Three‐dimensional computational comparison of mini pinned heat sinks using different nanofluids: Part one—the hydraulic‐thermal characteristics

The hydraulic‐thermal characteristics of 3D pinned heat sink designs have been numerically compared as the first part of a three‐part investigation. Five different pin geometries (circular, square, triangular, strip, and elliptic pins) and an unpinned heat sink with three types of nanofluids (Al₂O₃–H₂O, SiO₂–H₂O, and CuO–H₂O) are considered for laminar forced convection. The range of Reynolds number is from 100 to 1000, and volume fractions vary between 0% and 5%. The finite volume method is employed to solve the Navier–Stokes and energy equations by employing a SIMPLE algorithm for a computational solution. Three parameters are presented—the Nusselt number, the bottom temperature, and the hydrothermal performance of the heat sink with pressure drop data. The findings indicated that the overall hydrothermal performance of elliptic‐pinned (EP) heat sinks produces the most substantial value of 3.10 for pure water. For different nanofluids, the SiO₂–water nanofluids with EPs have the most significant hydrothermal performance. Also, this factor is enhanced with an increase in nanofluid concentration up to nearly 3.34 for 5% of SiO₂–water. Consequently, applying the elliptic‐pinned heat sinks is recommended with pure water for considering an increase in the pressure drop, with 5% of SiO₂–water nanofluids, regardless of an enlargement of pressure drop for heat‐dissipation applications.     

Experimental investigation of Al2O3–MgO hot hybrid nanofluid in a plate heat exchanger

Exergy–energy analysis of the plate heat exchanger is experimentally performed with different Al₂O₃–MgO hybrid nanofluid (HyNf) as a hot fluid. There were six combinations of fluids, namely, deionized (DI) water, ethylene glycol–DI water brine (1:9 volume ratio), propylene glycol–DI water brine (1:9 volume ratio), base fluids and their respective Al₂O₃–MgO (4:1 particle volume ratio) HyNfs of 0.1% total volume concentration. The effects of different flow rates and hot inlet temperatures on the heat transfer rate, heat transfer coefficient, pump work, irreversibility, and performance index (PI) are investigated. It is witnessed that the heat transfer rate, heat transfer coefficient, pump work, and irreversibility enhances with the flow rate and nanoparticle suspension. While the PI declines with a rise in the flow rate, the heat transfer rate, heat transfer coefficient, PI, and irreversibility rise up maximum for MgO–alumina (1:4) DI water HyNf upto 11.8%, 31.7%, 11.1%, and 4.05%, respectively. The pump work enhances upto 1.6% for MgO–alumina (1:4)/EG–DI water (1:9) HyNf.     

低阶煤颗粒-气/油泡间的诱导时间研究

为表征低阶煤颗粒-气/油泡间矿化过程的差异,通过Sutherland理论下固体颗粒进入泡沫产品的总概率(E)和浮选速率常数(k)之间关系,并结合低阶煤颗粒-气/油泡的浮选速率试验,求得了低阶煤颗粒-气/油泡间的诱导时间。浮选实验研究表明,在相同的捕收剂消耗量下低阶煤-油泡浮选产率均高于低阶煤-气泡浮选产率。诱导时间测试表明,低阶煤颗粒-油泡间的诱导时间(35 ms)要明显低于低阶煤颗粒-气泡间的诱导时间(93 ms)。上述实验结果表明,油泡表面的疏水性要强于传统浮选气泡表面的疏水性。然而,进一步利用Sutherland理论中固体颗粒进入泡沫产品的总概率和浮选速率常数之间的数学关系,并结合低阶煤颗粒-气/油泡的浮选速率试验求得的低阶煤颗粒-气/油泡间的诱导时间分别为9.67和8.46 ms,其与诱导时间测试仪分别测量的诱导时间差异很大。这主要是由于在实际浮选过程中气/油泡的上升速度分别为23.26和22.68 cm/s,其远高于2015EZ型诱导时间仪测试过程中气/油泡碰撞速度(2.0 cm/s)。因此,诱导时间理论计算表明气泡-颗粒间的碰撞速度对颗粒-气泡间的诱导时间影响很大。上述研究结果表明油泡浮选效果优于传统浮选的内在原因在于低阶煤颗粒-油泡间的诱导时间小于低阶煤颗粒-气泡间的诱导时间。     

