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  • Open access
  • 29 Reads
Multistage Power Amplification Storage Systems for Dedicated Photovoltaic Applications and Harvesting
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Published: 11 September 2020 by MDPI in The First World Energies Forum session Intermediate and Final Energy Use

The paper discusses the principle of power amplification, as it can be found in many systems powered by PV panels and buffered by batteries. Under different categories of application examples, one is given by compacting containers for plastic or other waste materials. The main goal of such systems is to supply high-power intermittent systems from low power sources. The studied example discusses an energy harvesting system using a low power solar PV collection system dedicated to energize a specific application, sequentially operated at high power. The transformation of the power level is achieved using intermediary storage, where the charging sequence is characterized by a very low power level for longer time, followed by a shorter discharge sequence of the storage means with a much higher instantaneous power. The performance of the PV harvesting system is discussed from the point of view of its energy efficiency. Several solutions are discussed, and finally, a new 2-stage harvesting system is introduced. The requirement of a multistage amplification system is related to the power amplification ratio itself. The design method for the system relies on the concept of the so-called “Modified Ragone Representation”, MRR, that is shortly introduced in the paper. A prototype realization of the two-stage system is also presented.

  • Open access
  • 44 Reads
A Note on the “ Optimal ” Design of Disc-Shaped heat Exchangers
Published: 11 September 2020 by MDPI in The First World Energies Forum session Exergy

The continuous quest for improving the performance of heat exchangers, together with evermore stringent volume and weight constraints, especially in enclosed applications (engines, electronic devices), stimulates the search for compact, high-performance units. One of the shapes that emerged from a vast body of research is the disc-shaped heat exchanger, in which the fluid to be heated/cooled flows through radial -often bifurcated- channels inside of a metallic disc. The disc in turn exchanges heat with the heat/cold source (the environment or another body). Several studies have been devoted to the identification of an “optimal shape” of the channels: most of them are based on prime principles, though numerical simulations abound as well. The present paper demonstrates that -for all engineering purposes- there is only one correct design procedure for such a heat exchanger, and that this procedure depends solely on the technical specifications (exchanged thermal power, materials, surface quality): the design in fact reduces to a zero-degree of freedom problem! The argument is described in detail, and it is shown that a proper application of the constraints completely identifies the shape, size and similarity indices of both the disc and the internal channels. Goal of this study is not that of “inventing” a novel heat exchanger design procedure, but that of demonstrating that -in this as in many similar cases-a straight forward application of prime principles and of diligent engineering rules may generate “optimal” designs. Of course, the resulting configurations may be a posteriori tested as to their performance, their irreversibility rates, their compliance with one or the other “techno-economical optimization methods”, but it is important to realize that they enjoy a sort of “embedded” optimality.

  • Open access
  • 42 Reads
Closed Irreversible Cycles Analysis Based on Finite Physical Dimensions Thermodynamics
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Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Fundamentals

The paper develops generalizing entropic approaches of irreversible closed cycles. The mathematical models of the irreversible engines (basic, with internal regeneration of the heat, cogeneration units) and of the refrigeration cycles were applied to four possible operating irreversible trigeneration cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs unifying the first law of thermodynamics and the linear heat transfer law, the mean log temperature differences, and four possible operational constraints, i.e., constant heat input, constant power, constant energy efficiency and constant reference entropy. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input process. The number of internal irreversibility allows the evaluation of the heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The operational constraints allow the replacement of the reference entropy function of the finite physical dimensions parameters, i.e., mean log temperature differences, thermal conductance inventory, and the proper external heat reservoir temperatures. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration cycles. At the limit, i.e., endoreversibility, we can re-obtain the endoreversible energy efficiency equation. The second part develops the influences between the imposed operational constraint and the finite physical dimensions parameters for the basic irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratio of refrigeration rate to power, e.g., engine shaft power or useful power delivered directly to power consumers. The final discussions and conclusions emphasize the novelties and the complexity of interconnected irreversible trigeneration systems design/optimization.

