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Abstract: Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000°C using CO2 as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO2 gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800°C while at elevated temperatures of 900 and 1000°C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H2 to exhibit after few minutes into the gasification that changed with gasification temperature. At 800°C gasification temperature peak in H2 was displayed at 3min into gasification while it decreased to only 2min, approximately, at gasification temperatures of 900 and 1000°C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (). The results show important role of CO2 gas for the gasification of wastes and low grade fuels to clean syngas. [Copyright &y& Elsevier]

Past studies of hybrid power cycles using multiple heat sources of different temperatures focused mainly on case studies and almost no general theory about this type of systems was developed. This paper is a first comprehensive study of their general thermodynamic performance, with their comparison to their corresponding single temperature heat source reference system, focusing on three types of power cycles: simple Rankine cycle, Rankine cycle with reheat and Rankine cycle with heat regeneration. The generalized expressions for the energy and exergy efficiency differences between the hybrid and the corresponding single heat source system were developed. A number of simulation case studies were performed to help the understanding and confirm the thermodynamic generalization of the results. The results show that the energy and exergy efficiencies of the hybrid systems are higher than those of their corresponding single heat source reference systems if and only if the energy andexergy conversion efficiency (defined in the paper) of the additional heat source (AHS) is larger than that of the original heat source. The conditions that defined the effects of the AHS temperature and heat addition rate on the energy and exergy efficiencies of the hybrid systems as convex or concave curves were described. Comparisons across the first two types of hybrid power cycles were made, showing that the energy and exergy efficiencies of the reheat Rankine cycle is generally higher than that of the simple Rankine cycle as AHS is changed. Recommendations were made for obtaining the maximal energy and exergy efficiency as a function of the AHS temperature, of the heat addition rate by the AHS, and of the AHS position in the power cycle flow sheet. For the hybrid power generation systems with heat regeneration it was found that when using an AHS to raise the net system power by a given amount, using it to replace the higher-pressure extracted steam will result in a higher system energy efficiency than when using it to replace lower-pressure extracted steam. Hybrid cycles can have significantly lower emissions, cost, and fuel depletion. [ABSTRACT FROM AUTHOR]

Based on an extensive dataset containing aggregated hourly energy consumption readings of residents during March 2011 and October 2012 in South Ontario, Canada, this paper estimates the energy consumption of circulating pumps of residential swimming pools (CPRSP) non-intrusively, and quantifies the impact of CPRSP on the power system. The main challenges are that, first, widely used non-intrusive appliance load monitoring (NIALM) methods are not applicable to this work, due to the low sampling rate and the lack of the energy consumption pattern of CPRSP; second, temperature-based building energy disaggregation methods are not suitable for this work, as they highly depend on the accurate base load estimation and predefined parameters. To overcome these issues, in this paper, first it is found that, during the pool season, for homes with and without swimming pools, the ratio between their base loads is approximately equal to the ratio between their temperature-dependent energy consumptions, then a novel weighted difference change-point (WDCP) model has been proposed. The advantages of the WDCP model are that, on one hand, it doesn’t depend on the base load estimation and predefined parameters; on the other hand, it has no requirement on the data sampling rate and the prior information of energy consumption patterns of CPRSP. Based on the WDCP model it is shown that, the average hourly energy consumption of CPRSP is 0.7425 kW, and the minimum and the maximum hourly energy consumptions are 0.5274 kW at 9:00 and 0.9612 kW at 17:00, respectively. At the peak hour 19:00, July 21, 2011, CPRSP contributes 20.36% energy consumption of homes with swimming pools, as well as 8.48% peak load of all neighborhoods. As a result, the peak load could be reduced by 8.48% if all CPRSP are stopped during the peak hour. [ABSTRACT FROM AUTHOR]

Power cycles running on carbon dioxide at supercritical pressure and temperature were introduced in the late ninety-sixties but, after a warm welcome to the theoretical performance announced, they were later abandoned in favour of standard combustion gas turbines. Nevertheless, the technology was brought forward about a decade ago and has since captured significant attention from the scientific and industrial community. The number of publications has risen exponentially and there are several experimental projects under development today. The performances of these cycles have been deeply analysed in literature, proving to be theoretically competitive. This paper reviews all the works published in the topic to date. Different cycle concepts (stand-alone and in combination with other cycles using the same or different technologies), layouts, fuels, applications (power only or combined heat and power) and operating conditions are reviewed and categorised according to the configuration of the cycle. This latter feature is thought to be an interesting added value of this paper since, rather than just listing the past work in the area of sCO 2 power cycles, it also organises the numerous cycles in different categories and provides a comparison of the claimed performance of each one of them. This comparison between the performances of the various configurations is based on the values declared in the original papers and thus applies to very different boundary conditions. Obviously, this great heterogeneity of the available data (in particular the temperatures and pressures considered) makes it impossible to establish a fair comparison between the configurations reviewed. Therefore, a future study seems to be mandatory where the performances of all cycles should be compared for the same set of operating conditions. [ABSTRACT FROM AUTHOR]

This paper presents methods for assessing the statistical interdependencies between solar irradiance and the outside temperature, which are used to assess the correspondence between the operation of technologies to meet the heat demands and the PV output. It is important to be able to assess the impact of heating technology changes and increased PV penetration on power system requirements. Considering the correlation between the PV outputs and heat loads, there exist multiple effects of weather variations on the “Source-Grid-Load.” Heat load, photovoltaic (PV), electric air conditioner (EC), natural gas-fuelled combined heat and power (CHP), and central heating boiler models are established to study the influences of the solar irradiance and the temperature of the outdoors. The energy dependence impacts on the “Source-Grid-Load” are simulated in a 41-bus distribution network, and the paper's results show how the correspondence between the temperature and solar irradiance can impact the system's requirements. [ABSTRACT FROM AUTHOR]

In this paper, the cooling feasibility of air flow via a novel air-water based TEC system (as an alternative air cooling unit) is experimentally investigated for different climate conditions. Contrary to previous studies, thermoelectric hot side temperature was adjusted by a low constant water flow rate (and not by an air fan) which significantly increased the cold side performance of TEM. Ten parameters including T a,inlet , T w,inlet , T a,outlet , T w,outlet , T c , T a , m ̇ a , m ̇ w and DC voltage and DC current were directly recorded by measurement instruments during the experiments. Six other parameters including q c , q h , COP c , COP max , COP c /COP max and q air were evaluated by formulas and correlations using of aforesaid measured data. Five numbers of aforementioned parameters were variant parameters. Indeed, the effect of m ̇ a , m ̇ w , DC voltage/current and T a,inlet (variant parameters) on other impressionable parameters were investigated in present study. Optimum working condition was evaluated from a new point of view. Indeed, in this paper, it was accidently found out that, despite the descending behavior of both COP c and COP max (due to changing of variants), the ratio of said parameters (COP c /COP max ) creates a peak point (ascending and then descending) in all cases. Said peak point can be considered as an appropriate working condition of thermoelectric units. Findings showed that, the cold side of thermoelectric system can act as an applicable air cooling system especially when the hot side of thermoelectric is cooled by a current liquid such as water. [ABSTRACT FROM AUTHOR]

