Search Results (29)

This study evaluates the real-world performance of a TiO₂ compound parabolic collector (CPC) photocatalytic reactor operated under natural sunlight for the treatment of agricultural runoff. The three objectives are to determine whether photocatalytic performance can be reliably predicted using a spectrally relevant UVA dose, quantify the impact of water-matrix optical attenuation on degradation efficiency, and lastly, to assess whether an adaptive irradiance-gated control strategy can improve operational throughput. Field Analytical Models are conducted by using a 5 L recirculating CPC slurry reactor treating three model agro-pollutants under mid-latitude outdoor conditions. Kinetics followed pseudo-first-order behaviour when analysed against cumulative UVA dose, which reduced inter-day variability in apparent rate constants from more than 30% (time-based analysis) to less than 10%. Natural river water shows a 20–35% reduction in removal efficiency relative to synthetic runoff, which was correlated with lower UV transmittance and higher UV254 absorbance. Catalyst reusability tests indicated only an 18% loss of activity after five cycles, with partial recovery after rinsing. Importantly, the proposed adaptive UVA dose control increased the daily treated volume by 25–35% compared with continuous operation. These results demonstrate that solar photocatalysis can be transformed into a predictable, optimisable treatment process when spectral irradiance, matrix optics, and intelligent operation are considered together. Full article

The surface morphology of lithium metal electrodes evolves markedly during cycling, modulating interfacial kinetics and increasing the risk of dendrite-driven internal short circuits. Here, we infer this morphological evolution from direct-current (DC) signals by analyzing open-circuit voltage (OCV) transients after constant current interruptions. The OCV exhibits a rapid initial decay followed by a transition to a slower long-time decay. With repeated plating, this transition shifts to earlier times, thereby increasing the contribution of long-term relaxation. We quantitatively analyze this behavior using an equivalent circuit with a transmission-line model (TLM) representing the electrolyte-accessible interfacial region of the electrode, discretized into ten depth-direction segments. Tracking segment-wise changes in resistances and capacitances with cycling enables morphology estimation. Repeated plating strongly increases the double-layer area near the current collector, while the charge-transfer-active surface shifts toward the separator side, showing progressively smaller and eventually negative changes toward the current-collector side. Together with the segment-resolved time constants, these trends indicate that lithium deposition becomes increasingly localized near the separator-facing surface, while the interior becomes more tortuous, consistent with post-mortem observations. Overall, the results demonstrate that DC voltage-relaxation analysis combined with a TLM framework provides a practical route to track lithium metal electrode surface evolution in Li-metal-based cells. Full article

HVAC systems are becoming increasingly important around the world due to the increasing need for climatization in recent years. While district heating systems have been used for a long time, district cooling systems tend to be something that is only reserved for large buildings, making decentralized cooling flourish, shaping the idea of considering it as the first choice when it comes to cooling devices, disregarding the efficiency of larger systems. This article compares two technologies for district energy solutions. One option features single-stage absorption chillers using solar thermal technologies (Fresnel collectors) for heat, while the other uses high-efficiency compression chillers with photovoltaic technologies. Parametric studies were used to determine system sizes and considerations were taken to perform such as comparison. This paper concludes that compression chillers are the better option for cooling systems with variable demand while absorption chillers are a good choice for systems with constant demand, like data centers, especially when there is a high-temperature heat source available. Full article

The presence of galena, sphalerite (cleiophane), and Carbonaceous Material (CM) in sulphide ore complicates the application of a direct-differential flotation flowsheet due to increased mutual interactions between both marketable concentrates and final tailings. Flotation tests, measurements of electrokinetic (zeta) potential, adsorption of sulphydric collectors, and colorimetric indicators were employed to elucidate the cause-and-effect relationships underlying the reduction in contrast of the flotation properties of galena and cleiophane surfaces. It was established that galena and cleiophane exhibit comparable flotation responses when using diesel oil within a pH range of 6–8. While high galena recovery is anticipated, the similar recovery of cleiophane is attributed to the ZnS zeta potential approaching zero in this pH interval. Experimental results demonstrated a distinct difference in the flotation behavior of galena and cleiophane, both with natural surface oxidation and following the removal of sulphoxy films. The application of Carbonaceous Material depressants derived from wood processing by-products (lignin-sulphonates) resulted in a significant decrease in sphalerite recovery. Although the flotation rate constant for Carbonaceous Material in the presence of lignin-sulphonate-based depressants decreases, the overall recovery to concentrate increases over time. The implementation of a bulk-differential flowsheet, involving the preliminary removal of CM prior to the bulk Pb-Zn flotation of lead-zinc sulphide ore, has been demonstrated to be effective. Full article

