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This paper presents a new methodology that allows to define a 100% renewable smart energy system in a sustainable manner. The authors integrate the EnergyPlan with a mathematical model that analyzes the energy system from an exergetic point of view taking into account the exergy of the whole energy system and its components. Once multiple scenarios are obtained by EnergyPLAN, the exergetic model identifies the scenario characterized by the highest exergetic efficiency and the lowest energy wasting. This approach is a novelty since the “exergetic” optimization criterion coupled with EnergyPLAN software has never been utilized. Since the best energy system could not be economically attractive, this methodology might support Municipalities in setting up focused incentives to make the sustainable solutions the most cost effective too. The authors present a case study by applying the new methodology to the city of Pompeii. The results show that the best solution provides 21.0 MWe capacity of PV plant, integrated to 8.10 MWe of CHP plant. Due to a high value of critical excess electricity production, 10 MWe heat pumps must be installed. Finally, a solar thermal plant is installed. The proposed system could be only realized if new incentives are provided.

The paper analyzes heat transfer between an oscillating compressible fluid and solid to evaluate the influence of finite thermal capacity on the heat exchanged between these media. This type of problem is often studied in porous media applications by assuming the solid to have its surface at a constant temperature. When this hypothesis fails, in the frequency domain, the analytical solutions of the thermal field involve a complex dimensionless parameter known in the literature as e s . It was introduced in thermo-acoustic applications to model the solid properties of the porous core. In this work, the parameter is revisited by deriving an analytical formulation valid for arbitrarily shaped channels of porous materials, and a physical interpretation of the parameter is proposed in terms of fluid and solid entropy oscillation. CFD-based simulations of the thermal coupling between solid and fluid on three different simplified geometries of porous material have been conducted to confirm this physical interpretation, by comparing numerical and analytical data. Furthermore, from a numerical point of view, the parameter e s has been written as the inverse of a dimensionless Robin boundary condition. In this work, it is verified that the latter can be adopted at the fluid-solid interfaces to reproduce the thermal effects of the solid material, without numerically simulating it, both in frequency and time domain.

Waste vegetable oil is generated from different sources, such as domestic, commercial and industrial activities, and it requires proper management. Due to the increase in the generation of waste vegetable oil, concern for its management has intensified. The most common management option for waste vegetable oil is the conversion into biodiesel, which improves the chemical-physical characteristics of raw waste vegetable oil for its use but is characterized by significant energy consumption and environmental impact. Therefore, straight waste vegetable oil as fuel, after mechanical pre-treatments and with suitable operational strategy, is suggested in the available literature. In this work, waste vegetable oil from the separate collection is proposed as a source to fuel a combined heat and power unit producing energy for wastewater and sludge treatment plants, which is high energy-demanding. The operation of the combined heat and power unit is analyzed considering data from an experimental campaign carried out to investigate the performance of internal combustion engines powered by waste vegetable oil. Such experimental data are used to carry out the feasibility analysis of a combined heat and power system for an actual wastewater treatment plant located in the Campania region, southern Italy. The system appears to be economically feasible with a simple payback around 3.44 years, a net present value higher than 19.0 M€ and an interest rate of return of 26.7%. Moreover, it produces 70.0% less equivalent carbon dioxide emissions, with respect to a similar system powered by fossil fuels. Therefore, waste vegetable oil as a locally available and renewable energy source may contribute to realize smart and resilient communities, since it improves securing domestic energy supply and waste valorization.

Domestic Vertical Axis Wind Turbines (VAWT) are able to operate also when the wind speed is low and can be installed in the open spaces of housing areas. The Darrieus turbine is the most promising since it is characterized by higher efficiency, even if for applications at higher wind speeds with respect to Savonius VAWTs. Several researchers try to optimize the aerodynamics of the Darrieus rotors, allowing wind turbines to start rotation even in the presence of low wind speeds. In this paper the authors propose a numerical investigation of the flow field around a 1:4 scaled model of a pair of blades installed on an innovative Darrieus-type VAWT. A Reynolds Averaged Navier-Stokes-based CFD model was validated on the basis of the wind tunnel data, and the scaled turbine performance was analysed by numerically evaluating the effect of different geometric configurations and rotation angles on the turbine torque coefficients. The results of the simulations confirmed the capabilities of the proposed configuration to give valuable performance even for low wind speeds.

