In the present work, the transport equations for mass, momentum, energy, and chemical species as given by the Euler-Euler formulation for multiphase flows are used together with the second law of thermodynamics to derive the entropy and exergy transport equations, suitable to the study of gas-particle reactive flows, such as those observed during pyrolysis, gasification, and combustion of biomass particles. The terms of the derived equations are discussed, and the exergy destruction contributions identified. Subsequently, a kinetic model is implemented in a CFD open source code for the sugarcane bagasse gasification. Then, the derived exergy destruction terms are implemented numerically through user-defined Fortran routines. Next, the second law analysis of the gasification process of sugarcane bagasse in bubbling fluidized beds is carried out. Detailed results are obtained for the local destructions of exergy along the reactor. This information is important to help improve environmental and sustainable practices, and should be of interest to both designers and operators of fluidized bed equipment.

This study investigates urban heating system (UHS) by taking a looking at the heat transportation flexibility of the system. We propose the heating system flexibility (HSF) concept to represent UHS's capability of meeting the heating demand under different operation conditions during the heating season and give out the corresponding evaluation method. Based on evaluation method, we investigate the impact of heating network enhancement measures upon HSF by taking a real UHS in Beijing as a demo site. We pick network-wise topological change (extra pipe) and booster pump installation as two representative renovation measures. When an extra pipe close to end-user is introduced to the network, the average flexibility increases but the median flexibility drops. The results show that introduction of extra pipe does not reduce the hydraulic imbalance among different substations. Booster pump are more suitable for improving local substation HSF, although such a measure is only effective to a portion of the substations. Overall, the concept of HSF has the potential of being used as an important criterion in the design, operation, and control of UHS and other energy systems.

The use of natural gas (NG) in heavy-duty internal combustion engines can reduce the dependence on petroleum fuels and greenhouse gas emissions. Diesel engines can convert to NG spark-ignition (SI) by installing a high-energy ignition system and a gas injector. The diesel combustion chamber affects the flow inside the cylinder, so some existing SI combustion models will not accurately describe the operation of converted diesels. For example, the single Wiebe function has difficulties in correctly describing the mass fraction burn throughout the combustion process. This study used experiments from a 2L single-cylinder research engine converted to port fuel injection NG SI and operated with methane at 1,300 rpm and equivalence ratio 0.8 (6.2 bar IMEP) to compare the standard Wiebe function to a triple-Wiebe function. Results indicated that lean-burn engine operation at an advanced spark timing produced three peaks in the heat release rate, suggesting a multi-stage combustion process. A “best goodness-of-fit” approach determined the values of the key parameters in the zero-dimensional Wiebe function model. The triple-Wiebe function described the mass fraction burn and combustion phasing more accurately compared to the single Wiebe function. Moreover, it provided the duration and phasing of each individual burning stage that can then characterize the combustion in such converted diesel engines. This suggests that a multiple Wiebe function combustion model would effectively assist in analyzing such a multi-stage combustion process, which is important for engine optimization and development.

This study presents findings on combined effects of Reynolds number and rotational effect for a two-pass channel with a 180-degree turn, numerically and experimentally. To have a better understanding of the flow behavior and to create a baseline for the future studies, a smooth wall channel with the square cross-section is used in this study. The Reynolds number varies between 6,000 and 35,000. Furthermore, by changing the rotational speed, the maximum rotation number of 1.5 is achieved. For the numerical investigation, Large Eddy Simulation (LES) is utilized. Results from the numerical study show a good agreement with the experimental data. From the results, it can be concluded that increasing both Reynolds number and rotational speed is in favor of the heat transfer coefficient enhancement, especially in the turn region.

This paper presents the results of thermal efficiency of two coal based oxy-combustion thermodynamic cycles that are modeled using ASPEN PLUS. The objective of the present study is to perform a parametric analysis, investigating the effect of different recirculation ratios at different pressures on the efficiencies of the ENEL and TIPS cycles using ASPEN PLUS® software. Variables include flue gas recycle flow rate, combustor temperature, and operational pressure. Five recirculation ratios were investigated, ranging from 20% to 75%. It was determined that as the amount of recycled gas into the combustor increased, the thermal efficiency increased for both the TIPS and ENEL cycles. The highest thermal efficiency for TIPS is 37% and for ENEL is 38%, both occurring at a 75% recirculation ratio. After investigation, since combustion temperature and specific heat capacity decreases at higher recirculation ratios, mass flow rate was the dominant factor that contributes to the increase in thermal efficiency of the cycle. At each recirculation ratio, the effect of pressure is also determined. For ENEL the increase in cycle efficiency is 10% over the pressure range of 1 to 12 bar at a recirculation ratio of 20%, while the increase in cycle efficiency is only 1.5% at a higher recirculation ratio of 75%. For TIPS the cycle efficiency increases by 4% at recirculation ratio of 20% and increases by 3% at recirculation ratio of 75% for a pressure range of 50-80 bar.

