Effects of thermal load on wheel–rail contacts: A review

This article presents a technical review on the effects of thermal loads evolved at the wheel–rail–brake contact interfaces. These dynamic contact interfaces develop heat transfer conditions of widely varied thermal level. Their modeling to identify the sources for a variety of defect formation, observable on wheel tread or rail surface, is very important. The railway system, in general, has to bear axle load, friction load, and thermal load arising from their contact conditions in addition to traction and dynamic loads. The defects arising from the interaction of thermal load and other loadings may be identified as hot spots, shelling, spalling, rolling contact fatigue (RCF), and corrugation. The mechanisms for the formation of such defects are pivoted over the existing thermal environment of dynamic interacting surfaces. This review summarizes the works of early investigations and recent advances in modeling the heat transfer conditions required to estimate the temperature distribution at the contact zone. The heat partitioning method for both drag and stop braking conditions, in the presence of rail chill effect, is emphasized. Thermal gradient, introduced by localized temperature rise in the contact zone, in the presence of variable friction coefficient, promotes the RCF process. These alter the residual stresses in the contact region to cause a structural shakedown, aggravate plastic flow and activates ratchetting phenomenon in rails. The evolution of thermomechanical surface and subsurface fatigue cracks are also discussed for the completeness of this article. The effect of all such defect formation, emerging from thermal loading condition, and their countermeasures for defect mitigation are presented in this review. This abridged technical documentation envisions attracting more research in the area to improve wheel–rail set design and performance standards to extend enhanced safety and comfort to rail transport operation. It is opined that the thermomechanical loading, their effects on promoting defect formation and propagation should be studied in combination instead of the current practice of treating them separately.     

Milk Derived Antimicrobial Bioactive Peptides: A Review

In recent decades, bioactive peptides have attracted increasing interest as health promoting functional foods. A variety of naturally formed bioactive peptides have been found in fermented dairy products such as yogurt, sour milk, and cheese. Initially these peptides are inactive within the sequence of the parent protein molecule and can be generated by gastrointestinal digestion of milk, fermentation of milk with proteolytic starter cultures, and/or hydrolysis by proteolytic enzymes. Milk derived peptides exert a number of health beneficial activities, even upon oral administration. Bioactive peptides have a great impact on major body systems including the digestive, nervous, endocrine, cardiovascular, diabetes type II, obesity, and immune systems. Antimicrobial peptides are also an important ingredient of innate immunity, especially at mucosal surfaces such as lungs and small intestine that are constantly exposed to a range of potential pathogens. Therefore, it plays an important role in boosting natural immune protection by reducing the risk of chronic diseases. Bioactive peptides are considered as potent drugs with well-defined pharmacological residues and also used to formulate health-enhancing nutraceuticals.     

Spatial Wavelet Approach to Local Matrix Crack Detection in Composite Beams with Ply Level Material Uncertainty

Wavelet coefficients based on spatial wavelets are used as damage indicators to identify the damage location as well as the size of the damage in a laminated composite beam with localized matrix cracks. A finite element model of the composite beam is used in conjunction with a matrix crack based damage model to simulate the damaged composite beam structure. The modes of vibration of the beam are analyzed using the wavelet transform in order to identify the location and the extent of the damage by sensing the local perturbations at the damage locations. The location of the damage is identified by a sudden change in spatial distribution of wavelet coefficients. Monte Carlo Simulations (MCS) are used to investigate the effect of ply level uncertainty in composite material properties such as ply longitudinal stiffness, transverse stiffness, shear modulus and Poisson’s ratio on damage detection parameter, wavelet coefficient. In this study, numerical simulations are done for single and multiple damage cases. It is observed that spatial wavelets can be used as a reliable damage detection tool for composite beams with localized matrix cracks which can result from low velocity impact damage.     

FINITE-ELEMENT SIMULATION AND VALIDATION OF STEPWISE DRYING OF BANANAS

A two-dimensional finite-element formulation and solution of a set of transient coupled heat and diffusive moisture transfer equations is presented. The solution procedure developed uses an alpha family of approximation for stepping in time for the solution of the coupled set of equations applied to simulate the stepwise convective drying behavior of banana slices. The model tested was validated with experimental data from different sources for stepwise drying of banana using a heat pump dryer (HPD) as well as continuous batch drying in both Cartesian and cylindrical coordinate systems. The maximum deviation of moisture content between experimental and simulation results was 0.05% wet basis (% w.b.). Good agreement of the simulated results with experimental data for stepwise as well as continuous convective drying of banana samples indicates the validity of the procedure and its incorporation in the optimization of drying processes.     

