Lei Hou

Effect of electric field distribution uniformity on electrospinning

Recent experiments demonstrated that the essential electrospinning mechanism is a rapidly whipping dielectric liquid jet in an electric field. The effects of three kinds of electric field distributions including a very nonuniform electric field, a slightly nonuniform electric field, and a uniform electric field were studied to analyze the influence of the electric field distribution on the electrospinning process and the fiber morphology. The average electric field strength Eav and the electric field nonuniformity coefficient f were used to describe the electric field. The results show that the length range of the straight jet path for stable electrospinning process was a function of the electric field distribution. The length of the jet straight part increased with the decreasing f. The initial angle of the looping envelope and the helical pitch decreased with decreasing f. The results also show that higher voltages can be used at the nozzle for a stable electrospinning when f is small. A higher voltage ...

A shield ring enhanced equilateral hexagon distributed multi-needle electrospinning spinneret

The multi-needle electrospinning system is a convenient way to produce fibers with special structures such as core-shell morphologies at a high production rate. In this paper, a specially designed multi-needle electrospinning system is presented. The spinnerets were built-up with an equilateral hexagon array. Each set of 3 needles of the spinnerets were distributed as an equilateral triangle. A coaxial shield ring was used to create an approximate uniform electric field near the tips of the needles and to restrict the collection area. The simulation results also show that the outside needles can help to create a more uniform electric field near the inside tips of the needles and restrict the path of the inside jets, which works almost the same as the additional shield ring. Based on the simulation results, several multi-needle systems were tested. A 7 cm diameter shield ring was used in a 7 needle system, a 9 cm diameter shield ring was used in a 19 needle system and a 10.5 cm diameter shield ring was used in a 37 needle system. Polyethylene Oxide (PEO) aqueous solution was used as the test solution in experiments. The electrospinning results demonstrated that the use of multi-needle spinnerets is robust and that uniform nanofibers can be produced. The more needles used, the smaller the mean fiber diameter for larger mean electric field strengths. These distributions of needles show the scale up possibility of special structure electrospun nanofiber manufacturing.

Multiple Jets in Electrospinning

The low fluid throughput in electrospinning may limit the industrial use of single needle system. To meet high liquid throughput requirements and uniform fibers, a special aligned multiple jets setup has been designed in this paper. The needles have been disposed as a regular hexagon. A 7 cm diameter iron ring has been used in one experiment and different heights of the 7 needles have been used in another experiment in order to received uniform fibers from 7 needles. The results demonstrate that the special setup could produce uniform fibers according to SEM images. Electrical field distribution from the spinning nozzle to the collector was also calculated, analyzed and presented in this paper

Included Angle Selection of V-Shape Insulator String for 750-kV Compact Transmission Line

Included angle selection for a V-shape insulator string applied in 750-kV compact transmission line is studied in this paper. The mechanical performance of V-shape insulator string is demonstrated from calculation and experiment. A new solution, which is based on the finite-element method and applied to calculate the deformation of V-string, is presented. This paper discusses the relation between deformation (displacements and force) and load on V-string. Loading experiment for V-string is conducted in order to verify the calculation results. Experimental data of displacements for V-shape composite and porcelain insulator string are obtained. Finally, combined with the calculation and experiment results, the selection of included angle for V-shape insulator string is discussed, and recommendations for the included angle value of V-shape insulator string in 750-kV compact transmission line are made.

Electrospun uniform fibres with a special regular hexagon distributed multi-needles system

A special design for the multi-jets electrospinning system is presented. In this work, a 6 (g/ml) % polyethylene oxide (PEO) water solution was electrified and pushed by air pressure through a spinneret. The spinnerets were built-up with needles with a regular hexagon distribution and each 3 needles have been designed as a regular triangle distribution. The outside needles modified the electrical field to uniform the electrical field strength on the inside nozzles and restrict the path of the inside jets. A coaxial iron ring was used in order to uniform the electrical field strength on the outside nozzles and restrict the collection area. In this paper, a 7 cm diameter ring was used in the 7 needles system, a 9 cm diameter ring was used in the 19 needles system and a 1lcm diameter iron ring was used in the 37 needles system test. The results demonstrated that the special design setup can produce uniform nanoscale fibres and the spinning process is insensitive with the atmosphere disturbance. The distribution of needles shows a possibility design for improving the production rate of nanofibres manufacturing.

Extreme bending of composite insulators on 750 kV compact transmission lines

In designing and constructing the first 750 kV double-circuit compact transmission line, much pioneering work is necessitated in the choice of tower, insulator strings and phase-to-phase spacers. In this paper the mechanical characteristics of three possible phase-to-phase composite spacers for such compact transmission lines are considered in respect of very large bending of the spacer. A large deflection theory is introduced to calculate the lateral deflections and longitudinal compressions caused by applied axial loads and these are compared with the results of tests on three spacers of different lengths and diameters. Agreement between calculation and test results was good and the necessity for the larger diameter demonstrated. No permanent damage due to the extreme bending was found and two of the spacer samples were found to be suitable for use in the compact transmission lines with a good safety margin in respect of such bending.

Dynamics characteristic of V-string composite insulators for 330kV overhead transmission line

Dynamics characteristic of composite insulators under horizontal load caused by wind load is studied in this paper. For the advantages, V-string insulators are widely used in overhead transmission lines. Earlier study proves that the buckling deformation of the composite insulator under compression load is stable. So it is reasonable to allow composite insulators bearing compression force. The new concept makes it possible to adopt smaller V-string included angle and reduce the costs of the overhead transmission line. The static loading characteristics of V-string at different included angle under different vertical and horizontal load have been determined in the V-string static load experiments. The possibility of adopting small included angle is verified. Because of the differences between dynamic wind load and static load, in certain circumstances, the dynamic effects need to be examined. Dynamics response of insulator-conductor system is analyzed in the paper. The mathematical model of the insulator-conductor system is presented. Finally, according to the experiment and simulation results and the theoretical analysis, the complete optimized designing solution of V-string composite insulators for 330 kV overhead transmission line is determined.

Mechanical parameter optimization of interphase composite spacer used for controlling conductor galloping

Interphase spacer is an effective galloping control device. For the conception that spacers must provide enough bearing force to conductors, the flexible composite spacers with integrated structure are widely used nowadays in China. To acquire adequate rigidity, the only way is to increase the core rod diameter. It results that the spacers are over long and over heavy, which raises the costs and manufacture difficulties. Furthermore the heavy weight of the spacers will severely increase the tension and the sag of the conductors and bring unfavorable influences to the transmission lines. In the paper, dynamic model for the overhead lines and mechanical models for several kinds of interphase spacers are presented. Then numerical method is used to simulate the vibrations of the conductors. Aiming at optimizing the mechanical parameter, the spacers with different structures and parameters are compared to examine the relationship between mechanical parameter and effectivity of controlling galloping. The results show that the rigidity of the spacer under compressive load is not important as we considered before, so the heavy structure is not necessary. Finally it is concluded that the spacers designed as light structures is reasonable.