Design and Development of a Series Switch for High Voltage in RF Heating

Plasma is the fourth state of matter. To sustain plasma in its ionic form very high temperature is essential. RF heating systems are used to provide the required temperature. Arching phenomenon in these systems can cause enormous damage to the RF tube. Heavy current flows across the anode–cathode junction, which need to be suppressed in minimal time for its protection. Fast-switching circuit breakers are used to cut-off the load from the supply in cases of arching. The crowbar interrupts the connection between the high voltage power supply (HVPS) and the RF tube for a temporary period between which the series switch has to open. The crowbar shunts the current across the load but in the process leads to short circuiting the HVPS. Thus, to protect the load as well as the HVPS a series switch is necessary. This paper presents the design and development of high voltage Series Switch for the high power switching applications. Fiber optic based Optimum triggering scheme is designed and tested to restrict the time delay well within the stipulated limits. The design is well supported with the experimental results for the whole set-up along with the series switch at various voltage level before its approval for operation at 5.2 kV.     

Synthesis of nano-carbon (nanotubes,nanofibres, graphene) materials

In the present study, we report the synthesis of carbon nanotubes (CNTs) using a new natural precursor: castor oil. The CNTs were synthesized by spray pyrolysis of castor oil-ferrocene solution at 850°C under an Ar atmosphere. We also report the synthesis of carbon nitrogen (C-N) nanotubes using castor oil-ferrocene-ammonia precursor. The as-grown CNTs and C-N nanotubes were characterized through scanning and transmission electron microscopic techniques. Graphitic nanofibres (GNFs) were synthesized by thermal decomposition of acetylene (C₂H₂) gas using Ni catalyst at 600°C. As-grown GNFs reveal both planar and helical morphology. We have investigated the structural and electrical properties of multi-walled CNTs (MWNTs)-polymer (polyacrylamide (PAM)) composites. The MWNTs-PAM composites were prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through SEM. A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It is shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. Enhanced electrical conductivity was observed for the MWNTs-PAM composites. Graphene samples were prepared by thermal exfoliation of graphite oxide. XRD analysis confirms the formation of graphene.     

Experimental investigation of continuous single‐phase rimming flow in a horizontal rotating cylinder

Rimming flow of water that leads to a thin film onto the inner surface of a horizontally rotating cylinder is studied in this work. At higher rotational speeds, axial flow of uniform thin film is established inside the rotating cylinder. Film thickness measurements under different flow conditions were performed in the annular flow regime using an optical interferometric technique. Dimensional analysis was also performed to understand the parametric dependence of key parameters involved in the rimming flow of water inside a horizontal rotating cylinder and expressions to determine average film thickness and average residence time are also presented. This study will provide a basis to estimate the transport characteristics in the thin film inside the horizontal rotating cylinder. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3939–3950, 2014     

Techno-economic viability of three different energy-supplying options for remote area electrification in India

Distributed power generation based on renewable energy sources brings new life and hope to electrify remote villagers. The proposed work suggests the techno-economic feasibility of three different energy-supplying alternatives namely the solar photovoltaic (SPV) system, diesel generator system and extending the grid connection for energy supply to a remote village located around 15 km away from the place where grid supply is available. Design of all the above three systems along with their economic analysis is carried out in this paper. A comparison on the basis of economic indicators like unit cost of electricity, net present value and payback period among the three systems is also discussed. The results show that the SPV system is economically more viable among the three options apart from environment benefits. This study may provide a new direction for energy planners to supply energy in remote non-electrified areas of India through SPV systems.     

Prediction and Comparison of Shelf Life of Solid Rocket Propellants Using Arrhenius and Berthelot Equations

The Arrhenius equation and the Berthelot equation for the prediction of shelf life of composite propellant formulations are compared. The elongation has a measurable variation with time and is taken as the fastest degrading parameter for HTPB/AP/Al based composite solid rocket propellants. An HTPB based aluminized composite propellant with 85 % solid loading and an initial elongation of 63.24 % is prepared. It is kept at an elevated temperature of 60 °C to achieve a higher rate of degradation for a prolonged time period (1 year). The elongation is monitored at regular intervals using JANNAF class C dog bone specimen in uni‐axial tensile mode. A reduction of the elongation to less than 50 % is taken as the end‐of‐shelf life of the propellant. The shelf life of the propellant is calculated to be 1.2 years at 60 °C. For the extrapolation of the shelf life at 60 °C to the shelf life at 27 °C, the results of both the Arrhenius equation and the Berthelot equation are compared. The activation energy (E) in the Arrhenius equation is obtained as 72.8 kJ mol⁻¹ and the 10 °C reaction rate rise factor (γ₁₀) is found to be 2.4. This comparison is independent of the propellant formulation and other researchers have reported a similar range of values for these parameters. The shelf life of this propellant formulation at 27 °C is conservatively predicted to be 20 years using both equations. In addition to estimation of shelf life by both equations using elongation as control parameter, this paper gives scaling curves, which are valid universally for predicting shelf life at 27 °C from data of shelf life at 60 °C. The use of scaling curves is independent of properties, propellant formulation and degradation mechanism considered for analysis.     

