The finite element method (FEM) for view factor calculation is prone to singularities due to the negative power of distance in the integrand. To address this issue, this study proposes a submesh FEM based on triangular mesh subdivision. Two submesh generation methods are developed using the nodes and integral points of triangular elements. The accuracy of the proposed method is validated through two benchmark cases, namely the view factor calculation of two perpendicular unit squares sharing a common edge and the radiative heat transfer in a typical radiant heating room. Parametric studies reveal that the computational performance is simultaneously affected by the submesh generation method, the integration order combination, and the number of subdivision cycles. The proposed method achieves high accuracy in both benchmarks, with a relative error as low as 0.0049% for the view factor calculation and a maximum relative error of 1.04% for the radiative heat transfer rate. The results demonstrate that the proposed submesh FEM effectively resolves the singularity issue of the conventional FEM for view factor calculations in radiative heat transfer.
Improving the efficiency of heat exchangers is crucial for meeting growing global energy demands, particularly in energy-intensive cryogenic applications such as liquefied natural gas (LNG) production. This work investigates the impact of dimple and protrusion surface features on the thermal-hydraulic performance of Coil Wound Heat Exchangers (CWHEs), vital components in cryogenic applications. Numerical simulations were conducted for methane-ethane mixtures under cryogenic conditions (220 K gas, 130 K liquid), varying flow rates with Reynolds numbers from 1000 to 25,000. The dimple-protrusion geometry significantly enhanced heat transfer, increasing the average Nusselt number by up to 18% for gaseous flow and 12% for liquid flow compared to a smooth tube. While this came with a pressure-drop penalty of up to 21% at peak flow rates, the Performance Evaluation Criterion (PEC) consistently remained above 1.1, indicating a net performance benefit.Furthermore, a novel geometry modification applied to the initial two loops of the CWHE increased PEC to 1.17 with a notable 7% reduction in pressure drop. This research uniquely accounts for simultaneous shell-side and tube-side flow dynamics. In addition, a new Nusselt number correlation for these enhanced geometries is presented. These findings offer a pathway for optimizing CWHE design through geometric modifications, promising substantial efficiency gains in industrial-scale cryogenic processes.
Replacing carbon-based fuels with carbon-free alternatives in domestic cooking burners is a practical pathway toward decarbonizing household energy use. This study numerically investigates ammonia–liquefied petroleum gas (NH₃-LPG) co-combustion in a conventional KB-5 domestic cooking burner fitted with a windproof cover, using a two-stage CFD methodology with cold-flow mixing, followed by reacting of hot flow in a simulation study at NH₃ fractions of 0%, 50%, and 100%. Twelve windproof cover geometries were evaluated by varying horn diameter, D = 20–30 mm, cover height, H = 15–20 mm, and burner-to-cover distance L = 10–15 mm. The results show that CO₂ emissions decrease monotonically with NH₃ fraction and are eliminated at 100% NH₃, while flame temperature and wall heat flux decrease, relative to pure LPG, owing to ammonia’s lower heating value and slower oxidation kinetics. NOₓ exhibits a non-monotonic trend, peaking near 50–70% NH₃ due to dominant fuel-NOₓ formation before declining at 100% NH₃ as flame temperature falls. Among the twelve configurations, D = 20 mm, H = 20 mm, and L = 10–12.5 mm consistently gave the highest heat flux and most stable thermal field by maximizing internal recirculation and heat retention. These findings indicate that windproof-cover geometry is an effective, low-cost passive lever for partially compensating the thermal penalty of ammonia blending, and they identify the 50–70% NH₃ range as the operating window requiring the most attention to NOₓ control before such burners could be considered for practical low-carbon cooking applications.
