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Abstract This study aims to optimize the power generation of a conventional Manzanares solar chimney (SC) plant through strategic modifications to the collector inlet height, chimney diameter, and chimney divergence. Employing a finite volume-based solver for numerical analysis, we systematically scrutinize influential geometric parameters, including collector height (h i = 1.85 to 0.1 m), chimney inlet diameter (d ch = 10.16 to 55.88 m), and chimney outlet diameter (d o = 10.16 to 30.48 m). Our findings demonstrate that reducing the collector inlet height consistently leads to increased power output. The optimal collector inlet height of h i = 0.2 m results in a significant power increase from 51 to 117.42 kW (~ 2.3 times) without additional installation costs, accompanied by an efficiency of 0.25%. Conversely, enlarging the chimney diameter decreases the chimney base velocity and suction pressure. However, as turbine-driven power generation rises, the flow becomes stagnant beyond a chimney diameter of 45.72 m. At this point, power generation reaches 209 kW, nearly four times greater than the Manzanares plant, with an efficiency of 0.44%. Nevertheless, the cost of expanding the chimney diameter is substantial. Furthermore, the impact of chimney divergence is evident, with power generation, collector efficiency, overall efficiency, and collector inlet velocity all peaking at an outer chimney diameter of 15.24 m (corresponding to an area ratio of 2.25). At this configuration, power generation increases to 75.91 kW, approximately 1.5 times more than the initial design. Remarkably, at a low collector inlet height of 0.2 m, combining it with a chimney diameter of 4.5 times the chimney inlet diameter (4.5d ch) results in an impressive power output of 635.02 kW, signifying a substantial 12.45-fold increase. To model the performance under these diverse conditions, an artificial neural network (ANN) is effectively utilized.

High-speed microjet hydrogen–air diffusion flames are investigated computationally. The focus is on the prediction of the so-called bottleneck phenomenon. The latter has been previously observed as a specific feature of the present flame class and has not yet been investigated computationally. In the configuration under consideration, the nozzle diameter is 0.5 mm and six cases with mean nozzle injection velocities (U) between 306 m/s and 561 m/s are considered. The flow in the nozzle lance is analyzed separately to obtain detailed inlet boundary conditions for the flame calculations. It is confirmed by calculation that the phenomenon is mainly determined by the transition to turbulence in the initial parts of the free jet. The transitional turbulence proves to be the biggest challenge in predicting this class of flames, as the generally available turbulence and turbulent combustion models reach the limits of their validity in transitional flows. In a Reynolds-Averaged Numerical Simulation framework, the Shear Stress Transport model is found to perform better than alternative two-equation models and is used as the turbulence model. By neglecting the interactions between the turbulence and chemistry (no-model approach), it is possible to predict the morphology of the bottleneck flame and its dependence on U qualitatively. However, the position of the bottleneck is overpredicted for U < 561 m/s. The experimental flames in the considered U range are all attached to the nozzle. This is also predicted by the no-model approach. The Eddy Dissipation Concept (EDC) used as the turbulence combustion model predicts, however, lifted flames (with increasing lift-off height as U decreases). With the EDC, no bottleneck morphology is observed for U = 561 m/s. For lower U, the EDC results for the bottleneck position are generally closer to the measurements. It is demonstrated that accuracy in predicting the bottleneck position can be improved by ad hoc modifications of the turbulent viscosity.

A comparative numerical analysis of the thermohydraulics of an enhanced geothermal system (EGS) project in Türkiye in Dikili area is presented. The fractured granodiorite is modelled as porous media, utilizing the numerically suggested data of other authors for the corresponding hydraulic characteristics. As the heat transmission fluid, two different mediums are alternatively considered. These are the more classical medium, water and the supercritical Carbon Dioxide (sCO2). Transient calculations are performed for a time period of twenty years, comparing the temporally developing results obtained for water and sCO2 with each other. Based on modeling parameters and assumptions, higher production temperatures are observed with sCO2, in comparison to water, implying an advantage for sCO2 usage as a working fluid in EGS. This is accompanied by the further advantage of a lower pressure drop for sCO2. On the other hand, the temperature advantage is relativized by the lower specific heat capacity of sCO2 causing a decrease in the production thermal power. In general, the present re found to be encouraging for a further and more detailed analysis of the employment of sCO2 as working fluid in EGS.

