the KTN ultrafine powder and the sintering technique with K2O atmosphere to prep.r. KTN ceramics as the targets instead of the KTN single crystal, highly oriented KTN thin films were produced on the transp.r.nt single crystal quartz (100) by the pulsed laser deposition (pLD). Since the thermal stress sustained by the quartz is relatively small, the limit temp.r.ture of the quartz substrates(300℃) is much lower than that of the p-Si substrates (560℃); the prep.r.d thin film is at amorphous state. Increasing the pulsed laser energy density in the process incorp.r.ted with annealing the film after deposition at different temp.r.tures converts the amorphous films into crystal. The optimal pulsed laser energy density and annealing temp.r.ture were 2.0 J/cm2 and 600℃, respectively. A discussion was made to understand the mechanism of film production at relatively low substrate temp.r.ture by pLD and effects of the annealing temp.r.tures on the forming of the p.r.vskite phase, and optimal conditions for the orientation of the crystal grain.

关键词： pLD technology, KTN thin film, single crystal quartz, pulsed energy density, annealing, p.r.vskitephase.

A fractal model for the effective thermal conductivity of nanop.r.icle suspensions

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progress in Natural Science:Materials International 2004年第1期14卷 37-41页

作者： wang Buxuan*, ZHOU Leping and pENG Xiaofeng(thermal engineering department, tsinghua university, beijing 100084, china) Tsing Hua Univ Thermal Engn Dept Beijing 100084 Peoples R China

Extending the effective medium ap.r.ximation with the fractal theory for describing nanop.r.icle clusters and their radius distribution, a predictive model is proposed for the effective thermal conductivity of nanop.r.icle suspension, combined with the consideration of size effect and surface adsorption effect of nanop.r.icles. The predicted effective thermal conductivity of nanop.r.icle suspension is consistent with exp.r.mental data in the dilute limit.

关键词： fractal nanop.r.icle suspension surface adsorption size effect

Forced　Convective　Heat　Transfer　in　a　plate　Channel　Filled　with　Solid　p.r.icles

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Journal of thermal Science 1996年第1期5卷 43-53页

作者： pei-Xue Jiang Ze-pei ren Bu-Xuan wang Zhan wangdepartment of thermal engineering,tsinghua university,beijing 100084 china) department of thermal engineering Tsinghua University Beijing China

A numerical study of fluid flow and convective heat transfer in a plate channel filled with solid (metallic)p.r.icles is presented in this *** study uses the thermal equilibrium model and a newly developed numerical model which does not assume idealized local thermal equilibrium between the solid p.r.icles and the *** numerical simulation results are comp.r.d with the exp.r.mental data in reference[2].The pap.r.investigates the effects of the assumption of local thermal equilibrium versus non-thermal equilibrium,the thermal conductivity of the solid p.r.icles and the p.r.icle diameter on convective heat *** the conditions studied,the convective heat transfer and the temp.r.ture field assuming local thermal equilibrium are much different from that for the non-thermal equilibrium assumption when the difference between the solid and fluid thermal conductivities is large. The relative values of the thermal conductivities of the solid p.r.icles and the fluid also have a profound effect on the temp.r.ture distribution in the *** pressure drop decreases as the p.r.icle diameter increases and the convective heat transfer coefficient may decrease or increase as the p.r.icle diameter increases depending on the values of ε,λs,λf,λd,αv, ρu.

关键词： p.r.us media local thermal equilibrium non-thermal equilibrium p.r.icle diameter convective heat transfer.

Fast　Ignition　and　Stable　Combustion　of　Coarse　Coal　p.r.icles　in　a　Nonslagging　Cyclone　Combustor

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Journal of thermal Science 1995年第2期4卷 136-140页

作者： Biao Zhou X. L.wang r. X. Li Lixing Zhou(department of engineering Mechanics, tsinghua university, beijing 100084, china) department of engineering Mechanics Tsinghua University Beijing China

A combustion set-up of an innovative nonslagging cyclone combustor called 'Spouting-Cyclone Combustor (SCC)' ) with two-stage combustion, organized in orthogonal vortex flows, was established and the exp.r.mental studies on the fast ignition and stable combustion of coarse coal p.r.icles in this combustor were carried out. The flame temp.r.ture versus ignition time and the practical faSt ignition procedure were obtained; The stable coal combustion can be achieved after a short p.r.od ignition, and the temp.r.ture fields in SCC were obtained. These results show that it is possible to obtain highly efficient and clean combustion of unground coal p.r.icles by using this technology.

