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A nonlinear model of coupled thermoelectricity is presented and implemented in the finite element method. The model accounts for the Seebeck, Peltier and Thomson effects in thermoelectric materials within the framework of the coupled thermal and electrical behaviors governed by the Fourier and Ohm’s laws. The resulting finite element system of equations is expressed directly in terms of the potential variables, i.e. voltage and temperature, and it is solved using the Newton method by formulating the stiffness and Jacobian matrices with respect to these fundamental variables. The model is verified by comparing its predictions with the analytical solution resulting from the system of ordinary differential equations that represent the simplified model for the one-dimensional case. Then, the finite element model is applied to estimate the energy conversion performance of nanostructured thermoelectric materials compared with that of traditional bulk materials. The study illustrates the excellent behavior of nanostructured materials in terms of their power output and conversion efficiency. The analysis shows the advantages of developing nanostructured thermoelectric materials for increased performance and miniaturization.

A hybrid energy utilization system, integrating dish solar SE and salinity gradient based energy storage system, was proposed to realize clean and stable power generation from solar energy. Power output of dish solar Stirling engine was utilized to pressurize the salt water into RO (reverse osmosis) for storing the energy in the form of concentration gradient, and stable power output was generated from the concentration gradient via PRO (pressure retarded osmosis). The system performance was systematically investigated under the ideal and non-ideal models, to evaluate the theoretical and realistic energy conversion ability. Results indicate that higher initial concentration presents better energy efficiency, for it has slower decreasing slope of transmembrane water flux in PRO. Optimal RO and PRO operating pressure exist for achieving the maximal energy efficiency. The ideal maximal overall energy conversion efficiency reaches 9.23% within the research scope. With the detrimental factors being considered, the maximal overall efficiency of 5.07% is achieved.

This paper presents a novel dynamic simulation model for the analysis of a hybrid turboexpander system coupled with innovative high-vacuum solar thermal collectors. The model is developed in MatLab and it is able to dynamically calculate the energy, exergy, environmental, and economic performances of the investigated system, by taking into account the hourly fluctuation of thermodynamic and economic parameters (e.g. electricity cost, natural gas temperature, and flow rates, etc.). In addition, a computer-based Design of Experiment (DoE) approach was implemented for achieving the optimal design of the proposed system. A suitable case study is presented in order to show the capabilities of the developed simulation tool. Conventional and non-conventional decompression systems located in the weather zone of Messina (South-Italy) are investigated with the aim of assessing the optimal system configuration. By means of the computer-based DoE analysis, the optimal values of several design parameters (such as the number of solar thermal collectors, the volume of the hot water storage tank, and the size of the water loop pump) are calculated. Numerical results show significant primary energy savings (1.36 TWh/year) and avoided carbon dioxide emissions (348 tCO2/year). From the economic point of view, a feasible simple pay-back period of 4.51 years is achieved. The destroyed exergy of the system components are calculated, obtaining the highest value for the turbo-expander, equal to 12.0 TWh/year.

In thermal energy conversion of biomass, the char conversion rate influences the design of industrial systems. Yet there is no consensus on the relative influences of O2, CO2 and H2O on the char conversion rate. The present study aims at clarifying the roles of these oxidizers on biomass char conversion. Single particles of different particles sizes were oxidized in mixtures of O2/N2, CO2/N2, H2O/N2 and O2/CO2/H2O/N2 at various temperatures. The results show that for large particles and high temperatures, CO2 and H2O gasification reactions play a dominant role, while for sufficiently small particles and low temperatures, the O2 oxidation reaction plays a dominant role in mixtures of O2/CO2/H2O/N2. Two different particle models were used to compute char conversions: a detailed single particle model, and a conventional particle model assuming that rates in mixtures of oxidizers can be predicted based on rates of single oxidizers. The results show that the char oxidation rates are strongly overestimated when predicting rates based on single oxidizers, while the detailed model shows a good agreement to the experimental measurements.

A looped-cascade thermoacoustic driven cryocooler is proposed and theoretically studied in this paper. This system is capable of achieving ideal acoustic fields by employing different-diameter resonance tubes. It overcomes the limitations of current configurations and possesses the advantages of high efficiency, large capacity and compact size. First, power matching between the engine-stage number and the working temperatures is investigated. Theoretical results show that either too few or too many engine stages induce negative effects: the former results in low efficiency and the latter results in over-high heating temperatures. Then, thermodynamic characteristics of the three-stage system are presented. Simulation results show that a cooling power of 1.17 kW and an overall relative Carnot efficiency of 15% can be achieved at 110 K, which is superior to the performance of the existing looped configurations. The distributions of key parameters are also presented for a better understanding of the energy conversion process. Finally, the effects of the crucial parameters—resonance-tube area-ratio and engine-regenerator area-ratio—are presented. Simulation results show that having an either too low or too high area-ratio has a significant negative effect on system performance due to improper phase relations and low acoustic impedance.

This study focuses on the performance and energy conversion process of cascaded induction motors (CIMs) operated under balanced and unbalanced conditions. In this paper, two mechanically combined induction motors having a similar rating (25 Hp) are investigated for comparing with a large induction motor (50 Hp) — imbalances can occur in the applied voltage, operating frequency, or both. The impacts of both unbalanced voltage and unrated frequency on maximum and steady-state torque, power factor, input active and reactive powers, stator and rotor copper losses, and total harmonic distortion (THD) in voltage and current, have been investigated through a simulated model created using Matlab/Simulink software. This work demonstrates that machine performance and efficiency are improved by introducing more electrical and mechanical advantages of cascading the electrical machines. The results show that the maximum torque of the CIMs is higher than that of a single one at different operation cases; it is increased by 18.4% during balanced operation. The total copper losses are reduced by 36.5% in balanced operation when using CIMs instead of the large motor. Consequently, the energy conversion process and performance were significantly improved.

A novel solar concentration photovoltaic (PV) and thermal combined system based on compact linear Fresnel reflector (CLFR) concentrator is proposed. The configuration and structural design approach of the PV and thermal combined system are introduced. The spectral beam splitter is designed by using the Needle optimization approach. Solar concentrating processes are simulated and relevant results show a high solar concentrating uniformity provided by the proposed combined system. The investigations of optical performance and relevant influential factors reveal that there is an optimal solar panel installation height for the proposed combined system when the slope angle and width of solar cells are settled. The effect of sun tracking error on the optical performance is also studied. The energy conversion analysis is carried out and the results show that the PV and thermal combined system has higher PV conversion and overall energy efficiencies in comparison with the solar concentration PV system without beam splitter. Furthermore, the effect of solar thermal collector temperature is investigated and the results reveal that there is an optimal tube collector operating temperature which can lead to the maximum total output power and overall energy efficiency.