A numerical study is carried out meticulously to scrutinize the impact of different shapes of chimneys like circular (outer dia, dc), convergent (outer dia, 0.5dc), divergent (outer dia, 1.5dc), sudden contraction (outer dia, 0.5dc), and sudden expansion (outer dia, 1.5dc) on the performance of an SCPP. Furthermore, the parametric impact with different chimney divergence angles (CDA, ϕ), and ground absorber slope angle (GSA, γ) on the SCPP performance is also scrutinized. Optimum divergence angle (ϕ=+0.75°) enhances the power generation up to ∼ 47% (76 kW) with a horizontal ground absorber surface. An increase or decrease in CDA lessens the power generation. With a sloped ground absorber angle γ=0.6°, the gain in power generation is 60% (82 kW). The study of combination of ground sloped absorber (γ=0.6°) and divergent chimney (ϕ=+0.75°) shows enhancement of the power generation upto 80% (92 kW) more than the classical Manzaranes plant.

Nowadays, the demand for obtaining high heat flux values in small volumes has increased with the development of technology. Condensing flow inside mini- and microchannels has been becoming a promising solution for refrigeration, HVAC, air-conditioning, heat pumps, heat pipes, and electronic cooling applications. In these applications, employing mini/microchannels in the condenser design results in the working fluid, generally refrigerant, undergoing a phase change inside the mini/microchannels. On the other hand, the reduction in the hydraulic diameter during condensation gives rise to different flow regimes and heat transfer mechanisms in the mini- and microchannels compared to the conventional channels. Therefore, the understanding of fluid flow and heat transfer characteristics during condensation of refrigerant inside mini- and microchannels has been gaining importance in terms of condenser design. This study presents a state-of-the-art review of condensation studies on refrigerants inside mini- and microchannels. The review includes experimental studies as well as correlation models, which are developed to predict condensation heat transfer coefficients and pressure drop. The refrigerant type, thermodynamical performance, and compatibility, as well as the environmental effects of refrigerant, play a decisive role in the design of refrigeration systems. Therefore, the environmental impacts of refrigerants and current regulations against them are also discussed in the present review.

A CFD simulation of the condensation flow of R600a and R290 within microchannels was conducted to explore the effect of mass flux, hydraulic diameter, and vapour quality on heat transfer rate and pressure drop. Data obtained from CFD simulations were used to develop new heat transfer and pressure drop correlations for the condensation flows of R600a and R290, which are climate-friendly refrigerants. Steady-state numerical simulations of condensation flow of refrigerants were carried out inside a single circular microchannel with diameters varying between 0.2 and 0.6 mm. The volume of fluid approach was used in the proposed model, calculating the interface phase change using the Lee model. The CFD simulation model was validated via a comparison of the simulation results with the experimental data available in the literature. It is found that the newly developed Nu number correlation shows a deviation, with an Ave-MAE of 11.16%, compared to those obtained by CFD simulation. Similarly, the deviation between friction factors obtained by the newly proposed correlation and those obtained by CFD simulation is 20.81% Ave-MAE. Widely recognized correlations that are applicable to the condensation of refrigerants within small-scale channels were also evaluated by comparing newly developed correlations. It is concluded that the newly proposed correlation has a higher accuracy in predicting the heat transfer coefficient and pressure drop. This situation can contribute to the creation of a sustainable system via the use of microchannels and climate-friendly refrigerants, like R600a and R290.

The main purpose of this investigation was to explore the heat transfer and flow characteristics of aero-foil-shaped fins combined with extended jet holes, specifically focusing on their feasibility in cooling turbine blades. In this study, a comprehensive investigation was carried out by applying impinging jet array cooling (IJAC) on a semi-circular curved surface, which was roughened using aerofoil-shaped fins. Numerical computations were conducted under three different Reynolds numbers (Re) ranging from 5000 to 25,000, while nozzle-to-target surface spacings (S/d) ranged from 0.5 to 8.0. Furthermore, an assessment was made of the impact of different fin arrangements, single-row (L1), double-row (L2), and triple-row (L3), on convective heat transfer. Detailed examinations were performed on area-averaged and local Nusselt (Nu) numbers, flow properties, and the thermal performance criterion (TPC) on finned and smooth target surfaces. The study’s results revealed that the use of aerofoil-shaped fins and the reduction in S/d, along with surface roughening, led to significant increases in the local and area-averaged Nu numbers compared to the conventional IJAC scheme. The most notable heat transfer enhancement was observed at S/d = 0.5 utilizing extended jets and the surface design incorporating aerofoil-shaped fins. Under these specific conditions, the maximum heat transfer enhancement reached 52.81%. Moreover, the investigation also demonstrated that the highest TPC on the finned surface was achieved when S/d = 2.0 for L2 at Re = 25,000, resulting in a TPC value of 1.12. Furthermore, reducing S/d and mounting aerofoil-shaped fins on the surface yielded a more uniform heat transfer distribution on the relevant surface than IJAC with a smooth surface, ensuring a relatively more uniform heat transfer distribution to minimize the risk of localized overheating.

