Efficient recovery of waste heat from flue gases is crucial in the design of waste heat recovery systems, particularly considering the low specific heat of exhaust gases, which makes energy extraction challenging. Attachments play a vital role in compact heat exchangers to ensure suitability in waste heat recovery systems. We have conducted a comprehensive comparison of the thermal and hydrodynamic performance of a staggered tube array with porous attachments. Two different attachment configurations, including complete circular (CC) and leeward cut (LC), were investigated. Porous samples with variable pore densities were utilized as fins and wrapping over the tube array. The energy and flow interactions within the porous media were modeled using the local thermal nonequilibrium (LTNE) and Darcy-Brinkmann-Forchheimer (DBF) models, respectively. All simulations were conducted within a Reynolds number range of 6000-9000 using the kappa-& varepsilon; turbulence model. The results show that porous wrapping achieved the highest heat transfer and pressure drop among all attachment configurations. Specifically, compared to a bare tube array, porous wrapping increased the Nusselt number by 20-25 times but resulted in a pressure drop that was 40-90 times higher. In contrast, porous fins yielded a fourfold increase in the Nusselt number with a nearly fivefold increase in pressure drop. When comparing the ratio of heat transfer per unit temperature difference to the pumping power (Z/E), porous fins emerge as the better option due to the significantly higher pressure drop associated with porous wrapping.

Toxic gases produced during a fire must be understood while assessing the fire threat. In reality, carbon monoxide poisoning brought on by inhaling the gas accounts for the majority of fire-related fatalities. Smoke is regarded as the greatest threat to human life in the event of unintentional building fires. Additionally, most countries’ building fire safety norms and regulations do not include smoke toxicity requirements. Commercial enterprises like chemical, nuclear, and thermal power plants have fuel placements inside enclosures elevated far above the floor. Additionally, the cabin position of the ship for storing marine diesel fuel is above the base, suggesting enhanced circumstances for a pool fire. From the fire safety perspective, assessing the toxicity of the gases produced under various pool fire circumstances inside the compartment is necessary. Therefore, this study investigates the effect of diesel pool fire in a full-scale compartment on different elevation levels. Full-scale compartment simulations were performed with 0.8 m diameter diesel fuel pans of varying heights in the central location. The analyzed parameters were the flame temperature, door temperature and smoke layer height. The effect of various crucial modeling Smagorinsky constants was studied on the elevated pool fires. Understanding the complexity of a large-scale test environment with changing combustion conditions both momentarily and geographically is crucial. Therefore, the Fire Dynamic Simulator software results were validated with the experiments, which agrees with the data. The results from the study are significantly valuable for understanding the behavior of hazardous gases in commercial enterprises, promoting disaster risk reduction in case of fire accidents.

This article investigates the laminar flow of power-law fluids through two porous square cylinders in a side-by-side configuration. The effects of power-law index (n), Darcy number (Da), and gap ratio (g/W) are examined within ranges of g/W = 0.5-5, n = 0.4-0.8, and Da = 10-6-10-2, respectively. Two flow conditions are considered: first, for a creeping flow (unseparated flow) at Re = 1 where Darcy's law is applicable; second, for a viscous dominant flow at Re = 100, where Darcy-Forchheimer-extended model is exercised. Flow patterns behind the porous cylinders are analyzed using streamlines, velocity profiles, pressure distribution curves, and vorticity structural parameters (Gamma). In low permeability levels, the flow exhibits an irregular nonperiodic vortex shedding characterized by a single large vortex street far off the downstream for g/W = 0.5. However, synchronized wake patterns were observed in either antiphase or in-phase modes for higher gap ratios. Leading-edge separation with two-side recirculation induces quasi-periodicity in the flow for all g/W. It was found that increasing the permeability can prevent the leading edge separation. Additionally, a transition from antiphase to in-phase mode occurs when the permeability is altered while maintaining constant flow-time. The presence of a jet-like flow between cylinders significantly impacts unsteady wake patterns. The impact of g/W, power-law index, and permeability on drag is also examined. A jump in some flow parameters was observed at higher Re for the midrange Darcy number, but no such increase was noted for the high shear-thinning behavior. These findings provide a potential approach for improving the design of fluidic systems involving porous cylinders.

