Computed X-ray tomography (CT), together with pulse and pressure decay permeability methods were used to evaluate a formula for absolute reservoir permeability. For this reason, 62 core samples representing geological material of tight, gas-bearing sandstones, mudstones, limestones, and dolostones were studied. Samples were divided into two groups with lower and higher permeability values. Images of the pore space were processed and interpreted to obtain geometrical parameters of the objects (pores, microfractures) with 0.5 × 0.5 × 0.5 µm3 voxel size. Statistical methods, which included basic statistical analysis, linear regression, and multiple linear regression analysis, were combined to evaluate the formula for absolute permeability. It appeared that the following parameters: Feret Breadth/Volume, Flatness/Anisotropy, Feret Max/Flatness, moments of inertia around middle principal axis I2/around longest principal axis I3, Anisotropy/Flatness, Flatness/Anisotropy provided the best res... [more]

The growth of renewable energy in the last two decades has led to the development of new power electronic converters. The DC microgrid can operate in standalone mode, or it can be grid-connected. A DC microgrid consists of various distributed generation (DG) units like solar PV arrays, fuel cells, ultracapacitors, and microturbines. The DC-DC converter plays an important role in boosting the output voltage in DC microgrids. DC-DC converters are needed to boost the output voltage so that a common voltage from different sources is available at the DC link. A conventional boost converter (CBC) suffers from the problem of limited voltage gain, and the stress across the switch is usually equal to the output voltage. The output from DG sources is low and requires high-gain boost converters to enhance the output voltage. In this paper, a new high-gain DC-DC converter with quadratic voltage gain and reduced voltage stress across switching devices was proposed. The proposed converter was an imp... [more]

This paper presents the effect of cavity-based injection in an axisymmetric supersonic combustor using numerical investigation. An axisymmetric cavity-based angled and transverse injections in a circular scramjet combustor are studied. A three-dimensional Reynolds-averaged Navier−Stokes (RANS) equation along with the k-ω shear-stress transport (SST) turbulence model and species transport equations are considered for the reacting flow studies. The numerical results of the non-reacting flow studies are validated with the available experimental data and are in good agreement with it. The performance of the injection system is analyzed based on the parameters like wall pressures, combustion efficiency, and total pressure loss of the scramjet combustor. The transverse injection upstream of the cavity and at the bottom wall of the cavity in a supersonic flow field creates a strong shock train in the cavity region that enhances complete combustion of hydrogen-air in the cavity region compared... [more]

This study optimizes pyrolysis conditions that will maximize energy recovery from the Beauty Leaf Tree (BLT; Calophyllum inophyllum L.) oil seed press cake. Response surface methodology (RSM) was used to determine the behavior of pyrolysis coproducts (solid, liquid and gas) at various temperatures and residence times. One significant discovery was that 61.7% of the energy (of the whole BLT oil seed) was still retained in the BLT oil seed cake after oil extraction. Controlled pyrolysis produced various proportions of biochar, bio-oil and syngas coproducts. Predictive models were developed to estimate both the mass and energy yields of the coproducts. In all experimental runs, the biochar component had the highest mass yield and energy content. Biochar mass yields were high at the lowest operating temperature used, but the energy yields based on a high heating value (HHV) of products were optimal at higher operating temperatures. From the RSM models, energy from the biochar is optimized... [more]

Recently, the interest in the plant factory-based crop production technologies is rising following the application of the smart farm technology to the agricultural arena. A lettuce production system platform is proposed in this study considering the effects of indoor environmental conditions and artificial light sources. The spectral characteristics of a visible ray according to growth performances were analyzed first to develop a control algorithm that can stimulate the plant’s growth for the proposal. Secondly, an imaging system was designed to analyze the plant’s growth characteristics based on the images and set up the system configuration. Lastly, a crop production system was proposed by using an experimental crop production group for environmental control and monitoring.

The paper focuses on the development of a thermal protection and energy requirements in relation to the issue of prefab residential housing buildings and prefab housing estates while emphasizing the need for a conceptual approach and environmental considerations. The development is recapitulated with examples of compositional sets of prefab residential housing on selected sites in the Czech Republic. Based on the comparison of archival documents and results of a long-term observation of the prefab residential housing resources, it outlines the direction of further expected development of prefab housing estates within a social context. The comparison also takes into account the impact of the European Union energy strategy and the implementation of directives into the legal rules and standards of the member states. The aim of the paper is to show the negatives and positives of current political and social strategies in relation to the thermal protection of buildings, the energy managemen... [more]

