HF etching of sacrificial layers with different The existing model cannot fit the experimental data well perimental data increases with etching time. A modified structures, namely channel, bubble, and joint-channel, i...HF etching of sacrificial layers with different The existing model cannot fit the experimental data well perimental data increases with etching time. A modified structures, namely channel, bubble, and joint-channel, is studied. The error of etching rate between the existing model and the exmodel considering the diffusion coefficient as a function of HF concentration and temperature is proposed. The etching rate coefficient as a function of temperature and the effect of reaction production are also considered in the modified model. For the joint-channel structure, a new mathematical model for the etching profile is also adopted. Experimental data obtained with channel, bubble, and joint-channel structures are compared with the modified model and the previous model. The results show that the modified model matches the experiments well.展开更多
One of the key problems by diffusion-rolling bonding with small reduction for carbon steel plates is the bonding assistant coat. Abonding assitant coat used below 850℃ was developed. It contained copper as basic elem...One of the key problems by diffusion-rolling bonding with small reduction for carbon steel plates is the bonding assistant coat. Abonding assitant coat used below 850℃ was developed. It contained copper as basic element and zinc as main alloy element. Other small elements and rear metals were added to decrease the melting point and to obtain a better clouding and bigh plasticity. Based on the theory of brazing and transient liquid diffusion welding, two carbon steel plates were rolled with small reduction by using self-made bonding assistant coat. Temperature, pressure and holding time are the main technology parameters for controlling the process of diffusion-rolling. The results show that the bonding strength is the greatest when the bonding temperature is 830℃, holding time is 3 min and the reduction rate is 9%.展开更多
Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visu...Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures.It is found that the relationship between the breakthrough pressure and the temperature is nearly linear(i.e.the pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment.The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.展开更多
文摘HF etching of sacrificial layers with different The existing model cannot fit the experimental data well perimental data increases with etching time. A modified structures, namely channel, bubble, and joint-channel, is studied. The error of etching rate between the existing model and the exmodel considering the diffusion coefficient as a function of HF concentration and temperature is proposed. The etching rate coefficient as a function of temperature and the effect of reaction production are also considered in the modified model. For the joint-channel structure, a new mathematical model for the etching profile is also adopted. Experimental data obtained with channel, bubble, and joint-channel structures are compared with the modified model and the previous model. The results show that the modified model matches the experiments well.
文摘One of the key problems by diffusion-rolling bonding with small reduction for carbon steel plates is the bonding assistant coat. Abonding assitant coat used below 850℃ was developed. It contained copper as basic element and zinc as main alloy element. Other small elements and rear metals were added to decrease the melting point and to obtain a better clouding and bigh plasticity. Based on the theory of brazing and transient liquid diffusion welding, two carbon steel plates were rolled with small reduction by using self-made bonding assistant coat. Temperature, pressure and holding time are the main technology parameters for controlling the process of diffusion-rolling. The results show that the bonding strength is the greatest when the bonding temperature is 830℃, holding time is 3 min and the reduction rate is 9%.
基金supported by the National Natural Science Foundation of China (No.50976011)Fundamental Research Funds for the Central Universities of China (No. 2009JBM090)
文摘Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures.It is found that the relationship between the breakthrough pressure and the temperature is nearly linear(i.e.the pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment.The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.