  • Open access
  • 43 Reads
Performance, Emissions and Durability Studies on Diesel Engine fuelled with a Preheated Raw Microalgal Oil
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Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Research and Development

Preheated Schizochytrium sp. raw MAO was evaluated as a fuel in a single-cylinder four-stroke diesel engine to produce a comparative study of MAO and DO critical parameters. In particular, brake power, brake specific fuel consumption, brake thermal efficiency, in-cylinder pressure, exhaust gas temperature, NOx and CO emission were investigated. Additionally, an engine durability test for longevity was undertaken over a 30 h period, using raw MAO as the fuel. The study demonstrated that the preheated MAO could be successfully used in a Diesel engine smoothly. The use of MAO reduced the engine brake power by 26% and increased brake specific fuel consumption by 20%. The most significant finding from this research study is that there was a significant reduction in NOx and CO emission by 42% and 60% when using raw MAO, respectively. Therefore, these findings demonstrate that algae oil is a highly credible fuel for use in diesel engines and offers a promising solution to diesel engine emissions.

  • Open access
  • 29 Reads
Geothermal Repurposing of Depleted Oil & Gas Wells in Italy
Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Conversion Systems

The decarbonisation of the energy sector is probably one of the main worldwide challenges of the future. Global changes urge a radical transformation and improvement of the energy-producing systems to meet the decarbonisation targets and a reduction of greenhouse gas emissions. The hydrocarbon industry also contributes to this transition path. In a mature stage of oil and gas fields, the production of hydrocarbons is associated with formation waters. The volume of produced water increases with the maturity of the assets and the conversion into geothermal wells could be an alternative to the mining closure. In the described transition scenario, the geothermal energy seems very promising because of its wide range of applications depending onthe temperature of extracted fluids. This flexibility enables to propose projects inspired to a circular economy vision with the integration in the territory and social acceptance. In Italy, since 1985, 7246 well has been drilled for hydrocarbonof which 898 are located on-shorewith a productive or potentially productive operational status. The paper presents a preliminary investigation on oil and gas fields located on shore in Italian territory based on the available informationon temperature distribution at different depth. Then, taking into account the local energy demand, existing infrastructure, and land use of the territory, a conversion strategy for the producing wells has been proposed for three case studies.

  • Open access
  • 53 Reads
Reducing the Cooling Energy Consumption of Telecom Sites by Liquid Cooling
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Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Conversion Systems

The use of mobile data has increased and will continue to increase in the future because more data is moved to wireless networks such as 5G. Cooling energy need is also expected toincrease in indoor telecom rooms, and can be as high as the equipment’s own power consumption. The world’s first liquid Base Transceiver Station (BTS) was taken into commercial use in 2018, in Helsinki, Finland. Conventional air-cooled BTS hardware was converted into liquid cooled BTS. Heat from the BTS was pumped out of the site room and thus ventilation or air conditioning was not needed for the heat load from the BTS. Heat stored in the liquid was released into the ventilation duct of the building, still providing annual cooling energy savings of 70%, when compared to air-cooling. In the future, 80% of the total dissipated energy, 13450 kWh/a in total, can potentially be used for heating purposes. In terms of CO2 emissions, adapting liquid cooling showed an 80 % reduction potential when compared to air-cooling.

  • Open access
  • 51 Reads
Investigation on the Lean Stable Limit of a Barrier Discharge Igniter and of a Streamer-Type Corona Igniter at Different Engine Loads in a Single-Cylinder Research Engine
Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Conversion Systems

Currently, the Radio-Frequency Corona Ignition systems represent an important solution for reducing pollutant emissions and fuel consumption related to Internal Combustion Engines while at the same time ensuring high performance. These igniters are able to extend the lean stable limit by increasing the early flame growth speed. Kinetic, thermal and ionic effects, together with the peculiar configuration of the devices, allow to start the combustion process in a wider region than the one involved by the traditional spark. In this work two corona igniters, namely a Barrier Discharge Igniter and a Corona Streamer Igniter, were tested in a single-cylinder research engine fueled with gasoline at different engine loads in order to investigate the igniters performance through indicated analysis and pollutant emissions analysis. For each operating point, the devices control parameters have been set to ensure maximum energy releasement into the medium with the aim of investigating, at the extreme operating conditions, the capability of the devices to extend the lean stable limit of the engine. The Corona igniters have been tested on a constant volume calorimeter as well, reproducing the engine pressure conditions at the corresponding ignition timing. The target is to give an estimation of the thermal energy released during the discharge and then to compare their capability to provide high-stability energy.

