Simulation, analysis, and mass-transport optimization in PEMFCs

textIn this dissertation, we present two major lines of numerical investigation based on a control-volume approach to solve coupled, nonlinear differential equations. The first model is developed to provide better understanding of the water management in PEMFC operating at less than 100ºC, under transient conditions. The model provides explanations for the observed differences between hydration and dehydration time constants during load change. When there is liquid water at the cathode catalyst layer, the time constant of the water content in the membrane is closely tied to that of liquid water saturation in the cathode catalyst layer, as the vapor is already saturated. The water content in the membrane will not reach steady state as long as the liquid water flow in the cathode catalyst layer is not at steady state. The second model is to optimize the morphological properties of HT-PEMFCs components so as to keep water generated as close as possible to the membrane to help reduce ionic resistance and thereby increase cell performance. Humidification of the feed gas at room temperature is shown to have minimal effects on the ionic resistance of the membrane used in the HT-PEMFC. Feed gases must be humidified at higher temperature to have effects on the ionic resistance. However, humidification at such higher temperatures will require complex system design and additional power consumption. It is, therefore, important to keep the water generated by the electrochemical reaction as close as possible to the membrane to hydration the membrane so as to reduce the ionic resistance and thereby increase cell performance. The use of cathode MPL helps keep the water generated close to the membrane and decreasing the MPL porosity and pore size will increase the effectiveness of the MPL in keep the water generated close to the membrane. The optimum value of the MPL porosity depends on the operating conditions of the cell. Similarly, decreasing the GDL porosity helps keep water close to the membrane and the optimum value of the GDL porosity depends on the operating conditions of the cell.Mechanical Engineerin

Eliminación simultánea de materia orgánica y nitrógeno en humedales construidos : revisión crítica

[Abstract]: Spurred by the needs to find a better treatment method for wastewater, a method that is cheap, less complex when compared to conventional methods, and more importantly, that is climate friendly and has low cost of maintenance and operations, the use of constructed wetlands that is well designed, optimally operated, and of the best type of configuration has been proven by environmental scientists to meet these objectives. Constructed wetlands have proven to be very useful for the simultaneous elimination of nitrogen and organic matter as well as the removal of solids and pathogens contained in wastewater; it can achieve an efficiency as high as 70-94% NH4+removal, 70-96% N removal, 80-95% BOD and 73-96% COD removal. In this study, a profound review is made of the broad treatment process of wastewater from the primary treatment to the tertiary treatment, with the use of the conventional methods, analysis of constructed wetlands, its components, types and functions of each components, the various types of macrophytes and in their best operating environment, as well as the types of micro-organisms present. Also, a special focus is made about the characterization of wastewater, the parameters that are used, the impact of fairly treated or when wastewater is not treated at all, on humans and the environment. Analysis of the physico-chemical and biological processes involved in the removal mechanisms of both nitrogen and organic matter and, of course, how environmental factors and operating parameters influence the effectiveness of the treatment process and lastly, analysis of promising methods, like CANON, ANAMMOX, or SHARON, that are being investigated with the aim of implementing them in the future designs of constructed wetlands.[Resumo]: Existe a necesidade de atopar métodos de xestión das augas residuais, máis sinxelos que os métodos convencionais, respectuosos co medio ambiente e con baixos custes de mantenimiento e operación. Entre estes métodos alternativos atópanse os humidais construidos que, deseñados e operados de maneira óptima, dan resposta a estes obxectivos. Se ten demostrado que os humidais construidos permiten a eliminación simultánea de nitróxeno e materia orgánica, así como de sólidos e patóxenos, en augas residuais. Os resultados amosan eficacias de eliminación entre 70-94% de NH4+, 70-96% de N, 80-95% de DBO e 73-97% de DQO. Neste traballo faise unha revisión do proceso de tratamento de augas residuais empregando os métodos convencionais, dende o tratamento primario até o terciario, para posteriormente centrarse na análise dos humedais cosntruidos, tipos e funcionalidades dos seus componentes, tipos de macrófitas empregadas e as mellores condicións ambientais, así coma microorganismos presentes. Préstase especial atención á caracterización das augas residuais, os parámetros que se estudan e o impacto das augas non tratadas ou moderadamente tratadas sobre os humanos e o medio ambiente. Analízanse os procesos físico-químicos e biolóxicos implicados nos mecanismos de eliminación de nitróxeno e materia orgánica e, por suposto, a maneira na que os factores medioambientais e os parámetros operacionais inflúen na eficacia do proceso. Por último, faise referencia a varios métodos prometedores, CANON, ANAMMOX e SHARON, que están sendo investigados para a súa implementación en futuros deseños de humedais construidos.[Resumen]: En la búsqueda de mejores métodos de gestión de aguas residuales, más simples que los métodos convencionales, respetuosos con el medio ambiente y con costes de mantenimiento y operación bajos, se ha encontrado que los humedales construidos, diseñados, configurados y manejados de manera óptima, dan respuesta a estos objetivos. Se ha demostrado que los humedales construidos permiten la eliminación simultánea de nitrógeno y materia orgánica, así como de sólidos y patógenos, en aguas residuales; los resultados muestran eficiencias de eliminación entre 70-94% de NH4+, 70-96% de N, 80-95% de DBO e 73-97% de DQO. En este trabajo se hace una revisión del proceso de tratamiento de aguas residuales empleando los métodos convencionales, desde el tratamiento primario hasta el terciario, para posteriormente centrarse en el análisis de los humedales construidos, tipos y funcionalidades de sus distintos componentes, tipos de macrofitos empleados y sus mejores condiciones ambientales, así como microorganismos presentes. Se presta una particular atención a la caracterización de las aguas residuales, los parámetros que se estudian y el impacto de las aguas no tratadas o moderadamente tratadas sobre los humanos y el medio ambiente. Se analizan los procesos físico-químicos y biológicos implicados en los mecanismos de eliminación de nitrógeno y materia orgánica y, por supuesto, el modo en que los factores medioambientales y los parámetros operacionales influyen en la eficacia del proceso. Por último, se mencionan varios métodos prometedores, CANON, ANAMMOX y SHARON, que están siendo investigados para su implementación en futuros diseños de humedales construidos.Traballo fin de grao (UDC.CIE). Química. Curso 2020/202

