Department of Mechanical Engineering

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A numerical model is developed to study Shrinkage induced convection and free surface evolution caused by the density difference between the solid and liquid phases during the solidification of pure aluminium. For the analysis, a 2-D rectangular cavity field with aluminium melt undergoing solidification process is considered. Conservation of mass, momentum, and energy are formulated based on volume averaging technique and are solved using the SIMPLER algorithm. The free surface evolution is captured using the Volume of fluid (VOF) method. The proposed model focuses on predicting macro-scale shrinkage induced surface defects during the solidification process. © The Authors, published by EDP Sciences, 2019.

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Shrinkage induced flow and Free surface evolution during solidification of pure metal

Thermal energy storage (TES) unit has become an integral part of thermal energy conservation. As the name implies, the device simply stores heat when energy from the source is available in excess, and releases the same when energy from the source falls short of the requirement. By doing so, such devices deliver heat energy across the temporal barrier, making thermal energy available for extended working hours of solar thermal power plants (STPP). High energy density and stable operation for long duration are desirable qualities which may be found in latent heat thermal energy storage (LHTES) system. To exploit the advantage of LHTES, the most common design reported in the literature is shell-and-tube type latent heat thermal energy storage (ST-LHTES) systems with phase change material filled in shell side, while (heat transfer fluid) HTF flows in the tubes (or vice versa). The present chapter gives a detailed classification of ST-LHTES systems based on geometry, orientation and relative position of PCM and HTF in heat exchanger along with the classification of phase-change materials. Numerical modelling of heat transfer phenomenon is presented along with some simulated results for enhanced PCM, clearly describing the coupling between PCM and HTF domain. Various heat transfer enhancement techniques and parametric analysis have been discussed with challenges and future scope. © 2019, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Shell-and-Tube Latent Heat Thermal Energy Storage (ST-LHTES)

A lot of activity has been taking place in the research community over the decades to efficiently harness solar energy. One way this is fuelled is by the support from the governments which promote the implementation of large-scale projects—whether it be for electric power generation (using PV), or for water heating using solar thermal collectors. These activities involve the efforts of the industry, which keep pace with the latest technology in the world, and are in a race to provide the most reliable technological solution to the customer for harnessing solar energy in an economical and robust manner. This has been the backdrop theme of almost all the chapters included in this book, which have been contributed by various authors from across the world. This is the first chapter of the book, and thus provides an overview of the various topics that will be covered in this book, ranging from an energy roadmap for the future, to technologies advances in the field of photovoltaics and solar cells (DSSC—Dye-Sensitized Solar Cells). It also includes details of solar thermal collector, along with the discussion about its heat transfer aspects. Apart from the two primary uses of solar energy—electric power generation and water heating—there are numerous applications for which it has been used over the years. Several such applications are also discussed in some of the subsequent chapters, such as refrigeration, desalination, gasification, and cooking. © 2019, Springer Nature Singapore Pte Ltd.

Introduction to Advances in Solar Energy Research

This article discusses the characterization of local clay-organic (CO) ceramics used in the microfiltration application in India. Local clay and sawdust were the raw materials for these ceramics. Wet mix with specified volume fractions of these raw materials was hydroplastically formed to square plates, cured, and fired at 850 degrees C. Once fired, these ceramics showed a prominent presence of silica, alumina, and oxides of iron. Quartz, potassium feldspar, and hematite are the major minerals in these ceramics. The dominance of pores orthogonal to the surface was a feature in this family of ceramics. The 50O composition of the CO ceramics is observed to have a maximum frequency of orthogonal pores. Therefore, an example of gravity-based filtration flow models of this material shaped in distinct forms is carried out to enumerate possible scaling. The surface roughness of the cured specimen plate varies linearly with the porosity of the mixture. The compressive strength shows a polynomial increase with an increase in the values of surface roughness. The fracture toughness is a linear function of the surface roughness of these CO ceramics.