The valorization of residual biomass plays today a decisive role in the concept of &ldquo, circular economy&rdquo, according to which each waste material must be reused to its maximum extent. The collection and energy valorization at the local level of biomass from forest management practices and wildfire prevention cutting can be settled in protected areas to contribute to local decarbonization, by removing power generation from fossil fuels. Despite the evident advantages of bioenergy systems, several problems still hinder their diffusion, such as the need to assure their reliability by extending the operating range with materials of different origin. The Italian project &ldquo, INNOVARE&mdash, Innovative plants for distributed poly-generation by residual biomass&rdquo, funded by the Italian Ministry of Economic Development (MISE), has the main scope of improving micro-cogeneration technologies fueled by biomass. A micro-combined heat and power (mCHP) unit was chosen as a case study to discuss pros and cons of biomass-powered cogeneration within a national park, especially due to its flexibility of use. The availability of local biomasses (woodchips, olive milling residuals) was established by studying the agro-industrial production and by identifying forest areas to be properly managed through an approach using a satellite location system based on the microwave technology. A detailed synergic numerical and experimental characterization of the selected cogeneration system was performed in order to identify its main inefficiencies. Improvements of its operation were optimized by acting on the engine control strategy and by also adding a post-treatment system on the engine exhaust gas line. Overall, the electrical output was increased by up to 6% using the correct spark timing, and pollutant emissions were reduced well below the limits allowed by legislation by working with a lean mixture and by adopting an oxidizing catalyst. Finally, the global efficiency of the system increased from 45.8% to 63.2%. The right blending of different biomasses led to an important improvement of the reliability of the entire plant despite using an agrifood residual, such as olive pomace. It was demonstrated that the use of this biomass is feasible if its maximum mass percentage in a wood matrix mixture does not exceed 25%. The project was concluded with a real operation demonstration within a national park in Southern Italy by replacing a diesel genset with the analyzed and improved biomass-powered plant and by proving a decisive improvement of air quality in the real environment during exercise.

The new standards on energy saving for new and existing buildings have animated both researchers and technicians in recent years, aiming at reducing the dependence on fossil fuels, improving indoor comfort, and systems efficiency. In this scenario, special attention must be paid to historical buildings that need to preserve their key testimonial heritage within the society. This paper describes the design and realization stages of a pilot system based on a ground-coupled heat pump, operating both in heating and cooling modes, installed in the monumental site of Saints Marcellino and Festo (SM&F), in Naples, Southern Italy. This study aims to demonstrate that low-enthalpy geothermal systems can be employed as energy retrofit applications in buildings of historical, artistic, and cultural interest and, at the same time, to prove that the use of this technology allows achieving the objectives, set at global level by the current regulations, and requiring a reduction of carbon dioxide emissions (tCO2) of 53% compared to technology using fossil fuels.

The present paper describes an experimental characterisation of a biomass powered micro-cogeneration system based on the coupling between a gasifier and an internal combustion engine. The ECO 20 unit is sized to deliver a maximum electrical and thermal power of 20 kWe and 40 kWth, respectively. In order to highlight possible inefficiencies along the biomass-to-energy conversion chain, the global energy balance of the system under real working conditions is derived. Ultimate and proximate analyses of the processed biomass are performed, accompanied by temperature and mass flow rate measurements and gas chromatograph characterization of collected samples of the produced syngas. The greatest inefficiency is found in the gasification section with a value of the cold gas efficiency in the range of 57–60%. The low quality of the syngas (lower heating value equal to 3731 kJ/Nm3) affects the engine combustion efficiency, hence its electrical efficiency that does not exceed 22.5%. The global electrical efficiency of the plant is equal to about 13.5%. As a further analysis, waste heat recovery is considered under different conditions by decreasing the temperature of the water flowing in the secondary circuit from 68.35 °C to 20.50 °C for the use of the provided thermal energy. This determines an increase of the thermal efficiency of the engine from 11.3% to 56.2%, while the global thermal efficiency increases from 6.46% to 33.72%. A feature of the ECO 20 system is the cooling of the syngas delivered to the engine by its same cooling water, for a considerable advantage on volumetric efficiency with respect to other analogous systems, also in the cases the thermal power is not utilised.

