Convective Heat Flux Research Articles

A comprehensive heat transfer prediction model for tubular moving bed heat exchangers using CFD-DEM: Validation and sensitivity analysis

This study established a complete heat transfer prediction model that integrates four heat transfer sub-models, including contact heat conduction, gas film heat conduction, heat radiation, and heat convection, along with an artificial softening correction based on combined approach of computational fluid dynamics and discrete element method (CFD-DEM). The model’s precision was confirmed by experimental results with relative errors below 5 %. The discussion on the heat flux contributions of the above four heat transfer mechanisms shows that with an initial particle temperature of 200℃, tube wall temperature of 30℃, and particle descent velocity of 1.3 mm/s, gas film conduction heat flux is the primary contributor to the total tube wall heat flux at 60.5 %, followed by radiation heat flux (19.5 %), contact conduction heat flux (12.1 %), and convection heat flux (7.9 %). Besides, the presentation of physical fields related to particles and the fluid showcases the model’s capability in elucidating the heat and mass transfer characteristics of the particle–fluid-wall system within tubular MBHEs. Furthermore, a local nominal range sensitivity analysis, along with a study of factors’ influence rules, was performed to quantify the effects of the 8 key model parameters on heat transfer results. The analysis indicates that fluid thermal conductivity is the predominant factor with its nondimensionalized first-order sensitivity coefficient of 54.9 %, succeeded by particle-to-wall angle factor (15.4 %), wall emissivity (14.4 %), gas film thickness (9.6 %), wall thermal conductivity (2.3 %), wall roughness (-1.6 %), particle Young’s modulus (-1.4 %), and particle specific heat capacity (0.4 %). Finally, their impacts on the heat prediction results were presented in detail.

CFD investigation on a novel pen partition-attached jet air supply for mitigating heat stress among lactating sows

To effectively mitigate heat stress among lactating sows, this study proposed a novel pen partition-attached jet air supply (PJAS) and compared its performance with commercial ceiling jet air supply (CJAS) by using computational fluid dynamics (CFD). Each PJAS unit, comprising a circular distribution duct with 5 slot orifices at each side, was installed at the pen partition between two adjacent pens to direct air towards lactating sows to enhance convective heat removal. The cooling performances of air supplier were primarily evaluated by assessing the convective heat flux from lying sows. The effect of jet angles induced by PJAS and CJAS on convective heat flux were investigated as well as the consequence of reducing the inlet dimension of CJAS. The results revealed that reducing the inlet dimension of CJAS doubled the speed of supplied air. However, it also limited the amount of air impinging on sow due to the narrowing of the inlet air jet. Consequently, the combined effect only marginally increased the convective heat flux when the inlet area of CJAS was reduced. By placing air supplier closer to lactating sows, the air jet induced by PJAS impinged on sows’ bodies directly and therefore significantly increased the convective heat removal. Compared to CJAS, PJAS required approximately 45% less ventilation rate to induce the same convective heat flux. When the ventilation rate was identical, PJAS could increase the convective heat flux by up to 27.6%. These results highlight PJAS as a promising energy-efficient localized cooling device for mitigating heat stress among lactating sows. To determine the optimal design and control strategy of PJAS based on industrial requirements, further research is still needed.

Characteristics of planar buoyant jets and plumes in a turbulent channel crossflow from direct numerical simulations

