A corresponding-states correlation for predicting the critical heat flux (CHF) in pool boiling conditions is proposed, and only requires knowledge of physical property constants of the fluid at any fluid temperature: molar mass, critical temperature, critical pressure, and the Pitzer acentric factor. If a fourth corresponding equation of state (EoS) parameter is added, a more accurate CHF correlation is obtained and matches Kutateladze−Zuber prediction within ±10% in the reduced temperature range of 0.55−0.95. This way, CHF can be easily predicted for any reduced temperature within the range of correlation’s validity by only knowing basic properties of the fluid. Additionally, two corresponding-states correlations for determining the capillary length are proposed and also do not rely on any temperature- and pressure-dependent fluid properties. A simpler correlation only using the Pitzer acentric factor is shown to be imprecise, and a more complex correlation also accounting for the fou... [more]

Seismic monitoring in areas where induced earthquakes could occur is a challenging topic for seismologists due to the generally very low signal to noise ratio. Therefore, the seismological community is devoting several efforts to the development of high-quality networks around the areas where fluid injection and storage and geothermal activities take place, also following the national induced seismicity monitoring guidelines. The use of advanced data mining strategies, such as template matching filters, auto-similarity search, and deep-learning approaches, has recently further fostered such monitoring, enhancing the seismic catalogs and lowering the magnitude of completeness of these areas. In this framework, we carried out an experiment where a small-aperture seismic array was installed within the dense seismic network used for monitoring the gas reservoir of Collalto, in North Italy. The continuous velocimetric data, acquired for 25 days, were analysed through the application of the... [more]

Organic Rankine cycles are often the best solution for the conversion of thermal energy. The many working fluids include silicon oils. One crucial issue that determines the choice of a working fluid is its thermochemical stability, as this sets a limit to the maximum temperature at which the fluid can be used in a power plant. A second subject, much debated today, is the use of mixtures in ORCs. In the first part of this study, an investigation into the thermal stability of siloxanes using two different approaches was carried out. The results confirmed a limit working temperature for the considered siloxanes of about 300 °C, with a degradation that advanced significantly over time at 350 °C. In the second part of the study, an analysis of the thermodynamic performances of some siloxane mixtures was carried out. It was found that the efficiencies of the corresponding thermodynamic cycles were substantially the same as for the pure fluids used today. By changing the composition of the mi... [more]

In Poland, there are low-temperature geothermal reservoirs that can be used for various purposes in many regions of the country. Low-temperature deposits of geothermal waters are common and occur much more frequently than high-temperature deposits. They contain water with temperatures lower than 150 °C. Their temperature normally ranges from 20 to 90 °C. Achieving a state of equilibrium depends on many factors, including the kinetics of reactions between the individual components of the system, temperature, reactivity of reservoir rock, concentration of chemical components in the water and the time the water remains in contact with the rock. Therefore, this article presents the possibility of checking the conditions of precipitation of inorganic sediments in geothermal waters with the use of PVT equipment. Tests were carried out with the use of geothermal waters under given dynamic conditions (pressure, temperature and flow). This paper confirms the suitability of using the equipment f... [more]

Electricity sector reforms have transformed the structure and organization of the sector worldwide. While outcomes of reforms in developed and developing countries have been extensively examined, there is limited analysis of the reforms in sub-Saharan Africa (SSA). This paper analyses the performance of electricity sector reforms in 37 SSA countries between 2000 and 2017. We use a stochastic frontier analysis approach to estimate a multi-input multi-output distance function to assess the impact of reform steps and institutional features on indicators of investment and technical efficiency. Results indicate a positive correlation between reforms and installed generation capacity per capita, plant load factor, and technical network losses. The presence of an electricity law, sector regulator, vertical unbundling, and private participation in the management of assets were positively correlated with reform performance. Perceptions of non-violent institutional features such as corruption, r... [more]

Social capital is currently perceived as one of the basic factors of economic development and economic success of enterprises. However, while there is already much research on social capital in enterprises, there has been little such research in the energy industry. The aim of the publication is to fill the gap in this regard. The basic question that the authors try to answer is whether there is a higher level of capital in energy companies compared to other industries, and if so, what the reasons are for this. Apart from answering this question, the authors present their own method of measuring the level of this capital. The first part of the article presents the results of a study on the level of social capital in Polish energy companies, whereas the second part compares the levels of social capital in energy companies and industrial companies in other sectors. According to the study, energy companies generally have higher levels of social capital than companies in other industries.... [more]

The results of experiments to determine the role of structural schemes for the ignition of a mechanically activated thermite mixture Al−CuO and the formation of its combustion flame are presented. The reaction initiated in the bulk of the experimental assembly transforms into torch combustion in an open space. The dynamics of the volume of the flame reaction region was determined. The stage of flame formation has a stochastic character, determined by the random distribution of the reaction centres in the initial volume of the components. A high-speed camera, a pyrometer and electro contact sensors were used as diagnostic tools. The ultimate goal of the study was to optimize the conditions for the flame formation of this mixture for its effective use with a single ignition of various gas emissions.

