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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. [ABSTRACT FROM AUTHOR]

Featured Application: Biochar, a carbon-rich material derived from organic matter through pyrolysis, enhances substrate quality by increasing water retention and nutrient availability, leading to healthier plant growth and increased biodiversity. It also plays a significant role in carbon sequestration, capturing and storing carbon that would otherwise be released into the atmosphere, thus contributing to climate change mitigation efforts. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ( R 2 ) 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Al2O3–water nanofluids along with stationary and rotating twisted tape inserts are used to increase the rate of heat transfer in a plain tube. The simulations are conducted through varying the design parameters including angular velocity of twisted tape, Reynolds number and nanofluid volume concentration. It is found that inserting a twisted tape inside a tube substantially increases the heat transfer coefficient and friction factor compared to the plain tube. Compared to the stationary twisted tape, the rotating twisted tape exhibits a great potential to modify the average Nusselt number by about 32.8–39.6% at Reynolds number of 250, depending on the angular velocity. This is attributed to the formation of conical tornado-shape structures in the flow pattern, causing more effective mixing in the flow. By increasing the Reynolds number, the enhancement in the average Nusselt number increases in stationary and decreases in rotating configurations compared with the plain tube. To assess the tradeoff between heat transfer enhancement and pressure loss penalty, the performance evaluation criterion (PEC) is calculated. The results suggest that the highest PEC is obtained at Reynolds number of 250, nanofluid volume concentration of 3% and the highest studied angular velocity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Radiation absorption is investigated in a particle curtain formed in a solar free-falling particle receiver. An Eulerian-Eulerian granular two-phase model is used to solve the two-dimensional mass and momentum equations by employing computational fluid dynamics (CFD) to find particle distribution in the curtain. The radiative transfer equation (RTE) is subsequently solved by the Monte Carlo (MC) ray-tracing technique to obtain the radiation intensity distribution in the particle curtain. The predicted opacity is validated with the experimental results reported in the literature for 280 and 697 μm sintered bauxite particles. The particle curtain is found to absorb the solar radiation most efficiently at flowrates upper-bounded at approximately 20 kg s-1 m-1. In comparison, 280 μm particles have higher average absorptance than 697 μm particles (due to higher radiation extinction characteristics) at similar particle flowrates. However, as the absorption of solar radiation becomes more efficient, nonuniform radiation absorption across the particle curtain and hydrodynamic instability in the receiver are more probable. [ABSTRACT FROM AUTHOR]

Vacuum fluidised beds have a distinct advantage of being operated with reduced mass consumption of the fluidising media. However, a low quality of fluidisation reduces the opportunity to utilise the bubbling regime in vacuum fluidised beds. Fluidisation maps are often used to depict the interface between the quiescent, bubbling and slugging regimes inside a fluidised bed. Such maps have been obtained by visual observations of the fluidisation interface in transparent fluidised beds. For beds which are visually inaccessible fluidisation maps are difficult to obtain. The present work therefore attempts to model the interface travel in a vacuum fluidised bed. The pressure gradient due to the bed weight has been determined to be a main contributor for fluidisation/defluidisation under vacuum. A simple analytical model based on the pressure gradient (PG model) is developed to predict the interface location in a vacuum fluidised bed. For a segregated bed, the Gibilaro-Rowe (GR) model is modified and used to predict the jetsam layer growth along with the fluidisation interface. The predictions are compared with the experimental data for minimally and highly segregated particles and it is seen that for non-segregated powders the predictions are quite accurate. Lack of sufficient knowledge of bubble characteristics, however, impeded accurate prediction of the jetsam growth especially at high flow rates. However, an approximate complete fluidisation interface is successfully predicted using the GR-PG model. [ABSTRACT FROM AUTHOR]

Abstract: Degradation in quality of fluidisation for Group B powders under vacuum conditions occurs due to an existence of a fluidisation interface that separates the bubbling and static bed near the minimum fluidisation conditions. The significant pressure gradient existing due to bed weight and the particle segregation mainly affects the quality. The aim of the present work is to investigate the relative contribution of the pressure gradient and the presence of the segregation on the quality of fluidisation in vacuum conditions. Further, the effect of morphology of the particles on fluidisation quality is also studied. In addition, fluidisation maps are also obtained that reveal the optimal area of operation for enhanced heat and mass transfer processes. The results indicate that the travel of interface in the bed is affected only when the level of segregation in the bed is high. For intermediate and minimal disparity in size, the quality degradation is caused by the presence of sharp pressure gradient. Changing the morphology of the particle also altered the fluidisation characteristics of the bed and improved the quality significantly. [Copyright &y& Elsevier]

