High Prandtl Number Research Articles

Limiting regimes of turbulent horizontal convection. Part 2. Large Prandtl numbers

Horizontal convection at large Rayleigh and Prandtl numbers is studied experimentally in a regime up to seven orders of magnitude larger in terms of Rayleigh numbers than previously achieved. To reach Rayleigh numbers up to $10^{17}$ , the horizontal density gradient is generated using differential solutal convection by a differential input of salt and fresh water controlled by diffusion in a novel experiment in which the zero-net mass flux of water is ensured through permeable membranes. This set-up allows us to accurately measure the Nusselt number in solutal convection by carefully controlling the amount of salt water exchanged through the membranes. Combined measurements of density and velocity across more than five orders of magnitude in Rayleigh numbers show that the flow transitions from the Beardsley & Festa (J. Phys. Oceanogr., vol. 2, issue 4, 1972, pp. 444–455), Shishkina & Wagner (Phys. Rev. Lett., vol. 116, issue 2, 2016, 024302) regime to the Chiu-Webster et al. (J. Fluid Mech., vol. 611, 2008, pp. 395–426) regime and frames the present results within the scope of Shishkina et al. (Geophys. Res. Lett., vol. 43, issue 3, 2016, pp. 1219–1225), and the theory of Part 1 (Passaggia & Scotti, vol. 997, 2024, J. Fluid Mech., A5). In particular, we show that, even for large Prandtl numbers, the circulation eventually clusters underneath the forcing horizontal boundary, leaving a stratified core without motion. Finally, the previous regime diagrams (Hughes & Griffiths, Annu. Rev. Fluid Mech., vol. 40, 2008, pp. 185–208; Shishkina et al., Geophys. Res. Lett., vol. 43, issue 3, 2016, pp. 1219–1225) are extended by combining the present results at high Prandtl numbers, the results at low Prandtl numbers of Part 1, together with previous results from the literature. This work sets a new picture of the transition landscape of horizontal convection over six orders of magnitude in Prandtl number and sixteen orders of magnitude in Rayleigh number.

Thermal conductivity impact on MHD convective heat transfer over moving wedge with surface heat flux and high magnetic Prandtl number

The present evaluation focused on heat transfer and magnetic flux along the moving non-conducting wedge shape with thermal conductivity and surface heat flux effects. A suitable and well-known similarity transformation for integration is used for the coupled non-linear partial differential equations with stream formulations. The Keller Box technique is utilized to integrate the final non-similar equations numerically. The discretized algebraic equations are displayed graphically and numerically using the MATLAB software. The physical characteristics like temperature, magnetic field, velocity profiles, skin friction, heat transfer and magnetic intensity are investigated with various factors. The influence of relevant characteristics like thermal conductivity ξ, Prandtl number Pr, wedge parameter β, variable viscosity ε, and Biot number Bi is interpreted graphically and numerically. It is noted that velocity graph effects are declined at lower value of Biot number and enhanced value is obtained at the higher value of Biot number. The fluid temperature with highest thermal slip effects is displayed with minimum value of thermal conductivity but minimum value is obtained at large value of thermal conductivity. The maximum heat flux value is obtained at large value of moving parameter.

Experimental study on coherent structures by small particles suspended in high aspect-ratio (Γ=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma =$$\\end{document} 2.5) thermocapillary liquid bridges of high Prandtl number

In time-dependent traveling-wave convection, it has been confirmed that small particles of low Stokes number (St≪\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{St}\\ll$$\\end{document} 1) form three-dimensional closed structures known as the particle accumulation structures (PASs). We focus on coherent structures formed in high aspect-ratio thermocapillary liquid bridges (Γ=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma =$$\\end{document} 2.5), where oscillatory convection due to the so-called hydrothermal wave instability of mHTW=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{\ extrm{HTW}}=$$\\end{document} 1 stably emerges, and carry out experimental explorations into the volume ratio dependence of the emergence of coherent structures. Variation in the volume ratio induces the presence of coherent structures with different azimuthal wave numbers, that is, different spatial structures. Among the particles added to the liquid bridge, we perform spatio-temporal tracking of particles to quantify the correlation between the behavior of particles and the spatial structures of coherent structures with different rational wave numbers.

