Various external-recycle configurations of multi-pass flat-plate solar air collectors were studied theoretically to examine the optimal thermal performance under the same working dimension and operation conditions. An absorber plate and insulation sheet were implemented horizontally and vertically, respectively, into an open rectangular conduit to conduct a recycling four-pass operation, which the device lengthens the air flow channel and increases the air mass flow rate within the collector, and thus, a more heat transfer efficiency is obtained. Four recycling types with different external-recycle patterns were introduced and expected to augment the heat transfer rate due to the turbulent convective intensity through four subchannels in the present study. Coupling energy balances into one-dimensional modeling equations were derived by making the energy-flow diagram within a finite element, which the longitudinal temperature distributions for each subchannel were obtained. The theoreti... [more]

Turbulent flow, mainly originating from the rotor-stator interaction (RSI), is closely associated with the normal and safe operation of the centrifugal pump. In the current research, to clarify turbulent flow in the centrifugal pump with a vaned diffuser, the non-intrusive LDA (Laser Doppler Anemometry) system is applied to measure velocity pulsation signals at different regions when the pump operates at various flow rates. Time and frequency domain analysis methods are combined to investigate the velocity signals, and the velocity distribution around the volute tongue region is reconstructed from twenty measuring points. Results show that the velocity spectrum is characterized by the discrete components at the blade passing frequency and its higher harmonics, and it is caused by the RSI between the impeller and the diffuser. For the points in the volute spiral and diffusion sections, due to the significantly reduced RSI effect, the velocity spectrum shows an evident difference from co... [more]

Major concerns of carbon dioxide (CO2) sequestration in subsurface formations are knowledge of the well injectivity and gas storage capacity of the formation, the CO2 pressure and saturation plume extensions during and after injection, and the risks associated with CO2 leakage and fault reactivation. Saline reservoirs are considered as one of the target formations for CO2 sequestration through structural, residual, dissolution, and mineral trapping mechanisms. The boundary condition of the saline reservoir dictates the pressure and saturation plume extension of the injected supercritical CO2 that could expand over large distances. This can lead to sources of risk, e.g., leakage and/or fault reactivation due to presence of wells, thief zones, and geological discontinuities. Therefore, there is a critical need to develop a model that describes how risk-related performance metrics (i.e., the CO2 saturation plume size, the pressure differential plume area, and the pressure differential at... [more]

Recently, high-speed motors are receiving a lot of attention in the industrial field. When driving a motor at high speed, the advantages include high power density, high efficiency, and miniaturization. However, the disadvantages of the high-speed operation of motors are mechanical and structural safety. This is because the bearings used in high-speed motors require characteristics such as precision and low friction. There are two prominent types of bearings mainly used in high-speed motors: rolling bearings and magnetic bearings. A feature of rolling bearings is that they reduce frictional resistance by contacting points or lines between the shaft and the bearing. However, the disadvantages of rolling bearings are high mechanical friction losses due to the need for contact with the lubrication system. Maintenance costs are high. For this reason, a lot of research on bearings is being conducted to reduce the frictional loss of bearings and increase their efficiency and reliability. Bea... [more]

A solid-state heat pump using the electrocaloric effect (ECE) provides a new idea for the future development of heat pumps. However, most of the electrocaloric (EC) heat pumps presented in the literature are low in efficiency and use at least one moving part, which significantly reduces the reliability of the heat pump and adds to its complexities. In this context, combining the positive and negative ECEs, we proposed a plate-laminar non-mobile EC heat pump adopting Gallium-based liquid metal as an intermediate medium to guarantee highly efficient heat transfer. Numerical simulation in COMSOL Multiphysics has been performed to investigate the correlation between different operating parameters and the performance of the EC heat pump. Changing the temperature span only, a COP of 8.13 and a UVHP of 746.1 W·dm−3 were obtained at a temperature span of 7 K. It was also found that the UVHP increased by 28.45% and COP increased by 25.46% after adding one layer of EC material. The electric-indu... [more]

The SARS-CoV-2 pandemic is spreading rapidly and threatening lives all over the globe. Due to the pandemic, economies all over the world are in deep distress due to disruption in work and operations across all sectors. The present case study was performed for a private Indian manufacturing company that has been affected to a great extent due to this pandemic, as India has the second highest number of SARS-CoV-2 cases after the USA. The deeply troubled company’s current predicament is very complex, as various factors are responsible for the crisis. In order to restore the company back to normal functioning, these factors were studied and evaluated. A diagnostic survey was conducted to obtain data about current working conditions of company. Data from the survey were analyzed qualitatively and quantitatively to identify and evaluate the disruptive factors. Based on this analysis, problems in operational activities were identified and appropriate improvement actions (best practices) were... [more]