This paper presents the results of a demonstrative Building Integrated Photovoltaic (BIPV) installation in Lugano where five BiPV modules with different integration solutions (fully integrated as Double Glaze Units (DGUs) and ventilated), different inclinations (30° and 90°) and different technologies (double junction amorphous silicon (a-Si/a-Si) and crystalline silicon (c-Si)) were investigated. The paper aims at evaluating the impact of the operating cell temperature on the modules’ performance for different investigating cases. Two models were used to calculate the junctions’ temperatures of the modules under operation: the simplified Nominal Operating Temperature (NOCT) model and the Equivalent Cell Temperature (ECT). The first was used in a simplified version and the second was used for all modules, regardless of its limitations for thin film technologies. The two models agree well and give satisfactory results regardless of the inclination, integration solution or technology. The difference between the NOCT and ECT calculated average daily temperatures of the modules was found to be less than 5–6 °C, with only one exception. As expected, fully integrated modules exhibit higher temperatures. In terms of performance, the integrated c-Si modules, regardless of their inclination, ranked lower – in terms of energy yield – than the integrated and ventilated a-Si/a-Si modules, for which the high operating temperatures proved to be beneficial. The inclination of 90° was found to be ideal for Lugano for both c-Si and a-Si/a-Si modules. [ABSTRACT FROM AUTHOR]

The integration temperature difference Δ T i considers the heat transfer routes, linking the heat transfer process with the thermodynamic behavior of heat exchangers. The first and second non-dimensional integration temperature differences are defined as Δ T i, h ∗ = Δ T i / T h, i and Δ T i, s ∗ = Δ T i / ( T h, i - T 0 ) respectively, where T h,i is the heat source temperature and T 0 is the environment temperature. This paper is the first to experimentally verify the significance of the non-dimensional integration temperature differences on organic Rankine cycle (ORC) systems. The first non-dimensional temperature difference is shown to have linear relationship with the revised entropy generation numbers ( N s ). With increases of the second non-dimensional integration temperature difference, the expander powers, system thermal and exergy efficiencies had parabola distributions. They simultaneously reached maximum at Δ T i, s ∗ = 0.282 , under which the vapor cavitation in the expander disappears and the exergy losses of heat exchangers are acceptable to elevate the expander efficiency. Beyond the optimal point, the ORC performance is worsened either due to the vapor cavitation in the expander, or due to the poor thermal matches in the evaporator and condenser. The second non-dimensional integration temperature difference comprehensively reflects the effects of heat source temperatures, heating powers and organic fluid flow rates and pressures, etc. It balances exergy destructions of various components to optimize the system. Thus, it can be an important parameter index to maximize the power or electricity output for a specific heat source. The usefulness of the integration temperature difference and the future work are discussed in the end of this paper. [ABSTRACT FROM AUTHOR]

Thermoelectric generators (TEGs) present good potential applications for the conversion of low level thermal energy into electrical power, especially applied to waste heat recovery systems. This paper presents an advanced mathematical model that uses multi-element thermoelectric components connected in series, and considers internal and external irreversibility and also the temperature gradients along the flow direction. A Fortran computation program was used for the numerical calculations. This paper focusses mainly on the thermoelectric performance study under four different types of cooling methods with temperature gradient modeling. The results showed that it is important in TEG system design to choose an optimal module area that is appropriate to the mass flow rate of the fluids, but this is not affected by the intake temperature of fluids. With the water cooling method, the coflow and counterflow methods did not need to be distinguished because of their small difference, but they should be distinguished for the air cooling method. The counterflow arrangement generally produced a small higher maximum power output, but needed a much larger module area compared to the coflow method. [ABSTRACT FROM AUTHOR]

Very little attention has been dedicated to the carrier re-oxidation in chemical looping systems. The work presented in this paper is for the re-oxidation of partially reduced hematite from a cyclic chemical looping fixed bed process. The underlying purpose of this work is to develop engineering rates and mechanisms for the re-oxidation of partially reduced hematite that can be included in CFD models for a chemical looping process. To this end, experiments were run using nominally 1000 g of hematite material in a fixed bed reactor cycling between reduction and re-oxidation. The cyclic processing began with the reduction step then proceeded to the oxidation step repeating this analysis for several cycles ranging from 5 to 10. The re-oxidation process was conducted at temperatures ranging from 745 °C to 825 °C and oxygen concentrations ranging between 9% and 11%. The reduction was carried out at the same temperature as the re-oxidation step at various CH 4 concentrations from 5% to 9%. In this paper, cyclic induced variations in performance are presented as well as the kinetic parameters for the first cycle. The re-oxidation of the depleted hematite occurs through a 2 step parallel process in which oxygen reacts to fill the surface of each grain within the particles and then migrates through oxygen vacancy diffusion to the depleted cores of each grain. [ABSTRACT FROM AUTHOR]

This paper shows a new advanced control approach for operations in hybrid systems equipped with solid oxide fuel cell technology. This new tool, which combines feed-forward and standard proportional–integral techniques, controls the system during load changes avoiding failures and stress conditions detrimental to component life. This approach was selected to combine simplicity and good control performance. Moreover, the new approach presented in this paper eliminates the need for mass flow rate meters and other expensive probes, as usually required for a commercial plant. Compared to previous works, better performance is achieved in controlling fuel cell temperature (maximum gradient significantly lower than 3 K/min), reducing the pressure gap between cathode and anode sides (at least a 30% decrease during transient operations), and generating a higher safe margin (at least a 10% increase) for the Steam-to-Carbon Ratio. This new control system was developed and optimized using a hybrid system transient model implemented, validated and tested within previous works. The plant, comprising the coupling of a tubular solid oxide fuel cell stack with a microturbine, is equipped with a bypass valve able to connect the compressor outlet with the turbine inlet duct for rotational speed control. Following model development and tuning activities, several operative conditions were considered to show the new control system increased performance compared to previous tools (the same hybrid system model was used with the new control approach). Special attention was devoted to electrical load steps and ramps considering significant changes in ambient conditions. [ABSTRACT FROM AUTHOR]

Three kinds of carbon sources obtained from carbon black, bamboo fiber and waste paper were investigated as anode fuels in an intermediate temperature direct carbon fuel cell. The carbon sources were characterized with X-ray photoelectron spectroscopy, thermal gravimetric analysis, etc. The results indicated that the waste paper carbon was more abundant in calcite and kaolinite, and showed higher thermal reactivity in the intermediate temperature range compared with the other two carbon sources. The cell performance was tested at 650 °C in a hybrid single cell, using Sm 0.20 Ce 0.80 O 2 − x as the electrolyte. As a result, the cell fed with waste paper carbon showed the highest performance among the three carbon sources, with a peak power density of 225 mW cm −2 . The results indicated that its inherent impurities, such as calcite and kaolinite, might favor the thermal gasification of renewable carbon sources, which resulted in the enhanced performance of the intermediate temperature direct carbon fuel cell. [ABSTRACT FROM AUTHOR]