Heat pipes filled with a thermodynamic medium are energy-saving and stable heat exchangers that have been used for years in various fields of science and technology, including building heating and cooling installations. This article presents the results of research on the energy efficiency of wall-mounted concrete heating and cooling modules with heat pipes, which can be a structural element of external and internal walls of buildings for various purposes. A series of measurement tests were performed, which allowed the determination of how the thermal power and control parameters of the module (amplification factor and time constants) change under operating conditions. A first- and second-order inertial model was used to describe the control properties of the module. The measurements were performed in heating and cooling mode for three different values of supply water flow, both when increasing the supply temperature and when decreasing it. Based on the results of the measurements, calculations and analysis, it was found that the thermal power and control parameters of the module change significantly; these changes result from both the design features of the module (the type of thermodynamic medium in the heat pipe and the technical aspects of the execution and assembly of the connections between the collector and the heat pipe) and the operating conditions (the value of the direction of temperature change and the flow of the supply water). It was shown that the supply temperature has a much greater impact on the values of the module’s control parameters than the flow rate of the supply water. The tested module is characterized by slow changes in temperature on its surface (high values of time constants). The time of stabilization of the temperature on the module’s surface, after step forcing, is 8–10 h. This can cause greater fluctuations in the indoor air temperature, lower thermal comfort in the room and lower energy efficiency of the process. These issues can be prevented by using complex algorithms for thermal comfort control, which in turn increase the cost of the control system. Full article

Frequency-response analysis is critical in circuit design. Frequency response encodes crucial information, like gain, accuracy, bandwidth, response time, phase shift, stability, and more. Unfortunately, existing methods are either algebraic and obscure or approximations with inaccuracies. So applying them to more complex circuits is often arduous or unreliable. This paper proposes recursive shunt-circuit transformations: a simple, rigorous, and insightful analytical method for conceptualizing and designing electronic circuits. The method asserts that (a) each equivalent capacitance shunts away its parallel resistance past its RC frequency. This (b) decreases the gain (induces a pole) and (c) changes the circuit. (d) The next dominant capacitance shunts its parallel resistance past the next pole and so on until all remaining capacitances shunt their parallel resistances past the poles they establish. The method also asserts that (e) bypass capacitances increase gain (induce zeros) and (f) cross-amp capacitances couple stages and poles. By applying this method and concepts, designers can (i) simplify an arbitrarily complex circuit into simpler coupled/decoupled stages and (ii) determine and manage poles and zeros with insight. This method was applied to design and analyze single- and multi- stage amplifier circuits and results were benchmarked against traditional methods and NGSPICE simulations, demonstrating its accuracy and broad applicability. Full article

Fresh tomato fruits (TFs) contain a high moisture content of 90–94%, which makes storage and transportation over long distances difficult. Lately, numerous investigators have employed diverse solar dryers (SDs) in conjunction with stationary solar collectors (SCs) to dry tomatoes; however, the effectiveness of this technique is limited due to the sun’s constant motion throughout the day. Consequently, the current study set out to create an SD that is outfitted with an autonomous sun tracking system and an internet of things (IoT)-based photovoltaic system connected to an SC to continually track the sun and increase the quantity of energy absorbed. Furthermore, we investigated some operating parameters that impact the SD’s performance, taking into account three tomato slice thicknesses (STs) (4.0, 6.0, and 8.0 mm) and three air velocities (1.0, 1.5, and 2.0 m/s). The obtained data demonstrated a notable rise in the efficiency of the SD integrated with the automatic SC tracker throughout the course of the day when compared to the fixed SC, where the latter’s efficiency improved by 21.6%, indicating a strong degree of agreement. The results demonstrated a notable 20–25% reduction in drying time and a 4.9 °C increase in air temperature within the SC integrated with an automatic solar collector tracker (ASCT) at 2:00 p.m., as compared to the SC integrated with a fixed SC. The results of this study also demonstrated that there were no appreciable variations in the air speeds used to dry the tomatoes; however, the thickness of the tomato slices (TSs) had a significant impact; using 4 mm thick tomato slices resulted in a 50% reduction in drying time. Furthermore, the highest efficiency of the PV system was discovered to be 17.45%. Although the two solar dryers have very similar payback times, there are more dried tomatoes available in the markets. Full article

