Maximum Heat Transfer Rate Research Articles

Hydromagnetic Convective Heat Transfer in a Square Cavity Filled with Fe3O4-Water Nanofluid Saturated Porous Medium

A numerical study is carried out to demonstrate the heat transmission events of nanofluid in a square cavity saturated by aluminum foam porous medium under the effect of slanted periodic magnetic field. The cavity wall is heated from left and cooled from right while horizontal walls are supposed to be adiabatic. The Brownian motion of nanoparticle is taken into consideration in the thermal conductivity model construction. The dimensionless governing equations including Darcy-Brinkman model are solved by Galerkin-FEM. The outcomes are exposed with depictions of streamlines, isotherms and average Nusselt numbers. The numerical investigation is performed for parameters: Darcy number, Rayleigh number, Hartmann number, porosity, leaning angle of the periodic magnetic field, period number, and nanoparticle volume fraction. The heat transfer rate upsurges noticeably for the rise of nanoparticle volume fraction, period number, Darcy number and Rayleigh number but the reverse trend is found for the parameter Hartmann number as well as porosity. From the acquired numerical outcomes, the maximum rate of heat transfer is attained at δ=π/4 when λ = 1. Jagannath University Journal of Science, Volume 10, Number II, Dec. 2023, pp. 145-158

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.

Performance improvement in a heat exchanger tube using discrete X–V baffle (DXVB) turbulators

Thermal performance improvement in a heating tube (HT) using discrete X–V baffle (DXVB) as turbulators is presented. The DXVB is designed with three main goals: 1. To decrease the pressure drop in the tested tube and 2. To increase the mixing quality in the heat exchanger tube and 3. To produce powerful vortex flows. Lower pressure drop, generated vortex flows and higher mixing quality will augment a heat transfer rate and thermo-hydraulic efficiency. This study examines effects of DXVB structures, DXVB distances and placements on laminar air flow and thermal structure with Reynolds number from 100 to 2000. The current problem is numerically investigated using the finite volume technique of a commercial program/code (ANSYS-FLUENT V.2022). The created model of the HT fitted with the DXVB is numerically validated. From the numerical results, the DXVB installed affects the air flow structure in the tested tube. The vortex streams are observed. The change in fluid flow influences thermal characteristics. The vortex streams destroy some parts of the thermal boundary layer and help to increase mixing quality. These perturbed thermal boundary layer (TB-layer) and better mixing quality are two important factors that contribute to convective heat transfer enhancement. In addition, the maximum heat transfer rate and pressure loss are 10.17 and 45.75 times upper than that in the circular plain tube, respectively, while the best thermal enhancement factor (TEF) of 3.09 is observed at 15b5g, +x at Re = 2000.

Numerical study on mixed convection heat transfer of copper-water nanofluid in a porous cavity with an isothermal solid block in local thermal non-equilibrium

This manuscript reports a numerical study on mixed convection heat transfer of Cu-water nanofluid in a porous cavity with an isothermal solid block in the state of local thermal non equilibrium. The set of governing equations are solved by finite volume method combined with SIMPLE algorithm. Through streamlines and isothermal contour plots as well as the average Nusselt number, the impact of various parameters like the nanoparticle concentration, Richardson number, Darcy number, and inter phase heat transfer coefficient is highlighted. The main findings indicate that the Local thermal non-equilibrium state (H = 1, 10) produces the maximum heat transfer rate than the local thermal equilibrium state (H = 1000).

Development of Electrodeposited Hierarchical Dendritic Wick Structure for Ultra-Thin Vapor Chamber Applications

Compact and light-weight electronic systems have posed stringent dimensional criteria for heat-dissipation components such as heat pipes and vapor chambers. An ultra-thin vapor chamber (UTVC) with an overall thickness below 1 mm requires an interior capillary wick structure less than 100 μm. The capillary wick layer provides a flow path for fluid circulation in an operational UTVC. The maximum UTVC heat transfer rate normally depends on liquid permeability (K) and capillary pressure (∆P) of the wick structure. Large K and ∆P values are rarely realized in typical homogeneous porous structure. In this study, a novel hierarchical dendritic copper wick was prepared to achieve large K and ∆P simultaneously by one-step electrodeposition and thermal sintering process. The effects of electrodeposition parameters, such as current density, deposition time, and solution conditions on the capillary performance of the dendritic copper wicks were investigated. The results indicate that the wicking capability is modulated by the dendritic morphology of Cu deposits. Moreover, a post-deposition sintering process can improve further the structural integrity of the Cu dendrites and the capillary performance of the electrodeposited wicks. An optimal dendritic copper wick of 30 μm in thickness possesses a promising capillary performance K/R eff of 0.811 μm, which is the thinnest wick reported in the literature.

