Uniform Heat Flux Research Articles

Influence of Entrance Geometry and Thermal Boundary Conditions on Heat Transfer in a Rectangular Channel with 45 Deg Angled Ribs on One or Two Principal Walls

The purpose of this paper is to numerically investigate the influence of the entrance geometry and thermal boundary conditions on the local and averaged heat transfer coefficient in a ribbed rectangular channel with an aspect ratio of 5. Ribs, angled at 45°, were periodically deployed on one or two opposite sides, while the remaining walls of the rectangular channel were assumed to be smooth and unheated. The effect of entrance conditions was addressed by considering either a smooth or a ribbed unheated section upstream of the ribbed heated section. The effect of the thermal boundary condition was studied by considering a uniform heat flux imposed at the inter-rib region, or at the inter-rib and the rib baseplate, or at the whole interface between the ribbed surface and the coolant. Results, presented in the form of spatially resolved and spatially averaged Nusselt numbers, show that a ribbed section preceding the heated test section affects the heat transfer coefficient, relative to a smooth entrance section, for several repetitive modules. The influence of the thermal boundary condition was found to be mainly concentrated in the surface regions immediately upstream and downstream of each rib, with small differences, in terms of spatially averaged Nusselt numbers. The presented investigation is meant to point out that heat transfer experiments on ribbed channels, massively provided by the heat transfer community according to the current technical literature, should provide an exhaustive description of the entrance and thermal boundary conditions assumed in the experiments and eventually to discuss how they could potentially affect the results.

Numerical and experimental study of a multiphase flow inside a self-contained drum motor drive system

The multiphase Taylor-Couette flow of air and oil enclosed within the annular space between two concentric cylinders has been studied experimentally and numerically. The outer cylinder rotates at a constant speed and exchanges heat by convection and radiation with ambient air. The inner cylinder is stationary and subjected to a constant uniform heat flux. Such flow can be found in a self-contained drum motor drive system (SCDMDS). The heat flux imposed on the inner cylinder mimics the amount of heat generated due to several thermal losses within the SCDMDS. A layer of lagging material is sometimes added to the outer cylinder to enhance belt traction.The effect of the inner-to-outer cylinder radius ratio (RR), Reynolds number (Re), oil volume (OV), outer cylinder surface emissivity (ε), and lagging material thickness (δ) on the flow and heat transfer between the two cylinders and the ambient has been investigated considering a quasi-steady state analysis. The current investigation considered the following ranges found in a typical SCDMDS: RR = 0.35–0.85, Re = 200–3000, OV = 50–100 %, ε = 0–0.95, and δ = 0–100 mm. The numerical part of the present study has been carried out using ANSYS-CFX software package. The numerical results have been validated using experimental data. Resultsindicated that increasing RR, Re and ε enhanced the heat transfer within the SCDMDS. The rate of heat transfer within the annular space reached its highest value at OV = 65 % above which the rate of heat transfer is deteriorated. Because the lagging material is acting as an insulation over the outer cylinder, a critical thickness of δ = 35 mm resulted in the minimum overall resistance above which the rate of heat transfer is deteriorated.The parametric study revealed that the best overall thermal performance was attained at RR = 0.85, Reynolds number = 3000, OV = 65 %, ε = 0.95 and δ = 35 mm. In this case, the heat transfer coefficient between the inner cylinder and the oil reached its highest value of 410 W/m2 °C, giving the lowest possible inner cylinder temperature. A correlation of Nusselt number in terms of the geometrical and operating parameters of a SCDMDS considered in the current study has been developed and validated. The developed correlation gave a maximum deviation of ±8 %.

Opposing Mixed Convection Heat Transfer for Turbulent Single-Phase Flows

Convection, wherein forced and natural convections are prominent, is known as mixed convection. Specifically, when a forced convection flow is downward, this flow is called opposing flow. The objectives of this study are to gain a comprehensive understanding of opposing flow mixed convection heat transfer and to establish the prediction methodology by evaluating existing correlations and models. Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Because the definition of nondimensional parameters and their validated range confirmed by experiments differ for each correlation reported in previous studies, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing flow mixed convection and the single-phase heat transfer correlations implemented in the thermal–hydraulic system codes. Furthermore, the authors evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations can accurately predict all the experimental data. The effect of the difference in the thermal boundary conditions, i.e., uniform heat flux and uniform wall temperature, on the turbulent mixed convection heat transfer coefficient is not substantial. The authors confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids. The authors investigated the extrapolation performance of the mixed convection heat transfer correlations for a wide range of nondimensional parameters and observed that the Jackson and Fewster, Churchill, and Aicher and Martin correlations exhibit excellent extrapolation performance with respect to natural and forced convection flows, indicating that they can be applied beyond the parameter range validated experimentally.