AbstractThis paper is motivated by an interest in understanding the characteristics of buoyant fluids discharged from the bottom wall of channels, such as encountered during tunnel fires or in river effluent discharge. Direct numerical simulation is used to model the upward release of a planar buoyant jet or plume from the bottom wall of a channel into an incoming turbulent crossflow. The well-studied jet-in-crossflow with only a momentum source is simulated first, and subsequently, fixing the incoming Reynolds number, buoyancy source as heat flux is added alongside varying momentum source, with two cases where only a buoyancy source is present. Appropriate five non-dimensional parameters relevant for this flow are defined, of which three are fixed and two—source to channel momentum ratio and Richardson number—are varied. The changes in turbulence characteristics as the buoyant jet or plume evolves downstream are presented. In all cases with buoyancy, except for the pure jet case, the plume is initially confined to the lower half of the channel before it suddenly lifts to the top half, an effect that occurs at an increasingly smaller downstream distance with increasing buoyancy, and dividing the flow into a near and far field. The distributions of mean and Reynolds stresses in the near and far field of the source are reported, and it is found that the channel flow becomes more turbulent downstream of the source, and further, the turbulent vertical temperature flux switches sign from near to far field owing the a change in the mean temperature gradient sign. From the input parameters and using the integrated temperature equation a reasonable estimate of the far field mean channel temperature can be obtained by a reference temperature based on the heat conservation that includes the convective and diffusive source heat flux. A monotonic behaviour of the back-layering distance is also observed a function of this reference temperature, which was difficult to obtain with the two specified non-dimensional parameters.

The influence of heterogeneous catalytic processes on the heat flux to the surface and the chemical composition of the shock layer at high-speed flow around blunt bodies

Numerical modeling of the high-speed flow of a multicomponent dissociated gas around a blunt body was carried out for the flow regime corresponding to the thermally stressed point of the gliding trajectory of entry into the Earth's atmosphere in the surface temperature range of 800–2000 K. As boundary conditions, a stage-by-stage model of heterogeneous catalysis of the interaction of dissociated air with the thermal protection material SiO2 was used, previously developed by the authors on the basis of transition state theory and quantum mechanical calculations. The dependence of the modes of heterogeneous chemical reactions on the surface temperature and the density of surface adsorption centers and their influence on the chemical composition of the shock layer and the convective heat flux to the streamlined surface are analyzed. The contributions of individual mechanisms of heterogeneous recombination to the total rate of formation of molecules on the surface are estimated. The possibility of using the density of adsorption sites as an effective parameter when setting boundary conditions on a real thermal protection surface in flow problems is shown.

Modelling flame-to-fuel heat transfer by deep learning and fire images

In numerical fire simulations, the calculation of thermal feedback from the flame to the solid and liquid fuel surface plays a critical role as it connects the fundamental gas-phase flame burning and condensed-phase fuel gasification. However, it is a computationally intensive task in CFD fire modelling methods because of the requirement of a high-resolution grid for calculating the interface heat transfer. This paper proposed a real-time prediction of the flame-to-fuel heat transfer by using simulated flame images and a computer-vision deep learning method. Different methanol pool fires were selected to produce the image database for training the model. As the pool diameters increase from 20 to 40 cm, the dominant flame-to-fuel heat transfer shifts from convection to radiation. Results show that the proposed AI algorithm trained by flame images can predict both the convective and radiative heat flux distributions on the condensed fuel surface with a relative error below 20%, based on the input of real-time flame morphology that can be captured by a larger grid size. Regardless of growing or decaying fires or puffing flames induced by buoyancy, this method can further predict the non-uniform distribution of heat transfer coefficient on the interface rather than using empirical correlations. This work demonstrates the use of AI and computer vision in accelerating numerical fire simulation, which helps simulate complex fire behaviours with simpler models and smaller computational costs. Highlights A total framework between AI model and fire simulation software is designed to further enhance the reliability of AI-based fire simulations. A standard pool fire simulation database is built using numerical model recommend by the IAFSS Computation Group. A deep learning model is developed to predict both the convective and radiative heat flux distributions on the condensed fuel surface using numerical images database. The demonstration showcases the application of AI and computer vision to accelerate numerical fire simulation.