Tailoring Substrate Topography to Enhance Wicking Performance of Electrodeposited Cu Porous Films

Porous metallic films have received emerging interests in the fields of catalysts, fuel cells, lithium batteries, and phase-change heat transfer devices. Substrate topography is known to have a strong impact on adhesion and morphology of porous coating layers prepared by electrodeposition. In this study, we have tailored the topography of a Cu substrate by wet etching in a sodium persulfate/sulfuric acid (SPS) solution prior to electrodeposition of porous Cu films. An analytic approach is proposed to quantitatively analyze nucleation and growth of dendritic Cu deposits on the SPS-treated Cu substrates. Such a dendritic porous Cu film can serve as a capillary wick to complete recirculation of condensed liquid in the phase-change heat transfer devices. The maximum heat transfer rate of a heat pipe or vapor chamber indeed is proportional to the capillary performance (K/Reff ) of the wick structure, where K and Reff stand for liquid permeability and effective pore radius of the wick, respectively. A large K/Reff value of 0.975 µm has been attained for the electrodeposited dendritic Cu film on a Cu substrate with an optimal SPS etching treatment. The influence of dendritic deposits on the wicking performance of the electrodeposited Cu film is investigated. Figure 1

Thermal performance investigation of transient natural convective nanofluid flow in a square cavity with inclined periodic magnetic field

The goal of this paper is to analyze the thermal exhibition of transient free convective nanofluid flow in a square cavity with inclined periodic magnetic field using one-component thermally equilibrium homogeneous model. Distinct thermal settings (constant, parabolic, and sinusoidal) for the left heated wall are deliberated when the right wall of the cavity is cold and the horizontal walls are insulated. For numerical simulations, eight types of nanofluids consisting Cu, Co, Zn, and Al2O3 nanoparticles along with H2O and kerosene as base fluids have been employed. During numerical computation, the impacts of different factors (Hartmann number, Rayleigh number, nanoparticles volume fraction, period, and inclination angle) on the fluid flow and heat transfer are examined. The numerical results show that cobalt-kerosene nanofluid distributes the maximum heat transfer rate compared to other 7 types of nanofluids. The results also indicate that sinusoidal thermal scenery at the left heated wall delivers the uppermost average Nusselt number compared to the other types of thermal approaches. The optimum thermal performance is achieved at magnetic field's inclination angle δ=π3 and period number λ = 1 for the case of sinusoidal scenery.

A numerical investigation into thermo-fluid characteristics of pulsating jet impingement on a dimpled surface

A two-dimensional axisymmetric numerical model is employed to study the flow and heat transfer attributes of the pulsating air jet impingement on a dimpled surface. The results are compared with the steady jet impingement. The results are examined at a fixed Reynolds number of 5000, over a Strouhal number range of 0.1–0.5, and pulsation amplitude of 15% and 25% for three different nozzle-to-surface separations (z/d = 2, 6, and 10). The pulsation amplitude of 15% has a minor effect on heat transfer from the dimpled surface. However, at 25% pulsation amplitude, significant improvements in the heat transfer rates are obtained in many combinations of jet Strouhal number and jet surface spacing. The value of the optimum Strouhal number provides conditions for the maximum heat transfer rate, which varied with nozzle-to-surface separation distances. Combinations of higher separations and lower Strouhal numbers (and vice versa) produced optimum heat transfer among the cases considered in the present study. The maximum improvement (17.41%) in the average heat transfer over the steady jet was found at z/d = 10 for pulsation at St = 0.1, while at z/d = 6, St = 0.2 provides the highest heat transfer rate. It is urged that the vortices formed in pulse jet close to the natural frequency of vortex formation provide a conducive environment for the vortex growth and their existence, significantly affecting the jet entrainment, mixing, and jet spread, which eventually play the decisive factor in determining the overall heat transfer rates on the dimpled surface.

