Modeling The Interactions Between Turbulence And Radiation In Oxy-Combustion Flames

In order to accurately estimate radiative heat transfer in turbulent combustion systems, one needs to take into account the non-linear interactions between the temporally fluctuating species and temperature variables and the radiation field. Simply employing time-averaged values of these variables in the radiation calculations to estimate absorption and emission (as is commonly done in the modeling community) can result in gross errors in the estimation of the radiative fluxes. Therefore, models that account for these Turbulence-Radiation Interactions (TRI) have been proposed in the literature to improve the fidelity of the radiative transfer calculations. TRI models accomplish this by computing appropriate time-averaged representations of the absorption and emission terms by taking into consideration the interactions and relationships between these terms and the fluctuating species and temperature fields. However, knowledge of the specie and temperature fluctuation statistics is key to developing these TRI relationships. In this thesis, statistical analysis of high-fidelity experimental measurements in five oxy-fuel flames with fuel jet Reynolds numbers ranging from 12,000 to 18,000 and fuel compositions in the range (50% H2-50% CH4 to 40% H2-60%CH4) were first carried out to formulate TRI models of absorption and emission. Statistical analysis of the measurements showed that in spite of the high concentrations of the radiatively participating gases in these flames, the temporal variations in the absorption field were determined to be insignificant. However, strong fluctuations in the emission field were observed and was found to correlate well with the root-mean-square of temperature. Next, a TRI model for emission based on this experimentally observed correlation was implemented as a User-Defined Function (UDF) in the computation fluid dynamic code ANSYS FLUENT. Time-averaged simulations of the five flames were then carried out to examine the impact of the new TRI model on the radiation field. Turbulence was modeled employing the realizable k-epsilon model and non-adiabatic mixture fraction relationships were employed to represent the chemistry. The radiative properties of the mixture were determined employing a weighted-sum-of-gray gases model developed at the University of North Dakota. The predicted temperature and CO2 mole fractions agreed well with the experimental measurements suggesting the adequacy of our modeling procedure. The radiant fraction in these flames without accounting for the effects of TRI was 8%. However, including the TRI model predicted a radiant fraction of 16% as a result of significant enhancement in the emission term. Therefore, numerical simulations that do not adequately account for the TRI effects in these flames can significantly under-estimate the resulting wall radiative fluxes. Further, despite the absence of fluctuations in the absorption term, the magnitude of the absorption term was nearly equal to that of the emission term across all flames. This also indicates that the “optically thin” radiation approximation (which neglects absorption) that has traditionally been employed to simulate similar laboratory flames can again result in a significant over-estimation of the radiative fluxes. Finally, our preliminary calculations indicate that despite the importance of TRI models for wall radiative flux estimations, the impact of their inclusion on the flame temperature and specie field predictions was negligible

Towards an integrated pollution management approach for the Buriganga River in Bangladesh