In the general monolayer electrode of constant porosity, the conflict between the available specific surface area and the hydraulic permeability is a momentous hinder in designing the high-performance electrodes of VRFB. In this paper, several novel electrode structures with gradient or double-layered porous media (GPM or DLPM) are installed in the stack to decouple the conflict and connection between hydraulic permeability and specific surface area. Ten kinds of electrode structures with constant, linear or stepwise decreasing/increasing porosity respectively are designed and compared. The lower concentration polarization loss, higher cell energy efficiency and capacity in the stepwise and linear increasing of porosity profiles are related to the electrolyte flow uniformity in porous electrode and alleviation of conflict between permeability and specific surface area. The higher pumping losses in these arrangements serve as deteriorative factor. In the stepwise increasing porosity mode, the effects of the thickness ratio between two porous layers with different porosities, electrode thickness and porosity variation amplitude were investigated. There is an optimum thickness ratio and electrode thickness to obtain the saturated cell capacity and more energy efficiency, and the rise amplitude of porosity will reduce the system efficiency while increasing the cell capacity.

A new hybrid system for the energy cascade utilization has been proposed, integrating the hybrid ventilations, the active PV cooling, the radiative cooling together with the PCMs’ storages. A mathematical modelling together with systematic energy performance evaluation criteria has been presented to disclose the heat transfer mechanism of the hybrid system involved with different energy forms, diversified energy conversions and thermal energy storages. Multivariable parametrical analysis has been conducted and technical solutions were thereafter proposed in terms of maximizing the energy performance with the robust design and operating parameters. From our results, the interior radiant cooling system results in a stable indoor temperature with considerable energy saving potentials. The new hybrid system shows an overwhelming energy performance over the traditional system. Moreover, the polynominal fitting method is more accurate and robust than the traditional linear fitting method in terms of acquiring critical knowledge about the design and operating parameters. Research results for different scenarios with different geometrical and operational parameters have been presented to demonstrate and verify the effectiveness of the proposed technique.

This paper reviews state-of-the-art methods of energy harvesting for implantable and wearable devices based on the available mechanical and heat energy sources in the human body. The development of a compatible and sustainable power supply for wearable and implantable devices is a demand to realize their continuous and high-performance operation, minimize the need for external energy sources, and increase the lifetime of the devices. Heat and mechanical movement are two available and reliable energy sources in the human body. Since mechanical and heat energy harvesting methods have been extensively studied over the past decades, researchers focus on developing techniques to integrate these energy harvesters with implantable and wearable electronics. Therefore, energy requirement for wearable and implantable devices, available energy level from the human body, and convenience and feasibility of the implementation are taken into account to provide full or partial power support. This survey aims to present recent findings and developments in the field of energy harvesting from continuous heat source and mechanical movements of the human body. In particular, working principles, technical details, and current status as well as issues and challenges of energy harvesting from human body including thermoelectric, photovoltaic, piezoelectric, electrostatic, electromagnetic, and triboelectric harvesters are discussed.

CO2 adsorption capture, which could be driven by various forms of energy, has been widely studied in recent years due to the equipment is easy to control with low energy consumption required. However, the existing research on the energy-efficiency aspects of temperature/vacuum swing adsorption (TVSA) for CO2 capture are primarily focus on the quantification of input energy in specific cases. As a classical concept in thermodynamics, entropy has been widely applied in researches on the energy conversion process, which could benefit an in-depth understanding on the mechanism of “heat-generalized chemical energy” conversion. However, an integrated thermodynamic research framework, which could clarify how to conduct a reasonable energy-consumption analysis of TVSA, has not been established yet. In this paper, a simplified thermodynamic cycle of 4-step TVSA was established, with the assumption of CO2 in adsorbed phase as loop fluid. With the application of the thermodynamic research framework proposed in this paper, the entropy analysis on the thermodynamic cycle was conducted. This study is concerned with application of thermodynamics concept to the CO2 adsorption engineering, which is mainly based on classical thermodynamics but also relying on adsorption physics to supply insight into the energy conversion and energy-efficient mechanism of TVSA technologies.

In this forward-looking perspective, the current technologies for low-temperature waste heat recovery are first analyzed from two aspects: (i) the local waste heat recovery technology and (ii) global optimization of energy flow network. Based on the analysis, barriers for the further promotion of waste heat recovery are outlined, and they include the lack of global optimization methodology, distributed waste heat recovery system with high costs, and mismatches between waste heat source and demand. To address these issues, perspectives on three aspects are provided. First, advanced graphical analysis and optimization methodology integrating the heat exchange and energy conversion can promote the user-friendly optimization. Second, concentrated waste heat recovery and supply can save the investment, installation area and operation costs, thereby making the waste heat recovery cost-effective. Third, thermal storage, thermal transportation and high temperature heat pump can better couple the waste heat source and user demand from time-scale, spatial scale and energy grade, respectively. Visions for the future are combined with technical details to provide comprehensive perspectives for the next-step waste heat recovery.

A hydrokinetic energy converter using Flow Induced Oscillations (FIOs) of a one-degree-of-freedom cylinder-oscillator, with nonlinear adaptive damping and linear spring stiffness, is introduced and studied experimentally. Comparison to a linear-oscillator in FIO shows that this new converter, with velocity-proportional damping coefficient, is more effective in galloping, where both flow and cylinder speeds are higher. It also impacts VIV, since the converter is no longer restricted by fixed damping, which results either in ceasing motion due to excessive damping, or in low harnessed energy due to insufficient damping. The impact is most profound in the VIV to galloping transition where adaptive damping prevents shutting down of hydrokinetic energy conversion. Damping-to-velocity rate, linear spring-stiffness, and flow-velocity are the experimental parameters with Reynolds number 30,000 ≤ Re ≤ 120,000. Experimental results for amplitude response, frequency response, energy harvesting, efficiency and instantaneous energy of the converter are presented and discussed. The main conclusions are: (1) The nonlinear, adaptive, velocity-proportional damping coefficient increases the harnessed power. (2) The operational range of flow velocities increases. (3) At lower flow speeds, the adaptive damping stabilizes the unstable oscillations typically occurring in this region. (4) At higher flow speeds, adaptive damping results in higher harnessed power than constant damping, thus, better emulating passively a corresponding, natural, active motion by fish. (5) Increase of 51%–95% in converted power by the nonlinear oscillator compared to linear oscillator has been measured. (6) The adaptive damping converter reaches a plateau in harnessed efficiency at high flow velocity (fully developed galloping).