Effects of vapor duct thickness on the thermal performance of ultra-thin vapor chambers under forced-convection cooling

Ultra-thin vapor chambers (UTVCs) have drawn considerable attention for the growing need of thermal management for thin portable electronic devices. In fact, our novel UTVC design has the potential for high-power applications. This work presents the performance test results under forced convective cooling for our novel UTVCs with thicknesses t = 0.40, 0.50 or 0.58 mm, having vapor duct thickness h = 0.15, 0.25, or 0.35 mm, respectively. The vapor duct thickness is shown to exert great effect on the maximum heat transfer rate (Qmax) and mild effect on the values of thermal resistance (Rvc) of the UTVC. These novel copper–water UTVCs simply comprise a top plate etched with arrayed pillars as the condenser and a mesh-wicked bottom plate as the evaporator and liquid path. The inner surface of the top plate contains cross parallel vapor ducts configured by aligned pillars for vapor spreading all over the vapor chamber. The pillars provide strong structural support, an enlarged condensation area, and a direct shortcut for liquid return. The condenser, with a footprint of 140 × 80 mm2, is cooled by a cold plate with running water of 50 °C. The UTVCs having h = 0.35 or 0.25 mm display values of Qmax of about 140 W or 90 W, respectively, with similar values of Rvc of 0.036–0.055 K/W. The UTVCs with h = 0.15 mm display greatly degraded values of Qmax of about 55 W with higher values of Rvc of 0.053–0.078 K/W. With a shorter return distance for the condensed water directly through the arrayed pillars, this UTVC design demonstrates a rather high Qmax of 140 W using only a single layer of #200 copper mesh wick at h = 0.35 mm.

Evaporation and heat exchange of a thin liquid layer under various heating methods: Advantages of local heating over uniform heating of the wall

Intensification of heat transfer and evaporation is widely used in modern technologies at limited dimensions of heat exchange surfaces and high energy density. To date, stationary heat transfer at uniform wall heating, has been most thoroughly investigated. Meanwhile, there is no comprehensive research providing a comparison of free convection, heat transfer and evaporation with different heating methods. The novelty of the work lies in the comparison of the heat transfer efficiency using one laser beam, two beams and homogeneous heating. When heated by a single laser beam, the average temperature of the layer interface is significantly lower than at homogeneous heating. However, due to the generation of intense Marangoni flow, a small heating spot provides more intense evaporation than homogeneous heating. The effectiveness of heat transfer is analyzed in terms of the total efficiency coefficient. If it is important to take into account power input, it is preferable to use a single laser beam. If it is not decisive, then two laser beams allow achieving maximum heat transfer and evaporation rate. Homogeneous heating is significantly inferior to local non-stationary heating in terms of all key criteria. The simple expressions serve to optimize the total efficiency coefficient.

Optimization of the effect of sinusoidal phase shift heating on mixed convective in an enclosure: LBM approach

This paper investigates the influence of mixed convective heat transfer in a two-dimensional enclosure with sinusoidal heat applied on the vertical walls by the Lattice Boltzmann Approach. Governing equations are resolved by the Single-Relaxation-Time Bhatnagar-Gross-Krook model. A two-dimensional, nine-directional lattice arrangement is chosen to attain better numerical stability with good accuracy. The results are presented for four different fluids having Prandtl numbers equal to 0.015, 0.7, 1.38, and 7.0 respectively for mercury, gaseous ammonia, noble gases, and water. This analysis is performed for selected Reynolds numbers (100 ≤ Re ≤ 2000) and Richardson numbers (0.0 ≤ Ri ≤ 10.0). The above parameters are optimized using the Design of the Experiment to achieve maximum heat transfer rate. Taguchi method is used to conduct the required numbers of numerical studies and the dominant parameters are quantitatively found using Analysis of Variance (ANOVA). The present numerical results are compared with the existing literature and found good agreements. Results show that the right-side wall has always a higher heat transfer rate than the left-side wall. The factor levels combination for maximum heat transfer rate is found as Pr = 7.0, Re = 2000, and Ri = 10.