Small-scale Dynamo with Nonzero Correlation Time

The small-scale dynamo is typically studied by assuming that the correlation time of the velocity field is zero. Some authors have used a smooth renovating flow model to study how the properties of the dynamo are affected by the correlation time being nonzero. Here, we assume the velocity is an incompressible Gaussian random field (which need not be smooth), and derive the lowest-order corrections to the evolution equation for the two-point correlation of the magnetic field in Fourier space. Using this, we obtain the evolution equation for the longitudinal correlation function of the magnetic field (M L ) in nonhelical turbulence, valid for arbitrary Prandtl number. The nonresistive terms of this equation do not contain spatial derivatives of M L of order greater than 2. We further simplify this equation in the limit of high Prandtl number, and find that the growth rate of the magnetic energy is much smaller than previously reported. Nevertheless, the magnetic power spectrum still retains the Kazantsev form at high Prandtl number.

Unsteady wake and heat transfer characteristics of three tandem circular cylinders in forced and mixed convection flows

In natural convection (high Richardson number Ri), a high Prandtl number (Pr) leads to thinner thermal boundary layers, enlarging the thermal gradient and hence the enhancement of buoyancy effect. In forced convection (low Ri), a high Pr introduces thicker velocity boundary layers. In mixed convection scenarios, where both forced and natural convection are significant, the interaction between Pr and Ri determines the resultant flow pattern and heat transfer characteristic. Three tandem circular cylinders with an identical spacing ratio of 4.0 in both forced and mixed convection flows were numerically investigated by using finite element method. The computations were carried out in the range of Pr = 5–50 and Ri = 0–2 at a low Reynolds number of Re = 150. The results of the squared strain rate and the vorticity shed light on the enstrophy transfer process. Thermal plume structures in the far wake originate from the upper dispersed vortices due to the high superimposed buoyancy at low Pr, while they are suppressed at high Pr. The increase in Pr plays a role as the flow stabilization, while the growth of Ri plays the reverse role. The time-averaged velocity, pressure coefficient, and temperature become more asymmetrical at high Ri. The Nusselt number of the upstream cylinder is approximately equal to the empirical result without the consideration of thermal buoyancy. Due to the thermal buoyancy, the migration of shear layers along the cylinder surface leads to the frequency alteration and harmonic frequency in the drag, lift, and Nusselt coefficients.

Non-Oberbeck–Boussinesq effects on a differentially heated vertical cavity with high-Prandtl number fluid

This study explores the non-Oberbeck–Boussinesq (NOB) effects on hydrodynamics and heat transport in two-dimensional glycerol-filled differentially heated vertical cavity (DHVC). The simulations span Rayleigh numbers (Ra) from 2×103 to 5×109 and temperature difference (Δθ̃) up to 50 K at a Prandtl number (Pr) of 2547. We showed the emergence of stratified flow structures, delineated the NOB effects on temperature distribution symmetry, and analyzed the scaling behaviors of the Nusselt number (Nu), Reynolds number (Re), and thermal boundary layer (BL) thicknesses (λ¯hθ and λ¯cθ) against Ra. For Ra≥3×105, the stratification number (S) shows reduced sensitivity to changes in Ra, stabilizing around 0.5. Additionally, the center temperature (θcen) appears to be unaffected by Ra and increases linearly with Δθ̃ for Ra>106, satisfying θcen≈2.99×10−3K−1Δθ̃. Our results also revealed that Nu∼Raγ Nu and Re∼RaγRe with 0.2649≤γ Nu≤0.2654 and 0.3633≤γ Re≤0.3643, respectively, where γ Nu and γ Re exhibit a monotonic decrease as NOB effects intensify. For all investigated Ra values, NuNOB/NuOB<1 and ReNOB/ReOB>1 hold consistently, with deviations from OB predictions capped at 6.38% and 2.63% for Ra≥108, respectively. The analysis of thermal BL thickness reveals distinct scaling behaviors, characterized by λ¯h,cθ∼Raγ λ¯ h, c, with scaling exponents ranging from −0.2690 to −0.2669 for both OB and NOB scenarios. Notably, it reveals a divergence from water-based DHVC trends, showing linear decreases in the hot wall's scaling exponent and increases for the cold wall.

