Sustaining Tomorrow

A new type of liquid–solid circulating fluidized bed, the conventional circulating fluidized bed (CCFB), which operates at a superficial liquid velocity lower than the particle terminal velocity, was numerically studied by the Eulerian-Eucerin two-fluid model. The flow structures in the upward CCFB where the liquid and solids flow upward by using heavy particles with a density higher than the liquid, and in the inverse CCFB where liquid and solids flow downward with light particles are compared in this work. Time-averaged axial and radial profiles of the liquid velocity, particle velocity, and solid holdup from the numerical results are presented. Instantaneous profiles representing the local flow structures are also provided.

Archimedes Screw Turbines (ASTs) are a new form of hydraulic energy converter for small hydroelectric powerplants. ASTs can operate even with very low levels of water and are a safer solution for wildlife and especially fish. It is very important to have an estimation about the volume of water that can pass through the screw for designing AST hydropower plants, making operation plans and operation. However, developing a general relationship for the volume of flow entering an AST as a function of inlet water level and other variables for all screw sizes is challenging: In ASTs, water flows through a helical array of blades that are wrapped around a central cylinder while there is a small gap between the trough and screw which could be considered as free flow. Screw geometry and rotation speed are two other important factors that intensify the scaling difficulties. In this study, an equation is developed to estimate the volume flow rate that passes through an AST based on its inlet water level, rotation speed and pitch. The resulting relationship is validated using data from five lab-scale and one full-scale AST. Then it is optimized using Genetic Algorithms to produce a general equation for all screw sizes. Data analysis is completed to find and control effective parameters by using principal component analysis (PCA) techniques. Finally, the equation is modified to maximize accuracy. Results indicate that the proposed equation can estimate the volume flow rates of both lab-scale and full-scale studied screws with reasonable accuracy.

Predicting the power output of Archimedes screws is computationally intensive. It takes a minimum of eight variables to geometrically define a screw and its operating conditions, and more are needed for more detailed performance modeling. The set of variables that describe the screw are all interrelated: the optimum value of one variable depends on the values of the others, and it is not possible to determine an optimum value of any individual variable in isolation from the others. Dimensional analysis was identified as a way to improve understanding of the effect of different variables on Archimedes screw performance, and a set of dimensionless variables were defined to describe Archimedes screws. Archimedes screws are geometrically similar for all useful screw sizes, from small laboratory prototypes to large grid-connected plants. This means that relationships between the non-dimensional variables from this study can be applied to screws of any scale and used to predict the performance of the screw. Relationships between the non-dimensional variables are explored using a previously developed comprehensive Archimedes screw performance model, leading to new insights into the relationship between screw geometric variables and power output. One result is that a two-dimensional solution space is proposed for the examination of the performance of a screw generator. An optimal relationship between flow rate and rotation speed which maximizes power production at each flow rate is determined for a given screw geometry.

Simulation of the soil water balance requires reliable representation of the main hydrological processes such as infiltration, drainage, evapotranspiration and run off. In a cropping system, the determination of the soil water balance is necessary to facilitate decisions regarding water management practices such as irrigation scheduling. This may require the coupling of hydrological and crop models. This study sought to determine the water use of cowpea under irrigated conditions in different environments of South Africa. The study considered two irrigation types, subsurface drip irrigation (SDI) and Moistube irrigation (MTI) and two environments characterized by clay and sandy soils. The study was accomplished using a hydrological model (HYDRUS 2D/3D) and AquaCrop (crop model). The crop characteristics were obtained using AquaCrop while HYDRUS 2D/3D was used to generate optimum irrigation schedules and the soil water balance. Thereafter, the water use and yield of cowpea was determined. The average grain yield and biomass was 2600 kg ha⁻¹ and 10,000 kg ha⁻¹, respectively, with the difference between the two sites being less than 5% under both SDI and MTI. The water use and water use efficiency (WUE) varied from 315 to 360 mm and 0.67 to 1.02 kg m⁻³, respectively, under the two irrigation types in the two sites considered. The WUE was higher under SDI than MTI, but the differences were less than 10%. This showed that response of cowpea under MTI was not different from SDI.

Sustainability is the most crucial aim that Organisation for Economic Co-operation and Development (OECD) countries strive for their long term targets. We aim at analysing environmental and energy economic performance of OECD countries via Multi Criteria Decision Making (MCDM) methods. The presented approach adopts Criteria Importance through Intercriteria Correlation (CRITIC) integrated Grey Relational Analysis (GRA) and Multi-Attribute Utility Theory (MAUT) approaches to weight the criteria and evaluate the performance of OECD countries over the 2013–2017 period. Initially, we compute weight criteria via CRITIC method. Then, we compare the results of GRA and MAUT method. According to results of these methods, Switzerland and Ireland perform better in terms of environmental and energy economic performance. As per to the empirical results, both methods have shown significant harmony in terms of performance figures. This paper intends to contribute energy performance literature by comparing different MCDM methods so as to evaluate environmental and energy economic performance of OECD countries.

