Modern civilization and economic development of humankind have been largely based on the exploitation and utilization of fossil energy [...]

Due to the use of welded finned tubes in heat exchangers, gas blocks are characterized by very good electric energy production performance, and their reliability can reach 98%. Finned tubes used in heat exchangers are usually welded. Such tubes should be characterised by the following properties: high thermal performance, good resistance to high-temperature corrosion in a flue gas atmosphere, and appropriate joint strength and hardness. The most popular technology for welding finned tubes is MAG. MAG-welded joints are characterised by considerable spattering, weld discontinuities (up to 60%), and non-axial fin alignment. Such irregularities result in a considerably reduced heat flux due to the heat transfer resistance occurring in the welded joint. It has been shown that with weld discontinuities of 20%, the thermal performance of welded finned tubes reduces considerably. This paper proposes the possibility of welding finned tubes with a laser. The thermal properties of laser-welded fi... [more]

In recent years, the open microchannel has drawn increasing interest, but severe local dryout limited the heat transfer capability of flow boiling. It was anticipated that nanostructures with exceptional capillary wicking abilities would overcome this problem. In this study, blade-like CuO nanostructures were created in the copper open microchannels to experimentally investigate water flow boiling. Experiments were carried out in nanostructured open microchannels (NMCs), and smooth-surface open microchannels (SMCs), as a comparison, were examined under identical operating conditions. Four main flow patterns, including bubbly flow, slug flow, and two kinds of stratified flow, dominated successively in NMCs and SMCs. Although the flow patterns were similar in NMCs and SMCs, the heat transfer coefficient (HTC) of flow boiling was greatly enhanced by nanostructures under conditions of medium and high heat flux, while the nanostructures’ influence on HTC was unnoticeable at low heat flux. A... [more]

A great number of factors determining the development of photovoltaics are associated with the assessment of possible volumes of solar energy use in correlation with the technical and economic characteristics of photovoltaic equipment. An appropriate assessment of solar energy potential that applies universally to any subsequent use option still remains a crucial task. This work is devoted to the assessment and analysis of the gross, technical and economic potentials of solar energy for photovoltaics. The smart analysis includes the basic program working in the context of connection to databases and to the programs used for determining required initial data or, as a limited option, in the context of full or partial initial data input by the user. Therefore, optimally, a smart network is formed, which for the purposes of obtaining the values of potentials, uses the most up-to-date values of initial data and other required information. This work sets out the tried and tested assessment p... [more]

This article presents a single-stage five-level boost inverter (5L-SBI) topology with reduced power components. The proposed topology falls under the self-balanced switch-capacitors (SCs) type and combines both a DC/DC boost converter and inverter with a switched-capacitor cell. The advantages of proposed topologies include the following: the number of switch counts is reduced, the maximum voltage gain is two times higher than the input voltage, and the capacitor’s charging current is suppressed. Further, the proposed topology cascaded, and three-phase extensions are presented. To attest, the advantages of the proposed topology are thoroughly compared with other recent SCI topologies. The proposed topology is verified under dynamic loading conditions, and the results are presented, considering a 600 W laboratory prototype model.

This paper aims to give a comprehensive energetic-exergetic performance analysis on the impacts of injecting-submillimeter of air bubbles into both sides of cold and hot water streams before the entrance port of a corrugated plate heat exchanger (C-PHE) having ten plates within counterflow configuration. Hence, optimize the energy and exergy effectiveness at different operating conditions for counter and parallel fluid flow configurations. Hot streams were studied in seven flow rates ranging from 280 L/h to 880 L/h with a regular step of 100 L/h, and constant hot water temperature and cold-water stream of 50 °C and 290 L/h, respectively. Hence, the air was discharged with four flow rates ranging between 150 and 840 L/h. The obtained results showed the vital role of the ABI technique in enhancing the NTU and effectiveness by 59% and 18.6%, respectively, for CWS. The entropy generation was reduced to 0.038 W/K and the augmentation entropy generation number to 0.087 at the low airflow rat... [more]

