CFD simulation of effects of dimension changes of buildings on pollution dispersion in the built environment

AbstractAs pollutions impose adverse effects on human health and environment, assessment of their dispersion within the urban regions can much help to control them. In urban regions, dynamics of pollutants will be affected by buildings and barriers, and to investigate the dispersion of the pollutants, these barriers must be considered. In this article, CFD simulation is done by applying the 3D approach, the k−ε Realizable turbulence model and two Schmidt numbers (0.3 and 0.7). It has seen that height, length and width of the building in front of the wind, and, the distance between the two buildings back to the main building (the building on which the stack is present), have much influence on the concentration of pollutions. Although there are some differences between the results with different Schmidt numbers, the trend of changes of the concentration in different locations is identical for the two Schmidt numbers

Lattice Boltzmann Method in Modeling Biofilm Formation, Growth and Detachment

Biofilms are a complex and heterogeneous aggregation of multiple populations of microorganisms linked together by their excretion of extracellular polymer substances (EPS). Biofilms can cause many serious problems, such as chronic infections, food contamination and equipment corrosion, although they can be useful for constructive purposes, such as in wastewater treatment, heavy metal removal from hazardous waste sites, biofuel production, power generation through microbial fuel cells and microbially enhanced oil recovery; however, biofilm formation and growth are complex due to interactions among physicochemical and biological processes under operational and environmental conditions. Advanced numerical modeling techniques using the lattice Boltzmann method (LBM) are enabling the prediction of biofilm formation and growth and microbial community structures. This study is the first attempt to perform a general review on major contributions to LBM-based biofilm models, ranging from pioneering efforts to more recent progress. We present our understanding of the modeling of biofilm formation, growth and detachment using LBM-based models and present the fundamental aspects of various LBM-based biofilm models. We describe how the LBM couples with cellular automata (CA) and individual-based model (IbM) approaches and discuss their applications in assessing the spatiotemporal distribution of biofilms and their associated parameters and evaluating bioconversion efficiency. Finally, we discuss the main features and drawbacks of LBM-based biofilm models from ecological and biotechnological perspectives and identify current knowledge gaps and future research priorities

Modelling phytoremediation: Concepts, methods, challenges and perspectives

Phytoremediation can be effective for the removal, immobilization, mineralization, and/or detoxification of various pollutants in soils and water, including inorganic and organic pollutants, and radioisotopes. Although the feasibility of phytoremediation has been proven in the last decades, its performance is uncertain due to the complex interactions among soil, water, plants, weather, microorganisms, and pollutants, leading to its underutilization globally. This paper aims to review the representations and methods for quantifying key phytoremediation processes via modelling. We examine the structures, methods and ability of phytoremediation models that characterize the biogeochemical, hydrological, and phenological processes accountable for phytoremediation dynamics, along with discussions about their advantages and limitations. Then, we identify the knowledge gaps and challenges in incorporating biogeochemical, hydrological, and phenological processes into phytoremediation models in contaminated sites and representing spatial heterogeneity and temporal variability in large-scale applications. The existing phytoremediation models are difficult to predict the phytoremediation period under real environmental conditions but it is a key assessment of phytoremediation performance and cost. Finally, we explore the opportunities to integrate the current knowledge from other disciplines, such as soil, agriculture, ecology, and plant research in a competition-based model. We highlight the key research priorities for effective integration of knowledge based on physical, chemical, and biological processes in modelling phytoremediation, including biogeochemical processes, soil amendments and agro-practices. Further studies need to consider the immobilization, mineralization and detoxification processes of pollutants in contaminated sites

EFFECT OF DISCRETE HEATER AT THE VERTICAL WALL OF THE CAVITY OVER THE HEAT TRANSFER AND ENTROPY GENERATION USING LBM

In this paper Lattice Boltzmann Method (LBM) was employed for investigation the effect of the heater location on flow pattern, heat transfer and entropy generation in a cavity. A 2D thermal lattice Boltzmann model with 9 velocities, D2Q9, is used to solve the thermal flow problem. The simulations were performed for Rayleigh numbers from 103 to 106 at Pr = 0.71. The study was carried out for heater length of 0.4 side wall length which is located at the right side wall. Results are presented in the form of streamlines, temperature contours, Nusselt number and entropy generation curves. Results show that the location of heater has a great effect on the flow pattern and temperature fields in the enclosure and subsequently on entropy generation. The dimensionless entropy generation decreases at high Rayleigh number for all heater positions. The ratio of averaged Nusselt number and dimensionless entropy generation for heater located on vertical and horizontal walls was calculated. Results show that higher heat transfer was observed from the cold walls when the heater located on vertical wall. On the other hand, heat transfer increases from the heater surface when it located on the horizontal wall