The paper proposes applying an in-house mathematical model of a liquid flat-plate solar collector to calculate the collector time constant. The described model, proposed for the first time in an earlier study, is a one-dimensional distributed parameter model enabling simulations of the collector operation under arbitrarily variable boundary conditions. The model is based on the solution of energy balance equations for all collector components. The formulated differential equations are solved iteratively using an implicit difference scheme. To obtain a stable numerical solution, it is necessary to use appropriate steps of time and spatial division. These were found by comparing the results obtained from the model with the results of the analytical solution available in the literature for the transient state, which constitutes the novelty of the present study. The accuracy of the results obtained from the model was verified experimentally by comparing the measured and calculated history of the fluid temperature at the outlet of the collector. The calculation of the collector time constant is proposed in the paper as an example of the model’s practical application. The results of the time constant calculation were compared with the values obtained experimentally on the test stand. This is another novelty of the presented research. The analysed collector instantaneous efficiency was then calculated for selected outdoor conditions. The presented mathematical model can also be used to verify the correctness of the collector operation. By comparing, on an ongoing basis, the measured and calculated values of the fluid temperature at the collector outlet, conclusions can be drawn about the process of solar glass fouling or glycol gelling. The simplicity of the model and the low computational demands enable such comparisons in an online mode. Full article

Gear pumps are hydraulic machines capable of transferring energy and performing work in pumping fluid. This study presents an analysis of the hydrodynamic model of an external multiple gear pump in order to analyze the fluid flow in combinations of single and different viscosities at the same and different pressures and speeds. Solidworks Flow Simulation 2016 was used to analyze fluid flow. When the radius of the rounding on the collector inner surface is increased from 3 to 15 mm, the pressure drop decreases by 13%. When the radius of the manifold is 3 mm, cavitations are observed. With a liquid distribution system with four input ports and one outlet port in the top cover, the gear pump can handle liquids of viscosity classes 5 to 10. The speed should not exceed 1200 rpm if the liquid has a kinematic viscosity of 10 cSt. The pressure drop and velocity distribution of the liquid in the pressure and suction lines are the same. When the speed changes from 400 to 1200 rpm, the pressure drop increases five times, and the velocity increases three times. At a constant speed of 1000 rpm and an inlet pressure of 10 MPa but with different viscosities, the pressure drop decreases 8 times, and the speed increases 1.5 times. When the inlet pressure is 6 to 24 MPa, with constant speed and the same viscosity, the pressure drop and fluid velocity practically do not change. The dependence of pressure drop on the number of revolutions and radius of the rounding of the inner surface of the collector is statistically significant. Full article