Dissipation-based proper orthogonal decomposition of turbulent Rayleigh–Bénard convection flow

We present a formulation of proper orthogonal decomposition (POD) producing a velocity–temperature basis optimized with respect to an H1 dissipation norm. This decomposition is applied, along with a conventional POD optimized with respect to an L2 energy norm, to a dataset generated from a direct numerical simulation of Rayleigh–Bénard convection in a cubic cell (Ra=107, Pr=0.707). The dataset is enriched using symmetries of the cell, and we formally link symmetrization to degeneracies and to the separation of the POD bases into subspaces with distinct symmetries. We compare the two decompositions, demonstrating that each of the 20 lowest dissipation modes is analogous to one of the 20 lowest energy modes. Reordering of modes between the decompositions is limited, although a corner mode known to be crucial for reorientations of the large-scale circulation is promoted in the dissipation decomposition, indicating suitability of the dissipation decomposition for capturing dynamically important structures. Dissipation modes are shown to exhibit enhanced activity in boundary layers. Reconstructing kinetic and thermal energy, viscous and thermal dissipation, and convective heat flux, we show that the dissipation decomposition improves overall convergence of each quantity in the boundary layer. Asymptotic convergence rates are nearly constant among the quantities reconstructed globally using the dissipation decomposition, indicating that a range of dynamically relevant scales is efficiently captured. We discuss the implications of the findings for using the dissipation decomposition in modeling and argue that the H1 norm allows for a better modal representation of the flow dynamics.

Reversed-direction 2-point modelling applied to divertor conditions in DIII-D *

A predictive form of the extended 2-point model known as the ‘reverse 2-point model’, Rev2PM, is applied to a range of detachment levels in the open lower divertor of DIII-D, showing that the experimentally measured electron temperature (Te ) and pressure (pe ) at the divertor entrance can be calculated within 50% from target measurements, if and only if a posteriori corrections for convective heat flux are included in the model. Unlike the standard 2-point model, the Rev2PM calculates upstream scrape-off layer (SOL) quantities (such as separatrix Te and pe ) from target conditions (such as Te and parallel heat flux), with volumetric power and momentum losses depending solely on target Te . The Rev2PM is tested against a database of DIII-D inter-ELM divertor Thomson scattering measurements, built from a series of 6 MW, 1.3 MA, LSN H-mode discharges with varied main ion density, drift direction, and nitrogen puffing rate. Measured target Te ranged from 0.4–25 eV over this database, and upstream Te ranged from 5–60 eV. Poor agreement is found between upstream measurements and Rev2PM calculations that assume purely conductive parallel heat transport. However, introducing a posteriori corrections to account for convective heat transport brings the Rev2PM calculations within 50% of the measured upstream values across the dataset. These corrections imply that up to 99% of the parallel heat flux is carried by convection in detached conditions in the DIII-D open lower divertor, though further work is required to assess any potential dependencies on device size or divertor closure.

Unraveling the surface heat flux heterogeneity in cone calorimetry of cylindrical charring material: Insights from experiments and 2D modeling

Although originally designed for planar samples, cone calorimeter is frequently used for the flammability assessment and pyrolysis modeling of non-planar objects, like electrical cables. Prescribing the boundary conditions for the numerical models of such objects requires knowledge about the radiative and convective heat fluxes along the sample circumference. In this work, we performed gasification and flaming experiments and 2D numerical simulations on birch cylinders. During the gasification of a single-rod, the char front propagated faster vertically than horizontally, while similar rates were observed in the flaming condition. With five rods, ∪- and ∩-shaped char fronts were observed in gasification and flaming conditions, respectively. From the simulations, we extracted detailed heat flux distributions, with main deviation from flat samples being the steep reduction in incident radiation between the top and sides of the cylinders. Moreover, in five-rod configurations, radiative flux to the sides of the central rod increases up to 10 (gasification) and 20 kW m−2 (flaming). On the outermost rod, the descending flame induces downward-moving waves of heat fluxes with amplitudes 20 kW m−2 for convection and 15 kW m−2 for radiation. Simplified expressions for the heat transfer boundary conditions were tabulated for practical engineering applications.

