Estimation of Fretting Wear-Limited Life of a Shell and Tube Heat Exchanger Tubes: Analytical Formulation,Computer Implementation and Qualification Against Actual Reported Failure

In a typical shell and tube-type heat exchanger, the tubes are clamped at the ends by tube sheets and supported by intermittent baffles with gaps. Vibration of tubes makes them susceptible to impacting and rubbing with the baffle support or adjacent tubes. Damage caused by these impacts and rubbing motions is termed fretting. An analytical tool is developed to carry out fretting wear-limited life of heat exchanger tubes. The developed tool is evaluated with reported cases of failure. The authors had earlier conducted this evaluation (Patil et al. in J Fail Anal Preven 17:126–135, 2017) in cases where the vibration was excited by vortex shedding. This paper extends the study to include the other flow-induced mechanism of turbulent buffeting, thus making the tool more comprehensive.

     

Spectroscopic analysis of Eu doped transparent CaF2 ceramics at different concentration

Pure and Eu doped CaF₂ transparent ceramics were prepared for the first time. The samples were subjected to spectroscopic analyses to study the variation of transmission, emission and vibrational properties at various concentrations of Eu ion. Pure CaF₂ shows a good transparency of more than 80% and the Eu doped samples exhibit different absorption peaks corresponding to Eu ion transitions. Emission studies confirm that the divalent Eu ions are dominant at lower concentration whereas trivalent states become dominant as the concentration was increased. Raman measurements show characteristic T_2g phonon band of cubic CaF₂ with spectral shifting and broadening as the dopant concentration was increased. The analyses confirm the major role of interstitial fluorine ion in the spectroscopic properties of the ceramics.     

Crystal growth and characterization of Deuterated Glycine Phosphite single crystals

Deuterated Glycine Phosphite single crystals were grown by low temperature solution growth method using high purity deuterated water as solvent. Deuteration content of the as grown crystals was improved by repeated recrystallisation process. Structural perfection, transparency and the functional groups present in the grown crystals were identified using different characterization analyses. Dielectric behaviors of the as grown specimens were examined through thermal and impedance analysis. Partial deuteration of the grown crystal was confirmed from the DSC and dielectric results.     

Insight into the microstructural characterization of ferritic steels using micromagnetic parameters

The influence of tempering-induced microstructural changes on the micromagnetic parameters such as magnetic Barkhausen emission (MBE), coercive force (H _c), residual induction (B _r), and maximum induction (B _max) has been studied in 0.2 pct carbon steel, 2.25Cr-1Mo steel, and 9Cr-1Mo steel. It is observed that, after short tempering, the micromagnetic parameters show more or less linear correlation with hardness, which is attributed to the reduction in dislocation density, but long-term tempering produces nonlinear behavior. The variation in each of these parameters with tempering time has been explained based on the changes in the size and distribution of ferrite laths/grains and precipitates. It has been shown that the individual variation in the microstructural features such as size and distribution of laths/grains and precipitates during tempering can be clearly identified by the MBE parameters, which is not possible from the hysteresis loop parameters (H _c and B _r). It is also shown that the MBE parameters can not only be used to identify different stages of tempering but also to quantify the average size of laths/grains and second-phase precipitates.     

Effect of Tm3+ Ions on the White Light Emission of Dy3+–Tm3+ Codoped SrMg2La2W2O12 Phosphors

Dy³⁺–Tm³⁺ ions codoped SrMg₂La₂W₂O₁₂ (strontium magnesium lanthanum tungstate) phosphors were synthesized by conventional high‐temperature solid‐state reaction method. X‐ray analysis of the end products revealed the well‐crystallized phases with orthorhombic structure. The functional groups present in the phosphors were studied by the Fourier transform infrared measurements. To know the potential applicability of these phosphors for white light emission, the excitation and emission spectra were recorded. The excitation spectra exhibited an intense broad band at 313 nm, pertaining to the O → W ligand‐to‐metal charge‐transfer state (LMCT) of the host. With the excitation of LMCT band (313 nm), the decay curves of singly doped SrMg₂La₂W₂O₁₂:Dy phosphors exhibited single exponential, where as the codoped SrMg₂La₂W₂O₁₂:DyTm phosphors exhibited double exponential nature. The luminescence colors of these phosphors were estimated from Commission Internationale de L'Eclairage (CIE) coordinates using the photoluminescence data. The color of singly doped SrMg₂La₂W₂O₁₂:Dy phosphor has been tuned by codoping with Tm³⁺ ions. It has been noticed that the CIE chromaticity coordinates (x,y) determined from the luminescence spectrum of singly Dy³⁺ doped SrMg₂La₂W₂O₁₂ phosphor shifted toward the white light region, when codoped with Tm³⁺ ions. The increase in correlated color temperatures (T_cct) has been noticed with the increase of Tm³⁺ ions concentration in SrMg₂La₂W₂O₁₂:DyTm phosphors.     

Effect of graft-copolymerization with poly(acrylamide) on rheological and thermal properties of cassava starch

Graft copolymers of different grafting levels were synthesised by the free radical initiated reaction of cassava starch with acrylamide in presence of ceric ammonium nitrate. The viscosity properties of the native granular starch and the grafted starches were determined using a Rapid visco analyzer (RVA) and rheological properties by frequency sweep test under different conditions using a rheometer. Some of the grafted starches exhibited significantly higher and some others exhibited drastically reduced peak viscosity values irrespective of the percentage grafting. All the grafted starches exhibited very good viscosity stability as evidenced from the highly reduced breakdown and higher final viscosity values in comparison to native cassava starch. Thermal analysis of the pure granular cassava starch and grafted starches was carried out using a differential scanning calorimetry (DSC) and thermogravimetry. DSC studies showed that in comparison to native starch, the grafted starches showed lower temperatures of transition. The thermal stability of cassava starch was enhanced by grafting as observed from the thermogravimetric data. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Measurement of effective piezoelectric coefficients of PZT thin films for energy harvesting application with interdigitated electrodes

