Cellulose nanofiber (CNF) is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. It has high strength comparable to steel, and it shows low environm...Cellulose nanofiber (CNF) is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. It has high strength comparable to steel, and it shows low environmental load during a cycle of production and disposal. Besides it has many excellent properties and functions such as high rigidity, light-weight, flexibility and shape memory effect, so it is expected as a next-generation new material. Usually it is composed of many cellulose micro fibrils (CMFs) in which molecular chains of cellulose are aggregated in a crystal structure, the knowledge of mechanical properties for each CMF unit is important. Since actual fibrils are complicatedly intertwined, it is also crucial to elucidate the transmission mechanism of force and deformation not only in one fibril but also in between fibrils. How the dynamic and hierarchical structure composed of CMFs responds to bending or torsion is an interesting issue. However, little is known on torsional characteristics (shear modulus, torsional rigidity, etc.) concerning CMF. In general, in a wire-like structure, it is difficult to enhance torsional rigidity and strength, compared with tensile ones. Therefore, in this study, we try to build a hierarchical model of CNF by multiplying CMF fibers and to conduct molecular dynamics simulation for torsional deformation, by using hybrid model between all-atom and united-atoms model. First, shear modulus was estimated for one CMF fibril and it showed a value close to the experimental values. Also, we assume a state in which two CMFs are ideally arranged in parallel, and create a hierarchical structure. We evaluate the dependence on the temperature for the bond strength and toughness in the hierarchical structures. Furthermore, we mentioned the transmission mechanism between components of a hierarchical structure.展开更多
By merging two standard swirl chambers,an alternative cooling configuration named double swirl chambers(DSC)has been developed.In the DSC cooling configuration,the main physical phenomena of the swirl flow in swirl ch...By merging two standard swirl chambers,an alternative cooling configuration named double swirl chambers(DSC)has been developed.In the DSC cooling configuration,the main physical phenomena of the swirl flow in swirl chamber and the advantages of swirl flow in heat transfer augmentation are maintained.Additionally,three new physical phenomena can be found in DSC cooling configuration,which result in a further improvement of the heat transfer:(1)impingement effect has been observed,(2)internal heat exchange has been enhanced between fluids in two swirls,and(3)“∞”shape swirl has been generated because of cross effect between two chambers,which improves the mixing of the fluids.Because of all these improvements,the DSC cooling configuration leads to a higher globally-averaged thermal performance parameter(Nu/Nu_(∞)/(f/f0)^(1/3))than standard swirl chamber.In particular,at the inlet region,the augmentation of the heat transfer is nearly 7.5 times larger than the fully developed non-swirl turbulent flow and the circumferentially averaged Nusselt number coefficient is 41%larger than the standard swirl chamber.Within the present work,a further investigation on the DSC cooling configuration has been focused on the influence of geometry parameters e.g.merging ratio of chambers and aspect ratio of inlet duct on the cooling perfomance.The results show a very large influence of these geometry parameters in heat transfer enhancement and pressure drop ratio.Compared with the basic configuration of DSC cooling,the improved configuration with 20%to 23%merging ratio shows the highest globally-averaged themal performance parameter.With the same cross section area in tangential inlet ducts,the DSC cooling channel with larger aspect ratio shows larger heat transfer enhancement and at the same time reduced pressure drop ratio,which results in a better globally-averaged themal performance parameter.展开更多
It is known that the leading edge has the most critical heat transfer area of a gas turbine blade.The highest heat transfer rates on the airfoil can always be found on the stagnation region of the leading edge.In orde...It is known that the leading edge has the most critical heat transfer area of a gas turbine blade.The highest heat transfer rates on the airfoil can always be found on the stagnation region of the leading edge.In order to further improve the gas turbine thermal efficiency the development of more advanced internal cooling configurations at leading edge is very necessary.As the state of the art leading edge cooling configuration a concave channel with multi inline jets has been widely used in most of the blades.However,this kind of configuration also generates strong spent flow,which shifts the impingement off the stagnation point and weakens the impingement heat transfer.In order to solve this problem a new internal cooling configuration using double swirl chambers in gas turbine leading edge has been developed and introduced in this paper.The double swirl chambers cooling(DSC)technology is introduced by the authors and contributes a significant enhancement of heat transfer due to the generation of two anti-rotated swirls.In DSC-cooling,the reattachment of the swirl flows always occurs in the middle of the chamber,which results in a linear impingement effect.Compared with the reference standard impingement cooling configuration this new cooling system provides a much more uniform heat transfer distribution in the chamber axial direction and also provides a much higher heat transfer rate.In this study,the influences of different geometrical parameters e.g.merging ratio of two cylinder channels,the jet inlet hole configurations and radius of blunt protuberances in DSC have been investigated numerically.The results show that in the DSC cooling system the jet inlet hole configurations have large influences on the thermal performance.The rectangular inlet holes,especially those with higher aspect ratios,show much better heat transfer enhancement than the round inlet holes.However,as the price for it the total pressure drop is increased.Using blunt protuberances instead of sharp edges in the DSC cooling can improve the heat transfer enhancement and reduce the total pressure drop.展开更多