The main challenges of wastewater treatment plants are high-energy demand and sludge disposal. A hybrid system for sewage sludge drying is proposed in this work to face both these issues. The developed layout is based on the integration of two renewable energy sources, biogas from anaerobic digestion of sludge and solar energy in order to increase sustainability and energy self-sufficiency of the plant. Biogas is used to fuel a combined heat and power system and solar energy is exploited through a parabolic trough collector field. Electrical energy produced by the combined heat and power is used to cover the plant demand, whereas thermal energy coming from the combined heat and power unit and solar field is employed to run an anaerobic digestion process and for thermal drying of the residual sludge. The considered case study is based on data collected for an existing wastewater treatment plant. The proposed system is studied through data obtained from the scientific literature, suppliers of the considered equipment and properly developed sub-models of the various components, to assess its feasibility and the overall energy, environmental and economic performance. The system is dynamically simulated and daily, weekly and yearly results are presented. For the considered desiccant flow temperatures, the solar collector field achieves a thermal efficiency of about 56.0%, while for the combined heat and power unit it is about 44.0%, which is slightly higher than the nominal one, due to the preheating of combined heat and power unit intake air. The integration of solar energy with the combined heat and power system leads to a primary energy saving of about 14.6% with respect to the existing plant, where the sludge is not digested and neither thermally dried. The economic analysis shows that the Simple Pay Back period of the system is less than 3.40 years.

In Operating Rooms (OR), the transport of Colony-Forming Units (CFU) can generate surgical site infections in patients and, as a consequence, CFU must be properly evacuated from the surgical site. Moreover, Fine Particles (FP) and UltraFine Particles (UFP) can be generated during surgeries by cutting and cauterizing surgical tools, with consequent effects on the health of patients and medical staff. Therefore, indoor air quality, comfort and safety conditions in OR must take into account CFU, FP and UFP concentrations. Due to the importance of the topic, the authors have carried out a review of the experimental, numerical and experimental-numerical combined works available in the literature, that analyse generation, diffusion and deposition of CFU, FP and UFP in ORs. Numerical studies have been majorly focused on the simulation of CFU using computational fluid dynamics, in order to model the motion inside ORs and the evaluation of factors that influence it. Experimental studies mainly deal with the analysis of particles and CFU motion and deposition. Based on the present analysis, it appears that more research effort is needed to analyse FP and UFP in ORs. Technical standards and national laws have been reviewed in order to analyse the constraints commonly used in the design and operation of ORs and ventilation systems, such as to find the technical aspects that are not yet properly considered.

Biomass gasification for the release of a syngas and its use in combined heat and power (CHP) generation systems are attracting realities in the European market, due to the perspective to provide energy to remote districts by using local renewable sources, as residuals of forest practices or agro-food industries. The syngas produced from biomass gasification is a feasible alternative to traditional fuels in internal combustion engines at the micro and small power scales, although the quality of the produced gas is poorer in terms of calorific value and laminar flame speed. Therefore, as a direct consequence, proper modifications and optimizations of engines are needed to enhance energy efficiency and reduce the environmental impact. In the present work, a numerical model for the simulation of a compression ignition engine fueled in the dual-fuel mode with syngas and biodiesel is presented. The aim is to highlight the main influences on the combustion process related to the use of syngas and the effects of different biomass moisture contents on power output and main pollutants emission. The used extended coherent flamelet model for turbulent combustion is preliminary validated on the basis of experimental data of engine pressure cycles collected under only biodiesel fueling.

Geothermal energy piles allow both heating and cooling of buildings by using the ground as a renewable energy source. In this paper, the authors propose an efficient numerical model, based on a mixed 1D-3D approach, to analyze the heat transfer process in the coupled system probe-pile-ground. The numerical model developed allows to simulate the three-dimensional heat transfer in the pile and in the surrounding ground, and the one-dimensional heat and fluid flow inside the probe, with consequent reduction of computational time with respect to full 3D models. The numerical model has been employed to investigate the heat transfer performance of different configurations of energy piles, analyzing the effects of both design and operating parameters, such as diameter of probe and pile, properties of the employed materials, flow rate and probe configurations (U-tube, Double U-tubes, Triple U-tubes, spiral coil). The obtained results show that a proper analysis of the system based on the chosen parameters is necessary.