Maxwell Fluid Model for Generation of Stress–Strain Curves of Viscoelastic Solid Rocket Propellants

Solid rocket propellants are modeled as Maxwell Fluid with single spring and single dashpot in series. Complete stress–strain curve is generated for case‐bonded composite propellant formulations by taking suitable values of spring constant and damping coefficient. Propellants from same lot are tested at different strain rate. It is observed that change in spring constant, representing elastic part is very small with strain rate but damping constant varies significantly with variation in strain rate. For a typical propellant formulation, when strain rate is varied from 0.00037 to 0.185 per second, spring constant (K) changed from 5.5 to 7.9 MPa, but damping coefficient (D) varied from 1400 to 4 MPas. For all strain rates, stress–strain curve is generated using developed Maxwell model and close matching with actual test curve is observed. This indicates validity of Maxwell fluid model for case‐bonded solid propellant formulations. It is observed that with increases in strain rate, spring constant increases but damping coefficient decreases representing solid rocket propellant as a true viscoelastic material. It is also established that at higher strain rate, damping coefficient becomes negligible as compared to spring constant. It is also observed that variation of spring constant is logarithmic with strain rate and that of damping coefficient follows a power law. The correlation coefficients are introduced to ascertain spring constants and damping coefficients at any strain rate from that at a reference strain rate. Correlation for spring constant needs a coefficient “H,” which is function of propellant formulation alone and not of test conditions and the equation developed is K₂=(K₁‐H)×{ln(dε₂/dt)/ln(dε₁/dt)}+H. Similarly for damping coefficient (D) also another constant “S” is introduced and prediction formula is given by D₂=D₁×{(dε₂/dt)/(dε₁/dt)}^S. Evaluating constants “H” and “S” at different strain rates validate this mathematical formulation for different propellant formulations. Close matching of test and predicted stress–strain curve indicates propellant behavior as viscoelastic Maxwell Fluid. Uniqueness of approach is to predict complete stress–strain curves, which are not attempted by any other researchers.     

CFD analysis of two‐phase cavitating flow in a centrifugal pump with an inducer

One of the most undesirable phenomena encountered in the operation of a centrifugal pump is cavitation. It causes structural damage, vibration, and blockage of mass flow, leading to a drop in performance and life of the pump. This study addresses cavitation modeling of a single‐stage centrifugal pump and aims at minimizing cavitation by introducing an inducer upstream of the impeller. Furthermore, it aims at understanding different multiphase modeling schemes by a computational fluid dynamics software and its variation from single‐phase flows. The results from the numerical model are first validated against standard experimental data to check the credibility of the model. After validation, a single‐phase analysis is performed for a wide range of operating conditions. Subsequently, the Schnerr‐Sauer cavitation model is invoked and a multiphase analysis is carried out for the same. The results obtained shows that the inducer is effective in reducing the amount of cavitation for a substantial number of operating conditions. The effectiveness of the inducer is calculated, and a 96% effectiveness is observed at the best efficiency point. Furthermore, data from single‐phase and multiphase analysis are compared, and a method based on absolute pressure is proposed, which can provide results with significant accuracy without the need for expensive computation. Finally, Zwart‐Gerber‐Belamri model is used for cavitation modeling, and the behavior of the scheme is compared with Schnerr‐Sauer model. The pump parameters are compared, and the obtained results show close similarity between the two models.     

NDT-6D for color registration in agri-robotic applications

Registration of point cloud data containing both depth and color information is critical for a variety of applications, including in-field robotic plant manipulation, crop growth modeling, and autonomous navigation. However, current state-of-the-art registration methods often fail in challenging agricultural field conditions due to factors such as occlusions, plant density, and variable illumination. To address these issues, we propose the NDT-6D registration method, which is a color-based variation of the Normal Distribution Transform (NDT) registration approach for point clouds. Our method computes correspondences between pointclouds using both geometric and color information and minimizes the distance between these correspondences using only the three-dimensional (3D) geometric dimensions. We evaluate the method using the GRAPES3D data set collected with a commercial-grade RGB-D sensor mounted on a mobile platform in a vineyard. Results show that registration methods that only rely on depth information fail to provide quality registration for the tested data set. The proposed color-based variation outperforms state-of-the-art methods with a root mean square error (RMSE) of 1.1–1.6 cm for NDT-6D compared with 1.1–2.3 cm for other color-information-based methods and 1.2–13.7 cm for noncolor-information-based methods. The proposed method is shown to be robust against noises using the TUM RGBD data set by artificially adding noise present in an outdoor scenario. The relative pose error (RPE) increased $~$14% for our method compared to an increase of $~$75% for the best-performing registration method. The obtained average accuracy suggests that the NDT-6D registration methods can be used for in-field precision agriculture applications, for example, crop detection, size-based maturity estimation, and growth modeling.