Computational differentiation has existed since the 1960's as a scientific and engineering methodology for automatically generating sensitivity partial derivative models for stability assessments and optimization studies. Two fundamentally different solution strategies have been evolved for building sensitivity models. First, the analysts, i.e. expressed in FORTRAN, C, or other languages, is used as a template for writing an application-specific sensitivity software solution for the problem. Not surprisingly, this approach leads to a very large executable for numerically evaluating the partial derivative model. Only a first order sensitivity model is produced. In theory, the derived first-order model can then be used as a template for the second and higher order sensitivity models; unfortunately, experience has shown that the resulting software products can become large and unmanageable from a software perspective; as well as being unreadable by analysts. The second approach uses operator-overloading for generating higher-order sensitivity models. Derivative capabilities are created by embedding the chain rule of calculus in the operator overloaded math libraries, and defining n-tuple data structures for storing final derivative results and generating derivative derived intermediate results for application-specific calculations. At second order and beyond, one quickly realizes that computer memory and computation are severely impacted by nonlinear scaling laws for tensor operations. Fortunately, however one quickly observes that the gradient tensors generated at second order and beyond are symmetric, which creates significant opportunities for reducing variable memory requirements and associated computational effort.
In this study, low-flux direct absorption solar collectors (DASCs) based on nanofluid volumetric absorbers were thermodynamically modeled and analyzed from first- and second-law perspectives. Radiation interfacial losses were accounted for in the present model where Rayleigh scattering approximation was used for finding the nanofluid optical properties. The radiative transfer and energy conservation equations were solved numerically using a second-order accurate scheme. The numerical model was validated against available experimental results in literature and was used to investigate the effects of various important parameters on the energy and exergy efficiencies. It was observed that despite the low exergy efficiency in low-flux DASCs, the design point at which exergy efficiency is maximized provides a balance between the power gain and temperature gain of thermal energy collected.
In light of the impacts of fossil fuel combustion and the mitigation efforts spearheaded internationally by the Paris Agreement, the UAE faces the challenge of reforming its domestic energy portfolio. This also consists of seeking sustainable alternatives for their primary sources of revenues, i.e. the export of crude oil and natural gas. The very high solar energy potential and large desert areas offer a significant opportunity to transition not only the domestic economy towards solar but also to become an exporter of solar energy through a suitable energy carrier. This work provides an in-depth analysis of a promising carrier option: ammonia. The objective is to optimize the design of a system for the large-scale production of ammonia as an energy carrier from renewably generated electricity as a form of Power-to-Liquids (PtL) in pursuit of developing an ammonia economy in the UAE. The hydrogen for this process is obtained from high temperature water electrolysis. It is then processed through a promising solution for ammonia production plants based on the Haber-Bosch process. We develop a chemical engineering simulation model of this process and perform an energy and economic analysis. We find that for a continuous large scale process producing about 1700 mt/day, the specific energy consumption of the entire process is approximately 13.0 kWh/kg of ammonia. The process consists of desalination, electrolysis, air separation, the Haber Bosch synthesis loop and storage and refrigeration of the produced ammonia. To accommodate for the intermittency of solar energy supply to the ammonia facility, the flexibility of each sub-system is investigated. For better understanding of the plant, system dynamics modeling is carried out to grasp the dynamic interaction between components in the system via illustrative and graphical means. Finally, results from this are used in a linear cost minimization model formulated to determine the capacities of desalination, electrolysis, hydrogen storage, PV scale, and batteries needed to run a continuous ammonia synthesis loop.
The presence of carbonaceous impurities within the strands of MWCNTs play an important role and our results reveal that the presence of impurities, in the form of both amorphous carbon (Carbon Black) and graphitic carbon (Fullerenes c60) provided a large amount of edge sites. The results give important directions for high performance electrode design for vanadium redox flow batteries. The findings suggest that costly purification processes may not be required for MWCNTs intended for electrode applications in VRFBs.
Environment friendly discharge of produced water is pertinent for achieving sustainable development in the Oil & Petroleum industry. Globally, around 250 million barrels of produced water are generated daily compared to 80 million barrels of oil. Produced water is also highly contaminated. Its treatment requires great investments from oil industries. The microbial desalination fuel cell is an emerging desalination technology offering great promise of highly efficient desalination with low sludge production, low energy input, and electricity generation. The objective of this work is to vary certain parameters to find the optimum operating conditions for best performance.
As the global demand for energy rises, a corresponding increase in the H2S emission is expected. For the safety and economic benefit of humans and the environment, the multi-step thermochemical splitting of H2S presents an approach to attain both the elimination of the toxic gas and the generation of H2 gas which can be applied in many areas. From the thermodynamic analysis, zirconium sulfide proved to be a promising metal sulfide for the two-step thermochemical splitting of H2S with an H2 yield of 91% along with a complete regenerative ability. Experimental studies were carried out to investigate the effect of temperature on the sulfurization reaction. Observations showed that a proper balance and tuning of operating conditions is required to effectively overcome the process constraints.
In order to implement RE strategies in any country, there is a need for a good market design in order to have successful outcomes. Market design depends of several factors such Infrastructure, Human Capacity and Institutions. This paper will explore that market design factors and subfactors that are relevant for RE adoption. A case study of Abu Dhabi will be conducted in order to determine if the RE strategy is on the right track.
Vibrations of rotating blades have been a subject of constant research interest due to their practical significance. There have been numerous linear and nonlinear models with different levels of complexity reported in the literature. The present study is concerned with the in plane largeamplitude vibrations of a rotating Euler-Bernoulli beam following the model developed by Turhan and Bulut [1]. A reduced-order model has been derived to simulate the dynamic behavior of the rotating blades and the fixed points and their stability have been investigated. It is shown that some key parameters, such as the effective blade length and the hub rotational speed, affect the system stability. The analytical results obtained using the method of multiple scales and the numerical results are in good agreement.
Industrial epoxy coating based on epoxy, amine curing agent and organic solvent were prepared, their mechanical property, curing kinetics were discussed in terms of solvent addition. The curing degree of epoxy coating was characterized by employing FTIR, the mechanical properties were studied by using tensile testing, the nonisothermal curing kinetics and glass transition temperature of the prepared epoxy coating were also investigated by differential scanning calorimetry (DSC). The results indicated that the addition of solvent could lower the curing degree which affect the formation of crosslinked structure, the tensile strength and modulus of elasticity were also weakened by the increasing amount of solvent, while the flexibility was highly improved in the presence of solvent. An lower curing rate was observed with solvent addition in comparison with that of pure epoxy, it also indicated that activation energy of curing reaction increases with rising conversion where crosslinking is regarded as diffusion controlled.
In this study, a facile way was developed to fabricate flexible carbon (CNT)/graphene foam by dipcoating graphene oxide and carbon nanotube mixed solution on the polyurethane foam templated, followed by pyrolysis at 900? for 30 min. The experimental results show that addition of CNT can significantly increase the flexibility of graphene foam, which makes it a promising candidate into flexible energy device.