The global spread of the COVID-19 virus has led to difficulties in many branches of the economy, including significant effects on the urban transport industry. Thus, countries around the world have introduced different mobility policies during the pandemic. Due to government restrictions and the changed behaviors of transport users, companies providing modern urban mobility solutions were forced to introduce new business practices to their services. These practices are also apparent in the context of the electric shared mobility industry. Although many aspects and problems of electric shared mobility have been addressed in scientific research, pandemic scenarios have not been taken into account. Noticing this research gap, we aimed to update a previously developed model of factors that influence the operation of electric shared mobility by incorporating aspects related to the COVID-19 pandemic and its impact on this industry. This article aims to identify the main factors influencing t... [more]

Thermal Energy Storage (TES) materials, such as Phase Change Materials (PCMs) are proven to enhance the energy efficiency in many fields, such as automotive and building sectors, which correspond to the most energy intensive ones. Shape-stabilized PCM and cascade PCM are procedures to overcome the most important barriers when PCMs are applied since PCMs need to be encapsulated for their technical use: the leakage of the liquid phase, corrosion, low heat transfer and narrow temperature of application. In the present study, a novel shape stabilized PCM with cascade performance (cascade shape stabilized phase change material, CSS-PCM) is synthesized via dissolution, which allows up to 60 wt.% of a paraffin-PCM in the final composition. The novel CSS-PCM is based on a biopolymer, the polycaprolactone (PCL), a low melting temperature polyester as polymeric matrix and RT27 and Micronal DS 5040 acting as PCM. To evaluate the performance of the new TES materials developed, several techniques h... [more]

The Egyptian irrigation system depends mainly on canals that take water from the River Nile; nevertheless, the arid climate that dominates most of the country influences the high rate of water losses, mainly through evaporation. Thus, the main objective of this study is to develop a practical approach that helps to accommodate solar photovoltaic (PV) panels over irrigation canals to reduce the water evaporation rate. Meanwhile, a solar PV panel can contribute effectively and economically to an on-grid system by generating a considerable amount of electricity. A hybrid system includes a solar PV panel and a diesel generator. Several factors such as the levelized cost of energy (LCOE), total net present cost, loss of power supply probability, and greenhouse gas emissions should be considered while developing a technoeconomically feasible grid-connected renewable integrated system. A mathematical formulation for the water loss was introduced and the evaporation loss was monthly estimated.... [more]

We examine energy efficiency in the European Union (EU) using an integrated model that connects labor and capital as production factors with energy consumption to produce GDP with a limited amount of environmental emissions. The model is a linear output-oriented BCC data envelopment analysis (DEA) that employs variables with non-negative values to calculate efficiency scores for a sample of 28 EU member states in the period 2010−2018. We assume variable returns to scale (VRS) considering the natural inclination of countries to adopt technologies that allow them to produce higher outputs over extended periods of time, which we observed through the trends of increasing labor productivity and decreasing energy intensity over the analyzed period. The average EU inefficiency margin in the sample period is 16.0%, with old member states being significantly more efficient (4.2%) than new member states (29.5%). Energy efficiency management does not improve over time, especially in new member st... [more]

Among the many different applications of geothermal energy, its use for agricultural production purposes is noteworthy. The use of geothermal water in greenhouse cultivation is the most modern form of production; it enables the implementation of the production cycle throughout the year while reducing energy costs. In this paper, based on basic heat transfer relations, the heat demand of modern greenhouse constructions was determined. The monthly and year-round heat demand was determined for facilities with diversified heights of the side walls. Depending on the type of unit of greenhouse area analysed (1 ha), the calculated annual heat demand ranged from 11.05 to 12.46 TJ. Based on data on the geothermal energy potential in Poland, investment costs and payback periods were determined for the analysed locations. The locations of the facilities were selected based on traditions of plant cultivation in the greenhouse facilities and the availability of geothermal energy. The analysis showe... [more]

The fossil-based energy system is transitioning towards a renewable energy system. One important aspect is the spatial and temporal mismatch between intermitted supply and continuous demand. To ensure a reliable and affordable energy system, we propose an integrated system approach that integrates electricity production, mobility, heating of buildings and water management with a major role for storage and conversion. The minimization of energy transport in such an integrated system indicates the need for local optimization. This study focuses on a comparison between different novel system designs for neighborhood energy and water systems with varying modes of system integration, including all-electric, power-to-heat and power-to-hydrogen. A simulation model is developed to determine the energy and water balance and carry out economic analysis to calculate the system costs of various scenarios. We show that system costs are the lowest in a scenario that combines a hydrogen boiler and he... [more]