The study of supply and demand match increasingly becomes an enormous challenge in park integrated energy system (PIES) because it has a comprehensive relationship between multiple energy sources and multiple energy demand. This paper proposes a new type of supply and demand matching to accomplish the economic optimality of match under the same criteria, considering supply and demand changing simultaneously. The quantitative indexes of supply and demand energy conversion technologies (ECTs) is established considering the economic and technical characteristics of full life cycle comprehensively, which are defined as supplied technical cost level and demand technical cost level. Then, the novel energy supply and demand matching model is established. The loop iteration algorithm of the new matching model is established based on linear programming model. Numerical study is introduced based on the data of the cooling, heating and electrical load in a typical day. The results show that the priority order of each ECT is different when the output of all ECTs increasing gradually. The investment payback period is only 1.94 years. The new supply and demand matching model can reduce carbon emissions by 80,555 tons.

Exergy-based methods are powerful tools for developing, evaluating, understanding, and improving energy conversion systems. This paper deals with integrated advanced exergy-based evaluations. In addition to conventional methods, advanced exergy-based analyses consider (a) the interactions among components of the overall system, and (b) the real potential for improving each important system component. The main role of an advanced analysis is to provide energy conversion system designers and operators with information useful for improving the design and operation of such systems. Splitting the exergy destruction, the capital investment cost, and the component-related environmental impact associated with each single component of an energy conversion system into endogenous/exogenous and avoidable/unavoidable parts and using a further splitting of the exogenous exergy destruction improves (a) our understanding of the processes that take place, and (b) the quality of the conclusions for improvement obtained from the analysis. This paper discusses the main features and some recent developments in the area of advanced exergy-based methods. Application of the method to a simple air refrigeration machine confirms the correctness of the approach.

In this paper a novel polymer-based platform is applied for the fabrication of an innovative two-electrodes self-powered device integrating energy harvesting and storage sections. A multifunctional polymeric layer, made of two poly(ethylene glycol)-based sections separated by a perfluorinated barrier, is obtained by oxygen-inhibited UV-light crosslinking procedure. For the energy harvesting section, one side of the polymeric layer is adapted to enable iodide/triiodide diffusion in a dye-sensitized solar cell (DSSC), while the other side empowers sodium/chloride ions diffusion and is used for on-board charge storage in an electrochemical double layer capacitor (EDLC). The resulting photocapacitor has a planar architecture appreciably simplified with respect to other recently proposed solutions and more easily exploitable in low power electronics. The measured photo-electrical conversion and storage total efficiency is 3.72% during photo-charge, which is a remarkable value for DSSC-EDLC harvesting-storage devices literature. The obtained high frequency discharge capability enlightens promising prospects for practical applications in low power portable electronics.

A solar-aided coal-fired power plant (SACFPP) facilitates the investment reduction and efficiency enhancement of concentrated solar power, having multiple input energy streams. The intermittent nature of solar energy requires new control strategies for SACFPP to generate controllable power. A revised control strategy considering solar/coal-to-power conversion characteristics is proposed, where the influences of solar irradiance changes are decomposed into the changes in live-steam working capacity and boiler heat absorption. Within the proposed control strategy, models to explicitly calculate the set points of coal consumption and feedwater mass flowrate are developed. The operational enhancement is evaluated with a 660 MW SACFPP where the trough collector system works in parallel with the second and third high-pressure heaters. The control effects on stability and energy conversion are analyzed under solar irradiance disturbances and actual conditions. Results show that the revised control strategy promotes the quick and smooth power stabilization. The settle time decreases from 1663 s to 701 s when solar irradiance step decreases from 700 W m−2 to 500 W m−2. Under actual conditions, the power ratio deviation reduces by 63.16% with the proposed strategy compared with the original strategy. The solar-to-electricity efficiency fluctuations are slightly reduced.

Operational optimization plays a vital role in ensuring the economy, security, and environmental friendliness of integrated energy systems (IES), while the nonlinear operating characteristics of energy converters have brought significant challenges to the accurate modeling and solution. Considering the nonlinear energy conversion processes, a novel adaptive piecewise linearized weighted directed graph model of IES is proposed in this paper. To accurately construct the complex energy flow relationship in IES, a weighted directed graph is first presented to describe the energy generation, conversion, storage, consumption, and demand response, thus realizing the automatic modeling of IES. On this basis, for the diverse partial-load performance of energy converters, an adaptive piecewise linearization strategy is developed to approximate the nonlinear operating characteristics of various energy converters adaptively. By taking the system operating cost, calculation time, energy mismatch, and optimization model complexity as evaluation indicators, the effectiveness of the proposed method is verified by the numerical simulations of a typical small-scale combined cooling, heating, and power (CCHP) system and a large-scale IES in a realistic industrial park. Compared with the constant efficiency method and the equispaced piecewise linearization method, the computational efficiency and accuracy are remarkably improved by the proposed method.

The vortex induced vibration (VIV) energy converter is a novel device to extract hydrokinetic energy from ocean currents. The flow velocity near the sea level is relatively higher, which makes ocean surface currents more exploitable. However, due to the influence from free surface (such as wave impact, etc.), the total system damping of the converter increases rapidly. Therefore, this study focuses on the effect of high damping on the converter near the free surface. The experiments are carried out in a towing tank to measure the VIV responses and energy conversion performance. The VIV energy converter is operated at high damping by changing the load resistor from infinity to 30Ω. Correspondingly, the damping ratio increases from 0.38 to 0.50. The main conclusions are: (1) High damping suppresses the VIV amplitudes. (2) Three typical VIV branches can't be distinguished when at high damping. (3) The VIV frequency increases with damping and approaches the vortex-shedding frequency of a stationary cylinder (Strouhal frequency). (4) When the damping ratio increases from 0.38 to 0.50, the maximum converted power decreases from 1.37W to 0.66W. (5) The optimal efficiency η V I V = 29% is achieved at the beginning of the VIV region.