Smart Parking is essential for any future smart cities due to the tremendous growth of the car fleet. Such infrastructures require a certain amount of equipment. Indeed, smart parking integrates a lot of actors, to manage the parking its equipment must be managed accordingly. Here, is proposed a distributed architecture to manage them by collecting efficiently their data. Two types of data relating to the parking must be collected: those coming from the deployed equipment in the parking and those coming from the internet due to remote users. Thus, a system of two main servers based on the multi-agent concept is proposed. This system manages the parking platform. The first server is dedicated to the parking equipment data collection (Processing Server−PS). The second server (Processing Web Server−PWS) collects the users’ online data such as reservation, and it is responsible for pricing policies, and receive post-processed data from the Processing Server. The parking equipment integrate... [more]

The U.S. Deepwater Gulf of Mexico (DGOM) area that has some of the most prolific oil reservoirs is still awaiting the development of a viable enhanced oil recovery (EOR) process. Without it, DGOM will remain severely untapped. Exorbitant well costs, in excess of $200 million, preclude having extensive injection patterns, commonly used in EOR design frameworks. Aside from injection patterns, even operationally waterflooding has met with significant challenges because of injectivity issues in these over pressurized turbidities. The gas-assisted gravity drainage (GAGD) EOR process, that holds promise for deepwater environments because of lesser injectivity issues, among others, has been adapted in this work to overcome these limitations. A novel design in the form of a single well—gas assisted gravity drainage (SW-GAGD) process, has been demonstrated to emulate the benefits of a GAGD process in a cost-effective manner. Unlike conventional GAGD processes, which need multiple injectors and... [more]

The subject of the article is a comparative long-distance transport analysis based on the relationship between central and eastern China and Poland. It provides an overview of issues related to long-haul China−Poland. The technique for order of preference by similarity to ideal solution (TOPSIS) method was proposed in the multi-criteria analysis. This method was briefly discussed, and its choice was justified. Then, the criteria adopted in the analysis were presented, i.e., time, cost, maximum number of containers, and ecology index. Multi-criteria analysis was carried out for three cases: the transport of one loading unit, 82 loading units, and 200 loading units. The geopolitical and operational situation on the transport route for the analyzed modes of transport was discussed.

In terms of service provision, the electricity sector is the most important critical infrastructure sector, on the supply of which the vast majority of society and its basic vital functions depend. Extensive disruption of these supplies would have negative effects not only on basic human needs, but also on the economy and security of the state. For this reason, it is necessary to ensure permanent and comprehensive monitoring of the infrastructure elements resilience level, especially against threats with a multispectral impact on several areas of security. For this reason, the authors of the article developed the Converged Resilience Assessment (CRA) method, which enables advanced assessment of the electricity critical infrastructure elements resilience from the converged security point of view. Converged security in this case combines (converges) physical, cyber and operational security into a complementary unit. This reflects the integral determinants of resilience across related are... [more]

This paper presents a computationally efficient novel heuristic approach for solving the combined heat and power economic dispatch (CHP-ED) problem in residential buildings considering component interconnections. The proposed solution is meant as a substitute for the cutting-edge approaches, such as model predictive control, where the problem is a mixed-integer nonlinear program (MINLP), known to be computationally-intensive, and therefore requiring specialized hardware and sophisticated solvers, not suited for residential use. The proposed heuristic algorithm targets simple embedded hardware with limited computation and memory and, taking as inputs the hourly thermal and electrical demand estimated from daily load profiles, computes a dispatch of the energy vectors including the CHP. The main idea of the heuristic is to have a procedure that initially decomposes the three energy vectors’ requests: electrical, thermal, and hot water. Then, the latter are later combined and dispatched c... [more]

Microalgae are currently considered to be a promising feedstock for biodiesel production. However, significant research efforts are crucial to improve the current biomass and lipid productivities under real outdoor production conditions. In this context, batch, continuous and semi-continuous operation regimes were compared during the Spring/Summer seasons in 2.6 m3 tubular photobioreactors to select the most suitable one for the production of the oleaginous microalga Nannochloropsis oceanica. Results obtained revealed that N. oceanica grown using the semi-continuous and continuous operation regimes enabled a 1.5-fold increase in biomass volumetric productivity compared to that cultivated in batch. The lipid productivity was 1.7-fold higher under semi-continuous cultivation than that under a batch operation regime. On the other hand, the semi-continuous and continuous operation regimes spent nearly the double amount of water compared to that of the batch regime. Interestingly, the bioch... [more]