This study investigates the influence of nanoparticle volume fraction, nanoparticle diameter, and Richardson number on the heat transfer across an array of cylinders arranged in inline and staggered formation in a heat exchanger. The Richardson number and the diameter of the nanoparticles varied from −1.5 to 1.5 and from 10 to 50 nm, respectively. The Reynolds number is fixed at 100. The investigation involves exploring different volume fractions of nanoparticles dispersed in the nanofluid, ranging from 0 to 0.05. The results show a stark increase in heat transfer rates when opposing buoyancy is introduced. A combination of opposing buoyancy, small nanoparticle diameter, and high volume fraction of nanoparticles can cause a significant increment in heat transfer rates. Opposing buoyancy induces chaotic flow with larger recirculation zones, leading to higher temperature gradients near the cylinders and elevated heat transfer rates. However, the rate of heat transfers in all operating conditions is notably lower when aiding buoyancy prevails. This behavior can be attributed to the stabilizing effect of aiding buoyancy in the flow, consequently reducing temperature gradients in the vicinity of cylinders and the nanofluid. The heat transfer rates are quantified using the mean Nusselt number of the arrays and the local Nusselt numbers on each cylinder within the arrays.

The objective of the current study is to analyse the hydro-thermal characteristics of leeward cut fins with various trimming values and finalise a specific fin that benefits by maximum material saving and negligible compromise in heat transfer. The leeward section of a fin is cut in two ways: angular and chordwise. For angular cutting, four different angles (15 degrees, 30 degrees, 60 degrees, and 90 degrees) are considered, while for chordwise cutting, a fin is trimmed along a chord present at D/3, 2D/3, and D mm from the vertical diameter. The spacing between fins is varied (2-4 mm). For turbulence modelling, the transition SST model is implemented. Streamlines reveal that the intensity of a vortex formed downstream of the tube depends on the fin-trimming value. For a higher fin cutoff, a lower pressure drop is obtained. The heat transfer rate analysis reveals that angular cutoffs of 15 degrees (8.3 % material saving) and 30 degrees (16.6 % material saving) have 2.5 %-3.1 % less heat transfer than the standard case. Chordwise cut at D gives 1.1 % less heat transfer but saves only 2.7 % fin material than the standard case of no cutoff. Z/E factor, a ratio of heat transfer for a unit temperature drop to power provided, is used to determine hydro-thermal performance. The value of the Z/E ratio is the highest for the benchmark case. However, for angular cutoffs of 15 degrees and 30 degrees, the Z/E factor is less by 4 and 6.7 %, respectively, than the standard case. Examining the outcomes of this study, we recommend using an angular cutoff of 30 degrees or lower to get significant material savings for an equivalent heat transfer.

This study deals with a 3D numerical analysis of annular finned tubes in crossflow. The impact of fin diameter on variables such as heat transfer coefficient, pressure drop and the heat transfer rate was considered in the Reynolds number range of 4630 ≤Re ≤ 9260. The rate of heat transmission has been seen to increase by nearly 19

Purpose This study describes a series of experiments investigating the upper hot layer temperature profile in a confined space under different ventilation conditions for porosity-controlled wood crib fires for pre-flashover conditions. Design/methodology/approach Full-scale compartment (4 m × 4 m × 4 m) experiments were carried out for four-door openings, i.e. 100%, 75%, 50% and 25% of the total vent area (2 m × 1 m) with the wood crib as a fuel load. The temperature of the upper hot smoke layers of the compartment was recorded with the help of four layers of thermocouples for varying vent areas. Findings The effect of ventilation on the properties, i.e. mass loss rate, enclosure temperature, heat release rate and carbon monoxide (CO) gas concentration, has been measured and analyzed. The effect of ventilation on heat flux and flame temperature has also been studied. Compartment gas temperature has been examined by five wood crib burning stages: Ignition, growth, steady burning, recess and collapse. Originality/value Findings demonstrate that the influence of vent openings varies for the burning parameters and upper layer temperature of the compartment. The current results are beneficial in analyzing thermal risks concerning compartment fire and fire safety engineering projects.