Melting heat transfer and irreversibility analysis in Darcy-Forchheimer flow of Casson fluid modulated by EMHD over cone and wedge surfaces

The present mathematical model analyses the melting heat transfer and irreversibility in Darcy-Forchheimer flow of Casson fluids modulated by the electroosmosis and magnetohydrodynamic mechanisms over the wedge and cone surfaces. The effects of thermal radiation, thermal buoyancy and heat generation/absorption are taken into consideration. Appropriate similarity transformations are utilized to establish a system of ordinary differential equations which are non-linear. The model has been numerically simulated using shooting approach in conjunction with the fourth order Runge-Kutta method under the bvp4c tool of MATLAB. Numerical results are computed for fluid velocity, fluid temperature, Nusselt number and Bejan number for analysing the fluid flow behaviour and heat transfer characteristics for the Casson fluid. A comparative analysis is performed to determine the irreversibility and heat transfer in the absence and presence of melting parameters, respectively. Variations in skin friction coefficient, local Nusselt number and Bejan number have also been examined under the effects of key parameters. Key findings of the present study indicate enhanced velocity distribution with increasing zeta potential and electric field parameters, while it diminishes with higher Prandtl number and Forchheimer terms. Moreover, fluid temperature reduces with rising zeta potential, while the Bejan number escalates with greater thermal radiation in the core region of geometries. The findings of the model may be useful in various applications of thermal systems.

Consequences of higher order chemical reaction on bioconvective carbon nanotubes flow implementing Buongiorno's model

In recent years, carbon nanotubes have been extensively explored based on numerous applications in fields such as carbon nanotube based electrodes, super capacitors, nanowires, sensors, coating with polymers, biomedical, and mechanical applications. Keeping in view the significance of carbon nanotubes in the heat transfer process in micro-electrochemical systems, this study is conducted to examine the heat transfer attributes of the carbon nanotubes using the mixture base working fluid. The focus of this investigation is to elaborate the consequence of higher chemical reactions on the bioconvective flow of carbon nanotubes. Additionally, modified Buongiorno's nanofluid model has been used, which undertakes thermophoresis and Brownian motion effects. Heated boundary condition has also been incorporated with the migration of motile microorganisms. The hybrid nanofluid mechanism has been followed in this work. Carbon nanotubes of single-layer and multi-layer have been used simultaneously with different working fluids, such as ethylene glycol (EG) and ethylene glycol/water (EG-water). Non-dimensional flow model equations have been tackled with the bvp-4c package. The obtained outcomes have been presented for distinct profiles and tabulated data sets for the surface skin friction and heat transfer coefficient. It has been observed that when the level of Brownian motion increases, the velocity profile decreases abruptly for SWCNT-MWCNT/EG as compared to SWCNT-MWCNT/EG-water hybrid nanofluid. Opposite behavior has been seen with raising values of magnetization. High Prandtl number decrease thermal boundary layer thickness for both types of hybrid nanofluids. The motile microorganism profile expands by raising the level of bioconvective Lewis number. Moreover, the outcomes of drag force and Nusselt number have been compared, and good agreement has been found.

Mathematical Solutions of Free Convection Flow of Casson Fluid in Channel with Accelerated Plate

Mathematical Solutions of Free Convection Flow of Casson Fluid in Channel with Accelerated Plate

Universal thermal profiles with polynomial thermal diffusivity in a channel flow

Fluids used in heat transfer applications range in a wide spectrum of Prandtl numbers. An aspect that is commonly neglected is the influence of variable thermal diffusivity in turbulent heat transfer. A mathematical model was developed in the past few years [1, 2] to address the influence of the variable thermal diffusivity on the turbulent heat transfer. In this work we explore the influence of the friction Reynolds number Reτ, the molecular Prandtl number Pr and the coefficients λi+ of the temperature dependent thermal diffusivity, up to the fourth-order, to the Universal Profiles in a channel flow. This choice minimizes the influence of the boundary and initial conditions. The numerical simulations in the limit of constant thermal diffusivity are validated against literature DNS data. The results show that the influence of the friction Reynolds number is limited, while high molecular Prandtl numbers increase the fluctuating thermal diffusivity heat flux. The factor that influences the solution the most is the thermal diffusivity coefficients, showing that, in certain conditions, the fluctuating thermal diffusivity heat flux is non-negligible even for low Prandtl numbers. The results show that the terms introduced by the model proposed in [1, 2] are non-negligible when the thermal diffusivity in the boundary layer doubles compared to its bulk value. It is suggested that the model presented in [1, 2] could be particularly suitable in cryogenic applications.