缓冷出口温度对连续退火SPCC冷轧薄板屈服强度的影响

研究了缓冷出口温度对连续退火SPCC冷轧薄板组织和屈服强度的影响。结果表明:连续退火SPCC冷轧薄板的组织由等轴的铁素体晶粒和晶界处的块状渗碳体及晶粒内的颗粒状渗碳体组成。随着缓冷出口温度从680 ℃提高至700 ℃,平均晶粒尺寸从10.1 μm增加至12.5 μm;此外,提高缓冷出口温度还能够抑制晶界处块状渗碳体的形成,促进晶粒内细小渗碳体更加细小弥散的析出。当缓冷出口温度从680 ℃提高至700 ℃时,冷轧薄板的屈服强度约降低了28 MPa。     

Discrete element method study on hopper discharge behaviors of binary mixtures of nonspherical particles

This study is aimed at unveiling the influence of binary mixtures of nonspherical particles on hopper discharge behavior, which remains poorly understood. The discrete element method (DEM) is employed to simulate seven particle types with aspect ratios between 0 and 2 (namely, a sphere, two ellipsoids, two cylinders, and two cuboids) with the same volume. Seven monodisperse systems and twelve binary-shape mixtures are assessed. For the monodisperse systems, particle shape is the dominant factor dictating discharge rate, compared to other factors like aspect ratio, preferential orientation, and packing. Regarding the binary-shape mixtures, the discharge rates are similar for all twelve mixtures, reflecting a surprising lack of shape effects, which in turn means the negligible impact of solid volume fraction, aspect ratio, and segregation extent. Moreover, collision force is generally negatively correlated with discharge rate.     

复杂流道结构料仓的下料流率预测

在实验室搭建的有机玻璃料仓下料平台上，分别以自由流动粉体玻璃微珠和黏附性粉体煤粉和聚氯乙烯为实验介质，针对无改流体(No-In)、封闭改流体(Con-In)和开放改流体(Ucon-In)三种情况所形成的不同流道结构，开展了粉体料仓下料及其流率建模研究，定量分析了改流体对粉体下料流率的促进作用，对比给出了玻璃微珠、煤粉和聚氯乙烯在不同流道结构料仓内的下料特性。研究表明，改流体的引入有利于提高料仓下料流率，Con-In促进流动效果最明显，对于流动性弱的煤粉，下料流率提升幅度达到最大的58%。基于剪切摩擦区的概念，提出流率校正因子F对最小能量理论方程进行了修正，将理想的料仓下料模型拓展至实际下料过程。进一步，对于Con-In，根据流道结构特征结合对粉体的受力分析，修正了模型中的锥角项；对于Ucon-In，基于粉体下料流动竞争机制，提出分阶段下料模式并关联了内层和夹层的下料流率，最终建立了复杂流道结构料仓的下料流率预测模型。该模型综合考虑了粉体物性、下料流型和流道结构的影响，可有效预测自由流动粉体和黏附性粉体流经传统料仓(No-In)和改流体料仓(包括Con-In和Ucon-In)的粉体下料流率，且预测偏差<10%。     

Facile approach for Z-scheme type Pt/g-C3N4/SrTiO3 heterojunction semiconductor synthesis via low-temperature process for simultaneous dyes degradation and hydrogen production