Local thermal nonequilibrium perspective of heat transfer and fluid flow in a slender anisotropic porous cavity due to lateral uniform heat flux

The influence of the local thermal nonequilibrium (LTNE) state on steady-state natural convection due to the heating and cooling of the side walls of the slender porous cavity has been addressed analytically and numerically. The porous medium is assumed to be hydrodynamically anisotropic. The Darcy model has been adopted. A closed-form solution, based on a parallel hypothesis, is reported for a slender cavity. The combined impact of media anisotropy and LTNE state on the heat transfer rate, as well as flow dynamics, have been analyzed. The help of boundary layer analysis is taken to report the boundary layer thickness and heat transfer rate of fluid flow analytically. It has been found that the maximum (minimum) heat transfer rate of the fluid phase as well as solid phase takes place at orientation angle, ϕ , equal to π / 2 when permeability along the horizontal (vertical) direction is higher than the same along vertical (horizontal) direction.

Effect of a static magnetic field on the falling-film evaporation on a vertical plate evaporator by mixed convection

The application of a magnetic field to a falling-film evaporation system can have several effects. The magnetic field can alter the liquid film's flow behavior and modify the system's heat transfer characteristics. The numerical study of falling film evaporation by mixed convection on a vertical channel under a static magnetic field has been investigated. The vertical channel is composed of two parallel plates. The right plate is dry and isothermal, while the left plate is wetted by a falling liquid film and exposed to a static, uniform heat flux from the outside. Water film makes up the liquid, while dry air and water vapor make up the gas mixture. The results relate to the effects of the magnetic field on heat and mass transfer and on liquid film evaporation. The results demonstrate that the static magnetic field has a weak effect on heat and mass transfer and water film evaporation. In fact, it is shown that an increase in the static magnetic field weakly enhances heat and mass transfer as well as liquid film evaporation.

CONVECTIVE HEAT TRANSFER INSIDE A ROTATING HELICAL PIPE FILLED WITH SATURATED POROUS MEDIA

In this paper, we study the hydrothermal characteristics of flow inside a rotating helical pipe filled with saturated homogeneous porous medium. The analysis is being carried out for the case of small curvature and torsion. Using the perturbation approach, velocity and temperature fields are solved for both uniform wall heat flux and uniform wall temperature boundary conditions. Perturbation expansion up to the third order is carried out to investigate the effect of rotation on the flow. The influence of rotation on velocity is noticed as early as the first order, and on temperature solution, it has an effect in the third order. The influence of rotation on the Nusselt number does not appear till third order, and it is discovered that the Nusselt number grows as dimensionless curvature increases. Moreover, the theoretical results have been verified against experimental data from existing literature for the special case of zero rotation and curvature of the pipe. The available experimental data align well with and support the theoretical results in this limiting case.

Numerical analysis of the binder angle effect on convective heat transfer and pressure drop in drilled-hollow sphere architected foams

Due to their capability of generating customized microstructures, additive manufactured cellular materials are promising to being employed in heat transfer devices. To this aim, among printable cellular materials Drilled-Hollow Spheres Architected (DHSA) foams are investigated. However, at the present status, limited data on pressure drop and heat transfer in DHSAs are available. Starting from hollow spheres, a metal DHSA foam is generated with CAD software in this study. Forced air convective heat transfer in the foam is investigated numerically, under the assumptions of air incompressible laminar flow and uniform wall heat flux from the solid to the fluid phase. Mass, momentum and energy equations in the fluid region are written and solved numerically, for various values of the foam binder angle and the velocity of the inlet air. The convective heat transfer coefficients, the pressure drop and the friction factor are predicted. The effects of the binder angle and the air inlet velocity on heat transfer and pressure drop are highlighted.