The efficiency of any thermal power plant is related to the maximum working temperature that some components can reach. Examples of material constraints are the first stage blades of a gas turbine or the receiver of a solar tower plant, but there are other temperature constraints, such as the ones related with the heat transfer fluid. Nowadays, this happens in the most common solar technology: parabolic trough collectors that use synthetic oil. This fluid must work below 400 °C. This limitation affects the power plant efficiency due to a poor Rankine cycle yield. To avoid this problem and go to higher temperatures, a gas can be used as heat transfer fluid, providing at the same time other significant advantages over synthetic oil: non-flammability and no environmental threats. The purpose of this paper is to justify the theoretical basis of the gas use in parabolic troughs and the problems related, and also to describe the test loop built at the PSA (Plataforma Solar de Almería) in order to demonstrate the technical feasibility of this new technology, testing all components required to build a pre-commercial power plant. This paper describes the main features of this technology, the theoretical basis, the validation of the design tools and the results of the operation. Of them, the more important aspects are that high working pressure can reduce pumping power to adequate levels, that good controllability of the technology with hard solar transients can be achieved and that ball joints leaks problems detected appeared as the main inconvenience, but promising solution has been found. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and model validation for a modular two-phase heat exchanger that recovers energy in heavy-duty diesel engines. The model is developed for temperature and vapor quality prediction and for control design of the waste heat recovery system. In the studied waste heat recovery system, energy is recovered from both the exhaust gas recirculation line and the main exhaust line. Due to the similar design of these two heat exchangers, only the exhaust gas recirculation heat exchanger model is presented in this paper. Based on mass and energy conservation principles, the model describes the dynamics of two-phase fluid flow. Compared to other studies, the model is able to capture multiple phase transitions along the fluid flow by combining finite difference approach with moving boundary approaches. The developed model has low computational complexity, which makes it suitable for control design and real-time implementation. To validate the model, experiments are performed on a state-of-the-art Euro-VI heavy-duty diesel engine equipped with the waste heat recovery system. Simulation results show good accuracy, over the complete engine operating range, with average error below 4%. This is demonstrated on transitions between stationary operating points and on a dynamic response to a standard world harmonized transient cycle for both cold-start and hot-start conditions. [ABSTRACT FROM AUTHOR]

Abstract: Waste and agricultural residues offer significant potential for harvesting chemical energy with simultaneous reduction of environmental pollution, providing carbon neutral (or even carbon negative) sustained energy production, energy security and alleviating social concerns associated with the wastes. Steam gasification is now recognized as one of the most efficient approaches for waste to clean energy conversion. Syngas generated during the gasification process can be utilized for electric power generation, heat generation and for other industrial and domestic uses. In this paper results obtained from the steam assisted gasification of oil palm trunk waste are presented. A batch type gasifier has been used to examine the syngas characteristics from gasification of palm trunk waste using steam as the gasifying agent. Reactor temperature was fixed at 800°C. Results show initial high values of syngas flow rate, which is attributed to rapid devolatilization of the sample. Approximately over 50% of the total syngas generated was obtained during the first five minutes of the process. An increase in steam flow rate accelerated the gasification reactions and resulted in reduced gasification time. The effect of steam flow rate on the apparent thermal efficiency has also been investigated. Variation in steam flow rate slightly affected the apparent thermal efficiency and was found to be very high. Properties of the syngas obtained from the gasification of oil palm trunk waste have been compared to other samples under similar operating conditions. Oil palm trunk waste yielded more syngas, energy and hydrogen than that from other types of biomass such as mangrove wood, paper and food waste. [Copyright &y& Elsevier]

Abstract: Thermal energy storage with phase change materials (PCMs) offers a high thermal storage density with a moderate temperature variation, and has attracted growing attention due to its important role in achieving energy conservation in buildings with thermal comfort. Various methods have been investigated by previous researchers to incorporate PCMs into the building structures, and it has been found that with the help of PCMs the indoor temperature fluctuations can be reduced significantly whilst maintaining desirable thermal comfort. This paper summarises previous works on latent thermal energy storage in building applications, covering PCMs, the impregnation methods, current building applications and their thermal performance analyses, as well as numerical simulation of buildings with PCMs. Over 100 references are included in this paper. [Copyright &y& Elsevier]

Abstract: In this paper, an attempt is made to investigate the thermal and electrical performance of a solar photovoltaic thermal (PV/T) air collector. A detailed thermal and electrical model is developed to calculate the thermal and electrical parameters of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, etc. Some corrections are done on heat loss coefficients in order to improve the thermal model of a PV/T air collector. A better electrical model is used to increase the calculations precision of PV/T air collector electrical parameters. Unlike the conventional electrical models used in the previous literature, the electrical model presented in this paper can estimate the electrical parameters of a PV/T air collector such as open-circuit voltage, short-circuit current, maximum power point voltage, and maximum power point current. Further, an analytical expression for the overall energy efficiency of a PV/T air collector is derived in terms of thermal, electrical, design and climatic parameters. A computer simulation program is developed in order to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. Since some corrections have been down on thermal and electrical models, it is observed that the thermal and electrical simulation results obtained in this paper is more precise than the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency and overall energy efficiency of PV/T air collector is about 17.18%, 10.01% and 45%, respectively, for a sample climatic, operating and design parameters. [Copyright &y& Elsevier]

Abstract: A data-driven approach for modeling indoor-air-quality (IAQ) sensors used in heating, ventilation, and air conditioning (HVAC) systems is presented. The IAQ sensors considered in the paper measure three basic parameters, temperature, CO2, and relative humidity. Three models predicting values of IAQ parameters are built with various data mining algorithms. Four data mining algorithms have been tested on the HVAC data set collected at an office-type facility. The computational results produced by models built with different data mining algorithms are discussed. The neural network (NN) with multi-layer perceptron (MLP) algorithms produced the best results for all three IAQ sensors among all algorithms tested. The models built with data mining algorithms can serve as virtual IAQ sensors in buildings and be used for on-line monitoring and calibration of the IAQ sensors. The approach presented in this paper can be applied to HVAC systems in buildings beyond the type considered in this paper. [Copyright &y& Elsevier]

Abstract: In this paper, we describe a new alternative control approach for indirectly connected district heating substations. Simulations results showed that the new approach results in an increased across the substation. Results were obtained for both ideal and non-ideal operation of the system, meaning that less water must be pumped through the district heating network, and a higher overall fuel efficiency can be obtained in the district heating power plants. When a higher fuel efficiency is achieved, the usage of primary fuel sources can be reduced. Improved efficiency also increases the effective heat transfer capacity of a district heating network, allowing more customers to be connected to an existing network without increasing the heating plant or network capacity. Also, if combined heat and power plants are used to produce the heat, the increased will result in a further improved overall fuel efficiency, as more electricity can be produced with colder cooling water. The idea behind the new control method is to consider the temperature of the water supplying the district heating substation with heat, often referred to as the primary supply temperature. This represents a logical next step, as currently, the only parameter generally taken into account or measured when controlling the temperature level of the radiator circuit is the local outdoor temperature. In this paper we show how the primary supply temperature together with thermodynamic knowledge of the building can be used to maximize the across the district heating substation. [Copyright &y& Elsevier]

Highlights • A transient model of the VRB system is developed. • The model is used for dynamic control for electrolyte flow rate of VRB. • Flow rate is optimized under varying (dis-)charge power and SoC conditions. • Concentration discrepancy of active species in the stack and tank is considered. • Relatively low electrolyte flow rates are preferred with high pressure drops. Abstract The vanadium redox flow battery (VRB) is considered to be one of the most promising technologies for large-scale energy storage, with the electrolyte flow rate capable of significantly affecting the mass transfer, temperature rise, and pump power losses of the VRB system. Although the flow-rate optimization under constant current has been addressed in the literature, few studies have investigated the control strategy for the electrolyte flow rate under varying (dis-)charge power that is common in practical applications. Moreover, fewer studies have considered the concentration discrepancy of the active species in the tank and stack in the flow-rate optimization. In this paper, the electrolyte flow-rate optimization is investigated by incorporating the influences of the flow rate on the mass transfer, temperature rise, and required pump power. A transient model of the VRB system is developed to derive the total power losses (by which the overall system energy efficiency is determined; include losses resulting from overpotentials, ohmic drops, and required pump power) as a function of the applied current, concentration of the active species in the stack, and flow rate of the electrolyte. Based on this model, a dynamic flow-rate control strategy is proposed for determining the optimal flow rate under varying (dis-)charge power and state-of-charge conditions. The simulation results show that the proposed control strategy can deliver a high VRB system efficiency of 87.7%, and manage the electrolyte temperature to the safe range during mild summer days. [ABSTRACT FROM AUTHOR]

