Application of exergy analysis in designing helium liquefiers

Exergy has proved to be a useful tool to analyze and optimize the design and operation of many systems. Some studies on helium refrigerators and liquefiers based on exergy are available in literature. In this paper, systematic evaluation of important operating and geometric parameters has been done to determine the exergy destructions in components as well as in the entire cycle of Collins helium liquefiers. Grassmann diagram of exergy flow has been shown to be of immense help in understanding relative importance of different components used in the system. Compressor pressure, expander flow rates, heat exchanger surface area are some of the parameters optimized considering both presence and absence of pressure drop in the heat exchangers. Non-dimensionalization of parameters makes the results applicable to plants of any capacity. Exergy-analysis based on Second Law proves to be far superior to the First Law based energy analysis in designing of the helium plant as the former is holistic in approach and capable of deriving some additional conclusions. Results derived on Collins cycle may be applicable in large-scale helium liquefiers by providing basic understanding of the influence of components on the plant performance and reasonable initial guess values in their design and simulation.     

Heat Priming of Lentil (Lens culinaris Medik.) Seeds and Foliar Treatment with γ-Aminobutyric Acid (GABA), Confers Protection to Reproductive Function and Yield Traits under High-Temperature Stress Environments

Gradually increasing temperatures at global and local scales are causing heat stress for cool and summer-season food legumes, such as lentil (Lens culinaris Medik.), which is highly susceptible to heat stress, especially during its reproductive stages of development. Hence, suitable strategies are needed to develop heat tolerance in this legume. In the present study, we tested the effectiveness of heat priming (HPr; 6 h at 35 °C) the lentil seeds and a foliar treatment of γ-aminobutyric acid (GABA; 1 mM; applied twice at different times), singly or in combination (HPr+GABA), under heat stress (32/20 °C) in two heat-tolerant (HT; IG2507, IG3263) and two heat-sensitive (HS; IG2821, IG2849) genotypes to mitigate heat stress. The three treatments significantly reduced heat injury to leaves and flowers, particularly when applied in combination, including leaf damage assessed as membrane injury, cellular oxidizing ability, leaf water status, and stomatal conductance. The combined HPr+GABA treatment significantly improved the photosynthetic function, measured as photosynthetic efficiency, chlorophyll concentration, and sucrose synthesis; and significantly reduced the oxidative damage, which was associated with a marked up-regulation in the activities of enzymatic antioxidants. The combined treatment also facilitated the synthesis of osmolytes, such as proline and glycine betaine, by upregulating the expression of their biosynthesizing enzymes (pyrroline-5-carboxylate synthase; betaine aldehyde dehydrogenase) under heat stress. The HPr+GABA treatment caused a considerable enhancement in endogenous levels of GABA in leaves, more so in the two heat-sensitive genotypes. The reproductive function, measured as germination and viability of pollen grains, receptivity of stigma, and viability of ovules, was significantly improved with combined treatment, resulting in enhanced pod number (21–23% in HT and 35–38% in HS genotypes, compared to heat stress alone) and seed yield per plant (22–24% in HT and 37–40% in HS genotypes, in comparison to heat stress alone). The combined treatment (HPr+GABA) was more effective and pronounced in heat-sensitive than heat-tolerant genotypes for all the traits tested. This study offers a potential solution for tackling and protecting heat stress injury in lentil plants.     

Optimization of operation and changeover time for production planning and scheduling in a flexible manufacturing system

This paper deals with the production planning problem of a flexible manufacturing system. It specifically addresses issues of machine loading, tool allocation, and part type grouping with the intent of developing an operation sequencing technique capable of optimizing operation time, non-productive tool change times, and orientation change times when processing a group’s design features. A hierarchical approach has been adopted to determine the part groups – depending on the operation, tool change and orientation change times at the upper level. At the next level, we sequence the operations of the part groups. Integer programming models are formulated to group the parts and to address the operation-sequencing problem. The model is illustrated with an example related to an auto engine cylinder head machining plant.     

Preparation of Fully Cubic Calcium-Stabilized Zirconia With 10 mol% Calcium Oxide Dopant Concentration by Microwave Processing

A novel, fast, and cheaper method has been developed for the synthesis of fully cubic calcium-stabilized zirconia (ZrO₂) of composition Ca_0.1Zr_0.9O_1.9 by dissolution of calcium oxide in monoclinic ZrO₂ for the first time using microwave energy. In this process, the precursors have been prepared by the mixed-oxide method taking the constituents in their stoichiometric ratio. The samples have been allowed to absorb microwave radiation in the presence of a polymeric susceptor. The susceptor absorbs the microwave radiation at room temperature and increases the temperature of the sample, where it starts interacting with microwave radiation. The susceptor burns off at a higher temperature without reacting with the sample. The cubic Ca_0.1Zr_0.9O_1.9 has been prepared at a temperature of 1100°C within 5 min.     

Independent field-oriented control of two split-phase induction motors from a single six-phase inverter

Split-phase (six-phase) induction motor stator windings consist of two sets of three phase windings, which are spatially phase separated by 30 electrical degrees. Due to mutual cancellation of the air gap flux for all the 6n/spl plusmn/1 (n=1,3,5...) order harmonic voltages, called zero sequence components, large harmonic currents are generated in the stator phases. Only the 12n/spl plusmn/1 (n=0,1,2,3...)-order harmonic voltage components contribute toward the air gap flux and electromagnetic torque production in the machine. In this paper, a novel scheme is proposed where two six-phase induction motors are connected in series with proper phase sequence so that the zero sequence component voltages of one machine act as torque and flux producing components for the other. Thus, the two six-phase motors can be independently controlled from a single six-phase inverter. A vector control scheme for the dual motor drive is developed and experimentally verified in this paper.     

Silicon,graphite and resin based hard carbon nanocomposite anodes for lithium ion batteries

Nanocomposite based on graphite (C), silicon (Si) and poly[(o-cresyl glycidyl ether)-co-formaldehyde] resin based amorphous hard carbon (HC), denoted as Si/C/HC, have been synthesized by thermal treatment of mechanically milled graphite, silicon and resin of nominal composition C–18 wt.% Si–40 wt.% resin at 973 K, 1073 K and 1173 K in ultrahigh purity argon atmosphere. The formation of the electrochemically inactive SiC is bypassed as well as the amorphization kinetics of graphite is reduced during prolonged milling of graphite and Si in the presence of the resin. Microstructural analysis has confirmed that the Si nanoparticle gets embedded, and is homogeneously dispersed and distributed on the graphite matrix after mechanical milling as well as after thermal treatment. Electrochemical studies have revealed that the Si/C/HC based nanocomposite, tested as a lithium ion anode, synthesized after thermal treatment at 1173 K exhibits a stable capacity of ∼640 mAh g⁻¹ with an excellent capacity retention when cycled at a rate of ∼160 mA g⁻¹. The nanocomposite anode also shows a moderate rate capability when cycled at different discharge/charge rates. Scanning electron microscopy analysis indicates that the structural integrity and the microstructural stability of the nanocomposite during the alloying/dealloying process contribute to the good cyclability observed in the above nanocomposites.     

Evaluation of Seasonal Variability of First-Order Ionospheric Delay Correction at L5 and S1 Frequencies Using Dual-Frequency NavIC System

Wireless Personal Communications - For the precise positioning applications it is important to determine and eliminate the positioning error introduced by various sources such as the ionosphere. To...