In this study, carbon-based nanofluids (CBNFs) were prepared using a revised vortex trap method and applied in the direct absorption solar collector (DASC) to evaluate the feasibility of CBNFs in DASC. The thermal storage performance of water and different concentrations of CBNFs (0.01, 0.025 and 0.05 wt%) was assessed with a 1000 W halogen lamp as a simulated light source under different volumetric flow rates (1.5, 3.0, and 4.5 L per minute [LPM]) at a constant thermal storage load (2.4 kg of water) and ambient temperature of 26 °C. The thermal storage capacity, system efficiency factor (SEF), and heating rate of the CBNFs as the working fluid were higher than those of water in most cases. The thermal storage capacity and SEF of 0.05 wt% CBNF at a volumetric flow rate of 3.0 LPM were 10.36% and 9.36% higher than that of water, respectively. The relevant experimental results demonstrate the great potential of CBNFs in DASC.

The aim of this study is to investigate the influence of biomass particle size on the torrefaction characteristics under different torrefaction temperatures and times. Paulownia wood with particle sizes ranging from 12 to <0.3 mm was selected. It was torrefied at 260 and 290 °C in a fixed-bed reactor for 30−90 min. The results showed that biomass particle size did affect the product’s evolution during biomass torrefaction. With the decrease in particle size from 12 to <0.3 mm, the yield of the solid product decreased by 5.41 and 3.54 wt.%, the yield of the liquid product increased by 5.87 and 3.25 wt.%, and the yield of the gas product changed insignificantly, at 260 and 290 °C, respectively. Comparatively, torrefaction temperature had a more significant effect on the composition of gas products than particle size and torrefaction time. At lower temperatures, decarboxylation reactions dominated in the torrefaction process with more CO2 produced. However, at higher temperatures, d... [more]

Owing to different temperature rages of power generation and refrigeration in the cogeneration system, for the sake of selecting the working fluids that are suitable for both power generation and refrigeration simultaneously, 17 commonly used working fluids are evaluated in this paper, based on an organic Rankine cycle coupled with a two-stage vapor compression cycle system in different geothermal fluid temperatures. The performances of working fluids under different working conditions, and the maximum power generation as well as cooling capacity are analyzed. Additionally, the main parameters are analyzed to optimize the system performance. The results indicate that net power output has a local maximum where it corresponds to the optimal evaporation temperature. Besides, the lower the critical temperature, the greater the thermal conductance, and the pressure ratio decreases with evaporation temperature. Hydrocarbons all have higher total heat source recovery efficiency. R1234yf, prop... [more]

Hydrogen is one of the prospective clean energies that could potentially address two pressing areas of global concern, namely energy crises and environmental issues. Nowadays, fossil-based technologies are widely used to produce hydrogen and release higher greenhouse gas emissions during the process. Decarbonizing the planet has been one of the major goals in the recent decades. To achieve this goal, it is necessary to find clean, sustainable, and reliable hydrogen production technologies with low costs and zero emissions. Therefore, this study aims to analyse the hydrogen generation from solar and wind energy sources and observe broad prospects with hybrid renewable energy sources in producing green hydrogen. The study mainly focuses on the critical assessment of solar, wind, and hybrid-powered electrolysis technologies in producing hydrogen. Furthermore, the key challenges and opportunities associated with commercial-scale deployment are addressed. Finally, the potential applications... [more]

Phase-homogeneous LiFePO4 powders have been synthesized. The content of impurity crystalline phases was less than 0.1%, according to synchrotron diffractometry (SXRD) data. Anisotropic crystallite sizes L¯Vhkl were determined by XRD. A low resistance covering layer of mechanically strong ferric-graphite-graphene composite with impregnated ferric (Fe3+) particles < 10 nm in size increases the cycleability compared to industrial cathodes. In accordance with the corrosion model, the destruction of the Fe3+-containing protective layer of crystallites predominates at the first stage, and at the second stage Fe escapes into the electrolyte and to the anode. The crystallite size decreases due to amorphization that starts from the surface. The rate capability, Q(t), has been studied as a function of L¯Vhkl, of the correlation coefficients rik between crystallite sizes, of the Li diffusion coefficient, D, and of the electrical relaxation time, τel. For the test cathode with a thickness of 8... [more]

