Numerical evaluation of the heat transfer in a shell and corrugated coil tube heat exchanger with three various water-based nanofluids

In this paper, turbulence heat transfer and nanofluid flow in a shell and corrugated coil tube heat exchanger are evaluated numerically. The three-dimensional numerical simulations have been done by finite volume method using a commercial computational fluid dynamics code. The spatial discretization of mass, momentum, turbulence dissipation rate, and turbulence kinetic energy equations has been achieved by a second-order upwind scheme. A SIMPLE algorithm has been used for velocity–pressure coupling. To calculate gradients, Green-Gauss cell-based method has been utilized. The cross-section of the coil tube is lobe shaped. First, the impact of corrugated tube cross-section type and then, the impact of utilizing different types of nanofluid on thermal performance are investigated. The outcomes indicate that at high Reynolds number, utilizing a five-lobe cross-section causes augmentation in Nusselt number and pressure drop by about 4.8% and 3.7%, respectively. However, the three-lobe type shows the highest thermal performance. Moreover, water/CuO has the most thermal performance. As the volume concentration of the nanofluid increases, the thermal performance declines.     

Orthotropic enriched element free Galerkin method for fracture analysis of composites

A new approach for modeling discrete cracks in two-dimensional orthotropic media by the element free Galerkin method is described. For increasing the solution accuracy, recently developed orthotropic enrichment functions used in the extended finite element method are adopted along with a sub-triangle technique for enhancing the Gauss quadrature accuracy near the crack. An appropriate scheme for selecting the support domains near a crack is employed to reduce the computational cost. In this study, mixed-mode stress intensity factors are obtained by means of the interaction integral to determine the fracture properties. Several problems are solved to illustrate the effectiveness of the proposed method and the results are compared with available results of other numerical or (semi-) analytical methods.     

Deposition,Characterization and Evaluation of Monolayer and Multilayer Ni,Ni–P and Ni–P–Nano ZnO<Subscript>p</Subscript> Coatings

Ni, Ni–P and Ni–P–ZnO_p monolayer films along with multilayer coatings containing different arrangements of these layers were produced on steel substrates by electrodeposition and electroless deposition techniques. Co-deposition of ZnO nano-particles, as well as morphology, cross-section, microstructure and microhardness of coatings were investigated. Corrosion behaviors of monolayer coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques, and the results were compared to multilayer films. Results revealed that, Ni–P–1.5 vol% ZnO_p monolayer film obtained from a bath with 4 g L^?1 of these particles had the highest hardness between all samples. Further addition of nano-particles to the bath lead to the formation of discontinuous films. Most of the multilayer coatings with different arrangements exhibited higher corrosion resistance as compared to monolayer films. Corrosion current density of three-layer Ni–P–ZnO_p/Ni/Ni–P coating, considered as the most corrosion resistant film, was about 538 times lower than monolayer Ni–P coating.     

An adaptive interface‐enriched generalized FEM for the treatment of problems with curved interfaces

An adaptive refinement scheme is presented to reduce the geometry discretization error and provide higher‐order enrichment functions for the interface‐enriched generalized FEM. The proposed method relies on the h‐adaptive and p‐adaptive refinement techniques to reduce the discrepancy between the exact and discretized geometries of curved material interfaces. A thorough discussion is provided on identifying the appropriate level of the refinement for curved interfaces based on the size of the elements of the background mesh. Varied techniques are then studied for selecting the quasi‐optimal location of interface nodes to obtain a more accurate approximation of the interface geometry. We also discuss different approaches for creating the integration sub‐elements and evaluating the corresponding enrichment functions together with their impact on the performance and computational cost of higher‐order enrichments. Several examples are presented to demonstrate the application of the adaptive interface‐enriched generalized FEM for modeling thermo‐mechanical problems with intricate geometries. The accuracy and convergence rate of the method are also studied in these example problems. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,properties, and applications of polylactic acid-based polymers

