Theoretical Prediction of Cavitation in Radial Inflow Turbines at Design and off-Design Conditions

A theoretical method for the prediction of cavitation in hydraulic radial turbines is developed in this work. The method combines a steady, quasi-three dimensional analyses which are based on the streamline curvature technique with an approach for the prediction of cavitation based on the definition of "available" and "required" cavitation coefficients. A radial inflow turbine is selected as a test case to investigate the capability of the present method as a cavitation prediction tool at design and offdesign conditions. The effects of various operating conditions on the cavitation inception are examined at constant values of total head and turbine suction head. It has been found that cavitation is formed near the outlet when the turbine operated at the design speed. While at off-design speeds and flow rates, cavitation covers longer distances along suction and pressure surfaces

A Finite-Time Robust Distributed Cooperative Secondary Control Protocol for Droop-Based Islanded AC Microgrids

In this research work, a resilient finite-time consensus-based distributed secondary control protocol is presented for droop-based distributed generating (DG) units of an islanded AC microgrid (MG). Through a multi-agent control structure, the DG units of the microgrid adjust their active power outputs so that they reach an agreed-upon value in a finite time. Concurrently, all the DG units are forced to operate with their frequencies regulated to the reference MG frequency in a finite time, despite time-varying load perturbations. Each DG unit is provided with a hierarchical control architecture, where the primary control is achieved using the droop control method, while the secondary control is established through the proposed distributed control protocol. The communication between DG units takes place over a sparse communication network. The proposed control protocol is robust to both small and sufficiently large communication latencies and it supports the plug-and-play feature of DG units. Different time-domain-based numerical simulations are carried out on a small as well as large microgrid testbenches in Matlab/Simulink and demonstrate the correctness and effectiveness of the proposed distributed control protocol. A comparative study is also presented with the existing distributed control protocol, and it is found that the proposed strategy is superior in its performance

Phase Evolution and Microstructural Studies in CaZrTi<SUB>2</SUB>O<SUB>7</SUB>-Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB>System

A series of compositions with general stoichiometry Ca<SUB>1−x</SUB>Zr<SUB>1−x</SUB>Nd<SUB>2x</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> has been prepared by high-temperature solid-state reaction of component oxides and characterized by powder X-ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi<SUB>2</SUB>O<SUB>7</SUB>–Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> structure types are observed in this system. The 4M-polytype of zirconolite structure is stabilized by substitution of Nd<SUP>3+</SUP> ion. The addition of Nd<SUP>3+</SUP> ions form a cubic perovskite structure-type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure-type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca<SUP>2+</SUP> and Zr<SUP>4+</SUP> are incorporated into the perovskite-type Nd<SUB>2</SUB>Ti<SUB>2</SUB>O<SUB>7</SUB> structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd<SUP>3+</SUP>-rich compositions

High temperature crystallographic and thermodynamic investigations on synthetic calzirtite (Ca<SUB>2</SUB>Zr<SUB>5</SUB>Ti<SUB>2</SUB>O<SUB>16</SUB>)

In the context of formation and stability of synthetic rock (SYNROC), studies on crystal structure and thermodynamic parameters of a mineral analogous material, namely calzirtite has been undertaken. The ambient temperature structural studies revealed a tetragonal (I41/acd) fluorite related super-structure with about 5% intermixing of Ti and Zr sites for calzirtite. High temperature structural studies indicated the retention of tetragonal structure of calzirtite up to 1673 K. The average axial thermal expansion coefficient of calzirtite between 297 and 1473 K is found to be 12.7 × 10−6/K for a-axis and 9.2 × 10−6/K along the c-axis. The thermodynamic parameters of calzirtite have been determined employing high temperature solution calorimetry. The standard molar enthalpy of formation of Ca2Zr5Ti2O16(s) at 298 K is found to be −8964.16 ± 12.59 kJ mol−1. The isobaric heat capacity of the compound has been derived from the enthalpy increment (HT-H298) data measured by drop calorimetric technique. Based on the experimental results thermodynamic functions like C0p,m, S0m, H0, G0, (G0T-H0298)/T, &#916;fH0298 and &#916;fG0T for calzirtite (Ca2Zr5Ti2O16,s) has been generated

Outdoor air pollution affects tuberculosis development based on geographical information system modeling

Background : Daily intake of air is 30 Ib as compared with 2-Ib of food and 4½ of water. Thereby, breathing-contaminated air is as harmful as drinking or eating contaminated water or food, respectively. Recent research has highlighted the extent of outdoor air pollution in large cities and warranted high-quality studies to clarify the magnitude of the problem. Here, we evaluated the possible association between tuberculosis (TB) development and exposure to outdoor air pollution in a metropolitan city of Tehran. Methods: Extraction and analysis of relevant data. Investigation performed on TB patients (n = 1167) that were residing in Tehran for the past 10 years. The average concentration of sulfur dioxide (SO2), nitrogen dioxide, carbon monoxide (CO), and particles with an aerodynamic diameter of ≤ 2.5μm (PM2.5) and ≤ 10.0 (PM10) was measured from Tehran Air Quality Control Corporation (TAQCC). Patient and ecological informations were analyzed using geographical information system. Results: Based on TAQCC, Tehran had an average of 180–250 polluted days per year for the last 10 years. The high incidence of pulmonary TB (18 to 31/100,000) was detected in populations which were exposed to high concentration of CO (2.7 to 5.2 parts per million, 95% confidence interval [CI]; 1.10 to 1.90) and PM2.5(35 to 42μg/m3; 95% CI 1.03 to 1.80). The level of SO2,NO, and PM10was also high but not significantly related to TB (P > 0.05). Conclusion: The long-term exposure to PM2.5 and CO was positively associated with TB development

Preparation and Structure of Uranium-Incorporated Gd₂Zr₂O₇ Compounds and Their Thermodynamic Stabilities under Oxidizing and Reducing Conditions

Gd₂Zr₂O₇ is being contemplated as a futuristic matrix for the incorporation of high-level radioactive nuclear waste. This compound has the unique ability to incorporate several fission products and heavy metal ions like uranium and thorium into its lattice sites without undergoing structural changes. X-ray diffraction analyses of Gd_2–<i>x</i>U_<i>x</i>Zr₂O_7+δ samples indicate that the parent compound can incorporate a substantial amount of uranium, both under oxidizing and reducing conditions. The oxidation state of these samples was investigated by X-ray photoelectron spectroscopy. The thermodynamic stability of uranium-substituted Gd₂Zr₂O₇ is an important parameter that will govern the long-term storage of uranium and minor actinides in this matrix. High-temperature calorimetry has been used to investigate the stability of the Gd_2–<i>x</i>U_<i>x</i>Zr₂O_7+δ (0.00 ≤ <i>x</i> ≤ 0.15) compositions. The standard molar free energy of the formation of Gd_2–<i>x</i>U_<i>x</i>Zr₂O_7+δ (0.00 ≤ <i>x</i> ≤ 0.15) compositions has been estimated. From the free energy of formation data, the sample corresponding to <i>x</i> = 0.15 was found to be most stable in the Gd_2–<i>x</i>U_<i>x</i>Zr₂O_7+δ (0.00 ≤ <i>x</i> ≤ 0.15) series. The relative stabilities of U⁴⁺ and U⁶⁺ substituted gadolinium zirconate have been discussed on the basis of the charge on the uranium ion and the incorporation of corresponding extra oxygen atoms into the lattice for charge compensation