Highlights • The infiltration is responsible for more than half of the total cooling load. • A direct method is developed for measuring the transient infiltration airflow rates. • The method is validated by the experiments of tracer gas decay technique. • The measurement errors of infiltration airflow rates are distributed between ±10%. • The practical application of the proposed method is discussed. Abstract The measurement of the infiltration airflow rates can support the calculation of the infiltration cooling load for the better understanding and optimizing the energy consumption of cold stores. However, the large temperature difference and the intense transient features make it difficult and complex to measure the airflow rates accurately. In this paper, a simple and practical method to measure the transient infiltration airflow rates is developed by using the local air velocity linear fitting. The proposed method is validated by the measurement results of the tracer gas decay method. It is concluded that the proposed method shows a good performance on the transient infiltration airflow rates measurement. The measurement errors are between ±10%. To enhance the application of this method, the layout of the measuring points of the air velocities are analyzed. The results show that, along the vertical layout direction, air velocity measuring points around the neutral level (where the cold and the warm air separate, about the middle height of the door) are not preferred when using this method. What’s more, the calculation of the infiltration cooling load by using this measuring method is also discussed. [ABSTRACT FROM AUTHOR]

In recent years, combined heat and power (CHP) systems have attracted increasing attention worldwide. Owing to their advantages of high overall thermal efficiency, fuel flexibility, low noise and vibration, and low emissions, Stirling engines, especially dynamic Stirling engines (i.e., free-piston Stirling engines, FPSEs) are promising candidates for micro-CHP systems. In this paper, recent progress in Stirling engine-based micro-CHP systems and FPSE modeling and analysis is first briefly reviewed, and then a hybrid calculation model based on thermoacoustic theory is proposed and developed to simulate the entire micro-CHP system. Finally, the construction and testing of a pilot setup is described in detail. The obtained experimental results clearly validate the numerical model and scheme, with the primary deviation within approximately 10%. CHP performance tests revealed a maximum CHP efficiency of 87.5% and an output electrical power of 2.9 kW, corresponding to a 28% thermal-to-electric efficiency, when the delivering temperature was above 60 °C. Furthermore, acoustic impedance analysis indicated that the CHP efficiency remains high over a large temperature lift, which was also confirmed experimentally. [ABSTRACT FROM AUTHOR]

Thermoelectric devices have potential energy conversion applications ranging from space exploration through to mass-market products. Standardised, accurate and repeatable high-throughput measurement of their properties is a key enabling technology. Impedance spectroscopy has shown promise as a tool to parametrically characterise thermoelectric modules with one simple measurement. However, previously published models which attempt to characterise fundamental properties of a thermoelectric module have been found to rely on heavily simplified assumptions, leaving its validity in question. In this paper a new comprehensive impedance model is mathematically developed. The new model integrates all relevant transport phenomena: thermal convection, radiation, and spreading-constriction at junction interfaces. Additionally, non-adiabatic internal surface boundary conditions are introduced for the first time. These phenomena were found to significantly alter the low and high frequency response of Nyquist spectra, showing their necessity for accurate characterisation. To validate the model, impedance spectra of a commercial thermoelectric module was experimentally measured and parametrically fitted. Technique precision is investigated using a Monte-Carlo residual resampling approach. A complete characterisation of all key thermoelectric properties as a function of temperature is validated with material property data provided by the module manufacturer. Additionally, by firstly characterising the module in vacuum, the ability to characterise a heat transfer coefficient for free and forced convection is demonstrated. The model developed in this study is therefore a critical enabler to potentially allow impedance spectroscopy to characterise and monitor manufacturing and operational defects in practical thermoelectric modules across multiple sectors, as well as promote new sensor technologies. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage is an attractive technique as it can provide higher energy storage density than conventional heat energy storage systems and has the capability to store heat of fusion at a constant (or a near constant) temperature corresponding to the phase transition temperature of the phase change material (PCM). This paper provides a state-of-the-art review on phase change materials (PCMs) and their applications for heating, cooling and electricity generation according to their working temperature ranges from (−20 °C to +200 °C). Four working temperature ranges are considered in this review: (1) the low temperature range from (−20 °C to +5 °C) where the PCMs are typically used for domestic and commercial refrigeration; (2) the medium low temperature range from (+5 °C to +40 °C) where the PCMs are typically applied for heating and cooling applications in buildings; (3) the medium temperature range for solar based heating, hot water and electronic applications from (+40 °C to +80 °C); and (4) the high temperature range from (+80 °C to +200 °C) for absorption cooling, waste heat recovery and electricity generation. Different types of phase change materials applied to each temperature range are reviewed and discussed, in terms of the performance, heat transfer enhancement technique, environmental impact and economic analysis. The review shows that, energy saving of up to 12% can be achieved and a reduction of cooling load of up to 80% can be obtained by PCMs in the low to medium–low temperature range. PCM storage for heating applications can improve operation efficiency from 26% to 66%, depending on specific applications. Solar thermal direct steam generation (DSG) is the most common electricity generation application coupled with PCM storage systems in the high temperature range, due to the capability of PCMs to store and deliver energy at a given constant temperature. The recommendations for future research are also presented which provide insights about where the current research is heading and highlights the challenges that remain to be resolved. [ABSTRACT FROM AUTHOR]

This paper presents a numerical analysis of the ignition process of an n -heptane spray in a compression ignition engine using a post-processing tool developed by West Virginia University. Such a tool is able to process the CFD simulation data for the examination of chemical reaction process without revising the CFD source code. The main functions of the post-processing tool include: (1) The calculation of the instantaneous rate of production (ROP) using CHEMKIN with the temperature, pressure and species concentration in each cell simulated using CFD; (2) the development of the representative destruction reaction (RDR) and destruction pathway of the key species involved in a specific area; and (3) the visualization of the analysis results. Such a tool was applied to examine the chemical reaction process during ignition delay of the n -heptane spray in a direct injection compression ignition engine. The H abstraction of n -heptane by O 2 , OH, HO 2 , and H radical during ignition period was further examined. The destruction pathway of key species in RDR OH /RDR HO2 region and their development leading to the autoignition of n -heptane were studied. It is found that both the n -heptane/air mixture and bulk gas movement play an important role in the formation of RDR HO2 region. The RDR HO2 region featured with medium temperature (around 1000 K) produces more H 2 O 2 /HO 2 radical before the auto-ignition of n -heptane than low - temperature combustion. The rapid dissociation of H 2 O 2 provides a large amount of OH radical that enhances the chain branching reaction as well as heat release process which then initiates the autoignition of n -heptane. The reaction rates of nC 7 H 16  + OH = C 7 H 15  + H 2 O and nC 7 H 16  + HO 2  = C 7 H 15  + H 2 O 2 were examined to reveal their competition in destructing n -heptane. The H atom is also found to promote the chain branching during auto-ignition. Such a tool provides the convenience for commercial CFD research community to conveniently elaborate the CFD simulation results for better understanding of the fundamental aspects of the combustion and emissions phenomenon observed using CFD code. [ABSTRACT FROM AUTHOR]