This work aims at analyzing and architecting natural and artificial parameters to model a water-film cooling system for photovoltaic modules for some months under warm conditions. Methodologically, the theoretical and technical aspects were structured to develop, implement, monitor, and assess the cooling system at an on-grid, outdoor testing unit, considering the following: (i) the criteria to select and to approve the implementation site (infrastructure and climatologic and solarimetric conditions); (ii) the types, frequency and qualities of the monitored data; (iii) the system measurement, monitoring and control equipment; (iv) the commissioning of the system as a whole; and (v) the tests and results empirically obtained. The water-film cooling system reduces the temperature by 15−19%, on average, and up to a maximum of 24−35%. In terms of electric power, there was an average gain of 5−9% at the time of day with the highest solar radiation, and maximum gains of 12% on days with sola... [more]

In this paper the results of the EMC tests of the wideband power sources: the PWM-based power source and audio power amplifier are discussed. They are intended to be used to supply the measuring system developed for evaluation of the wideband transformation accuracy of instrument transformers. Therefore, it is required to detect possible interferences that may be caused by the power supply to its operation and that may cause a decrease in its accuracy. The tests concern the conducted emission in the frequencies range from 150 kHz to 30 MHz and the radiated emission in the frequencies range from 30 MHz to 1 GHz. Moreover, the level of conducted disturbances in frequencies range from 100 Hz to 5 kHz generated into the supplying current is measured and the immunity of both wideband power sources to low frequency conductive disturbances in the supplying voltage and current is tested. Then, the voltage gain error and phase shift of the output voltage are measured. The EMC tests of both powe... [more]

The objective of this study was to modify an existing liquid desiccant and indirect/direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) for humidification operation in winter. The energy benefit of the liquid desiccant-assisted humidification approach during the operation of LD-IDECOAS over the conventional method with a steam humidifier was evaluated through a detailed energy simulation. The humidification and enthalpy effectiveness values of the liquid desiccant humidification measured from laboratory tests were 0.41 and 0.49, respectively, which were applied to the energy simulation for the modified system. Both systems with the proposed and conventional humidification approaches were simulated using an engineering equation solver combined with a TRNSYS 18 energy simulation program. The results demonstrated that the modified LD-IDECOAS consumes less energy for humidification compared to the existing system with a steam humidifier. The proposed system also exhibi... [more]

Settings of protection are essential to ensure the sensitivity and selectivity needed to detect defects. Making the correct settings requires the calculation of the fault currents with as little error as possible. Fault currents are influenced by the parameters of the electrical networks, including the state of the insulation and the Petersen coil, which changes during their operation electrical networks. This paper analyzes how the insulation parameters of medium voltage power lines, the parameters of the Petersen coil used to treat the neutral of the medium voltage electrical network and the value of the resistance at the fault location influence the fault current in the case of a single-phase fault. The large number of single-phase faults that occur in medium voltage electrical networks justifies this analysis. The symmetrical components method was used to calculate the fault current. The results obtained by calculation were verified experimentally by causing a single-phase-to-groun... [more]

The replacement of conventional generation sources by DER creates the need to carefully manage the reactive power maintaining the power system safe operation. The principal trend is to increase the DER volume connected to the distribution network in the coming years. Therefore, the microgrid represents an alternative to offer reactive power management due to excellent controllability features embedded in the DER, which enable effective interaction between the microgrid and the distribution network. This paper proposes a microgrid−iterative reactive power management approach of power-electronic converter based renewable technologies for day-ahead operation. It is designed to be a centralised control based on local measurements, which provides the optimal reactive power dispatch and minimise the total energy losses inside the microgrid and maintain the voltage profile within operational limits. The proposed optimal-centralised control is contrasted against seven local reactive power cont... [more]

Calculating Repeating Thermal Bridges (RTBs) for Timber Frame (TF) closed panels that could occur in Offsite Manufactured (OSM) Modern Methods of Construction (MMC), such as exterior walls for nearly-to-zero operational energy dwellings to be constructed in Wales, United Kingdom (UK) is discussed in this paper. Detailed calculations for linear RTBs due to the TF components are often neglected when evaluating thermal transmittance (known as U-values hereafter). The use of standard TF fractions does not allow the designer to perceive their detrimental impact on RTBs and consequent U-values for exterior walls. With the increase of the thermal performance of exterior walls and as such lower U-values due to ever-tightening Building Regulations, specifically related to the energy use and carbon emissions from the space heating of dwellings, then the impacts of RTBs requires more investigation. By not calculating the potential of linear RTB at the design stage could lead to a performance gap... [more]