Heating, ventilation, and air conditioning (HVAC) systems must be specifically designed for operating theaters in hospitals in order to reduce the risk of infections and maintain adequate thermo-hy...

Small and medium size district heating networks have seen some spread over the last two decades, especially in cities which are not supplied by natural gas grids. In this paper, the authors investigate the energetic feasibility of a small district heating network feeding two schools in a city of Southern Italy (Mondragone). In particular, the district heating is powered by a low-temperature geothermal fluid pumped from a well located 2.1 km away from the city center. Geothermal fluid has a temperature of 34 degrees C and a flow rate of 6 l/s. The buildings have been rehabilitated by an energy point of view and are equipped of low-temperature fan-coils in order to ensure their compatibility with the 4th generation district heating system. Energy analysis were conducted through the implementation of transient simulation model in TRNSYS environment. The feasibility of two configurations of the system is compared: the first, with one heat pump installed nearby the geothermal well feeding the grid, and the second one with the heat pumps installed in each building substation. Transient simulations results show that the first configuration is energetically less efficient than the second one due to the high thermal losses (55% of the total consumption) of the district supply pipes.

The need to address the global challenge of using clean energy, mitigating climatic changes and favoring sustainable development, has promoted the diffusion of new technologies for the use of renewable energy resources. Geothermal technologies can generate electricity and/or heating and cooling while producing very low levels Green House Gas (GHG) emissions and therefore play an important role in realizing these targets. In particular, low temperature applications have known a great development over the last years, thanks to the larger availability, compared to high temperature traditional ones, and to the increasing cooling demand that is also related to the global warming. A sustainable and profitable use of low enthalpy geothermal resources is strictly related to a correct analysis of ground thermal response to energy extraction/injection: in fact, sizing methodologies and optimization strategies are based on a balance of plant׳s energy demand and predictions of ground thermal variations due to these energy requirements. Therefore, an accurate mathematical modeling of thermo-dynamic behavior of the ground is fundamental for optimal design of geothermal plants for two reasons: it is the basis for the estimation of ground thermo-physical properties from the analysis of the Thermal Response Test, and it is essential in order to predict hour by hour (or short term) responses of the ground to continuously changing energy loads and therefore to estimate system energy consumption. Besides, there is a great interest in modeling thermo-fluid dynamic phenomena which occur in geothermal wells and geothermal heat exchangers as these can significantly affect the performance of the whole system. In this work, the numerical models that are currently available for simulation of the thermo-fluid dynamic phenomena occurring in low enthalpy geothermal energy systems are analyzed, underlying the main differences and recent advances in modeling approaches.

The highest economic and environmental costs of wastewater treatment plants are related to waste disposal, which is mainly sludge disposal, and energy supply. Such challenges are even more critical in islands, where there are many environmental, landscape, and geographical constraints that make the use of conventional technologies difficult. For this reason, a geothermal energy system for wastewater and sludge treatment, and power production is proposed. Such a system is assessed through an exergoeconomic analysis, performed in Engineering Equation Solver environment, that allows determining the exergoeconomic costs of geo-fluid, electricity production, and sludge drying. The sensitivity analyses, carried out to assess the effect of several design parameters, have highlighted that the geothermal source temperature significantly affects the system operation and consequently the exergoeconomic costs, which range 77–95 c€/kWhex for sludge treatment and between 4.8 and 6.6c€/kWhex for electricity production. Finally, multivariate optimization has been carried out to find the conditions that minimize the exergoeconomic costs of the system. The total hourly exergoeconomic cost of the system products, namely sludge and electricity, is minimized when the geothermal source temperature is equal to 110 °C and the 58.91% of the desiccant flow is recycled. Overall, this study outlines that an exergy-based economic analysis is fundamental to assess the economic viability of innovative integrated solutions based on renewables.