Water pollution management in the Buriganga River, which encompasses the south-western periphery of the capital city Dhaka, has been a major concern for the Government of Bangladesh at least for the last two decades. Several policies based on direct regulatory measures have been adopted by the government in different times to address this issue. In spite of this, no significant improvement in the river water quality has been achieved. In addition, an updated, detailed and systematic analysis of water quality along the full length of the river has not been conducted for some time. Hence, this research aimed to postulate a new management system to control pollution in the Buriganga River based on a recently conducted qualitative and quantitative assessment of river water and wastewater that are discharged into the river. The study also aimed to evaluate the existing system for river pollution control and to determine the economic costs that are likely to result under alternative policy instruments for pollution mitigation, such as, uniform reduction, uniform taxes and tradable permit system. In the study, a conceptual framework was recommended for an integrated pollution management approach in the Buriganga River. The river water quality was found to be unacceptable (as per the standards set by the Department of Environment in Bangladesh) for the parameters such as dissolved oxygen (DO), biochemical oxygen demand on five days (BOD5), chemical oxygen demand (COD), ammonia-nitrogen (NH3-N) and chromium (Cr) during both dry (low flow condition) and wet (high flow condition) seasons and for electrical conductivity in water (ECw) during only dry season. For the river water, the average concentration of DO ranges between 0.9 mg/L in dry and 2.8 mg/L in wet season, BOD5 between 34.5 mg/L in dry and 2.5 mg/L in wet season, COD between 60.1 mg/L in dry and 17.2 mg/L in wet season, ECw between 661 µS/cm in dry and 83 µS/cm in wet season, NH3-N between 4.1 mg/L in dry and 3.3 mg/L in wet season, Cr between 0.06 mg/L in dry and 0.07 mg/L in wet season. Temperature, pH, phosphate-phosphorus (PO4-P) and lead (Pb) were found within the DOE acceptable limits in both dry and wet seasons. Moreover, along the length of the river, relatively higher ambient concentration of BOD5, COD, NH3-N and Cr was observed at Kholamora station for both dry and wet seasons compared to four other selected stations (receptor points) along the river. The study established that the water of the Buriganga River is polluted by a combination of wastewater from both municipal and industrial sources, located within its basin area, which are discharged through three main drainage channels. The wastewater was found hypoxic to anoxic in most cases associated with very high concentration of BOD5, COD, ECw, Cr and NH3-N compared to the guidelines. For the incoming wastewater, the minimum and the maximum average concentration (including three major discharge points) of BOD5 ranges between 251.0 to 1003.4 mg/L, COD between 378.9 to 1261.1 mg/L, ECw between 458.9 to 3939.3 µS/cm, Cr between 0.02 to 13.3 mg/L and NH3-N between 4.1 to 83.5 mg/L throughout the year. The average BOD5 pollution loading rates for the three major discharge points at Rayerbazar sluice gate, Shahidnagar drainage outlet and Pagla Sewage Treatment Plant (PSTP) effluent outfall were estimated as 83, 71 and 32 tons/day respectively. The study identified that the existing command and control (CAC) based regulatory approaches to pollution management for the Buriganga River are not functioning effectively. The compliance and enforcement of these regulatory measures are not satisfactory, which contributes to continuing pollution problems. The present pollution control measures do not provide any economic incentives for pollution prevention and adoption of new technologies. Despite the provisions made within the national policies, no specific role has been outlined to ensure the effective contribution of Non-Government Organisations/Community Based Organisations for pollution control. However, the current study found that the local community is willing, and has the potential, to directly participate in the pollution control process of this river. The research used a spreadsheet based decision support tool in order to conduct a simulation exercise for evaluating the economic efficiency of the several alternative pollution abatement policies, while meeting specific water quality targets. The method generated empirical estimates on costs of BOD5 reduction from three major discharge points in the Buriganga River using three alternative policies. The results from the simulation exercise showed that application of the approaches based on economic incentives (uniform tax or tradable permit system) could achieve significant cost savings (up to about 50 per cent) for BOD5 pollution control in the Buriganga River in contrast to the CAC based approach (uniform reduction system). Further, considering the prerequisites for the tradable permit system and the marginal difference of economic benefit to be gained from this system compared to the uniform tax system, it is recommended that at this stage the uniform pollution tax system with revenue recycling should be considered as an effective alternative policy for water quality improvement in the Buriganga River. Finally, through this interdisciplinary study a conceptual framework of an integrated pollution management system for the Buriganga River was developed taking into account the state of water quality, the weaknesses encountered in the present system, the empirical evidence of the potential benefits from economic incentive based approaches to regulating pollution and from the experiences of river pollution management in other countries. The integrated management framework was recommended by combining appropriate pollution control instruments which encourages coordination of different stakeholders, public participation and application of economic incentive based measures. The proposed new approaches (economic incentive and community involvement) do not replace the present regulatory measures (particularly the ambient water quality standards) but they rather complement them. The research also proposed a set of policy initiatives that should be implemented within the integrated management framework. It would necessitate legislative changes to incorporate a legal basis for pollution taxing. The legal reform should incorporate the scope to vary the emission tax rate from time to tome and/or to impose strict regulations in short notice in case of emergency situation. In this context, legal agreements between polluters and regulatory authorities could be formed in order to ensure the proper collection of pollution taxes. The study also suggested the strengthening of organisational capacity at the cost of aborting the involvement of multiple government authorities, in favour of a single authority that would be invested with full power and responsibility for pollution control in the Buriganga River. Hence it was recommended that a Buriganga River Management Authority be established, to work under the supervision of the Ministry of Environment and Forests (MOEF). This agency could be assigned with legislative power and would hold sole responsibility to manage and coordinate all activities related to pollution control and conservation of the Buriganga River. Moreover, the study noted the significant positive contributions of community participation and commitments towards managing the pollution problem of the Buriganga River and the catalytic role it could play. With this end in view, the proposed integrated approach recommended formulating a standard procedure and guideline for water quality monitoring by community groups to ensure ease and efficiency of their work. In addition, necessary training programs should be directed by experts in the field to equip in the community for this purpose. Giving the community a responsible role in monitoring and recording failures and improvements could provide the necessary focus of attention and impetus required to resolve the Buriganga River pollution problem. Application of economic incentive based instruments and continual disclosure of information were also recommended in the study. The study concluded that a sustainable pollution management system for the Buriganga River could be achieved by bringing together all the stakeholders concerned at a local level and by applying appropriate pollution control measures along with the suggested set of policies