Investigating hybrid nanoparticles for drug delivery in multi-stenosed catheterized arteries under magnetic field effects

This groundbreaking study pioneers the exploration of the therapeutic implications of a constant magnetic field simultaneously with hybrid nanoparticles on blood flow within a tapered artery, characterized by multiple stenosis along its exterior walls and a central thrombus, employing three-dimensional bio-fluid simulations. In addition, a magnetized catheter is inserted into the thrombus to increase the therapeutic potential of this novel method. The flow condition under consideration has applications in targeted medication distribution, improved medical device design, and improved diagnostics, as well as in advancing healthcare and biomedical engineering. Our investigation primarily aims to optimize blood flow efficiency, encompassing key parameters like pressure, velocity, and heat fluctuations influenced by diverse geometric constraints within the stenotic artery. Precise solutions are obtained through the finite element method (FEM) coupled with advanced bio-fluid dynamics (BFD) software. Hybrid nanoparticles and magnetic fields impacted pressure and velocity, notably reducing pressure within the stenosis. Convective heat flux remained uniform, while temperature profiles showed consistent inlet rise and gradual decline with transient variations. This approach promotes fluid flow, and convection within stenosed arteries, enhances heat transport, evacuates heat from stenotic regions, and improves heat dispersion to surrounding tissues. These findings hold promise for targeted therapies, benefiting patients with vascular disorders, and advancing our understanding of complex bio-fluid dynamics.

Modelling solar water desalination system using natural convection

In recent times, solar energy has emerged as one of the most promising energy sources. Numerous scholars and researchers are exploring various applications of solar energy. This presented work focused on solar water desalination system to evaluate its thermal performance in natural convection mode. Three-dimensional Computational fluid dynamics CFD model is built in Comsol Multiphysics 6.1. Numerical model simulations have been carried out by using Heat transfer in Solid &Fluid and Laminar flow interfaces. The surface temperature varies between 19.5℃ and 102℃ while the velocity magnitude was between 0.05 m/s and 0.5 m/s. Variations of the surface temperature, velocity magnitude, pressure, convective and conductive heat flux magnitudes in Solar water desalination system are presented in the discussion section of the article.

Improving indoor environmental quality in an affordable house by using a vegetated wall: A case study in subtropical Brazil

Indoor environmental quality of buildings, including thermal, acoustic, visual comfort, and air quality, directly impacts the comfort, health, and productivity of occupants. However, in Brazil, the high deficit of affordable housing units has led to a situation where environmental quality is often overlooked in favour of low investment costs, prioritizing quantity over quality. Furthermore, the poorest segments of the population, who rely on affordable housing, are disproportionately affected by energy costs. Therefore, it is crucial to conduct research on low-cost energy solutions for social housing to improve the sustainability of people's lives. In this light, a study was conducted to monitor the energy performance of a vegetated wall made of deciduous species and compare it to a bare wall used in an affordable house in subtropical Brazil. Parameters, such as internal and external surface temperatures, nearby microclimatic conditions, and heat transfer through the vegetated and bare walls, were monitored every 5 min over a two-year period. The heat flux analysis revealed that the vegetated wall reduced conductive heat up to 83 % during summer days, significantly lowering the external surface temperature by 8.6 °C due to the presence of the plant layer. Moreover, the vegetated wall generally exhibited lower shortwave and longwave radiative and convective heat fluxes. These findings contribute to our understanding of energy transfer through vegetated walls in subtropical Brazil, including the impact of adjacent microclimatic conditions. Furthermore, the results confirm the potential of vegetated walls to effectively reduce cooling and heating demands at a minimal additional cost.

Experimental and Numerical Study of the Trench Fire Spread Rule over a Sloped Uniform Fuel Bed: Rate of Fire Spread, Flame Morphology, and Heat Flux