Waste management and energy production are becoming critical issues in geographically disadvantaged areas, like small islands. For waste disposal the most common strategy is shipping to the mainland, due to the scarcity of land and local suitable treatments. Electricity generation is based on the importation of fossil fuels for local production, due to the lack of connections with continental energy networks. Both, waste shipping and fuels importation determine strong dependence on the mainland, as well as high economic and environmental cost for small islands. Therefore, using local renewable energy sources is extremely attracting. In this work, geothermal energy is considered for thermal drying of wastewater sludge and electricity supply of the whole wastewater treatment. The system is analysed for the case study of Pantelleria, a small island in Southern Italy, where sludge is currently dewatered to a final water content of 70–80%, and then shipped to mainland. The proposed system decreases wastewater sludge to be transported and disposed by 73.3%. Its profitability is demonstrated by several economic indicators, showing a Simple Payback time equal to 8.34 years and a Net Present Value of 502 k€. In addition, a sensitivity analysis for the main parameters affecting plant operation is carried out.

This paper presents an economic and energy feasibility analysis of a renewable energy system for a small city in southern Italy to convert it to zero greenhouse gas city by 2030. The proposed energy infrastructure utilises different technologies: wind turbine, photovoltaic panels and biogas cogeneration plants to produce electric energy, and thermal solar panels, cogeneration and heat pumps to meet the thermal energy demand of the city. The electrification of transport sector is also considered. The whole city energy system is analysed by the EnergyPLAN software to evaluate streams combination and potential synergies between the different sectors. In order to improve the analysis, PhotoVoltaic technology has been simulated in TRNSYS environment, to obtain detailed prediction of this component of the energy infrastructure. The system behaviour was analysed considering different time bases: daily, weekly and yearly. The EnergyPLAN outputs include the aggregated yearly production and demands of all modelled energy conversion systems, as well as hourly values useful to identify the measures to make Altavilla Silentina nearly zero carbon city. Every measure identified becomes a new input in EnergyPLAN to evaluate its effect on city energy balance. The economic analysis has been performed to evaluate the electricity and thermal energy costs.

Purpose This paper aims to provide a comprehensive literature review on modelling electro-osmotic flow in porous media. Design/methodology/approach Modelling electro-osmosis in fluid systems without solid particles has been first introduced. Then, after a brief description of the existing approaches for porous media modelling, electro-osmotic flow in porous media has been considered by analysing the main contributions to the development of this topic. Findings The analysis of literature has highlighted the absence of a universal model to analyse electro-osmosis in porous media, whereas many different methods and assumptions are used. Originality/value For the first time, the existing approaches for modelling electro-osmotic flow in porous have been collected and analysed to provide detailed indications for future works concerning this topic.

The authors would like to add some corrections to the published paper “An integrated system for sewage sludge drying through solar energy and a combined heat and power unit fuelled by biogas”, Energy Conversion and Management, Volume 171, 1 September 2018, Pages 587-603. The corrections provided here do not affect main findings and conclusions of the original paper.

Direct use of Waste Vegetable Oil (WVO) as fuel is very attractive to reduce fossil fuels utilization and increase sustainability. WVO incorrect disposal causes serious damages to sewage systems and wastewater treatment plants. Moreover, if WVO reaches natural ecosystems, such as rivers, aquifers or subsoil, the environmental consequences can be severe. In recent years, the main reuse of WVO has been in biodiesel production, which is remunerative under current tax allowance policies. However, biodiesel production requires complex physical–chemical treatments, while direct use of WVO just needs mechanical treatment. As a consequence, WVO direct use in energy conversion systems lower the impact, from the economic, energetic and environmental points of view, with respect to biodiesel production. Moreover, as concerns the environmental impact, it should be considered that the direct use of WVO as fuel produces less polluting emissions when considering the whole life cycle: carbon dioxide produced during combustion, in fact, can be partially absorbed by crops used for oil production. This paper presents a comprehensive review of the work done to evaluate the effects of direct use of WVO in internal combustion engines. Many authors have shown the advantages of using straight vegetable oils or biodiesel produced from WVO as fuel, while the benefits of WVO direct use have not yet been clearly presented. The available literature still presents few papers about this topic, therefore also the use of vegetable oil, that presents physical chemical characteristics very similar to those of WVO, has been taken into account. After a brief introduction, the characteristics of WVO most affecting its use as fuel have been studied. Then several applications of WVO direct use in internal combustion engines and the available fuel supply technologies have been considered. Finally, the energetic performance and the pollutant emissions reported in literature have been deeply analyzed.