Experimental investigation of the Reynolds analogy for high Prandtl number fluid with repeated rib roughness

Reynolds analogy describes the relationship between friction (f/2) and heat transfer (St) owing to their superficial resemblance. However, Reynolds analogy is limited to simple geometries with a Prandtl number (Pr) close to unity. To extend Reynolds analogy, we measured the St and f/2 simultaneously using a high Pr fluid in duct flow in vertical duct flow with repeated rib roughness. The experiments were performed at a fixed value of Pr, 2014, Reynolds number (Re) ranging from 9.1 × 103 to 9.6 × 104, and relative roughness (e/D) ranging from 0.01 to 0.04. In the high Pr fluid, the St was much lower than f/2, as most of heat exchange occurred in the conduction sublayer, resulting from a thin thermal boundary layer. On the rough surface, both f/2 and St were higher than on the smooth surface. However, the influence of Re and e/D was different. The differences stem from that the corresponding phenomenon to pressure drag in friction does not exist in heat transfer. The extended Reynolds analogy correlation was developed. In addition, the efficiency factor was defined as the ratio of the enhancement rates of St and f/2 on the rough surface to those on the smooth surface. The efficiency factor decreased with Re and e/D, while it increased with Pr.

Molten salt flow visualization to characterize boundary layer behavior and heat transfer in a natural circulation loop

Experimental data for the natural circulation of high-Prandtl number fluids in molten salt systems has not yet been sufficiently studied to ensure safe operation in the event of a loss of forced coolant. A natural circulation loop facility was designed to mitigate major challenges in flow visualization experiments of molten salt. Experiments were conducted with molten salt and water, and four experimental data sets were obtained for each working fluid at increased heater power. Particle image velocimetry (PIV) measurements were performed, and the boundary layer was analyzed as a function of the Prandtl number. Velocity peaks near the walls were found in results for molten salt due to the underdevelopment of the thermal boundary layers, in contrast to the parabolic velocity profile found in results for water. The overall system behavior was characterized using velocity and temperature measurements. Temperature distributions in the loop demonstrated the developing thermal boundary layers at high Prandtl numbers. The wall shear stress was obtained from near-wall PIV measurements to determine the friction factor and a non-dimensional analysis of the boundary layer showed the expected relationship for laminar flow in all test cases. The local and mean Nusselt numbers were calculated and compared between fluids. The local Nusselt number for water stabilized as expected for the laminar flow, while results for salt showed evidence of continually developing flow. Results for the Nusselt number and friction factor were compared with correlations, and the most accurate predictions were identified for the current application.

Time-dependent stagnation point flow of nano Casson fluid with Joule heating over an elongated surface subjected to viscous heating and exponential space-based heat source/sink: Boungiorno model

The unsteady two-directional flow of a non-Newtonian magneto-Casson nanoliquid flow over an elongated flat surface with the porous matrix is investigated. The flow is subjected to space-based exponential heat generation/absorption (ESHS), thermophoresis, Brownian motion of nanoparticles, and transverse magnetic field. Within the base fluid, the diffusion of chemically reactive nanoparticles is assumed to be highly significant; hence considered. The governing equations of the flow model admit self-similar equations and are numerically solved by employing the Runge-Kutta-based shooting technique (RKSM). The significance of key parameters on the temperature, velocity, friction factor at the surface, heat transfer rate, and mass transfer rate distributions is analyzed. The use of high-Prandtl number base fluid and nanoparticles of high thermal conductivity could be of practical use to increase the heat transfer rate and avoid nanoparticle accumulation. The occurrence of nanoparticles in the operating liquids reduces the shearing stress at the plate surface to avoid backflow.

Approximate Analytical Solution of the Influences of Magnetic Field and Chemical Reaction on Unsteady Convective Heat and Mass Transfer of Air, Water, and Electrolyte Fluids Subject to Newtonian Heating in a Porous Medium