This paper presents a method that has been developed to reduce the torque ripples under healthy and open-circuit fault-tolerant (OCFT) conditions for a multiphase permanent magnet (PM) machine. For smooth torque, both the phase current and the back electromotive force (back-EMF) should be purely sinusoidal. To improve the torque in a multiphase machine, higher-order current harmonics are injected, which are related to the harmonics in the back-EMF. For this reason, generally, multiphase machines are designed with higher-order back-EMF harmonics. However, these harmonics produce ripples in the torque. In light of this, a torque ripple cancellation method has been developed that first determines an additional current component from the harmonic content of the back-EMF and then injects these additional components to cancel the torque ripple. It has been found that this new torque ripple cancellation method works for both faultless and faulty conditions in a five-phase PM machine. The meth... [more]

For corrugated pipes with a square groove, it is known that there is no interaction between the main flow and groove flow when the aspect ratio is less than four. When the groove length and height are different, the interaction occurs in the pipe. In previous studies, it was investigated whether this interaction is dependent on groove length. However, when changing the groove height, the shape of the vortex generated inside the groove changes, which may cause the interaction to occur. Therefore, in this paper the interaction between the main and groove flow of corrugated pipes is investigated when changing both groove height as well as groove pitch, corresponding to an aspect ratio of less than four. For the groove height, the flow out of the groove after impingement changes with the shape of the secondary vortex in the groove. This flow deforms the velocity distribution in the main flow, and thus the friction factor is different. For the groove pitch, there is no difference in v-veloc... [more]

The rotor wake aerodynamic characterization is a fundamental aspect for the development and optimization of future rotary-wing aircraft. The paper is aimed at experimentally and numerically characterizing the blade tip vortices of a small-scale four-bladed isolated rotor in hover conditions. The investigation of the vortex decay process during the downstream convection of the wake is addressed. Two-component PIV measurements were carried out below the rotor disk down to a distance of one rotor radius. The numerical simulations were aimed at assessing the modelling capabilities and the accuracy of a free-wake Boundary Element Methodology (BEM). The experimental and numerical results were investigated by the Γ2 criterion to detect the vortex location. The rotor wake mean velocity field and the instantaneous vortex characteristics were investigated. The experimental/numerical comparisons show a reasonable agreement in the estimation of the mean velocity inside the rotor wake, whereas the... [more]

The problem of low accuracy and low convenience in the existing state of health (SOH) estimation method for vehicle lithium-ion batteries has become one of the important problems in the electric vehicle field. This paper proposes an improved cuckoo search particle filter (ICS-PF) algorithm based on a charging time segment from equal voltage data to estimate battery health status. Appropriate voltage ranges of charging time segments are selected according to the battery charging law, and in the meantime, the charging time segments are collected as a health indicator to establish the corresponding relationship with battery capacity attenuation value. An improved cuckoo search particle filter algorithm based on the traditional particle filter (PF) and cuckoo search (CS) algorithm is proposed by enhancing the search step size and discovery probability to estimate the capacity attenuation. The estimation result shows that this method is superior to the traditional particle filter and cuckoo... [more]

Rock yielding may well take place during hydraulic fracturing in deep reservoirs. The prevailing models based on the linear elastic fracture mechanics (LEFM) are incapable of describing the evolution process of hydraulic fractures accurately. In this paper, a hydro-elasto-plastic model is proposed to investigate the hydraulic fracture propagation in deep reservoirs. The Drucker−Prager plasticity model, Darcy’s law, cubic law and cohesive zone model are employed to describe the plastic deformation, matrix flow, fracture flow and evolution of hydraulic fractures, respectively. Combining the embedded discrete fracture model (EDFM), extended finite element method (XFEM) and finite volume method, a hybrid numerical scheme is presented to carry out simulations. A dual-layer iterative procedure is developed based on the fixed-stress split method, Picard iterative method and Newton−Raphson iterative method. The iterative procedure is used to deal with the coupling between nonlinear deformation... [more]

Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used in building energy simulations because of the short computation time but often do not include flow-rate dependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, and two convection eddy-diffusivity models were compared with experimental data sets for discharging a 50-gal residential tank and recharging the tank with hot water from an external hot-water source. A minimum and maximum relationship for the eddy diffusivity factor were found at Re 10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold water at the bottom. The root mean s... [more]

The growth of the renewable energy industry is happening at a swift pace pushed, by the emergence of Industry 4.0. Smart technologies like artificial intelligence (AI), Big Data, the Internet of Things (IoT), Digital Twin (DT), etc. enable companies within the sector of renewable energies to drastically improve their operations. In this sectoral context, where upgraded sustainability standards also play a vital role, it is necessary to fulfil the human capital requirements of the imminent technological advances. This article aims to determine the current skills of the renewable energy industry workforce and to predict the upcoming skill requirements linked to a digital transition by creating a unified database that contains both types of skills. This will serve as a tool for renewable energy businesses, education centers, and policymakers to plan the training itinerary necessary to close the skills gap, as part of the sectoral strategy to achieve a competent future workforce.