Polylactic acid (PLA) is known as one of the greatest promising bioabsorbable and compostable polyesters with the capability of high molecular weight synthesis. Lactic acid condensation, azeotropic dehydration, and condensation ring-open polymerize of lactide are three methods for PLA polymerization. Comprehension of material properties is critical for choosing the right processing method and adjusting PLA characteristics. A variety of mechanical properties of this material, from soft and elastic to stiff and high strength makes PLA suitable for a wide range of applications. Besides, PLA can be blended or copolymerized with other polymeric or non-polymeric substances. Thus, this polymer can achieve suitable chemical, mechanical, and rheological properties. Understanding the role of these properties and selecting a suitable processing technique is necessary for its intended consumer and various applications. This study elaborated a general summary of the polymerization, processing, and characteristics of PLA (i.e., structural diversities, rheological performances, mechanical properties, and permeability). Besides, this work presented some information regarding essential factors that can be used for modifying PLA properties to address the requirements for various applications such as biomedical, food packing, biocomposite, and additive manufacturing.     

Comment on S. Ahmed,H. Wang,and Y. Tian, “Robust adaptive fractional-order terminal sliding mode control for lower-limb exoskeleton,” Asian J. Control,vol. 21, no. 1, pp. 1–10 (2019)

In this comment, it is shown that there are some non-negligible big mistakes in the analyses and stability proof of the proposed controller in the quoted paper, which makes the main results of this paper to be incorrect. The main unavoidable mistakes in the stability analysis of the main theorem (Theorem 1) are stated and some remarks are also mentioned to fix some of them.     

Investigating on performance parameters and flow field of centrifugal compressor based on the splitter blade leading edge’s location effect

Impeller design in turbomachines is one of the most challenging issues in these machines’ systems, which still plays a significant role in their efficiency and performance. This article considers different designs for splitter blades. Therefore, the CFD methods modify the position of the splitter blades leading edge at the hub and shroud. This modification shall lead to a different splitter blade profile from the main blades. Then, the effects of splitter blades are discussed, and the performance parameters have also been studied to improve this method’s implementation. The results revealed that the compressor’s efficiency was improved by approximately 1.5 % in one specific case. This finding proves that the previous design methods were not the optimum ones for compressors and how to increase the compressor’s efficiency by CFD methods and by changing the splitter blades’ location.

     

Numerical Procedure for Fractional HBV Infection with Impact of Antibody Immune

The current investigations are presented to solve the fractional order HBV differential infection system (FO-HBV-DIS) with the response of antibody immune using the optimization based stochastic schemes of the Levenberg-Marquardt backpropagation (LMB) neural networks (NNs), i.e., LMBNNs. The FO-HBV-DIS with the response of antibody immune is categorized into five dynamics, healthy hepatocytes (H), capsids (D), infected hepatocytes (I), free virus (V) and antibodies (W). The investigations for three different FO variants have been tested numerically to solve the nonlinear FO-HBV-DIS. The data magnitudes are implemented 75% for training, 10% for certification and 15% for testing to solve the FO-HBV-DIS with the response of antibody immune. The numerical observations are achieved using the stochastic LMBNNs procedures for soling the FO-HBV-DIS with the response of antibody immune and comparison of the results is presented through the database Adams-Bashforth-Moulton approach. To authenticate the validity, competence, consistency, capability and exactness of the LMBNNs, the numerical presentations using the mean square error (MSE), error histograms (EHs), state transitions (STs), correlation and regression are accomplished.     

Integrated process design and control of divided-wall distillation columns using molecular tracking

This work explores the dynamic and control behavior of dividing wall distillation columns from two different steady-state design approaches (molecular tracking and optimization method) for three different mixtures. The controllability of the six design cases was evaluated using singular value decomposition and the closed-loop performance was evaluated using integral absolute error in Aspen Dynamics. The results demonstrate that the side-draw location obtained by molecular tracking (MT) provides optimal controllability. As a result, there is a slight advantage in control properties while obtaining designs by reducing the time to find the optimal solution through the MT method.