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Abstract This work shows work flows supported by experimental work to analyse the efficiency of a plasma system in biomass conversion processes. The most common set of problems encountered when using biomass-to-energy (BTE) processes relate to tar formation and product gas composition. However, using plasma technology to convert biomass provides a solution because it unlocks more energy than can be achieved by other BTE systems by using a heat supply derived from electricity. The research presented in this paper focuses on the conversion of biomass to chemical energy (in gaseous form) with the aid of the electrical energy supplied by a water-cooled nitrogen plasma torch. The authors conducted a series of experiments in a continuous pyrolysis set up in which wood pellets were converted to syngas in a small-scale laboratory nitrogen plasma torch reactor with a maximum power supply of 15 kW. The efficiency of the process was measured in terms of the carbon conversion to all product gases which changed from 43 to 77%, at temperatures ranging from 400 °C to 1000 °C respectively. The combined carbon monoxide and hydrogen mole concentration in the product gas (without nitrogen) was 86% at 1:1 ratio for all temperatures studied. Syngas yield increased with increase in temperature. The overall biomass conversion obtained increased from 46% to 82% for the temperatures 400 °C to 1000 °C respectively, with the balance comprising carbon-rich solid residue and liquid. The work flow shows that a plasma system can get to high temperatures but work is also degraded in the overall process. Exergy analysis shows that the work lost by the overall process decreases with increase in process temperature.

Abstract The present study numerically investigates the oblique flow of a Walter-B type nano fluid over a convective surface. Effects of transversely applied magnetic field are also taken into account. The governing system is presented in the form of coupled differential equations by means of suitable similarity transformations which are then solved by using Spectral Quasilinearisation Method (QLM) and the Spectral Local Linearization Method (LLM). The results for velocities temperature as well as nano particle concentration are plotted against pertinent flow parameters. It is found that applied magnetic field M has opposite influence on normal and tangential components of local shear stress and it decays the local heat flux and mass flux rate at the stretching convective surface. Thermophoresis and Brownian diffusion effects on the local heat and mass flux rate are found to be non-similar in a quantitative sense. In order to signify the validity of current numerical scheme, a remarkable agreement is presented with the previous literature for some limiting cases.

AbstractThis work presents a theoretical numerical study of the bioconvection flow of Prandtl–Eyring nanofluid through a stretching cylinder with gyrotactic microorganisms. The mathematical model developed also incorporated the inclined magnetic field and heat generation effects. Further, stratification conditions are considered at the boundary of the stretched cylinder. The described flow problem conducting coupled high‐order partial differential equations (PDEs) is first reduced to the nonlinear system of ordinary differential equations (ODEs) by introducing suitable mathematical transformations. The resulting highly nonlinear flow equations are treated numerically by applying the shooting method. A comparison of the adapted method with previously reported data is also made to validate the presented results. The comparisons are in excellent agreement. The individual effect of controlling flow parameters/numbers on the flow profiles and physical quantities of engineering interest are represented graphically with physical descriptions. The significant results of the present analysis revealed that a rise in bioconvection Rayleigh number, thermal Grashof number, and angle of inclination boosts the velocity profile. The study shows that thermal stratification, mass stratification, and motile density stratification parameters diminish the temperature, concentration, and microorganism profiles, respectively. The nondimensional Sherwood number is decelerated significantly by thermophoresis and mass stratification parameters.

Frequency of supply is an important aspect of electrical power system. Active power balance and frequency control are important tasks in the daily management of a power system. Due to variation in power demand as a result of load changes based on consumer usage, resultant change in frequency impacts on power system operation. The phenomena i.e. load fluctuation creates a burden on the generator prime mover. When the load demand is greater than the generation, generator speed drops, thus initiating a drop-in frequency. An unstable power system condition could lead to generator falling out of synchronism or overheating machines or malfunction of equipment. Should the frequency drop below certain limits automatic load shedding will occur. Minimization of frequency error will enable the matching of frequency system generation to load frequency to nullify sudden blackouts and system imbalance. Increasing economic pressures for power system efficiency and reliability have led to a requirement for maintaining system frequency and power flows closer to specified values as much as possible. Therefore, in a modern power system, load frequency control plays a fundamental role, as a help service, in supporting and providing better conditions for the electricity trading. This paper presents a case study of PID controllers that can withstand load variations and produce improved functionality outputs (results) in a power system. The PID controller is incorporated with a trignometric function of a fourier series to mimimise the change in frequency. To ascertain the proficiency of the proposed technique, different versions of the PID controller in operation was undertaken. The proposed adaptive controller design provided the best results in terms of both frequency deviation and speed drop.

Abstract In order to uncover the inner working mechanism and performance of solid oxide fuel cell (SOFC) with biomass gasification syngas as fuel, a two dimensional SOFC multi-physical field model is established. This study makes up for the deficiency that the previous studies of coupling biomass gasification unit and SOFC stack mostly stay at the system level. The results show that the SOFC fueled by the syngas produced from gasification of biomass with steam as the agent has the best performance. The peak power density could achieve approximately 10240 W m−2. With the improvement of operating temperature, the peak power density of SOFC will be increased. At the temperature of 1123 K, the peak power density could achieve about 15128 W m−2. The average reaction rate of water gas shift (WGS) reaction is −29.73 mol m−3 s−1 when the operating temperature is 1123 K. This indicates that the WGS reaction will proceed in reverse direction at high temperatures, thereby reducing the hydrogen concentration. In addition, increase in the anode flux and decrease in the cell length lead to the increase of SOFC current density. In general, this work could provide guidance for the optimization and practical application of SOFC using biomass syngas as fuel.

This paper presents the application of quantitative feedback design techniques for tuning stabilizers in multi-machine power systems. This approach facilitates easy handling of multiple plant models thereby yielding robust and reliable stabilizer parameters. Methods of incorporating closed-loop stability and damping performance requirements into the design are explained. In the proposed sequential tuning technique, bounds on the stabilizer frequency response are computed for stability and performance at each of the given set of operating conditions of the system. A manual controller shaping then yields the desired stabilizer parameters. Application to an illustrative textbook example of an 11-bus, four-generator system is also included.