文摘Cellulose nanofiber (CNF) is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. It has high strength comparable to steel, and it shows low environmental load during a cycle of production and disposal. Besides it has many excellent properties and functions such as high rigidity, light-weight, flexibility and shape memory effect, so it is expected as a next-generation new material. Usually it is composed of many cellulose micro fibrils (CMFs) in which molecular chains of cellulose are aggregated in a crystal structure, the knowledge of mechanical properties for each CMF unit is important. Since actual fibrils are complicatedly intertwined, it is also crucial to elucidate the transmission mechanism of force and deformation not only in one fibril but also in between fibrils. How the dynamic and hierarchical structure composed of CMFs responds to bending or torsion is an interesting issue. However, little is known on torsional characteristics (shear modulus, torsional rigidity, etc.) concerning CMF. In general, in a wire-like structure, it is difficult to enhance torsional rigidity and strength, compared with tensile ones. Therefore, in this study, we try to build a hierarchical model of CNF by multiplying CMF fibers and to conduct molecular dynamics simulation for torsional deformation, by using hybrid model between all-atom and united-atoms model. First, shear modulus was estimated for one CMF fibril and it showed a value close to the experimental values. Also, we assume a state in which two CMFs are ideally arranged in parallel, and create a hierarchical structure. We evaluate the dependence on the temperature for the bond strength and toughness in the hierarchical structures. Furthermore, we mentioned the transmission mechanism between components of a hierarchical structure.
文摘By merging two standard swirl chambers,an alternative cooling configuration named double swirl chambers(DSC)has been developed.In the DSC cooling configuration,the main physical phenomena of the swirl flow in swirl chamber and the advantages of swirl flow in heat transfer augmentation are maintained.Additionally,three new physical phenomena can be found in DSC cooling configuration,which result in a further improvement of the heat transfer:(1)impingement effect has been observed,(2)internal heat exchange has been enhanced between fluids in two swirls,and(3)“∞”shape swirl has been generated because of cross effect between two chambers,which improves the mixing of the fluids.Because of all these improvements,the DSC cooling configuration leads to a higher globally-averaged thermal performance parameter(Nu/Nu_(∞)/(f/f0)^(1/3))than standard swirl chamber.In particular,at the inlet region,the augmentation of the heat transfer is nearly 7.5 times larger than the fully developed non-swirl turbulent flow and the circumferentially averaged Nusselt number coefficient is 41%larger than the standard swirl chamber.Within the present work,a further investigation on the DSC cooling configuration has been focused on the influence of geometry parameters e.g.merging ratio of chambers and aspect ratio of inlet duct on the cooling perfomance.The results show a very large influence of these geometry parameters in heat transfer enhancement and pressure drop ratio.Compared with the basic configuration of DSC cooling,the improved configuration with 20%to 23%merging ratio shows the highest globally-averaged themal performance parameter.With the same cross section area in tangential inlet ducts,the DSC cooling channel with larger aspect ratio shows larger heat transfer enhancement and at the same time reduced pressure drop ratio,which results in a better globally-averaged themal performance parameter.
文摘It is known that the leading edge has the most critical heat transfer area of a gas turbine blade.The highest heat transfer rates on the airfoil can always be found on the stagnation region of the leading edge.In order to further improve the gas turbine thermal efficiency the development of more advanced internal cooling configurations at leading edge is very necessary.As the state of the art leading edge cooling configuration a concave channel with multi inline jets has been widely used in most of the blades.However,this kind of configuration also generates strong spent flow,which shifts the impingement off the stagnation point and weakens the impingement heat transfer.In order to solve this problem a new internal cooling configuration using double swirl chambers in gas turbine leading edge has been developed and introduced in this paper.The double swirl chambers cooling(DSC)technology is introduced by the authors and contributes a significant enhancement of heat transfer due to the generation of two anti-rotated swirls.In DSC-cooling,the reattachment of the swirl flows always occurs in the middle of the chamber,which results in a linear impingement effect.Compared with the reference standard impingement cooling configuration this new cooling system provides a much more uniform heat transfer distribution in the chamber axial direction and also provides a much higher heat transfer rate.In this study,the influences of different geometrical parameters e.g.merging ratio of two cylinder channels,the jet inlet hole configurations and radius of blunt protuberances in DSC have been investigated numerically.The results show that in the DSC cooling system the jet inlet hole configurations have large influences on the thermal performance.The rectangular inlet holes,especially those with higher aspect ratios,show much better heat transfer enhancement than the round inlet holes.However,as the price for it the total pressure drop is increased.Using blunt protuberances instead of sharp edges in the DSC cooling can improve the heat transfer enhancement and reduce the total pressure drop.