Worldwide escalating energy consumption of recent years, due to the earth population growth and the spreading of industrialization, has resulted in an increased concern about the environmental impact of energy conversion systems. Heavy exploitation and extensive use of fossil fuels have indeed also led to envisage their foreseeable depletion, thus opening the way to the use of alternative fuels as biomass. Among thermo-chemical treatments of biomass, gasification is particularly attractive for its release of syngas (or producer gas), suitable of being used in various combustion systems, including internal combustion engines. In principle, biomass contaminants and heavy hydrocarbons can be removed during syngas cleaning, before the actual combustion process, thus leading to an overall cleaner conversion process. At present, demonstrating operational feasibility and effectiveness of gasification technologies and proving long term sustainability, also through the enhancement of fuel flexibility, are recognized as key elements for the development and market diffusion of biomass energy systems. In fact, although gasification has been known for a long time, its control has long requested serious efforts by researchers and manufacturers. Nowadays, new perspectives are imaginable thanks to the use of simulation tools that may reveal particularly useful to improve gasification efficiency and increase the quality of the producer gas. In recent years, several numerical models have been indeed proposed to characterise and predict such a complex process, where drying, pyrolysis, gasification and combustion take place simultaneously. This article presents a general overview of gasification models available, with emphasis on those based on the stoichiometric method. Although this last may seem too restrictive under some circumstances, equilibrium models are useful to predict the maximum yield attainable by a reagent system, since they reproduce an ideal gasification performance. Due to their simplicity and the reduced computational time, these models are suitable of being employed in a first stage of an analysis or within optimization procedures, where the influence of a number of parameters has to be investigated or a choice of the optimal biomass to be treated for a certain scope is to be made.

This paper presents a numerical procedure for the simulation of heat and fluid flow in a heat exchange system for exploitation of low enthalpy geothermal reservoirs. The authors employ for the first time the generalised model for the mathematical description of heat and fluid flow through saturated porous media in order to study down-hole heat exchanger, well and aquifer, using a single domain approach. Steady state operation of the system is considered and the results obtained are validated against experimental data collected for a geothermal convector prototype installed in an existing geothermal well on the island of Ischia in southern Italy. The comparison shows that the proposed procedure can be successfully used for the simulation of this type of problems, and represents an excellent tool for down-hole heat exchangers optimization. The results of the present model are employed here to analyse the approximate boundary conditions that were previously developed for the simulation of a simplified aquifer model.

The interest of calculating the effects of thermal bridges in buildings energy consumption is growing, due to recent energy saving regulations applied in different countries. The widespread use of insulating materials to reduce energy requirements of buildings, often employed for intermediate insulation of the building envelope, makes thermal bridges a crucial point in the energy analysis of building envelopes. Furthermore, heat losses through thermal bridges often lead to building pathologies due to moisture condensation. Therefore, thermal bridges need to be correctly characterized in the building design stage in order to reduce heat losses and avoid materials degradation. The authors numerically simulate, by using finite elements, the steady-state and dynamic three-dimensional (3D) heat and vapor transport in inhomogeneous thermal bridges and building envelopes. The aim of the present work is to show the importance of taking into account the presence of inhomogeneities (i.e., metal stud) in building materials for the calculation of actual heat losses and water condensation in 3D thermal bridges. The obtained heat transfer results are verified against the reference data of the technical standard UNI EN ISO 10211. The proposed microscopic approach is essential to calculate the actual heat losses of three-dimensional thermal bridges and building envelopes and to overcome condensation problems.

The operation of waste-to-energy plants based on incineration inevitably implies the production of greenhouse gases and the emission of harmful species to the human health. The European Directive on the construction and operation of incineration plants fixes strict rules concerning the temperature and the residence time of the combustion products within the combustion chamber. Indeed, acting directly on the combustion process to limit the emission of pollutants at the source is a well assessed alternative to post combustion technologies. The peculiar characteristics of the treated waste or Refuse Derived Fuel (RDF) may also cause problems to the long term operation of the burner, as in the case of deposits formation due to the presence of ash. The ash particles, entrained in the in-chamber flow, may stick on the walls even at relatively low temperatures, thus modifying the heat transfer coefficient, reducing the system efficiency and imposing frequent stops for overhauling. Therefore, the characterization of the phenomena occurring in a RDF combustor through experimental and/or numerical techniques is strongly demanded for assisting its optimal maintenance. This work presents the assessment and validation of a Computational Fluid Dynamics (CFD) model of a real scale waste-to-energy plant operating in central Italy, which couples the thermo-chemical conversion of the solid RDF to the gaseous combustion of the released syngas. The model allows to characterise into detail the temperature and residence time of the combustion products, for the verification of the fulfilment of the existing regulation for dioxin formation in incineration plants.