The study provides for the first time a life cycle inventory model for the fluidized bed gasification of wastes, based on a large amount of high-quality data. All of them have been obtained from a pilot scale fluidized bed gasifier, fed with ten types of waste and biomass, under a wide range of operating conditions. The model refers to commercial scale gasifiers having a “thermal configuration”, where the generated syngas is immediately burned downstream of the reactor. Key relationships between process and waste-specific parameters have been defined. The model quantifies the main inputs and outputs of the gasification process (emissions, energy recovery, ash disposal, resource consumptions), providing high-quality data that could contribute to improve life cycle assessment modelling of waste gasification. Finally, some case studies have been implemented in the EASETECH software to illustrate the model applicability, evaluate the role of main parameters, and compare the environmental performances of gasification power units with that of the European electricity mix. The performances appear highly affected by metal contents in the waste-derived fuels, while the model results to a limited extent are sensitive to the equivalence ratio and the net electrical efficiency of the energy conversion. The study provides for the first time a life cycle inventory model for the fluidized bed gasification of wastes, based on a large amount of high-quality data. All of them have been obtained from a pilot scale fluidized bed gasifier, fed with ten types of waste and biomass, under a wide range of operating conditions. The model refers to commercial scale gasifiers having a “thermal configuration” where the generated syngas is immediately burned downstream of the reactor. Key relationships between process- and waste-specific parameters have been defined. The model quantifies the main inputs and outputs of the gasification process (emissions, energy recovery, ash disposal, resource consumptions), providing high-quality data that could contribute to improve life cycle assessment modelling of waste gasification. Finally, some case studies have been implemented in the EASETECH software to illustrate the model applicability, evaluate the role of main parameters, and compare the environmental performances of gasification power units with that of the European electricity mix. The performances appear highly affected by metal contents in the waste-derived fuels, while the model results to a limited extent are sensitive to the equivalence ratio and the net electrical efficiency of the energy conversion.

Waves and ocean currents have been widely researched worldwide as possible renewable energy sources. Recent findings related to viable energy sites with high power output focus on local dynamic impacts and disregard long-term viability. This study underlines the importance of resource assessment performed through long-term simulations and attempts to improve the understanding of how spatial-temporal variability controls the dynamic patterns of feasible sites for oceanic renewable energy. Hydrodynamic and spectral wave models Telemac-3d and TOMAWAC were performed over a 10-year period from 2003 to 2012. Sources of high current intensity and wave height were found in five sites around the Southern Brazilian Shelf (SBS) and the Southeast Brazil Bight (SBB) and were further analyzed for frequency of high occurrence, variability over months and seasons, and spatial and temporal variability. The results indicate that renewable energy from ocean currents has more stability for conversion in the SBS, while waves present better conditions in the SBB. The weaker seasons for energy conversion were autumn and summer, with the stronger seasons varying. Wave variability demonstrates a high correlation with atmospheric dynamics regarding the passage of frontal systems as opposed to currents that are mainly forced by local wind-driven conditions.

Achievement of satisfactory results of measurements data reconciliation in energy conversion processes is possible only in the case of application of the so-called generalized advanced method of data validation and reconciliation. An application of this method made it possible to complete the validation model of the process (conditional equations of optimization task) including substance and energy conservation principles with additional equations describing energy conversion processes. The criterion of selection of the form of additional equations in the validation model in reconciliation calculation has been formulated based on the derived characteristic property of variables uncertainty after data reconciliation. The developed methodology has been used for example calculations of data reconciliation in the selected steam power unit. At the design stage of energy conversion systems, the problem of the number of redundant measurements, as well as their location, appears. Example calculations for the redundant measurement systems of selected energy conversion processes have been carried out. As objective functions of the combinatorial optimization tasks, the relative uncertainty of the selected energy effectiveness indicators was assumed. The results of calculations confirm the influence of the number of redundant measurements and their location in the measurement systems on the accepted criteria of optimization. An idea to apply in the data reconciliation method the measurements uncertainties expressed by fuzzy numbers has been presented. As a criterion for comparison of the results of calculations for both types of uncertainties, the relative entropy of information as well as the complex standard uncertainties of main assessment indicators of analysed combined heat-and-power unit operation supervision has been chosen. The advanced data validation and reconciliation method was introduced and developed in Poland to the thermodynamic analyses of energy conversion processes by professor Jan Szargut. The above issues constitute further researches on the development and application of this method in thermodynamics analyses performed by the author of this paper.

In this paper a new mechanistic model for the diabatic annular two-phase flow is presented and applied to prediction of dryout and post-dryout heat transfer in various channels. The model employs a computational fluid dynamics code – OpenFOAM® – to solve the governing equations of two-phase mixture flowing in a heated channel. Additional closure laws have been implemented to calculate the location of the dryout and to predict wall temperature in the post-dryout region. Calculated results have been compared with experimental data obtained in pipes and good agreement between predictions and measurements has been achieved. The presented model is applicable to complex geometries and thus can be used for prediction of post-dryout heat transfer in a wide variety of energy conversion systems.

The flow in a side channel pump exhibits complex, three-dimensional and unsteady features. The present study investigates the transient flow interaction between the moving impeller region and the static side channel in a side channel pump which consists of 24 blades and a circular side channel. In this study, the transient flow features under different blade suction angle profiles have been investigated. The transient pressure distribution, velocity field, streamline plots, and mass flow exchange between the impeller and side channel are analyzed. Comparison shows that the side channel pump's flow mechanism is influenced by irregular flow characteristics and a number of vortex impulses at certain positions. Thus, zones of large vortices that cause low pump efficiency are demonstrated. The pressure fluctuation in the side channel pump is greatly influenced by the flow exchange between the impeller region and the side channel, and the pressure fluctuation frequency is related to the flow exchange frequency. This work helps understand the transient flow characteristics and serves as a guide for conducting further research in high-efficiency side channel pumps.