The objective of this study is to investigate the impact of different porous metal samples on the hydro-thermal characteristics of a single cylinder with porous fins using computational fluid dynamics. Commercially used porous samples with pore densities of 10, 20, and 40 PPI were used in this study for heat recovery from exhaust flue gas. The three-dimensional computational domain with porous aluminum fins attached to a tube over which high-temperature exhaust gas flows in a crossflow arrangement mimics a waste heat recovery system. Computations were performed at Reynolds number of 6000-9000, using the realizable kappa-epsilon turbulence model. Three fin diameter-to-tube diameter ratios (D-f/D = 2, 2.5, and 3) were considered. The local thermal nonequilibrium model is implemented for energy transfer, as it is more accurate for a high-temperature gradient scenario in a waste heat recovery system. The foam sample with the highest pore density was observed to have the highest pressure drop due to low permeability. A maximum heat transfer and Nusselt number were achieved for a 40 PPI foam sample due to a reduced flowrate inside the porous zone. The overall performance of metal foam samples at varying fin diameters was evaluated based on the area goodness factor (j/f) and a heat transfer coefficient ratio to pumping power per unit heat transfer surface (Z/E). The analysis of these two parameters suggests using 20 PPI foam at D-f/D = 2.

In this study, we have investigated the flow around two side-by-side porous cylinders in a confined channel. The study reports various flow patterns as well as an absolute suppression of the vortex-shedding process at high permeability levels. An unsteady flow at Reynolds number Re = 150 at two different parameters, Darcy number (Da) and gap ratios (s/d) for the ranges of Da = 10–6−10–2 and s/d = 1.5–6, is found to exhibit asymmetric flip-flop and synchronized anti-phase wake patterns. A jet-like flow in the vicinity of cylinders, mainly on the gap side, controls the wake patterns. A jump in the flow characteristics in the intermediate range of Darcy number is also explained by means of backflow phenomena. The velocity profiles on the freestream sides, the gap side, and the surface pressure distribution curve are discussed to give insight into the formation and suppression of wakes. The effects of gap ratios and Darcy number on the drag coefficient are also examined.

Heat transfer enhancement through porous media are of interest in many thermal applications. Forced convection through a triangular array of circular cylinders embedded in a fluid-saturated porous media has been investigated using extended Darcy Brinkman-Forchheimer momentum equations and Local Thermal Equilibrium (LTE) model. Detailed results are illustrated, for high permeability levels (Darcy number varied from 1/10³ to 1/10) and different cylinder spacings (0.7 ≤ φ ≤ 0.99) at Re = 100. It is anticipated that porous media would enhance heat transfer, but it emanates multiple order in pressure drop.

Purpose This study seeks to understand the connection of methodology by finding relevant papers and their full review using the “Preferred Reporting Items for Systematic Reviews and Meta-Analyses” (PRISMA). Design/methodology/approach Concrete-filled steel tubular (CFST) columns have gained popularity in construction in recent decades as they offer the benefit of constituent materials and cost-effectiveness. Artificial Neural Networks (ANNs), Support Vector Machines (SVMs), Gene Expression Programming (GEP) and Decision Trees (DTs) are some of the approaches that have been widely used in recent decades in structural engineering to construct predictive models, resulting in effective and accurate decision making. Despite the fact that there are numerous research studies on the various parameters that influence the axial compression capacity (ACC) of CFST columns, there is no systematic review of these Machine Learning methods. Findings The implications of a variety of structural characteristics on machine learning performance parameters are addressed and reviewed. The comparison analysis of current design codes and machine learning tools to predict the performance of CFST columns is summarized. The discussion results indicate that machine learning tools better understand complex datasets and intricate testing designs. Originality/value This study examines machine learning techniques for forecasting the axial bearing capacity of concrete-filled steel tubular (CFST) columns. This paper also highlights the drawbacks of utilizing existing techniques to build CFST columns, and the benefits of Machine Learning approaches over them. This article attempts to introduce beginners and experienced professionals to various research trajectories.