Corporate power purchase agreements (CPPA)s made up the majority of new wind energy PPAs signed in the U.S. in the last several years. Companies such as Google and Amazon have realized the environmental and economic benefits of partnering with renewable energy (RE) developers, directly, virtually, or through their utility, to bring new projects into the markets in which they operate. CPPAs allow companies to meet sustainability goals, reduce carbon costs, and achieve stable energy prices. What about the rest of North America? As carbon pricing comes into effect and technology costs decrease, RE CPPAs can efficiently lower environmental costs while addressing climate change goals. Some North American wind farm owners are approaching the end of their original utility PPA. A new CPPA to replace an expiring PPA enables the maximization of profit over the lifetime of the assets. There are challenges associated with these agreements such as term length, complex and poly-aggregated contracts, and policy barriers. This works focuses on delineating the barriers and potential benefits of CPPAs in North American markets to inform prospective stakeholders and provide insights for policy development in this space. The methodology consists of (1) jurisdictional scans to uncover lessons learned elsewhere and (2) gathering stakeholders through workshops to gather insights and educate developers, corporations, utilities, and policy makers. The workshops will also identify available projects, interested corporations, and potential collaborations. The main findings from this work demonstrate that developers and corporations are interested in pursuing CPPAs, with additional revenue (developers) and sustainability goals (corporations) being the main drivers. While interest is high, several barriers were identified including lack of appropriate market for implementation, policy uncertainty, complexity of negotiations and contract lengths. The workshops served as a critical first step outlining the barriers and towards informing policy development to enable CPPAs.

Building Information Modeling technology, which has been actively used in developed countries (such as USA, UK, Japan) in the world in recent years and even required in the design and construction process of public buildings; is an innovative approach to eliminate human-oriented errors and defects in the design and construction of buildings and to ensure interdisciplinary integration. With the 3D laser scanning technology, the current state of the structures can be scanned in 3D and transferred to digital media. Building Information Modeling -3D Laser Scan integration; it enables dimensional quality assessment of the building under construction and the application of professional approaches such as time management and cost management. This study aims to obtain the dimensional quality evaluation of the structural, structural and manufacturing standards and dimensional defects of x, y, z dimensions of the joinery on the façade surfaces of the traditional structures by using Building Information Modeling and 3D laser scanning integration technique, quality standards and to detect human-caused structural errors.

Implementation of renewable energy technologies will prevent damages caused by overreliance on fossil fuels, improve the health of the public, maximize job creation because they produce little or no atmosphere pollutants. To encourage the adoption of renewable energy in the built environment, this study investigated the means of promoting the integration of renewable energy. Quantitative research approach was adopted and a well-structured questionnaire survey was designed. The survey was conducted using construction professionals in Gauteng province of South Africa. From the 155 questionnaires distributed, 103 were retrieved which represents 67% response rate. The retrieved data were analysed using descriptive and inferential statistical procedures. The findings revealed that training and education of professionals, energy sector reforms and awareness creation are the highly ranked drivers of renewable energy integration. The drivers were further factored into clusters using exploratory factor analysis. This yielded three clusters namely collaborative action, government’s action, and policies and economic action with collaborative action accounting for the larger variance of the factors. The study concluded that moving towards renewable energy technologies is the best way to supply an environmentally friendly and affordable energy to all people. This study recommended that policies/regulations should be put in place by the government to keep users of non-renewable energy in check.

A delta winglet (DW) with an aspect ratio (c/h) of 2 and an attack angle of 30 degrees was mounted on a heated flat plate to scrutinize the role of its inclination angle (60°, 90° and 120°) on convection heat transfer enhancement. The experiment was conducted at a Reynolds number, Re_h, of 6300 in a wind tunnel. The heat transfer enhancement deduced from a thermal camera was expressed in terms of Nusselt number normalized by the reference no-winglet case for streamwise distance from 0 to 16 h. It was found that the largest tested inclination angle of 120° resulted in the most heat transfer enhancement. The results were explained in terms of the vortical flow characteristics detailed at 13 h, where the most substantial downwash velocity and affected area were obtained for the 120° inclination angle case. This vertical downwash caused a larger enhancement than the slightly larger turbulent kinetic energy produced by the 90° inclination angle winglet.

This work deals with the efficiency of cavern-based compressed air energy storage (CAES) facilities. Due to the complex interactions of the components of cavern-based CAES plants, a small deviation from designed for operating conditions can significantly alter the efficiency of the system. In this work, the sensitivity of individual system components to off-design working conditions are investigated, and components with the highest effect on both the exergy efficiency and the system efficiency are identified. The interaction between system components is also studied to identify the weak points of the system. The results show that the overall system efficiency is most sensitive to deviations in approach temperature in heat exchangers, energy leakage (as heat or compressed air) while the system is in a standby state, and leakage from compressors. For instance, a change of 10 °C in the approach temperature in the heat exchangers can lower system efficiency by 3.5%. System standby for 18 h with an air leakage rate of 4% per day from the cavern drops system efficiency by 2.1%. Additionally, a leakage rate of only 0.06% in the compressors can lower the system efficiency by 1.7%. This work also reveals that the combined effect of having multiple system components working at off-design conditions is more than the linear sum of their individual effects because of the exogenous influence these components have on peripheral components. The results from this study can help to improve the efficiency of CAES facilities.

The present investigation deals with the flow behind a torus, placed normal to the flow direction in three different aspect ratios (defined as the main diameter to the cross-sectional diameter of the torus) of 2, 3 and 5 at a constant Reynolds number of 9000. The Large Eddy Simulations (LES) are carried out to model the three-dimensional flow field around the torus. Wake structure, turbulence properties and force characteristics are investigated. Three shedding frequencies are detected at the Reynolds number studied. The highest frequency is attributed to the small-scale instability of the separating shear layer, the second one is a vortex shedding frequency that increases with aspect ratio, and the lowest one is due to the pulsation of the inner shear layer that can be observable for aspect ratios of 2 and 3. The torus has a blockage effect on the flow which is dependent on the center hole size. For the higher aspect ratio, the flow structure develops quickly, the wake flow is influenced by both inner and outer shear layers, thus forming the regular vortex ring patterns. For the lower aspect ratios, the flow pattern is mainly governed by the interaction of the outer shear layers. The results align well with documented experiments in the literature.