NANOFLUID FILM FALLING ON A NON-DARCY POROUS VERTICAL PLATE EVAPORATOR

A numerical analysis of the falling nanofilm evaporation on a vertical porous wetted wall by mixed convection was performed. The right-wall was dry and isothermal, while the left wall was embedded in a non-Darcy porous medium filled with nanofilm (water + low fraction volume of copper nanoparticles) and exposed to a uniform heat flux from the outside. The nanofluid film made up the liquid, while dry air and water vapor comprised the gas mixture. The results obtained from this study pertain to the impact of porosity, thickness of the porous layer, concentration of nanoparticles on heat and mass exchange, and liquid film evaporation. The results indicate that mass and heat exchange, as well as liquid film evaporation, are improved in the case of nanofilm by introducing a liquid-saturated porous medium. It is shown that in the case of a porous layer, the dispersion of the nanoparticles into water film ameliorates the liquid film evaporation of the plate evaporator and weakly improves the mass and heat exchange.

Numerical Study of the Thermal and Hydraulic Characteristics of the SiO2–Water Nanofluid through a Backward-Facing Step

The work of this paper is devoted to the two-dimensional numerical investigation of the turbulent forced convection through backward-facing step. Two cases are taken into account. For the first, the bottom wall is smooth; but for the second case, it is corrugated with a triangular base containing ten corrugations. A uniform heat flux is imposed on the bottom wall. A flow of a nanofluid consisting of silicon dioxide SiO2 nanoparticles dispersed in a base fluid (water) flows through this step.The flow equations were discretized by the finite volume method. For modeling turbulence, the K-ɛ-RNG model was applied to analyze Reynolds number effect, the volume fraction and the size of the particle. Numerical simulations were conducted for various Reynolds between 10,000 and 40,000; volume fractions of nanoparticles which vary from 0 to 5% and particle diameter dp equal to 30; 50 and 70 nm. We noted that the obtained findings are in good conformity with those of the literature.

Numerical investigation on the effect of Al2O3-water nanofluid on direct steam generation in parabolic trough collectors

The utilization of solar energy through direct steam generation (DSG) in parabolic trough collectors is a novel approach. In addition, due to higher thermophysical properties, the effect of using nanofluid as the coolant has been the subject of some of the recent studies but the applicability of the nanofluids in DSG process has not been studied before. In this study, the flow boiling of Al2O3 nanofluid at volume fractions 1%, 1.5% and 2%, under uniform and non-uniform heat fluxes has been studied numerically. The Eulerian model was used and non-equilibrium RPI was applied as the boiling model. The validation was done for flow boiling of pure water and Al2O3 nanofluid separately, with the available data in the literature. The results showed that the vapor volume fraction at the outlet is higher under non-uniform heat flux and adding nanoparticles would increase the vapor generation in the tube. Adding nanoparticles to the pure water increased the vapor volume fraction at the outlet up to about 8.64% in respect to pure water under uniform and non-uniform heat fluxes. The average Nu was up to 544% higher under non-uniform heat flux compared to uniform heat flux. Due to the presence of stratified flow, increasing nanofluid concentration reduced the average Nu up to 21.24% and 10.24% under uniform and non-uniform heat flux, respectively.

Heat Transfer in Simultaneously Developing Turbulent Mixed Convection Flows in Vertical Tubes

This article investigates the simultaneously developing pure turbulent mixed convective regime and compares the hydrodynamic and thermal features of both buoyancy-assisted and opposed flows in a vertical tube. Two-dimensional (2D) axisymmetric steady-state simulations were carried out for Reynolds number, 5,000–20,000; Grashof number, 1.25 × 106 to 108; and Richardson number, 0.05–0.25 for a length-to-diameter ratio of 150 with uniform heat flux boundary condition and water as the working fluid. Three Reynolds-averaged-Navier–Stokes turbulence models were compared and then the most suitable model was used for the simulations. At a given Richardson number, the friction factor and Nusselt number are lower in the case of buoyancy-assisting flow compared to buoyancy-opposing flows. Similar friction factors and heat transfer trends were obtained at a given Grashof number. At varying Grashof numbers and Richardson numbers keeping the Reynolds number constant, no discernible variations were observed for both flows. The entry length was also examined, and it has been found that the hydrodynamic and thermal entry lengths are restricted to a length-to-diameter ratio of 25 and 20 for assisting and opposing flows, respectively. Correlations were developed for both flows to quantify the friction factor, Colburn factor, and Nusselt number in terms of the Reynolds number.