Abstract The present study performs a three-dimensional CFD analysis to investigate the hydrodynamic and thermal properties of annular finned tubes in a heat exchange system. All computations are performed in the turbulent flow regime (4330 ≤ Re ≤ 8790), and the Transition SST model is applied for turbulence modelling. The impact of Prandtl number (0.7 ≤ Pr ≤ 50) on the various parameters, such as the heat transfer coefficient, heat transfer rate, and pressure drop, are considered. The results indicate that the thermo-hydraulic behaviour is significantly affected by incrementing both Reynolds and Prandtl numbers. The fin’s surface temperature distribution is examined to get a better insight into its thermal performance, and it is observed that the rear portion of the fin contributes the least to heat transfer. Other important parameters like the fin efficiency and Colburn heat transfer factor are found to significantly impact the performance of the heat exchange system for the above range of settings. The velocity contours show the horseshoe vortex formation near the fin-tube junction, and the channelling effect is observed between consecutive tubes. Different fluids are compared based on the j/f factor for enhanced heat transfer at the minimum possible flow resistance.

Concrete-filled steel tube (CFST), which has a long-standing relationship for their exceptional mechanical performance and cost-effectiveness, is frequently utilized as the primary load-bearing element in various constructions. In CFSTs, there are challenging constraints between steel tubular and core concrete, and there is a highly nonlinear relationship between geometric and material parameters and high-temperature behavior. Therefore, a thorough understanding of the fire performance of these columns is required. Fifty-six experimental tests from the literature are collected for circular CFST columns into a database and statistically assessed for their residual strength index (RSI). The database was then divided into a test set and a training set, which were used to train and improve the machine learning models. In this study, models to forecast the RSI of circular CFST columns are developed using four machine learning (ML) techniques with feature ranking analysis, namely: Gaussian progress regression (GPR), ensemble, support vector machines (SVM), and artificial neural network (ANN). Quadratic SVM and bi-layered ANN models outperformed the other ML models with R 2 values of 0.93 and 0.98, respectively. The relevant experimental test results corroborated the parametric study's findings that the trained ML models could typically represent the influence of each key input attribute. As a result, ML is an adequate substitute for empirical and theoretical formulations. The use of ML models will reduce the research expense, and practicing engineers will find it especially helpful to evaluate the performance of these columns at higher temperatures.

An investigation of the laminar flow and enhanced heat transfer rate through a triangular array of cylinders embedded in a fluid-saturated porous media is considered. Mixed convection covering forced convection cases has been studied using a finite-volume approach considering the local thermal equilibrium model. Darcy-Brinkman-Forchheimer momentum equations are used to characterize the porous media in question. The study is constrained to the low and intermediate Peclet number (Re = 5 to 40, Pr = 50) and high range of Darcy number (Da = 10(-3) to 10(-1)) for different cylinder spacings (0.7 <= phi <= 0.99). It is anticipated that porous media would enhance heat transfer, but it derives a multiple order in pressure drop indubitably not desirable in many heat applications. Investigation reveals that both mean drag coefficient (C-D) and Nusselt number (Nu) are strong functions of Da and phi; however, the influence of the buoyancy parameter is mainly witnessed in higher permeability levels and high Peclet numbers. The study also details the effect of governing parameters on mean gap velocities and pressure coefficients. Surprisingly, recirculation wakes exist for the lowest cylinder spacing (phi = 0.7) in high fluid momentum. Low phi and high permeability are desirable in a forced convection regime, whereas both phi and Da should be high in the case of mixed convection. This article also quantifies the combined effect of the Darcy number and buoyancy parameter on the heat-transfer enhancement ratio. A maximum of 112% increase in Nu for phi = 0.7 and 452% for phi = 0.99 are reported at Da = 10(-1), but at the cost of higher pressure drop in the latter case.

Study of external fluid flow over various shaped bodies has a special importance within the domain of fluid mechanics. These studies provide useful perceptions into the nature of physical phenomena such as drag coefficients and lift. The flow characteristics are the functions of the field variables (Re and Pr), body geometry, and degree of confinement (β). In this study, drag coefficients results have been reported for the non-Newtonian fluid flow over an object having circular geometry with range of parameters as: (1 ≤ Re ≤ 50, 0.1 ≤ n ≤ 2), (Pr = 1) and (β = 1.1, 4, 6 and 10). Overall drag coefficient increases with the decrease in Re for all values of β. Regardless of the β value, drag coefficient increases with an increase in the value of power-law index and slightly decline at higher values of n.

