Fluid Heat Research Articles

Numerical analysis of the effect of baffle length and arrangement on the thermal performance of solar air channels

Improving heat transfer in solar air ducts is crucial to increasing the efficiency of solar heating systems. The addition of baffles is an effective technique for optimizing this heat transfer. This work presents an in-depth analysis of the effect of baffle length and arrangement in an air channel with rectangular baffles to direct and disrupt airflow, thereby increasing the rate of heat transfer. Computational fluid dynamics was employed for the calculations. The Finite volume method was used to discretize the governing equations, and the SIMPLE algorithm was used to the pressure-velocity coupling. A standard k−ε turbulence model based on Reynolds number ranges of 8000≤Re≤30000 has been used to numerically study flow properties and heat transfer. The results show that adapting baffle length plays a crucial role in controlling flow velocity, which directly influences temperature distribution in the system. In addition, the study reveals that periodic arrangement of baffles (Case C) increases maximum velocity values and optimizes flow by increasing fluid acceleration and dynamic pressure. For a Reynolds number of 30,000, periodic arrangements achieve the highest value for TPF, i.e. 3.267. This indicates that periodic baffles create optimized recirculation zones, improving fluid mixing and heat transfer without excessively increasing flow resistance.

Three-dimensional heat transport and fluid flow in a channel with heat-generating source and heat removal ribs

Three-dimensional heat transport and fluid flow in a channel with heat-generating source and heat removal ribs

Analysis of heat transfer of second-grade hybrid nanofluid and optimization using response surface methodology for thermal enhancement

The fluid flow and heat transfer applications in coaxial double-revolving disks are extensive and encompass multiple engineering and scientific disciplines. This study presents a comprehensive heat transfer analysis in a second-grade hybrid nanofluid. The fluid, influenced by variable thermal conductivity, is confined between two rotating disks in a magnetohydrodynamic Darcy-Forchheimer flow. The hybrid nanofluid combines titanium dioxide (TiO2) and cobalt ferrite (CoFe2O4) nanoparticles with engine oil. These issues have not been addressed in previous research. Similarity transformations make flow equations dimensionless. The resulting equations are solved using a semi-analytical approach called the homotopy analysis method (HAM). This approach provides flexibility in selecting the base function and an initial estimate. The temperature profile improved with higher values of the variable thermal conductivity parameter. Furthermore, the heat transfer rate was enhanced by increasing the variable thermal conductivity, the volume fraction concentration of TiO2, and the Reynolds number.The sensitivity analysis is performed using response surface methodology (RSM). Both the R-squared and adjusted R-squared values attain 100%. The heat transfer rate is found to have a maximum sensitivity of 0.50243 towards varying thermal conductivity parameters and a minimum sensitivity of -0.00666 towards magnetic field parameters. The research utilizes RSM to elucidate methods for improving heat transfer. This work offers practical solutions for developing more efficient thermal management systems. This research provides practical strategies for improving thermal management systems. These solutions are especially useful in rotating machinery-intensive industries. Designing biochemical and pharmaceutical microfluidic pumps and mixers requires understanding hybrid nanofluid flows between spinning disks.

Numerical Analysis of Heat Transfer and Flow Characteristics of Jeffrey Nanofluid Over Stretched Surfaces With MHD and Slip Effects

ABSTRACTThis study employs the Jeffrey fluid model to investigate stress relaxation in non‐Newtonian fluids, offering a more precise representation than conventional viscous models. It explores the influence of multiple slip conditions and magnetohydrodynamics (MHD) on Jeffrey fluid flow and heat transfer across irregular surfaces. Additionally, the impact of thermal radiation and internal heat sources on heat transfer is examined, essential for a comprehensive understanding of the system's thermal dynamics. Using the Buongiorno model, the diffusion and thermophoresis of nanoparticles within the flow are analyzed. Nonlinear coupled governing equations covering flow dynamics, heat transfer, and nanoparticle transport are transformed into ordinary differential equations (ODEs) through similarity transformations and solved numerically using the Runge–Kutta fourth‐order (RK4) method combined with shooting techniques. Results indicate significant effects of physical parameters on temperature, velocity, and mass profiles: a 20% decrease in temperature profiles with an increase in the dimensionless thermal slip coefficient from 0.1 to 0.5 and a 15% reduction in velocity profiles from a 0.1 unit increase in the magnetic parameter . The study also quantifies mass and heat transfer rates to elucidate their impacts. These findings have profound implications for engineering applications involving non‐Newtonian and nanofluids in complex geometrical configurations.

