Model for drying during fluidized-bed combustion of wet low-rank coals

An unsteady state heat conduction model with a convective boundary condition is proposed for the drying of low-rank, high-porosity coals, such as lignites, during fluidized-bed combustion. The drying front is assumed to be the receding surface of a wet core. The solution technique for this moving boundary problem is based on the heat balance integral approach with immobilization of the moving boundary by a change in space variable. The governing cubic equation describing the drying curve in dimensionless form may be solved easily by the Newton—Raphson method. The model predictions are compared with experimental data for Mississippi lignite with excellent agreement. A correlation for estimation of total drying time is proposed. The temperature profiles obtained may be used for the study of the coupled drying and devolatilization in fluidized-bed combustors. The profiles could also be of importance in the study of formation of fissures/cracks in lignites subjected to intense heating conditions encountered during fluidized-bed combustion.     

Drag reduction characteristics of graft copolymers prepared by the gamma irradiation of poly(oxyethylene) in the presence of acrylic acid

Graft copolymers were prepared by irradiation of poly(oxyethylene), PEO, aqueous solutions in presence of acrylic acid. Chain transfer to PEO controls the graft length, the measured chain transfer constant of the acrylic acid radicals to PEO being 4.11 × 10^?4 at 25°C. The drag reduction characteristics of the graft copolymers were measured in the Reynolds number range 10⁴–10⁵ in a smooth-walled tube, 0.635 cm inside diameter. The drag reduction falls to near zero as the solution pH is lowered to 3, evidence of the formation of a PEO-poly(acrylic acid) coacervate.     

Electric field assisted solid-state interfacial joining of TaC-HfC ceramics without filler

The application of ultra-high-temperature ceramics (UHTCs) demands effective ways of joining in overcoming the problems associated with the fabrication of complex-shaped components. In this study, we choose to investigate a new method of rapidly joining pre-sintered TaC and HfC ceramics without any filler material using the spark plasma sintering (SPS) technique. A well-bonded TaC–HfC interface was observed with no apparent cracking and porosity at the joint. The joining mechanisms were predominantly driven by solid-state diffusion and localized plastic deformation. The nanomechanical properties of the TaC-HfC joint are better than the HfC while comparable to that of the TaC. High-load indentation (up to 200 N) results suggest that the TaC–HfC interface is stronger than the parent UHTCs with no crack propagating at the interface. Upon comparison with the parent UHTCs, the damaged area and the average crack length at the interface, reduced up to ~94% and ~56%, respectively. This study shows that the SPS technique can also apply to joining other UHTCs without any filler, resulting in the new field of developing complex components for the thermal protection system (TPS).     

Fabrication and characterization of electrospun psyllium husk-based nanofibers for tissue regeneration

The present study reports for first time the blending of psyllium husk (PH) powder/gelatin (G) in the polymer-rich composition of polyvinyl alcohol (PVA) to make an electrospinnable solution. The composite was prepared in 3 different ratios viz., 100% (wt/wt) (PVA + PH), 75% + 25% (PVA + 75PH + 25G) (wt/wt) and 50% + 50% (PVA + 50PH + 50G) (wt/wt) in 6% PVA solution. Optimum electrospinning parameters were evaluated for all the prepared blends. The fabricated nanofibers were characterized by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared, differential scanning calorimetry, porosity percentage, and fiber orientation using ImageJ software. A qualitative in vitro degradation study at room temperature is supported by SEM images. The cellular interactions were characterized by MTT assay of NIH-3T3 fibroblast cells for 2 and 4 days with an optimum cell growth of >50% by fourth day of culture and long-term cultivation of L929-RFP cells was observed for 10 days. The nanofibers were formed in the range of 49–600 nm. PVA + 75PH + 25G when cultured with L929-RFP cells exhibited highest fluorescence intensity and thus supported cellular proliferation significantly. Based on the results obtained from various analyses, we anticipate that fabricated psyllium-based nanofiber can be used as a promising candidate for wound healing and other biomedical applications.     

The determination of the enthalpy of formation and the enthalpy increment of Cd0.5Te0.5 by Calvet calorimetry

The enthalpy of formation of Cd_0.5Te_0.5(s) has been determined using a Calvet calorimeter at 785 K by direct reaction calorimetry. The heat changes were measured for the additions of Cd(s) or Te(s) from 298 K to a reaction crucible containing the other liquid metal at 785 K. Measurements were also carried out to determine the enthalpy changes due to the direct reaction of the Te(l) and Cd(l) at 785 K. The enthalpies of formation of Cd_0.5Te_0.5 calculated from the two sets of experiments were in agreement. The H_T°---H₂₉₈° values of the Cd_0.5Te_0.5 compound have also been determined in the temperature range 406–826 K by the drop method. Using ΔH_fm° at 785 K and H_T---H₂₉₈° values of Cd_0.5Te_0.5, ΔH_fm° at 298 K was determined to be −(50.349±0.510) kJ mol⁻¹.     