Time- and frequency-asynchronous aloha for ultra narrowband communications

A low-power wide-area network (LPWAN) is a family of wireless access technologies which consume low power and cover wide areas. They are designed to operate in both licensed and unlicensed frequency bands. Among different low-power wide-area network (LPWAN) technolo-gies, long range (LoRa), Sigfox, and Narrowband Internet of Things (NB-IoT) are leading in IoT deployment in large-scale. However, Sigfox and LoRa both have advantages in terms of battery lifetime, production cost and capacity whereas lower latency and better quality of service are of-fered by Narrowband Internet of Things (NB-IoT) operating licensed cellular frequency bands. The two main approaches for reaching wide coverage with low transmission power are (i) spread spectrum, used by LoRa, and (ii) ultra-narrow band (UNB) which is used by Sigfox. This thesis work focuses on the random-access schemes for UNB based IoT networks mainly. Due to issues related to receiver synchronization, two-dimensional time-frequency ran-dom access protocol is a particularly interesting choice for UNB transmission schemes. Howev-er, UNB possess also some major constraints regarding connectivity, throughput, noise cancel-lation and so. This thesis work investigates UNB-based LPWAN uplink scenarios. The throughput perfor-mance of Time Frequency Asynchronous ALOHA (TFAA) is evaluated using MATLAB simula-tions. The main parameters include the interference threshold which depends on the robust-ness of the modulation and coding scheme, propagation exponent, distance range of the IoT devices and system load. Normalized throughput and collision probability are evaluated through simulations for different combinations of these parameters. We demonstrate that, using repeti-tions of the data packets results in a higher normalized throughput. The repetition scheme is designed in such a way that another user's packets may collide only with one of the target packets repetitions. The power levels as well as distances of a user’s all repetitions are consid-ered same. By using repetitions, reducing the distance range, and increasing the interference threshold, the normalized throughput can be maximized

Two-Dimensional Nanomaterials and Nanocomposites for Sensing, Separation, and Energy Applications

Two-dimension (2D) nanomaterials have gained popularity for the last few decades due to their excellent mechanical, electrical and thermal properties. These unique properties of 2D nanomaterials can be exploited in various applications specially in sensor, energy, and separation devices. In this study, the sensing and energy generation performance of PVDF/PAni fiber mat systems made by the forcespinning method with and without graphene coating. The graphene-coated nanocomposites show an average output voltage of 75 mV (peak-to-peak) which is 300% higher compared to bare fiber mats and an output current of 24 mA (peak-to-peak) by gentle finger pressing. Moreover, the graphene-coated PVDF/PAni was investigated as a promising system for temperature (5 times better sensitivity), vibration (2 times better voltage generation), and airflow sensing. The graphene-coated composite has been further investigated as a water tide energy harvesting piezoelectric nanogenerator, the system generates ~ 40 mV for a synthetic ocean wave with a flow rate of 30 mL/min. Additionally, fabricated a low-cost, single-step, sophisticated graphene-enhanced elastomeric nanocomposite sensor for multifunctional usage by using a batch mixer. This nanocomposite ink was then fabricated into flexible keypad & forecepad and separation devices. Furthermore, the study also showed the enhanced battery performance of chemical vapor deposited pyrolytic carbon coatings on nanoparticles and nanofibers