Thermoelastic study of a functionally graded annular fin with variable thermal parameters using semiexact solution

Abstract

In this paper, the thermoelastic behavior of a functionally graded material (FGM) annular fin is investigated. The material properties of the annular fin are assumed to vary radially. The heat transfer coefficient and internal heat generation are considered to be functions of temperature. A closed form solution of nonlinear heat transfer equation for the FGM fin is obtained using the homotopy perturbation method (HPM) which leads to nonuniform temperature distributions within the fin. The temperature field is then coupled with the classical theory of elasticity and the associated thermal stresses are derived analytically. For the correctness of the present closed form solution for the stress field, the results are compared with the ANSYS-based finite element method (FEM) solution. The present HPM-based closed form solution of the stress field exhibits a good agreement with the FEM results. The effect of various thermal parameters such as the thermogeometric parameter, conduction-radiation parameter, internal heat generation parameter, coefficient of variation of thermal conductivity, and the coefficient of thermal expansion on the thermal stresses are discussed. The results are presented in both nondimensional and dimensional form. The dimensional stress analysis discloses the suitability of FGM as the fin material in practical applications.     

Optimization of Heat Fluxes on the Heater and the Design Surfaces of a Radiating-Conducting Medium

In a radiating-conducting planar medium with a boundary as the heater surface using an inverse analysis, this work deals with the design methodologies to understand the inherent relationship between heater surface temperature/flux, design surface temperature/flux, and medium properties. The heat flux on the heater surface is chosen as the fitness function. Subsequently, to achieve maximum and minimum design surface heat fluxes, an optimization was done to evaluate the zone of operation of the heater. In addition, the effect of medium properties on the temperature-flux relationships on both surfaces has been studied. The distance between the two surfaces is also considered a parameter. The medium properties, the distance between the surfaces, and the heater surface temperature have been found to have a great impact on the design surface heat flux. The inverse mixed boundary problem has been solved using the lattice Boltzmann method (LBM), the finite-volume method (FVM), and the genetic algorithm (GA). Results of the present study provide a guideline towards the efficient design of a heater in which conduction and radiation are the dominant modes of heat transfer.     

Effect of drainage height on concentration‐dependent propane dispersion in vapex

This article examines the effect of drainage height (i.e. height of saturated porous medium) on concentration‐dependent dispersion coefficient of propane in vapour extraction (Vapex) of heavy oil. For this purpose, Vapex experiments are carried out at 21°C using propane as a solvent at 0.689 MPa pressure for three different drainage heights of the heavy oil medium. Subsequently, the concentration‐dependent dispersion coefficients of propane are determined. The results show that the dispersion coefficient of propane (at all concentrations) in heavy oil increases with the drainage height. © 2011 Canadian Society for Chemical Engineering     

Preparation and characterization of graphene and Ni-decorated graphene using flower petals as the precursor material

A simple method is reported for preparing graphene and nickel-decorated graphene from the petals of lotus and hibiscus flowers by heating the original petals and petals soaked in a nickel(II) chloride solution ranging 800–1600 °C under a flowing argon atmosphere for 0.5 h. The products have been characterized by scanning and transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Graphene prepared at high temperature (>1200 °C) is purer than that obtained at a lower temperature (800 °C). The presence of nickel has been found to have improved the quality of the graphene and electron density near the Fermi energy level.     

Influence of Grain Size on the Superconductivity of?La1.85Sr0.15CuO4

We study the influence of varying grain size on superconductivity of bulk La_1.85Sr_0.15CuO₄ superconductor. The samples are synthesized by a sol-gel method. The grain size is varied by sintering the samples at various temperatures between 700?°C to 1050?°C. The samples are characterized by X-Ray Diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), resistivity and magnetization measurements. The electrical resistivity measurements revealed considerable lowering of the superconducting transition temperature ( $T_{\mathrm{c}}^{R=0}$ ) and broadening of the transition width (??T _c) with decreasing grain size though the onset of transition temperature ( $T_{\mathrm{c}}^{\mathrm{onset}}$ ) changes only marginally. The magnetic measurements carried out are consistent with each other and scale well with the grain size. Critical current density has been calculated from the magnetization hysteresis, assuming that supercurrents flow throughout the sample as a whole and within the individual grains as well. The observed results have been discussed on the basis of inter- and intra-granular boundary characteristics of high-temperature superconductors (HTSc). It is found that lowering of grain size deteriorates the superconducting properties in general.     

Performance analysis of an open-loop resonator loaded terahertz microstrip antenna

In this paper, an enhanced electrical performance of the open-loop loaded microstrip patch antenna at terahertz frequency has been investigated. The proposed antenna is designed to radiate at frequencies in the range of 0.5-0.7 THz with high gain and radiation efficiency. The effect of various substrate parameters on the electrical performance of the proposed antenna has been analyzed and simulated. The simulation has been performed using the CST Microwave studio, a commercial simulator based on finite integral technique. The directivity and radiation efficiency of the proposed antenna is 22.58 dBi and 94.50%, respectively, at 600 GHz. Further, the simulated results have been compared with Ansoft HFSS, a commercially available simulator based on the finite element method. We have also compared this proposed analytical result with reported literature with scale down approach.