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A bibliographical review on the heat and mass transfer in gravity assisted Closed Loop Two Phase Thermosyphons (CLTPT) with channels having a hydraulic diameter of the order of some millimetres and input power below 1 kW is proposed. The available experimental works in the literature are critically analysed in order to highlight the main results and the correlation between mass flow rate and heat input in natural circulation loops. A comparison of different experimental apparatuses and results is made. It is observed that the results are very different among them and in many cases the experimental data disagree with the conventional theory developed for an imposed flow rate. The paper analyses the main differences among the experimental devices and try to understand these disagreements. From the present analysis it is evident that further systematic studies are required to generate a meaningful body of knowledge of the heat and mass transport mechanism in these devices for practical applications in cooling devices or energy systems. [ABSTRACT FROM AUTHOR]

Abstract: A multidisciplinary approach for the design of geothermal power plants for water dominant resources is here proposed. The importance of a strategic approach is underlined, considering all the connections between the analysis of the geothermal potential of the reservoir (geophysical exploration and geochemical analysis) with the design of the plant based on thermodynamic and energy considerations, mainly regarding ORC (Organic Rankine Cycles) power plants. This multidisciplinary approach is fundamental for the objective of a sustainable exploitation of medium to low enthalpy sources. The aim of this study is to propose the optimization and management of the global system “reservoir-power plant” as the task of geothermal projects. This approach can be pursued only in a multidisciplinary perspective in which both Engineering and Geological aspects are involved. Numerical simulation appears to be an essential interacting step. After analyzing the problems caused by an incorrect characterization of geothermal source, reinjection temperature and strategy, a method for the numerical simulation of geothermal reservoirs long-term behavior/capacity is discussed. This could be the key instrument to synthesize the strategy inputs. A numerical modeling is performed, using as reference data the history matching of a well known and completely analyzed geothermal field. [Copyright &y& Elsevier]

Abstract: Much remains to be done in binary geothermal power plant technology, especially for exploiting low-enthalpy resources. Due to the great variability of available resources (temperature, pressure, chemical composition), it is really difficult to “standardize the technology”.The problem involves many different variables: working fluid selection, heat recovery system definition, heat transfer surfaces sizing and auxiliary systems consumption. Electricity generation from geothermal resources is convenient if temperature of geothermal resources is higher than 130°C. Extension of binary power technology to use low-temperature geothermal resources has received much attention in the last years. This paper analyzes and discusses the exploitation of low temperature, water-dominated geothermal fields with a specific attention to regenerative Organic Rankine Cycles (ORC). The geothermal fluid inlet temperatures considered are in the 100–130°C range, while the return temperature of the brine is assumed to be between 70 and 100°C. The performances of different configurations, two basic cycle configurations and two recuperated cycles are analyzed and compared using dry organic fluids as the working fluids. The dry organic fluids for this study are R134a, isobutane, n-pentane and R245fa. Effects of the operating parameters such as turbine inlet temperature and pressure on the thermal efficiency, exergy destruction rate and Second Law efficiency are evaluated. The possible advantages of recuperated configurations in comparison with basic configurations are analyzed, showing that in a lot of cases the advantage in terms of performance increase is minimal but significant reductions in cooling systems surface area can be obtained (up to 20%). [Copyright &y& Elsevier]

Abstract: Renewable energy sources (RES) are mainly used in the electrical sector. Electricity is not a storable commodity. Hence it is necessary to produce the requested quantity and distribute it through the system in such a way as to ensure that electricity supply and demand are always evenly balanced. This constraint is actually the main problem related to the penetration of new renewables (wind and photovoltaic power) in the context of complex energy systems. Moreover the design of optimal energy resource mixes in climate change mitigation actions is a challenge faced in many places. The paper analyzes the problem of new renewable energy sources penetration. The case of Italian scenario is considered as a meaningful reference due to the characteristic size and the complexity of the same. The various energy scenarios are evaluated with the aid of a multipurpose software taking into account the interconnections between the different energetic uses. In particular it is shown how the penetration of new renewable energy sources is limited at an upper level by technological considerations and it will be more sustainable if an integration of the various energy uses (thermal, mobility and electrical) will be considered. A series of optimized scenarios are developed. In each case the maximum RES penetration feasible with the constraints was defined. Then analysis is applied to an energy system model of Italy showing how an integrated development of CHP and electric mobility can aid a further integration of wind and photovoltaic energy power. Finally the primary energy consumption saving possible in case of consistent penetration of intermittent renewables and CHP was identified. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an analysis of Selective Laser Sintering (SLS) from an energy standpoint. Selective Laser Sintering (SLS) has a potential as an environmental benign alternative to traditional processes but only few authors deal with the process optimisation including energy aspects. In the present paper an analysis of the energetic aspect of SLS is proposed. In addition, with respect to the classical technological parameters (resolution, productivity) attention is paid to energetic elements (energetic productivity, laser parameters) showing how the perspective of a sensible development of such a kind of technology could be beneficial not only from a technological point of view, but also for energy saving in a lot of manufacturing fields. A polyamide powder is the material tested to acquire some characteristics data of the process. It is shown that the Volumetric Energy Intensity (VEI) of the process in optimal condition could be of the order of 0.2J for each mm3 of material agglomerated. [ABSTRACT FROM AUTHOR]

