Natural circulation studies in a lead bismuth eutectic loop

Lead Bismuth Eutectic (LBE) is increasingly getting more attraction as the coolant for advanced reactor systems. It is also the primary coolant of the Compact High Temperature Reactor (CHTR), being designed at BARC. A loop has been set up for thermal hydraulics, instrument development and material related studies relevant to CHTR. Steady state natural circulation experimental studies were carried out for different power levels. Transient studies for start-up of natural circulation in the loop, loss of heat sink and step power change have also been carried out. An 1D code named LeBENC has been developed at BARC to simulate the natural circulation characteristics in closed loops. The salient features of the code include ability to handle non-uniform diameter components, axial thermal conduction in fluid and heat losses from the piping to the environment. This paper deals with the experimental studies carried out in the loop. Detailed validation of the LeBENC code with the experimental data is also discussed in the paper.     

Synthesis of base impurity distributions for improved figure of merit of transistors

This paper deals with the problem of determining the impurity distribution which will improve the minority carrier base transit time and figure of merit of transistors. From the study of a special form of doping distribution which presents a point of inflection in the resulting built-in electric field configuration, it is concluded that the optimum doping distributions derived through variational methods [2–4] do not necessarily offer a unique minimum for base transit time. A new technique called “The Segmentation Technique” is evolved to synthesise base impurity distributions for improved high frequency performance of present-day junction transistors. It is shown that typical impurity distributions presenting retarding field over a small portion of the base and an aiding field over the rest of the base region offer a significant improvement in base transit time and the high frequency figure of merit.     

Generalized Filter Topology Using Grounded Components and Single Novel Active Element

This paper introduces a new active element combining the useful features of differential voltage, dual-X and first generation current conveyors. The new proposed active element is further utilized to introduce a new generalized filter topology employing grounded components only. The proposed single active element-based topology benefits from first-order and second-order filter realization by appropriate impedance specialization. The circuit topology with single current input provides two output currents and voltages in each case. A thorough study of proposed active element along with extensive simulations is carried out to validate the filter topology. A detailed non-ideal study is also given. To further support the usefulness of filter topology, higher-order filters are also realized. The new active element and the new filter structure provide advancement to the existing knowledge; with the scope of active element being further exploited for analog signal processing applications in general. The proposed differential voltage dual-X first generation current conveyor (DV-DXCCI) and its filtering applications are simulated using TSMC 0.25  \(\upmu \) m technology.     

A new nonlinear directional overcurrent relay coordination technique, and banes and boons of near-end faults based approach

Considerations of weight factors and far-end faults in the directional overcurrent relay coordination problem formulation do not affect the optimal solution. This paper investigates this viewpoint and verifies that indeed by such an approach the optimality is not lost. But, this study reveals that in doing so, the coordination quality is sacrificed to some extent. It is also observed that if all remaining valid constraints (after relaxing few constraints based on the back-up coordination philosophy and strength of fault level generated) are considered and if the objective function is changed to running sum of all violating constraints, all valid considered constraints are satisfied. This study is done by simultaneously optimizing all settings in nonlinear environment by Sequential Quadratic Programming method using Matlab Toolbox. The results of the analysis on a sample 6-bus and IEEE 30-bus systems are presented in this paper.     

Solubility of fatty acids in supercritical carbon dioxide

The solubilities of lauric, linoleic, myristic, oleic, palmitic and stearic acid in supercritical carbon dioxide (SC-CO₂) at different pressures and temperatures were measured. The solubility values obtained in this work were compared with previously published data, and possible causes for observed discrepancies were discussed. The solubilities of the six fatty acids were modeled by Chrastil’s equation, and estimated model parameters were used to plot the solubility isotherms of fatty acids at 313, 323 and 333°K (40, 50 and 60°C) as a function of SC-CO₂ density. The comparison of solubility isotherms of fatty acids and vegetable oil suggests that separation of fatty acids from triglycerides might be possible by using SC-CO₂ at densities less than 700 kg/m³. From the effect of temperature on fatty-acid and vegetable-oil solubility, it seems that the extraction yield could be increased without sacrificing the selectivity of SC-CO₂ for fatty acids by choosing a higher operating temperature. The data also suggest that fractionation of certain fatty acids might be possible by manipulating the processing conditions. Given the values of the constants, Chrastil’s equation could serve as a guideline for choosing appropriate processing conditions and predicting the effect of pressure and temperature of SC-CO₂ on solute solubility.     

Evaluation of elastic moduli of composite materials by linear programming

A method of applying linear programming to evaluate the elastic moduli of unidirectionally fiber-reinforced composite materials is presented. Based on the theory of elasticity, the stresses and displacements of the fiber and of the resin are expressed in terms of harmonic series. The coefficients of the series are determined by the simplex algorithm to minimize the deviations which occur when the stresses and displacements are matched at the fiberresin interface and at the outer boundary of the representative element of the composite. By applying the energy principle, the Young's modulus in the fiber direction and the major Poisson's ratio of the E-glass/resin composite are found to be in good agreement with existing results, while the gap of the bounds for its bulk modulus is considerably narrowed in comparison to earlier results.     

Particulate pollution from biomass combustion in three cookstoves

The release of suspended particulate matter (SPM) in the indoor environment from the combustion of fuelwood, agri-residue, dung cakes and a mixture of fuelwood and dung cakes in traditional as well as improved biomass cookstoves is studied. The SPM emission is monitored at two positions in the kitchen and also at the centre of the living room. A comparative performance evaluation of several biofuel-cookstove combinations is undertaken. Some important results are plotted graphically and briefly discussed.