Chemical and Morphological Characteristics of Malaysian Cultivated Kenaf (Hibiscus cannabinus) Fiber

In this study, an attempt is made to understand the chemical and morphological characteristics of Malaysian cultivated kenaf fractions (bast, core, and whole stem). Results based on morphologyand chemical analysis indicate that bast and core fiber fractions in the kenaf are significantly different, although the chemical composition of kenaf is quite similar to the woody mass. In the case of whole stem fibers, it is concluded that the effective length of fibers from the whole stem is reasonably good for the purpose of making printing papers.     

An evolutive framework for server placement optimization to digital twin networks

Digital twin network (DTN) is a foremost enabler for efficient optimization in modern networks, as it owns massive real-time data and requires interaction with the physical network in real-time. When constructing a DTN, it is necessary to deploy many servers in the physical network for digital models' storage, calculation, and communication. Evolutionary algorithms show outstanding global optimization capabilities compared to the constructive heuristic method in such an optimization problem. However, due to the high dimensionality of the problem and the complicated evaluation of the deployment plan, evolutionary algorithms easily fall into the optimum local at a high computational cost, given that the server placement problem is an NP-hard combinatorial optimization problem. In this research, we propose an evolutionary framework for server layout optimization that significantly improves the optimization efficiency of evolutionary algorithms and reduces the algorithm's computational cost. An offline-learning-based approach is used to reduce the search space, and a self-examining guided local search method is proposed to improve the search efficiency. Additionally, a look-up table-based hybrid approach is used for solution evaluation, reducing computational overhead. Experimental results show that the proposed framework and optimization strategy can significantly improve the evolutionary algorithm search efficiency and achieve excellent convergence performance.     

Synthesis and evaluation of novel aromatic acrylic monomers for optically clear adhesive with high refractive index

Conventional optical polymers have low refractive index; (RI <1.5) which limit their usage in the field of optoelectronics. Therefore, two types of aromatic monomers with high RI value were developed; that is, ionic monomer (PA.HEMA.NEt3.H⁺) with RI = 1.5150 and monomer (PA.BA.GMA) with RI = 1.5403. The monomers were then individually combined with a newly synthesized oligomer based on phthalic anhydride epoxy acrylate; that is, (EA.PA) with RI = 1.5567. The structures of the synthesized monomers and oligomer were confirmed by NMR and FTIR spectroscopy and the chemical titration of the structure end groups. Different combinations of the monomers with oligomer EA.PA were examined to develop a UV-curing adhesive with appropriate viscosity. According to TGA and DMTA test results, the composition containing oligomer EA.PA showed improved thermal degradation stability and high glass transition temperature. The lap shear adhesion test showed positive effect of oligomer EA.PA and PA.BA.GMA with an adhesion strength of up to 1.2 MPa. The RI value of the composition containing PA.BA.GMA and oligomer EA.PA was measured as 1.55 which is qualified for the most applications in optoelectronic. The improvement in RI value may be well attributed to the presence of aromatic rings in the polymer chain backbone. The high degree of aromaticity is in favor with the improved thermal stability in adhesive composition.     

The effect of Lewis and Damk?hler numbers on the flame propagation through micro-organic dust particles

In this study, the role of Lewis and Damköhler numbers on the premixed flame propagation through micro-organic dust particles is investigated. It is presumed that the fuel particles vaporize first to yield a gaseous fuel, which is oxidized in the gas phase. In order to simulate the combustion process, the flame structure is composed of four zones; a preheat zone, a vaporization zone, a reaction zone and finally a post flame zone, respectively. Then the governing equations, required boundary conditions and matching conditions are applied for each zone and the standard asymptotic method is used in order to solve these differential equations. Consequently the important parameters on the combustion phenomenon of organic dust particles such as gaseous fuel mass fraction, organic dust mass fraction and burning velocity with the various numbers of Lewis, Damköhler and the onset of vaporization are plotted in figures. This prediction has a reasonable agreement with experimental data of micro-organic dust particle combustion.     