Abstract Bioconvective heat and mass transport phenomena have recently been the subject of interest in diverse fields of applications pertaining to the motion of fluids and their thermophysical properties. The transport processes in a system involving triple convective phenomena, irregular geometry, and boundary conditions constitute a complex phenomenon. This work aims to explore the mixed thermo-bioconvection of magnetically susceptible fluid containing copper nanoparticles and oxytactic bacteria in a novel W-shaped porous cavity. The buoyant convention is generated due to the isothermal heating at the wavy bottom wall, whereas the mixed convection is induced due to the shearing motion of the top-cooled sliding wall. Furthermore, the bioconvection is induced due to the manifestation of oxytactic bacteria or organisms. The inclined sidewalls are insulated. The geometry is packed with water based Cu nanoparticle mixed porous structure, which is subjected to a magnetizing field acted horizontally. The complex transport equations are transformed into nondimensional forms, which are then computed using the finite volume-based developed code. The coupled triple-convective flow physics are explored for a wide range of involved controlling parameters, which could provide helpful insight to the system designer for its proper operation. The shape of geometry can be considered one of the important parameters to control the heat and mass transport phenomena. In general, the influence of amplitude (δ) is more compared to the waviness number (m) of the undulations. The magnitude of heat (Nu) and mass (Sh) transfer rate for the W-shaped cavity is high compared to conventional square and trapezoidal-shaped cavities. The output of the analysis could be very helpful for the designer for modeling devices operating on nanotechnology-based bioconvection, microbial fuel cells, and others.

Abstract Stringent emission standards and greater fuel economy have forced scientists to develop an advanced combustion technology (homogeneous charge compression ignition; HCCI) useful in internal combustion engines in the future. Citronella biodiesel prepared through transesterification process which is auspicious an energy source for the CI engine. Cobalt chromium nanoparticles were mixed with the biodiesel at 30 ppm with the help of an ultrasonicator. The present experimental investigation was conducted to analyze various performance (brake thermal efficiency (BTE) and brake‐specific fuel consumption (BSFC)), combustion (pressure and heat release rate (HRR)), and emission (unburnt hydrocarbon (UBHC), CO, NOx, and smoke) parameters of the HCCI engine with neat diesel, CBD 5% (citronella biodiesel 5% + 95% diesel), CBD 10% (citronella biodiesel 10% + 90% diesel), CBD 15% (citronella biodiesel 15% + 85% diesel), CBD 20% (citronella biodiesel 20% + 80% diesel), and CBD 15% + C30 (citronella biodiesel 15% + 85% diesel +30 ppm cobalt). To carry out the experiment, a fuel vaporizer was adopted in a 5.2 kW, 1500 rpm, single‐cylinder, four‐stroke, vertical, direct‐injection diesel engine. Nanoparticles were used to improve surface area/volume ratio, heat conduction, and heat transfer rate within the oil layers. The result showed that CBD 15% had given better results than the other citronella biodiesel‐blended fuels. CBD 15% + C30 fuel increased the BTE and HRR by 5.49% and 6.8%, respectively, due to a shorter ignition delay and greater cetane number of the fuel. The percentage of BSFC, UBHC, CO, NOx, and smoke was decreased by 33.33%, 34.32%, 5.1%, and 17.34%, respectively, compared to neat biodiesel in the HCCI engine at 80% load.

Solar chimney power plants (SCPPs) are encouraging sustainable energy sources due to their low cost, abundance, low maintenance, and eco-friendliness. However, despite significant efforts to optimize SCPP design, their efficiency and power generation capabilities remain limited. Researchers have explored modifications in plant geometry and hybridization to improve efficiency. Despite extensive work in this area, commercialization of SCPPs has not yet been achieved. Most of the research is numerical and may differ from real-world practical use. The number of experimental studies is also relatively small. To facilitate commercialization, further investigation with practical and feasible dimensions is required. This comprehensive review paper aims to provide an in-depth analysis of experimental approaches and advancements in the field of SCPPs. The paper begins with an introduction, highlighting the background, significance, and objectives of the review. It provides an overview of the plants, discussing their principles and operation as innovative renewable energy systems. The historical development and evolution of solar chimneys are explored, shedding light on their progression over time. Case studies of operational hybrid SCPPs are examined to showcase real-world applications and performance. The paper also addresses environmental impacts and sustainability considerations associated with SCPPs. Furthermore, recommendations for future research and development in this field are provided to guide researchers and industry professionals. This study focuses on the possibility of commercialization of both standalone and hybrid SCPPs.