Innovative low-temperature disintegration (process temperature 55 °C and oxygen concentration 0.2 mg/dm3) can be an economically rational technology to intensifying energy production from renewable sources. The proposed process can achieve a degree of disintegration—under optimal conditions—of about 50%, which is excellent when compared with other methods of feed pre-treatment. The low-temperature disintegration of distillation residue and waste-activated sludge before the co-fermentation process increased biogas production by 30% and methane production by 65% (over a 26 d duration). The obtained results confirm that the low-temperature disintegration method can be effectively used to pre-prepare this type of feed. At the same time, it was discovered that the Gompertz model can be used to mathematically describe the biogas accumulation curves in the methane co-fermentation processes of the tested feeds (the correlation coefficients were higher than 0.98).

The aim of Energies’ Smart Cities and Urban Management Section is to present new research results and new proven practices aimed at optimizing the energy use of smart cities and improving the energy efficiency in urban management [...]

Due to water scarcity, in the last few decades, air-to-water generator (AWG) technology, whose useful effect is the extraction of water from air, has been improved. In particular, in the last few years, advanced AWG integrated systems have been developed. Such systems permit, not only to condense water from air, but also the smart use of the by-side effects of the process in order to partially or totally cover the heating ventilation air conditioning (HVAC) needs of a building. Presently, there are no evaluation tools that permit a complete comparison among AWG machines, taking into account all the useful effects that can be obtained at the same time and with the same energy input. The current work, starting from the need for such a tool, proposes a global index whose formulation considers all useful effects of an integrated system, the energy required to obtain them, and the integration degree of the machine. The index translates into a single number the system global efficiency, by m... [more]

In this study, a plucking-driven piezoelectric wave energy harvester (PDPWEH) consisted of a buoy, a gear train frequency up-conversion mechanism, and an array of piezoelectric cantilever beams was developed. The gear train frequency up-conversion mechanism with compact components included a rack, three gears, and a geared cam provide less energy loss to improve electrical output. Six individual piezoelectric composite beams were plucked by geared cam to generate electrical power in the array of piezoelectric cantilever beams. A sol-gel method was used to create the piezoelectric composite beams. To investigate PDPWEH, a mathematical model based on the Euler−Bernoulli beam theory was derived. The developed PDPWEH was tested in a wave flume. The wave heights were set to 100 and 75 mm, the wave periods were set to 1.0, 1.5, and 2.0 s. The maximum output voltage of the measured value was 12.4 V. The maximum RMS voltage was 5.01 V, which was measured by connecting to an external 200 kΩ res... [more]

The installation of base isolation systems in nuclear power plants can improve their safety from seismic loads. However, nuclear power plants with base isolation systems experience greater displacement as they handle seismic loads. The increase in relative displacement is caused by the installed base isolation systems, which increase the seismic risk of the interface piping system. It was found that the failure mode of the interface piping system was low-cycle fatigue failure accompanied by ratcheting, and the fittings (elbows and tees) failed due to the concentration of nonlinear behavior. Therefore, in this study, the limit state was defined as leakage, and an in-plane cyclic loading test was conducted in order to quantitatively express the failure criteria for the SCH40 6-inch carbon steel pipe elbow due to low-cycle fatigue failure. The leakage line and low-cycle fatigue curves of the SCH40 6-inch carbon steel pipe elbow were presented based on the test results. In addition, the li... [more]

The formula of engaging an energy service company (ESCO) in Poland is not a new form of accounting for investments in improving energy efficiency. The results of our survey confirm that many entities still lack sufficient knowledge about this subject. The research problem this paper is concerned with is the conditions of applying the ESCO formula (a model of investment financing with the participation of a specialised company) to support local government units and enterprises in energy-industry project development. For the purpose of this study, the research questions were formulated to analyse of the following issues: the reasons for interest in the ESCO formula and the sources of knowledge about this solution; activities and other factors that can increase or reduce interest in the ESCO formula; services in terms of ESCO formula implementation; the attractiveness of alternative instruments for financing energy industry projects, the benefits of using the ESCO formula and the influenc... [more]