This study numerically investigates the blood hammer phenomenon in an occluded posterior cerebral artery, accounting for fluid–structure interaction between the arterial wall and the blood. The non-Newtonian characteristics of blood—such as shear-thinning and viscoelasticity—are modeled using suitable constitutive equations, while rigid, hyperelastic, or visco-hyperelastic models represent the arterial wall. To examine the impact of different wall rheological models, blood dynamics are primarily described using the five-mode Phan–Thien–Tanner (PTT) viscoelastic model, which captures the complex interaction between blood flow and the arterial wall. For the visco-hyperelastic wall case, alternative constitutive equations for blood are also employed to explore model sensitivity. Key hemodynamic parameters—including velocity profiles, tensile stress distributions, pressure wave histories, and wall shear stresses—are compared across the various combinations of blood and wall models. Results show that when the arterial wall is modeled as visco-hyperelastic, the pressure wave period shortens, and both pressure and wall shear stress histories exhibit the best attenuation. Velocity and tensile stress distributions are also strongly dependent on the wall's rheological properties. When blood is modeled with viscoelastic constitutive equations, attenuation of pressure waves and wall shear stress is weaker compared with viscoplastic or purely shear-thinning models. Under fluid–structure interaction conditions, the maximum wall shear stress predicted by the FENE-P model is reduced by 100%, 43.26%, and 8% relative to the Carreau, Casson, and PTT models, respectively. Hemolysis analysis indicates that red blood cell damage is highest at the arterial midpoint along the wall, rather than at the occlusion site. This effect is most pronounced during the first period of the process, with a peak hemolysis value of 0.954%, indicating a potential health risk.
The innovative aspect of the current study employs the Physics Informed Neural Network(PINN) with SHAP(Shapley Additive Explanations) analysis to understand the flow behavior of the trihybrid nanofluid between the two coaxial cylinders, the outer rotating cylinder with some fixed angular velocity including the inner stretching horizontal cylinder. The trinanofluid consists of gold(Au), copper(Cu), titanium(Ti) embedded as nanoparticles with blood as the base fluid. The flow in between the annular gap has a wide range of theoretical model in many fields like spacecraft thermal management, hypersonic vehicle leading edge cooling, satellite attitude control systems and bio medical diagnosis. To understand this crucial fluid flow which is applicable in rotating machinery, the internal cylinder surface incorporates the first- order slip condition, the Darcy-Forchheimer medium and the local thermal non-equilibrium model were considered. Transform the conservation of mass, Navier–Stokes, and energy equations into dimensionless ODEs by applying appropriate transformations, which were solved numerically using the ND-solver by following the shooting strategy in MATHEMATICA environment. These equations are constructed into residuals using the PINNs along with the initial and boundary conditions and it is validated by mean squared error(MSE) and regression value which are closely match the numerical results. The calculated outcomes of the Nusselt number for both phases, the skin-friction coefficient, and the Sherwood number were trained using Keras with the Adam optimizer, which exhibits the ANN data and regression, demonstrating the fit of the fluidic model with an accuracy of 95%. The response surface methodology and sensitivity analysis also included for the parameter studies. The angular velocity parameter shows the impact of 66.13% decrease and curvature parameter 21.23% increase in the skinfriction coefficient by discussing the SHAP analysis.
The low thermal conductivity of conventional heat transfer fluids limits the thermal performance of shell-and-tube heat exchangers used in many industrial applications. To overcome this limitation, the present study numerically investigates three-dimensional mixed convective heat transfer and entropy generation in a shell-and-tube heat exchanger employing an Ag–Fe₃O₄–MWCNT/water tri-hybrid nanofluid. The governing continuity, momentum, and energy equations are solved using the finite element method (FEM) implemented in COMSOL Multiphysics. The effects of the Reynolds number (10–100), Richardson number (0.2–1.0), and nanoparticle volume fraction (2–4%) on the flow behavior, temperature distribution, average Nusselt number, heat exchanger effectiveness, and entropy generation are systematically analyzed. The results reveal that increasing both the Reynolds number and nanoparticle concentration significantly enhances the convective heat transfer performance owing to improved effective thermal conductivity and stronger fluid mixing. At Re = 100 and φ = 4%, the average Nusselt number increases by 24.7% compared with the reference case, while the heat exchanger effectiveness improves by 18.3%. However, the enhanced thermal performance is accompanied by an increase of 11.5% in entropy generation due to greater thermal and fluid friction irreversibilities. Furthermore, increasing the Richardson number strengthens buoyancy effects, leading to additional enhancement in heat transfer. The novelty of this work lies in providing a comprehensive three-dimensional FEM analysis of an Ag–Fe₃O₄–MWCNT/water tri-hybrid nanofluid in a shell-and-tube heat exchanger, together with a detailed evaluation of the combined effects of Reynolds number, Richardson number, and nanoparticle concentration on heat transfer enhancement and thermodynamic performance. The findings demonstrate the considerable potential of tri-hybrid nanofluids for improving the efficiency of compact thermal systems and provide useful guidelines for the design and optimization of advanced heat exchangers.
