Browsing by Author "Sarma, Upasana"

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    Design and control of PEM fuel cell-battery-hybrid energy system for locomotive applications
    (2021) Sarma, Upasana
    The development of economically feasible renewable energy technologies to replace the fossil fuel run machineries is one of the significant areas of research in this century. Over the years, the proton exchange membrane fuel cell (PEMFC) based hybrid energy system (HES) has emerged as a promising source of electrical power for use in transportation. This is because the PEMFC has the advantages of being clean energy, low operating temperature, high efficiency, etc. In this thesis, the PEMFC-battery-HES is proposed to retrofit the diesel locomotives which are currently used to haul the passenger trains operating in North Eastern Frontier Railway (NEFR), Assam, India. However, the investment and operational costs are the important factors associated with a HES. Thus, it is important to optimise the sizes of the HES components and to design an energy management strategy (EMS) for optimum distribution of load in the HES. In this thesis, the optimal component sizing of the PEMFC and battery that constitute the HES is carried out to provide the similar driving force as the WDM-3D class of diesel locomotives to pull the intercity passenger trains in Assam, India. To do this, single-objective and multi-objective design optimization approaches are formulated. The objective function of single-objective optimization is the minimization of the total cost of HES. The objective functions of multi-objective optimization are the simultaneous minimization of the total cost of HES and the PEMFC fuel consumption. In both the approaches, the optimization is carried out under the operational constraints of the battery state-of-charge limit, the PEMFC capacity constraint, and the instantaneous power balance between the source and load. Two EMSs are designed and are suitably incorporated into the particle swarm optimization (PSO) based solution algorithm to solve the design optimization problems. The application of PEMFC-battery-HES in locomotives requires the maintenance of a constant DC-bus voltage across the load against the wide variation in the PEMFC output voltage with changing operating and loading conditions. This can be achieved through the use of DC/DC converters. In view of this, the design and control of a multi-input single-output (MISO)-DC/DC boost converter are carried out in this thesis. The feedback controllers regulate the pulse width modulation of the converter switches to implement the EMS and to maintain the DC-bus voltage. The performances of the designed MISO converter and the controllers are validated on MATLAB/SIMULINK and on developing an experimental set-up. Both the simulation and hardware results show that the PWM controlled MISO converter provides the desired performances. Another vital aspect of a HES is the design of an efficient EMS to regulate the power flow in the HES based on the operational characteristics of the energy sources. Hence, two energy management optimization (EMO) approaches are devised that aim to generate the PEMFC power references at each loading point with the objective function of the minimization of the total fuel consumption of the PEMFC. The constraints of the first EMO approach include the limits on battery state-of-charge variation, the dynamic change in the PEMFC output power and the instantaneous power balance between the source and load. However, in the second EMO model, the durability limits of the energy sources are also considered in addition to the aforementioned operational constraints. The EMO approaches are executed using General Algebraic Modeling System. The performance comparison of the proposed approaches with some of the already available approaches confirms its proficiency in the reduction of fuel consumption with optimum utilization of the capacities of the energy sources. All the above studies are carried out using the data of the dynamically varying locomotive power demand for practical drive cycle scenarios of NEFR, Assam, India. The viable deployment of the hydrogen powered passenger trains requires a proper refueling infrastructure. In view of this, the optimal allocation planning of the hydrogen refueling stations (HRS) for the rollout of hydrogen powered passenger trains in NEFR, Assam, India is presented in this thesis. The problem of optimal allocation planning is firstly addressed as a single-objective optimization approach with the objective function of the minimization of the total cost ownership (TCO) of the HRS for a specified planning period. A multi-objective optimization approach is then designed with the objective functions of simultaneous minimization of the TCO and the average cost of refueling of the HRS. The optimization problems are solved using binary PSO based solution algorithms with the real-time data of the intercity railway traffic of NEFR, Assam, India as the input. Besides this, the total investments incurred in the HRS infrastructure development under the different scenarios of installed HRS capacity are also investigated
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    Experimental and Numerical Investigations into Laser-Induced Plasma Assisted Ablation (LIPAA) of Transparent Polycarbonate for Fabrication of Microchannels
    (2022) Sarma, Upasana