It is my immense pleasure to assume the role of Editor-in-Chief for the “Mathematical Modelling and Numerical Simulation of Combustion and Fire” Section of Fire, which is intended to take a leading role in the dissemination of high-quality research in this area [...]

Sharing renewable energies, reducing energy consumption and optimizing energy management in an attempt to limit environmental problems (air pollution, global warming, acid rain, etc.) has today become a genuine concern of scientific engineering research. Furthermore, with the drastic growth of requirements in building and industrial worldwide sectors, the need for proper techniques that allow enhancement in the thermal performance of systems is increasingly being addressed. It is worth noting that using sensible and latent heat storage materials (SHSMs and phase change materials (PCMs)) for thermal energy storage mechanisms can meet requirements such as thermal comfort in buildings when selected correctly. However, as the operating temperature changes, a series of complex technical issues arise, such as heat transfer issues, leaks, corrosion, subcooling, supercooling, etc. This paper reviews the most recent research advances in the area of sensible and latent heat storage through the porous media as potential technology while providing useful information for researchers and engineers in the energy storage domain. To this end, the state and challenges of PCMs incorporation methods are drawn up, and an updated database of various research is provided while discussing the conclusions concerning the sensible and latent heat storage in porous media, their scopes of application and impact on energy consumption. In the light of this non-exhaustive review, it turns out that the adoption of porous matrices improves the thermal performance of systems, mitigates energy consumption and drops CO2 emissions while ensuring thermal comfort within buildings. In addition, at the representative elementary volume (REV) and pore scales, the lattice Boltzmann method (LBM) is examined as an alternative method to the commonly used, traditional numerical methods. These two approaches are compared based on results available in the literature. Through these means, their ability to handle latent and sensible heat storage process in a porous medium is demonstrated. To sum up, to be more complete, perspectives of sensible and latent energy storage technologies are covered.

The settling velocities of helminth eggs of three types, namely Ascaris suum (ASC), Trichuris suis (TRI), and Oesophagostomum spp. (OES), in clean tap water are computationally determined by means of computational fluid dynamics, using the general-purpose CFD software ANSYS Fluent 18.0. The previous measurements of other authors are taken as the basis for the problem formulation and validation, whereby the latter is performed by comparing the predicted sink velocities with those measured in an Owen tube. To enable a computational treatment, the measured shapes of the eggs are parametrized by idealizing them in terms of elementary geometric forms. As the egg shapes show a variation within each class, “mean” shapes are considered. The sink velocities are obtained through the computationally obtained drag coefficients. The latter are defined by means of steady-state calculations. Predicted sink velocities are compared with the measured ones. It is observed that the calculated values show a better agreement with the measurements, for ASC and TRI, compared to the theoretical sink values delivered by the Stokes theory. However, the observed agreement is still found not to be very satisfactory, indicating the role of further parameters, such as the uncertainties in the characterization of egg shapes or flocculation effects even in clean tap water.

Thermoelectric generators (TEGs) have the ability to convert waste heat into electrical energy under unfavorable conditions and are becoming increasingly popular in academia, but have not yet achieved a broad commercial success, due to the still comparably low efficiency. To increase the efficiency and economic viability of TEGs, research is performed on the materials on one hand and on the system connection on the other. In the latter case, the net output power of the cooling system plays a key role. At first glance, passive cooling seems preferable to active cooling because it does not affect the net electrical output power. However, as shown in the present review, the active cooling is to be preferred for net output power. The situation is similar in air and water-cooling. Even though air-cooling is easier to set up, the water-cooling should be preferred to achieve higher net output power. It is shown that microchannel cooling has similar hydraulic performance to conventional cooling and inserts increase the net output power of TEG. As the review reveals that active water-cooling should be the method of choice to achieve high net output power, it also shows that a careful optimization is necessary to exploit the potential.

