Pyrocumulonimbus (pyroCb) thunderstorms from intense bushfires are major lightning sources, igniting secondary fires and damaging electrical infrastructure. Unlike conventional lightning surge studies based on generic thunderstorm conditions, this study develops a novel modeling framework rooted in atmospheric pyroCb thundercloud dynamics. A numerical model is employed to simulate downward leader propagation in pyroCb lightning via the dielectric breakdown model, explicitly coupling charge structure, wind-shear-driven displacement, and leader dynamics with surge analysis. Results show wind shear extensions of 0-12 km significantly influence charge distribution and lightning type, shifting from intracloud to negative cloud-to-ground (-CG) discharges as initiation potential changes from 49.34 MV (4 km extension) to -450.69 MV (12 km extension). Findings indicate that CG flashes predominantly strike within 26-27 km, emphasizing charge density variations in leader development. The extracted return stroke current, peaking at 350 kA, is modeled as a MATLAB time-series function and applied to a grid-connected photovoltaic (PV) system to analyze surge effects. Results show pyroCb lightning surges propagate through electrical networks, causing extreme overvoltages, equipment failure, and operational disruptions. By directly linking pyroCb atmospheric processes with renewable energy infrastructure response, this study makes the first integrated assessment of bushfire-driven lightning surges on PV systems. These findings emphasize the need to assess renewable energy infrastructure vulnerabilities to extreme weather-driven lightning events. By clarifying leader dynamics and surge impacts, this study advances lightning protection research and highlights the importance of robust mitigation strategies to safeguard electrical systems against pyroCb lightning hazards.

Understanding and predicting pyrocumulonimbus (pyroCb) thunderclouds is challenging due to their unpredictable nature and potential to exacerbate wildfires. This study employs a three-dimensional (3D) numerical model with a non-inductive electrification mechanism to explore how fire-produced aerosol concentrations influence the charge structure and lightning activity in pyroCb. Aerosol particle concentrations ranging from 100 to 20,000 cm(-3) were considered to generate realistic thundercloud charge structures, with the cumulus cloud setup based on environmental conditions derived from an inverted-V sounding profile. The SP98 non-inductive electrification scheme models charge transfer in pyroCb, and the Poisson equation is solved to identify regions where lightning discharges are likely to initiate, though actual discharges are not simulated. For aerosol concentrations between 500 and 5000 cm(-3), negative non-inductive charging dominates, while extreme aerosol cases (>= 5000 cm(-3)) enhance positive charging at altitudes of 3-7 km. These findings suggest that non-inductive charge separation between ice crystals and graupel leads to realistic charge structures under pyroconvective conditions simulated in this study, reflecting moderate-to-high aerosol environments characteristic of wildfiredriven pyroCb events. As aerosol concentrations increase from 500 to 5000 cm(-3), the charge structure evolves from a dipole to a tripole (at 1000 cm(-3)) and eventually to an inverted dipole, enabling intra-cloud (IC) and negative cloud-to-ground (-CG) lightning. At higher concentrations (10,000-20,000 cm(-3)), a multi-layer charge configuration emerges, favoring intense positive cloud-to-ground (+CG) strokes. Sensitivity analysis reveals that low-to-moderate aerosol levels with strong wind shear promote IC lightning, while high aerosol levels favor +CG flashes. These findings highlight the complex interactions driving pyroCb dynamics and the importance of integrated modelling to predict wildfire-induced thunderstorms.