• Contact line region in sodium boiling flows is studied; • Compared contact line characteristics of high and low Prandtl number fluids; • Analyzed factors characterizing sodium boiling-high superheat, electron pressure; • Evaporative heat flux decreases with increase in electron pressure. The use of boiling liquid metals such as sodium is attractive for providing a near-isothermal heat source for engineering applications. However, previous use of boiling sodium as a coolant in nuclear reactors and as a heat transfer fluid in solar thermal applications has shown that the boiling process is unstable. To stabilise the flow, it is imperative to gain a better understanding of the boiling phenomena. An integral part of the boiling process is the evaporation of the region where the liquid-vapour interface meets the heater wall, referred to as the contact line region. The heat transfer modelling of this region formed below a single bubble in nucleate pool boiling of sodium is considered in this study. A contact line model previously developed for high Prandtl number flows is extended by including the effect of an electron pressure component which is unique to liquid metals. The assumptions made in the model are critically assessed to determine their validity for modelling micro-scale evaporation in sodium. The model was used to show that the evaporative heat flux from the contact line region in sodium can be up to six times larger compared to a high Prandtl number fluid FC-72 for a superheat of 15 K, owing to the high thermal conductivity of sodium. Furthermore, a study on the influence of specific characteristics of sodium — high boiling superheat and presence of an electron pressure — showed that the evaporative heat flux increases with increasing superheat and decreases with increasing electron pressure. [ABSTRACT FROM AUTHOR]

An abstract of the article "The Evolution of Bone Anchored Hearing Aids (BAHA) in the Indian Subcontinent" by Sunil Narayan Dutt and others is presented.

Optical and radiative properties of alumina–silica-based ceramic materials are determined in the spectral range of 3–10 μm as a function of temperature in the range of 150−650°C. The investigated materials are commercial CARBO HSP samples and in-house fabricated samples with sintering temperatures of 1400°C and 1500°C. Spectral normal emittance of the samples is measured in the spectral range of 3–20 μm using Fourier transform infrared spectroscopy. A two-step inverse methodology consisting of analytical and numerical solutions to the radiative transfer equation is employed. The analytical solution is based on the modified two-flux approximation and the transport approximation, and is used to determine the transport scattering albedo. The iterative Monte Carlo ray-tracing method is used to obtain the transport extinction coefficient. The spectral normal emittance increases non-monotonically with the thermal treatment temperature of the samples due to the sintering extent increasing with the temperature during the preparation process. The spectral normal emittance of all investigated samples also increases non-monotonically with the increasing actual sample temperature. The maximum difference in total normal emittance at studied temperatures is 7.9%, 22% and 5.5% for the commercial sample and the in-house prepared samples sintered at 1400°C and 1500°C, respectively. With the sample temperature varying in the range of 150–650°C, the spectral normal emittance in the spectral range of 4–20 μm maximally varies by 23.2%, 44.3% and 23.4% for the commercial sample, and in-house prepared samples sintered at 1400°C and 1500°C, respectively. The transport scattering albedo decreases with increasing temperature for all samples in the considered spectral range. For all samples, the absorptive index increases non-monotonically with the increasing sample temperature. The most significant increase in the absorptive index, as the sample temperature increases, is found in the spectral range of 3–5 μm for the commercial material, and it increases by up to 31.6%, 116%, 170%, 186% and 194% when the temperature increases from 150°C to 250°C, 350°C, 450°C, 550°C and 650°C, respectively. • Radiative properties of ceramics are studied in the spectral and temperature ranges of 3–10 μm and 150–650°C, respectively. • An experimental–numerical methodology involving two-flux approximation and Monte Carlo ray-tracing is applied. • The spectral normal emittance increases non-monotonically with the thermal treatment temperature. • The absorptive index of the ceramics investigated increases non-monotonically with temperature. [ABSTRACT FROM AUTHOR]

Alumina–mullite particles are used in high-temperature solar thermal applications such as solar particle receivers. In this study, optical properties of alumina–mullite materials with variable content of alumina and mullite are determined in the spectral range of 0.193–1.69 μ m. Variable angle spectroscopic ellipsometry is performed for alumina–mullite thin films, which are fabricated by magnetron sputtering. The thin films are characterised by scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy methods. The B-spline model is employed to generate ellipsometric parameters to fit the measured data and to obtain the optical properties. The investigated materials of variable content of alumina and mullite have a similar refractive index in the considered spectral range. The absorptive index of the alumina–mullite materials in the spectral range of 0.193–0.4 μ m is higher than in the range 0.4–1.69 μ m. The absorptive index decreases with increasing content of alumina in the spectral range of 0.193–0.4 μ m. The material composed of similar proportions of alumina and mullite yields the highest absorptive index in the spectral range of 0.4–1.1 μ m. The optical properties determined for the alumina–mullite materials are applied to obtain the radiative properties of spherical homogeneous particles. Mie theory is used to calculate absorption and scattering efficiency factors, as well as the scattering phase function. In addition, the scattering phase functions are obtained using the Henyey–Greenstein approximation and the transport approximation. The Monte Carlo ray-tracing method is employed to study the radiative transfer in a model one-dimensional particle curtain containing polydisperse particles exposed to high-flux solar irradiation. It is found that the overall reflectance, absorptance and transmittance of the particles only weakly depend on the optical properties of the materials investigated. • Optical constants of alumina–mullite materials are determined in the spectral range of 0.193–1.69 μm. • The material having similar proportions of alumina and mullite has the highest absorptive index in the visible spectral range. • Radiative transfer in an alumina–mullite particle polydispersion weakly depends on the particle material composition. • Transport approximation is accurate to compute radiative transfer in media for small optical thickness and asymmetry factor. [ABSTRACT FROM AUTHOR]