A swirling pulverized coal flame is computationally investigated. A Eulerian–Lagrangian formulation is used to describe the two-phase flow. Turbulence is modelled within a RANS (Reynolds averaged numerical simulation) framework. Four turbulence viscosity- (TV) based models, namely the standard k-ε model, realizable k-ε model, renormalization group theory k-ε model, and the shear stress transport k-ω model are used. In addition, a Reynolds stress transport model (RSM) is employed. The models are assessed by comparing the predicted velocity fields with the measurements of other authors. In terms of overall average values, the agreement of the predictions to the measurements is observed to be within the range 20–40%. A better performance of the RSM compared to the TV models is observed, with a nearly twice as better overall agreement to the experiments, particularly for the swirl velocity. In the second part of the investigation, the resolution of the discrete particle phase in modelling the turbulent particle dispersion (TPD) and particle size distribution (SD) is investigated. Using the discrete random walk model for the TPD, it is shown that even five random walks are sufficient for an accuracy that is quite high, with a less than 1% mean deviation from the solution obtained by thirty random walks. The approximation of the measured SD is determined by a continuous Rosin–Rammler distribution function, and inaccuracies that can occur in its subsequent discretization are demonstrated and discussed. An investigation on the resolution of the SD by discrete particle size classes (SC) indicates that 12 SC are required for an accuracy with a less than 1% mean deviation from the solution with 18 SC. Although these numbers may not necessarily be claimed to be sufficiently universal, they may serve as guidance, at least for SD with similar characteristics.

Within the framework of a Reynolds averaged numerical simulation (RANS) methodology for modeling turbulence, a comparative numerical study of turbulent lifted H2/N2 flames is presented. Three different turbulent combustion models, namely, the eddy dissipation model (EDM), the eddy dissipation concept (EDC), and the composition probability density function (PDF) transport model, are considered in the analysis. A wide range of global and detailed combustion reaction mechanisms are investigated. As turbulence model, the Standard k-ε model is used, which delivered a comparatively good accuracy within an initial validation study, performed for a non-reacting H2/N2 jet. The predictions for the lifted H2/N2 flame are compared with the published measurements of other authors, and the relative performance of the turbulent combustion models and combustion reaction mechanisms are assessed. The flame lift-off height is taken as the measure of prediction quality. The results show that the latter depends remarkably on the reaction mechanism and the turbulent combustion model applied. It is observed that a substantially better prediction quality for the whole range of experimentally observed lift-off heights is provided by the PDF model, when applied in combination with a detailed reaction mechanism dedicated for hydrogen combustion.

Turbulent reacting flows in a generic swirl gas turbine combustor are investigated numerically. Turbulence is modelled by a URANS formulation in combination with the SST turbulence model, as the basic modelling approach. For comparison, URANS is applied also in combination with the RSM turbulence model to one of the investigated cases. For this case, LES is also used for turbulence modelling. For modelling turbulence-chemistry interaction, a laminar flamelet model is used, which is based on the mixture fraction and the reaction progress variable. This model is implemented in the open source CFD code OpenFOAM, which has been used as the basis for the present investigation. For validation purposes, predictions are compared with the measurements for a natural gas flame with external flue gas recirculation. A good agreement with the experimental data is observed. Subsequently, the numerical study is extended to syngas, for comparing its combustion behavior with that of natural gas. Here, the analysis is carried out for cases without external flue gas recirculation. The computational model is observed to provide a fair prediction of the experimental data and predict the increased flashback propensity of syngas.

The purpose of this study is the development of an automated two-dimensional airfoil shape optimization procedure for small horizontal axis wind turbines (HAWT), with an emphasis on high thrust and aerodynamically stable performance. The procedure combines the Computational Fluid Dynamics (CFD) analysis with the Response Surface Methodology (RSM), the Biobjective Mesh Adaptive Direct Search (BiMADS) optimization algorithm and an automatic geometry and mesh generation tool. In CFD analysis, a Reynolds Averaged Numerical Simulation (RANS) is applied in combination with a two-equation turbulence model. For describing the system behaviour under alternating wind conditions, a number of CFD 2D-RANS-Simulations with varying Reynolds numbers and wind angles are performed. The number of cases is reduced by the use of RSM. In the analysis, an emphasis is placed upon the role of the blade-to-blade interaction. The average and the standard deviation of the thrust are optimized by a derivative-free optimization algorithm to define a Pareto optimal set, using the BiMADS algorithm. The results show that improvements in the performance can be achieved by modifications of the blade shape and the present procedure can be used as an effective tool for blade shape optimization.