源在外延片直径方向上的耗尽导致了外延片上局部各点的生长速率及掺杂浓度是个随位置变化的量,因此造成了外延片厚度及浓度的不均匀性。通过引入基座气浮旋转可以有效降低这种不均匀性,在典型工艺条件下,采用基座旋转,76.2 mm 4H-SiC外...源在外延片直径方向上的耗尽导致了外延片上局部各点的生长速率及掺杂浓度是个随位置变化的量,因此造成了外延片厚度及浓度的不均匀性。通过引入基座气浮旋转可以有效降低这种不均匀性,在典型工艺条件下,采用基座旋转,76.2 mm 4H-SiC外延片厚度不均匀性、p型掺杂浓度不均匀性和n型掺杂不均匀性分别为0.21%、1.13%和6.96%。基座旋转并不能完全消除外延片n型掺杂浓度不均匀性。优化主氢流量及C/Si比能够改变掺杂源的耗尽曲线,将76.2 mm SiC外延片n型掺浓度不均匀性优化至2.096%(σ/mean)。展开更多
One of the most important and effective hardware elements for improvement of efficiency and power density of proton exchange membrane fuel cells is the flow field plate. The design and the pattern of the flow field pl...One of the most important and effective hardware elements for improvement of efficiency and power density of proton exchange membrane fuel cells is the flow field plate. The design and the pattern of the flow field plate have a considerable effect on the effectiveness of mass transport as well as on the electrochemical reactions inside the cell. The configuration of the flow field plate aims at ensuring a low pressure-drop over all channels in the stack. In this work, a FPFFP （fractal parallel flow field plate）, with bio-inspired configuration by insertion of fractals in a classic PFFP （parallel flow field plate）, is proposed, increasing the flow area of the hydrogen at anode side without increasing the section＇s area of the flow field plate. By simulating was observed that, the use of channels in fractal shape can increase the hydrogen flow area without occuring pressure loss in the cell. The fluid dynamic behavior in the FPFFP at smaller scales was replicated in the same plate, with better advantage of the active area of the electrode. Increasing the hydrogen flow area without causing pressure loss could be a good tactic to increase the power density of fuel cells, and consequently improving the cell performance.展开更多
Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether(DME).A systemic procedure was employed to determine the suitable experimental conditions.It was found tha...Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether(DME).A systemic procedure was employed to determine the suitable experimental conditions.It was found that DME conversion first increased up to the maximum and then decreased slightly with the increase of added water and air.The increase of total feed gas flow rate resulted in the decrease of DME conversion and hydrogen yield,but hydrogen energy consumption dropped down to the lowest as total feed gas flow rate increased to76 ml·min 1.Larger electrode gap and higher discharge voltage were advantageous.Electrode shape had an important effect on the conversion of DME and production of H2.Among the five electrodes,electrode 2#with valid length of 55 mm and the radian of 34 degrees of the top electrode section was the best option,which enhanced obviously the conversion of DME.展开更多
Exothermic hydrogenation reaction of acetone is an important part of an IAH-CHP, and the performance of IAH-CHP is affected directly by this reaction. This paper studies the influence of space velocity, temperature, h...Exothermic hydrogenation reaction of acetone is an important part of an IAH-CHP, and the performance of IAH-CHP is affected directly by this reaction. This paper studies the influence of space velocity, temperature, hydrogen flow rate and pressure on conversion and selectivity experimentally. The byproducts are analyzed and classified into three types: hydrogenation product, cracking products and condensation products. Both the conversion and selectivity of this reaction have the same trend with the change of space velocity, temperature and hydrogen flow rate, and has the opposite trend with the change of pressure. As the space velocity increases, the conversion curve is a gradual decline parabola but the selectivity curve is close to a straight line. Hydrogen flow rate has a more obvious influence on conversion than temperature, whereas on selectivity the situation is opposite. High pressure increases the conversion of acetone to all products, but the increment of byproducts is more than that of isopropanol, so the selectivity decreases as pressure increases.展开更多
The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ide...The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. The present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. The axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. The real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. The computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.展开更多
文摘源在外延片直径方向上的耗尽导致了外延片上局部各点的生长速率及掺杂浓度是个随位置变化的量,因此造成了外延片厚度及浓度的不均匀性。通过引入基座气浮旋转可以有效降低这种不均匀性,在典型工艺条件下,采用基座旋转,76.2 mm 4H-SiC外延片厚度不均匀性、p型掺杂浓度不均匀性和n型掺杂不均匀性分别为0.21%、1.13%和6.96%。基座旋转并不能完全消除外延片n型掺杂浓度不均匀性。优化主氢流量及C/Si比能够改变掺杂源的耗尽曲线,将76.2 mm SiC外延片n型掺浓度不均匀性优化至2.096%(σ/mean)。
文摘One of the most important and effective hardware elements for improvement of efficiency and power density of proton exchange membrane fuel cells is the flow field plate. The design and the pattern of the flow field plate have a considerable effect on the effectiveness of mass transport as well as on the electrochemical reactions inside the cell. The configuration of the flow field plate aims at ensuring a low pressure-drop over all channels in the stack. In this work, a FPFFP （fractal parallel flow field plate）, with bio-inspired configuration by insertion of fractals in a classic PFFP （parallel flow field plate）, is proposed, increasing the flow area of the hydrogen at anode side without increasing the section＇s area of the flow field plate. By simulating was observed that, the use of channels in fractal shape can increase the hydrogen flow area without occuring pressure loss in the cell. The fluid dynamic behavior in the FPFFP at smaller scales was replicated in the same plate, with better advantage of the active area of the electrode. Increasing the hydrogen flow area without causing pressure loss could be a good tactic to increase the power density of fuel cells, and consequently improving the cell performance.
基金Supported by the National Natural Science Foundation of China(21176175,20606023)
文摘Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether(DME).A systemic procedure was employed to determine the suitable experimental conditions.It was found that DME conversion first increased up to the maximum and then decreased slightly with the increase of added water and air.The increase of total feed gas flow rate resulted in the decrease of DME conversion and hydrogen yield,but hydrogen energy consumption dropped down to the lowest as total feed gas flow rate increased to76 ml·min 1.Larger electrode gap and higher discharge voltage were advantageous.Electrode shape had an important effect on the conversion of DME and production of H2.Among the five electrodes,electrode 2#with valid length of 55 mm and the radian of 34 degrees of the top electrode section was the best option,which enhanced obviously the conversion of DME.
基金supported by the National Natural Science Foundation of China under Grant No 51276181the National Basic Research Program of China under Grant No 2011CB710705
文摘Exothermic hydrogenation reaction of acetone is an important part of an IAH-CHP, and the performance of IAH-CHP is affected directly by this reaction. This paper studies the influence of space velocity, temperature, hydrogen flow rate and pressure on conversion and selectivity experimentally. The byproducts are analyzed and classified into three types: hydrogenation product, cracking products and condensation products. Both the conversion and selectivity of this reaction have the same trend with the change of space velocity, temperature and hydrogen flow rate, and has the opposite trend with the change of pressure. As the space velocity increases, the conversion curve is a gradual decline parabola but the selectivity curve is close to a straight line. Hydrogen flow rate has a more obvious influence on conversion than temperature, whereas on selectivity the situation is opposite. High pressure increases the conversion of acetone to all products, but the increment of byproducts is more than that of isopropanol, so the selectivity decreases as pressure increases.
文摘The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. The present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. The axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. The real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. The computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.
