Engineering Journal (Faculty of Engineering, Chulalongkorn University, Bangkok)
Not a member yet
1223 research outputs found
Sort by
Enhanced Oxygen Reduction Reaction of LSCF Cathode Material Added with NiO for IT-SOFC
Get PDFLa0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is one of the mixed ionic electronic conductors that could be feasibly used in an intermediate temperature solid oxide fuel cell (IT-SOFC). In this study, LSCF and NiO were prepared using a modified Pechini method and calcined at three different temperatures ranging from 600 °C to 900 °C. The prepared LSCF was added with 5% NiO (denoted as LSCF-NiO) as cathode material. The physical and electrical properties of the prepared cathode were investigated. X-ray diffraction data revealed that at calcination temperatures of 600 °C–900 °C, NiO and LSCF maintained their phases and conformed the cubic structure for NiO and orthorhombic structure for LSCF. The calcination temperature showed significant influence on the particle size of the prepared LSCF-NiO, as depicted by scanning electron microscopy (SEM), and all the powders reached a nanoscale size. The SEM cross section of LSCF-NiO layer on gadolinium-doped cerium electrolyte showed an acceptable percentage of cathode porosity and good adhesivity at cathode/electrolyte interface. Energy dispersive X-ray analysis further verified the purity of the samples. Brunauer–Emmett–Teller surface area analysis was conducted, and the results revealed a trend of decreased surface area with an increase in calcining temperature. At an operating temperature of 800 °C, the electrochemical impedance spectroscopic results showed that LSCF-NiO 800 had a low Rp of 0.07 Ω cm2, and its Ea was found to be 159.5 kJ/mol, indicating that LSCF-NiO 800 is fit to be used as cathode material in IT-SOFC application
A Practical Nonbinary Decoder for Low-Density Parity-Check Codes with Packet-Sized Symbols
Get PDFThis paper presents a practical decoder for regular low-density parity-check (LDPC) codes with flexible packet-sized symbols. The proposed hMP-VSD (Combined hard-decision message-passing with vector symbol decoding) is much less complex than the conventional VSD and has the same decoding performance. Regular LDPC codes with systematic encoding are selected for implementation. The channel is assumed to be the q-ary symmetric channel (q-SC). Different code lengths and column weights of LDPC codes are investigated. The results show that the codes with a column weight of 7 provide the best performance for hMP-VSD, while hMP works best with codes having a column weight of 5. With packet-sized symbols, even the rather short (60, 30) code structure has code lengths of 1,920 to 245,760 bits with symbol sizes of 32 to 4,096 bits. Both the decoder and its encoder were implemented on Raspberry-pi 4 model B boards and these results confirm that the computation time of hMP-VSD is 60% to 70% lower than that of VSD for pe in the range 0.05 to 0.1
Verification-Based Decoding for Rateless Codes in the Presence of Errors and Erasures
Get PDFIn this paper, verification-based decoding is proposed for the correction and filling-in of lost/erased packets for multicast service in data networks, which employs Rateless codes. Patterns of preferred parity-check equations are presented for the reduction of the average number of parity-check symbols required. Since the locations of unverified symbols are known, the effect of erasures and errors is the same in terms of the overhead required for successful decoding. Simulation results show that for an error-only, an erasure-only or a combination of both at 10% error/erasure probability, 78% of the messages can be recovered with a 50% overhead, whereas 99% of the messages can be recovered with a 100% overhead
Optimization Of Hydrocarbon Ejector Using Computational Fluid Dynamics
Get PDFEjector is a powerful emerging thermo-compressor, which is more effective when used with hydrocarbon refrigerants because of its unique thermophysical properties. Therefore, in the present work, a steam ejector model is designed and validated with experimental results to evaluate its accuracy, followed by a detailed comparative study of hydrocarbons and synthetic refrigerants namely pentane, propane, butane, iso-butane, R1234-ze and R1234-yf by computational fluid dynamics and literature Review. The effectiveness of both classes of refrigerants is measured through entrainment ratio, critical backpressure, and thermophysical properties (Literature Review). Pentane was selected as a working fluid since it has comparatively high combination of entrainment ratio and critical back pressure with refrigeration compatible properties. Lastly, the optimized geometry was simulated by varying diameter of constant area zone, nozzle exit position and nozzle expansion angle through Computational Fluid dynamics. The simulation results provide insight into shockwaves, boundary layer separation, vortex formation of ejector flow
Finite Element Analysis to Estimate Bearing Capacity of Strip Footing in Coastal Sandy Soils in Bengkulu City, Indonesia
Get PDFThis study presents results of bearing capacity analysis for strip footing in coastal sandy soils. Three sites located at coastal area are investigated. The site investigation and laboratory tests are conducted to obtain soil properties. Variations on depth and width of strip footing are considered. Finite element analysis is conducted to observe failure mechanism and bearing capacity of strip footing. Several results such as relationship between ultimate bearing capacity and foundation dimensions, factor of safety, displacement, and failure mechanism are discussed. The comparison between finite element results and exact solutions is also presented. The results show that variations of dimension tend to influence the bearing capacity and failure mechanism. The results also shows that finite element result is generally consistent with the exact solution. The results states that the footing dimension of 1.1. m embedded at 1.0 m below ground surface as the suitable strip footing in the study area. This study can also benefit local engineers designing strip footing for the coastal sandy soils
