Steam reforming of methane over Ni catalyst in micro-channel reactor

A comprehensive study on the catalytic performance of Ni catalyst to implement millisecond steam reforming of methane (SRM) reaction in micro-channel reactors was conducted in this work. A new method to manufacture the metal-ceramics complex substrate as catalyst support was presented, that is, a layer of nano-particles, α-Al₂O₃, was thermally sprayed on a metallic substrate, usually FeCrAlloy. Ni or Rh catalyst was then impregnated on the substrate, forming firm and active catalyst coatings. The fall-off rate of the catalyst can be neglected after the plates experienced the high-temperature SRM reaction, showing the reliability in long-term use and the excellent catalytic performance for SRM reaction in micro-channel reactors. In comparison with the expensive Rh catalyst, Ni also showed wonderful performance to catalyze the SRM reaction in micro-reactors within milliseconds. Using the appropriate reactor design, CH₄ conversion reached above 90% when the residence time was as short as 32 ms for catalyst loading of 6.8 g/m². When the residence time was longer than 100 ms, CH₄ conversion was above 98%. Besides, catalyst deactivation was not detected for 500 h on stream with S/C ratio of 3.0, and for 12 h with S/C of 1.0 as well. Extensive characterizations on these Ni catalyst plates using XRD, SEM, TEM and XPS demonstrated that Ni catalysts prepared in this work did not show any sign of deactivation after being used in the micro-channel system under high-temperature operation.     

Numerical investigation of fluid flow and heat transfer under high heat flux using rectangular micro-channels

A 3D-conjugate numerical investigation was conducted to predict heat transfer characteristics in a rectangular cross-sectional micro-channel employing simultaneously developing single-phase flows. The numerical code was validated by comparison with previous experimental and numerical results for the same micro-channel dimensions and classical correlations based on conventional sized channels. High heat fluxes up to 130 W/cm² were applied to investigate micro-channel thermal characteristics. The entire computational domain was discretized using a 120 × 160 × 100 grid for the micro-channel with an aspect ratio of (α = 4.56) and examined for Reynolds numbers in the laminar range (Re 500–2000) using FLUENT. De-ionized water served as the cooling fluid while the micro-channel substrate used was made of copper. Validation results were found to be in good agreement with previous experimental and numerical data [1] with an average deviation of less than 4.2%. As the applied heat flux increased, an increase in heat transfer coefficient values was observed. Also, the Reynolds number required for transition from single-phase fluid to two-phase was found to increase. A correlation is proposed for the results of average Nusselt numbers for the heat transfer characteristics in micro-channels with simultaneously developing, single-phase flows.     

Energy and exergy analysis of hybrid micro-channel photovoltaic thermal module

In this communication, an attempt has been made to evaluate energy and exergy analysis of a hybrid micro-channel photovoltaic thermal (MCPVT) module based on proposed micro-channel solar cell thermal (MCSCT) under constant mass flow rate of air in terms of design and climatic parameter. The performance in terms of overall annual thermal and exergy gain and exergy efficiency of micro-channel photovoltaic thermal module have been evaluated by considering four weather conditions for different climatic conditions of India. Further analysis has also been carried out for single channel photovoltaic thermal (SCPVT) module and the results of micro-channel photovoltaic thermal module and single channel photovoltaic thermal module have been compared.On the basis of numerical computations, it has been observed that an overall annual thermal and exergy gains have been increased by 70.62% and 60.19% respectively for MCPVT module for Srinagar climatic conditions. Similar observations have been made for Bangalore, Jodhpur and New Delhi.     

Micro injection molding of a micro-fluidic platform

Micro fabrication of polymers is becoming increasingly important and is considered a low-cost alternative to silicon- or glass-based MEMS technologies. However, very little work has been done to study the influence of polymer resin on the replication accuracy of the micro features in micro injection molding. In this study, micro injection molding was applied to a micro-featured fluidic platform used for DNA/RNA testing. LIGA-like processes were used to prepare a silicon-based SU-8 photoresist, followed by electroforming to make a Ni–Co-based stamp. The micro features in the stamp consisted of a micro-channel array 50 μm in pitch size. COC, PC, PMMA and PS were used as the injection molding materials. The effect of various polymer resins and molding conditions on the replication accuracy of the micro features was investigated. The width and depth of the micro-channels within the molded devices were measured and analyzed. For the micro-injection-molded devices, the accuracy of the width and depth of the micro-channels increased with increasing mold temperature, melt temperature, injection velocity and packing pressure within the regular processing window. The molded parts showed excellent replication accuracy for the COC polymer resin due to its low viscosity and low, isotropic shrinkage. The PS resin also achieved acceptable micro-channel replication accuracy under specific molding conditions.     