The ever-growing concerns about global warming and the rapid depletion of fossil fuels have triggered a rising interest in the research for cleaner, more efficient, and cost-effective energy generation. Organic Rankine cycle systems have immense potential to become a strong alternative to conventional methods of energy generation. However, such systems’ efficiency is limited by the performance of the incorporated gas expanders or prime movers. Conventional gas expanders often utilize ports or cam-operated valves. Ported expanders offer limited efficiency and controllability and produce high emissions, causing a large amount of heated and compressed gas to be wasted. Cam-operated valves, in contrast, increase expansion performance compared to ported expanders; however, they have no variability and adaptability to changes in system parameters such as gas pressure, temperature, dryness fraction, and load variation, to name a few. On a positive note, this issue can be addressed by adopting a variable timing and fast-operating, control valve with an accurate and adaptive control mechanism at the expander inlet. A properly designed and controlled valve can greatly improve the system performance of gas expanders and pave the way for an efficient low-cost alternative energy generation. This manuscript provides a comparative review of recent progress on the design, modeling, optimization, and control aspects of valves for gas expanders. A clear pathway on the scope of further development is also drawn based on the present state of the art.

Pyrocumulonimbus (pyroCb) thunderclouds, produced from extreme bushfires, can initiate frequent cloud-to-ground (CG) lightning strikes containing extended continuing currents. This, in turn, can ignite new spot fires and inflict massive harm on the environment and infrastructures. This study presents a 3D numerical thundercloud model for estimating the lightning of different types and its striking zone for the conceptual tripole thundercloud structure which is theorized to produce the lightning phenomenon in pyroCb storms. More emphasis is given to the lower positive charge layer, and the impacts of strong wind shear are also explored to thoroughly examine various electrical parameters including the longitudinal electric field, electric potential, and surface charge density. The simulation outcomes on pyroCb thunderclouds with a tripole structure confirm the presence of negative longitudinal electric field initiation at the cloud’s lower region. This initiation is accompanied by enhancing the lower positive charge region, resulting in an overall positive electric potential increase. Consequently, negative surface charge density appears underneath the pyroCb thundercloud which has the potential to induce positive (+CG) lightning flashes. With wind shear extension of upper charge layers in pyroCb, the lightning initiation potential becomes negative to reduce the absolute field value and would generate negative (−CG) lightning flashes. A subsequent parametric study is carried out considering a positive correlation between aerosol concentration and charge density to investigate the sensitivity of pyroCb electrification under the influence of high aerosol conditions. The suggested model would establish the basis for identifying the potential area impacted by lightning and could also be expanded to analyze the dangerous conditions that may arise in wind energy farms or power substations in times of severe pyroCb events.

Green roofs (GRs) are a well-established green infrastructure (GI) strategy that have been extensively studied for decades to address a growing array of social and environmental challenges. Research efforts have been continuously made to contribute to the awareness of benefits of GRs and towards their widespread application. The substrate, which is one of the crucial layers of a GR system, plays a major role in the serviceability of GRs. Thus, several studies have been undertaken to alter the substrate characteristics by applying innovative substrate additives. Biochar, a carbon-rich material with a highly porous structure and large specific surface area, has been found advantageous in several areas such as agriculture, water filtration, environmental remediation, construction, and so on. However, the application of biochar in GRs has been insufficiently studied, partially because biochar amendment in GRs is a relatively recent innovation. Furthermore, a comprehensive review of the performance of biochar-amended GR substrates is lacking. This review paper aims to summarize the past performance of GRs enhanced with biochar by considering the various benefits that biochar offers. The results indicate that most of the reviewed studies observed increased retention of runoff and nutrients when utilizing biochar. Additionally, the capabilities of biochar in improving thermal insulation, plant performance, and microbial diversity, as well as its effectiveness in sequestrating carbon and controlling soil erosion, were mostly agreed upon. Notwithstanding, a definitive conclusion cannot yet be confidently made due to the limited research information from biochar–GR systems and the uneven research focus observed in the studies reviewed. The influence of biochar-related variables (including amendment rates, application methods, processed forms, and particle size) on the effectiveness of biochar was also discussed. Opportunities for future research were suggested to fill the research gaps and address challenges restricting the application of biochar in GRs. Detailed information from past research findings could serve as a foundation for further investigations into the large-scale implementation of biochar in GRs.