Experimental and Computational Heat Transfer Study of sCO2 Single-Jet Impingement

Abstract This study experimentally and computationally investigates the heat transfer capability of supercritical carbon dioxide (sCO2) single jet impingement. The evaluated jet Reynolds number range is between 80,000 and 600,000, with a nondimensional jet-to-target surface spacing of 2.8. CO2-impinging jet stagnation conditions were maintained at approximately 200 bar and a temperature of ∼400 °C for most experiments. The goal is to understand how changes in the aforementioned parameters influence heat transfer between the working fluid and the heated surface. Additionally, due to the elevated Reynolds numbers and difference in thermodynamic properties between air and CO2, air-derived impingement correlations may not be appropriate for CO2 impingement; these correlations will be evaluated against experimental sCO2 impingement data. At the time of this study, no sCO2 impingement data was available relevant to sCO2 power cycles. The target surface is a 1.5-in. diameter copper block centered on the 3 mm jet orifice. A mica heating element bolted to the bottom of the copper block provides a uniform heat flux. Thermocouples embedded in the copper block are used to determine the surface temperature. Nusselt numbers obtained from experimental sCO2 test data are compared to area-averaged Nusselt numbers from air-derived correlations. The comparisons showed that air correlations drastically underpredict the heat transfer when sCO2 is used as the working fluid. A modified sCO2 correlation using experimental data at discussed conditions is derived based on an existing air correlation. A CFD study is also performed to further investigate sCO2 heat transfer characteristics, and assess the numerical model applicability to this problem type.

Dean number only can not determine characteristics of fluid flow and heat transfer in helically coiled tubes with large curvature

The majority of reported findings indicate that the fluid flow and heat transfer characteristics within helically coiled tubes (HCTs) with small curvature can be determined solely by Dean number. Due to a scarcity of published investigations pertaining to HCTs with large curvature, the extent to which Dean number can ascertain the attributes of HCTs with large curvature remains uncertain. However, the advancement of technology has enabled the production and utilization of HCTs with large curvature. Consequently, there is a significant demand for understanding the fluid flow and heat transfer characteristics of HCTs with large curvature. The present study employs a numerical approach to investigate the characteristics of laminar fluid flow and heat transfer in HCTs with large curvature, where the ratio of coil radius to tube radius (D/d) is less than 5. The findings indicate that the fluid flow and heat transfer characteristics in HCTs cannot be solely determined by Dean number. In addition to the (D/d)0.5 included in Dean number, the fluid flow friction factor is also influenced by (D/d)−0.1902. When considering uniform wall temperature boundary, Nusselt number is mainly determined by Dean number. However, for uniform wall heat flux boundary, Nusselt number is additionally influenced by (D/d)0.1222.

Numerical study on the mixed convection with nanofluids in vertical channel asymmetrically heated

Mixed convection heat transfer in cavities is of great interest in many industrial applications, such as the development of crystals, the thermal control of electronic components, the nuclear reactors and various manufacturing processes. Components are generally located on the wall of a channel, that can be also tilted and their thermal control is carried out by the fluid flow. They can be schematized as thermal sources on vertical boards and the heat flux is removed by natural or mixed convection. As to the mixed convection, the interaction between the buoyancy forces and the external flow plays a significant role in the thermal design of systems. When natural convection is not strong enough to remove heat flux, mixed convection is adoptedIn particular, mixed convection due to moving surfaces is very important is these applications. Mixed convection because of buoyancy and motion of one of the channel walls has received little research attention and few guidelines are available for choosing the best performing channel configuration. Moreover, to optimize the transfer through natural convection, it is possible to modify the geometric parameters of the component, thus maximizing the convective heat transfer coefficient. If this is not possible or if one chooses to keep the geometry of the component unchanged for design choices, a possible alternative is the use of nanofluids. The properties of nanofluids exhibit a behaviour ranging between the properties of the base fluid and the properties of the nanoparticles. However, the addition of nanoparticles in the working fluid is considered to enhance the thermal behaviour of the base fluid. In this study a numerical investigation of mixed convection in nanofluids due to the interaction between a buoyancy flow and a moving plate induced flow in a vertical channel is carried out. The moving plate has a constant velocity and moves in the same direction with respect to the buoyancy force. The channel principal walls are heated with uniform heat flux. The numerical analysis is obtained by means of the commercial code Fluent. The effects of the different wall heat fluxes and moving plate velocities are investigated and results in terms of the channel wall and moving plate temperatures and Nusselt numbers are given.