The Impact of Aluminium Salt Dosing for Chemical Phosphorus Removal on the Settleability of Activated Sludge

The use of metal salts like aluminium in the precipitation of phosphorus in activated sludge plants has increased considerably in recent years due to the need to achieve tighter discharge consents for phosphorus in treated wastewater effluent. The impact of aluminium salt (Al3+) dosing on the settleability of activated sludge as a function of zone settling velocity (ZSV) and stirred specific volume index (SSVI) were investigated in batch settleability tests over a three-year period. The results showed that ZSV increased with increasing dose of aluminium salt as SSVI decreased. This trend was observed for dosing concentrations of less than 100 mg/L. At a dose concentration >100 mg/L, the trend was reversed as ZSV decreased and SSVI increased. At dose concentrations of <100 mg/L, Al3+ helped in the bioaggregation of dispersed activated sludge flocs, thereby improving settleability. The surface morphology from the scanning electron microscope (SEM) images indicated that the initial potential of interfloc bridging, open floc formation, and spindly bulking noticed in the undosed activated sludge flocs were remarkably reduced as the flocs became more compacted after Al3+ treatment. At >100 mg/L of Al3+, the sludge settleability started to disintegrate due mainly to surface charge reversal linked to the formation of aluminium hydroxides and the resultant disintegration of the activated sludge floc structure

Effect of Aluminium Salt Dosing on Activated Sludge Settleability Indicators: A New Settleability Model Development

There has been a significant rise in the use of aluminium salts (Al3+) for the chemical precipitation of phosphates in wastewater treatment plants due to growing stricter regulatory requirements for wastewater effluent release to the environment. The modelling of the settleability of the resultant Al3+ sludge in present engineering practice for design and optimisation are still based on conventional sludge settleability models. This paper describes a novel activated sludge settleability model which is designed to analyse the effects of Al3+ dosing on activated sludge settleability indicators, zone settling velocity (ZSV), and stirred specific volume index (SSVI). The impact of Al3+ dosing concentrations on ZSV and SSVI of full scale activated sludge plant were analysed in the laboratory over a three years’ period and the exponential form of the Vesilind equation was optimised and validated to include alum chemical dosing parameters. The proposed model equation was found to effectively describe the settleability of Al3+ dosed sludge for dosing concentrations range of 0 to 100 mg/L