This paper studies the stability of a real-world wind farm, Bison Wind Generation System (BWGS) in the state of North Dakota in the United States. BWGS uses an AC collector grid rated at 34.5 kV and a symmetrical bipolar high-voltage DC (HVDC) transmission grid rated at ±250 kV. The HVDC line transfers a total power of 0.5 GW, while both the HVDC rectifier and inverter substations use line-commuted converters (LCCs). The LCC-based rectifier adopts constant DC current control to regulate HVDC current, while the inverter operates in constant extinction angle control mode to maintain a fixed HVDC voltage. This paper proposes a frequency scan-based approach to obtain the d–q impedance model of (i) BWGS AC collector grids with Type 4 wind turbines that use permanent magnet synchronous generators (PMSGs) and two fully rated converters, and (ii) an LCC-HVDC system. The impedance frequency response of the BWGS is acquired by exciting the AC collector grid and LCC-HVDC with multi-sine voltage perturbations during its steady-state operation. The resulting voltage and current signals are subjected to a fast Fourier transform (FFT) to extract frequency components. By analyzing the impedance frequency response measurement of BWGS, a linear time–invariant (LTI) representation of its dynamics is obtained using the vector fitting (VF) technique. Finally, a Bode plot is applied, considering the impedance of the BWGS and grid to perform stability analyses. This study examines the influence of the short circuit ratio (SCR) of the grid and the phase lock loop (PLL) frequency bandwidth on the stability of the overall system. The findings provide valuable insights for the design and verification of an AC collector and LCC-based HVDC transmission systems. The findings suggest that the extraction of the impedance model of a real-world wind farm, achieved through frequency scanning and subsequent representation as an LTI system using VF, is regarded as a robust, suitable, and accurate methodology for investigating the dynamics, unstable operating conditions, and control interaction of the wind farm and LCC-HVDC system with the AC grid. Full article

For the first time, a systematic study to investigate the electrospinnability of cyclic olefin polymer (COP) was performed. Different solvents and mixtures were tested together with different electrospinning parameters and post-treatment types to prepare bead-free fibers without defects. These were successfully obtained using a chloroform/chlorobenzene (40/60 wt.%) solvent mixture with a 15 wt.% COP polymer, a 1 mL/h polymer solution flow rate, a 15 cm distance between the needle and collector, and a 12 kV electric voltage. COP fibers were in the micron range and the hot-press post-treatment (5 MPa, 5 min and 120 °C) induced an integrated fibrous structure along with more junctions between fibers, reducing the mean and maximum inter-fiber space. When the temperature of the press post-treatment was increased (from 25 °C to 120 °C), better strength and less elongation at break of COP fibers were achieved. However, when applying a temperature above the COP glass temperature (T_g = 138 °C) the fibers coalesced, showing a mechanical behavior similar to a plastic film and a low elongation at break with a high strength. The addition of a high dielectric constant non-solvent, N,N-dimethylacetamide (DMAc), resulted in a considerable reduction in the COP fiber diameter. Based on the cloud point approach, it was found that the use of DMAc and the solvent chloroform or chlorobenzene improved the electrospinnability of COP polymer solution. Full article

Solar energy is one of the most promising forms of alternative energy because it has no adverse effects on the environment and is entirely free. Converting solar energy into thermal energy is the most common and straightforward method; the efficiency of solar thermal conversion is approximately 70 percent. The intermittent nature of solar energy availability affects the performance of solar water heaters (SWH), which lowers the usefulness of solar energy in residential and commercial settings, particularly for water heating. Even at low temperatures, the performance of a collector can be improved by using low-density polyethylene (LDPE) glazing instead of traditional glass because it is less expensive and lighter than glass. Using a comprehensive experimental-simulative study, the Glass Solar water heater (glass SWH) and the low-density polyethylene solar water heater (LDPE SWH) are analyzed, examined, and compared in this work. These solar water heaters have galvanized iron (GI) as their absorber material. The SWHs were operated in a closed loop at a constant mass flow rate of 0.013 kg/s, and a 4E analysis (which stands for energy, exergy, economics, and efficiency recovery ratio) was carried out. This analysis included a look at the dynamic time, uncertainty, weight reduction, carbon footprint, and series connection. An LDPE SWH has an energy efficiency that is 5.57% and an exergy efficiency that is 3.2% higher than a glass SWH. The weight of the LDPE SWH is 32.56% lower than that of the glass SWH. Compared to the price of a conventional geyser, installing our SWH results in a cost savings of 40.9%, and monthly energy costs are reduced by an average of 25.5%. Compared to October, September has the quickest dynamic time to reach the desired temperature, while October has the most significant dynamic time. The efficiency recovery ratio (ERR) of a glass SWH is 0.0239% lower than that of an LDPE SWH. LDPE SWHs had a carbon credit worth INR 294.44 more than glass SWHs. The findings of these tests demonstrate that the LDPE SWH is a practical replacement for traditional means of heating water, such as SWHs and geysers. Full article