The COVID-19 pandemic is having a strong influence in all areas of society, like wealth, economy, travel, lifestyle habits, and, amongst many others, financial and energy markets. The influence in standard energies, like crude oil, and renewable energies markets has been twofold: from one side, the predictability of volatility has strongly decreased; secondly, the linkages of the price time series have been modified. In this paper, by using DCC-GARCH and Price Leadership Share methodology, we can investigate the changes in the influences between standard energies and renewable energies markets by analyzing one-minute time series of West Texas Intermediate crude oil futures contract (WTI), the Brent crude oil futures contract (BRENT), the STOXX Europe 600 oil & gas index (SXEV), and the European renewable energy index (ERIX). Our results confirm volatility spillover between the time series. However, when assessing the accuracy of the predictability of the DCC-GARCH model, the results sh... [more]

Zinc−air batteries feature high energy density, but they usually suffer from their short storage life after they start working, restricting their commercial applications. In the past, scholars did not reach an agreement on the influencing factors of the performance degradation of zinc−air batteries when exposed to air. Here, a series of comparative experiments were conducted to confirm the changes of the battery during storage after being exposed to air. The morphology and composition of the components of the battery were characterized by scanning electron microscopy (SEM) and X-ray diffraction analyses. SEM images revealed that with the increase of storage days, the corrosion of the zinc anode gradually deepens, but the surface morphology of the air cathode does not change much. The electrolyte of the batteries stored for different periods was examined through inductively coupled plasma spectroscopy and titration. After 20 days of storage, the concentration of CO32− reached 2.694 mol... [more]

This paper presents a method for the performance analysis of high-speed electric machines supplied with pulse-width modulated voltage source inverters by utilizing a fast analytical model. By applying a strict mathematical procedure, effective expressions for the calculation of rotor eddy current losses and electromagnetic torque are derived. Results obtained by the approach suggested in this study are verified by the finite element model, and it is shown that the proposed method is superior in comparison to the finite element method in terms of computation time. The proposed method enables fast parameter variation analysis, which is demonstrated by changing the inverter switching frequency and electric conductivity of the rotor and analyzing the effects of these changes on rotor eddy current losses. The presented work separately models effects of the permanent magnet and pulse-width modulated stator currents, making it suitable for the analysis of both high-speed permanent magnet mach... [more]

In this study, a thermal energy storage tank filled with commercial phase change material flat slabs is investigated. The tank provides heat at around 15 °C to the evaporator of a seasonal thermal energy storage system developed under the EU-funded project SWS-Heating. A 2D numerical model of the phase changed material storage tank based on the finite control volume approach was developed and validated with experimental data. Based on the validated model, an optimization was performed to identify the number, type and configuration of slabs. The final goal of the phase change material tank model is to be implemented into the whole generic heating system model. A trade-off between results’ accuracy and computational time of the phase change material model is needed. Therefore, a comparison between a 2D implicit and 2D explicit scheme of the model was performed. The results showed that using an explicit scheme instead of an implicit scheme with a reasonable number of nodes (15 to 25) in t... [more]

This paper demonstrates the procedure of blade adjustment in a Kaplan-type water turbine, based on calculations of the flow system. The geometrical adjustment of a twisted blade with varying chord length is described in the study. Computational fluid dynamics (CFD) analysis was used to characterise aerofoil and turbine performance. Furthermore, two turbines, with a different number of blades, were designed, manufactured, and tested experimentally. The numerical model results were then compared with the experimental data. The studies were carried out with different rotational velocities and different stator blade incidence angles. The paper shows a comparison of the turbine efficiencies that were assessed, using numerical and experimental methods, of a flow system with four- and five-bladed rotors. The numerical model results matched up well with those of the experimental study. The efficiency of the proposed turbines reached up to 72% and 84% for four-bladed and five-bladed designs, re... [more]

Remote and Indigenous communities in Canada have a unique opportunity to mobilize the vast amount of wood-based biomass to meet their energy needs, while supporting a local economy, and reducing greenhouse gas (GHG) emissions. This study realized in collaboration with five remote and Indigenous communities across Canada investigates the main barriers and potential solutions to developing stable and sustainable wood-based bioenergy systems. Our results highlight that despite the differences in available biomass and geographical context, these communities face common policy, economic, operational, cultural, social, and environmental risks and barriers to developing bioenergy. The communities identified and ranked the biggest barriers as follows; the high initial investment of bioenergy projects, the logistical and operational challenges of developing a sustainable wood supply chain in remote locations, and the limited opportunities for community leadership of bioenergy projects. Environm... [more]