Leakage on Water Cooling Distribution Pipe in a Hydroelectric Power Plant

Journal of Failure Analysis and Prevention - This paper reported the investigation of leakage occurred on the water cooling distribution pipe in a 175 MW hydroelectric power plant. The...     

Effects of Ni–TiO2 Pillared Clay–Montmorillonite Composites for Photocatalytic Enhancement Against Reactive Orange Under Visible Light

Journal of Inorganic and Organometallic Polymers and Materials - In this study, a composite material based on Ni–TiO2 Pillared Clay-Montmorillonite (Ni–TiO2/CMMT) was synthesized using...     

Finite element analysis of flush end-plate connections connected to column web

Eurocode 3: Part 1.8 (2005b) does not cover the empirical design for flush end-plate connections connected to column web. Thus, experimental works need to be performed to investigate the behaviour of the minor axis end-plate bolted connection. However, the experimental tests are expensive, tedious and time consuming to be conducted. Alternatively, finite element modelling and analysis can be adopted to predict the behaviour of the connection accurately. Five specimens of flush end-plate connections connected to column web with variable parameters have been tested and the results are compared with finite element analysis. Finite element models with enhanced strain solid and contact joint elements are used to stimulate the connection behaviour. The objective of this paper is to compare and validate the accuracy and reliability of the finite element model by correlating moment rotation (M-Φ) curves between the finite element model and experimental tests. The comparison shows a reasonable agreement between the predicted results from FEA and the experimental tests.     

Effect of Fe2O3/SiO2 ratio on maghemite-silica particulate nanocomposites

Abstract： Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic maghemite nanoparticles were successfully produced using Massart＇s procedure. Nanocomposites consisting of synthesized maghemite nanoparticles and silica were produced by dispersing the as-synthesized maghemite nanoparticles into the silica particulate form. The system was then heated at 140 ℃for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to maghemite nanoparticles and a visible wide band at 20 from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated maghemite nanoparticles is smaller than the as-synthesized maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites （360-390 m^2/g）. This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.     

Direct numerical simulation and experimental validation of flow resistivity of nonwoven fabric filter

We numerically study and then experimentally validate the flow resistivity of commercial nonwoven fabric filters used for a bag filter system. To represent a realistic flow field inside the filters during simulation, a numerical method that coordinates the filter structure obtained by X-ray computed tomography imaging with computational fluid dynamics using the immersed boundary method is developed. The effects of superficial velocity, porosity of the filter domain, and type of filter on pressure drop are investigated and analyzed based on Darcy's law. The predictions from our numerical method are quantitatively in good agreement with the experimental measurements. We demonstrate that the Kozeny constants of the filters can be estimated by utilizing the solid volume fraction. These results demonstrate that our simulation method can be used to clarify the effects of porosity, fiber arrangement, and fiber shape on the pressure drop. Finally, its application to water droplet permeation is demonstrated.     

Performance and stability of single and 6-cell stack passive direct methanol fuel cell (DMFC) for long-term operation

A passive, air-breathing, 6-cell direct methanol fuel cell (DMFC) stack is designed, fabricated and tested based on the performance of a passive single-cell DMFC. A large methanol reservoir in a hexagonal shape is considered in designing the stack in order to increase the DMFC operation time without any interruption, i.e., to refill the methanol solution. Hence, the ratio of methanol solution volume in the reservoir for the single cell, i.e., 8 ml, and hexagonal stack, i.e., 240 ml, is 1:30. The power output of 500 mW is achieved at 1.5 V using a 5 M methanol solution at room temperature. With a large volume of methanol, i.e., 240 ml of 5 M methanol in the hexagonal stack, it can be operated continuously at 1.5 V for more than 40 h, whereas for a small volume, i.e., 8 ml in a single cell, the operation can reach only 3 h–4 h with a similar reduction of 25% from the initial power output. Moreover, the DMFC stack is used for long-term operation more than 3000 h, and the morphology of MEA is analyzed.     

Estimation of Dynamic Mixed Hitting Time Model Using Characteristic Function Based Moments

We present a characteristic function-based method for the estimation of dynamic mixed hitting time model for duration between events and price changes. The model specifies duration between events as the first time a latent component of multivariate Brownian motion crosses a random boundary. Meanwhile, another (correlated) Brownian component generates the prices. The proposed estimation method facilitates computation and overcomes problems related to the discretization error in the moment conditions and the non-tractability in the joint probability density function. An empirical application using transaction level data on stocks of a large capitalization company traded on the Indonesia Stock Exchange is illustrated. Estimation results suggest that durations and return volatility have strong persistence and, further, there is a negative instantaneous relation between volatility and contemporaneous duration. The impact of considering the causality relation between volatilities and durations on instantaneous volatility estimate are also investigated.     

Electrochemical properties of a PEMFC operating with saturated hydrogen and dry air

The electrochemical properties of a single-cell proton exchange membrane fuel cell (PEMFC) were characterized. A single serpentine flow field design with an active area of 200 cm² was employed in this investigation. The flow field consisted of grooves on a plate with a width of 5 mm, a depth of 2.5 mm and a 2.5-mm rib. Several operating temperatures were tested (25, 40, 50 and 60 °C), and the pressure was fixed at 1 bar on both the anode and the cathode sides. The gas inlet velocities of hydrogen and air were fixed at 3 L min⁻¹ and 6 L min⁻¹, respectively. The inlet gases were saturated hydrogen and dry air. A polarization curve for the experimental data was fitted to an empirical model equation, and a good-fitting correlation was obtained. The kinetic parameters of the cell, namely, the Tafel slope, the area resistance and the mass transport parameters, were obtained from the model fitting. The proton conductivity of the membrane was found to be inversely proportional to the area resistance. Electric yield rates in the range of 45.9%–56% were obtained.