[Objective] The paper was to summarize the research of system of rice intensification（SRI） technology in China.[Method] Through combination screening and factor analysis,the effect of appropriate system of rice inte...[Objective] The paper was to summarize the research of system of rice intensification（SRI） technology in China.[Method] Through combination screening and factor analysis,the effect of appropriate system of rice intensification technology on yield formation of rice was studied.[Result] The technology has strong adaptability with good effort of yield increase in China,which can improve air and light in fields,reduce the incidence of sheath blight,increase photosynthetic capacity of rice plants,increase root activity,enhance nutrient transportation,increase the rate of paddy milled rice,reduce the chalky grain rate,and simultaneously save input and labor,increase revenue.[Conclusion] System of rice intensification broke the China＇s traditional practice of larger planting density,and preliminarily demonstrated a larger yield potential.展开更多
The properties of styrene-butadiene rubber (SBR) reinforced by modified silica was investigated according to national standards. Silica was modified by silane coupling agents KH-570, KH-590, and KH-792. The optimized ...The properties of styrene-butadiene rubber (SBR) reinforced by modified silica was investigated according to national standards. Silica was modified by silane coupling agents KH-570, KH-590, and KH-792. The optimized geome-tries of molecular modified silica reinforced SBR were obtained by using B3LYP calculation of density functional theory with the 6-31+G basis sets. The natural bond orbital analyses were carried out. The Si—O bond length of silica modified by KH-792 was the shortest and the electronegative of O was the highest. It indicated that the connection between silica and KH-792 was the tightest. Higher tensile strength and elongation of reinforced SBR was obtained by silica modified with the KH-792. It was caused by large delocalization of lone pair electrons of the two N atoms in KH-792. The S—C bond length in silica modified by KH-590 was longer than the ordinary S—C bond length. Then the sulfur free radical (·S·) was produced more easily in vulcanization. The degree of crosslink was increased by the cross-linkage of the rubber molecule and the sulfur free radical. That was why the highest stress and tear strength of reinforced SBR was produced when silane coupling agent KH-590 was used. The calculation results was in accord with experimental data.展开更多
With isopentane as working fluid, the heat transfer performances for corrugated, nodal and horizontal grain tubes are simulated. The structural parameters of the three kinds of tubes are compared with those of the pla...With isopentane as working fluid, the heat transfer performances for corrugated, nodal and horizontal grain tubes are simulated. The structural parameters of the three kinds of tubes are compared with those of the plain tube. The numerical results using computational fluid dynamics are validated with theoretical values. For the corrugated, nodal and horizontal grain tubes, the heat transfer enhancements(HTEs) are 2.31—2.53, 1.18—1.86 and 1.02—1.31 times of those of the plain tube, respectively. However, the improved HTEs are at the expense of pressure losses. The drag coefficients are 6.10—7.09, 2.06—11.03 and 0.53—1.83 higher, respectively. From the viewpoint of comprehensive heat transfer factor, the corrugated tube is recommended for engineering applications, followed by the horizontal grain tube.展开更多
The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis(CHFS)system to enhance the heat transfer and minimize the required length of the heat e...The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis(CHFS)system to enhance the heat transfer and minimize the required length of the heat exchanger.For this purpose,numerous numerical simulations are performed to investigate performance of the system with porous media.First,the numerical simulation for the heat exchanger in CHFS system is validated by experimental data.Then,porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness,based on the minimum required length of the heat exchanger.Finally,by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate,the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed.The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%.The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness.Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.展开更多
The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes （CDs） and converging-diverg）ng tubes.equi.pped with twin counter-swirling twisted tapes...The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes （CDs） and converging-diverg）ng tubes.equi.pped with twin counter-swirling twisted tapes （CDTs）. The effects of Reynolds number （Re= 10000-20000）, pitch length （P= 11.25, 22.5 mm）, rib height （e = 0.5, 0.8, 1.1 ram）, pitch ratio （8= 1 ＂ 8, 5 ＂ 4, 8 ＂ 1）, gap distance between twin t）visted tapes （b = 0.5, 4.5, 8.5 mm） and tape number （n = 2, 3, 4, 5, 6） on Nusselt number （Nu）, Iriction tactor 0＇） and thermal enhancement factor （r/） are investigated under uniform heat flux conditions,using water as working fluid. In order to illustrate the heat transter and tlu^d tlow mechamsms, flow structures m ~StJs and ~SDIs are presented. The obtained results reveal that all geometric parameters have important effects on the thermal performance of CD and CDT, and both CD and CDT show better thermal performance than plain tube at the constant pumping power. It is also found that the increases in the Nusselt number and friction factor for CDT are, respectively, up to 6.3%-35.7% and 1.75-5.3 times of thecorresponding bare CD. All CDTs have good thermal perbrmance with greater than 1 which indicates that the compound heat transfer technique of CDT is commendable for the maximum enhanced heat transfer rate.展开更多
Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transf...Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transfer enhancement and have developed various techniques and methods. As a passive heat transfer technique, twisted tapes are widely used in various industries for their cost savings, lower maintenance requirements and the fact that they are easily set up. This paper introduces the principle of heat transfer enhancement of twisted tapes and reviews some of the experimental works done by researchers on this technique in recent years. The variously modified twisted tape inserts are widely researched and used to enhance heat transfer efficiency for heat exchangers. Twisted tapes perform better in low Re conditions and in square tubes. However, they could also cause higher pressure drops. Twisted tapes have great potential and profound implications if they can be used in traditional heat exchangers. Besides this, some correlations between the Nusselt number and friction factors are presented in this paper.展开更多
文摘[Objective] The paper was to summarize the research of system of rice intensification（SRI） technology in China.[Method] Through combination screening and factor analysis,the effect of appropriate system of rice intensification technology on yield formation of rice was studied.[Result] The technology has strong adaptability with good effort of yield increase in China,which can improve air and light in fields,reduce the incidence of sheath blight,increase photosynthetic capacity of rice plants,increase root activity,enhance nutrient transportation,increase the rate of paddy milled rice,reduce the chalky grain rate,and simultaneously save input and labor,increase revenue.[Conclusion] System of rice intensification broke the China＇s traditional practice of larger planting density,and preliminarily demonstrated a larger yield potential.