Comparative wear performance of titanium based coatings for automotive applications using exhaust gas recirculation

This paper reports tribological characterization of titanium based coatings ion bonded on steel balls for automotive applications using exhaust gas recirculation (EGR). It is well known that lubricating oil drawn from EGR operated engine is contaminated with soot and higher amounts of wear debris compared to non-EGR operated engine. In this study, steel balls coated with TiN, TiAlN and TiCN are investigated in both fresh lubricating oil and EGR stressed oil for a comparative assessment of their wear characteristics in two mediums. Normal load was applied on the samples, tested against a rotating cast iron disk, simulating ring-liner interaction. In each experiment, about one quarter of disk was dipped in the oil (a) to ensure the presence of a thin oil film on the disk-ball interface during the experiment, and (b) to avoid exposure of the worn surface to atmospheric air. The results reveal that the wear rates of the coatings based on the change in the scar diameters of the samples, tested in EGR oil was 2-4 times higher than that of fresh lubricating oil. It was found that despite lowest hardness, TiN coated samples showed smaller scar diameters than TiAlN and TiCN coated samples in both lubricating oil environments. A simple geometric model was used to calculate the thickness of the coating removed as a function of the test duration. Results show that TiN coatings last for 120 min in fresh oil as compared to 30 min in the EGR oil under normal loading, whereas TiAlN and TiCN coating last for 60 and 30 min respectively in fresh oil and wear out in 15 min in EGR oil.     

The spray forming of nanostructured Aluminum Oxide

Research Summary Nanostructured ceramics and their composites possess improved properties such as tensile strength, fatigue strength, hardness, and wear resistance. Freestanding, near-net shape, nanostructured Al₂O₃ components can be synthesized via plasma-spray forming. In this study, plasma-spray parameters were optimized and an innovative substrate cooling technique was developed to retain nanosize Al₂O₃ in the spray deposit. Nanosize Al₂O₃ particles were partially melted and trapped between the fully melted coarser, micrometersize Al₂O₃grains. Densification of the spray-deposited Al₂O₃occurred via solidification and sintering. A similar processing approach can be adopted for fabrication of near-net shapes of a variety of nanostructured materials (metals, ceramics, and intermetallics) and their combinations by selecting suitable powder-treatment and plasmaspray parameters.     

An efficient fragile watermarking scheme with multilevel tamper detection and recovery based on dynamic domain selection

Self-recoverable fragile watermarking is meant for accurate tamper localization as well as image recovery with superior visual quality. However, most of the existing state of art approaches perform authentication and recovery on block basis owing to which the entire block is categorized as tampered in case of alteration of one or more pixels of it. This, results in staircase formation of tamper detected regions, hence lacking in accuracy. Furthermore, the visual quality of the recovered image also deteriorates as an approximate value is assigned to all the block pixels corresponding to the altered region. The proposed watermarking scheme performs both authentication and recovery pixelwise. The authentication of each pixel is done via multi level tamper detection(MLTD) through three authentication bits based on value, location and neighbourhood information. The domain for image recovery is chosen dynamically based on the content of the block, may it be in spatial domain for smooth blocks or frequency domain for the rough ones. This provides high accuracy in recovery. As the embedding of recovery information is done in the frequency domain, the imperceptibility of the watermarked image scheme remains high. Also, embedding of authentication information in the spatial domain maintains its fragile nature. Even for higher tampering ratios, the lost content is rebuilt with high peak signal to noise ratio(PSNR) of the recovered image. The probabilities of false rejection and false acceptance head towards the ideal value for most of the empirical analysis. Comparative study via metric evaluation of probability of false rejection (PFR), probability of false acceptance (PFA) and PSNR of recovered image for different standard test cover images demonstrate the efficacy of the proposed scheme over other existing state of art approaches. Further, the security of the proposed scheme remains high due to usage of multi-layered secret keys and chaos based random mapping handling worst tamper scenarios.     

Viscoelastic flow in an obstructed microchannel at high Weissenberg number

Detailed measurements of the flow instability of dilute shear-thinning viscoelastic aqueous solutions, with relatively low zero-shear viscosities, in an obstructed microchannel flow are reported. We examine the flow behaviour resulting from a 100 μm post placed in the channel centreline over a range of Reynolds numbers (\(5<Re<300\)) and Weissenberg numbers (\(20<Wi<10^3\)). Micro-particle image velocimetry measurements show the onset of an upstream instability within a Reynolds number range and at a critical elasticity number corresponding to polymer concentrations above 25 ppm of long-chain polyacrylamide. The instability results in significant local fluctuations in the flow field approaching 30 % of the mean velocity. The magnitude of the local viscosity ratio in the region upstream of the post is proposed as a driving mechanism for the instability which resembles a buckling flow. Additionally, the classical instability owing to separation and vortex formation downstream of the post in Newtonian flow is suppressed and a very long stable wake is observed extending over 10 post-diameters downstream.