This study presents a combined thermal and optical, three-dimensional analysis of an asymmetric compound parabolic collector (ACPC) with an integrated hybrid photovoltaic/thermal (PV/T) receiver with the aim of establishing a sustainable approach in two ways: firstly, by determining the optimal tilt angle for operations, and secondly, by introducing an innovative simulation method which reduces computational cost while calculating thermal performance. Initially the Incident Angle Modifier ($IAM$) was calculated for a wide range of incident angles, and the ray-tracing results were verified using three different simulation tools (Tonatiuh, COMSOL, and SolidWorks) with mean deviations being lower than 4%. The optimal tilt angle of the collector was determined for seven months of the year by conducting a detailed ray-tracing analysis for the mean day of each month considering whole day operation. In the thermal analysis part, the authors introduced novel numerical modeling for numerical simulations. This modeling method, designed with sustainability in mind, enables lighter computational domains for the air gap while achieving accurate numerical results. The approach was established using two distinct simulation tools: COMSOL and SolidWorks. From the optical analysis, it was found that in all months examined there is a four-hour time range around solar noon in which the optimum tilt angle remains constant at a value of 30°. The numerical models constructed for the thermal analysis were verified with each other (6.15% mean deviation) and validated through experimental results taken from the literature regarding the examined collector (<6% mean deviation). In addition, the two simulation tools exhibited a deviation of around 6% between each other. Finally, the thermal performance of the collector was investigated for the mean day of September at solar noon by adopting the optimal tilt angle for that month according to the optical analysis, considering inlet temperatures from 20 °C up to 80 °C. Full article

The glass cover is often situated at the aperture of a cavity receiver in concentrating collectors to reduce heat dissipation. However, the decrease in optical efficiency due to the reflection loss on the surface of the glass cover will directly reduce the thermal efficiency of a collector, especially for a fixed-focus solar concentrator, whose optical axis is generally not coincident with the central axis of the receiver. To fundamentally evaluate the effect of a glass cover on the efficiency of a fixed-focus Fresnel lens solar concentrator/conical cavity receiver system, its performances with and without a glass cover considered under different incidence angles were comparatively investigated. To obtain the optical performance, optical models of the system were first built with TracePro^® 7.0 software. An experimental setup was then constructed to test the thermal performance of the system. The results show that the optical efficiency of a system without a glass cover is much higher than that with a glass cover. The difference between them remains unchanged for incidence angle at a range of 0–20°. The time constant of the system with a glass cover is much less than that without a glass cover, in the ranges of 29–33 s and 48–59 s, respectively. The system with a glass cover for a wide range of higher temperature differences also has better thermal efficiency. Full article

The desalination of saltwater is a viable option to produce freshwater. All the desalination processes are energy-intensive and can be carried out on a large scale. Therefore, producing freshwater using renewable energy sources is the most desirable option considering the current energy crisis and the effect that fossil-fuel-based energy has on our carbon footprint. In this respect, the tray-type still, one of several solar power desalination still varieties, is popular owing to its straightforward design, economic materials of construction, and minimal maintenance requirements, especially in isolated island regions with restricted energy and natural water supplies. The traditional tray-type solar power has a few drawbacks, such as the inability to recover latent heat from condensation, reduced thermal convection, a large heat capacity, and comparatively minimal driving power through evaporation. Therefore, the improvement of heat and mass transfer capabilities in tray-type stills has been the subject of many studies. However, there is a lack of a comprehensive review in the open literature that covers the design and operational details of multistage solar stills. The purpose of this paper is to present a thorough overview of the past research on multistage solar stills, in terms of configurations, capabilities, and cutting-edge options. In comparison to a unit without a salt-blocking formation, the review indicates that a multistage distillation unit may run continuously at high radiation and generate pure water that is around 1.7 times higher than a unit without a salt-blocking formation. The most effective deign is found to be “V”-shaped solar still trays that attach to four-stage stills, since they are less expensive and more economical than the “floor” (Λ-shape) design, which requires two collectors. Additionally, it can be stated that the unit thermal efficiency, solar percentage, and collected solar energy (over the course of a year) increase by 23%, 18%, and 24%, respectively, when the solar collectors are increased by 26% (at the constant inflow velocity of the water). Full article