This paper addresses the unsteady hydrodynamic convective heat and mass transfer of three fluids namely air, water, and electrolyte solution past an impulsively started vertical surface with Newtonian heating in a porous medium under the influences of magnetic field and chemical reaction. Suitable dimensionless parameters are used to transform the flow equations and the approximate analytic method employed to solve the flow problem. The results are illustrated graphically for the velocity, temperature, and concentration profiles. Though, low Prandtl numbers produce high-thermal boundary layer thickness, however, as a novelty, the presence of the magnetic field delayed the convection motion hence, the thermal boundary layer thickness is greater for water with high Pr = 7.0 as compared to air with low Pr = 0.71 and electrolyte solution with low Pr = 1.0. Practically, water with a high-Prandtl number can effectively absorb and release heat. This makes water useful in applications such as geothermal heat pumps and solar thermal collectors, industrial processes such as chemical reactions, distillation, and drying, and in oceanography in predicting the movement and behavior of ocean currents, which in turn can impact weather patterns and climate. Another major observation from the study is that the rate of cooling associated with air, water, or electrolyte impacts differently on the product being cooled.

Averaging theory for heat transfer in circular hydraulic jumps with a separation bubble

Analytical investigations of heat transfer during the vertical impingement of an unsubmerged axisymmetric liquid jet on a horizontal plate have been limited to the regions ahead of the jump. This limitation is due to the complex flow physics in the jump region arising from sudden changes in the flow field. This is addressed in here by extending the averaging theory (AT) introduced by Bohr et al. (Phys. Rev. Lett., vol. 79, issue 6, 1997, pp. 1038–1041) which was further developed by Watanabe et al. (J. Fluid Mech., vol. 480, 2003, pp. 233–265), to describe the heat transfer problem in circular hydraulic jumps including separation. The applicability of the resulting theory to determine the temperature field in the jump region is evaluated using the data available in the literature and also by means of fully resolved numerical solutions. Good agreement is observed for moderate Prandtl numbers. However, for sufficiently high Prandtl numbers, deviations become notable. The reasons for the deviations according to their relevance are (i) monotonically decreasing temperature profile inherent to the AT, whereas the fully resolved numerical solutions exhibit a local maximum in the temperature profile away from the plate; and (ii) inapplicability of the concept of dividing the flow field into a region affected and a region unaffected by heat transfer according to the thermal boundary layer thickness. This concept leads to the overestimation of the temperature close to the wall and to the existence of a threshold Prandtl number, for which the thermal boundary layer thickness does not meet the free surface anymore. Around this threshold Prandtl number, the temperature field shows a discontinuous behaviour.

Three-dimensional effects during thermocapillary-driven melting of PCMs in cuboidal containers in microgravity

The melting of a phase change material (PCM) in a cuboidal domain under microgravity conditions is investigated numerically. The upper surface of the PCM is free (in contact with air, for example) and variations in its surface tension drive thermocapillary convection in the liquid phase, which significantly enhances heat transfer and accelerates melting. Furthermore, the change in liquid fraction during melting is associated with transitions among various modes of thermocapillary dynamics, including an oscillatory instability to hydrothermal waves. While the characteristics of PCM melting and thermocapillary dynamics have previously been investigated in this system using a two-dimensional model, the current work examines the important question of transverse dynamics and their effect on the melting process. Careful quantitative comparisons are made between the three- and two-dimensional models in terms of melting times, solid/liquid interface evolution, thermal fields, and spectrograms. The results show that transverse modes are often, but not always, reflection symmetric about the midplane and that their influence on melting and PCM performance is relatively minor in most cases. Thus, two-dimensional models may be used to reduce computational costs while still providing a reasonable approximation of the melting process for high Prandtl number materials, especially when compared to the midplane of the full cuboidal domain.

CFD assessment of RANS turbulence modeling for solidification in internal flows against experiments and higher fidelity LBM-LES phase change model

Generation-IV nuclear reactors’ potential coolant candidates include molten salts and liquid metals. Owing to their high melting temperature, both the design and safety assessments of these reactors need to take into consideration potential solidification events during normal or abnormal operation. This work assesses the Finite Volume Computational Fluid Dynamics (FV-CFD) enthalpy-porosity method combined with the Reynolds Averaged Navier Stokes (RANS) model k−ω to model internal solidification under turbulent flow conditions for high and low Prandtl numbers at a moderate computational cost, which is required for full-core nuclear reactor analyses. Concerning high Prandtl numbers, the predictions of macroscopic quantities generated by the FV-CFD RANS model are contrasted against a well-known internal solidification experiment on water (Thomason et al., 1978). A key factor in the satisfactory agreement between the CFD RANS model and the experiment is the addition of an interface turbulence-damping source to the specific dissipation rate equation (ω). For the low Prandtl numbers involved in liquid metals, there is a lack of high-fidelity experiments due to the complicated measurements. Thus, to perform the FV-CFD RANS model assessment, we develop and validate a high-fidelity phase-change model based on the Lattice Boltzmann Method (LBM) with a Large Eddy Simulation (LES) turbulence model. To the author’s knowledge, this is the first attempt to integrate LES turbulence models with phase-change solidification in the LBM context. Considering the computational time advantage of the FV-CFD RANS model over higher fidelity models and the good agreement of its predictions against experiments and the LES model demonstrated, this work demonstrates that FV-CFD RANS is an attractive tool to model internal turbulent solidification.