  • Open access
  • 38 Reads
Sustainable Energy Solutions for Rural Communities
Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Policy

The RECENT project intended to enhance the utilization of unused assets in remote and sparsely populated areas and communities. The objectives were to enhance energy efficiency, implement renewable energy solutions and help communities to have more resilient and energy efficient public infrastructures capable of handling climate change related risks. The nexus approach was used to promote the efficient management of resources, i.e., water, waste and energy, while considering the interdependencies between them. The project developed 25 pilots related to energy, energy efficiency, waste, and water solutions across five Northern Periphery and Arctic Programme (NPA) partner regions (Finland, Sweden, Northern Ireland, Ireland, and Scotland). The project assessed energy generation and reduction potential; investment costs and payback times of the pilots. A sustainability assessment tool was also developed, to assess the environmental, social and long-term sustainability of the pilots. The combined benefit of the 25 pilots was 20 GWh/year renewable energy and saving 6070 t of CO2/year. The sustainability assessment also highlighted the social benefits to the community. The project established opportunities for new ways of providing environmental goods and services and supporting innovative infrastructures based on the nexus approach of water-energy-waste-land resources. These innovative infrastructures would be based on decentralized systems which allow for synergies between different assets. These synergistic solutions can contribute significantly to the reduction of resource consumption and related emissions and to the sustainable development of European communities.

  • Open access
  • 32 Reads
Solar Thermal Technologies for Low-Carbon Industrial Processes: Dynamic Modelling, Techno-Economic Analysis and Environmental Impact
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Published: 11 September 2020 by MDPI in The First World Energies Forum session Energy Conversion Systems

Solar thermal technologies are already available in the market, robust and relatively cheap. Unfortunately, the solar heat is little used in the industrial processes, and the main obstacles of the solar heat diffusion are often the lack of adequate predictive modelling of solar plant integration, identifying its energy potential, economic feasibility and environmental benefits. In this paper, to investigate and evaluate the possibility of supplying solar heat for the pasta drying process located in the north-east of the Italian Alps (Felicetti). The methodology proposed is structured with the combination of several software PVGIS®, Matlab®, Dymola®. The methodology developed is tested, considering solar thermal energy as primary source, in different geographical contexts.

  • Open access
  • 33 Reads
Selecting the Optimal Use of the Geothermal Energy Produced with a Deep Borehole Heat Exchanger: Exergy Performance
Published: 11 September 2020 by MDPI in The First World Energies Forum session Exergy

Geothermal sector has a strength point respect to other renewable energy sources: the availability of a wide range of both thermal and power applications depending on source temperature. Several researches have been focused on the possibility to produce geothermal energy without brine extraction, by means of a deep borehole heat exchanger. This solution may be the key to increase the social acceptance, to reduce environmental impact of geothermal projects, and to exploit the unconventional geothermal systems, where the extraction of brines in technically complex. In this work, exergy efficiency has been used to investigate the best utilization strategy downstream the deep borehole heat exchanger. Five configurations have been analyzed: a district heating plant, an absorption cooling plant, an Organic Rankine Cycle, a cascade system composed by district heat and absorption chiller, a cascade system composed by the Organic Rankine plant and the district heating plant. District heating results a promising and robust solution: it ensures high energy capacities per well depth and high exergy efficiency. Power production shows performances in line with typical geothermal binary plants, but the system capacity per well depth is low and the complexity increases both irreversibilities and sensibility to operative and source conditions.

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