Abstract: Exploitation of lower temperature, water-dominated geothermal fields is analyzed, and a methodology for optimizing geothermal binary plants is discussed. The geothermal fluid inlet temperatures considered are in the 110–160°C range, while the return temperature of the brine is assumed to be between 70 and 100°C. The analysis shows that the brine specific consumption, ranging from 20 to 120kgs−1 for each net MW produced, and the efficiency of the plants, ranging from 20% to 45% in terms of Second Law efficiency, are dictated mainly by the combination of the brine inlet temperature, the brine rejection temperature and the energy conversion cycle being used. For given operating conditions and with correct matching between working fluid and energy conversion cycle, it is possible to obtain very similar performances in a number of different cases. It is shown that optimization of the plant can yield improvements of up to 30–40% in terms of reduction of brine specific consumption compared to conventional design. [Copyright &y& Elsevier]

Coal offers an abundant widely spread fossil energy resource. It is available at a quite-stable price from many international suppliers and it will continue to play a significant role in new generating capacity, if security and diversity of supply remain fundamental. In this paper we point out the state of the art in the field of “clean coal technologies” evidencing the perspectives of improvement and the critical elements. Both the emission control of NO x , SO x , and particle matter and the advanced coal conversion pathways like ultra-supercritical (USC), pressurized fluidized bed combustion (PFBC), and integrated gasification combined cycle (IGCC) are reviewed and analyzed. At the end some elements concerning the perspectives of CO2 emission control strategies are outlined. [Copyright &y& Elsevier]

Background. The restrictive, but not the obstructive respiratory dysfunction, is associated with an increased risk of developing type 2 diabetes mellitus. Our aim was to verify in an elderly nondiabetic population whether a restrictive respiratory pattern was associated with a higher prevalence of metabolic syndrome and increased insulin resistance than were obstructive and normal respiratory patterns. Methods. We performed a cross-sectional study of 159 consecutive nondiabetic elderly persons attending two social centers. According to their spirometric pattern, volunteers were classified into the following categories: normal spirometry, obstructive (forced expiratory volume in 1 second/forced vital capacity < 0.70), and restrictive pattern (forced vital capacity < 80% predicted, forced expiratory volume in 1 second/forced vital capacity ≥ 0.70). Independent correlates of the metabolic syndrome were identified. Results. The prevalence of metabolic syndrome was higher in restrictive (56%) than in both normal (21.4%, p = .001) and obstructive volunteers (12.9%, p = .001 ). Insulin resistance, as assessed by the log transformation of the HOmeostasis Model Assessment (HOMA), was higher in restrictive than in obstructive and normal volunteers (1 ± 0.6 vs 0.3 ± 0.6 and 0.5 ± 0.5, p < .001). Restriction was an independent correlate of metabolic syndrome, also after adjustment for waist circumference and body mass index (odds ratio = 3.23, 95% confidence interval, 1.23-8.48; p = .01). Conclusion. Restrictive, but not obstructive respiratory pattern, is associated with metabolic syndrome and insulin resistance, and does not only reflect a limitation of ventilation due to visceral obesity. Metabolic abnormalities likely mediate cardiovascular risk in patients with restrictive respiratory impairment. [ABSTRACT FROM AUTHOR]

