Experimental investigations on liquid flow and heat transfer in rectangular microchannel with longitudinal vortex generators

The behaviors of improved Heat transfer and the associated higher pressure drop for liquid flow in rectangular micochannels with longitudinal vortex generators (LVGs) were determined experimentally for the Reynolds numbers of 170–1200 with hydraulic diameter of 187.5 μm and aspect ratio of 0.067 for LVGs with different number of pairs and angles of attack. It was found that the range of critical Reynolds numbers (600–730) were at a much smaller value by adding LVGs than the one without (Re ～ 2300); heat transfer performance was improved (9–21% higher for those with laminar flow and 39–90% for those with turbulent flow), while encountering larger pressure drop (34–83% for laminar flow and 61–169% for turbulent flow). Empirical correlations for these two parameters were then obtained by curve-fittings for a variety of rectangular microchannels under study.     

液相等离子喷涂La2O3-Y2O3-ZrO2涂层的组织结构与性能

采用一定化学配比的ZrOCl2·8H2O、YCl3和LaCl3三种盐溶液合成前驱体溶胶作为等离子喷涂液体喂料,制备二元稀土氧化物氧化镧与氧化钇共稳定的氧化锆陶瓷涂层,并测试分析了该涂层的组织结构、高温相稳定性及隔热性能。结果表明,氧化镧与氧化钇共稳定的氧化锆陶瓷涂层具有良好的隔热性能及高温相稳定性。     

柔性基底上电沉积法制备铜铟硒太阳电池薄膜

采用简单的二电极系统,以大面积的铂网为阳极,钼或不锈钢薄片为阴极,以氯化铜、三氯化铟、亚硒酸的水溶液为电沉积液,利用一步电沉积技术在不锈钢薄片柔性基底上电沉积制备铜铟硒(CIS)薄膜前驱体,该前驱体经热处理后得到具有黄铜矿型晶体结构CIS薄膜.采用XRD、SEM和EDAX等对制备的CIS薄膜进行了表征,结果表明所制备CIS多晶薄膜物相纯净、晶型发育好,表面无裂纹,晶粒均匀.     

Investigation of thermal performance of microchannel heat sink with triangular ribs in the transverse microchambers

A numerical investigation is conducted to predict the thermal and hydraulic performances of the microchannel heat sink (MCHS) with different geometric parameters of triangular rib in the transverse microchamber. The parametric variables of width, length and height of the triangular rib are studied to find optimum design. The flow structure and characteristics of the interrupted MCHS are interpreted in details. The dimensionless ratios of average Nusselt number, friction factor and thermal enhancement factor are evaluated. It is found that the heat transfer rate is increasing with the increase of rib width and height, but decreasing with the increase of rib length. The boundary layer interruption and redevelopment effects introduced by the triangular rib are discussed. The results of thermal enhancement factor reveals an optimum geometrical parameters for the triangular rib with width = 100 μm, length = 400 μm and height = 120 μm for about Reynolds number of 500, yielding 43% enhancement relative to non-interrupted rectangular MCHS at equal pumping power. The results of mean Nusselt number ratio reveal an optimum enhancement of 56% relative to non-interrupted MCHS.     

Ni-Mo太阳光谱选择性吸收涂层的制备与性能研究

以自制Ni-Mo团聚型复合粉末为喷涂原料,采用超音速火焰喷涂法制得Ni-Mo太阳光谱选择性吸收涂层,表征了复合粉末和涂层的表面形貌,涂层的组成元素、相组成和光学性能,研究了粉末粒径大小、涂层组分比例和表面处理对涂层选择性吸收性能的影响.结果表明:当所用复合粉末粒径r≤45μm,粉末中Ni,Mo质量比为7:3时,制备的涂...     

