The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fl...The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number （Re） from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are aty/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number （Nu） and friction factor 00, respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.展开更多
采用Matlab与Excel联合编程开发了纵轴式掘进机截割头辅助设计与优化软件,通过输入截割头必要的几何及运动学参数,便可实现其辅助设计与优化,并自动生成截齿排列图、载荷曲线、切削图及基于Pro/E的截割头3D模型;获取横摆速度、截割头转...采用Matlab与Excel联合编程开发了纵轴式掘进机截割头辅助设计与优化软件,通过输入截割头必要的几何及运动学参数,便可实现其辅助设计与优化,并自动生成截齿排列图、载荷曲线、切削图及基于Pro/E的截割头3D模型;获取横摆速度、截割头转速、螺旋升角、叶片头数及截齿排列方式与截割功率、截割比能耗、截割阻力、切削面积之间的参数关系,指导截割头的优化设计使其整体性能达到最优;能够独立运行的EXE文件使软件更具普适性、操作更简单。以某公司研发的EBZ220掘进机为工程对象,基于实际工况,找到了截割头最佳设计方案及最优运动参数,在截割电机额定功率下,保证切削面积最大达854.95 mm2,截割比能耗最低至4.9 k W·h/m3。展开更多
Polymer nanowire(NW)organic field-effect transistors(OFETs)integrated on highly aligned large-area flexible substrates are candidate structures for the development of high-performance flexible electronics.This work pr...Polymer nanowire(NW)organic field-effect transistors(OFETs)integrated on highly aligned large-area flexible substrates are candidate structures for the development of high-performance flexible electronics.This work presents a universal technique,coaxial focused electrohydrodynamic jet(CFEJ)printing technology,to fabricate highly aligned 90-nm-diameter polymer arrays.This method allows for the preparation of uniformly shaped and precisely positioned nanowires directly on flexible substrates without transfer,thus ensuring their electrical properties.Using indacenodithiophene-co-benzothiadiazole(IDT-BT)and poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8-BT)as example materials,5 cm^(2) arrays were prepared with only minute size variations,which is extremely difficult to do using previously reported methods.According to 2D-GIXRD analysis,the molecules inside the nanowires mainly adopted face-onπ-stacking crystallite arrangements.This is quite different from the mixed arrangement of thin films.Nanowire-based OFETs exhibited a high average hole mobility of 1.1 cm^(2) V^(−1) s^(−1) and good device uniformity,indicating the applicability of CFEJ printing as a potential batch manufacturing and integration process for high-performance,scalable polymer nanowire-based OFET circuits.This technique can be used to fabricate various polymer arrays,enabling the use of organic polymer semiconductors in large-area,high-performance electronic devices and providing a new path for the fabrication of flexible displays and wearable electronics in the future.展开更多
基金the Thailand Research Fund(TRF)(Grant No.Ph D/0143/2552)
文摘The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number （Re） from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are aty/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number （Nu） and friction factor 00, respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.
文摘采用Matlab与Excel联合编程开发了纵轴式掘进机截割头辅助设计与优化软件,通过输入截割头必要的几何及运动学参数,便可实现其辅助设计与优化,并自动生成截齿排列图、载荷曲线、切削图及基于Pro/E的截割头3D模型;获取横摆速度、截割头转速、螺旋升角、叶片头数及截齿排列方式与截割功率、截割比能耗、截割阻力、切削面积之间的参数关系,指导截割头的优化设计使其整体性能达到最优;能够独立运行的EXE文件使软件更具普适性、操作更简单。以某公司研发的EBZ220掘进机为工程对象,基于实际工况,找到了截割头最佳设计方案及最优运动参数,在截割电机额定功率下,保证切削面积最大达854.95 mm2,截割比能耗最低至4.9 k W·h/m3。
基金This research was supported by the National Key R&D Program of China(Grant No.2018YFA0703200,D.W.)National Natural Science Foundation of China(51975104 and 62074138,D.W.52003274,Z.Z.)+2 种基金the Fundamental Research Funds for the Central Universities(DUT22LAB405,DUT22QN227)Defense Industrial Technology Development Program(JCKY2020204B004)Ningbo Institute of Dalian University of Technology.The 2D-GIXRD data were obtained at 1W1A,Beijing Synchrotron Radiation Facility.The authors gratefully acknowledge the assistance of researchers of the Diffuse X-ray Scattering Station during the experiments.Special thanks are due to Dr.Cai Rui in the Instrumental Analysis Center of Dalian University of Technology for assistance with AFM analysis.
文摘Polymer nanowire(NW)organic field-effect transistors(OFETs)integrated on highly aligned large-area flexible substrates are candidate structures for the development of high-performance flexible electronics.This work presents a universal technique,coaxial focused electrohydrodynamic jet(CFEJ)printing technology,to fabricate highly aligned 90-nm-diameter polymer arrays.This method allows for the preparation of uniformly shaped and precisely positioned nanowires directly on flexible substrates without transfer,thus ensuring their electrical properties.Using indacenodithiophene-co-benzothiadiazole(IDT-BT)and poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8-BT)as example materials,5 cm^(2) arrays were prepared with only minute size variations,which is extremely difficult to do using previously reported methods.According to 2D-GIXRD analysis,the molecules inside the nanowires mainly adopted face-onπ-stacking crystallite arrangements.This is quite different from the mixed arrangement of thin films.Nanowire-based OFETs exhibited a high average hole mobility of 1.1 cm^(2) V^(−1) s^(−1) and good device uniformity,indicating the applicability of CFEJ printing as a potential batch manufacturing and integration process for high-performance,scalable polymer nanowire-based OFET circuits.This technique can be used to fabricate various polymer arrays,enabling the use of organic polymer semiconductors in large-area,high-performance electronic devices and providing a new path for the fabrication of flexible displays and wearable electronics in the future.