The COVID-19: Socioeconomic Crisis and Its Management on a Bangladeshi Coastal Island

This study aimed to investigate the socio-economic crisis aroused due to the COVID-19 pandemic and associated prevention measures on the coastal riverine island Nalua in Bangladesh. The cross-sectional household questionnaire survey was done among the randomly selected households in the study area. This study revealed that more than 70 percent of the surveyed households had at least one member with COVID-19 symptoms. The local administration and community-based organizations have taken initiatives to enforce the government’s order on the island, but about three-fourths of households did not test their family members having COVID-19 symptoms because of fear of isolation and societal barriers. However, whether tested or not, approximately 15 percent of households took steps to isolate the infected person from the rest of the family. The demand for hand washing agents, face masks, and gloves increased in the study area. Island dwellers' food supplies were hampered and about 74 percent were supposed to buy food items at an increased price. For recovering from the educational crisis, the students watched live television classes, participated in online class lectures, and submitted their desired assignments to their institutions. According to survey results, about 39 percent of economically active family members lost their income-generating occupations. To manage their livelihoods, island dwellers have switched their income sources and, in most cases, taken consumer loans. This study suggests that governments, non-government organizations, and community-based organizations need to take effective steps to reduce socioeconomic crises during pandemics

Causes and Impacts of Rural Land Fragmentation in the Coastal Belt of Bangladesh

Identification of root causes and associated impacts of land fragmentation is necessary to reduce future fragmentation and mitigate its impacts. Thus, the purpose of this study was to explore the causes and impacts of land fragmentation in a purposively selected coastal Upazila (sub-district) of Bangladesh. This study is carried out mainly based on the collected information from the individual representative of the selected 133 households. It discloses that most of the households observed the land fragmentation during their possession because of rapid population growth and breaking the joint/extended families into nuclear families. In fact, land fragmentation can increase or decrease a particular land use type. However, the results of this research confirm that there are no significant (p >0.07, based on the number of households) associations found between increasing and decreasing homestead land. In contrast, the number of households with cropland significantly (p <0.0001) decreased, whereas the number of households having wetlands significantly (p <0.04) increased. The surveyed households have been practicing high-yielding varieties of crops, using biofertilizers, possessing new land, and changing their income sources for adapting to new land use behavior. The surveyed villagers opine that the land fragmentation problem could be managed by encouraging people living with extended/joint families, vertical use of land, adopting land use policy, etc. The results of this community-reported study can be used to mitigate the impacts of land fragmentation in the coastal rural area of Bangladesh.

How do different devices impact users' web browsing experience?

The digital world presents many interfaces, among which the desktop and mobile device platforms are dominant. Grasping the differential user experience (UX) on these devices is a critical requirement for developing user focused interfaces that can deliver enhanced satisfaction. This study specifically focuses on the user's web browsing experience while using desktop and mobile. The thesis adopts quantitative methodology. This amalgamation presents a comprehensive understanding of the influence of device specific variables, such as loading speed, security concerns and interaction techniques, which are critically analyzed. Moreover, various UX facets including usability, user interface (UI) design, accessibility, content organization, and user satisfaction on both devices were also discussed. Substantial differences are observed in the UX delivered by desktop and mobile devices, dictated by inherent device attributes and user behaviors. Mobile UX is often associated with personal, context sensitive use, while desktop caters more effectively to intensive, extended sessions. A surprising revelation is the existing discrepancy between the increasing popularity of mobile devices and the persistent inability of many websites and applications to provide a satisfactory mobile UX. This issue primarily arises from the ineffective adaptation of desktop-focused designs to the mobile, underscoring the necessity for distinct, device specific strategies in UI development. By furnishing pragmatic strategies for designing efficient, user-friendly and inclusive digital interfaces for both devices; the thesis contributes significantly to the existing body of literature. An emphasis is placed on a device-neutral approach in UX design, taking into consideration the unique capabilities and constraints of each device, thereby enriching the expanding discourse on multiservice user experience. As well as this study contributes to digital marketing and targe­ted advertising perspe­ctives

How do different devices impact users' web browsing experience?