Energy needs of air conditioning systems are constantly growing worldwide, due to climate change and growing standards of buildings. Among the possible systems, solar heating and cooling based on reversible heat pumps and thermally driven chillers are a viable option for ensuring space heating and cooling for different users. The high installation costs are a limit to their diffusion, however, under specific circumstances (climate, type of the building, type of the user, etc.), the investment in this technology can be profitable in a long term. The presented paper describes an energy-economic assessment of a solar heating and cooling system integrating a solar dish concentrator with thermal collectors coupled with a reversible heat pump and an absorption or adsorption chiller. The system integrated with a household building is developed and dynamically simulated in the Transient System Simulation (TRNSYS) environment under different circumstances −adoption of absorption or adsorption c... [more]

The COVID-19 pandemic and the associated lockdown can be regarded as a forced social experiment, the results of which show how to use energy under specific conditions. During this period, there was a reduction in electricity consumption at the level of the power system, but a different specificity distinguishes the group of household users. The article aims at presenting and analysing the identified issues concerning residential electricity users based on the experience from the COVID-19 pandemic lockdown. Data from energy meters from almost 7000 flats in Warsaw’s housing estates during the lockdown in 2020 and the analogous period before the pandemic were used. The analysis showed that, on average, residential users staying practically the whole day in their flats increased their energy consumption, but without increasing their average daily peak power, smoothing the profile in the morning hours to the level reaching the peak power that had occurred in the analogous period before the... [more]

This paper presents a new approach based on the optimization of the blade pitching strategy of offshore wind turbines in order to maximize the global energy output considering the Gaussian wake model and including the effect of added turbulence. A genetic algorithm is proposed as an optimization tool in the process of finding the optimal setting of the wind turbines, which aims to determine the individual pitch of each turbine so that the overall losses due to the wake effect are minimised. The integration of the Gaussian model, including the added turbulence effect, for the evaluation of the wakes provides a step forward in the development of strategies for optimal operation of offshore wind farms, as it is one of the state-of-the-art analytical wake models that allow the evaluation of the energy output of the project in a more reliable way. The proposed methodology has been tested through the execution of a set of test cases that show the ability of the proposed tool to maximize the... [more]

This paper varies load conditions in a single-phase induction motor and deals with consequent effects on the electromagnetic characteristics in terms of a balanced and unbalanced operation. Based on a balanced-load condition, the magnetic field, electromagnetic losses, magnetic torque are quantified by the time-stepping finite element method at six different loads. The spatial distribution of the air-gap magnetic field are investigated to characterize the existence between the load variation and unbalanced operation. The components of electromagnetic losses are analyzed in terms of main parameters degrading the operating efficiency according to the load variation. The result can show the importance of building the magnetic balance for a high performance, and the design guideline for SPIMs running at multiple operating points is discussed.

The modular multilevel converter is capable to reach high-voltage levels with high flexibility, high reliability, and high power quality as it became the standard solution for high-power high-voltage applications that operate with fixed frequency. However, in machine-drive applications, the modular multilevel converter shows critical problems since an extremely high submodule-capacitor voltage ripple occurs in the machine start-up and at low-speed operation, which can damage the converter. Recently, a new converter solution named modular multilevel series converter was proposed as a promising alternative for high-power machine-drive applications since it presented many important structural and operational advantages in relation to the modular multilevel converter such as the reduced number of submodule capacitors and the low submodule-capacitor voltage ripple at low frequencies. Even though the modular multilevel series converter presented a reduced number of capacitors, the size of th... [more]

Despite large amounts of available roof space, long pay-back periods for investments in photovoltaic (PV) power plants often hinder PV installations in industrial parks. Photovoltaic citizen participation initiatives (PV-CPI) are an alternative way of financing PV power plants that add non-financial benefits to these investments. This paper analyzed the feasibility of the installation of PV power plants focused on high rates of self-consumption financed by citizen participation initiatives on the roofs of five companies located in the Austrian Ennshafen industrial business park based on the net present value and the discounted pay-back period and compared it to a standard financing scheme, assuming a predetermined interest rate for participants as well as economies of scale with respect to the specific installation costs due to a joint purchase of the PV power plants. To calculate the feasibility, site-specific data and literature input have been used. The results show that despite an... [more]

Well killing is an important technological stage before conducting workover operation, one of the tasks of which is to preserve and restore the natural filtration characteristics of the bottomhole formation zone (BFZ). Special attention should be paid to the choice of well killing technologies and development of wells in complicated conditions, which include abnormally low reservoir pressure, high oil-gas ratio and carbonate reservoir type. To preserve the filtration characteristics of the productive formation and prevent fluid losses in producing wells during well killing operation, blocking compositions are used. At the same time, an informed choice of the most effective well killing technologies is required. Consequently, there is a need to conduct laboratory physicochemical and coreflood experiments simulating geological, physical, and technological conditions of field development, as similar as possible to actual reservoir conditions. The article presents the results of experiment... [more]