The paper analyzes the links among energy, economy, and the natural environment. This matter requires the reconsideration of energy efficient and low emission technologies and the definition of new instruments for the analysis of energy systems as well as for the definition of energy policies. After an overview of the methods available in the literature, dealing with a multidimensional analysis of energy system, the authors propose a quantitative approach based on the use of two different thermodynamic based utility functions. The utilization of those functions permits to join thermodynamic and environmental performance of the energy system, to analyze the effects of their interaction and to obtain a more logical comparison among different energy systems, accepting the multidimensional nature of the problem but maintaining a system analysis in the way engineers are accustomed to. Two cases are discussed and analyzed. [ABSTRACT FROM AUTHOR]

Abstract: The optimization of the heat recovery steam generator (HRSG) is one of the key elements for increasing the efficiency of combined plants. According to the current technical practice, it can be organized at different levels of complexity with objectives sequentially defined: operating parameters, geometrical details and technological elements. According to this point of view, in the paper a complete strategy for the optimum design of the HRSG is outlined. The optimization is organized at two levels: the first one enables to obtain the main operating parameters of the HRSG, while the second involves the detailed design of the component concerning the geometric variables of the heat transfer sections. The output of the first-level optimization is the input of the second level. In particular, the second level of the optimization can be articulated in two different steps. The first step can be aimed to the minimization of the pressure drop for a given heat flow. The second step leads to a reduction of the overall dimensions, maintaining the imposed performance of the HRSG in terms of heat flow and pressure drop. The whole procedure is tested with reference to a case of existing HRSG structures; it shows the possibility of improving performance maintaining a constrained packaged size. [Copyright &y& Elsevier]

The paper proposes an analysis of the feasibility of highly efficient combined plants. The aim of the paper is to discuss and analyze different strategies for the increase of the efficiency of the combined cycle power plants with respect to those usually proposed in the literature. Resorting to the optimization of the components, joined with the use of regeneration and postcombustion (reheat) in the topping cycle it is shown how the combined plant efficiency can rise well over the actually well known limit of 60%. The possibility of obtaining such a high efficiency value is confirmed also by the proposed thermoeconomic optimization, based on the minimization of the total cost of the plant per unit power, obtained referring to a common economic basis the cost of the exergy losses and the costs of the components. The feasibility of obtaining combined plant with efficiency higher than 62%, simply by best fitting the available technology and without waiting for meaningful technological improvement of the gas turbines, is demonstrated. [Copyright &y& Elsevier]

Food stores and supermarkets are buildings, often with rather similar structures characterized by large surfaces and a single floor, that are particularly energy intensive. The energy uses associated with them are mainly electrical, in connection with air conditioning and food refrigeration. These buildings are particularly interesting for a systematic application of photovoltaic (PV) generation technology. After an analysis of the main energy consumption parameters and of the most common benchmarking approaches, standard solutions for the sizing of photovoltaic systems are proposed based on different design objectives, highlighting the potential of each solution proposed. Two specific indicators are defined for the sizing processes. The methodology is tested with reference to two different stores under the zero grid-injection restriction. The results showed how the degree of self-sufficiency for a supermarket obtained with a PV plant can be of the order of 20% in cases without storage system and can be increased over 50% and up to 70–75% but only using relevant battery storage dimensions. [ABSTRACT FROM AUTHOR]

The paper analyzes and compares the perspectives for reducing the energy consumption associated to the operation of Heating Ventilation and Air Conditioning system for climatic control of large-size non-residential buildings. Three different control strategies are considered comparing the use of boiler and heat pumps as heating systems and analyzing the use of demand-controlled ventilation, operating on the effective occupancy of the building. The control strategies are applied to two different educational buildings with shapes representative of typical educational structures. The results of the analysis show how the energy consumption can be reduced up to 70%, shifting from the actual values of the energy intensity of over 300 kWh/m2 for year to values of less than 100 kWh/m2 per year. The significance of the energy savings achieved in such different buildings has led to the identification of a possible benchmark for HVAC systems in the next future years which could help reach the environmental targets in this sector. [ABSTRACT FROM AUTHOR]