In order to realize the large-scale and normal implementation of power-to-gas technology, as well as the large-capacity storage and long-distance transportation of gas in the later stage of electric hydrogen production, a power-to-gas technology with real-time energy conversion characteristics and large-scale energy storage characteristics is studied in this paper. Firstly, the water-electricity-gas coupling process between the electrolytic cell and the methanation reactor in the power-to-gas system is discussed in detail, and the model of the power-to-gas system based on the coordination of real-time energy conversion and large-scale energy storage is proposed. Then, based on a multi-energy coupling regional integrated energy system, a highly decoupled multi-step modelling method is adopted to construct its optimal operation model, and the equivalent variable substitution method is used to transform it into a linear programming problem. Finally, the calculation results show that the proposed power-to-gas technology can further improve the energy utilization efficiency due to the complementary characteristics of the two functions, so as to effectively promote the implementation of large-scale power-to-gas projects in the future.

In order to strengthen the internal flow and heat transfer and increase the stability of the flame, various methods to improve combustion efficiency were proposed. In terms of spatial structure, the optimization methods are divided into two categories: insertion geometry and internal molding. Both of them change the combustion efficiency by affecting the flow and heat transfer, but the degree is different; for catalytic combustion, heat and mass transfer, heterogeneous/homogeneous reaction and other derivative processes are the key to improve the combustion efficiency; as for fuels, changing the type and mixing mode are effective means to improve combustion efficiency. In addition, the research on improvement of the energy conversion and emission performance of micro thermophotovoltaic(MTPV) system, micro thermoelectric(MTE) system and micro engine(ME) was reviewed. Compared with the existing research, it is found that the single optimization method has limitations, it cannot guarantee the positive effect under all operating conditions, the future research direction is to combine the advantages of a variety of optimization methods, besides, with the development and maturity of technology, the number of studies on diffusion combustion is increasing, and its practicability has been improved. Meanwhile, the further research and development of micro-energy mechanical system(MEMS) technology can be effectively promoted by the application of field synergy principle and Molecular Dynamics in numerical simulation. Based on this work, the research status of flow, heat transfer and performance improvement in combustion-based MEMS can be presented to relevant researchers more clearly.

The internal resistance of a battery represents the losses due to heat generation during energy conversion. The state-of-health is used to quantify the increase (degradation) of resistance with usage. However, the current state-of-health analysis merges the total internal resistance into one component. Consequently, the underlying cause of resistance degradation is not understood leading to incorrect estimate of battery health. Therefore, this paper presents a comprehensive framework based on energy equilibrium for the categorization and health analysis of total internal resistance. It is divided into 2 components: one based on irreversible overpotential (includes polarization) effects and a new second resistance component originated from reversible entropy changes. For LiFePO4 cells used in this work, it is observed that the contribution of entropy changes (hitherto unrecognized) to the overall losses increases from 4−10% to more than 40% as state-of-charge reduces. State-of-health of each component is obtained by the determination of its associated degradation factor to quantify the underlying mechanism of resistance degradation. In conclusion, the increase in irreversible resistance is primarily attributed to the permanent loss of active material. Correspondingly, the reversible resistance increase is associated to the formation of concentration gradients in the electrodes due to past load profile and ambient conditions. Maritime and Port Authority of Singapore (MPA) Accepted version The research conducted in this paper is funded jointly by ABB Pte Ltd, Singapore and Maritime and Port Authority (MPA) of Singapore.

The challenges associated with energy of the todays world including climate change, growing demand, and interdependence of gas, heat, and electricity have encouraged energy system planners to consider the integrated exploitation or hybrid strategies, which is so-called as the energy hub. According to different definitions presented for the energy hub, various models have been proposed so far for it. In general, the equipment of an energy hub can be divided into three categories: 1) direct connections, 2) converters, and 3) energy storage system. In this paper, a linear model of the energy hub including heating, cooling, and electrical equipment for energy conversion, production, or storage was considered. The proposed model consists of two parts of design and operation, formulated for an annual period in four seasons. The e-constraint method and fuzzy weighted method were used to solve the proposed model, and the two parts of design and operation were introduced as the main problem and sub-problem, respectively. In addition to deterministic model, problem-solving space was considered as scenario-based random taking into account uncertainty in amount of load, energy price, and also production of renewable wind resources. Scenarios were simulated for production of wind resources using historical information and other scenarios were simulated using the Monte Carlo simulation method. Given solution of the problem annually, for reducing volume of calculations, number of scenarios was decreased using the K-Means method. Mathematical model of the proposed model was of the mixed-integer linear type and included binary variables of design and continuous and binary variables of operation. Capacity selection for installation was based on appropriate candidates for each of the equipment, in order to prevent installation of unrealistic capacities in design sector.

Exergy and environmental analyses have been developed to determine the performance of the electricity generation in the Dutch mix. A comparative assessment of diverse technological routes, including fossil and renewable energy resources consumption, is carried out in terms of the exergy costs and specific CO2 emissions. Hence, an exergoeconomy methodology is used to properly allocate the renewable and non-renewable exergy costs and specific CO2 emissions among the various products of the polygeneration energy systems. By using a suitable methodology, the distribution of irreversibility throughout the different steps of the energy conversion processes of the Dutch electricity mix is characterized in the light of the Second Law of Thermodynamics. The results may help to propose performance indicators that support the Dutch government and research institutions. To identify sustainable energy planning strategies and fairly comparing electricity generation and end-use processing stages with other types of energy resources, such as fuels used in transportation, residential and industrial sectors. In brief, the weighted average of the renewable and non-renewable unit exergy costs and the specific CO2 emissions of the electricity generated in each route of the Dutch mix is calculated and compared to another electricity mix with a higher share of renewable energy resources. The weighted average renewable and non-renewable unit exergy costs of the electricity generated in the Netherlands are calculated as cR = 0.8375 kJ/kJE/W and cNR = 1.7180 kJ/kJE/W, respectively (cR/cNR= 0.49). Furthermore, the specific CO2 emissions in the Dutch electricity generation achieve 373.21 gCO2/kWhE/W.