The current situation in world energy requires a new approach to the control of the power flow in power systems. On the one hand, regulations within the EU require the transition to renewable energy. On the other hand, there are no conventional sources available. Thus, there is a need to use known control tools in non-standard applications. One such example is the use of a regulating transformer inside the power grid to use it to shape the power flow in the system. This article presents a proposal of an algorithm for determining new locations for regulating transformers from the point of view of active power control. By analyzing the parameters of the power grid, it is possible to determine which branch of the grid is the most suitable for installing a regulating transformer in it. The use of a regulating transformer inside the grid improves the transmission capabilities of the national power system.

This work focuses on the occurrence and composition of flammable pyrolysis gases which can be expected from stimulation of heavy oil with superheat steam. These gases can have commodity value or be used to fire a conventional boiler to generate steam vapor for superheater feed. Seven oil samples taken from different US locations were tested via thermogravimetric analysis (TGA) with off-gas analysis of light hydrocarbons via mass spectrometry (MS). The samples were heated up to 500 °C at 5 °C/min in a gas flow of moist carbon dioxide and held at 500 °C until no further mass loss was noted. Then, carbonaceous residue was exposed to air at 500 °C to determine enthalpy of combustion by differential scanning calorimetry (DSC). To demonstrate that pyrolysis was indeed occurring and not simple de-volatilization, a high-molecular-weight reagent-grade organic molecule, lactose, was first demonstrated to produce components of interest. After treatment under moist CO2 at 500 °C, all samples were... [more]

Different configurations of on/off-grid-connected hybrid renewable energy systems (HRESs) are analyzed and compared in the present research study for optimal decision making in Sub-Saharan Africa, facing the problems of electricity deficit. A multi-criteria analysis is performed for this purpose using MATLAB software for simulation. The obtained results show that the levelized cost of energy (LCOE) corresponding to 0% power supply deficit probability (PSDP) is 0.0819 USD/kWh, 0.0925 USD/kWh, 0.3979 USD/kWh, 0.3251 USD/kWh, 0.1754 USD/kWh, 0.1641 USD/kWh, 0.5385 USD/kWh, and 1.4515 USD/kWh, respectively, for the Grid-PV/Wind/Battery, Grid-PV/Battery, Grid-Wind/Battery, Grid-Wind, PV/Wind/Battery, PV/Battery, Wind/Battery, and stand-alone Wind systems. The CO2 emissions are 14,888.4 kgCO2/year, 16,916.6 kgCO2/year, 13,139.7 kgCO2/year, 6430.4 kgCO2/year, 11,439 kgCO2/year, 14,892.5 kgCO2/year, 10,252.6 kgCO2/year, and 1621.5 kgCO2/year, respectively, for the aforementioned systems. It is... [more]

A new explicit sequentially coupled technique for chemo-thermo-poromechanical problems in shale formations is developed. Simultaneously solving the flow and geomechanics equations in a single step is computationally expensive with consequent limitations on the computations involving well or reservoir-scale geometries. The newly developed solution sequence involves solving the temperature field within the porous system. This is followed by the computation of the chemical activity constrained by the previously computed temperature field. The pore pressure is then computed by coupling the pore thermal and chemical effects but without consideration of the volumetric strains. The geomechanical effect of the volumetric strain, stress tensors, and associated displacement vectors on the pore fluid is subsequently computed explicitly in a single-step post-processing operation. By increasing the borehole pressure to 20 MPa, it is observed that the rock displacement and velocities concurrently in... [more]

