CFD study of forced convective heat transfer enhancement in a 90° bend duct of square cross section using nanofluid

In this paper, the forced convective heat transfer enhancement with nanofluids in a 90° pipe bend has been presented. Numerical investigation is carried out for the turbulent flow through the pipe employing finite volume method. The governing differential equations are discretized using hexahedral cells, and the resulting algebraic equations are solved using Commercial solver Fluent 6.3. In order to close the time averaged Navier–Stokes equations, the two-equation k–? turbulence model with a standard wall function have been used. The duct Reynolds number is varied in the range of 2,500–6,000. It is observed that the heat transfer is enhanced significantly by varying the volume fraction of the nanofluid. It is also found that the heat transfer is increased with Reynolds number. A strong secondary flow is observed due to the presence of the wall. Turbulent kinetic energy near outer wall is found to be higher than the inner wall of the bend. A comparative assessment for the heat transfer enhancement with different types of nanofluids is also presented. The computed results of area weighted average Nusselt numbers are validated with some of the existing literature.     

Optimization of process variables in drilling of carbon fiber reinforced plastics using various multi criteria decision making approaches

Carbon fiber-reinforced polymers are one of the lightweight materials used in structural design due to their exceptional mechanical performances. The drilling operation is indispensable as it facilitates the assembling of various manufactured components. However, drilling of fibrous laminates is deemed difficult in comparison to the traditional metals because of the anisotropic and non-homogeneous nature. The present work addresses the parametric effect on the drilled hole delamination and further reduces it with an optimal combination of parameters for multi-objectives using different multi-criterion decision-making techniques. Initially, the response surface-based regression model of delamination as a function of three static inputs has been developed, further revised with induced thrust as well as mean torque for the improvisation of the prediction capability. Finally, for the overall improvement, a decision-making model has been used that includes grey relation analysis, technique for order performance by similarity to ideal solution, and VIšekriterijumsko Kompromisno Rangiranje method. The delamination was found to be minimum at a low drill point angle (100°), high spindle rotation (2150 min⁻¹ ), and low feed rate (0.025 mm/rev) due to reduced thrust force. The mean absolute prediction error was significantly improved considering root mean square torque rather than axial thrust with process variables.     

A new stiffened plate element for the analysis of arbitrary plates

In spite of the large number of finite elements developed so far, most of these lack in generality, and are found to be inadequate and inefficient in some way or other, when it comes to analyzing plates of arbitrary geometrical configurations. So far the isoparametric element has been the most successful among available elements because of its ability to model a curved boundary successfully. However, the shear-locking problem inherent in the isoparametric element makes it unsuitable for analyzing thin plates of arbitrary shapes. Though research has been conducted using reduced integration and stabilization to overcome the problem, the formulations either do not converge to the correct solution in the thin-plate limit or they make the stiffness matrix a singular one. In this paper, a four-noded stiffened plate element is developed. This has the advantages and elegance of an isoparametric element in modelling arbitrary shaped plates, but without the disadvantage of shear-locking phenomena. Though this element is a high-order element, only the usual degrees of freedom have been considered, and performance is superior to that of the low-order ones. The stiffened plate element has the feature of accommodating the arbitrary shape of the plate geometry, and the stiffener modelling has been done in a general manner, with the stiffener lying anywhere with arbitrary orientation, and not necessarily following the nodal lines. The new element has been successfully used for the static, free vibration and stability analyses of arbitrary bare and stiffened plates. The results are found to agree quite satisfactorily with those of previous investigators.     

Design of a compact orthogonal fed self‐diplexing bowtie‐ring slot antenna based on substrate integrated waveguide

In this article, a novel design of compact cavity‐backed slot antenna based on substrate integrated waveguide (SIW) technology is presented for dual‐frequency communication services. A single layer printed circuit board is applied to implement the proposed antenna. The bowtie‐ring slot engraved on the SIW square cavity is excited using two orthogonal microstrip feed lines to operate at two distinct frequencies (6.62 GHz and 11.18 GHz). The proposed antenna allows each of these frequencies to be designed independently. A prototype of the proposed cavity‐backed antenna that radiates at both 6.62 GHz and 11.18 GHz is fabricated and measured. The port isolation better than 29.3 dB is achieved by utilizing the transmission zeros (TZs), which are produced due to the orthogonal feed lines, TE₁₁₀ mode and coupling between the TE₁₂₀ and TE₂₁₀ modes. The measured peak gains of the proposed diplexing antenna are 5.77 dBi and 5.81 dBi at lower and upper resonating frequencies, respectively. The proposed dual‐frequency antenna exhibits the front‐to‐back‐ratio (FTBR) and cross‐polarization level greater than 26 dB and 21 dB, respectively, at both resonating frequencies.     

Discharge characteristics of plasma display panels with Si-doped MgO protective layers

We report on our study of the influence of varying concentrations of Si doping on the secondary electron emission (SEE) yield of MgO thin films prepared by electron beam evaporation technique. The series of Si-doped MgO films were microstructurally characterized with various tools like X-ray diffraction, scanning electron microscopy and atomic force microscopy. The optimization of the concentration of Si doping is seen to enhance the SEE yield. We discuss the correlation of SEE yield in the context of different deposition and measurement conditions and crystalline orientation.     

Identification, cloning, and mutational analysis of the casein kinase 1 cDNA of the malaria parasite, Plasmodium falciparum. Stage-specific expression of the gene

The cDNA for casein kinase 1 (CK1) of Plasmodium falciparum was cloned, sequenced, and expressed in bacteria. The single major open reading frame of the 1.2-kilobase pair cDNA coded for a 324-amino acid polypeptide of approximately 37 kDa, the predicted sequence of which showed strong identity with known CK1 isoforms. The purified recombinant enzyme exhibited properties characteristic of CK1, such as inhibition by CK1-7, the ability to phosphorylate a highly specific peptide substrate, and a strong preference for ATP over GTP. A casein kinase activity, partially purified from soluble extracts of P. falciparum by affinity chromatography through CK1-7 columns displayed identical properties. The activity showed a stage-specific expression in the parasite, in the order trophozoite > ring > schizont. Northern analysis indicated the existence of two major CK1 mRNAs, 2.4 and 3.2 kilobase pairs long, the levels of which were in the order ring > schizont > trophozoite. Mutagenesis of recombinant CK1 defined important amino acid residues and their potential role in the conformation of the enzyme. The malarial CK1 appeared to be the one of the smallest and perhaps the most primitive CK1 enzymes known, containing little sequence information beyond the minimal catalytic domain.     

Delamination of Mg-Al Layered Double Hydroxide on Starch: Change in Structural and Thermal Properties

Mg-Al layered double hydroxide decorated starch bionanocomposites (starch/layered double hydroxide) are prepared by solution intercalation method. The bionanocomposites are systematically characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy techniques. The thermal stability of starch is enhanced due to dispersion of layered double hydroxide within the starch matrix. The chemical resistance property of starch is improved substantially with slight sacrifice in biodegradation behavior by the delamination of layered double hydroxide in starch matrix. Herein, layered double hydroxide acts as potential laminated filler for change in structural, thermal, and chemical resistance properties of starch with little sacrifice in biodegradable behavior.