The dehydration of organic solvents using molecular sieves is a critical industrial process, yet the conventional regeneration of saturated adsorbents via Temperature Swing Adsorption (TSA) or Pressure Swing Adsorption (PSA) remains energy-intensive, costly, and operationally complex. This study introduces a novel electro-thermal regeneration system that directly supplies the thermal energy required for water desorption through an integrated electric heater embedded within the vessel walls, thereby eliminating the need for hot purge gases and auxiliary equipment. Through a systematic three-dimensional Computational Fluid Dynamics (CFD) analysis using COMSOL Multiphysics, we optimize the design parameters—including internal fin configurations (3, 6, and 12 fins), heater arrangements (belt vs. integrated), vessel materials (iron, aluminum, copper), and cylinder geometry—to enhance temperature uniformity and minimize cycle time. The results demonstrate that an optimized design featuring 12 internal aluminum fins achieves a regeneration cycle time of 21.5 h under ideal environmental conditions (-5 °C). However, under realistic high-ambient-temperature conditions, the cooling phase becomes the primary bottleneck, extending the total cycle time to 42 h. To maintain the required system throughput under these adverse conditions, the cylinder length is increased from 150 cm to 445 cm, effectively decoupling the regeneration time from the 15-hour operational cycle. The novelty of this work lies in: (i) the proposal of a direct electro-thermal regeneration method that bypasses traditional TSA/PSA complexities; (ii) the first systematic numerical optimization of finned adsorbent beds for thermal regeneration; and (iii) the critical evaluation of design performance under realistic industrial boundary conditions, bridging the gap between idealized simulations and practical implementation. This study provides a robust framework for the design of next-generation, energy-efficient molecular sieve regeneration systems.
This paper reports local condensation heat transfer coefficients (HTCs) of low-pressure, low-GWP refrigerants inside a brazed plate heat exchanger (BPHE), targeting applications in heat pumps (HPs) and organic Rankine cycles (ORCs). The study considers the classical refrigerant R245fa alongside two low-GWP alternatives: R1233zd(E) and R1234ze(Z). The experiments were conducted in a prototype BPHE specifically designed for measuring local condensation HTCs inside BPHEs at a saturation temperature of approximately 30 °C, over a refrigerant mass velocity range of 10–35 kg m−²s−¹. The experimental tests reveal that the condensation phenomenon is gravity-dominated in the lower section of the plate and vapour shear-dominated in the upper section. The local HTCs in the lower section of the plate agree well with Nusselt's (1916) analysis for gravity-dominated condensation, while those in the upper section agree well with the Longo et al. (2015) model for refrigerant condensation in BPHEs under vapour shear control. This experimental characterization of the local behaviour during condensation along the entire plate may prove valuable in the design of BPHE condensers to enhance the thermodynamic efficiency of HP and ORC systems. Moreover, a specific entropy generation (SEG) rate analysis is applied, highlighting very similar condensation performance for the innovative refrigerants R1233zd(E) and R1234ze(Z), which outperform the traditional refrigerant R245fa.