Numerical Investigation of Fin Shape Optimization and Entropy of Magnetohydrodynamics Natural Convection Nanofluid Flow in a Cavity

The purpose of the investigation is to analyze the effect of fin length and position in terms of rotational angle on heat transmission and entropy generation. Different parameters such as Prandtl numbers, Hartmann numbers, Rayleigh numbers, and particle volume fractions are used to analyze nanofluid laminar flow behavior and temperature distribution. The fin has a significant impact on both the isotherm and the streamlines. Findings revealed that increasing the rotational angle of a spinning heat exchanger might result in more consistent temperature distribution along isotherms; larger fins, on the other hand, frequently provide greater heat dissipation due to increased surface area. Furthermore, when Rayleigh numbers increase, so does the temperature distribution between the fins and the surrounding fluid. The presence of a magnetic field affects fluid dynamics and contributes to the generation of entropy. Higher Prandtl numbers can result in the enhancement heat transfer phenomena and the generation of entropy.

Analysis of convective heat transfer in triple diffusive free convection flow of Williamson nanofluid along a horizontal plate

ABSTRACTThis research investigates the concurrent effects of three different diffusion mechanisms, species diffusion, thermal diffusion, and nanoparticle diffusion, on the convective heat transfer and mass transfer properties of a nanofluid. As a part of the study, a further level of complexity is added using the convective boundary condition by considering the interaction between surface heat flow and surrounding fluid dynamics. Further the transformed governing equations are obtained with the help of similarity solutions. The Runge-Kutta-Fehlberg method is used with the shooting approach to get numerical solutions for the simplified equations. The influences of various involved parameters on velocity profiles, temperature profiles, concentration, local skin friction, local Nusselt and Sherwood numbers are discussed. The significant outcomes of the study are observed as the decrease in the velocity and fluid temperature during the increase of the suction parameters, and the indication of the evacuation of fluid from the surface that lessens the heat transmission and lowers the temperature profiles. The fluid temperature is raised by the augmentation in the conductive parameter. It has also been found that the mass transfer rate increased as the salts are included. The heat transfer decreases with higher thermophoresis strength but increases with higher Prandtl number.

Numerical investigation on the thermal-hydraulic performance of high Prandtl number fluid in offset strip fin with different offset

To rigorously analyze the thermo-hydraulic performance of offset strip fin operating with high Prandtl number fluid and variable fin offset values, numerical simulation was employed to investigate changes in the Colburn j and the Fanning friction f under varying fin offsets. The results, obtained using a reliable numerical model, indicated that an increase in offset led to a 33.08% and 33.97% rise in j and f, respectively, demonstrating the offset's influence on the thermal-hydraulic performance of offset strip fins. By employing orthogonal design techniques, a set of 49 design points for fin pitch, fin thickness, fin height, interrupted length, fin offset, Reynolds number, and Prandtl number were obtained. Regression analysis was conducted on the simulation results of these 49 design points, ultimately deriving correlations for j and f within the Reynolds number range of 100–1000 and the Prandtl number range of 2–13. A comparison between the predicted and simulated data revealed that j and f fell within the error range of 20% for 91.84% and 93.88% of the data, respectively, confirming the accuracy of the proposed correlations. Furthermore, comparing the correlations from this study with other previously established correlations demonstrated that the proposed correlations were more suitable for predicting the thermal-hydraulic performance of offset strip fins with high Prandtl number fluids. For fluids with Prandtl number range of 30–150, the predicted data of j and f exhibited errors within 15% and 20% of the experimental data, respectively, further validating the applicability of these correlations for predicting the thermo-hydraulic performance of offset strip fins with higher Prandtl number fluids as the working medium.