Exploring heat transfer efficiency in non-boiling spray cooling

Spray cooling today is one of the most effective methods for high heat flux application. Since there are numerous factors influencing the heat transfer in spray cooling, some issues related to the effect of the nozzle-to-surface distance, heat flux and liquid subcooling on the heat transfer efficiency in non-boiling mode remain debated. This study is dedicated to a comprehensive experimental investigation of the impact of various factors, including the distance from the nozzle to the heater (2–35 mm), heat flux density (up to 6.9 MW/m2), liquid flow rate (8.8–25.2 mL/s), and initial liquid temperature (20 and 80 °C) on heat transfer in non-boiling spray cooling using different nozzles with varying spray angles (30–90°). Heat transfer results were obtained based on field temperature measurements using high-speed infrared thermography. It is shown that the nozzle-to-surface distance has a significant effect on the spatial distribution of the temperature field and the heat transfer rate in spray cooling. It is shown that for each nozzle and heating surface there is an optimum distance at which the maximum heat transfer rate at non-boiling spray cooling is observed and relationship for their determination are proposed. The heat transfer coefficient for deeply subcooled liquid (80 K) is practically independent of the heat flux. At low subcooling levels (20 K), the heat transfer coefficient increases with the increase in heat flux associated with the influence of evaporation from the liquid film surface on the total heat transfer. The results obtained are analyzed, compared and generalized with data from the literature, and a correlation is proposed for determining the heat transfer in non-boiling spray cooling.

Optimization of the aero-engine thermal management system with intermediate cycle based on heat current method

Reliability and efficiency of the aero-engine thermal management system (ATMS) is of great importance to ensure the required working condition. Conventional methods on modeling ATMS are complex and difficult to solve for optimizing the whole system under multiple conditions. This study combines the heat current method and artificial neural network (ANN) to develop the optimization models with the objectives of maximum heat transfer rate and minimum thermal conductivity respectively. The ATMS experimental platform with intermediate cycle using water as the simulated medium is constructed to verify the optimization reliability. After optimization, the maximum heat transfer rate of ATMS is increased from 7740 W to 8402 W by 8.6%. The minimum thermal conductivity decreases from 1628 W/K to 1032 W/K by 36.6% comparing with the initial working condition. While considering the conditions of artificial control on the fuel oil side, the optimal thermal conductivity decreases from 1628 W/K to 1101 W/K by 32.3%. The optimal findings provide powerful guidance for improving the heat dissipation and reducing weight of the aircraft.

Converging Jet Impingement for Enhanced Liquid Cooling

Abstract Jet impingement cooling is an advanced thermal management technique for high heat flux applications. Standard configurations include single, axisymmetric jets with orifice, slot, or pipe nozzles. This choice in nozzle shape, number of jets, and jet inclination greatly influences the turbulence generated by fluid entrainment due to differences in initial velocity profiles and location of secondary stagnation points. Regarding high power electronics with integrated jet impingement schemes, turbulence, and heat transfer rates must be optimized to meet the extreme cooling requirements. In this study, the heat transfer rates of dual inclined converging jets are investigated experimentally. Emphasis is placed on the comparison of different jet schemes with respect to geometrical parameters including nozzle pitch, incline angle, and nozzle-to-target plate spacing. A parametric experimental investigation is performed as a point of comparison using a modular, additively manufactured jet setup. Computational simulations are used to evaluate the effect of jet configuration on stagnation pressure associated with maximum heat transfer rates, and an empirical Nusselt number model is provided. The results show the effects of convergence height on jet behavior and the associated impacts on heat transfer.