The interest in utilizing ternary hybrid nanofluid (THN) coolants in microchannel heat sinks (MCHS)s has been ignited by the need for more effective thermal management of electronic devices. Nevertheless, optimizing these heat sinks comes with high costs and time requirements, leading to the search for more efficient methods. This study aims to optimize MCHS with sinusoidal cavities and rectangular ribs by employing a new hybrid method. Additionally, CuO/MgO/TiO2 aqueous THN with 0.5% volumetric concentration and water are evaluated as the working coolants. For this purpose, after conducting numerical simulations to generate datasets, artificial neural network (ANN) models are trained to predict two objective functions, including average Nusselt number and average friction factor, based on four operational and design parameters consisting of relative cavity amplitude, relative rib width, relative rib length, and Reynolds number. The trained ANNs achieve prediction accuracies above 95%, with coefficients of determination close to unity and mean square error values below 0.036. These models are coupled with the non-dominated sorting genetic algorithm II to obtain Pareto-optimal designs with maximized heat transfer and minimized friction losses. Results show that THN enhances the average Nusselt number by up to 57% compared to water, while increasing the friction factor by up to 30%. Among the optimal solutions, the best THN-cooled design achieves a maximum performance factor of 1.451 at a Reynolds number of 800. Furthermore, sensitivity analysis indicates that rib width and rib length are the most influential parameters, whereas cavity amplitude has a minor effect.
The continuous increase in high heat flux densities in advanced electronic systems is challenging the operational limits of conventional cooling technologies. Two-phase immersion cooling with dielectric fluids is attracting interest as passive efficient cooling technique. However, its large-scale adoption is increasingly constrained by environmental concerns, including high Global Warming Potential (GWP) and the persistence of per- and polyfluoroalkyl substances (PFAS). These issues are motivating the development and adoption of coolant fluids with low GWP values and reduced environmental impact. In this work, the pool boiling performance of FC-72, Novec 649, HFE 7100, TMC 49, and SF 33 is experimentally investigated using the same operating conditions to enable direct comparison. Boiling curves, Critical Heat Flux (CHF), and Heat Transfer Coefficients (HTC) are systematically measured, providing a unified dataset across fluids spanning different chemical classes and environmental impact levels. The results highlight that low-GWP alternatives can effectively match or overcome the performance of traditional fluids. Novec 649 and TMC 49 show boiling behavior comparable to FC-72, while significantly reducing environmental impact. SF 33 and HFE 7100 exhibit enhanced CHF and HTC values, with SF 33 combining high thermal performance and low GWP, making it a promising candidate. Comparison with predictive models shows that classical CHF correlations provide acceptable agreement with the experimental data, whereas HTC predictions show a stronger dependence on the correlation. This study provides clear experimental evidence supporting the ongoing shift toward environmentally sustainable dielectric fluids, identifying candidates capable of competitive pool boiling performance, under increasingly stringent environmental regulations.
A falling liquid film evaporator can provide high heat transfer rates for evaporating palm-based bio-oil in biofuel production through fluid catalytic cracking. Although liquid-film hydrodynamics strongly affects heat transfer and evaporation, the hydrodynamic characteristics of palm-based bio-oil falling liquid film flow remain insufficiently investigated. The optical opacity of palm-based bio-oil prevents direct use of standard optical diagnostics, requiring an alternative measurement approach. This study experimentally investigates palm-based bio-oil flow on the outer surface of a vertical tube under various Reynolds numbers. Flow visualization was performed using a standard DSLR camera, while film thickness was measured using image stacking and average-intensity projection methods. Results demonstrate that increasing Reynolds number accelerates the transition from smooth-to-wavy flow and from two-dimensional to three-dimensional wavy regimes, shifting transition points upstream along the tube through secondary instability mechanisms. Comparisons with empirical correlations show that the Nusselt model significantly overestimates film thickness by 78.6%. Tube-based correlations, such as Takahama and Kato, provide closer approximations but still underestimate the experimental results by approximately 38%. These discrepancies indicate that geometric or fluid-property similarity alone is insufficient for accurate prediction, highlighting the need for dedicated empirical correlations for palm-based bio-oil falling films on vertical tubular geometries.