The platinum/graphite-like carbon nitride/strontium titanate (Pt/g-C₃N₄/SrTiO₃) heterojunction semiconductor was synthesized using a facile approach for simultaneous photocatalytic dye degradation and hydrolysis of hydrogen production from simulated dyeing wastewater. Using SrTiO₃, trace Pt, and the addition of an appropriate amount of electron donors, it can effectively absorb sunlight and achieve 93% dye degradation and 471 μmol h⁻¹ g⁻¹ hydrogen yield. The analysis result indicates that the semiconductor is a Z-scheme type composite. It was also showed that the addition of electron donors effectively promoted the degradation rate, whereas the addition of Pt changed the photocatalytic reaction pathway, which resulted in a reduced degradation rate and a significant improvement of hydrogen evolution. A reaction mechanism for this phenomenon is also proposed.     

月柿提取物体外抗氧化活性研究

目的以月柿提取物为原料,研究其对2,2-联苯基-1-苦基肼基(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基的清除能力,并测定其多酚类物质没食子酸的含量。方法检测波长为518 nm,反应时间为40 min条件下,以IC_(50)值(清除率为50%时,抗氧化剂的浓度值)作为抗氧化能力评价指标,并采用高效液相色谱法测定其没食子酸含量。结果月柿提取物对于DPPH自由基有良好的清除作用,其IC50值为0.1868 mg/mL,与常用抗氧化剂作用相当,且月柿提取物中没食子酸含量为1.65 g/kg。结论月柿提取物具有很强抗氧化活性,作为化妆品及功能性食品原料有广阔的开发前景。     

煤粉锅炉脱硫系统中除尘器压差过高原因及解决方案

高倍率灰钙循环烟气脱硫技术在神东矿区的煤粉锅炉环保改造项目中已投入建设并成功运行,脱硫率可达95%以上。在NGD系统的运行调试期,布袋除尘器压差的数值及其上升速度均较改造前有大幅提高,影响了锅炉系统的正常运行并降低了布袋除尘器的运行效率。为了解决此问题,先分析滤料透气性降低而导致布袋除尘器压差上升的根本原因,再结合现场调研情况对NGD系统工况下的烟气含湿量、烟气温度、烟气灰浓度、除尘器本体的问题以及上游锅炉系统问题逐一进行对比和分析,并找出问题产生的各主要因素。NGD系统中布袋除尘器差压升高的原因包括多方面,为了使NGD系统的运行更加稳定,需要使除尘器适应NGD系统的工况并对系统中部分设备进行改造。在未来NGD系统的设计中,布袋除尘器需按高浓度烟气设计,且针对煤粉工业锅炉的运行、维护特性应加入对烟气中含水量的监测及对布袋除尘器的相应保护措施。     

Ultrasonic-vibration-assisted laser annealing of fluorine-doped tin oxide thin films for improving optical and electrical properties: Overlapping rate optimization

An ultrasonic-vibration-assisted laser annealing method was developed to enhance the performance of fluorine-doped tin oxide (FTO) thin films. The influences of ultrasonic vibration, laser scan line overlapping rate (L_OR) and laser spot overlapping rate (S_OR) on surface morphology, FTO layer thickness, RMS roughness, crystal structure and photoelectric properties of the FTO films were investigated. The results indicated that the presence of ultrasonic vibration during laser annealing could significantly enhance the film compactness, and using moderate L_OR and S_OR values resulted in significantly decreased FTO layer thicknesses and RMS roughnesses as well as slightly increased crystallite sizes, thus yielding significantly improved optical transmittance values and slightly enhanced electrical conductivity values. It was found that the optimal L_OR and S_OR values for ultrasonic-vibration-assisted laser annealing of the FTO films were 80% and 90%, respectively. The as-obtained film possessed the best overall photoelectric property with an average transmittance (400–800?nm) of 85.9%, a sheet resistance of 8.7?Ω/sq and a figure of merit of 2.51?×?10^–2 Ω^–1. This work may be of great significance in terms of performance optimization of transparent conducting oxide (TCO) thin films.