文摘The properties of styrene-butadiene rubber (SBR) reinforced by modified silica was investigated according to national standards. Silica was modified by silane coupling agents KH-570, KH-590, and KH-792. The optimized geome-tries of molecular modified silica reinforced SBR were obtained by using B3LYP calculation of density functional theory with the 6-31+G basis sets. The natural bond orbital analyses were carried out. The Si—O bond length of silica modified by KH-792 was the shortest and the electronegative of O was the highest. It indicated that the connection between silica and KH-792 was the tightest. Higher tensile strength and elongation of reinforced SBR was obtained by silica modified with the KH-792. It was caused by large delocalization of lone pair electrons of the two N atoms in KH-792. The S—C bond length in silica modified by KH-590 was longer than the ordinary S—C bond length. Then the sulfur free radical (·S·) was produced more easily in vulcanization. The degree of crosslink was increased by the cross-linkage of the rubber molecule and the sulfur free radical. That was why the highest stress and tear strength of reinforced SBR was produced when silane coupling agent KH-590 was used. The calculation results was in accord with experimental data.
基金Supported by the National High Technology Research and Development Program of China("863"Program,No.2012AA053001)
文摘With isopentane as working fluid, the heat transfer performances for corrugated, nodal and horizontal grain tubes are simulated. The structural parameters of the three kinds of tubes are compared with those of the plain tube. The numerical results using computational fluid dynamics are validated with theoretical values. For the corrugated, nodal and horizontal grain tubes, the heat transfer enhancements(HTEs) are 2.31—2.53, 1.18—1.86 and 1.02—1.31 times of those of the plain tube, respectively. However, the improved HTEs are at the expense of pressure losses. The drag coefficients are 6.10—7.09, 2.06—11.03 and 0.53—1.83 higher, respectively. From the viewpoint of comprehensive heat transfer factor, the corrugated tube is recommended for engineering applications, followed by the horizontal grain tube.
文摘The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis(CHFS)system to enhance the heat transfer and minimize the required length of the heat exchanger.For this purpose,numerous numerical simulations are performed to investigate performance of the system with porous media.First,the numerical simulation for the heat exchanger in CHFS system is validated by experimental data.Then,porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness,based on the minimum required length of the heat exchanger.Finally,by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate,the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed.The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%.The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness.Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.
基金Supported by the Science and Technology Key Projects of Shanxi Province(2011A080804012)
文摘The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes （CDs） and converging-diverg）ng tubes.equi.pped with twin counter-swirling twisted tapes （CDTs）. The effects of Reynolds number （Re= 10000-20000）, pitch length （P= 11.25, 22.5 mm）, rib height （e = 0.5, 0.8, 1.1 ram）, pitch ratio （8= 1 ＂ 8, 5 ＂ 4, 8 ＂ 1）, gap distance between twin t）visted tapes （b = 0.5, 4.5, 8.5 mm） and tape number （n = 2, 3, 4, 5, 6） on Nusselt number （Nu）, Iriction tactor 0＇） and thermal enhancement factor （r/） are investigated under uniform heat flux conditions,using water as working fluid. In order to illustrate the heat transter and tlu^d tlow mechamsms, flow structures m ~StJs and ~SDIs are presented. The obtained results reveal that all geometric parameters have important effects on the thermal performance of CD and CDT, and both CD and CDT show better thermal performance than plain tube at the constant pumping power. It is also found that the increases in the Nusselt number and friction factor for CDT are, respectively, up to 6.3%-35.7% and 1.75-5.3 times of thecorresponding bare CD. All CDTs have good thermal perbrmance with greater than 1 which indicates that the compound heat transfer technique of CDT is commendable for the maximum enhanced heat transfer rate.
文摘Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transfer enhancement and have developed various techniques and methods. As a passive heat transfer technique, twisted tapes are widely used in various industries for their cost savings, lower maintenance requirements and the fact that they are easily set up. This paper introduces the principle of heat transfer enhancement of twisted tapes and reviews some of the experimental works done by researchers on this technique in recent years. The variously modified twisted tape inserts are widely researched and used to enhance heat transfer efficiency for heat exchangers. Twisted tapes perform better in low Re conditions and in square tubes. However, they could also cause higher pressure drops. Twisted tapes have great potential and profound implications if they can be used in traditional heat exchangers. Besides this, some correlations between the Nusselt number and friction factors are presented in this paper.