Prediction of silica carry-over and solubility in steam of boilers using simple correlation

Silica content of the boiler water is critical for steam turbines and scaling of boiler heat transfer surfaces. Silica (SiO₂) can volatilize with the steam in sufficient concentrations to deposit in steam turbines leading to scale formation on boiler surfaces. In this work, a simple correlation is presented to predict silica (SiO₂) solubility in steam of boilers as a function of pressure and water silica content. The solubility of silica in steam directly depends on both the density and temperature of steam. With decreasing temperature and density, solubility of silica reduces. As the pressure affects steam density which has a strong bearing on steam temperature, it has an important effect on the solubility of silica in steam. The proposed correlation predicts the solubility of silica (SiO₂) in steam for pressure up to 22,000 kPa and boiler water silica contents up to 500 mg/kg. The predictions from the proposed correlation have been compared with reported data and found good agreement with average absolute deviation being around 4%. This simple-to-use correlation can be of immense practical value for the engineers to have a quick check on silica (SiO₂) solubility in steam of boilers as a function of pressure and water silica content at various conditions without performing any experimental measurements. In particular, personnel dealing with the utility boilers would find the proposed approach to be user friendly involving no complex expressions with transparent calculations.     

Predictive tools for the estimation of downcomer velocity and vapor capacity factor in fractionators

Fractionation is one of the pivotal unit operations in refineries and gas processing industries which is single largest energy-degrading processing unit utilized to separate mixtures into individual products. A reliable design method for sizing tray fractionators must take into account of foaming which is a major consideration in many process systems. The aim of this study is to develop simple predictive tool, which is simpler to use than current available techniques avoiding large number of parameters requiring less complicated and shorter computations, for accurate determination of downcomer velocity and vapor capacity factor as a function of tray spacing and density. The results can be used in follow-up design calculations to size fractionators without foaming formation for tray spacing up to 1.2 m, vapor densities up to 100 kg/m³ and liquid and vapor density differences up to 950 kg/m³. The accuracy of the proposed equations was tested and found to be in excellent agreement with the reported data for the wide range of conditions, wherein the average absolute deviation percent of proposed equations are 0.77% and 2.35% for downcomer design velocity and vapor capacity factor respectively. The proposed predictive tool detailed in the paper can be very helpful for design engineers to handle sizing calculations for tray fractionators.     

Performance and carbon deposition over Pd nanoparticle catalyst promoted Ni/GDC anode of SOFCs in methane,methanol and ethanol fuels

The electrochemical performance and carbon deposition on palladium catalyst promoted Ni/Gd_0.1C_0.9O_1.95 (Ni/GDC) anode in methane and alcohol fuels like methanol and ethanol are investigated at open circuit potential and under dc bias using electrochemical impedance spectroscopy technique. Presence of Pd nanoparticle catalyst significantly promotes the electrocatalytic activity of Ni/GDC for the electrooxidation reaction in methane and in particularly in methanol and ethanol fuels. For instance, in the case of methanol oxidation reaction, there is clear separation of the impedance arcs at high and low frequencies and activation energy for the reaction is reduced by ∼33% on a 0.15 mg cm⁻² PdO impregnated or infiltrated Ni/GDC anode. The transitional impedance response study when the inlet gas is switched from hydrogen to methane or alcohol fuels indicates that the oxidation reaction in methane and alcohol fuels is most likely dominated by adsorption, dissociation and diffusion steps of the reaction. Carbon deposition is also observed on Pd-infiltrated Ni/GDC in methanol and ethanol, but different from that observed in methane, there is no filament carbon fibers formation on the Pd-impregnated Ni/GDC surface in methanol fuel.     

Systematic definition of progress variables and Intrinsically Low-Dimensional,Flamelet Generated Manifolds for chemistry tabulation

A systematic method to define progress variables for chemistry tabulation is presented. The method is based on a Principal Component Analysis (PCA) of species mass fractions in the composition space. Analogous to an eigenvalue analysis of the Intrinsic-Low-Dimensional-Manifold method, the present study provides a rigorous mathematical formulation for flamelet-based tabulation methods. In addition, the method yields the minimum number of linearly independent progress variables for a user-prescribed desirable accuracy. Hence, the flamelet-based tabulations created with the new approach is called Intrinsically Low-Dimensional, Flamelet Generated Manifolds (IL-FGM). This approach is used to define progress variables for sample mono-dimensional, and multi-dimensional flamelet libraries of CH₄–air combustion. The results show that the flamelets are tabulated and retrieved with better accuracy using the new method than those tabulated using ad hoc progress variables.