Articles written in Sadhana

    • A design for intrinsic control of anaerobic digestion

      R Ashok Kumar

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      The article reports on a novel layout which achieves intrinsic control of anaerobic digestion of a wide range of feeds on a continuous basis. The feed is automatically controlled to match the digestion rate. The design consists of a shallow tank concentric with a gas holder resting on stoppers on the tank bottom. The height of the digesting fluid is maintained using the plug flow principle. The feed material is dropped into the annular space which is thereafter covered with a black plastic sheet to enable anoxic conditions to prevail. The bioliquid hydrolyses the material, with the help of prefermenting bacteria, into volatile acids. A steady migration of these volatile acids into the anaerobic digester is maintained by the concentration gradient, which is constantly replenished by the action of a syntrophic community of bacteria, producing methane. Further, the feasibility of the concept is reported on a system with a 45 m3 concrete tank and a 35 m3 steel gas holder by using a mix of domestic wastes and producing gas with 70% methane content reliably for hundred days continuously. A novel simulator is developed to predict the performance of the design at various parameters of operation. It is shown that the performance data for digesters analogous to the design reported here are interchangeable. Based on this, the average productivity of gas for various loadings is predicted within ±10% of the actual yields for the analogous digesters. Because of the nature of the design, digestion of a wide range of feeds are permitted: without the problems faced in conventional layouts. This tremendous potential is realised by maintaining the integrity of the ecosystem of anaerobic digestion through the medium of the bioliquid which pervades the annular space as well as the confines of the anaerobic digester. By utilising the design in practice at normal loadings, its potential for reliable and economic digestion at a fraction of the cost of deep digesters could be realised if the predictions are confirmed at higher loadings by further work.

    • Design and characterization of in-plane MEMS yaw rate sensor

      K P Venkatesh Nishad Patil Ashok Kumar Pandey Rudra Pratap

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      In this paper, we present the design and characterization of a vibratory yaw rate MEMS sensor that uses in-plane motion for both actuation and sensing. The design criterion for the rate sensor is based on a high sensitivity and low bandwidth. The required sensitivity of the yaw rate sensor is attained by using the inplane motion in which the dominant damping mechanism is the fluid loss due to slide film damping i.e. two–three orders of magnitude less than the squeeze-film damping in other rate sensors with out-of-plane motion. The low bandwidth is achieved by matching the drive and the sense mode frequencies. Based on these factors, the yaw rate sensor is designed and finally realized using surface micromachining. The inplane motion of the sensor is experimentally characterized to determine the sense and the drive mode frequencies, and corresponding damping ratios. It is found that the experimental results match well with the numerical and the analytical models with less than 5% error in frequencies measurements. The measured quality factor of the sensor is approximately 467, which is two orders of magnitude higher than that for a similar rate sensor with out-of-plane sense direction.

    • Effect of metal coating and residual stress on the resonant frequency of MEMS resonators

      Ashok Kumar Pandey K P Venkatesh Rudra Pratap

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      MEMS resonators are designed for a fixed resonant frequency. Therefore, any shift in the resonant frequency of the final fabricated structure can be a denting factor for its suitability towards a desired application. There are numerous factors which alter the designed resonant frequency of the fabricated resonator such as the metal layer deposited on top of the beam and the residual stresses present in the fabricated structure. While the metal coating, which acts as electrode, increases the stiffness and the effective mass of the composite structure, the residual stress increases or decreases the net stiffness if it is a tensile or compressive type respectively. In this paper, we investigate both these cases by taking two different structures, namely, the micro cantilever beam with gold layer deposited on its top surface and the MEMS gyroscope with residual stresses. First, we carry out experiments to characterize both these structures to find their resonant frequencies. Later, we analytically model those effects and compare them with the experimentally obtained values. Finally, it is found that the analytical models give an error of less than 10% with respect to the experimental results in both the cases.

    • Indigenous development and airworthiness certification of 15–5 PH precipitation hardenable stainless steel for aircraft applications

      Ashok Kumar Y Balaji N Eswara Prasad G Gouda K Tamilmani

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      In this paper, we discuss the optimization of chemical composition, processing (forging and rolling) and heat treatment parameters to obtain the best combination of mechanical properties in case of a Fe–15Cr–5Ni–4Cu precipitation hardenable stainless steel. The 𝜀-copper precipitates that form during aging are spherical in shape and coherent with the matrix and principally provide strengthening in this alloy. The orientation relationship is found to be Kurdjumov–Sachs (K–S), which is common in fcc–bcc systems. Results obtained from metallurgical evaluation (mechanical property and metallography) on 15–5 PH alloy during type certification on 3 different melts were used for the optimization, attempted in this study. The mechanical properties following strain deformation has been carried out using optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). In the aged conditions, the 15–5 PH alloy exhibited brittle failure with extensive cleavage and/or quasicleavage fracture. This paper reports all results and also factually shows that indigenously developed and produced 15–5 PH stainless steel matches in its properties with the equivalent aeronautical grade precipitation hardening stainless steels globally produced by internationally renowned manufactures.

    • Recovery of naringin from kinnow (Citrus reticulata Blanco) peels by adsorption–desorption technique using an indigenous resin


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      A process technology has been developed for recovery of naringin from kinnow (citrus) peels,which is a waste. The kinnow peels were boiled with water to extract naringin into water. It was adsorbed on an indigenous macroporous resin, Indion PA-500. Naringin was recovered from the saturated resin by desorption with ethanol as a solvent. The equilibrium and kinetic studies for both adsorption and desorption are presented.The Langmuir isotherm described the adsorption equilibrium data. However, desorption data were best described by the Toth isotherm. Adsorption and desorption kinetic data were found to follow a pseudo-secondorder rate equation and second-order rate equation, respectively. Recovery of naringin was about 49% w/w (based on naringin present in peel-boiled extract). The purity of final products was 91–94% w/w.

    • Variability in large-sample postbuckling behavior of two small thin walled structures


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      In thin shell buckling, geometric imperfections are important contributors to observed scatter in experimentally determined postbuckling behavior. Buckling experiments with large shells are difficult and expensive to conduct, and hence the sample sizes of buckling tests reported in the literature are generally small.To study statistical variability of buckling loads for a large number of notionally identical thin shells, we have carried out 100 buckling experiments each for two thin shell geometries. One shell geometry is a dome-like shell with a flat base (a bowl), and the other is a truncated cone with a flat base (a tumbler). The test shells are industrially produced, inexpensive, made of stainless steel, and easily available in India as utensils for domestic use. We provide detailed geometric and material characterization of these thin shell specimens. These shells were compressed axially between rigid plates. Buckling for both shell geometries was elastoplastic in nature. The experimental buckling load–displacement curves of 100 specimens for the bowl show variability in buckling loads by a factor of two, and stable postbuckling response. The corresponding curves for 100 specimens of the tumbler show variations of as much as a factor 5, with many snap-throughs, and unstable postbuckling response for larger compressions. We present two sets of axisymmetric elastoplastic finite element simulations of the tumbler, with both (a) tractions directly applied on a predetermined region and (b) through contact with a rigid plate. The latter set of simulations show approximately twice as much sensitivity to geometrical imperfections. Our results may guide new assessments of factors of safety in buckling, as laid downin design codes, when there is a chance of such interactions between contact loading and geometry.

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