A 4 × non-imaging optically concentrated solar thermoelectric generator (STEG) was simulated and its layout was optimized depending on materials characteristics. The performances of seven state-of-the-art thermoelectric materials were realistically compared considering direct normal irradiances (DNI) between 400 and 900 W/m2 and temperature dependence of the thermoelectric parameters. The model was tested with experimental data from literature and leg aspect ratios, fill factor (or thermal concentration), and leg number per STEG unit area were also used as variables. Due to the high values of thermal concentrations at maximum efficiency, different materials filling the gap among STEG legs were also considered. Maximum efficiency weakly decreases for filler thermal conductivities typical of common insulating materials, opening novel opportunities for STEGs not requiring vacuum. Results of the analysis show that skutterudites, lead telluride and bismuth telluride exhibit the highest efficiencies (≈7%) in the studied range of thermal concentrations and for a DNI equal to 900 W/m2. However, skutterudites and lead telluride were found to be very sensitive on the DNI level, differently from bismuth telluride, which therefore qualifies as the best solution for energy conversion. Moreover, optimal layouts for STEGs based on bismuth telluride more easily meet manufacturing constraints.

A novel hydro-kite like ocean energy converter is proposed in this paper to harness both ocean current and wave energy. The proposed ocean energy converter is typically designed to consist of a hydro-kite like kite floating or submerged in the ocean and an energy conversion unit set on a ship. The ocean wave or current energies can be generated by pulling a pre-tensioned flexible tether that connects the hydro-kite-like kite and the energy conversion unit. The general dynamics of the novel ocean energy converter is basically described and modelled based on the dynamics of key components under both ocean wave and current conditions. The feasibility and effectiveness of the proposed ocean energy converter are evaluated through computational fluid simulations under both fully submerged ocean current and semi-submerged ocean wave conditions. The simulation results verify that the hydro-kite can be used to generate power from both ocean current and wave conditions and the design parameters of the hydro-kite such as the angle of attack, draft should be optimally controlled or designed to maximize the ocean energy generations under different ocean current speeds, wave periods and heights.

Fossil fuels cannot provide all the required energy in future due to their exhaustibility. Their utilization also leads to huge environmental problems. Therefore, it is vital to find a new inexhaustible and clean source of energy which could be easily stored and transported. Hydrogen produced by renewable energy sources has all the above mentioned advantages. There are many hydrogen production methods which could be coupled with renewable energy sources. Among them, electrolysis process is the most mature one. In this paper, a review is performed on different methods of coupling electrolyzer systems with different renewable energy sources, including solar energy, wind energy, geothermal energy, ocean thermal energy conversion system and hydroelectric energy. The focus of this study is on how these systems can be integrated and which one has the highest total efficiency. Finally, cost of hydrogen production by different energy sources is compared.

It is significant to evaluate accurately energy efficiency of ethylene cracking furnace as the highest energy consumption device in ethylene production. However, previous energy efficiency evaluation methods mainly concentrate on system-level evaluation of ethylene production and fail to consider effects of production load on operation conditions, which are unsuitable for detailed evaluation online. Considering single energy efficiency content and impractical improvement scheme of DEA and unreasonable static baselines in TOPSIS, a modified TOPSIS energy efficiency evaluation method is proposed. A set of new energy efficiency indicators is designed through matter conversion and energy transformation together with matter and energy interaction. To acquire real-time energy efficiency a simulation model of cracking furnace is established by employing radial basis function neural network. To improve evaluation accuracy, the relations among energy efficiency and operation conditions and production load are quantified by calculation formulas of energy efficiency indicators and functions extracted from simulation model. The sequential quadratic programming algorithm is suggested to solve dynamic baselines according to real-time production load by adjusting operation conditions within constraints. Furthermore, optimal operation conditions are provided by searching for maximum comprehensive energy efficiency. Finally, validity of proposed evaluation method is illustrated by applying in a practical cracking furnace.

The prediction of thermodynamic properties performance in porous silicon (pSi) photonic crystals (PhCs) was studied for enhancement of light conversion into different types of energy based thermophotovoltaic energy conversion system. The unit-cell for 2D square and triangular lattices of circular air holes were formulated and solved using plane wave expansion (PWE) method. This was used to investigate the thermodynamic properties and the effect of lattice dynamic on these properties at different porosities in silicon PhCs; which are regarded as isolated and non-interacting particles systems. This was achieved by connecting density of states (DOS) and thermodynamic quantities as described in statistical physics. It revealed that irrespective of lattice type, increasing porosity ensued a decline in thermodynamic properties. Novel insights and theoretical concepts that could be integrated in thermophotovoltaic system were revealed. Regarding the square lattice, the optimum value of these properties except the free energy was obtained at R / a = 0.30 for 20% and 50% porosities, and at R / a = 0.25 for 80% porosity. Regardless of the porosity, the optimum value for the triangular lattice was found at R / a = 0.25 . These characteristics have attempted to provide contributions with regards to the selection of the appropriate design for PhC in order to achieve high efficiency conversion.

Well-designed multi-energy conversion systems have the potential to reduce energy consumption and carbon emissions. Based on the literature review and the typical energy flow network of multi-energy conversion systems, the necessity of stakeholders' taking part in multi-energy projects have been emphasized. Considering of different stakeholders have different interest demand and theirs' decision-making behaviors interact with each other, both the final results and decision process are important for stakeholders in multi-energy system planning. Game analysis, which is an analysis method for the conveying scheme evolution in different situations, was proposed to descript the complex relationship between stakeholders' profits and technical schemes. A hierarchical game playing scheme and a simplified multi-energy system optimization method were put forward to assist stakeholders to participate in techno-economic analysis process. Annual equivalent full capacity operation time and hourly earnings of each energy conversion technology are used to calculate returns on investment. The total revenues and every stakeholders' economic returns in different situations (energy price) and technical proposals can be acquired and compared. The proposed method is also illustrated and verified along with a case study. Results indicated that all parties can make contingent decisions under multi-partner negotiation with the assist of game analysis method.