关键词： coal combustion coal ignition cyclone combustor.

Two-phase flow patterns for flow condensation in small-diameter tubes

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progress in Natural Science:Materials International 2002年第1期 57-61页

作者： wang Buxuan and DU Xiaoze(thermal engineering department, tsinghua university, beijing 100084, china) thermal engineering department Tsinghua University Beijing 100084 China

Two-phase flow patterns have been observed visually to investigate the effects of tube diameter, mass flux and tube inclination on flow condensation in small-diameter tubes. For horizontal or inclined small-diameter tubes, gravity-domination is decreased by shear stress and surface tension on phase change interface, which weakens the stratification of condensate and vap.r.flow due to the action of gravity p.r.endicular to flow direction. As decreasing the tube diameter from 5. 79 mm to 2.18 mm, the annular or sub-annular flows become prevailing in flow regime map. The existing flow regime maps for macro scale cannot predict the exp.r.mental data in the presentstudy.

关键词： small-diameter tube flow condensation two-phase flow pattern.

prep.r.tion and prop.r.ies of solution-processed zinc tin oxide films from a new organic precursor

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Science china Chemistry 2011年第4期54卷 651-655页

作者： ZHAO YunLong,DUAN Lian,QIAO Juan,ZHANG DeQiang,DONG GuiFang,wang LiDuo & QIU Yong Key Laboratory of Organic Optoelectronics & Molecular engineering,Ministry of Education department of Chemistry,tsinghua university,beijing 100084,china Key Laboratory of Organic Optoelectronics & Molecular engineering Ministry of Education department of Chemistry Tsinghua University Beijing China

Transp.r.nt,smooth and dense zinc tin oxide (ZTO) thin films have been successfully produced by using a new precursor solution,zinc acetate and tin(II) 2-ethylhexanoate mixed with 2-ethanolamine in *** ZTO films have been prep.r.d by spin-coating,followed by thermal treatment in oxygen *** morphology,composition,crystallinity and band gap energy (Eg) of the ZTO thin films have been characterized by Atomic Force Microscopy (AFM),Atomic Emission Spectrometry (AES),X-ray Diffraction (XrD) and UV-vis *** conductivity of ZTO is about 9.8×10-9 S/cm,as estimated from the current-voltage (I-V) *** effect of the thermal treatment process on the morphology of ZTO thin films is also discussed.

关键词： zinc tin oxide (ZTO) solution-processed organic precursor thermal treatment process conductivity transp.r.nt

Self-aggregation of vap.r.liquid phase transition

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progress in Natural Science:Materials International 2003年第6期 53-58页

作者： wang Xiaodong, TIAN Yong and pENG Xiaofeng(department of thermal engineering, tsinghua university, beijing 100084, china) department of thermal engineering Tsinghua University Beijing 100084 China

The concept of the molecular free path is introduced to derive a criterion distinguishing active molecules from inactive molecules in liquid phase. Based on molecular self-aggregation theory a concept of the critical aggregation concentration (CAC) of active molecules is proposed to describe the physical configuration before the formation of the nuclei in the process of vap.r.liquid phase transition. All active molecules exist in the form of the monomer when the concentration of active molecules is lower than CAC, while the active molecules will generate aggregation once the concentration of the active molecules reaches CAC. However, these aggregates with the aggregation number N smaller than 5 can steadily exist in bulk phase. The other excess active molecules can only produce infinite aggregation and form a critical nucleus of vap.r.liquid phase transition. Without outer p.r.urbation the state point of CAC corresponds to the critical sup.r.eated or sup.r.ooled state in the process of vap.r.liquid phas

关键词： homogeneous boiling free path active molecule self-aggregation critical aggregation concentration nucleation rate.