Control of a Solid Oxide Fuel Cell Power Plant in a Grid-Connected System

The fastest and yet most prudent ways of changing the output power level of a solid oxide fuel cell power plant connected to the ac-grid are explored. The operating state of the fuel cell power plant is examined in term of the concept of feasible operating area of a cell. The utilization factor of the cell stack is maintained constant in steady-state by feeding natural gas to the fuel processor at a rate proportional to the current drawn from the stack. The fluctuations of the utilization factor in the transient state due to a change in operating power level can be constrained to the allowable range by strategically controlling the current drawn by the power conditioning unit. Based on measured variables and dynamic characteristics of the fuel processor, four strategies of controlling current are compared to arrive at the strategy that results in minimum transient time for a given power change. The proposed control schemes are verified through computer simulations.     

Preparation of aerochitin‐TiO2 composite for efficient photocatalytic degradation of methylene blue

An aerochitin–titania (TiO₂) composite was successfully synthesized and characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, field emission scanning electron microscopy, and N₂ adsorption isotherms. The photocatalytic activity of the composite was investigated on the degradation of the model organic pollutant, methylene blue (MB) dye, under UV irradiation. The aerochitin–TiO₂ composite showed excellent adsorptive and photocatalytic activity with a degradation degree of 98% for MB. The first‐order rate constants for the photodegradation MB by TiO₂ nanoparticles and aerochitin–TiO₂ composite were found to be (3.49 ± 0.04) × 10^?3 and (1.82 ± 0.02) × 10^?2 min^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45908.     

An analysis of the control and operation of a solid oxide fuel-cell power plant in an isolated system

The concept of a feasible operating area for a solid oxide fuel-cell power plant is introduced by establishing the relationship between the stack terminal voltage, fuel utilization, and stack current. The analysis shows that both the terminal voltage and the utilization factor cannot be kept constant simultaneously when the stack current changes. This leads to the two possible control strategies as constant utilization control and constant voltage control. By controlling the input hydrogen fuel in proportion to the stack current, constant utilization control can be accomplished. By incorporating an additional external voltage-control loop, stack terminal voltage can be maintained constant. The detailed design of the control schemes is described. The effectiveness of the proposed schemes is illustrated through simulation. Using the numerical results, the maximum value of load power change that the plant can handle safely is predicted.     

Modelling and experimental studies on a mixed-mode natural convection solar crop-dryer

A mathematical model for drying agricultural products in a mixed-mode natural convection solar crop dryer (MNCSCD) using a single-pass double-duct solar air-heater (SPDDSAH) is presented. The model was developed in parallel with experimental work. The model comprises the air-heating process model, the drying model and the technical performance criteria model. The governing equations of the drying air temperature and humidity ratio; the material temperature and its moisture content; and performance criteria indicators are derived. The model requires the solution of a number of interrelated non-linear equations and a set of simultaneous differential equations. Results from experimental studies used for generating the required experimental data for validating the model are presented. Results of simulation runs using the model are presented and compared with the experimental data. It is shown that the model can predict the performance of the MNCSCD fairly accurately and therefore can be used as a design tool for prototype development.     

Design of mixed-mode natural convection solar crop dryers: Application of principles and rules of thumb

A mixed-mode natural convection solar crop dryer (MNCSCD) designed and used for drying cassava and other crops in an enclosed structure is presented. A prototype of the dryer was constructed to specification and used in experimental drying tests. This paper outlines the systematic combination of the application of basic design concepts, and rules of thumb resulting from numerous and several years of experimental studies used and presents the results of calculations of the design parameters. A batch of cassava 160 kg by mass, having an initial moisture content of 67% wet basis from which 100 kg of water is required to be removed to have it dried to a desired moisture content of 17% wet basis, is used as the drying load in designing the dryer. A drying time of 30–36 h is assumed for the anticipated test location (Kumasi; 6.7°N,1.6°W) with an expected average solar irradiance of 400 W/m² and ambient conditions of 25 °C and 77.8% relative humidity. A minimum of 42.4 m² of solar collection area, according to the design, is required for an expected drying efficiency of 12.5%. Under average ambient conditions of 28.2 °C and 72.1% relative humidity with solar irradiance of 340.4 W/m², a drying time of 35.5 h was realised and the drying efficiency was evaluated as 12.3% when tested under full designed load signifying that the design procedure proposed is sufficiently reliable.     

Fabrication of hydrophobic PLA filaments for additive manufacturing

Journal of Materials Science - There is an ever-greater need for self-cleaning and water-repelling properties of hydrophobic materials at this time in history, mainly due to the coronavirus disease...     

A technique for the steady-state analysis of a self-excitedinduction generator with variable speed

A method to analyze the steady-state open loop behaviour of a self-excited induction generator with an unregulated prime mover is presented. The proposed method needs little mathematical effort and does not require an assumption about the generator speed. The proposed approach based on nodal analysis allows one to use arbitrary functions for the torque-speed characteristic of the prime mover and for the saturation of the magnetizing inductance without complicating the solution process. It always leads to a single equation for the frequency. An example is presented demonstrating the advantages of the proposed method. The analytical results are verified by measurements     

Experimental investigations of a chimney-dependent solar crop dryer

An experimental investigation into the performance of a solar crop dryer with solar chimney and no air preheating is described. Tests were first performed on the cabinet dryer, using a normal chimney. The trials were repeated with a solar chimney. Still with the solar chimney, further trials were carried out with the roof of the drying chamber inclined further to form a tent dryer.The described tests include no-load tests for airflow rate measurements and drying tests, with cassava as the crop. Air velocities, temperatures, ambient relative humidity and the drop in crop moisture contents at different stages of the drying process are also presented. The effects of the various configurations described above on the drying process are deduced and discussed while comparing the experimental results with one another. In addition, the performance of the dryer in relation to other natural convection dryers is discussed. The results show that the solar chimney can increase the airflow rate of a direct-mode dryer especially when it is well designed with the appropriate angle of drying-chamber roof. However, the increase in flow rate only increases the drying rate when the relative humidity (RH) of the ambient air is below a certain mark (60% for cassava).