The ever-growing concerns about global warming and the rapid depletion of fossil fuels have triggered a rising interest in research for cleaner, more efficient and cost-effective energy generation. Organic Rankine cycle systems have immense potential to become a strong alternative to conventional methods of energy generation. However, such systems’ efficiency is limited by the performance of the incorporated gas expanders or prime movers. Conventional gas expanders often utilize ports or cam-operated valves. Ported expanders offer limited efficiency and controllability, and produce high emissions causing a large amount of heated and compressed gas to be wasted. Cam-operated valves, in contrast, increase expansion performance compared to ported expanders, however, they have no variability and adaptability to changes in system parameters such as gas pressure, temperature, dryness fraction, and load variation to name a few. On a positive note, this issue can be addressed by adopting a variable timing and fast-operating, control valve with an accurate and adaptive control mechanism at the expander inlet. A properly designed and controlled valve can greatly improve the system performance of gas expanders and pave the way for an efficient low-cost alternative energy generation. This manuscript provides a comparative review of recent progress on the design, modeling, optimization, and control aspects of valves for gas expanders. A clear pathway on the scope of further development is also drawn based on the present state of the art.

In this work, an artificial neural network (ANN)-based model is proposed to describe the input–output relationships in a Limaçon-To-Circular (L2C) gas expander with an inlet valve. The L2C gas expander is a type of energy converter that has great potential to be used in organic Rankine cycle (ORC)-based small-scale power plants. The proposed model predicts the different performance indices of a limaçon gas expander for different input pressures, rotor velocities, and valve cutoff angles. A network model is constructed and optimized for different model parameters to achieve the best prediction performance compared to the classic mathematical model of the system. An overall normalized mean square error of 0.0014, coefficient of determination (R2) of 0.98, and mean average error of 0.0114 are reported. This implies that the surrogate model can effectively mimic the actual model with high precision. The model performance is also compared to a linear interpolation (LI) method. It is found that the proposed ANN model predictions are about 96.53% accurate for a given error threshold, compared to about 91.46% accuracy of the LI method. Thus the proposed model can effectively predict different output parameters of a limaçon gas expander such as energy, filling factor, isentropic efficiency, and mass flow for different operating conditions. Of note, the model is only trained by a set of input and target values; thus, the performance of the model is not affected by the internal complex mathematical models of the overall valved-expander system. This neural network-based approach is highly suitable for optimization, as the alternative iterative analysis of the complex analytical model is time-consuming and requires higher computational resources. A similar modeling approach with some modifications could also be utilized to design controllers for these types of systems that are difficult to model mathematically.

Renewable energy-based compact energy-generation systems based on the organic Rankine cycle (ORC) can be employed to meet the ever-growing thirst for affordable and clean energy. The overall performance and effectiveness of ORC systems are constrained by the low efficiency of the gas expander, specifically the positive displacement expander, which is responsible for energy conversion from the working fluid. This low-efficiency scenario can be significantly improved by employing a control valve to regulate and restrict the flow of the working fluid into the expander. A control valve can effectively curve the loss of costly compressed and energized working fluids by allowing them to expand in the expander chamber before discharging through the outlet port. They can thus be used to regulate the amount of energy yield and output power. In this work, two direct drive rotary valves (DDRVs) operated by a stepper motor (SM-DDRV) and rotary solenoid (RS-DDRV) are suggested, and the behavior of the valves is examined. The effect of friction and temperature on the valve response is also studied. Additionally, the effect of inlet control valves on the overall system performance of the limaçon expander is assessed. Thermodynamic properties such as the isentropic efficiency and filling factor are also computed. The effect of leakage due to valve response delay is analyzed at different inlet pressures. The performance indices are compared to the expander performance without any inlet valve. The SM-DDRV setup results in a 14.86% increase in isentropic efficiency and a 220% increase in the filling factor, whereas the RS-DDRV performs moderately with a 2.58% increase in isentropic efficiency and an 80% increase in the filling factor compared to a ported expander. The SM-DDRV provides better performance indices compared to the RS-DDRV and without valve setups. However, the performance of the limaçon expander with the SM-DDRV is sensitive to the inlet pressure and degrades at higher pressure. Overall, the valves proposed in this work present key insights into improving the performance characteristics of gas expanders of ORC systems.