Earth−air heat exchanger (EAHE) systems are used to pre-heat or pre-cool air before entering into a building using shallow geothermal energy. Assessment of EAHE systems is important to quantify the profitability of these systems. For this purpose, an EAHE system built at ICUBE at the University of Strasbourg in the northeast of France was studied using energy and exergy analyses for a typical heating period (between 25 February and 3 March). Energy analysis was used to determine the heat gained by the air in the system during the studied period and to determine the Coefficient Of Performance (COP) of the system. Additionally, exergy analysis, which considered temperature, pressure, humidity, and the variation in the control volume boundary temperature, was realized to determine inefficiencies in the system by determining the exergy destroyed in each component of the system and evaluating its exergetic efficiency. Results showed that the heat energy gained using the system was around 63... [more]

The article presents the research on navigation algorithms of a wheeled mobile robot with the use of a vision mapping system and the analysis of energy consumption of selected navigation algorithms, such as RRT and A-star. Obstacle maps were made with the use of an RGBW camera, and binary occupation maps were also made, which were used to determine the traffic path. To recreate the routes in hardware, a programmed Pure Pursuit controller was used. The results of navigation were compared on the basis of the forward kinematics model and odometry measurements. Quantities such as current, except (x, y, phi), and linear and angular velocities were measured in real time. As a result of the conducted research, it was found that the RRT star algorithm consumes the least energy to reach the designated target in the designated environment.

This paper presents a novel structure of Integrated SiC MOSFETs with a high-frequency transformer (I-SiC-HFT) for various high-power isolated DC−DC converters. Several resonant converters are considered for integration in this paper, including the phase-shift full-bridge (PSFB) converter, inductor−inductor−capacitor (LLC) resonant converter, bidirectional PSFB converter, and capacitor−inductor−inductor−capacitor (CLLC) resonant converter. The applications of I-SiC-HFT are focused on V2G EV battery charging systems, energy storage in DC and AC microgrids, and renewable energy systems. SiC devices, including MOSFETs, Schottky diodes, and MOSFET modules, are used in this novel structure of I-SiC-HFT. The high-frequency magnetic structure uses distributed ferrite cores to form a large central space to accommodate SiC devices. The optimized architecture of I-SiC-HFT and heatsink structure is proposed for thermal management of SiC devices. To prove the concept, a small-scale 1.5 kW prototype... [more]

The current study focuses on the synthesis of Cerium oxide (CeO2) nanocatalyst via Tragacanth Gum (TG) using the wet impregnation method and its application for sustainable biodiesel production from a novel, non-edible Descurainia sophia (L.) Webb ex Prantl seed oil. The D. sophia seed oil has higher oil content (36 wt%) and free fatty acid (FFA) value (0.6 mg KOH/g). Innovative analytical methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy, were used to characterize the newly synthesized, environmentally friendly, and recyclable CeO2-TG phytonanocatalyst (FT-IR). The results show that the CeO2-TG phytonanocatalyst was 22 nm in diameter with a spherical shape outer morphology, while the inner structure was hexagonal. Due to low FFA content, the D. sophia seed oil was pretreated and transesterified via a single ste... [more]

Building energy efficiency has grown strong in a context of soaring energy prices, especially in Europe. The use of energy-saving devices strongly influences its improvement, but in many cases, it is far from sufficient., especially if the energy comes from renewable sources with forced production. In the case of buildings, these are usually photovoltaic (PV) sources. For this reason, energy management systems (EMS) are becoming increasingly popular as they allow the increase in self-consumption and reduce the size of energy storage. This article presents analyses of historical energy consumption profiles in selected small- and medium-sized buildings powered by renewable energy sources. The implementation limitations of this type of systems, depending on the profile of the building, were identified and guidelines were presented to assess low-cost solutions dedicated to small buildings and considering the actual conditions of existing systems. Statistical analyzes were conducted for the... [more]