This paper presents a simple approach to estimate the state of charge of the LiFePO 4 batteries in electric vehicles under dynamic loads and variable temperature, which are inevitable during practical working conditions. This approach employs a highly adaptive estimation algorithm based on the recursive least-squares method and an original simple model of the open circuit voltage to the state of charge over a wide range of temperature. The modeling and the estimation in this approach are based on a new term for the state of charge, which is defined based on experimental findings to take into account the battery recovery capacity due to temperature variations. The proposed approach is validated through Urban Dynamometer Driving Schedule experiments including harsh temperature conditions, which have been mostly overlooked in previous research. The obtained results show that this approach maintains an accurate state of charge estimation, with an error of less than 5.2% under such conditions. The accuracy and the simplicity of the proposed algorithm are crucial for a feasible battery management system to be used in electric vehicles. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to explore deep decarbonization pathways for the Canadian energy sector that would allow Canada to participate in global mitigation efforts to keep global mean surface temperatures from increasing by more than 2 °C by 2100. Our approach consists in deriving minimum cost solutions for achieving progressive emission reductions up to 2050 using the North American TIMES Energy Model (NATEM), a detailed multi-regional and integrated optimization energy model. With this model, we analyze a baseline and two 60% reduction scenarios of combustion related emissions by 2050 from 1990 levels, with different assumptions regarding projected demands for energy services and availability of technology options for carbon mitigation. The first reduction scenario includes only well-known technologies while the second one considers additional disruptive technologies, which are known but are not fully developed commercially. Results show that three fundamental transformations need to occur simultaneously in order to achieve ambitious GHG emission reduction targets: electrification of end-use sectors, decarbonization of electricity generating supply, and efficiency improvements. In particular, our results show that electricity represents between 52% and 57% of final energy consumption by 2050, electricity generating supply achieves nearly complete decarbonization by 2025 and final energy consumption decreases by 20% relative to the baseline by 2050. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method to improve the efficiency of the perturbation and observation (P&O) maximum power point tracking (MPPT) algorithm. The proposed method can improve the dynamic tracking response of P&O, reduce the steady state oscillation of P&O and eliminate the possibility of the algorithm to lose its tracking direction. To estimate the optimal duty ratio of the boost converter at the maximum power point, an optimal duty ratio estimation algorithm based on a four-parameter model of a photovoltaic (PV) module is proposed. Furthermore, the ratio of the power-voltage curve slope to the current in the PV module is defined as K pvi . Because K pvi has a small variation range at different irradiations, a piecewise linear function dependent on K pvi is developed to generate the optimal step size of P&O. Finally, K pvi is utilized to avoid drift phenomenon in case of fast change in irradiation. To prove its effectiveness, the proposed P&O algorithm is compared with conventional P&O and adaptive P&O using the sudden step change test, Ropp test, and four one-day irradiation and temperature profile tests in Simulink. The proposed algorithm is also benchmarked by MPPT efficiency ( η MPPT ) calculation. The results show that the η MPPT of the proposed P&O is increased by 0.65% in one-day irradiation and temperature profile with light cloud test. In addition, the η MPPT of the proposed P&O can be further improved up to 1.27% and 1.24% in one-day profile with heavy cloud test and one-day profile with dark cloud test, respectively. Moreover, it needs neither additional sensors nor expensive microcontrollers. [ABSTRACT FROM AUTHOR]

Lithium-ion battery fast charging issues have become a main bottleneck of large-scale deployment of electric vehicles. This paper develops a polarization based charging time and temperature rise optimization strategy for lithium-ion batteries. An enhanced thermal behavior model is introduced to improve the solution accuracy at high charging current, in which the relationship between polarization voltage and charge current is addressed. Genetic algorithm (GA) is employed to search for the optimal charging current trajectories. The effects of weighting coefficients of charging time and temperature rise on battery charging performance are discussed. The charging time of the optimized charging protocol is reduced by 50%, and the associated temperature rise is almost identical, compared to 1/3C constant current-constant voltage (CC-CV) charging. Aging experiments demonstrate that the proposed charging method has a similar capacity retention ratio to that of 0.5 CC-CV charging after 700 cycles, thereby accomplishing a good balance between charging speed and lifetime. [ABSTRACT FROM AUTHOR]

Despite extensive research into alternative methods, the internal combustion engine is expected to remain as the primary source of vehicular propulsion for the foreseeable future. There are still significant opportunities for improving fuel efficiency, thus directly reducing the harmful emissions. Consequently, mitigation of thermal and frictional losses has gradually become a priority. The piston-cylinder system accounts for the major share of all the losses as well as emissions. Therefore, the need for an integrated approach, particularly of a predictive nature is essential. This paper addresses this issue, particularly the role of cylinder liner temperature, which affects both thermal and frictional performance of the piston-cylinder system. The study focuses on the top compression ring whose critical sealing function makes it a major source of frictional power loss and a critical component in guarding against further blow-by of harmful gasses. Such an integrated approach has not hitherto been reported in literature. The study shows that the cylinder liner temperature is critical in mitigating power loss as well as reducing Hydrocarbon (HC) and Nitrogen Oxide (NOx) emissions from the compression ring – cylinder liner conjunction. The results imply the existence of an optimum range for liner working temperature, independent of engine speed (at least in the studied cases) to minimise frictional losses. Combined with the study of NOx and HC emissions, the control of liner temperature can help to mitigate frictional power loss and reduce emissions. [ABSTRACT FROM AUTHOR]

Cellular burning speeds and mass burning rates of premixed syngas/oxidizer/diluent (H 2 /CO/O 2 /He) have been determined at high pressures and temperatures over a wide range of equivalence ratios which are at engine-relevant conditions. Working on high pressure combustion helps to reduce the pollution and increase the energy efficiency in combustion devices. The experimental facilities consisted of two spherical and cylindrical chambers. The spherical chamber, which can withstand high pressures up to 400 atm, was used to collect pressure rise data due to combustion, to calculate cellular burning speed and mass burning rate. For flame structure and instability analysis the cylindrical chamber was used to take pictures of propagating flame using a high speed CMOS camera and a schlieren photography system. A new differential based multi-shell model based on pressure rise data was used to determine the cellular burning speed and mass burning rate. In this paper, cellular burning speed and mass burning rate of H 2 /CO/O 2 /He mixture have been measured for a wide range of equivalence ratios from 0.6 to 2, temperatures from 400 to 750 K and pressures from 2 to 50 atm for three hydrogen concentrations of 5, 10 and 25% in the syngas. The power law correlations for cellular burning speed and mass burning rate were developed as a function of equivalence ratio, temperature and pressure. In this study a new developed parameter, called cellularity factor, which indicates the cell formation effect on flame surface area and burning speed has been introduced. The total flame surface area and cellularity factor for syngas at high pressures and temperatures have been calculated by combining the multi-shell model via the experimental pressure data with free flat flame simulation using detailed chemical mechanism. The results show that the cellularity factor has a positive relation to pressure, equivalence ratio and hydrogen concentration while it has a negative dependency to temperature. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion is one of the routes to have carbon dioxide as the main component of the combustion products stream, enabling carbon capture and sequestration. However, oxy-fuel combustion presents challenges in terms of higher temperatures and flame speed, dictating the need for dilution using entrainment of non-reactive diluents. This need for dilution presents opportunities for developing oxy-fuel combustion using distributed combustion technique. Distributed combustion has been investigated in different configurations and geometries, demonstrating near zero emissions, uniform thermal field and much reduced combustion noise. Key element to achieve distributed combustion is mixture preparation with controlled entrainment of hot reactive species from within the combustor and their subsequent mixing with the fresh reactants to form reduced oxygen concentration-high temperature oxidizer to achieve distributed combustion in the combustor. This necessary entrainment can be beneficial in oxy-fuel combustion as it satisfies the need to utilize CO 2 back into the reaction zone for dilution. In this paper, distributed combustion was investigated with focus on oxy-methane combustion. Experiments were performed on a swirl flame combustor with oxygen concentration ranging between 40 and 21% of the oxidizer mixture. Results showed the possibility of achieving distributed combustion using oxy-fuel combustion. This is demonstrated through OH ∗ chemiluminescence wherein the reaction zone extended to cover larger portion of the combustor as opposed to that of a traditional swirl flame. Emissions measurements showed the elimination of NO emission with low CO emissions, demonstrating the benefits of incorporating distributed combustion concept using oxy-fuel combustion for carbon capture with the product stream containing mostly CO 2 . [ABSTRACT FROM AUTHOR]