Interdigitated electrode (IDE) systems with lead zirconate titanate (PZT) thin films play an increasingly important role for two reasons: first, such a configuration generates higher voltages than parallel plate capacitor-type electrode (PPE) structures, and second, the application of an electric field leads to a compressive stress component in addition to the overall stress state, unlike a PPE structure, which results in tensile stress component. Because ceramics tend to crack at relatively moderate tensile stresses, this means that IDEs have a lower risk of cracking than PPEs. For these reasons, IDE systems are ideal for energy harvesting of vibration energy, and for actuators. Systematic investigations of PZT films with IDE systems have not yet been undertaken. In this work, we present results on the evaluation of the in-plane piezoelectric coefficients with IDE systems. Additionally, we also propose a simple and measurable figure of merit (FOM) to analyze and evaluate the relevant piezoelectric parameter for harvesting efficiency without the need to fabricate the energy harvesting device. Idealized effective coefficients e(IDE) and h(IDE) are derived, showing its composite nature with about one-third contribution of the transverse effect, and about two-thirds contribution of the longitudinal effect in the case of a PZT film deposited on a (100)-oriented silicon wafer with the in-plane electric field along one of the <011> Si directions. Randomly oriented 1-μm-thick PZT 53/47 film deposited by a sol-gel technique, was evaluated and yielded an effective coefficient e(IDE) of 15 C???m(???2). Our FOM is the product between effective e and h coefficient representing twice the electrical energy density stored in the piezoelectric film per unit strain deformation (both for IDE and PPE systems). Assuming homogeneous fields between the fingers, and neglecting the contribution from below the electrode fingers, the FOM for IDE structures with larger electrode gap is derived to be twice as large as for PPE structures, for PZT-5H properties. The experiments yielded an FOM of the IDE structures of 1.25 × 10(10) J/m(3) and 14 mV/μ strain.     

Nanoscale chemical and structural characterization of transient metallic nanowires using aberration-corrected STEM-EELS

Direct chemical and structural characterization of transient iron-nickel alloy nanowires was performed at subnanometer spatial resolution using probe spherical aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy. Nanowires with diameter less than 2 nm retaining their nominal bulk alloy composition were observed. In some cases, the nanowires were oxidized. Before rupture, a nanojunction as thin as three atoms in width could be imaged. The time-dependent structural analyses revealed the nanowire rupture mechanisms. It is found that the atoms on the {111} planes were the easiest to be removed by electron irradiation and fluctuations between low-energy and high-energy facets were observed. The hitherto unknown rich variety of structural and chemical behavior in alloyed magnetic nanojunctions should be considered for understanding their physical properties.     

Corrosion of High Chromium and Conventional Steels Embedded in Concrete

Corrosion rates of high chromium and conventional steel rebars were measured and compared by conducting two studies. One was on concrete blocks and the other was on bare steel rebars. In the former study, concrete blocks that had been made with two different steel rebars were placed in sodium chloride solutions, and air was blown through the solutions to accelerate corrosion of the embedded steel rebars. These blocks were taken out of the solution periodically, and the corrosion rates of the rebars were measured with a 3LP device. In the latter study, the bare rebars of the two steels were also corroded in sodium chloride solutions through which air was blown, withdrawn periodically, dried, and weighed after the corrosion products were removed. The corrosion rates were measured by the reduction of the weight of the rebars. In the study on concrete blocks, it was found that the corrosion rate increases for both steels as the concentration of sodium chloride in solution increases. It was also found that the corrosion rate of concrete blocks reinforced with conventional steel was about twice as much as that of the concrete blocks reinforced with high chromium steel after 132 days of exposure. From the study on bare steel rebars, it was found that the rate of corrosion of conventional steel was 12 times as much as that of high chromium steel at 0.1% sodium chloride, and the ratio decreased to 2 times as much when the sodium chloride concentration was increased to 3%. It was also found that the corrosion rate of high chromium steel was very sensitive to sodium chloride concentrations whereas that of conventional steel was not sensitive. The corrosion products were analyzed using x-ray diffraction and atomic absorption spectroscopy to identify the minerals present in them. It was found that corrosion products produced on the high chromium steel were predominantly lepidocrocite (γ-FeOOH) and hematite (Fe2O3), whereas that on the surface of conventional steel was predominantly magnetite (Fe3O4). It appears that the former iron oxides form an adherent and nonporous protective layer while the latter iron oxides (magnetite) do not, which can explain the distinct difference in corrosion rates of the two steel rebars.     

Dynamic qualification of complex structural components of nuclear power plants

The safety requirements and the lack of accessibility for any future repair, impose the design requirement that the integrity of reactor components of nuclear power plants be assured for the lifetime of the plant. To meet this design requirement it is essential to qualify the component, i.e. prove its capability to perform the design function for the design life. In performing its design function, the component is subjected to both static and dynamic loads. The qualification for static loads is rather simple and reliable, but qualification for dynamic loads is complex and often uncertain. This is because analytical tools are often inadequate for a realistic dynamic qualification and exact structurally simulated experimental models are almost always difficult to build. In such a situation, methods using tests on simple experimental set-ups supplemented by conservative analytical back-ups must be evolved. This paper highlights the intricacies involved in the conservative dynamic qualification of the complex components by considering the example of the moderator sparger tube. This component is a perforated tube submerged in water and excited by flow. For such a case, a completely analytical or a totally experimental qualification is not possible. This paper describes a procedure by which the required dynamic characteristics such as added mass, damping and fluid forces are generated from simple experiments and the component is qualified by analysis using these data.