KNOWLEDGE SHARING AMONG EMPLOYEES OF PUBLICLY OWNED BOOK PUBLISHING FIRMS IN NIGERIA

Knowledge sharing is crucial to the success of any organization as it is needed for knowledge creation, organizational learning and performance. This is especially the case with book publishing firms where their outputs are repositories of knowledge. However, a lack of technical expertise in the publishing industry has been reported in literature which might not be unconnected with knowledgeable workers in the sector leaving, retiring or passing on with their knowledge. Moreover, little is known about knowledge sharing among employees in this industry. Hence, in order to explore and understand this behaviour, descriptive survey design was adopted to investigate knowledge sharing among employees of publicly owned book publishing firms in Nigeria. Purposive sampling was used in selecting three publicly owned book publishing firms namely, Heinemann Publishers Plc, University Press Plc and Learn Africa Plc. Using both purposive and snowballing sampling techniques, 15 employees were selected from each firm. Data was collected through face-to-face interview, digitally recorded, transcribed and analysed thematically. Employees viewed knowledge sharing as a norm in the publishing industry since the process of book production requires team work; and knowledge sharing with subordinates reduces the burden of work on managers. Majority of the respondents would not share knowledge with colleagues from other publishing firms due to loss of competitive advantage and employee loyalty. Reciprocal benefit was the major motivating factor for knowledge sharing while others included enjoyment in helping others as well as personal and organizational reputation enhancement. Fear of loss of power, perceived pride, and competition were reported as challenges to knowledge sharing. Limiting inter-organizational knowledge sharing can restrict organizational learning and innovation which could have a negative impact on the industry’s performance overtime. Leadership styles that support and encourage knowledge sharing should be promoted in this industry

Predictors of the usuage of contraceptive implants among women of reproductive age in Ondo State, Southwest Nigeria.

ABSTRACT Background A major characteristic of all developing countries is rapid population growth which is due to high fertility, birth rates and poor utilization of contraceptive methods. This study therefore assessed the predictors of contraceptive implants utilization among women of reproductive age in Ondo State, Nigeria. Methods A descriptive cross sectional study design was used and a total of 230 women were selected by multi-stage sampling technique. Questionnaire administration was interviewer-based majority of the women could not read. Data analysis was conducted using SPSS version 23. Research questions and hypotheses were answered and tested with descriptive statistics (frequency, percentages), chi-square test of significance and binary logistic regression. Levels of significance was set at p ≤ 0.05. Results The prevalence of contraceptive utilization (any method) and contraceptive implant utilization were 92.2% and 31.1% respectively. Variables such as education (χ2 = 6.91, p = 0.03) and lack of counseling from providers (χ2 = 5.05, p = 0.03) were significantly associated with the utilization of contraceptive implant. These two variables were also the predictors of contraceptive implant utilization. Women with secondary and tertiary education have higher odds of utilizing contraceptive implants (OR = 1.21, 95% CI = 1.01 – 7.82, p = 0.04) and (OR = 2.53, 95% CI = 1.49 – 11.47, p = 0.03) compared to women who had primary or no education while those who claimed to be adequately counseled by providers are about two times more likely to use contraceptive implants (OR = 2.33, 95% CI = 1.08 – 5.51) Conclusion This study showed the important role of education and health workers in providing information about contraceptive implants. Therefore, health workers’ knowledge of family planning counseling and services should be constantly upgraded so as to improve their roles in educating, mobilizing, counseling the women regarding contraceptive implant insertion.                           &nbsp

Naturalistic decision making and decision drivers in the front end of complex projects.

Decision making plays a crucial role in the front end of projects, which is a critical stage for maximising the performance of complex projects. Although it has been suggested that project managers rely more on analytical approaches to decision making as opposed to an intuitive mode, there is emerging evidence of project managers using intuitive decision processes. Yet, little is known about how this occurs during the frontend phase, with few attempts to study the underlying cognitive processes and what influences project decision making. This research gap is addressed by interviewing project managers experienced in front-end decision making (n =16) of large-scale complex projects within the oil and gas industry. Adopting a naturalistic decisionmaking (NDM) methodology and using a form of cognitive task analysis, a thematic coding of their accounts of decision making during the front end of large complex projects identified key decision processes and influencing factors (drivers). Formal analytical processes (e.g., data-driven calculations, software rating tools) were favoured, but - and in line with emerging findings - these experienced project managers also used intuitive decision-making processes, such as pattern recognition and feelings/associative memory. Decision drivers were grouped into 5 clusters - project external factors, project internal factors, social dimensions, individual differences, and time pressures. The findings suggest that project managers should be trained on how to recognise when intuitive decision making is occurring, and how to use it while being aware of its strengths, weaknesses and influencing factors. A focus on building descriptive models of actual decision making in complex environments for the training of project managers by applying NDM methods will enhance the management of the front end of projects