微通道板次级电子发射层中各元素随深度的分布

本文应用XPS研究微通道板次级电子发射层中各元素浓度随深度的分布,以及不同烧氢还原温度对此分布的影响,并讨论了不同烧氢还原温度对次级电子发射性能的影响,在此基础上提出了改进微通道板性能的几个途径。     

压电泵驱动闭式水冷环路传热实验研究

设计并研制全金属双腔串联有阀压电泵,利用压电泵驱动水工质在闭式环路内循环稳定流动。水冷环路热端设计为微通道结构,微通道结构能显著增强液相工质流动过程中与壁面换热速率。在压电泵驱动下,工质在微通道热端吸热,冷端放热,实现热量从热端到冷端高效传递。搭建实验测试系统,研究压电泵工作性能以及压电泵驱动水冷环路传热性能。结果表明,压电泵在开放系统和闭式系统工作性能一致。压电泵驱动电压越大,回路内液相工质流动速度越快,传热速率越高,系统热阻越低。双腔串联压电泵在120V驱动电压下,泵水流量达到167 mL/min,水冷环路热阻达到0.12℃/W。压电泵驱动闭式水冷环路具有热阻小,结构紧凑,能耗低,智能控制等优点,能更好地应用于大功率电子器件散热领域。     

Experimental analysis of plasma and heating effect on H2 permeation behavior through Pd–Cu40% membranes in 1mm gap length plate reactor

In this work, experimental analysis of hydrogen permeation behavior under heating only and plasma-heating effect were studied in 15  μm and 20  μm Pd–Cu40% membrane thicknesses. Apure hydrogen gas at feeding pressure of 100 kPa was injected in 1 mm gap length plate micro-channel reactor (PMCR). The permeated hydrogen flux through Pd–Cu40% membranes was measured under heating only experiment at PMCR heating temperature range of 423–573 K and hydrogen flow rates of 0.1–1 L/min. In the plasma-heating experiments, dielectric barrier discharge plasma (DBD) were used at the applied voltage ranges of 10–16 kV, PMCR heating temperatures 423–573 K and hydrogen flow rate 0.1 L/min. The hydrogen permeability was calculated according to the Fick's and Sievert's law equation. It was found that the hydrogen permeability of heating only experiments lower than that obtained from plasma-heating experiments for both Pd–Cu membrane thickness. Further, the hydrogen permeability of the plasma-heating experiments has shown anon-linearity effect which it was presented in the pre-exponential factor and the activation energy pattern. However, it was observed that the hydrogen permeability decreased while the DBD-plasma applied voltage was high, due to the hydrogen gas reverse reaction. A comparison between the hydrogen permeability and the permeation rate% of both experiments has been developed to investigate the dependence on the membrane thickness in both experiments. The analysis shows that the permeability of 15  μm membrane thickness was always higher than 20  μm membrane thickness results and the maximum hydrogen permeability was at PMCR heating temperature of 573 K.     

Investigations of the unsteady diffusion process in microchannels

This paper is concerned with the investigations and modeling of the unsteady diffusion process along a straight micro-channel with a cross section of 380 μm×360 μm. The studied process is characterized by small Reynolds numbers (Re<10) and high Péclet number (Pe>1000). The 3D computations of the coupled momentum and diffusion equations for isochoric motions are performed with the FLUENT code using the unsteady solvers for both equations. In the limit of stationary solutions, the numerical results are validated by direct flow visualizations and experimental data using confocal microscopy. The computed distributions of concentration provide qualitative and quantitative information on the transitory diffusion process and the rate of solute spreading within the investigated geometry. In particular, the pattern of the “butterfly effect” is represented and analyzed during the non-stationary dynamical process. The work is relevant for the design of novel microfluidics applications where the control of diffusion processes at the walls are important (absorption, extraction, capture of molecules or nano-particles).     

黏弹性流体在尺寸渐变型微观孔道流动规律研究

随着国民经济的快速发展,为满足对于石油产品的大量需求,油田对于三次采油技术进行了积极的探索,聚合物溶液驱油作为一种有效地提高采收率手段得到了广泛的应用和迅速的发展。建立了黏弹性流体流动的微观孔道模型;采用上随体Maxwell本构模型;运用POLYFLOW有限元流体力学软件对模型进行求解;得到了模型的有关速度等值线、流函数分布图;分析了松弛时间、流量、孔喉比对于微观波及效率的影响。     

应用于中子照相的热中子敏感微通道板

介绍了中子成像探测技术的应用。由于直接在微通道板(MCP)玻璃中掺加中子灵敏核素可使MCP对热中子敏感,从而可将MCP事件计数成像探测器的优势成功地应用于以中子为探针的成像探测技术,本文开展了热中子敏感微通道板的研究。通过在MCP玻璃中掺摩尔百分比为3%的Gd2O3,并沿用MCP的制作方法,完成了直径为50mm和106mm的大面阵热中子敏感MCP的制作,并进行了基于这种大面阵热中子敏感MCP的中子事件计数成像探测器的中子成像实验。理论和实验结果都验证了掺摩尔百分比为3%的Gd2O3 MCP可取得对热、冷中子30%~50%的探测效率。最后,进一步介绍了目前开展的封装式中子敏感MCP增强管的研制工作。基于掺Gd2O3的MCP增强管并经光学耦合到CCD或CMOS相机的紧凑混合传感器结构是实现高时空分辨能力的中子照相无损检测技术的有效途径。