A Two-Dimensional Numerical Investigation of Aerodynamic Noise from an Inclined Plate
Get PDFDirect computations of acoustic noise of flow over an inclined plate are performed at two Mach numbers by solving the compressible Navier--Stokes equations without invoking any form of modelling. The flat plate has a sharp leading edge and sharp trailing edge and is inclined at incidence of 20°. The simulations are performed at a chord-based Reynolds number of 1000, and the freestream Mach numbers of 0.4 and 0.6. The numerical results reveal the effect of the Mach number on both of the hydrodynamic near-field and the acoustic far-field. Increasing the Mach number results in an increase in the shedding frequency and a decrease in the acoustic wavelength. The directivity plots show that additional lobes are present on the plate suction side at higher Mach number
Review on Key Factors of Wireless Power Transfer Technology for Electric Vehicles
Get PDFElectric vehicles (EVs) have become an alternative option for a clean energy society. A new charging technology which is wireless charging has been developed to satisfy the limitations of EVs which are the electric drive range and battery storage. Companies like Tesla, BMW, and Nissan have already started to develop wireless charging for EVs. This paper presents a literature review on wireless charging of EVs. The existing technologies for Wireless Power Transfer (WPT) system are summarized for different power applications. Coil design plays the most vital role in the WPT system so the different coil design with the transferred efficiency is reviewed. The other important parameters and technical components like significant factors of WPT system, track layout of dynamic wireless charging, foreign object detection method, and position alignment method that are affecting the efficiency of the wireless charging system are also discussed. Lastly, health and safety concerns for human beings and living things are investigated
Bread Browning Stage Classification Model using VGG-16 Transfer Learning and Fine-tuning with Small Training Dataset
Get PDFConvolutional neural network (CNN) is a popular tool to recognize image features even though its weakness requirement of massive training dataset. However, the implementation of the network in production process needs to worry about, that is, the deal with at least two constraints, small training dataset and the less diversity of browning stages among the bread production batches. This paper is aimed to achieve a high predictive accuracy model to classify the bread browning stage that is capable to deal with these constraints. With small training dataset of 900 original images from a production batch, the research performs five steps, starting with a few convolutional layers, adding image augmentation technique and transfer learning with pre-trained CNN model to enhance feature extraction with fine-tuning in final step. The final model of VGG-16 transfer learning and fine-tuning, trained with 18,000 artificial images, successfully achieves very high training accuracy of 98.89% and a very low loss of 2.86% at a small number of epochs 30 with its predictive accuracy of 100%
A 3D End-Effector Robot for Upper Limb Functional Rehabilitation of Hemiparesis Patients
Get PDFRobot-assisted therapy is a new type of rehabilitation that allows for highly repetitive, intensive, adaptable, and quantifiable physical training. It is increasingly being used to restore motor function, particularly in stroke survivors with upper limb paresis. The end-effector type robot allows natural movements without complex structure which is ideal for functional rehabilitation training. A 3D end-effector base on a five-bar linkage has been proposed to improve the common end-effector type that covers mechanical design, dynamic control strategy, and application of rehabilitation training or exercise. The dynamic controllers are deweighting with gravity compensation, passive mobilization or active assistive, and the virtual spring-damper wall concept. These controllers are used for developing functional rehabilitation training or exercise from an engineering point of view based on experiences in developing various types of rehabilitation robots. The experiments, based on the performance of the controllers, have been conducted with healthy subjects. The experimental results have shown very promising results and can be extended to various types of functional rehabilitation
The Application of Two Echelon Distribution Network Zoning in an Organic-Chemical Fertilizer Distribution: The Case Study in Northeastern Thailand
Get PDFThis research introduced the two-echelon capacitated plant location problem (2E-CPLP) to increase the efficiency of organic-chemical fertilizer distribution in Northeastern Thailand. The consequences of this unsolved problem either lead to lower productivity or increased use of less environmentally friendly fertilizers. Though centroid with equal demand zoning was previously used in this area, the unique characteristics of Northeastern Thailand cause this approach to yield less acceptable results. The introduction of the two-echelon concept is important for practitioners to adopt a better way of operating. This case-based study compared two facility location problem (FLP) approaches by using the geographical zoning and equal demand zoning methods as a baseline, then introducing the 2E-CPLP method as an alternative. The problem was solved by IBM ILOG CPLEX software and ArcGIS for Desktop 9.3 with outputs of the total cost, the maximum distance from plants to retailers, and the average distance from plants to retailers. The results showed that the 2E-CPLP method with geographical zoning outperformed equal demand zoning, with a lower total cost of 246.84 million baht or 1.05%, significantly less computational time, and lower maximum and average distances from plants to retailers