One of the main elements for increasing energy efficiency in large-scale buildings is identified in the correct management and control of the Heating Ventilation and Air Conditioning (HVAC) systems, particularly those with Heat Pumps (HPs). The present study aimed to evaluate the perspective of energy savings achievable with the implementation of an optimal control of the HVAC with HPs. The proposed measures involve the use of a variable air volume system, demand-controlled ventilation, an energy-aware control of the heat recovery equipment, and an improved control of the heat pump and chiller supply water temperature. The analysis has been applied to an academic building located in Pisa and is carried out by means of dynamic simulation. The achieved energy saving can approach values of more than 80% if compared with actual plants based on fossil fuel technologies. A major part of this energy saving is linked to the use of heat pumps as thermal generators as well as to the implementation of an energy efficient ventilation, emphasizing the importance of such straightforward measures in reducing the energy intensity of large-scale buildings. [ABSTRACT FROM AUTHOR]

The paper provides results from a hardware-in-the-loop experimental campaign on the operation of an air-source heat pump (HP) for heating a reference dwelling in Pisa, Italy. The system performances suffer from typical oversizing of heat emission devices and high water-supply temperature, resulting in HP inefficiencies, frequent on-off cycles, and relevant thermal losses on the hydronic loop. An experimentally validated HP model under different supply temperatures and part-load conditions is used to simulate the installation of a thermal storage between heat generator and emitters, in both series and parallel arrangements. Results relative to a typical residential apartment show that the presence of the thermal storage in series configuration ensures smoother heat pump operation and energy performance improvement. The number of daily on-off cycles can be reduced from 40 to 10, also saving one-third of electric energy with the same building loads. Preliminary guidelines are proposed for correctly sizing the tank in relation to the HP capacity and the average daily heating load of the building. A storage volume of about 70 L for each kilowatt of nominal heating capacity is suggested. [ABSTRACT FROM AUTHOR]

The paper provides a methodology for the optimal control of heating, ventilation, and air conditioning (HVAC) systems used in public buildings, with the purpose of obtaining high comfort and safety standards along with energy efficiency. The combination of the two concurrent objectives of minimizing energy use and guaranteeing high standards of occupant comfort is obtained by means of multi-objective optimization, in which a comfort model is combined along with a dynamic energy model of the building. The use of dynamic setpoints for the HVAC and the inclusion of comfort indicators represent a step forward, compared to the current design and operation procedures suggested by technical standards. The utilization of the proposed methodology is tested with reference to a case study, represented by an academic building used by the University of Pisa for educational purposes, whose extensive and variable occupancy can help to emphasize the importance of comfort in the operation of HVAC systems in different climatic conditions and with different occupancy profiles. We show how this optimization brings interesting results in terms of energy-saving (up to 30%), obtaining an increased comfort level (of more than 25%) compared to the operating conditions suggested by technical standards. [ABSTRACT FROM AUTHOR]

Flat-plate solar collectors are one of the cleanest and most efficient heating systems available. Studies on the presence of covalently functionalized graphene (Gr) suspended in distilled water as operating fluids inside an indoor flat-plate solar collector (FPSC) were experimentally and theoretically performed. These examinations were conducted under different testing conditions namely 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%, 0.5, 1, and 1.5 kg/min, 30, 40, and 50 °C, and 500, 750, and 1000 W/m2. Various techniques were used to characterize the functionalized nanofluids' stability and morphological properties namely UV/Vis spectrophotometry, EDX analysis with a Scanning Electron Microscope (SEM), zeta potential, and nanoparticle size. The results showed that the collected heat improved as the percentage of GrNPs and the fluid mass flow rates increased, although it decreased as the reduced temperature coefficient increased, whereas the maximum increase in collector efficiency at higher concentration was 13% and 12.5% compared with distilled water at 0.025 kg/s. Finally, a new correlation was developed for the base fluid and nanofluids' thermal efficiency as a function of dropped temperature parameter and weight concentration with 2.758% and 4.232% maximum deviations. [ABSTRACT FROM AUTHOR]

Worldwide increasing awareness of energy sustainability issues has been the main driver in developing the concepts of (Nearly) Zero Energy Buildings, where the reduced energy consumptions are (nearly) fully covered by power locally generated by renewable sources. At the same time, recent advances in Internet of Things technologies are among the main enablers of Smart Homes and Buildings. The transition of conventional buildings into active environments that process, elaborate and react to online measured environmental quantities is being accelerated by the aspects related to COVID-19, most notably in terms of air exchange and the monitoring of the density of occupants. In this paper, we address the problem of maximizing the energy efficiency and comfort perceived by occupants, defined in terms of thermal comfort, visual comfort and air quality. The case study of the University of Pisa is considered as a practical example to show preliminary results of the aggregation of environmental data. [ABSTRACT FROM AUTHOR]