The main obstacle to the widespread dissemination of fuel cells is the high cost, so researchers are actively searching for ways to replace the expensive platinum catalyst with cheaper analogs. In this paper we studied the Ag- and Pd-containing carbon catalysts based on carbon nanotubes and graphene oxide. The study of the textural characteristics of the catalysts showed that the greatest specific surface area has a catalyst based on MWCNT containing 10% silver, all synthesized catalysts are mainly mesoporous, and the content of micropores is insignificant. Raman spectroscopy and SEM data indicate a significant change in the structure of the modified carriers compared to pure MWCNT and GO. An electrochemical experiment was performed and linear voltammetric diagrams were obtained and compared with the voltammetric diagrams obtained on the platinum catalyst. GO_Ag 10% and MWCNT_Ag 10% Pd 10% are closest in the values of kinetic parameters in both kinetic and diffusion regions. GO_Ag 10%... [more]

Carbon-dioxide-enhanced shale gas recovery technology has significant potential for large-scale emissions reduction and can help achieve carbon neutrality targets. Previous theoretical studies mainly focused on gas adsorption in one-dimensional pores without considering the influence from the pore geometry. This study evaluates the effects of pore shape on shale gas adsorption. The pure and competitive gas adsorption processes of CO2 and CH4 in nanopores were investigated using molecular simulations to improve the prediction of shale gas recovery efficiency. Meanwhile, quantitative analysis was conducted on the effects of the pore shape on the CO2-EGR efficiency. The results indicate that the density of the adsorption layer in pores is equally distributed in the axial direction when the cone angle is zero; however, when the cone angle is greater than zero, the density of the adsorption layer decreases. Smaller cone-angle pores have stronger gas adsorption affinities, making it challeng... [more]

There is a constant push towards increasing use of renewable energy-based distributed generators around the globe. While they provide a clean and sustainable source of energy, they employ technologies that are unknown to traditional power systems. These generators are interfaced via inverters that lack the inertia of large synchronous machines. This manifests itself as a more volatile frequency profile that is susceptible to disturbances. This phenomenon is more amplified in stand-alone microgrids which are utilized as a popular electrification alternative in isolated or underserved communities. One solution approach takes its inspiration from nature, e.g., behavior of bees, butterflies, or ants. When employed in a suitable way, animals’ natural behavior helps optimize interaction between different renewable-energy based generators and create a more stable microgrid. There are different approaches to stabilizing such systems with novel optimization approaches. Some of them optimize the... [more]

Deformations affect the structural integrity of wind turbine towers. The health of such structures is thus assessed by monitoring. The majority of sensors used for this purpose are costly and require in situ installations. We investigated whether Multiple-Input Multiple-Output Synthetic Aperture Radar (MIMO-SAR) sensors can be used to monitor wind turbine towers. We used an automotive-grade, low-cost, off-the-shelf MIMO-SAR sensor operating in the W-band with an acquisition frequency of 100 Hz to derive Line-Of-Sight (LOS) deformation measurements in ranges up to about 175 m. Time series of displacement measurements for areas at different heights of the tower were analyzed and compared to reference measurements acquired by processing video camera recordings and total station measurements. The results showed movements in the range of up to 1 m at the top of the tower. We were able to detect the deformations also with the W-band MIMO-SAR sensor; for areas with sufficient radar backscatte... [more]

Currently, Pakistan is facing severe energy crises and global warming effects. Hence, there is an urgent need to utilize renewable energy generation. In this context, Pakistan possesses massive wind energy potential across the coastal areas. This paper investigates and numerically analyzes coastal areas’ wind power density potential. Eight different state-of-the-art numerical methods, namely an (a) empirical method, (b) graphical method, (c) wasp algorithm, (d) energy pattern method, (e) moment method, (f) maximum likelihood method, (g) energy trend method, and (h) least-squares regression method, were analyzed to calculate Weibull parameters. We computed Weibull shape parameters (WSP) and Weibull scale parameters (WCP) for four regions: Jiwani, Gwadar, Pasni, and Ormara in Pakistan. These Weibull parameters from the above-mentioned numerical methods were analyzed and compared to find an optimal numerical method for the coastal areas of Pakistan. Further, the following statistical indi... [more]