This paper aims to present detailed numerical solutions of natural convection flow of contaminated air and water along the vertical wavy frustum of a cone. This investigation is particularly conducted to characterize the flow behavior of spherical particles suspended in radiating Newtonian liquids. The governing equations are converted into dimensionless equations by using a set of suitable continuous transformations and solved through the implicit finite difference method. Comprehensive flow formations of the gas and particle phases are given with the aim to predict the enhancement of heat transport across the heated wavy frustum cone. It is recorded that the air–metal mixture can promote the rate of heat transfer drastically whereas water–metal mixture contributes a little in this regard.

Wastewater treatment plants are high energy-consuming systems, and their electric energy consumption contributes to 25–30% of the total operating costs. A significant part of thermal energy is needed for management of the sludge produced during the process. Sludge drying by Combined Heat and Power (CHP) systems is attractive to obtain substantial economic and energy savings, especially if all the waste heat can be used. Since biogas production, where available, is insufficient for sludge drying, the direct use of the exhaust gases of a CHP system fuelled with syngas derived from sludge gasification and waste vegetable oil, is proposed. The profitability of this system is comparable with that of the systems currently employed in advanced wastewater treatment plants. The economic convenience derives from the reduction of sludge to be disposed and the overall energy saving in the plant. The simple payback of the proposed system, equal to 6.8 years, is only one year higher than that found for of an analogue conventional system, while the Net Present Value is 30% higher than that calculated for a conventional system. In terms of environmental impact, the layout presented is more efficient as biomass-derived fuels are used instead of fossil fuels.

The need for environmental friendly energy conversion systems has been increasing over the last decade, also in relation to the world’s growth in energy demand. High Temperature Solid Oxide Fuel Cells (HT-SOFCs) represent a very promising technology since they can be directly fed with traditional fuels, other than hydrogen, and offer the possibility of cogeneration. Furthermore, the low dependence of their efficiency on the system size makes them suitable for distributed micro-scale energy conversion. However, SOFCs are still today in a development stage, and a great research effort is still required before commercialization becomes a reality. From this point of view, on-site experiments are crucial in order to deeply understand HT-SOFCs based cogeneration modules’ performance and applicability to residential energy sector. Even though some work is appearing in the recent literature, very often experimental data are not accompanied by measurement uncertainties analysis, which is an important aspect of any experimental campaign. In the present paper, on the basis of the on-board instruments metrological characteristics declared by the manufacturer, the a-priori uncertainty analysis of a cogenerative module based on HT-SOFCs is presented. Therefore, for each performance parameter, the value of the related uncertainty has been calculated. In the authors’ opinion, these quantities are very important for a proper evaluation of the performance of HT-SOFCs based cogeneration units and also for the essential validation of results obtained from fuel cells modeling.

In this paper, the authors present an efficient three-dimensional algorithm, based on the fully explicit matrix inversion free finite element version of the Characteristic Based Split (CBS) scheme, and apply it for the first time to the simulation of complex thermo-fluid-dynamic problems in domains containing simultaneously a fluid and a porous layer. The stability analysis recently developed for the two-dimensional version of the algorithm is here extended to the three-dimensional version. Unstructured grids have been successfully employed to solve complex interface problems. The present code produces an effective solution for complex 3D problems, and does not require large computing resources. The advantages deriving from the algorithm’s stability, the use of unstructured meshes and the low computing requirements make the present three-dimensional procedure a powerful and flexible tool for efficient modeling of real life problems. The present 3D code is used to solve both forced and natural convection in partially porous domains.