3D convective flow in a hybrid nanofluid filled bi-truncated-pyramid equipped with adiabatic cylinders

This study consists of an investigation of the 3D convective flow of hybrid nanofluids (HNFs) within a bi-truncated pyramid equipped with adiabatic cylinders, with a focus on the enhancement of natural convection (NC) heat transfer (HT). The use of HNFs, which is based on the combination of two different nanoparticles (NPs), provides improved thermal conductivity and stability, and leads to significant advantages in thermal management systems. Numerical simulations based of the FEM were performed to analyze the effects of Rayleigh number (Ra), nanoparticle volume fraction (φ), and cylinders size (D) on the heat transfer and fluid flow (FF) within the pyramid. The results showed that at higher Ra and nanoparticle concentrations a significant enhancement of the HT occurs, and the average Nusselt number (Nua) was increased by up to 23% at a Ra = 106 and φ = 0.045. Concerning the adiabatic cylinders, it was found that the optimal cylinder diameter is D = 0.15, (balance between flow disturbance and heat transfer rate). The outputs of the current study are valuable in the optimization of the hybrid nanofluid applications for advanced thermal management solutions.

Mixed Convection Heat Transfer and Fluid Flow of Nanofluid/Porous Medium Under Magnetic Field Influence

This study aims to investigate the effect of a constant magnetic field on heat transfer, flow of fluid, and entropy generation of mixed convection in a lid-driven porous medium enclosure filled with nanofluids (TiO2-water). Uniform constant heat fluxes are partially applied to the bottom wall of the enclosure, while the remaining parts of the bottom wall are considered to be adiabatic. The vertical walls are maintained at a constant cold temperature and move with a fixed velocity. A sinusoidal wall is assumed to be fixed and kept adiabatic at the top enclosure. Three scenarios are considered corresponding to different directions of the moving isothermal vertical wall (±1). The influence of pertinent parameters on the heat transfer, flow of fluid, and entropy generation in an enclosure are deliberated. The parameters are the Richardson number (R~i = 1, 10, and 100), the Hartmann number (0 ≤ H~a ≤ 75 with a 25 step), and the solid volume fraction of nanoparticles (0 ≤ Φ~ ≤ 0.15 with a 0.05 step). The Grashof and Darcy numbers are assumed to be constant at 104 and 10−3, respectively. The finite element method, utilizing the variational formulation/weak form, is applied to discretize the main governor equations. Triangular elements have been employed within the studied envelope, with the elements adapting as needed. The results showed that the streamfunction and fluid temperature decreased as the solid volume fraction increased. The local N~u number increased by more than 50% at low values of Φ~ (up to 0.1). This percentage decreases between 25% and 40% when Φ~ is in the range of 0.1 to 0.15. As H~a increases from 0 to 75, these percentages increase at low values of the value of R~i=1 and 10. These variations are primarily dependent on the value of the Richardson number.

Comparison of Brake Cooling System on Bus: Simulation and Evaluation of Natural vs Forced Air through Machine Learning Processing

Intense braking can cause heat accumulation that can reduce the braking system’s efficiency and damage the braking system components due to changes in material structure. The high temperature in the braking system of heavy vehicles requires an air-cooling system that produces high-pressure air. This study compares the cooling process results between natural air and forced air. CFD modeling was chosen as the method to simulate the cooling process of bus drum brakes. The CFD method works by involving a network of elements in a system called a mesh. In CFD, the mesh is a component that focuses on dividing the fluid domain into small elements to analyze fluid flow, heat transfer, and dynamic phenomena. Using a cooling process, the brake system temperature gradually decreased as the wind speed increased. The examination proved that natural air could reach the highest temperature of 168.73 °C and the lowest temperature of 63.01 °C. Meanwhile, forced air could reach the highest temperature of 73.8 °C and the lowest temperature of 30.73 °C. Statistical models and machine learning were carried out to predict the accuracy of simulation from SOLIDWORKS. The values of average temperature after the cooling process are examined by employing the Gradient Boosting algorithm with the highest accuracy of prediction (R2) value of 0.999895 in natural conditions and 0.999822 in forced conditions. Overall, forced air shows better temperature reduction than natural air. By lowering the operating temperature, drum brake systems can extend their lifespan.

Dynamic Simulation of Photothermal Environment in Solar Greenhouse Based on COMSOL Multiple Physical Fields

Solar greenhouses are essential facilities for agricultural production in northern China, where uneven internal environments pose significant challenges. This study established a numerical model of photothermal conditions in solar greenhouses. Utilizing COMSOL MultiphysicsTM, we established a microclimate model that encompasses the greenhouse exterior and the soil directly below it, without considering the crops. This model coupled multiphysical fields with fluid flow and heat transfer processes. The boundary conditions and initial values of the external environment and soil were derived from meteorological data and an efficient interpolation function method, with the time step updated every 1h. The results demonstrate that the simulated values were in good agreement with the measured values. Our findings reveal the temporal dynamics of radiation and temperature changes, as well as spatial heterogeneity, within solar greenhouses under different winter weather conditions. Additionally, the potential of integrating with other real-time monitoring and control models was discussed. This study provides a theoretical foundation for developing microclimate models and predicting photothermal environments in greenhouses.

