Hydraulic and sediment removal performance of a modified hydrocyclone

Traditionally, settling basins have been used to exclude suspended sediment in hydropower plants. However, due to the inability of such basins to exclude fine sediment (predominantly hard minerals such as quartz and feldspar) and the excessive sediment loads in Himalayan Rivers, hydro-mechanical equipment and accessories in these plants have been severely damaged. Not only does this involve huge maintenance costs, but there is also a substantial revenue loss due to reduced equipment efficiencies. Thus, more efficient devices such as hydrocyclones are required to remove sediment particles. However, the geometry of a hydrocyclone plays an important role in hydraulic and sediment removal efficiency, and this paper analyses the experimental results of a test rig consisting of a hydrocyclone, 0.38 m in diameter, with a modified geometry. The results were compared with those of other investigators, and show that the modified hydrocyclone gives better hydraulic and sediment removal. The implications for suspended sediment exclusion in hydropower plants of Himalayan region are pointed out.     

Microwave assisted hydrothermal synthesis of well-dispersed and thermally stable Ag@SnO2 core–shell nanocomposites for propane sensing applications

A simple microwave assisted hydrothermal precipitation (M–H) technique for the synthesis of Ag@SnO₂ core–shell structure nanoparticles (NPs) is reported. Ag NPs were synthesized via chemical reduction of metal salt followed by M–H deposition of tin dioxide shell for fabrication of monodispersed core–shell particles. The phase and morphology has been investigated by X-ray diffraction technique (XRD) and transmission electron microscopy (TEM) respectively. Ag@SnO₂ core–shell nanocomposites have shown distinct surface Plasmon spectrum in the range of 407–440 nm. The core–shell morphology is confirmed from the TEM images. XRD patterns have suggested the formation of silver and tin dioxide in the face-centered cubic and Cassiterite form respectively. Our investigations suggested that the formation of core–shell structure results in the enhanced thermal stability of the system. Synthesized material is used for the detection of propane gas. To understand the multi gas sensing ability and selectivity for detection of propane gas by Ag@SnO₂ core–shell materials based devices, Sinha–Tripathy soft-sensor model has been proposed.     

A novel process for precipitation of ultra-fine particles using sub-critical CO2

Supercritical CO₂ has been utilized as solvent, cosolvent or antisolvent in several processes for production of ultra-fine solid particles with narrow size distribution. The key to the precipitation of such particles is to produce a very large, rapid and uniform supersaturation in the solution of a solid substance. This can be achieved either by a rapid and large reduction in the temperature of solution or by drastically increasing the CO₂ solubility for imparting the antisolvent effect. Most of these CO₂ processes require high-pressure pumps, specially designed nozzles and accurate control of process parameters. In order to obviate these requirements, a simple technique of precipitation by pressure reduction over the gas-expanded liquids (PPRGEL), such as CO₂-expanded organic solutions has been utilized to impart a large, uniform and rapid reduction of temperature in the solution for instantaneous precipitation of ultra-fine particles. This process utilizes sub-critical CO₂ at relatively low pressures of 40-70 bar and near ambient temperature of 303 K for creating a temperature drop of 30-70 K in the solution within seconds, without using any specially designed nozzle or high-pressure pumps. The present paper validates the process principle for precipitation of Zinc acetate (ZnAc) nanoparticles from its organic solution in a mixed solvent of acetone and dimethyl sulfoxide (DMSO). Nanoparticles are produced with the average size of 20-250 nm (from 100 ml of solution in a high-pressure vessel of 1.09 L working volume), and vary in shapes such as long needles, rods and near spherical depending on pressure (40-70 bar at 303 K), solid concentration (0.01-0.05 g/ml) and addition of stabilizer.     

Design of a Low-Cost Thermal Dispersion Mass Air Flow (MAF) Sensor

There is a need for a low-cost sensor to be used in many practical applications, such as the control of the air–fuel ratio in combustion burners, which measures the mass flow rate of fluid. This paper focuses on the design, calibration, and testing of a mass flow sensor operating on the principle of thermal dispersion. The developed sensor implements a digital proportional-integral controller which regulates the body temperature of a heated element, recognized as a thermistor, located in the stream of the fluid flow to a constant difference with respect to the ambient air temperature. The power dissipated by this heated element was referenced to known mass flow rates of air to determine the relationship between the dissipated power and ambient temperature to the measured mass flow rate. The inclusion of air flow conditioners, which filtered unwanted debris and delivered a more laminar air flow, was imperative to the success of the design. The designed sensor was proven to measure the incoming mass air flow through a duct, in the presence of moderate disturbances in the intake air pipe and for a wide range of ambient air temperatures, with a maximum full-scale error of 5.5% and a range up to 80 kg/h.     

A Markovianity based optimisation algorithm

Several Estimation of Distribution Algorithms (EDAs) based on Markov networks have been recently proposed. The key idea behind these EDAs was to factorise the joint probability distribution of solution variables in terms of cliques in the undirected graph. As such, they made use of the global Markov property of the Markov network in one form or another. This paper presents a Markov Network based EDA that is based on the use of the local Markov property, the Markovianity, and does not directly model the joint distribution. We call it Markovianity based Optimisation Algorithm. The algorithm combines a novel method for extracting the neighbourhood structure from the mutual information between the variables, with a Gibbs sampler method to generate new points. We present an extensive empirical validation of the algorithm on problems with complex interactions, comparing its performance with other EDAs that use higher order interactions. We extend the analysis to other functions with discrete representation, where EDA results are scarce, comparing the algorithm with state of the art EDAs that use marginal product factorisations.     

Mass and heat transfer analysis of SAS: effects of thermodynamic states and flow rates on droplet size

The supercritical antisolvent (SAS) process entails attainment of extremely high supersaturation in an atomized solution droplet by a very rapid increase in the antisolvent CO₂ mole fraction in it during its flight through a CO₂ continuum. In this work the droplet dynamics has been studied for a single droplet of CO₂–acetone solution falling in a flowing CO₂ environment in terms of variations in its concentration, temperature and size due to the two-way mass transfer of CO₂ and solvent. A model based on the SAS mechanism of simultaneous mass and heat transfer has been simulated to study the effects of the thermodynamic states and the individual flow rates of CO₂ and solution. The hydrodynamics of the droplet and the convective mass and heat transfer have been combined in the model to ascertain the individual number of moles of CO₂ and solvent transferred and their directions at any instant of time during the flight. The effects of process parameters have been analyzed for the initial droplet size of the solution. The swelling or shrinking of the droplet has been analyzed with time till the solvent is completely evaporated, in the pressure range of 71–350 bar, temperature range of 313–333 K, SC CO₂ flow rate of 0.1136–1.136 mol/s and the ratio of the volumetric flow rates of CO₂-to-solution in the range of 100–1000. The mole fraction of CO₂ attained inside the non-isothermal droplet has been analyzed with time, which is needed in the design of supersaturaton and nucleation kinetics in the SAS process.