DESALINATION AND WATER TREATMENT

Establishing correlations among pore structure, surface roughness, compressive strength, and fracture toughness of ceramic water filters local to Rajasthan, India

This study aims to investigate the physicochemical and thermophysical behavior of the electrode coatings produced using CaO-CaF2-SiO2 and CaO-SiO2-Al2O3 ternary phase systems. Electrode coating compositions for welding power plant materials are either patented or not available in the public domain so researchers need to explore the flux coatings to improve the properties of welds produced. An extreme vertices design methodology was used to obtain the different flux combinations to study the effect of electrode coating constituents on weight loss, density, specific heat, change in enthalpy, thermal diffusivity and thermal conductivity. These properties play an important role in achieving better weld quality. X-ray diffraction and Fourier-transform infrared spectroscopy techniques were used to analyze the different phases present and their structural behavior. Multi-response optimization was carried out to obtain the optimum flux composition and study the effect of individual constituents and their interaction effects on the thermophysical and physicochemical properties. © 2019, The Minerals, Metals & Materials Society.

Design and Development of Shielded Metal Arc Welding (SMAW) Electrode Coatings Using a CaO-CaF2-SiO2 and CaO-SiO2-Al2O3 Flux System

Dissimilar welding of low alloy ferritic steel to martensitic or stainless steels is an essential requirement in modern thermal and nuclear power plants. Shielded metal arc welding (SMAW) is most commonly used to weld dissimilar metals using the flux coated electrodes. Suitable filler wire selection and electrode coating composition play an important role along with the welding parameters on the quality of welded joints. These parameters also affect the mechanical properties of the welded joints. This article deals with design and development of electrode coatings for joining low alloy steels. Electrode coatings were developed using CaO–SiO2–CaF2 and CaO–SiO2–Al2O3 flux systems with the help of mixture design and extreme vertices approach. Twenty one multipass weld beads were made using developed shielded metal arc welding electrodes. Weld chemistry was obtained using spectrometer for all the twenty-one welds. Microstructural and microhardness analysis was performed on all the welded specimens to observe the metallurgical and mechanical behavior of the welds. Multi-response optimization was carried out to obtain optimum flux composition. The effect of individual constituents and their interactions on the weld chemistry, grain size, and microhardness has been investigated. © 2019 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Design and development of CaO–SiO2–CaF2 and CaO–SiO2–Al2O3 based electrode coatings to weld low alloy ferritic steels for power plant applications

The influence of processing variables was experimentally studied for glass fiber reinforced epoxy–clay nanocomposites manufactured using vacuum-assisted wet layup method. The tensile strength, flexural strength, and interlaminar shear strength of these nanocomposites were significantly influenced by the processing variables including the temperature of resin–clay mixture, speed of homogenization, and ultrasonic probe amplitude during premixing of clay minerals in epoxy. The glass transition temperature of glass fiber reinforced composites increased with incorporation of clay minerals in epoxy. Also, the postcuring of the laminates was carried out at three different temperatures, e.g. 100, 130, and 150 ℃ for 3 h. A decrease in tensile modulus, tensile strength, and flexural strength of nanocomposites postcured at 130 and 150 ℃ was observed. Also, the use of non-stoichiometric epoxy resin and hardener ratios had an adverse effect on mechanical properties of fiber reinforced epoxy–clay nanocomposites. In fiber reinforced composites incorporating clay minerals, a uniform dispersion of clay minerals besides a strong interfacial adhesion between clay minerals and polymer and optimum conditions of curing of matrix is a crucial aspect for improved performance over conventional fiber reinforced composites. © IMechE 2018.

Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications

Effect of mixing parameters, postcuring, and stoichiometry on mechanical properties of fiber reinforced epoxy–clay nanocomposites

Submerged arc welding is widely used in pipeline manufacturing due to higher efficiency as compared to the other welding processes. In present study, TiO2-SiO2-CaO and SiO2-CaO-Al2O3–based submerged arc welding fluxes were developed for joining of linepipe steel. Twenty-one fluxes were formulated based on mixture design methodology. Fluxes were analysed using X-ray florescence (XRF), thermogravimetric, differential-scanning calorimetry, Hot-disc and X-ray diffraction (XRD) techniques. The structural behaviour of rutile basic fluxes were analysed using Fourier transformed infrared spectroscopy (FTIR). Thermo-gravimetric analysis and differential scanning calorimetry were performed from 25 ℃ to 900 ℃ in order to determine the thermal stability and change in enthalpy of fluxes. Thermal conductivity, thermal diffusivity and specific heat of each flux were evaluated by hot disc technique. The density and grain fineness number for flux particles was evaluated at room temperature. Multi objective optimisation was performed to derive the optimised flux formulations. Individual effect of all the mixture constituents is rarely observed on the physicochemical properties of fluxes as compared to the binary and ternary mixture effects. The binary compositions significantly affect the density. TiO2-CaO is the most effective binary mixture which has increasing effect on density while all remaining binary mixture constituents have decreasing effect. The weight loss of fluxes observed during thermogravimetric analysis is affected by binary and ternary mixture constituents. Both binary and ternary flux mixtures affect change in enthalpy observed during differential scanning calorimetry. SiO2.Al2O3 is the only most effective binary mixture constituent of flux having increasing effect on thermal conductivity. Binary mixture constituents TiO2.CaF2, SiO2.Al2O3 and CaO.Al2O3 are the most effective and having synergistic effect on thermal diffusivity. © IMechE 2018.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Design and development of submerged arc welding fluxes using TiO2-SiO2-CaO and SiO2-CaO-Al2O3 flux system

The objectives of the present work are to study the influence of curvature on local heat transfer coefficient, two-phase pressure drop and CHF in helical coils. The curvature of coil generates secondary flow of fluid which affects the mechanism inside helical coils. Very less information is available on the influence of curvature on flow boiling system. The present work investigates the characteristics of single phase flow and flow boiling in helical coils. Infra-red thermal imaging technique is used to measure the local wall temperature in the axial direction (along the length of coil) and in the circumferential direction. Experiments are performed with six helical coil test sections made of SS 304 circular tubes having three different tube diameters with two different coil diameters. The tube inner diameters are varying from 5.5 to 9.5 mm with wall thickness of 0.25 mm. The coil diameter to the tube diameter ratio ranges from 14 to 58 and coil pitch is 50 mm. The system pressure is varying from 1.1 bar to 3.6 bar. The analysis is performed for different heated lengths of test section. The experimental data of pressure drop and CHF are compared with available helical coil correlations. In fully developed flow boiling region, the circumferential averaged heat transfer coefficient in helical coils is same as in straight tubes. Correlations are suggested to predict local heat transfer coefficient in single phase and in flow boiling process, two-phase pressure drop and CHF in helical coils. © 2017 Elsevier Masson SAS

International Journal of Thermal Sciences

Boiling pressure drop, local heat transfer distribution and critical heat flux in helical coils with R123

The objective of the present work is to study the two-phase pressure drop in helical coils. Literature on the two-phase pressure drop in a helical coil suggests the complexity in flow boiling inside a helical coil due to secondary flow. Most of correlations reported in the literature on the two-phase pressure drop in a helical coil are limited to a specific operating range. No general correlation is available for a helical coil which is applicable for all fluids. In the present study, an experimental databank collected containing a total of 832 data points includes the data from the present study and from the literature. The data includes diabatic pressure drop of two fluids namely water and R123. Data covers a range of parameters namely a mass flux of 120–2058 kg/m2 s, a heat flux of 18–2831 kW/m2, an exit quality of 0.03–1, a density ratio of 32–1404 and a coil to tube diameter ratio of 14–58. The databank is compared with eighteen empirical correlations which include well referred correlations of straight tubes and the available correlations of helical coils. The straight tube correlations are not working well for the present data set. The helical coil correlations work reasonably well for the present databank. A correlation is suggested to predict the two-phase pressure drop in helical coils. The present study suggests that the influence of a helical coil is completely included in the single phase pressure drop correlation for helical coils. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.