Papers by Author: Zhen Ping Wan

Abstract: This study explores the feasibility of using a novel process, micro planing with multi-cutter, to fabricate graphite composite bipolar plates of proton exchange membrane fuel cells (PEMFCs). Through the use of multi-cutter, this study succeeds in machining micro flow channels with dimensions of 0.2 mm×0.23 mm×0.4 mm (channel width × rib width × depth size) on graphite composite bipolar plate (21 mm × 80 mm × 1.5 mm), in a reaction area of 10 mm × 60 mm. The graphite composite plates fabricated by multi-cutter are tested for cell performance under varying back-pressures. Results show that the cell performance increase with the rising back-pressures and can be promoted apparently by decreasing the size of flow channels.

Abstract: Metallic bipolar plates with unique wave-like microstructure on the bottom of microflow channel have shown promising prospects for the application in proton exchange membrane microfuel cell. A novel method—milling with special thin slotting cutters is developed for fabrication of wave-like microstructure on the bottom of microflow channels. The special thin slotting cutter is manufactured by removing one or several teeth every one tooth of the traditional slotting cutter regularly. Forming mechanism of wave-like microstructure is presented and experimental tests have been conducted for validation of the feasibility of the novel method. Results show that the wave-like microstructure can be successfully fabricated on the bottom of microflow channel. The bottom of bipolar plates with wave-like microstructure is not a flat plane, but a wavy groove. The wavelength and amplitude of wave-like microstructure increase with the increase of feed speed and the number of removed teeth.

Abstract: The influence of microstructures on wettability on stainless steel was investigated. Two kinds of different microstructures were manufactured by a laser processing method with micro parallel grating and square pillars array. The experimental and theoretical values of contact angle (CA) were obtained. Furthermore, within the groove spacing processing size range in micron scale, the experimental results agreed with the theoretical predictions based on the Wenzel. By the influence of machining and measuring conditions, the experimental values of CA were smaller than the predicted theoretical values. A linear relationship between the CA and the micro-scale structures was obtained, which showed the CA was increased with an increase of groove spacing. With the same structural parameters, the CA of square pillars array microstructures was larger than parallel grating microstructures.

Abstract: The porous metal fiber sintered felt (PMFSF), a new catalyst support, was successfully used to construct a methanol steam reforming microreactor for hydrogen production. To study the transport characteristics of PMFSFs, a three-dimensional model with the cubic pore cell structure for PMFSFs was established. Using computational fluid dynamics fluent software, the velocity and pressure distribution when the fluid through the PMFSFs was investigated by changing the porosity of PMFSFs and inlet velocity of the fluid. In addition, fluid temperature distribution was analyzed under different inlet velocities by setting the temperature of fluid and wall. The result shows that the PMFSFs greatly enhance the transport characteristics because of its three-dimensional network structure and microchannel structure, it will become an ideal candidate for catalyst support material.

Abstract: Ribs with triangular cross section can be obtained by rolling process on copper tube surface. The ribs are the basis for machining 3D Integral External Finned Tube. Triangular ribs on a red copper tube with 12.6mm diameter and 1.25mm wall thickness are fabricated under, the feed rate of 0.15mm/r, the speed of 2m/min, and rolling depth from 0.1mm to 0.85mm.In this study, four kinds of ribs are obtained. After the analysis of the relationship between rolling depth and the rib structure, the optimal single triangular rib can be obtained on condition that the rolling depth is 0.75mm.

Abstract: A new method of rolling-plowing-extrusion is proposed for fabricating outside 3D integral fins on the stainless steel tube. The fabricated process of fins is divided into two stages, rolling and plowing-extrusion, at first ribs are obtained on the stainless steel tube by the rolling process, and then 3D integral fins are obtained by the plowing-extrusion process. In this study, the principle of the rolling-plowing-extrusion is briefed; rolling process and plowing-extrusion process are analyzed, respectively. Through the experiments, the effect of technical parameters on fins forming and structures is investigated; experimental results are shown that accurate matching technical parameters and plowing tool angles is the key to the fins forming and structures; further analytical results indicate that when rolling speed and plowing speed is 50r/min, rolling feed rate is 0.16 mm/r, rolling depth is approximately 0.80-1.00mm, plowing feed rate is above 2.16mm/r, plowing depth is approximately 0.25-0.45mm, the optimal fins are obtained

Abstract: In order to manufacture slim long metal fibers efficiently, a new type multi-tooth tool is developed. multi-tooth tool has chip-splitting action, namely the whole cutting layer will be split into pieces of metal fibers as all tiny teeth contacting the workpiece are involved in cutting. The oblique cutting model of multi-tooth tool and that of a tooth in the tool are built. The formation mechanism of metal fiber cross section is presented according to different feedrate.

Abstract: In this paper the formation and growth of bubbles during the melt foaming process are studied from microcosmic aspect. The forming process of liquid film between two neighboring bubbles is also analyzed. According to the cavity effect of ultrasonic wave, the effect of ultrasonic wave on the fragmentation of cell structures of aluminum foam is investigated. Results show that the effect of ultrasonic wave on the cell structure fragmentation decreases with the increase of the distance from the ultrasonic wave source to the cell structure. Therefore, a new concept, namely aluminum foam of biomimetic gradient structure, is proposed.

Abstract: Microstructure of machined copper chips at very low velocity was characterized by transmission electron microscopy. The structure of the machined chip produced by reasonable combinations of machining parameters is virtually entirely occupied by isolated equiaxed submicron grains of 100~300nm in size with high-angle boundaries. A finite element model was developed to study large plastic deformation in plain orthogonal machining copper. The numerical results show most of the grain refinement associated with the formation of ultra-fine grained chip may be attributed to the large shear strain imposed in the deformation zone. It is feasible to take machining process as a method of preparing ultra-fine grained materials. But the optimal design of the machining process requires a precise and quantitative understanding of the mechanics of deformation-induced subgrain microstructure.

Abstract: With more and more applications of glass in advanced fields of science, the demand for glass machining precision and efficiency has increased greatly. More and more attention is being paid to glass cutting by ordinary tool because precise glass parts with various shapes can be obtained at high efficiency and low cost. But, in this method, rounded cutting edge radius of tool has important influence on precision and integrity of surface. This paper presents the laws of glass crack initiation and propagation when a cylindric indenter is used for glass indention. Research results show that two cracks that are symmetrical to the normal plane of the indentation surface occur suddenly when the load increases to a critical value. Closing occurs in the two cracks during unloading. The interior angle between the two cracks and critical load increase with rounded edge radius of cylindric indenter linearly.