Turbulent forced convection flow of water-based nanofluids with temperature-dependent properties over backward-facing step channel with upwardly deflected downstream wall

The heat transfer performances of various water-based nanofluids (NFs) relative to the base fluid in turbulent forced convection flow within a 2-D backward-facing step (BFS) channel with an upwardly deflected downstream wall with a uniform heat flux are analyzed using the package OpenFOAM. The k-ω shear stress transport (SST) model based on the Euler-Euler single-phase framework is used. The performance evaluation criterion (PEC) is defined to assess the relative importance of the enhanced heat transfer and intensified resistance (pressure drop) caused by Cu/water NFs and MWCNT-Fe3O4/water hybrid NFs (low concentration NFs), Fe3O4/water NFs, and Cu-MWCNT/water hybrid NFs (high concentration NFs). At Re = 30215, the maximum enhancement of the average Nusselt number (ANN) is 7% when the copper NPs are added to the water. In addition, the increment of the deflection angle from 0.0 to 1.27 enhances the ANN values by 44 ∼ 45% concerning low-concentration NFs. At Re = 7940, the friction factor increases by 24.3% and 32.1% when copper and MWCNT-Fe3O4 hybrid NPs are dispersed in the base fluid, respectively. The highest PEC value (1.07) is achieved when the copper NPs with ϕ = 0.003 are used in configuration BFS1 at Re = 7940. Using MWCNT-Fe3O4 hybrid NPs is only proposed at lower Re numbers when the downstream wall is deflected and ϕ = 0.001. At Re = 30215, due to the addition of magnetic NPs, the ANN value abates by 28.5% and 30.7%, respectively, in the canonical case and configuration BFS2. Among the high-concentration NFs, the highest PEC (1.05) is obtained using Cu-MWCNT hybrid NPs with ϕ = 0.01 at Re = 30215 when the downstream wall is deflected upwardly. As Mouromtseff (Mo) number-based figure-of-merit (FOM) verifies, the worst scenario (PEC < 1.0) is substituting the base fluid with Fe3O4/water NFs. Cu-MWCNT/water hybrid NFs with ϕ = 0.02 become an effective coolant (PEC > 1.0) when the deflection angle and Re number increase simultaneously.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF TUBE BUNDLE HEAT EXCHANGER ARRANGEMENT EFFECT ON HEAT TRANSFER PERFORMANCE IN TURBULENT FLOWS

This study examines the friction factor, convective heat transfer, and area goodness factor of both inline and staggered tube bundles. The Finite Volume Method (FVM) is used for numerical simulations. Experimental and numerical approaches are utilized. Both 18.0 mm and 21.6 mm longitudinal distances are investigated. It is recommended to use ratio coefficients to reduce computation time. The proportion coefficients are used to obtain predictions for the three-dimensional cases based on the two-dimensional results or to transfer the 2D results to 3D. In addition, three turbulence models were utilized and compared within an Unsteady Reynolds Averaged Navier-Stokes (URANS) formulation. Experimental results validated numerical predictions. The thermal boundary conditions consist of a constant inlet temperature and a uniform heat flux on the support plate. Reynolds number is changed from 989 to 6352, while the Prandtl number remains at 0.70. Nusselt number and friction factor values have been observed to increase with increasing Reynolds number in all geometric configurations. The staggered configurations result in greater Nusselt number and friction factor values compared to inline configurations. The Nusselt number and pressure drop experience negative and positive effects, respectively, as the distance between rows decreases. SST turbulence models typically predict reasonable outcomes for all geometric configurations.