A great amount of researches on thermodynamic cycles have been active in recent years, such as ORC (organic Rankine cycle), Kalina cycle, et al. However, the ultimate aim of such researches, which could even be traced back to more than one century ago, has not changed with a tireless pursuing to Carnot cycle. In exiting researches, the working fluid, as a medium for energy conversion, is commonly considered to play an important role in the thermodynamic cycle: (1) relative to ideal cycle, most of actual power cycles in the engineering field cannot operate without working fluid; (2) energy efficiency, considering the analysis of second-law efficiency, of actual cycle has a significant decrease due to the introduction of working fluid. Thus, working fluid is a hot spot in the research of thermodynamic cycle in recent years. Zeotropic mixture, which commonly consists of two or more pure working fluids, has flexibility in thermos-physical properties with a possible potential to enhance the cycle performance. The effects of thermos-physical properties of zeotropic mixture should be considered when determining the cycle structure and the design of components. This paper presents a novel construction method of thermodynamic cycle based on the zeotropic mixture. By adding the thermodynamic coordinate of working fluid, a 3D cycle diagram based on the traditional temperature and entropy cycle diagram is applied for performance analysis of cycle. According the proposed construction method, a baseline cycle, composed by ORC sub-system and compositions regulating sub-system, is put forward and available compositions regulating techniques for such cycle are discussed as well. Finally, a representative case is described briefly and the features are summarized. This work provides a new methodology view to guide researchers in energy-efficient design of thermodynamic cycles.

Graphene has been subjected to widespread attention, and its highly extraordinary properties have led to abundant scientific researches. The present study shows that fluffy graphene can ignite in a fairly short time upon exposure to a conventional flash light, even in an extremely low temperature environment. The ignition process is fierce and multi-points are distributed with temperatures as high as 1840K with few residues. This kind of ignition can be attributed to the graphene nanostructure efficiently converting light to heat and causing a large amount of heat to accumulate within a very short flash time with the temperature quickly exceeding the ignition point. It is further demonstrated that graphene can ignite in an environment as low as about −50 °C. When fluffy graphene was added to extremely lean methane/oxygen/nitrogen mixtures, ignition of the mixtures was successfully triggered by flash light. The ignition characteristics make graphene a promising alternative for ignition fields in harsh environment.

In future energy systems, storage technologies for electrical energy are considered to be a key component for increasing the share of renewable energy use. Pumped thermal energy storage technologies represent a promising approach to complement established storage technologies such as pumped-hydro power storages without their geological restrictions. Assuming an ideal, reversible and adiabatic energy conversion process, the stored electrical energy can be entirely recovered. However, the efficiency of real processes is limited by irreversibilities. These exergy losses can be compensated by the integration of low temperature heat. The exergetic efficiency can be further increased by using thermal energy provided during discharging. In this paper, a fully heat-integrated, subcritical PTES using butene as the working fluid is presented. The results of a detailed numerical simulation of the cycle regarding exergy losses during heat transfer, efficiencies of machinery and parasitic energy consumption are shown. A maximum net electrical power ratio between charging and discharging of 125% is obtained, while the maximum exergetic efficiency is 59%. The conducted numerical simulation includes pressure losses and pinch points, allowing for a more in-depth understanding and for a pre-optimization of the hydraulic design.

This study is focused on the utilization of oceanic methane hydrate as an energy resource under the real production situations of Nankai Trough, Japan. Due to the complex geological conditions and the sensitive thermal-mechanical properties of methane hydrate bearing layers, it is very difficult to extract and utilize the methane hydrate stably and economically. The current status of development in Japan and major challenges from real reservoir-scale analysis are discussed. Low-carbon emission process is discussed and shown into detail with careful numerical modeling procedures. The numerical model is constructed based on the geological conditions of Nankai Trough of Japan. Numerical model is also scaled-up from single thin-layer to thick multi-layer model for real reservoir conditions, based on the recent geological survey data. In the current study, the production behaviors, boundary conditions and reservoir parameter effects are discussed into detail. The predicted production rate level in this simulation agrees with recent real tests. It is found that proper selection of layer models and production strategy is very important for large-scale simulation and prediction. Combined methods and strategic production design are recommended in future real tests.

A novel coupled hydro-pneumatic energy storage system is proposed to improve the energy and power performance of the energy storage system in hybrid mining trucks. Based on four basic layouts, representing different energy conversion and storage approaches, of compressed air energy storage system and hydraulic energy storage system, a coupled layout is proposed for the hybrid mining truck application through a comparative study of the four basic layouts in this paper. Simulation and analysis results show that the coupled layout can effectively balance the power and energy performances of the pressure energy storage system. The total benefit of hybrid mining trucks with the coupled layout in ten years is increased by 9.7% as compared with the compressed air energy storage system, and by 91.2% as compared with the hydraulic energy storage system. Moreover, the weight and volume of the coupled layout are reduced by 15.4% and 24.8% as compared with the compressed air energy storage system, respectively, and by 83.1% and 92.8% as compared with the hydraulic energy storage system, respectively.

Supercritical carbon dioxide (S-CO2) cycle is proven to be one promising alternative to provide high efficiency and has been developed for a wide range of energy conversion applications. Thermal efficiency of the S-CO2 cycle can be further improved by incorporating an appropriate bottoming cycle utilizing the residual heat. In this paper, an Organic Rankine Cycle (ORC) is added to the S-CO2 cycle for heat recovery. Different recuperative ratios of the topping S-CO2 cycle are considered and the influence of heat source initial temperature and total heat load on the bottoming ORC is evaluated. Two configurations of the S-CO2-ORC combined cycle system are presented, one without a pre-cooler and the other still with a pre-cooler, corresponding to total and partial residual heat recovery respectively. Though the entire residual heat recovery by the bottoming cycle could definitely increase the system thermal efficiency, the low ORC evaporation temperature and mediocre ORC performance leads to a limited improvement. While in the combined cycle system with a pre-cooler, higher ORC evaporation temperature could be attained and it has a remarkable effect on the ORC performance, even though part of the topping cycle residual heat is discharged to the ambient. The simulation results reveal that the S-CO2-ORC combined cycle system performance could be significantly improved through this parametric optimization. The recompression S-CO2 cycle with bottoming ORC is then analyzed and thermal performance is improved based on the previous optimization results. The bottoming ORC could effectively recover the residual heat of the topping S-CO2 cycle and increase the system thermal efficiency, thus it can be considered and applied in similar practical cases.