Organic Rankine Cycle (ORC)–based small-scale power plants are becoming a promising instrument in the recent drive to utilize renewable sources and reduce carbon emissions. But the effectiveness of such systems is limited by the low efficiency of gas expanders, which are the main part of an ORC system. Limaçon-based expansion machines with a fast inlet control valve have great prospects as they could potentially offer efficiencies over 50%. However, the lack of a highly reliable and significantly fast control valve is hindering its possible application. In this paper, a push–pull solenoid valve is optimized using a stochastic optimization technique to provide a fast response. The optimization yields about 56–58% improvement in overall valve response. A performance comparison of the initial and optimized valves applied to a limaçon expander thermodynamic model is also presented. Additionally, the sensitivity of the valve towards a changing inlet pressure and expander rotor velocity is analyzed to better understand the effectiveness of the valve and provide clues to overall performance improvement.

This work presents a mechanistic model to simulate the growth of a sodium bubble from nucleation to departure in sodium pool boiling. A previously developed and validated heat transfer sub-model is coupled to a force balance sub-model to predict the growth rate and departure radius of a sodium bubble. The model accounts for the change in the contact angle of a bubble as it grows, and the shrinkage of the bubble base prior to departure. The developed model is used to quantify and analyse the heat transfer from different regions, i.e. the microlayer, the macrolayer, the thermal boundary layer and the bulk liquid sur-rounding the bubble. In addition, bubble growth rate and departure radius are calculated for different values of wall superheat, rate of change of contact angle and bulk liquid tem-perature. It is found that the departure radius of a sodium bubble is on the order of a few centimetres and the wall superheat has a significant influence on the shape of a sodium bubble at departure. (c) 2022 Elsevier Inc. All rights reserved.

Energy flow and conversion in high-temperature solar particle receivers are investigated by theoretical, numerical, and experimental approaches. Alumina–silica-based ceramic particle materials are synthesised, and optically and radiatively characterised. Advanced numerical models of particle–gas two-phase flows under direct high-flux solar irradiation are developed to understand the flow physics, predict receiver thermal characteristics, and enable receiver technology advancement.

A mechanistic model to study the growth of a bubble from nucleation to departure in pool boiling is proposed in this work taking into account the change in shape of a bubble as it grows. The model consists of three sub-models: (a) a heat transfer sub-model to compute the bubble growth rate based on the evaporation of the microlayer, the macrolayer, the thermal boundary layer and the bulk liquid surrounding the bubble; (b) a force sub-model to calculate the forces acting on a bubble; and (c) a contact angle and bottleneck sub-model to account for the change in shape of the bubble. Analysis of past experiments on bubble growth in nucleate pool boiling has shown that the shape of a bubble transitions from a truncated sphere to a balloon-like shape before departure. In the present work, a novel method to model this balloon-like shape of the bubble as a truncated sphere atop a conical bottleneck is presented. The model is validated against high-fidelity CFD simulations and pool boiling experiments of water and methanol from literature. In particular, the bubble departure time, wall temperature, bubble shape and microlayer profile obtained from the model are in good agreement with experimental and CFD results.

Organic Rankine Cycle (ORC) based small-scale energy generation systems can be utilized to address the rapidly increasing demand for low-cost power. But the overall efficiency of these systems is limited by the efficiency of the gas expander which extracts work from the working fluid. This efficiency can be greatly improved by regulating the flow of working fluid into the expander chamber using a control valve. In this manuscript, a rotary valve driven by a direct drive stepper motor (DDRV) is proposed and the dynamics of the valve is studied. The overall performance of the limaçon expander equipped with this valve on the inlet port is also analyzed. The thermodynamic performance of the system such as isentropic efficiency and filling factor are calculated. An increase in isentropic efficiency of 14.86% with a decrease in filling factor of 16.88% is achieved compared to the ported, without an inlet valve, expander.