EFFECT OF DISCRETE HEATER AT THE VERTICAL WALL OF THE CAVITY OVER THE HEAT TRANSFER AND ENTROPY GENERATION USING LATTICE BOLZMANN METHOD

In this paper lattice Boltzmann method was employed for investigation the effect of the heater location on flow pattern, heat transfer and entropy generation in a cavity. A 2-D thermal lattice Boltzmann model with 9 velocities, D2Q9, is used to solve the thermal flow problem. The simulations were performed for Rayleigh numbers from 10 3 to 10 6 at Pr = 0.71. The study was carried out for heater length of 0.4 side wall length which is located at the right side wall. Results are presented in the form of streamlines, temperature contours, Nusselt number, and entropy generation curves. Results show that the location of heater has a great effect on the flow pattern and temperature fields in the enclosure and subsequently on entropy generation. The dimensionless entropy generation decreases at high Rayleigh number for all heater positions. The ratio of averaged Nusselt number and dimensionless entropy generation for heater located on vertical and horizontal walls was calculated. Results show that higher heat transfer was observed from the cold walls when the heater located on vertical wall. On the other hand, heat transfer increases from the heater surface when it is located on the horizontal wall. Key words: natural convection, cavity, entropy generation, lattice Boltzmann metho

Numerical and experimental investigation on the performance of hybrid PV/thermal systems in the north of Iran

Solar energy is greatly recommended as a source of renewable energy in wide range of in-house applications to large power plants. Photovoltaic (PV) panels utilized for absorbing solar energy have some limitations: low efficiency, large occupied space and high dependency on environmental conditions. Panel surface temperature is one of the main conditions affecting PV panels. High temperatures would lead to lower panel efficiency. Therefore, researchers have proposed hybrid PV/thermal systems where maintaining panel temperature for higher efficiency is participated in heat production. This benefit made it attractive for household consumption. In this paper, a numerical method is deployed to find an appropriate cooling tube configuration for a specified panel. The selected configuration was prepared for experimental studies on a hybrid PV/thermal system in the northern part of Iran. As this region receives lower irradiation compared to southern parts, People are not persuaded to use photovoltaic systems, so using hybrid systems can motivate them to use solar energy on a small scale. Results showed that serpentine tube configuration would lead to a 7.3% increase in electrical efficiency compared to the no-cooling state, and also thermal efficiency raised to 48.4%. Total efficiency reached 51.76% at the highest performance. Therefore this design provides a possible platform for increasing PV/T systems performance

Numerical Modeling of the Melting Process in a Shell and Coil Tube Ice Storage System for Air-Conditioning Application

Cold thermal energy storage, as a promising way of peak-shifting, can store energy by using cheap electricity during off-peak hours and regenerate electricity during peak times to reduce energy consumption. The most common form of cold storage air conditioning technology is ice on the coil energy storage system. Most of the previous studies so far about ice on coil cold storage system have been done experimentally. Numerical modeling appears as a valuable tool to first better understand the melting process then to improve the thermal performance of such systems by efficient design. Hence, this study aims to simulate the melting process of phase change materials in an internal melt ice-on-coil thermal storage system equipped with a coil tube. A three-dimensional numerical model is developed using ANSYS Fluent 18.2.0 to evaluate the dynamic characteristics of the melting process. The effects of operating parameters such as the inlet temperature and flowrate of the heat transfer fluid are investigated. Also, the effects of the coil geometrical parameters—including coil pitch, diameter, and height—are also considered. Results indicate that conduction is the dominant heat transfer mechanism at the initial stage of the melting process. Increasing either the inlet temperature or the flowrate shortens the melting time. It is also shown that the coil diameter shows the most pronounced effect on the melting rate compared to the other investigated geometrical parameters

Modelling Watershed and River Basin Processes in Cold Climate Regions: A Review

Watersheds in cold regions provide water, food, biodiversity and ecosystem service. However, the increasing demand for water resources and climate change challenge our ability to provide clean freshwater. Particularly, watersheds in cold regions are more sensitive to changing climate due to their glaciers’ retreat and permafrost. This review revisits watershed system and processes. We analyze principles of watershed modelling and characteristics of watersheds in cold regions. Then, we show observed evidence of their impacts of cold processes on hydrological and biogeochemical processes and ecosystems, and review the watershed modeling and their applications in cold regions. Finally, we identify the knowledge gaps in modeling river basins according to model structures and representations of processes and point out research priorities in future model development