Enhancing the melting rate in latent heat storage (LHTES) systems is critical for improving power density, yet it requires balancing conductive enhancement against convective facilitation a fundamental trade-off in finned heat exchanger design. This study presents a focused numerical investigation that quantifies this trade-off by comparing two advanced fin configurations for a vertical shell-and-tube LHS unit: perforated annular fins designed to promote natural convection versus high-density solid fins maximizing conductive surface area. Three-dimensional transient simulations using the enthalpy-porosity approach in ANSYS Fluent are conducted to examine the melting of paraffin wax under diverse heat-transfer-fluid (HTF) conditions. The results show that perforated fins (10 fins) speed up melting by 38.8% compared to regular solid annular fins. This is mostly because the holes in the fins help create vortices, allowing fluids to move more easily. But a high-density fin array (20 solid fins) works better overall, cutting the total melting time by 40.6% compared to the perforated version. This improvement is due to shorter thermal diffusion lengths and longer conductive channels, which outweigh the convective benefits in the end. Parametric analysis indicates that HTF temperature is the most important operational parameter. A 5°C increase in temperature reduces melting time by 21–35%, whereas changes in flow rate yield only small improvements (<8.5%). The study reveals a clear design hierarchy: for the examined vertical geometry, conductive optimization via increased fin density yields larger final performance improvements than convective augmentation via geometric characteristics. under a fixed PCM-volume design constraint, doubling fin count via solid fins yields a greater melting-time reduction than adding perforations to a sparser array, though this comparison does not yet isolate whether the benefit stems from the added material/area or from the conductive mechanism per se; a mass- and area-matched control study (Cases A and B) is required to resolve this and is reported as the immediate next step of this research program .These results give clear instructions for making thermal storage systems that work better and charge faster.
This paper explores the synthesis of high-entropy alloy via thermochemical pressing, an alternative to traditional melting and powder metallurgy. Research was conducted on Al28Ni22Co17Fe15Cu10Mn8 high entropy alloy. By leveraging internal exothermic reaction energy under a 100 MPa load, thermochemical pressing facilitates rapid consolidation and phase stabilization. Thermodynamic modeling predicted a mixed FCC+BCC phase structure, supported by a high configurational entropy. Experimental validation through DSC/TG identified an exothermic synthesis peak at 495 °C, with the resulting alloy maintaining thermal stability up to 900 °C. Microstructural analysis revealed a fine-grained, homogeneous matrix with a porosity of 10…15 %, outperforming conventional sintering. These results demonstrate thermochemical pressing as an efficient, low-energy method for producing high-quality, multicomponent high-entropy alloy with refined microstructures.
This study investigates the unsteady flow and heat transfer of a ternary hybrid nanofluid (zinc oxide, silicon dioxide, and cobalt ferrite in water or ethylene glycol) over a stretching surface. Embedded in a variable porous medium, the system is analysed under a transverse magnetic field, velocity and thermal slip, viscous dissipation, Joule heating, and temperature-dependent thermal conductivity. Motivated by advanced thermal-management needs, this work captures spatially heterogeneous porous structures by allowing wall-normal variations in permeability and porosity. Consistent with the unsteady-stretching framework, transient scalings are assigned to the magnetic field strength, reference permeability, and the Forchheimer inertial-drag coefficient; the latter is uniquely introduced so inertial resistance shares a common temporal behaviour with other momentum contributions. The governing equations are transformed using a third-level local non-similarity formulation to preserve critical streamwise dependencies. Solved numerically via MATLAB’s bvp4c routine, the scheme yields validation errors below 0.04%. Concurrently, Bayesian-regularized deep neural networks trained on 8,000 solutions are deployed as rapid surrogates for skin-friction and local heat-transfer rates, achieving a test-set correlation of R=1.0000 with generalization confirmed by minute point-wise errors. Quantitative analysis reveals that variable permeability reduces skin-friction magnitude by approximately 31%, whereas variable porosity increases it by 45%. Increasing the magnetic parameter raises skin friction by 32% but reduces heat transfer by 17%. Notably, thermal slip dominates thermal performance, reducing the local heat-transfer rate by over 80%. Finally, despite similar velocity profiles, the higher Prandtl number of ethylene glycol (approximately 204, versus 6.2 for water) produces substantially higher heat-transfer rates. Ultimately, this validated numerical and deep-learning framework enables highly efficient predictions of heat-transfer characteristics in magnetically controlled systems.