Comparison of Heat Transfer Characteristics between Supercritical N-Decane and Supercritical Carbon Dioxide in a Single Square Minichannel

Numerical investigations were conducted to analyze the heat transfer characteristics in a single square minichannel with supercritical C10H22 (sC10H22) and supercritical CO2 (sCO2). A single symmetric minichannel with a square cross-section of 1 mm × 1 mm and a length of 400 mm was selected, the top surface of which is applied with a uniform heat flux from 100 to 300 kW/m2. The inlet temperatures are varied from 20 to 150 °C and the inlet mass fluxes are ranged from 300 to 500 kg/(m2·s) in the physical model. The flow and heat transfer processes of the fluids were simulated in COMOSOL Multiphysics® software with RANS k-ω low-Reynolds number turbulence model. Results show that the heat removal capacity of sCO2 at 8 MPa is superior, which is 8 times that of sC10H22 at 3 MPa at the inlet temperature of 20 °C. When the inlet temperature and heat flux increase, the heat transfer performance of sCO2 drops sharply, while the overall performance of sC10H22 rises steadily. It suggests that sCO2 is more suitable for the heat transfer process with high-efficient cooling system at a lower inlet temperature, while sC10H22 is capable of a stable and long-time heat transfer process at a higher inlet temperature.

Closed-Form Solution for a Circular Nanohole with Surface Effects Under Uniform Heat Flux

Closed-Form Solution for a Circular Nanohole with Surface Effects Under Uniform Heat Flux

Thermohydraulic performance study of the effect of winglet inserts and a corrugated wall in a rectangular channel

This numerical study investigates the enhancement of heat transfer and pressure drop characteristics in rectangular channels with transverse corrugations and longitudinal winglet vortex generators. Numerical simulations cover a range of Reynolds numbers (Re) (5000–20000) using channels with uniform wall heat flux and fixed wavelength. The study evaluates the influence of geometrical parameters (corrugated channel amplitude and winglet length) on flow and temperature characteristics, average Nusselt number (Nu), and pressure drop. Corrugated channels alone create stationary transverse vortices that impede heat transfer. However, integrating winglet vortex generators introduces beneficial longitudinal vortices, disrupting stationary vortices, perturbing the thermal boundary layer, enhancing near-wall turbulence, and improving fluid mixing and heat transfer compared to smooth and corrugated channels. At Reynolds number (Re)20,000, corrugated channels with winglets exhibit 167.7 % and 61.8 % higher Nusselt numbers compared to smooth and corrugated channels, respectively. However, this enhanced heat transfer accompanies increased pressure drop. Both heat transfer and pressure drop rise with higher Reynolds numbers (Re), corrugation amplitude, and winglet length. This study provides insights into heat transfer mechanisms in corrugated channels and the potential for improvement through winglet vortex generators.

Influence of upstream and downstream flow on different packed bed configurations in phase change process

One approach to storing latent heat in large quantities is through PBSS (Packed bed storage system) with spheres filled with PCM (Phase Change Materials). In these storage systems, an HTF (heat transfer fluid) flows over the spheres. So, both the sphere wall temperature and the heat flux can vary depending on the geometric conditions of the bed of spheres, the PCM thermodynamic conditions, and the HTF thermal conditions. Thus, this work aims to verify the influence of the thermal conditions of the external flow on the PBSS filled with PCM in the melting process. Cases with variable heat flux as well as uniform temperature and uniform heat flux conditions were tested. Three sphere positions, 4 sphere spacing ratios (blockage ratio), and three temperature differences between HTF and PCM phase change temperature were also analyzed, for two external flow directions (upstream and downstream), totaling 74 different configurations. The study found that the uniform temperature condition resulted in a 33 % faster total melting time than the uniform heat flow condition. Additionally, the upstream flow showed a total melting time that was approximately 24 % shorter than the flows in the opposite direction. The relationship between the total melting time and the temperature differences was found to be non-linear. Moreover, the blockage ratio showed a non-linear dependence with total melting time. The configuration with a blockage ratio of 1.125 demonstrated the shortest total melting time, with values on average 22.4 % shorter than the blocking ratio of 0.550, which had the longest melting times. These results demonstrate that optimizing external flow thermal conditions is crucial for improving the performance of PBSS with PCM-filled spheres in large-scale latent heat storage systems.