The application of laser ignition in the aerospace field has promising prospects. Based on the constant volume combustion chamber, the laser ignition of CH4/O2/N2 mixture with different initial pressure, different laser energy, different equivalence ratio and different oxygen content has been carried out. The development characteristics of the flame kernel and shock wave under different conditions are analyzed. In addition, the Taylor model and Jones model are also used to simulate the development process of the shock wave, and a new modified model is proposed based on the Jones model. The experimental results show that under pure oxygen conditions, the chemical reaction rate of the mixture is too fast, which makes it difficult for the flame kernel to form the ring and third-lobe structure. However, the ring structure is easier to form with the pressure and laser energy degraded; the flame kernel morphology is easier to maintain at a rich equivalence ratio, which is caused by the influ... [more]

In this study, a low-air temperature sludge drying system was constructed and the effects of temperature and relative humidity on the characteristics of the system were investigated. The results showed that the drying rate of sludge increased with an increase in air temperature and a decrease in the air’s relative humidity. The influence of temperature on the average drying rate exhibited an approximate quadratic distribution, while the influence of relative humidity on the average drying rate exhibited an almost linear distribution. The relationship equations of the average drying rate, temperature, and humidity were summarized and compared with the experimental results, and the maximum relative error was 7.6375%. By comparing the experimental results with the commonly used thin-layer drying models, it was found that the sludge drying characteristics were more consistent with the Midilli model. Based on the relevant parameters of the Midilli model, the relationship between the segment... [more]

In this work, a novel biomass, the extraction residue of Sapindus pericarp (SP), was torrefied by using an electronic oven under a wide range of temperature (i.e., 200−320 °C) and residence times (i.e., 0−60 min). From the results of the thermogravimetric analysis (TGA) of SP, a significant weight loss was observed in the temperature range of 200−400 °C, which can be divided into the decompositions of hemicellulose (major)/lignin (minor) (200−320 °C) and cellulose (major)/lignin (minor) (320−400 °C). Based on the fuel properties of the feedstock SP and SP-torrefied products, the optimal torrefaction conditions can be found at around 280 °C for holding 30 min, showing that the calorific value, enhancement factor and energy yield of the torrefied biomass were enhanced to be 28.60 MJ/kg, 1.36 and 82.04 wt%, respectively. Consistently, the values of the calorific value, carbon content and molar carbon/hydrogen (C/H) ratio indicated an increasing trend at higher torrefaction temperatures an... [more]

Most of the UK Continental Shelf (UKCS) oil and gas (OG) installations have traditionally adopted in situ power generation, which is not only inefficient but also generating about 70% of the offshore CO2 emissions. The offshore wind and energy storage technologies for deep water are developing at a fast pace, enabling great opportunities for the OG installations located in the North Sea. In this paper, a pathway for the UKCS offshore OG installations electrification is introduced. The aim is to provide different power architectures that facilitate the OG installations’ electrification, while benefiting from the existing and planned UK offshore wind power. Four hypothetical case studies (based on real data) were created, along the UKCS, where the corresponding power architectures were proposed. The selection of each architecture power component (e.g., transformers, converters and cables), as well as the transmission and distribution technology (e.g., AC or DC), is also provided and just... [more]

The successful deployment of the solar water heater (SWH) in the residential sector relies on the household’s bounded rational decision-makers to accept this system. The decision is shaped by a wide spectrum of predictors that form heterogeneous behaviour. Over the past years, research has employed a wide range of these predictors to understand their role in the decision and predict the behaviour and diffusion rate of SWHs. This review primarily identifies economic and technical predictors of 100 quantitative and qualitative studies on the residential SWH adoption decision. For the identified predictors, their characteristics and popularity are explored in a structured and coherent framework. The review further investigates the correlation between the identified predictors and the adoption decision from 97 of the 100 initially reviewed studies. The outcome of the research revealed 123 (56 economic and 67 technical) predictors that were classified into seven categories. ‘Financial incen... [more]

We review the methods based on the measurement of CO2 emissions for the computation of geothermal heat flow, both at a local (hydrothermal sites, a few km2) and regional scale (hundreds km2). At the local scale, we present and discuss the cases of the Latera caldera and Torre Alfina (Italy) geothermal systems. At Torre Alfina and Latera, the convection process sustains a CO2 emission of ~1 kg s−1 and ~4 kg s−1, and heat flows of 46 MW and 130 MW, respectively. At the regional scale, we discuss the case of the central Apennine (Italy), where CO2 mass and enthalpy balances of regional aquifers highlights a wide and strong thermal anomaly in an area of low conductive heat flow. Notably, the CO2/heat ratios computed for the central Apennines are very similar to those of the nearby geothermal systems of Latium and Tuscany, suggesting a common source of CO2-rich fluids ascribed to the Tyrrhenian mantle.