The digital world presents many interfaces, among which the desktop and mobile device platforms are dominant. Grasping the differential user experience (UX) on these devices is a critical requirement for developing user focused interfaces that can deliver enhanced satisfaction. This study specifically focuses on the user's web browsing experience while using desktop and mobile. The thesis adopts quantitative methodology. This amalgamation presents a comprehensive understanding of the influence of device specific variables, such as loading speed, security concerns and interaction techniques, which are critically analyzed. Moreover, various UX facets including usability, user interface (UI) design, accessibility, content organization, and user satisfaction on both devices were also discussed. Substantial differences are observed in the UX delivered by desktop and mobile devices, dictated by inherent device attributes and user behaviors. Mobile UX is often associated with personal, context sensitive use, while desktop caters more effectively to intensive, extended sessions. A surprising revelation is the existing discrepancy between the increasing popularity of mobile devices and the persistent inability of many websites and applications to provide a satisfactory mobile UX. This issue primarily arises from the ineffective adaptation of desktop-focused designs to the mobile, underscoring the necessity for distinct, device specific strategies in UI development. By furnishing pragmatic strategies for designing efficient, user-friendly and inclusive digital interfaces for both devices; the thesis contributes significantly to the existing body of literature. An emphasis is placed on a device-neutral approach in UX design, taking into consideration the unique capabilities and constraints of each device, thereby enriching the expanding discourse on multiservice user experience. As well as this study contributes to digital marketing and targe­ted advertising perspe­ctives

Automatic Dispersion, Defect, Curing, and Thermal Characteristics Determination of Polymer Composites using Micro-Scale Infrared Thermography and Machine Learning Algorithm

Infrared thermography is a non-destructive technique that can be exploited in many fields including polymer composite investigation. Based on emissivity and thermal diffusivity variation, components, defects, and curing state of the composite can be identified. However, manual processing of thermal images that may contain significant artifacts, is prone to erroneous component and property determination. In this study, thermal images of different graphite/graphene-based polymer composites fabricated by hand, planetary, and batch mixing techniques were analyzed through an automatic machine learning model. Filler size, shape, and location can be identified in polymer composites and thus, the dispersion of different samples was quantified with a resolution of ~ 20 µm despite having artifacts in the thermal image. Thermal diffusivity comparison of three mixing techniques was performed for 40% graphite in the elastomer. Batch mixing demonstrated superior dispersion than planetary and hand mixing as the dispersion index (DI) for batch mixing was 0.07 while planetary and hand mixing showed 0.0865 and 0.163 respectively. Curing was investigated for a polymer with different fillers (PDMS took 500s while PDMS-Graphene and PDMS Graphite Powder took 800s to cure), and a thermal characteristic curve was generated to compare the composite quality. Therefore, the above-mentioned methods with machine learning algorithms can be a great tool to analyze composite both quantitatively and qualitatively

An Analysis of Strengths & Weaknesses of SME Financing Program in Bangladesh:A Study on Social Islamic Bank Ltd

After decades of researches and experiments with various enterprises model SMEs have emerged as the cornerstone of economic development in developing countries providing the platform for job creation and economic growth. So SMEs play an important role both in the developed and the developing countries including Bangladesh socially and economically. Lasting private sector development depends on them. Small industry involving simple technology and less investment has enormous potentiality for future growth and development in Bangladesh. The enterprises need financial aid to grow up SMEs through banking sector. Social Islamic bank is a leading Islamic bank in our country and the main target of this bank is to make credit available according to the Islami Sariah to the poor people. The main strengths of their SME practices are they are providing enough capital to the customers for starting their business and customers are satisfied about the collateral requirement for the loan amount. Another major strength of this bank is that according to the customers the special scheme for SME financing is successful to create positive impact in improving our socioeconomic condition. One of the major weaknesses of their SME practice is their high interest rate. Their SME service centers are also not convenient and available to all customers. Keywords: SME, socioeconomic, strengths, weaknesses, Bangladesh