A bidirectional (Bi) DC/DC converter is one of the key components in a hybrid energy storage system for electric vehicles and plug-in electric vehicles. Based on the detailed analysis of the losses in the converter, this paper firstly develops a model to theoretically calculate the efficiency of the converter. Then, the influences of temperature, switching frequency, duty cycle and material of switching device on the converter’s efficiency are experimentally investigated. The analysis of the experimental results has shown that (1) The efficiency at the switching frequency of 15 kHz is about 2% higher than that of 25 kHz. (2) The efficiency at 25 °C is similar to that at 85 °C for the MOSFET SiC while the efficiency at 25 °C is 2% higher than that at 85 °C for the IGBT Si for both buck and boost modes. (3) In buck mode, when the duty cycles are decreasing from 66.7%, 50% to 33.33%, the peak efficiencies are also decreasing from 97.6%, 94.5% to 90.3%, respectively. In boost mode, when the duty cycle is increasing from 33.33%, 50% to 75%, the peak efficiency is decreasing from 96.9%, 96.5% to 92.4%, respectively. (4) The developed model can calculate the converter’s efficiency accurately [ABSTRACT FROM AUTHOR]

Sorption thermal energy storage (STES) is perceived as one prospective way of thermal energy storage (TES) owing to the advantages of high energy density, negligible heat loss, flexible working modes and long-term storage capability. Based on STES, this paper exhibits an innovative resorption thermal energy storage (RTES) system, and the experimental prototype is established for heat and refrigeration cogeneration. Working pair of MnCl 2 CaCl 2 NH 3 is chosen, 4.8 kg MnCl 2 and 3.9 kg CaCl 2 impregnated in expanded natural graphite treated with sulfuric acid are filled in two sorption beds respectively. Experimental results indicate that the largest energy storage density reaches 1706 kJ/kg when charging and discharging temperature are 160 °C and 30 °C, respectively. The maximum average cooling power achieves 1.07 kW during discharging phase and corresponding SCP is 27.33 W/kg within the overall cycle period. When charging temperature increases from 135 °C to 160 °C, the energy efficiency of the resorption system for heat and refrigeration cogeneration augments steadily from 0.72 to 0.87 while the exergy efficiency rises slowly from 0.29 to 0.35. [ABSTRACT FROM AUTHOR]

An industrial heat pump can upgrade heat from a low temperature level to a high temperature level with the aid of an external energy source. It has received considerable attention as an efficient means of waste energy recovery in the recent years in China. This paper summarizes the research work done and advances in the application of industrial heat pump systems in China, including advances in refrigerants, multistage system, double-effect absorption system, compression–absorption system, solar assisted system, and chemical heat pump system. Industrial heat pumps used in three industrial fields (drying of wastewater sludge, crude oil heating in oil field, and process heating in printing and dyeing) are discussed in detail. Three basic problems in designing an engineering heat pump system, i.e., selection of the type of heat pump and determination of its capacity, energetic and exergetic analyses of the heat pump, and estimation of investment payback time are discussed in the above three industries, respectively. Further research needs in China on industrial heat pumps are proposed, which may also be beneficial to the international community. [ABSTRACT FROM AUTHOR]

This paper studies the provision of secondary frequency control in electric power systems based on demand response (DR) activation on thermostatically controlled loads (TCLs) and quantifies the computation resource constraints for the control of large TCL population. Since TCLs are fast responsive loads, they represent a suitable alternative to conventional sources for providing such control. An experimental investigation with domestic fridges representing the TCLs was conducted in an islanded power system to evaluate the secondary frequency control. The investigation quantifies the flexibility of household fridge performance in terms of response time and ramp-up rate, as well as the impact on fridge temperature and behaviour after the control period. The experimental results show that TCLs are fast responsive loads for DR activation, with the average control signal response time of 24 s and an equivalent ramping rate of 63% per minute, which could also comply with the requirements for primary frequency control. [ABSTRACT FROM AUTHOR]

This paper provides a systematic approach for quantifying the influence of building size, construction category, climate, occupancy schedule, setpoint, and deadband on HVAC energy consumption in office buildings. Simulating the DOE reference office buildings of three sizes and three construction categories in all United States climate zones, using the EnergyPlus, we conducted several N-way ANOVA analyses to study the interrelationships between setpoints, deadbands and several building related and environment related factors. In summary, daily optimal deadband selection of 0, 1, 2, 4, 5, and 6 K would result in an average energy savings of −70.0%, −34.9%, −13.7%, 9.6%, 16.4%, and 21.2%, respectively, compared to baseline deadline of 3 K. Selecting the daily optimal setpoint in the range of 22.5 ± 1 °C, 22.5 ± 2 °C, and 22.5 ± 3 °C would result in an average savings of 7.5%, 12.7%, and 16.4%, respectively, compared to the baseline setpoint of 22.5 °C. Additionally, we found that when the outdoor temperature is within −20 to 30 °C, the optimal setpoint depends on the building size. We also observed a range of outdoor temperatures (e.g., 9–14 °C for small buildings and 8–11 °C for medium buildings) where the setpoint selection would only slightly influence the energy consumption. However, the choice of setpoints becomes very influential (up to 30% of energy savings) where the outdoor temperatures are slightly outside the mentioned ranges on either direction. The potential savings from selecting daily optimal setpoints in the range of 22.5 ± 3 °C in different climates and for small, medium and large office buildings, would lead to 10.09–37.03%, 11.43–21.01%, and 6.78–11.34% savings, respectively, depending on the climate. [ABSTRACT FROM AUTHOR]