The present article focuses on the incompressible flow around two identical porous cylinders for a side-by-side configuration in a closed channel. The formation of various flow patterns behind permeable cylinders is more intriguing and further compelling to assimilate the underlying flow physics. The effects of three critical parameters, gap ratio (s/d), Reynolds number (Re), and the Darcy number (Da), on the flow behavior are investigated for the ranges of s/d = 1.5–6, Re = 5–100, and Da = 10−6–10−2. Both attached standing and detached vortices are observed in a steady flow regime. One secondary wake structure is also observed for s/d = 1.5, whose size gradually reduces with increased permeability. In an unsteady flow regime, the jet-like flow in the gap section mainly governs the unsteady wake patterns. In the low range of Darcy numbers (10−6–10−3), asymmetric flip-flopping patterns are observed for s/d = 1.5 and 2; and synchronized wake patterns either in anti-phase or in-phase mode are observed for higher gap ratios. The velocity profiles in the gap and free sides of the cylinders and pressure distribution along the porous surface are also discussed to facilitate the understanding of different wake patterns. Surprisingly, a case of pattern shifting from anti-phase to in-phase mode is observed when permeability is altered for the same flow-time. Symmetric and clustered strands of vorticity near the centerline are observed for all cases of s/d at Da = 10−2. The effects of Re, s/d, and Da on the drag coefficient and critical Reynolds number are also discussed. A jump in the drag values, a maximum of 13.9% for s/d = 3.5, is witnessed for the mid-range of Da at higher Re.

An analysis has been carried out to understand the consequences of side-by-side gap-ratio on thermal buoyancy-assisted two-dimensional flow past a pair of heated circular cylinders for a dominant viscous flow field. This is implemented through studies at Reynolds number (Re) ranging from 5 to 40, Prandtl number (Pr) 0.7, gap-ratio (T/D) 1.5 to 4 and Richardson number (Ri) 0 to 1. An ANSYS-based incompressible flow solver is used with Boussinesq approximation to account for density variations in the momentum equation. One can realize features like the steady-separated and steady-unseparated flow on varying flow and thermal parameters. Unlike streamlines, non-interacting isotherms are non-existent in the current numerical framework. The influence of gap-ratio on enhancement in Nusselt number (Nu) is the best realized at T/D = 1.5 and buoyancy-aided effects play a dominant role for enhancement in Nu at diffusion and/or viscous-dominant conditions occurring at Re = 5. Correlations are developed to quantify the impact of T/D, Re, and Richardson number Ri on Nu. For the first time, Nu's correlation based on varying side-by-side gap-ratio has been stated in a single expression. Finally, a comparison for the heat transfer enhancement/reduction in Nu under a similar numerical framework is provided with cases of high-Pr flow and/or different relatable flow arrangements for circular and square cylinders.

Mixed convection heat transport from multi-cylinders finds numerous applications in chemical, petroleum, and food industries. This study presents the mixed convection characteristics of an inline array of heated circular cylinders in non-Newtonian power-law fluids for the following governing parameters: fluid volume fractions; 0.70≤ φf ≤0.99, power-law index; 0.4≤ n ≤ 1.8, Reynolds number; 1≤ ReD ≤40, Prandtl number; 1≤ PrD ≤50 and Richardson number; 0≤ RiD ≤2. Mathematical model equations are solved using the Finite Volume Method within the framework of Boussinesq approximations. Thermal features are explored using isotherms, local and averaged Nusselt numbers. Qualitatively, isotherms display a complex relationship with the governing parameters. Local and average Nusselt numbers improve with increasing Reynolds, Prandtl and Richardson numbers, shear-thinning natures. An opposite nature is noted for shear-thickening fluids. Nusselt numbers were further improved with increased fluids volume fractions contrary to decrease in forced convections cases. At maximum Reynolds, Prandtl and Richardson numbers, Nusselt number increased by 30.53% and 13.11% for shear-thinning (n = 0.4) fluids, respectively for φf = 0.70 and 0.99. An unsteady nature was also found in shear-thinning regions at larger volume fractions. Lastly, statistical analysis is presented for the average Nusselt numbers to depict additional physical insights of the numerical outcomes.