This paper demonstrates a 2-D numerical model to represent two conceptual pyrocumulonimbus (pyroCb) thundercloud structures: i) tilted dipole and ii) tripole structure with enhanced lower positive charge layer, which are hypothesized to explain the occurrence of lightning flashes in pyroCb storms created from severe wildfire events. The presented model considers more realistic thundercloud charge structures to investigate the electrical states and determine surface charge density for identifying potential lightning strike areas on Earth. Simulation results on dipole structure-based pyroCb thunderclouds confirm that the wind-shear extension of its upper positive (UP) charge layer by 2–8 km reduces the electric field and indicates the initiation of negative surface charge density around the earth periphery underneath the anvil cloud. These corresponding lateral extensions have confined the probable striking zone of –CG and +CG lightning within 0–23.5 km and 23.5–30 km in the simulation domain. In contrast, pyroCb thundercloud possessing the tripole structure with enhanced lower positive charge develops a negative electric field at the cloud's bottom part to block the progression of downward negative leader and cause the surface charge density beneath the thundercloud to become negative, which would lead to the formation of +CG flashes. Later, a parametric study is conducted assuming a positive linear correlation between the charge density and aerosol concentration to examine the effect of high aerosol concentration on surface charge density in both pyroCb thunderclouds. The proposed model can be expanded into 3-D to simulate lightning leader movement, aiding wildfire risk management.

Bushfire is known as one of the ascendant factors to create pyrocumulus thundercloud that causes the ignition of new fires by pyrocumulonimbus (pyroCb) lightning strikes mostly of positive polarity, and causes massive damage to nature and infrastructure. A conceptual model-based risk planning would be beneficial to predict the lightning striking zones on the surface of the earth underneath the pyroCb thundercloud. In this paper, a simple line charge structured thundercloud model is constructed in 2-D coordinates using the method of images to predict the probable +CG (positive cloud-to-ground) lightning striking zones on the earth's surface for tilted dipole thundercloud charge configuration. The electric potential distribution and ground surface charge density for tilted dipole thundercloud is investigated via continuously adjusting the position and charge density of its charge regions. Simulation results confirm the initiation of negative charged density for the wind shear extension of upper positive charge region by 2 to 8 km, and would expect +CG lightning to strike within 7.88 to 20 km around the earth periphery particularly in the direction of the cloud's forward flank. The proposed model would serve as the foundation to identify the probable lightning affected area as well as can also be extended to analyze the hazardous situation appears in wind energy farms or agricultural fencing situated nearby the power grid during pyroCb events.

Two‐step solar thermochemical water splitting is a promising pathway for renewable fuel production due to its potential for high thermal efficiency via full‐spectrum sunlight utilization. Such a promise critically relies on simultaneous innovation in the redox materials and the reactor systems. Most prior efforts on material design are focused on improving the fuel yield at lower reduction temperatures. However, developing materials with both high fuel output and efficiency remains a key challenge, requiring a rigorous understanding of the effects of material thermodynamic properties. Herein, a generic thermodynamic framework is described to decipher the material effects by studying both the state‐of‐the‐art and hypothetical materials within a counterflow reactor system. A global efficiency map is presented for redox materials, revealing inevitable tradeoffs among competing factors such as thermal losses, sweep gas and oxidizer demand, solid preheating, and reduction enthalpy. The choice of the most efficient material is closely linked to the system conditions. Ceria‐based materials outperform perovskites under most scenarios, and the optimal hypothetical materials tend to favor higher reduction enthalpies and entropies than existing materials. This work offers a valuable material design roadmap to identify solutions toward efficient solar fuel production.