A mechanistic model to predict saturated pool boiling Critical Heat Flux (CHF) in a confined gap

Boiling enables high rates of heat transfer from a surface made possible at a relatively low thermal resistance motivating the use of two-phase cooling for increasingly compact thermal management solutions. However, extreme geometrical confinement of the liquid above the boiling surfaces is known to have detrimental effects on maximum heat transfer rate by inducing premature onset of film boiling. Moreover, previously developed critical heat flux (CHF) models for confined geometries focused on triggering mechanisms associated with unconfined pool boiling and, thus, are not generalizable. This work proposes a new mechanistic model for predicting CHF during boiling within in narrow gap, specifically developed to account for confinement effects on the triggering mechanism. The model postulates that occurrence of CHF coincides with the irreversible growth of a dry spot on the boiling surface. Three competing forces govern the two-phase interface dynamics, namely vapor momentum, surface tension, and hydrostatic forces. Dryout is triggered when the vapor momentum force due to vaporization at the two-phase interface balances the combined surface tension and hydrostatic forces leading to irreversible growth of the dry spot. The present work offers a predictive confined CHF model that accounts for confined boiling surface shape, size, orientation, confinement gap spacing, and working fluid properties, with a single fluid-specific fitting coefficient that represents the ratio of vapor area to the confinement opening area near CHF conditions. Notably, the developed CHF model is also effective in predicting the threshold gap below which confinement reduces pool boiling CHF. The model is compared to 197 experimentally measured confined CHF data points available from 10 studies in the literature that represent 7 different working fluids and a range of boiling surface inclinations and shapes. The model predicts the confinement-reduced CHF values with a root mean square error of 21%, which is less than half of the error compared to all other available predictive models. This clarification of the triggering mechanism and improved prediction accuracy of CHF, as offered by the current study, will enable broader practical system implementation of compact two-phase cooling technologies.

Thin film flow, heat transfer and viscous dissipation effects on vertical stretching sheet for different shapes of (Au-Np) dispersed in water

In this article, we present numerical investigation and analysis of thin film flow and heat transfer effects for different shapes of gold nanoparticles on a vertical stretching sheet. There are several uses for thin liquid films, including antireflection coating for lenses. Coating systems must have a smooth, polished surface, low friction, clarity, and strength to satisfy the demands of all of these applications. We consider thin film flow of nanoparticles on a vertical stretching sheet due to their numerous applications. Additionally, we employed water as the base fluid and considered different shapes of gold nanoparticles (blades, cylinders, and platelets). After formulating the problem, we convert nonlinear partial differential equations (PDEs) into ordinary differential equations (ODEs) using a transformation. The resulting nonlinear differential equations have been computed by the BVP4c method. It is examined and graphically assessed how the Nusselt number, temperature, skin friction, and fluid velocity are related. This research suggests that the blade shape has the maximum heat transfer rate and the lowest skin friction coefficient value.

Nanoencapsulated phase change material in a trapezoidal prism wall under the magnetic field effect for energy storage purposes

Recently, Nano-encapsulated phase change materials (NEPCM) have attracted the attention of researchers due to their promising application in thermal management. This research investigates magnetohydrodynamic mixed convection of NEPCM contained within a lid-driven trapezoidal prism enclosure containing a hot-centered elliptical obstacle. The upper cavity wall is moving at a constant velocity; both inclined walls are cold, while the rest of the walls are insulated. The Galerkin Finite Element Method was used to solve the system's governing equations. The influence of Reynolds number (Re 1–500), Hartmann number (Ha = 0–100), NEPCM volumetric fraction φ (0–8%), and elliptical obstacle orientation α (0–3π/4) on thermal fields and flow patterns are introduced and analyzed. The results indicated that the maximum heat transfer rate is observed when the hot elliptic obstacle is oriented at 90°; an increment of 6% in the Nu number is obtained in this orientation compared to other orientations. Reducing Ha from 100 to 0 increased Nu by 14%. The Maximum value of the Bejan number was observed for the case of Ha = 0, α = 90° and φ = 0.08.

Lattice Boltzmann simulation of natural convection heat transfer phenomenon for thermal management of multiple electronic components