This paper presents an exergy-based sustainability analysis of manufacturing roof tiles from plastic waste in Uganda. This work focuses specifically on the developing country context and on utilizing waste material. A summary of the current Ugandan plastic waste situation, environmental and health issues associated with plastic waste, current means of recycling plastic waste into new products, and an analysis of the Ugandan roofing market are presented. The total exergy consumed to produce one batch of seventy-five tiles is over 210 MJ, the potentially recoverable exergy is nearly 17 MJ (8% of consumed exergy), and the realistic recoverable exergy is over 6 MJ (3% of consumed exergy). Recycling plastic waste into roof tiles saves a net 188 kg of CO 2 from entering the atmosphere compared to open burning. If all of Kampala's plastic waste was converted to roofing tiles, nearly 560 tons of CO 2 could be saved per year.

This work presents an application of a reduced chemical kinetic mechanism using Computational Singular Pertubation (CSP) based on the significant indices of the modes on evolution of species and the degree of participation of reactions. This approach enabled us to reduce the mechanism of Yang and Pope to 22 reversible reactions. In this study, the tabulation of ignition delays has been made using a Yang and Pope mechanism, GRI 3.0 and reduced mechanism; the results obtained showed a good agreement among the three mechanisms. “Modele Intermittent Lagrangien” (MIL) has been used to calculate the chemical source term of the transport equation of the species. The calculation of this unclosed term requires a library of ignition delays which takes into account a detailed chemical kinetic mechanism, a probability density function (PDF) of the mixture fraction which is presumed by a beta distribution. The scalar variance, one of the key parameters for the determination of the presumed beta function, is obtained by solving its own transport equation with the unclosed scalar dissipation rate modeled using either an algebraic model or a transport equation. All these models are introduced in the CFD SATURNE code and applied to simulate a turbulent CH 4 /H 2 /N 2 jet flame (DLR Flame A) proposed by the German aerospace center. A set of comparisons is made; the results of simulations show a good agreement among the three mechanisms and also with the experimental data.

Thermal management is an important factor in securing the safe and effective operation of a fuel cell vehicle (FCV). A parameterized stack model of 100 kW proton exchange membrane fuel cell (PEMFC) is constructed by MATLAB/Simulink to design and asses the thermal management characteristics of a 100 kW full-powered FCV. The cooling components model, with parameters obtained by theoretical calculation on the basis of the cooling requirement, is developed in the commercial solver GT-COOL. A thermal management simulation platform is constructed by coupling the stack model and cooling components. The accuracy of the modeling method for the stack is validated by comparing with the experimental data. The relationship between the operating temperature and output performance of the fuel cell stack is revealed on the basis of the simulation model. Results show that operating temperature has a considerable influence on stack performance under high-current operation, and the inlet and outlet temperatures of the stack change nearly linearly with the increasing environment temperature. The heat dissipation potential of the thermal management system under high-load condition is also verified. The temperatures and coolant flow of core components, including the stack, DC/DC, air compressor, and driving motor, can meet the cooling requirements.

One of the main solutions to climate change is to source the energy from renewable sources. A novel Ocean Thermal Energy Conversion (OTEC) system is proposed for the production of methanol, cooling and power is developed and energetically analyzed. In this proposed trigeneration system, a two-stage Rankine cycle that operates on the inherent temperature difference along the oceans depth is used for power production, along with an Electrolytic Cation Exchange Membrane (ECEM) reactor for carbon dioxide and hydrogen production to feed the methanol production system. The carbon dioxide is sourced from the deep cold seawater. The proposed system performance is modeled and simulated on Aspen Plus, where the performance of the proposed system is assessed under various operating conditions. It was found that the maximum net power output of the cycle was found to be 51.5 GW, with a fixed rate of district cooling of 69.0 GW. The maximum methanol production rate was found to be 1.36 kg/s at the power input of 51.5GW. Furthermore, the systems performance was tested in three different cases. Case 1: ECEM reactor operates at its current efficiency with fuel production and district cooling being the only products, Case 2: ECEM reactor operates at Proton Exchange Membrane (PEM) efficiency, and Case 3: Only power was produced with no fuel. The maximum overall energy efficiency of the cycle was found to be 8.0, 8.6, and 7.3% for cases 1, 2 and 3, respectively.

This research provides an in-depth analysis of the flow around the rotor and in the wake of a single Horizontal Axis Wind Turbine (HAWT) model at different free stream velocities and Tip Speed Ratios (TSRs). Moreover, it extracts some recommendations that might be beneficial for large scale projects such as wind farm layout design and power output prediction. For this purpose, a modeling and experimental testing of a wind tunnel test section, including a single wind turbine model inside were created and validated against present experimental data of the same model. The Large Eddy Simulation (LES) was used as a numerical approach to model the Naiver-Stokes equations. The computational domain was divided into two areas; rotational and stationary. The unsteady Rigid Body Motion (RBM) model was adopted to represent the rotor rotation accurately.