    Microchannel-based devices are widely used in microelectronic devices, turbine blade cooling, microfluidics for drug delivery devices, etc. Therefore, microchannel-based devices require the use of materials with high optical, chemical, and mechanical properties, and thus, transparent materials have become a significant material for the production of microchannels. Transparent polycarbonate (PC) is a highly durable material, making it resistant to impacts and fracture, providing safety and comfort in applications that demand reliability and high performance. As such, PC can be considered as an ideal material for the biomedical and optical industries. PC-based microchannels can be fabricated using a variety of processes such as lithography, wire moulding, micro-milling, laser micro-machining etc. Nonetheless, the mentioned techniques have limited applicability. Further, the high transmissivity of PC over a wide range of wavelength makes the laser based fabrication of microchannels on it a challenging task. However, with Laser-Induced Plasma Assisted Ablation (LIPAA), lasers may have the potential to process transparent PC. In view of this, in the present research work, systematic and extensive experimental as well as numerical studies have been carried out to assess the feasibility, productivity and product quality during LIPAA for microchannel fabrication on PC. LIPAA is a technique, by which transparent materials can be ablated on its rear side with the aid of laser-induced plasma. The first phase of the research work presents the successful fabrication of microchannels on transparent PC using the LIPAA technique. Besides, the effect of properties of metal targets on microchannel fabrication was also investigated. Three different metal targets utilized during the process are namely aluminium, copper and stainless steel. Evaluation was then performed to investigate the influence of metal target properties such as thermal conductivity and specific heat on the geometrical characteristics of the microchannels. The study concludes by stating that the higher thermal conductivity value of the metal target leads to the formation of a narrow microchannel, while the higher specific heat value leads to a deeper microchannel fabrication. In addition, the metal target resulting in the highest microchannel aspect ratio was recommended for further study in our research. In second phase of research work, experiments are carried out based on a full factorial 34 experiments on PC by the appropriate selection of the laser parameters viz. pulse power density, pulse repetition rate, pulse duration and laser scanning speed. The influence of the laser parameters on channel width, channel depth and the channel roughness has been studied. Analysis of Variance (ANOVA) is also carried out to determine the most influential parameters. Second order mathematical relations among the input laser parameters, their interactions and the responses were developed. To analyse the accuracy of the developed mathematical model, confirmation experiments are performed and is found to be in good agreement. Based on the confidence gained from the confirmation experiments performed, multiple objective (response) optimization of the input parameters to predict a better quality channel geometry and channel roughness is carried out. For a width of 250 μm, depth of 150 μm and minimum roughness on a single pass, the optimized condition of laser parameters is found to be 40 Hz repetition rate, 2 ms pulse duration and 4.79 MW/cm2 pulse power density. Using the optimal laser parameters, open microchannels are fabricated and were closed by using a thermal bonding process. Further, a fluid flow test carried out on the closed microchannel to prove its potentiality to be used as a microfluidic device has also been described in the chapter. Different configuration channels on PC have also been fabricated using the optimal laser parameters. he third phase of the work represents a two-dimensional transient numerical model to understand the physics of material removal during the LIPAA process. A realistic model is developed concerning the effect of plasma along with the effect of input laser irradiation. The channel dimensions, i.e., the width and the depth of the channel, were computed from the numerical study. The computed results have been duly verified with our experimental results and found in good agreement. Also, considering the effect of moving heat flux, it is witnessed that the peak temperature attains a constant value on reaching a certain distance, thus assuring a channel of uniform dimension. A three-dimensional nonlinear transient modelling was also developed to simulate the LIPAA process for microchannel fabrication on transparent polycarbonate. The merit of the approach lies in simulating simultaneous ablation of both transparent polycarbonate and aluminium metal target during the process. The developed model has the potential of estimating spatial-temperature distribution along the traverse direction and direction perpendicular to it. The spatial distribution lent a hand in predicting the width and depth of the microchannel. Temporal-temperature distribution for pulse-on and pulse-off time was also explored. A channel index (CI) has also been estimated which determines channel formation in or out of the micron-scale (1-999 μm) for a selected set of process conditions.