SiC纤维/YSZ复合热障厚涂层韧性及热震性能研究

采用大气等离子喷涂(APS)技术, 以ZrO₂-8wt%Y₂O₃(8YSZ)和团聚的P7216(8YSZ和珍珠岩粉)粉末为原料, 在基体上制备了厚度大于4 mm的SiC纤维/YSZ(SFY)复合厚热障涂层, 通过扫描电子显微镜(SEM)分析了涂层的显微结构, 发现SFY涂层具有钢筋混凝土结构, 这种结构能够防止因为涂层厚度增加而引起的失效。此外, 基于计算机的断层成像技术分析热障涂层孔隙率的变化, 考察了SFY涂层和YSZ 热障涂层的抗热震性能、断裂韧性以及热导率性能, 并探讨了纤维的增韧机制。研究结果表明, SFY涂层具有更高的断裂韧性值和更好的抗热震性能, 25℃时SFY涂层的热导率为0.632 W/(m·K), 大约是传统YSZ热障涂层热导率的一半。SiC纤维对涂层内部裂纹的偏转和截止作用, 防止了裂纹扩散长大, 形成网状微裂纹结构, 有效提高了涂层的抗热震性能和断裂韧性。     

Simulation of heat and mass transfer in activated carbon tank for hydrogen storage

The charging process of hydrogen storage tank based on bed of activated carbon in a steel container at room temperature (295 K) and medium storage pressure (10 MPa) is simulated with an axisymmetric geometry model using the finite volume commercial solver Fluent. The mass flux profile at the entrance is established using user-defined functions (UDFs). The heat and mass transfer processes in the cylindrical steel tank packed with activated carbon are discussed considering the influence of viscous resistance and inertial resistance of the porous media. The velocity distribution and its effect on the temperature distribution are analyzed. The effects of the flow rate at the inlet and of the adsorption factor on the charging process are studied. A computational fluid dynamics (CFD) approach based on finite volume simulations is used. Results show that the temperature near the bottom of the tank is higher than that at the entrance, temperature in the center of the tank is higher than that near the wall and rises somewhat faster along the axial compared to the radial direction. The highest hydrogen absolute adsorption occurs at the entrance of the tank. A good agreement is found between the simulation results and the available experimental data. The maximum magnitude of the axial velocity is much higher than that of the radial component, resulting in more heat energy transfer along the axial direction than radial direction. In addition, the pressure reaches equilibrium earlier when the mass flow is higher, and the temperature reaches a maximum value faster.     

纳米ZrO2-Al2O3基高温封严涂层的结构与性能研究

研制了3种不同Al2O3含量(质量分数分别为5%,10%,15%)的纳米ZrO2-Al2O3基高温可磨耗封严涂层粉末材料,采用大气等离子喷涂(APS)工艺,制备了3种涂层材料的双层结构封严涂层和Al2O3含量逐层递增的多层结构封严涂层.对涂层材料的沉积效率,涂层的微观结构、硬度和结合强度等进行了测试与分析.结果表明:封严涂层材料的沉积效率随Al2O3含量的增加而升高;由于熔融条件的不同,涂层内ZrO2的形态不唯一;封严涂层的硬度和结合强度与厚度和Al2O3含量有紧密的关系;与双层结构封严涂层相比,多层结构封严涂层的综合性能良好,基本可以满足封严涂层对厚度、硬度和结合强度的要求.     

PEMFC阴极面带增湿槽道的模拟分析

对阴极面为带增湿槽道流场的单电池使用FLUENT软件建立了一个完整的三维数学模型。通过耦合气体控制方程、电化学反应Butler-Volmer方程、膜中水传递方程和水的相变方程,以及分析膜的水含量、阴极催化层水浓度、氧气浓度和膜中电流密度分布;结果表明,最后得到增湿槽道在实现阴极增湿的同时损失了其对应的活性面积。     

纳米氧化锆基热障烧蚀复合涂层的制备与研究

在纳米ZrO2中加入适量低熔点无机烧蚀材料SiO2和Cu,利用大气等离子喷(APS)技术,在TC4基体上制备出一种复合防热涂层.应用等离子火炬对涂层进行模拟烧蚀防热试验,运用X射线衍射(XRD)、扫描电镜(SEM)、电子探针(EPMA)等测试方法对粉末及涂层烧蚀前后的物相组成、显微结构和成分分布进行了观察和确定.研究结果表明,复合涂层表层烧蚀防热作用明显,内部仅出现液化现象,总体上涂层防热性能仍优于单一PYSZ涂层.涂层平均结合强度为47.7MPa.