Ground Source Heat Pump (GSHP) systems, if improperly designed may lead to overheating or overcooling of the ground. Good designs ensure properly balanced energy storage through adequately sizing ground-loops. Hybrid systems combine conventional Heating, Ventilating, and Air Conditioning (HVAC) with GSHPs in order to significantly reduce the high installation costs of GSHPs. The hybrid systems are designed in such a way that GSHPs provide the base building energy demands while the conventional HVAC is used only during the peak hours. In general, all buildings can be divided into two main categories: cooling dominant and heating dominant. If a building is cooling dominant, ground temperature increases with time and in heating dominant cases it decreases. A severe ground temperature increase/decrease is referred to as ‘ground fouling’ because it can render the GSHP inoperable, as temperature differences are required to maintain controlled heat flow. This paper compares long-term operation of hybrid and non-hybrid GSHP systems in order to investigate the effectiveness of hybridization at alleviating ‘ground fouling’. A homespun 2D finite-volume model is proposed to study heat transfer in ground coupled heat pump systems and is verified against an analytical solution as well as experimental data. Through simulation of different building types, it is demonstrated that hybridization has potential to reduce ‘ground fouling’ but only in limited cases for which a large portion of the energy demands is being met by the conventional HVAC. [ABSTRACT FROM AUTHOR]

The use of photovoltaic thermal (PVT) technologies enables improvement in the electrical efficiency of a photovoltaic (PV) module by reducing the temperature of the PV module via active waste heat removal. In current PVT systems, the removed heat is mainly used for specific applications, such as water and/or room heating, but their need is intermittent and seasonal. For a more efficient and versatile use of the removed waste heat, we propose a new architecture where the PV module is integrated with a dual-functional electrolyzer that removes the waste heat by active cooling and produces hydrogen via electrolysis. The excess heat from the PV cell is utilized to enhance the reaction kinetics of the electrolysis process (due to an increase in temperature) inside an electrolyzer, which is located below the PV module. In this paper, we used finite-element analysis (FEA) simulations to optimize the geometry and operating conditions of an electrolyzer to maximize overall energetic efficiency and hydrogen production. To evaluate the practical feasibility of the approach, we performed a comprehensive energy analysis of the PVTE system using data from Phoenix, AZ. The energetic efficiency of the proposed PVTE system was calculated to be 56–59%, which is comparable to those of current PVT systems. Additionally, the integration of the electrolyzer with the PV module led to an almost 2.5-fold increase in hydrogen production compared to a stand-alone electrolyzer operated at ambient temperature. The analyzed hybrid approach potentially represents a viable and useful alternative for utilization of waste heat energy from PV cells. This approach may further increase the use of photovoltaic technologies as a renewable energy source. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to considering the effect of seasonal changes in soil temperature on the performance of a horizontal geo heat exchanger. It is different from extant models which consider the seasonal changes in soil temperature by applying a real energy balance on the ground surface. In the new model, the seasonal changes in soil temperature, which are affected by the thermal interaction between the ground and the atmosphere, are expressed as an internal source term. The value of the internal source term depends on the soil density, soil specific heat, soil temperature difference during summer and winter, and time period. The simulation results show that the new approach, which takes into account the effect of periodic soil temperature fluctuations on the performance of the horizontal geo heat exchanger, is valid. The validated model is then used to conduct a sensitivity analysis to investigate the effects of the pipe length, fluid flow rate, inlet fluid temperature, and burial depth on the thermal performance of the horizontal geo heat exchanger. [ABSTRACT FROM AUTHOR]

In order to extend the cycle life of power battery pack within electric vehicle, a phase change material (PCM)/mini-channel coupled power battery thermal management (BTM) system, as well as the three-dimensional battery thermal model, was designed in this paper. The effect of various influencing factors, especially mass flow rate of water, phase change temperature and thermal conductivity of PCM, were investigated numerically. The results showed that the liquid volume fraction of PCM was greatly influenced by the thermal conductivity and the phase change temperature of PCM. The increasing number of channels results in a decrease of the maximum temperature ( T Max ) and maximum temperature difference (Δ T ) of battery packs. The optimal phase change temperature and thermal conductivity of PCM were 308.15 K and 0.6 W m −1 K −1 respectively when the number of channel was eight and the mass flow rate was 8 × 10 −4 kg s −1 . Moreover, a maximum temperature of 320.6 K was predicted for the PCM/mini-channel coupled BTM system, while a maximum temperature of 335.4 K was predicted for the PCM-based BTM system. Additionally, the PCM/mini-channel coupled BTM system presented more effective thermal performance and the research will be a clear indicator for the design of the PCM/liquid coupled BTM system. [ABSTRACT FROM AUTHOR]

This paper presents a systematic technique to select the optimal design target for the heat exchanger network ( HEN ) synthesis by using a new trade-off plot which considers aspects of design, controllability in terms of steady state flexibility and sensitivity analysis, and cost. By selecting the HEN design target according to this guideline, the designer is able to predict the design, operability, and controllability of the designed HEN at the beginning of the synthesis stage. In this study, the HEN design target that needs to be optimized is the value of the minimum temperature difference ( Δ T min ). In traditional HEN synthesis, designers only consider the trade-off between capital and operating costs in selecting the best Δ T min . As a result, the HEN design at the selected Δ T min may not be optimum in terms of steady state controllability. In addition to considering the capital and operating costs, the proposed new method provides additional design insights in terms of energy recovery, operability, controllability (steady state) through the flexibility and sensitivity. The proposed trade-off plot allows designers to choose the most suitable design target either for the purpose of improving a network’s energy recovery and/or controllability. A case study has been applied to test the capability of the new proposed trade-off plot. The results show that Δ T min = 40 °C is the optimal design target to synthesize flexible and operable HEN . [ABSTRACT FROM AUTHOR]

A battery fuel gauge (BFG) helps to extend battery life by tracking the state of charge (SOC) and many other diagnostic features. In this paper, we present an approach to validate the SOC and time-to-shutdown (TTS) estimates of a BFG. Hardware-in-the-loop (HIL) testing under realistic usage scenarios provides a means for BFG algorithm evaluation and provides insights into practical implementation and testing of BFG algorithms in battery management systems. We report the details of a HIL system that was designed to validate the SOC and TTS estimation capability of BFG algorithms; different current load profiles were synthesized to replicate typical battery usage in portable electronic applications; the HIL system is automated with the help of programmable current profiles and is designed to operate at various controlled temperatures; three performance validation metrics are formulated for an objective assessment of SOC and TTS tracking algorithms. The HIL setup and the performance validation metrics are used to evaluate a BFG developed by the authors using three different batteries at temperatures ranging from - 20 ° C to 40 ° C . [ABSTRACT FROM AUTHOR]

High intensity colorless distributed combustion (CDC) provides high efficiency combustion with stable operation and ultra-low emissions. The role of internal entrainment of hot reactive gases requires further investigation in order to obtain minimum requirements for distributed combustion. In this paper, the impact of internal entrainment of reactive gases on the flame behavior and structure is investigated with focus on fostering distributed combustion. A mixture of nitrogen and carbon dioxide was introduced to the air stream prior to mixing with the fuel to simulate the recirculated product gases from within the combustor. Increase dilution with nitrogen or carbon dioxide increased the reaction zone volume to result in uniform distribution of CH ∗ and OH ∗ chemiluminescence signal and uniform equivalence ratio (measured optically). These conditions replaced the normally present blue flame with a uniform almost invisible faint bluish flame. The increased entrainment also decreased NO chemiluminescence significantly for the same amounts of fuel burned. The chemiluminescence data suggested that lowering oxygen concentration from 21% to 15% resulted in improved distributed combustion conditions with the reaction volume occupying most of the combustor. These conditions provide the minimum entrainment requirement and reduction of oxygen concentration for achieving distributed combustion. Results obtained at different equivalence ratios and entrained gas temperatures showed similar behavior at oxygen concentration of 15%. The reaction distribution was further enhanced at lower oxygen concentration (∼11%) with further reduction in pollutants emissions. [ABSTRACT FROM AUTHOR]