The artificial ground freezing (AGF) method is widely used for soil reinforcement in underground engineering. The AGF method has been confirmed very effective, however, it consumes a great deal of energy during construction. Therefore, it is of great significance to study its energy conversion and utilization, which is very important for better and more energy-efficient employment of this method. In this paper, a novel method, which could effectively calculate the energy utilization rate (EUR), is proposed to evaluate the energy conversion efficiency of a typical AGF project. First of all, the brine temperature and ground temperature are monitored and analyzed. Secondly, according to the monitored data and actual layout of freezing pipes, a sophisticated three-dimensional solid model is established, which considers the thermal-mechanical coupling and ice-water phase change. Based on the numerical simulation, the variation of the temperature field as well as the expansion process of the frozen soil curtain are analyzed, and the effectiveness of the numerical model is further validated by comparison between the measured and simulated results. Thirdly, variations of three key parameters including the output energy, elastic strain energy and heat energy during the active freezing period are calculated and analyzed. Finally, the EUR curve during the AGF process is acquired based on the calculated indicators. The trend of EUR can be divided into four stages, while the EUR is zero in the initial stage, reaches a peak of 0.79 in the rise stage, and then decreases slowly in the decline stage and stable stage. According to the EUR curve, constructive measures to improve energy conversion and utilization are proposed. It is concluded that this novel method is very effective for the assessment of energy utilization in AGF projects.

In the next decades, energy storage technologies will play a major role in decarbonizing the European heating and cooling sector. In this regard, the deployment of complementary technologies is of paramount importance for the energy transformation of the Polish heating sector. This work addresses the challenge of sizing large-scale thermal energy storage (TES) systems for combined heat and power (CHP) plants connected to district heating networks and participating in day-ahead electricity markets. In this paper, a method based on a mixed-integer linear programming approach is proposed to find the optimal capacity of TES units connected to coal-fired CHP systems. The model considers the specific investment costs of the storage technology and optimizes the annual operation scheduling of the CHP-TES system. The model is applied to the case study of a coal-fired CHP system. Four scenarios are used to investigate the performance of the CHP system and evaluate the effects of rising carbon prices on the optimal capacity of the TES unit. The results reveal that the integration of the TES leads to a significant drop in the utilization of the heat-only boilers, helping mitigate fuel and environmental costs.

Thermoelectric generators (TEGs) are usually working in intermittent heat source environments, and thus the phase change material (PCM) has been widely adopted in to maintain relatively stable temperature difference. The property matching between the PCM and the TEGs is one of the crucial problems to influence the performance of the PCM-TEG system. In this work, the influence of the phase change temperature of the PCM on the output power and generated electricity of PCM-TEG system is studied. Classic Enthalpy model and three-dimensional coupled thermo-electric equations are applied to study the heat transfer and energy conversion mechanisms. Our results show that the output electric energy of a PCM-TEG system can be optimized by tuning the phase change temperature of PCM. The total generated electricity can be enhanced as large as 15.6% by matching the PCM with the thermoelectric properties of the thermoelement. Moreover, by comparing three cases with different thermoelectric materials, we give relationship between the optimal phase change temperature of PCM and the temperature for maximum figure of merit (ZT) of the thermoelement, which provides a selection criterion of PCM for TEG module. Our work could be helpful to realize further high efficiency thermoelectric generators for intermittent heat sources.

The axial-flow impulse turbine is recently utilized for oscillating water column wave energy conversion because of its wider operating range and having no stalling point. Most previous experimental studies conducted in the oscillating air flow testing rigs can give little information of the steady-state performance of impulse turbines. A constant flow test rig was set up in this study. The steady state performance of an axial-flow impulse turbine was studied by carrying out over 140 cases. The total pressures at the chamber and atmosphere sides and torque output under various incident flow velocities and prescribed rotation speeds are presented. Effects of Reynolds number on the dimensionless coefficients are reported, which are also compared by a previous study. The scatter diagram of efficiencies provides detailed information of turbine performance under different testing conditions. The peak value of turbine efficiency is found to be 0.48 at the flow coefficient of 1.0.

A comprehensive optimization study considering both system configurations and operation signals is needed for microgrid energy systems. For this, this study provides an advanced optimization based design framework that extends existing energy system optimization studies in following four aspects: complete system optimization from the beginning, comprehensive energy conversion equipment modeling, modeling of cascaded configurations, and consideration of transient loads and weather profiles. This framework aims to find optimum system configurations and operation signals for any given equipment options, and load- and weather-profiles. The framework is presented through a case study on an oceanic container transportation application. Optimized system configurations and operation signals are found under three different scenarios: minimizing life cycle cost as single objective, minimizing capital cost and annual fuel energy consumption as bi-objective, and minimizing life cycle cost considering uncertainties in load profiles. The optimized system could reduce system life cycle cost by 40% in single objective scenario and 45–52% at different levels of robustness. Exploring waste heat from the main ship propulsion engine is the key to reduce life cycle cost. The framework can be applied for a wide range of applications as an efficient tool to search for novel system designs and their evaluations.

Fuel cell technology is one of the most promising, emissions free, energy conversion technology under renewable energy systems because of its wide ability in most of the commercial applications like electrical vehicles, building cogeneration and standby power supply. Mathematical models are trusted as important tools for designing and performance analysis of fuel cell based systems. Many mathematical models based on thermal, electrochemical and electrical steady states as well as dynamic have been reported in literature to evaluate performance of Proton Exchange Membrane (PEM) fuel cell, but all these models are complex and needs huge amount of data for modeling and performance testing. The present paper proposes simple, but more realistic MATLAB SIMULINK model for PEM fuel cell to evaluate its performance under different operating conditions. The performance of the proposed model is compared with single practical, 25 cm 2 active area, PEM fuel cell for model validation. The presented model is also valid for a stack having any number of cells.

Many countries have passed governmental action plans to support the installation of renewable energy sources. However, most studies dealing with the optimization of building energy systems neglect a precise modeling of such subsidies, although these subsidies are specifically designed to strongly influence system setups. Therefore, this paper extends a model for the optimization of energy systems by a more accurate consideration of storage units and enhance both models by accounting for major German pieces of legislation aimed at supporting renewable energies. Additionally, we consider typical German market characteristics, in particular the availability of multiple gas and electricity tariffs. We compare our model with the original formulation regarding a pure cost minimization and a forced reduction of CO2 emissions for three new buildings located in Germany. The results imply that the considered subsidies strongly support the installation of PV modules and CHP units. Without these subsidies, batteries and solar thermal collectors become more important. Additionally, the findings illustrate that the new storage model is slightly more accurate, but only marginally affects the total annual costs and required computing times. The conducted sensitivity analysis has shown that the obtained results are relatively robust to variations in energy tariff costs and demands.