Trench fires on sloped terrain are always complicated due to the corresponding flame dynamics and heat transfer mechanisms. Flame attachment may increase the rate of fire spread (ROS) by enlarging the heating area of unburned vegetation. In addition, variations in radiative and convective heat flux are of great importance to fire behavior characteristics. In this work, trench fire tests under different slopes (θ) and inclined sidewalls (A) were performed by numerical simulations based on the Lagrangian Particle Model (LPM) and Boundary Fuel Model (BFM) in the Fire Dynamics Simulator (FDS) and small-scale experiments, and the ROS, flame characteristics, and radiative/convective heat flux of the fire front are discussed in detail. The results indicate that the flame tends to adhere to the fuel bed with increasing slope angle and sidewall inclination. In particular, the flame becomes fully attached with a greater pressure difference than the buoyancy, which is caused by the unequal air entrainment between the front and behind the flame. When A = 90°, the critical slope angle of the flame adhesion (from slight tilt to full attachment) is identified as ~20°. The ROS (θ ≤ 15°) predicted by the BFM and LPM are closer to the small-scale experiments. The heat fluxes based on the experiments confirm the predominant mechanism of radiative heat transfer in trench fires at low slopes (θ ≤ 20°). Furthermore, convective heat transfer is more significant than radiative and becomes the main heating mechanism for θ ≥ 20°.

Convection instability in phase-change Rayleigh–Bénard convection systems at a finite Stefan number

In this paper, we revisit the convection instability in phase-change Rayleigh–Bénard convection systems at a finite Stefan number, where a pure solid substance confined between two horizontal walls is isothermally heated from below in order to induce melting, assuming no heat conduction in the solid phase. By establishing a connection between the heat transfer behaviors in the conduction and convection melting regimes through the jump events in the temporal evolution of the heat flux and the melted liquid fraction, two criteria (the critical average fluid temperature θ¯fc and the critical melted liquid fraction flc) are derived to characterize the convection onset. In contrast to the conventional instability analysis, the derivation in the present work is much more convenient and removes the limitation of a vanishing Stefan number (Ste→0). The two obtained criteria are successfully validated by the data available in the literature, together with the numerical simulations conducted in this paper. The validations revealed that the proposed θ¯fc and flc work well at a finite Ste and that flc is slightly less accurate than θ¯fc, due to the error inherited from the employed scaling law describing the convective heat flux. With the relation between the effective and global parameters, flc is further converted into the commonly used critical effective Rayleigh number by Raec=Raflc3, which is found depending on Ste only, being the same as the criterion of θ¯fc, while its precision is less satisfying due to amplified error from the cubic power operation of flc3.

Heat transfer mechanism and emergency operating speed of moving train fires in a metro tunnel

The primary strategy for a burning train in metro tunnels is to drive it out of the tunnel, or to the station or safe area ahead. However, the heat transfer mechanism and the emergency operating speed of moving train fires in tunnels have not been addressed. In this study, a 1:10 train-tunnel model was designed to conduct a series of moving model experiments. The results show that with the increasing train speed in tunnels, the flame height decreases, the flame width and length first increase and then decrease, and the flame tilt angle increases. The maximum temperature at the train top increases by 81.7 % when the train speed increases from 2 to 6 m/s. A piecewise model is proposed to predict the maximum temperature at the train top. The maximum temperature rise at the tunnel ceiling is 17.4 K and exponentially decreases with the train speed, posing a limited threat to the tunnel structure. The convective heat flux received by the train accounts for 82.1 %–94.4 %. The heat transfer between the train, tunnel and flame is codetermined by the train-tunnel aerodynamic effect and fuel-rich zone. The emergency operating speed of the train is suggested to be 22.8 km/h when the heat release rate is 7.5 MW. This study innovatively reveals the combustion behavior of moving train fires in a metro tunnel and proposes guidelines for determining the emergency operating speed of burning trains. The results can provide references for the fire safety design and running capacity improvement of metro trains.

An engineering model for creeping flame spread over idealized electrical wires in microgravity