As the interest for energy recovery from waste incineration has increased over the years, concern for the impact such processes have on the environment has also grown. To reduce such an impact, the legislation enforced in Italy and Europe imposes important restrictions on the temperature of the exhausts in the combustion chamber, which must be kept above certain values depending on the type of waste that is being incinerated, for a given period of time. Such conditions can be rather difficult and certainly very expensive to monitor with acceptable accuracy. In this work, a numerical approach is presented for modelling waste combustion in a full scale incineration plant. Both solid and gas phase reactions are considered. Various modes of heat and mass transfer between the waste bed, the air and the combustion products are taken into account, as well as radiation from the combustion chamber walls and the combustion products. The temperature distribution in the combustion chamber is obtained considering either forced or mixed convection. It is therefore shown that neglecting buoyancy effects may lead to appreciable errors. Verification of the code performance is based on comparison with the results of an experimental campaign at a full scale plant in Italy.

The interest for energy recovery from waste incineration has increased over the years, in order to reduce the number of landfills and produce electricity and heat. At the same time, concern for the impact such processes have on the environment has also grown, and to reduce such an impact, new legislation is being enforced in Europe and Italy. In particular, important restrictions are imposed on the temperature of the exhausts in the combustion chamber, which must be kept above certain values for a given period of time, depending on the type of waste that is being incinerated. Such conditions can be rather difficult and certainly very expensive to monitor with acceptable accuracy. For this reason, in practical applications the temperature of the exhausts in the chamber is usually calculated through semi-empirical and approximate models that relate the temperatures in different sections of the chamber. In this work, the authors present a numerical approach for the analysis of such models that can be used to quantify the uncertainty on this type of measurement due to the common approximations used in full scale incineration plants. The analysis is based on the CFD simulation of the thermo-fluid-dynamic field in the combustion chamber of a full scale plant in Italy, whose results have verified based on a comparison with the data collected during an experimental campaign.Copyright © 2008 by ASME

Generally, flow conditioner efficiency is experimentally evaluated on the basis of the effects that these devices produce on a particular type of flowmeter. This approach, beside being very expensive, has certainly obstructed the development of a general theory and consequently the optimal design of flow conditioners. The present paper presents a comparison of the performance of different flow conditioners, independently from their effects on particular flowmeters. Therefore, the authors propose the use of several efficiency parameters to evaluate and compare flatness, uni-directionality and axi-symmetry of the velocity profiles produced downstream from the conditioners. In order to compare the main conditioners, a brief description of their characteristics is reported. Then, the numerical analysis is carried out using the finite volume technique. From the results obtained it was possible to calculate the efficiency of the conditioners under low-level disturbance conditions, such as those produced by an out of plane double elbow configuration.

Although (Direct Digital Control) DDC-based air conditioning systems can potentially carry out efficiency checks, the instrumentation installed in these systems is not always suitable for making reliable plant status estimations. In order to verify the metrological performances of these systems and to define how reliable measurements can be made the authors set up a small-sized HVAC (Heating Ventilating and Air Conditioning) system provided with standard HVAC type sensors. The measurement instrumentation was verified by means of calibration and field tests, and the operating conditions in which it is possible to estimate in a sufficiently reliable manner the performances of each system component using the same instrumentation were determined experimentally. This analysis has shown that the normally used sensors are often highly dependent on operating and installation conditions and, consequently, the efficiency estimation of each component is very unreliable using uncalibrated sensors.

Fuel cells have been very much studied in the last few years as promising future energy conversion systems. In fact, these systems have a number of advantages with respect to more traditional energy conversion systems, such as, for instance, higher potential efficiency, flexibility for distributed generation, and reduced emissions. Accurate and physically representative numerical models are essential for the future development of energy conversion systems based on fuel cell technology. In the present paper, a general and detailed numerical model is proposed, in which all the quantities of interest are calculated locally, on the basis of general governing equations for the phenomena involved. The model proposed in this work is based on the solution of the appropriate set of partial differential equations that describe the phenomena that occur in the different parts of the fuel cell: 1) anodic compartment, which includes fuel channel, electrode and catalyst layer; 2) electrolyte; and 3) cathode compartment. To solve the momentum, energy and species conservation equations in the anodic and cathodic compartments, a finite element procedure is employed, based on the Characteristic Based Split (CBS) algorithm. The CBS, thanks to its generality and modularity, is able to successfully predict fuel cell performances. The results obtained from the simulations show a good agreement with other data available in the literature.Copyright © 2006 by ASME