Absorption Refrigeration Systems (ARS) are potential alternatives to direct expansion (DX) refrigeration systems. This review focused on the incorporation of an ejector into absorption refrigeration cycles to constitute Hybrid Ejector-Absorption Refrigeration Systems (HEARS). The ejector adds several advantages to the absorption refrigeration systems depending on its location in the cycle. The two prevalent configurations of HEARS are Triple pressure level (TPL-HEARS), and Low Pressure Condenser (LPC-HEARS). Previous studies revealed the preference of the latter configuration as it allows lower circulation ratios, enhances the refrigeration effect, and could achieve a COP up to 1. Moreover, LPC configuration is suitable with single, double, and variable-effect absorption systems with a COP of above unity. In turn, the TPL-HEARS notably enhances the absorption process, particularly when a variable geometry ejector is utilized. This configuration could obtain a COP around 1.1, but only w... [more]

Wakes appearing downstream of disturbances on the surface of a water flow in a concave open channel were examined experimentally. The investigated channel geometry was similar to the liquid lithium target in DONES (Demonstration fusion power plant Oriented NEutron Source). The objective of the measurements was to analyze the effect of a disturbance on the downstream layer thickness. For measuring the height profiles in the channel, an optical measurement system based on laser triangulation was developed. It was shown that the wake of the undisturbed flow emerged from the nozzle corner, which was in accordance with analytical solutions. For sufficiently large disturbances at the nozzle edge, the height profiles located downstream showed symmetrical minima and maxima on both sides of the disturbance. The wake depth strongly depended on the diameter and penetration depth of the disturbance, as well as the circumferential position in the channel, which yields to a critical wake depth of on... [more]

A study on forced ignition characteristics of RP-3 jet fuel-air mixture was conducted around a constant volume combustion vessel and a nanosecond pulsed plasma discharge power supply. Experiments were carried out at different initial pressures (pu = 0.2, 0.3, 0.5 atm), equivalence ratios (ϕ = 0.7, 0.8, 1.1), steam concentrations (ZH = 0%, 10%, 15%) and oxygen concentrations (ZO = 13.5%, 16%, 21%). The relationship between ignition probability and ignition energy is investigated. The experimental results show that the decrease in pressure, equivalence ratio, oxygen concentration and the increase in steam concentration all lead to an increase in minimum ignition energy (MIE). In order to further analyze the experimental data, one existing fitting equation is reformed with the initial conditions taken into account. Multivariate fitting is carried out for different conditions, and the fitting results of ignition probability are in good agreement with the experiments. The MIE results under... [more]

Advances in power electronics and their use in Miscellaneous Electric Loads (MELs) in buildings have resulted in increased interest in using low-voltage direct current (DC) power distribution as a replacement for the standard alternating current (AC) power distribution in buildings. Both systems require an endpoint converter to convert the distribution system voltage to the MELs voltage requirements. This study focused on the efficiency of these endpoint converters by testing pairs of AC/DC and DC/DC power converters powering the same load profile. In contrast to prior studies, which estimated losses based on data sheet efficiency and rated loads, in this study, we used part load data derived from real-world time-series load measurements of MELs and experimentally characterized efficiency curves for all converters. The measurements performed for this study showed no systematic efficiency advantage for commercially available DC/DC endpoint converters relative to comparable, commercially... [more]

Developing wind energy in Lithuania is one of the most important ways to achieve green energy goals. Observational data show that the decline in wind speeds in the region may pose challenges for wind energy development. This study analyzed the long-term variation of the observed 2006−2020 and projected 2006−2100 near-surface wind speed at the height of 10 m over Lithuanian territory using data of three models included in the Coupled Model Intercomparison Project phase 5 (CMIP5). A slight decrease in wind speeds was found in the whole territory of Lithuania for the projected wind speed data of three global circulation models for the scenarios RCP2.6, RCP4.5, and RCP8.5. It was found that the most favorable scenario for wind energy production is RCP2.6, and the most unfavorable is the RCP4.5 scenario under which the decrease in wind speed may reach 12%. At the Baltic Sea coastal region, the decline was smaller than in the country’s inner regions by the end of the century. The highest red... [more]

Pyrolysis is an optimal thermochemical process for obtaining valuable products (char, oil, and gas) from waste tires. The preliminary research was done on the three groups of samples acquired by cutting the same waste tire of a passenger vehicle into cylindrical granules with a base diameter of 3, 7, and 11 mm. Each batch weighed 10 g. The heating rate was 14 °C/min, and the final pyrolysis temperature was 750 °C, with 90 s residence time. After the pyrolysis product yields were determined for all of the three sample groups, further research was performed only on 3 mm granules, with the same heating rate, but with altered final pyrolytic temperatures (400, 450, 500, 550, 600, 650, 700, and 750 °C). The results of this study show that thermochemical decomposition of the waste tire sample takes place in the temperature range of 200−500 °C, with three distinct phases of degradation. The highest yield of the pyrolytic oil was achieved at a temperature of 500 °C, but further heating of vola... [more]