The primary goal of this paper is to investigate the catalyst characterization and biodiesel yield of a biodiesel converted from a used cooking oil source via heterogeneous catalysts derived from very rare type of eggshell: ostrich-eggshell (ostrich-eggshell derived CaO). It also aims to compare the performance of CaO catalyst derived from both waste ostrich-eggshell and the conventional chicken-eggshell, and to find the optimum conditions for biodiesel production. The prepared catalysts were then characterized by using XRD, FT-IR, BET, SEM, TGA and CO 2 -TPD. The parametric effects on the biodiesel production, such as catalyst concentration, molar ratio of methanol to oil, reaction temperature, reaction time, speed and reusability of the catalyst were investigated. The experimental result showed that 1.5 wt.% catalyst, 12:1 M ratio of methanol to oil, 65 °C reaction temperature, 2 h reaction time with speed of 250 rpm gave the best results. It was found that the ostrich-eggshell derived CaO catalyst shows higher surface area, higher basicity and smaller particle size. The maximum biodiesel yield is 96% and 94% for calcined ostrich-eggshell and chicken-eggshell, respectively. The CaO catalyst derived from waste calcined ostrich and chicken-eggshell maintained a good catalytic activity even after being repeatedly used for 5 cycles with yield around 70%, which implies potential saving and affordable biodiesel production possibilities. [ABSTRACT FROM AUTHOR]

Chemical Looping Combustion (CLC) is conventionally carried out in circulating fluidized bed systems involving various kinds of fluidized beds and solid handling devices. Scale-up of these systems is a research and development challenge associated with various risks and uncertainties. Gas bypassing, poor gas–solid contact and poor performance of solid circulation control devices are among the major considerations in this regard. This paper presents impacts of temperature on the fluidization properties in CLC application. Impacts of temperature on the minimum fluidization velocity and the onset of turbulent regime are studied in various temperatures up to 900 °C. Increase of temperature decreases the minimum fluidization velocity and increases the onset of transition to turbulent regime. Impact of size and temperature on the performance of pneumatic valves (L-valve and loop-seal) are investigated using valves in a range of 2–24 cm in a temperature range of 25–750 °C. Geldart group B particles of 100–300 μm and density of 2600–4750 kg/m 3 are used in these experimental tests. [ABSTRACT FROM AUTHOR]

Current temperature levels in European district heating networks are still too high with respect to future conditions as customer heat demands decrease and new possible heat source options emerge. A considerable reduction of temperature levels can be accomplished by eliminating current faults in substations and customer heating systems. These faults do not receive proper attention today, because neither substations nor customer heating systems are centrally supervised. The focus of this paper has been to identify these faults by annual series of hourly meter readings obtained from automatic meter reading systems at 135 substations in two Swedish district heating systems. Based on threshold methods, various faults were identified in 74% of the substations. The identified faults were divided into three different fault groups: Unsuitable heat load pattern, low average annual temperature difference, and poor substation control. The most important conclusion from this early study of big data volumes is that automatic meter reading systems can provide proactive fault detection by continuous commissioning of district heating substations in the future. A complete reduction of current faults corresponds to approximately half the required reduction of the current temperature levels in the effort toward future low-temperature district heating networks. [ABSTRACT FROM AUTHOR]

In this paper, performances of some zeotropic mixtures in Organic Rankine Cycle (ORC) have been assessed and evaluated for potential of utilizing the low-temperature and -caloric geothermal water. The options of single power generation and Combined Heat and Power (CHP) production through the common series and parallel configurations have been considered. The possible optimization of these applications when using the mixtures opposite pure fluids is the main objective and has been largely discussed. To reach this, the maximal power output level has been mainly focused as evaluation factor for variety of the heat source temperatures (up to 120°) and heat consumer parameters. The results showed that in case of stand-alone ORC the mixtures: R438A, R422A and R22M are more efficient than the pure fluids advised and can enhance the power productivity and geothermal water utilization at the sources’ temperatures 80, 100 and 120 °C, respectively. R407A and R22D also offer attractive outputs at source temperatures of 80 °C and 100 °C, respectively. Furthermore, compared to R601a in the series CHP option using R22M in the parallel CHP circuit at heat source temperature 120 °C is more feasible and enables considerable promotions for a wide field of conditions. Similarly, R422A at source temperature 100 °C is also energetically favorable, but only at conditions matching the low till moderate heat loads or high supply temperatures. Finally, R22M and R422A are always much better than the pure R227ea in the parallel ORC–CHP system within this study. [ABSTRACT FROM AUTHOR]

The organic Rankine cycle (ORC) is a promising technology for heat recovery. However, evaporator leads to the highest irreversible loss and results in reducing cycle efficiency. In this paper, the heat source was segmented into two temperature ranges, which provides the possibility of two-stage evaporation. Based on cycle configuration, parallel two-stage organic Rankine cycle (PTORC) and series two-stage organic Rankine cycle (STORC) were put forward. The objective is to evaluate system performances, thereby elucidating their respective availability. Geothermal water inlet temperature (GWIT) ranges from 90 to 120 °C, with R245fa as the working fluid. The ratio of net power output to the total thermal conductance was chosen as the objective function. The results show that PTORC and STORC are significantly influenced by intermediate geothermal water temperature (IGWT) and evaporating temperatures. PTORC and STORC could evidently reduce the irreversible loss, and STORC is more significant. PTORC and STORC can output more net power, depending on cycle configuration and GWIT. STORC enhances the net power output with GWIT, whereas PTORC is just the opposite. The total thermal conductance of PTORC and STORC are almost equal with that of ORC. STORC presents more excellent system performance and deserves to be popularized in engineering applications. [ABSTRACT FROM AUTHOR]

A novel linear Fresnel reflector which employs the evacuated tube, CPC secondary reflector, and uses molten salt as the heat transfer fluid (HTF) was designed and studied in this paper. A 3D optical model was developed to simulate the radiation transmission within the system with Monte Carlo Ray Tracing (MCRT) method. Based on the model, firstly, the optical performance of the systems using cylindrical and parabolic mirrors was compared. Then the local solar flux distribution on the absorber surface and the optical efficiency were computed. Then the effects of the slope error, time and location, etc. were investigated. Finally, the thermal performance was investigated by coupling the MCRT with the Finite Volume Method (FVM). The optical simulation results indicate that the system with optimized cylindrical mirrors can achieve nearly the same performance as the one with parabolic mirrors. The solar flux distribution on the absorber exhibits a non-uniform characteristic which can be improved by using mirrors with proper slope error. The instantaneous optical efficiency of 65.0% at normal incidence and the annual mean optical efficiency which ranges between 55.2% and 34.8% from the equator to N50° can be achieved. The numerical results indicate that the temperature profiles on the absorber follow the non-uniform solar flux. The collector efficiencies are all above 46.0% under the studied conditions. Both the thermal efficiency and the collector efficiency increase with decreasing salt temperature and with increasing radiation. These results suggest that the introduced system is a feasible choice for using molten salt as the HTF in Fresnel system. [ABSTRACT FROM AUTHOR]