Thermal management of electronic components is becoming a vital necessity in view of the rapid development of electronics technology. It is a concern imposed by the miniaturization of electronic chipsets. The present work addresses this issue numerically, using the lattice Boltzmann method (LBM). It consists of an air-filled heat sink containing multiple protruding electronic components. The problem is modelled using 2D continuity, momentum, and energy conservation equations. The thermal and dynamic fluid flow are analysed for various enclosure inclinations (0°, 45°, and 90°) and Rayleigh numbers (Ra=103-106). A twin protruding heat sources are considered at the bottom wall. The top cold wall can be at a uniform temperature (case 1) or consisting of two protruding sinks maintained at a constant temperature (case 2). The results showed that the maximum heat transfer rate corresponding to Nusselt number (Nu¯=5.51) is achieved for Ra=106 on the hot wall for the horizontal cavity in case 1, illustrating the cavity with top cold uniform wall. Indeed, the heat transfer is improved by 80% by varying the Rayleigh number (Ra) from 103 to 106. Furthermore, for case 2 with a twin cold protruding, a quite complicated heat transfer behaviour is observed on the hot wall. For Ra>106, the horizontal cavity outperforms the other cavities in terms of heat transfer rate, however the horizontal position is the less performant for Ra<104. With a horizontal disposition and Ra=106, the heat exchange ratio is improved by 32.32% in case 2 compared to case 1. The outcomes of this study provide insights into design and implementation of natural convection cooling solutions for electronic devices, which can have significant practical implications in various industries.

Empirical study for Nusselt number optimization for the flow using ANOVA and Taguchi method

ANOVA and Taguchi is an optimization tool used to find the optimal combination to achieve the highest heat transmission rate for a Casson-Carreau nanofluid flow over a curved surface. Exponentially generating heat, thermal radiation, Joule heating, chemical reaction along with velocity slip, and Stefan blowing peripheral conditions are employed for the current investigation. The rate of heat and mass transmission has been analyzed using the Cattaneo-Christov duplexed diffusion model. Entropy synthesis in the fluid flow system is also planned for the research. The graphs of solutions to the topic under consideration have been compiled by a tool called the Runge-Kutta-Fehlberg scheme. According to the outcomes of the present study, when thermal and solutal relaxation parameters are increased, the corresponding thermal and solutal profiles decrease. Both the speed and concentration panels benefit from the Stefan blowing parameter. The Nusselt number falls when Eckert number and Prandtl number increase. When the velocity slip factor is enhanced, the velocity has slowed down, while a rise in the second-order velocity slip factor encourages the same. The Taguchi optimization method has disclosed that the highest signal-to-noise ratio is attained when the magnetic parameter is 0.7, the thermophoresis parameter is 0.05, the Prandtl number is 7, the Eckert number is 0.06, and the thermal relaxation parameter is 0.05. Thus, the maximum heat transfer rate obtained is 2.75354. The thermophoresis parameter has a huge contribution of about 93.83%, whereas the thermal relaxation parameter has the least contribution, i.e., 0.03%, on heat transport rate.

A novel oval-shaped coaxial ground heat exchanger for augmenting the performance of ground-coupled heat pumps: Transient heat transfer performance and multi-parameter optimization

Ground-coupled heat pumps (GCHP) are highly impactful and promising systems for extracting geothermal energy. Nevertheless, the effectiveness of GCHP can be further improved by reshaping and optimizing the configuration of the coaxial ground heat exchanger (CGHE), which represents the core component of the GCHP and has a significant influence on the heat extraction performance of the system. This paper introduces a detailed comparative numerical study on a novel CGHE with an oval cross-section for enhancing the performance of the GCHP. The proposed design's simplicity stems from altering the outer tube to an oval shape, compared to the commercially used circular CGHE. The conjugate fluid flow and heat transfer are simulated utilizing a three-dimensional numerical model. Heat flux, GHE thermal resistance, and pressure drop within the tube are computed and analyzed. A comparison between circle and oval cross-sections is carried out. The adopted 3-D model shows a fit verification with their experimental pairs via a field experiment. Parametric study and sensitivity analysis are performed, and the effect of groundwater flow on heat transfer is also examined. An optimization approach is developed to explore the optimal inner tube position and incorporate multi-inner tubes that attain the maximum heat transfer efficiency of the oval-CGHE. The results reveal that oval-CGHE significantly surpasses the conventional circle-CGHE, improving the maximum and average heat transfer by 21.03% and 10.24%, corresponding to a reduction in thermal resistance by 28.83% and 9.06%, respectively. Additionally, optimizing the inner tube position and incorporating multi-inner tubes further enhances the performance of oval-CGHE by maximum and average heat transfer rates of 33.01% and 22.91% for inner tube position optimization and 39.08% and 28.84% for multi-inner tube optimization, respectively.