Flame spread over an insulated electrical wire is a major source of fire scenario in a space vehicle. In this work, an engineering model that predicts the creeping flame spread over cylindrical wires in microgravity is developed. The model is applied to interpret experimental data obtained in parabolic flights for wires composed by a 0.25 mm radius nickel-chromium (NiCr) metallic core coated by low-density polyethylene (LDPE) of different thicknesses ranging from 0.15 mm to 0.4 mm. The model relies on the assumption that, in the pyrolysis region, the NiCr and the LDPE are in thermal equilibrium. This assumption is supported by more detailed numerical simulations and the model reduces then to solving the heat transfer equations for both NiCr and LDPE in the pyrolysis region and in the region ahead of the flame front along with a simple degradation model for LDPE, an Oseen approximation of opposed oxidizer flow and an infinitely fast gas-phase chemistry. The flame spread rate (FSR) is controlled by two model parameters, which are measurable from intrinsic material and ambient gas properties: the convective flame heat flux transferred to the solid ahead from the flame front and the gaseous thermal heat length near the flame front. These parameters are then calibrated from experimental data for a given wire geometry and the calibrated model is validated against experimental data for other wire geometries and ambient conditions. The heat transfer mechanisms ahead of the pyrolysis front are investigated with a special emphasis on the LDPE thickness and the conductivity of the metallic core. In addition to NiCr, metallic cores of lower and higher conductivities are considered. The polymer is shown to be thermally thick for all tested wire geometries and core conductivities. The flame heat flux is found to dominate the heat transfer in the preheat zone where it applies. The core has nevertheless a significant impact in the heating of the LDPE with its contribution increasing with the core conductivity and when decreasing the LDPE thickness.

Experimental investigation of heating augmentation by particle kinetic energy conversion in dust-laden supersonic flows

The presence of particles in supersonic flows can cause significant increases in stagnation point heat fluxes (Dunbar et al. in AIAA J 13:908–912, 1975). This effect is commonly named ‘particle-induced heat flux augmentation’ or just ‘heating augmentation.’ Heating augmentation can be described as the sum of the conversion of kinetic energy of the particles into thermal energy, characterized by the energy conversion efficiency, also called accommodation coefficient, and the increase of convective heat flux (Polezhaev et al. in High Temp 30:1147–1153, 1992; Vasilevskii and Osiptsov in Experimental and numerical study of heat transfer on a blunt body in dusty hypersonic flow 33rd thermophysics conference, American Institute of Aeronautics and Astronautics, 1999). Although the accommodation coefficient is fundamental for heating augmentation characterization, there is only a small number of experimental datasets for it. This work focusses on the experimental determination of the accommodation coefficient in flow regimes at Mach number 2.1, Reynolds number, based on the probe nose diameter, from approx. 6e5 to 1.8e6, and nominal particle sizes of approx. 20 µm. The decrease of particle velocity and kinetic energy flux in the shock layer is measured with highly resolved shadowgraphy for individual particles. The particle kinetic energy flux is decreased by 29% on average by particle deceleration in the shock layer. Negligible kinetic energy fluxes of rebounded particles were measured. The accommodation coefficient is approx. 0.36 for Al2O3 and SiO2 particles, while it is approx. 0.09 for MgO particles. Hence, it is significantly smaller than the widely used value of 0.7, based on the study of (Fleener and Watson in Convective heating in dust-laden hypersonic flows 8th thermophysics conference, 1973), but in good agreement with values given in (Hove and Shih in Reentry vehicle stagnation region heat transfer in particle environments 15th aerospace sciences meeting, 1977) and (Molleson and Stasenko in High Temp 55:87–94, 2017. https://doi.org/10.1134/S0018151X1701014X ). No difference between erosive and elastic particle reflection mode was detected on the conversion efficiency. The data from a simplification of the modeling approach of the conversion efficiency for elastic particle reflection by Molleson and Stasenko (2017) are in poor agreement with experimental data.

Synergistic effect of ribs and particles on flow and heat transfer in channels using the CFD-DEM-IBM method

To investigate the synergistic effect of the surface structure and particles on flow and heat transfer during forced convection, a model for two-phase flow and heat transfer was established using the computational fluid dynamics-discrete element method-immersed boundary method (CFD-DEM-IBM). The effects of rib size and particle physical properties on the flow and heat transfer were studied. The results showed that large-scale vortices rolling forward were formed in the particle-laden flow, and heat transfer in the rib gaps was intermittently enhanced. Convective heat flux was weakened, and conductive heat flux was strengthened when the height of the ribs was too high or the spacing was too small. Particles with high thermal conductivity promoted conductive and convective heat transfer. Small particles easily entered the rib gaps to strengthen the heat transfer, but this inhibited heat conduction at flat surface. Fluid laden with a mixture of particle sizes enhanced the convective heat transfer.