The fundamental challenge in the synthesis/design optimization of energy systems is the definition of system configuration and design parameters. The traditional way to operate is to follow the previous experience, starting from the existing design solutions. A more advanced strategy consists in the preliminary identification of a superstructure that should include all the possible solutions to the synthesis/design optimization problem and in the selection of the system configuration starting from this superstructure through a design parameter optimization. This top–down approach cannot guarantee that all possible configurations could be predicted in advance and that all the configurations derived from the superstructure are feasible. To solve the general problem of the synthesis/design of complex energy systems, a new bottom–up methodology has been recently proposed by the authors, based on the original idea that the fundamental nucleus in the construction of any energy system configuration is the elementary thermodynamic cycle, composed only by the compression, heat transfer with hot and cold sources and expansion processes. So, any configuration can be built by generating, according to a rigorous set of rules, all the combinations of the elementary thermodynamic cycles operated by different working fluids that can be identified within the system, and selecting the best resulting configuration through an optimization procedure. In this paper, the main concepts and features of the methodology are deeply investigated to show, through different applications, how an artificial intelligence can generate system configurations of various complexity using preset logical rules without any “ad hoc” expertise.

To evaluate the feasibility of the performance enhancement of a thermophotovoltaic (TPV) converter by using a thermoelectric generator (TEG), a new model of a combined system is established, where the TEG is attached on the backside of the TPV converter to harvest the heat produced in the TPV converter. The effects of the voltage output of the TPV converter, band gap energy of the TPV converter, dimensionless current of the TEG, and emitter temperature on the performance of the combined system are examined numerically. It is found that the performance of the TPV converter can be enhanced by using the TEG. The percentage increment of the maximum power output density is larger than that of the maximum efficiency. There are optimally working regions of the converter voltage, dimensionless current, and band gap energy. The elevated emitter temperature results in the increase of the power output density of the combined system. However, there is an optimal emitter temperature that yields the maximum efficiency of the combined system. Moreover, the TEG is not suitable to harvest the heat produced in the TPV converter when the emitter temperature is sufficiently high.

Thermocells convert heat energy directly into electrical energy through charge-transfer reactions at the electrode–electrolyte interface. To perform an analytical study on the behavior of thermocells, the Onsager flux relationship was applied to thermocells, which used aqueous copper II sulfate and aqueous potassium ferri/ferrocyanide as the electrolyte. The transport coefficient matrices were calculated for each electrolyte and applied to several simulations, which were subsequently validated through experimental testing and comparison to previous literature results. The simulation is shown to correctly predict the short circuit current, maximum power output, and power conversion efficiency. Validation demonstrates that the simulation model developed, using the Onsager flux equations, works for thermocells with different electrode materials (platinum, copper, charcoal, acetylene black, and carbon nanotube), electrode spacing, and temperature differentials. The power dependence of the thermocell on concentration and electrode spacing, with respect to the Seebeck coefficient, maximum power output, and relative efficiency, is also shown.

The design, construction, and experimental evaluation of a cascade thermoacoustic engine are presented in this paper. The system was designed and built under the constraint of an inexpensive device to meet the energy needs of the people based in remote and rural areas. From the cost and straightforward system point of view, the air at atmospheric pressure was applied as a working fluid, and the main resonator tubes were then constructed of conventional polyvinyl chloride (PVC) pipes. Such device consists of one standing-wave unit and one traveling-wave unit connected in series. This topology is preferred because the traveling-wave unit provides an efficient energy conversion, and a straight-line series configuration is easy to build and allows no Gedeon streaming. The system was designed to operate at a low frequency of about 57 Hz. The measured results were in a reasonably good agreement with the predicted results. So far, this system can deliver up to 61 W of acoustic power, which was about 17% of the Carnot efficiency. In the further step, the proposed device will be applied as the prime mover for driving the thermoacoustic refrigerator.

Vortex-induced energy converters (VIECs) are attracting the attention of researchers looking for energy-harvesting systems in the marine environment. These energy converters, while probably less efficient than many other specialized devices, have very few moving parts and are particularly suitable for operation in harsh environments, such as those encountered in the ocean and in offshore platforms. The principle of operation of VIECs is tapping the transverse vibration of a blunt slender body immersed in a stream, induced by unsteady flow separation (Von Karman vortex street). The simplest device is an array of cylinders: under specific conditions and with careful design, it is possible to work close to resonance and thereby to obtain large amplitudes of oscillation, which are converted into electricity by suitable devices (linear electrical generators or piezoelectric cells). The system was developed experimentally at University of Michigan, with several patents pending and scientific material published on preliminary tests. Numerical simulations of system dynamics allow to simulate more realistic operating conditions and to perform the mechanical optimization of the system in relation to a specific sea location. A model of the system was thus developed, resulting in a nonlinear dynamic mathematical formulation; this last is solved in the time domain using matlab/simulink programming. The sensitivity of the efficiency to the main design variables is investigated. The results demonstrate that the efficiency and power density are not attractive for the typical Mediterranean Sea conditions; however, as energy can be harvested over large surfaces, the system appears to deserve attention.