This study presents a combined experimental and numerical investigation of the thermo-fluid behavior and thermal performance of a two-phase closed thermosiphon (TPCT) under subatmospheric conditions, targeting data center cooling applications. The TPCT is constructed from a copper tube with a 20 mm inner diameter and a total height of 500 mm, with water as the working fluid. The filling ratio (FR) is varied from 50% to 150%, and the input power (Qin) from 100 W to 500 W, representing the operating range of high-performance AI and HPC CPUs. Numerical simulations are performed in STAR-CCM+ using the Volume of Fluid (VOF) method coupled with the Lee phase-change model. Experimental validation confirms the fidelity of the numerical model, with maximum absolute relative errors remaining below 2.74%. Five distinct flow patterns are identified across the investigated parameter space: Churn–Annular, Churn–Slug, Churn–Slug–Annular, Churn–Slug–Bubbly, and Slug–Bubbly. Both permanent and intermittent liquid-trapping phenomena are observed and characterized with respect to their influence on flow structure and thermal performance. The spatiotemporal evolution of the local heat transfer coefficient (HTC) along the inner wall is analyzed, clearly distinguishing between no-trapping, intermittent-trapping, and permanent-trapping regimes. Thermal performance metrics, including the time-averaged heat transfer coefficients at the evaporator (h̄e) and condenser (h̄c), and thermal resistance (R̄th), are evaluated across all investigated conditions. Heat partitioning analysis further reveals that the latent heat contribution (Q̄lat) remains below 20% in all cases, confirming that sensible heat transfer constitutes the dominant thermal transport mechanism in the system.
Parabolic Trough Solar Collectors (PTSCs) are among the most efficient solar thermal technologies; however, further improvements in their performance are still required to meet the growing demands of high-temperature industrial applications. This study investigates the synergistic thermal-hydraulic enhancement of a cylindrical PTSC absorber tube through the combined use of Twisted Tape Inserts (TTIs) and Syltherm 800-based nanofluids. Three types of nanoparticles, TiO2, Al2O3, and Cu were dispersed in Syltherm 800 at volume fractions ranging from 2% to 8%, and Reynolds numbers from 4000 to 20000. Three-dimensional CFD simulations were conducted using the finite volume method (FVM) with the standard k–ε turbulence model and an appropriate y+ value to accurately resolve the near-wall treatment. The results were validated against established empirical correlations and experimental data from the literature. The thermal-hydraulic performance is assessed through the outlet fluid temperature, Nusselt number, friction factor, Performance Evaluation Criterion (PEC), and exergy efficiency. The results show that TTI significantly intensifies turbulence and enhances convective heat transfer, while nanoparticle addition further improves thermal conductivity and heat transfer. The nanofluid Cu/Syltherm 800 at φ = 6% achieved the highest Nusselt number enhancement of 62.4% and a PEC of 1.52. The outlet temperature and heat transfer rate exhibited opposing trends with Reynolds number, and an optimal exergy efficiency of 52.8% was identified at Re = 12000, representing the best thermodynamic operating point for industrial solar thermal applications. These findings confirm that the synergistic combination of TTI and Cu-based nanofluid constitutes an effective and practically viable strategy for advancing PTSC thermal performance.
The effect of thermophoresis and Brownian motion on flow and heat and mass transfer of a micropolar nanofluid between parallel plates of uniform height is examined. The upper and lower plates are assumed to be alternately injected and the suction, concentration, and temperature are kept constant at both plates. Using appropriate similarity transformations, the set of governing nonlinear partial differential equations is reduced to a set of ordinary differential equations and then solved numerically using the fourth–order Runge–Kutta method along with the shooting technique. In detail, the influence of the governing dimensionless parameters on the velocity, micro rotation, temperature and concentration of nanoparticles profiles are analyzed. The numerical results show that thermophoresis is able to increase the thermal and concentration boundary layers, while Brownian motion significantly increases the fluid temperature and decreases the concentration of nanoparticles. Moreover, the velocity and microrotation fields will be greatly affected by the parameters associated with the micropolar and suction/injection. The skin-friction coefficient, Nusselt number and Sherwood number are also presented and discussed due to the corresponding changes. Good agreements are found when comparing the present results with those found in previous studies, which confirms the accuracy and reliability of the proposed numerical Methodology.