Field-Scale Physical Modelling of Grassfire Propagation on Sloped Terrain under Low-Speed Driving Wind

Driving wind and slope of terrain can increase the rate of surface fire propagation. Previous physical modelling under higher driving wind (3–12.5 m/s) on slopes (Innocent et al., IJWF, 2023, 32(4), pp. 496–512 and 513–530) demonstrated that the averaged rate of fire spread (RoS) varied from that of empirical models. This study investigates the potential for better agreement at lower wind velocities (0.1 and 1 m/s), since empirical models are typically developed from experimental studies conducted under benign wind conditions. The same physical model WFDS is used. The results are analysed to understand the behaviour of various parameters (RoS, fire isochrone progression, fire intensity, flame dynamics, and heat fluxes) across different slopes. The RoS–slope angle relationship closely fits an exponential model, aligning with the findings from most experimental studies. The relative RoSs are aligned more closely with the Australian and Rothermel models’ slope corrections for 0.1 and 1 m/s, respectively. The relationship between flame length and fire intensity matches predictions from an empirical power–law correlation. Flame and plume dynamics reveal that the plume rises at a short distance from the ignition line and fire propagation is primarily buoyancy-driven. The Byram number analysis shows buoyancy-dominated fire propagation at these lower wind velocities. Convective heat fluxes are found to be more significant at greater upslopes. The study confirmed that “lighter & drier” fuel parameters accelerated the fire front movement, increasing the RoS by approximately 57–60% compared to the original parameters. Overall, this study underscores the nuanced interplay of wind speed, slope, and other factors in influencing grassfire behaviour, providing valuable insights for predictive modelling and firefighting strategies.

CFD-DEM simulation of heat transfer in spout-fluid beds

It is necessary to study the flow regimes of spout-fluid beds before considering their application in the industry. A three-dimensional computational fluid dynamic coupled with the discrete element method (CFD-DEM) was employed to study the heat transfer of the jet-in-fluidized bed flow, spouting-with-aeration flow, and intermediate/spout-fluidization flow regimes of the spout-fluid bed. To determine the efficiency of heat transfer in these flow regimes, extensive CFD-DEM simulations were conducted along with a heat transfer model. The heat transfer in these flow regimes was investigated using particle temperature distributions, mean convective heat flux, and average particle temperature. Compared to the other flow regimes, the jet-in-fluidized bed flow regime demonstrated a higher degree of heat transfer due to the presence of bubbles in the annulus. Moreover, it was observed that the spouting-with-aeration flow regime exhibits a better convective heat transfer compared to the intermediate/spout-fluidization. The stable and continuous spout channel of the spouting-with-aeration flow regime helps convective heat transfer more than the interrupting spout channel of the intermediate/spout-fluidization.

Experimental and computational study of convective heat fluxes in swirling two‐phase flows

AbstractThe convective mode of heat transfer is mainly due to the bulk motion of the fluid. Its turbulent nature and enhanced heat transfer coefficients have always attracted the academic, scientific community, and industrialists for many decades. The current research is based on the experimental and theoretical investigations on the turbulent convective heat transfer in swirling (60–300 rpm) steam (1–3 bars) injection into cocurrently flowing water. An exponential increase in the convective heat transfers up till the most swollen part of the swirling steam‐water volume of fluids has been observed. However, the convective heat transfer of the remaining part of the steam's plume shows an almost stagnant decreasing trend. The range of Rayleigh number that supports the transition in trends of the convective heat fluxes is 2.84 × 1011–3.71 × 1011. This transition affects the magnitude of the convective heat fluxes and the extent of the effective momentum fluxes, which is evident in the dominant role of the flow instabilities acting across the length of the steam's plume. Computational Fluid Dynamic analysis also has supported the exhibition of the heat fluxes magnitudes under the influence of the interacting Kelvin–Helmholtz instabilities and inertial instabilities across and along with the cocurrently acting shear layer.