Numerical analysis on heat transfer enhancement of Al2O3 and CuO-water nanofluids in annular curved tubes

The present investigation presents numerically the thermo-hydraulic performance of annular curved tubes in the turbulent flow region. The three-dimensional (3D) computational fluid dynamic (CFD) model was developed by using a commercial ANSYS 14.5 package to get additional insights on the thermo-hydraulic performance on a level of detail that is not always available in experiment results. The turbulent k-ε realize model was employed to examine the effect of Al2O3-water and CuO-water nanofluids on the heat transfer and fluid flow characteristics at different key design parameters. Three coil geometry shapes (including helical, spiral, and conical), five annular cross-section shapes (including circular, elliptical, square, rectangular, and triangular), and three cross-section areas were also investigated in this study. The numerical simulations were carried out at Reynolds numbers of 4700 to 26,700 and nanofluid volume concentrations, φ of 1%, 3%, and 5%, with constant wall temperature (CWT) heat transfer boundary conditions. The result showed that the addition of Al2O3 (45 nm) and CuO (29 nm) nanoparticles to water improves the heat transfer coefficient by 48.8%, 25.7%, and 8.4% and 37.1%, 20%, and 8.7%, respectively, at φ of 5%, 3%, and 1%, while the penalty of pressure drop is approximately negligible. The heat transfer rate per unit pumping power for helical design achieved 21.6% and 5.34% higher than conical and spiral designs, respectively, for the same curvature ratio, cross-section area, and coil length. Also, the circular shape achieved a higher heat transfer enhancement than elliptical, square, rectangular, and triangular shapes by 4%, 14.6%, 17.8%, and 30.1%, respectively. The maximum thermo-hydraulic performance index reached 1.68 and 1.58 for both Al2O3-water and CuO-water nanofluids, respectively, at φ of 5%.

Entropy analysis of convective nanofluid flow with Brownian motion in an annular space between confocal elliptic cylinders

Purpose This study aims to provide an in-depth analysis of entropy generation (EG) during natural convection within the annular space between confocal elliptic cylinders, with a specific focus on the influence of Brownian motion on nanofluid behavior. Design/methodology/approach A finite volume control method was used to conduct a detailed numerical analysis, examining the behavior of various nanofluids across a range of volume concentrations (2%–6%) and Rayleigh numbers. The study explores heat transfer (HT) and fluid flow mechanisms, particularly highlighting the role of nanoparticle Brownian motion in enhancing thermal conductivity. Findings The findings reveal that increased Rayleigh numbers significantly improve HT rates, while at lower Rayleigh values, EG is primarily governed by thermodynamic irreversibility. At higher Rayleigh numbers, this irreversibility plays a less dominant role in overall entropy production. Originality/value This study offers a novel perspective on the interplay between Rayleigh numbers, Brownian motion and EG, providing valuable insights for optimizing HT processes in engineering applications involving nanofluids.

Analysis of Magnetized Free Convective Flow of Casson-Type Fluid Over A Vertical Plate: A Caputo–Fabrizio Fractional Model Approach

The purpose of this investigation is to examine the impacts of fractional calculus on fluid dynamics and heat transfer of a nanofluid in drilling applications. More specifically, the study explores how free convection and electrical conductivity impact clay nanoparticles dispersed in engine oil—which is modeled as a Casson fluid—as they pass over a flat vertical plate. The key objectives are to: (1) determine the effects of memory effects at different timescales on temperature and momentum profiles via the Caputo–Fabrizio fractional derivative; and (2) analyze the consequences of varying different physical parameters such as magnetic field, Grashof number, nanoparticle volume fraction and Prandtl number. The objective of the investigation is to provide insight into controlling these parameters to optimize drilling processes. The Laplace method is applied to find solutions to the governing equations, and MathCad15 is utilized for illustrating the physical results. The results expose that the temperature and momentum fields are enhanced (at large times) when the fractional parameter is increased and both profiles show opposite behavior at small times. The heat transmission is enlarged with growing estimations of the volume fraction for clay nanoparticles, whereas the momentum field is declined by growing estimations of the volume fraction of nanoparticles. Further, the nanofluid motion declines by growing the magnetic field but accelerates by increasing the Grashof number. Further, this model has applications in engineering to optimize drilling operations, where performance and efficiency in refining depend upon controlling fluid flow and heat transmission. It can also be applied in fields where nanofluids are utilized to enhance heat transfer and fluid dynamics, such as petrochemicals, manufacturing and material engineering. Overall, this study establishes a vigorous foundation for further research and delivers a structure for exploring non-Newtonian NF systems from the perspective of magnetized-driven free convection flow.

FLUID FLOW CHARACTERISTICS IN A SHELL AND TUBE HEAT EXCHANGER WITH SWIRL BAFFLES

This paper presents a numerical investigation into the fluid flow and heat transfer characteristics of a shell and tube heat exchanger (STHeX) equipped with baffles that induces swirl flow. A Computational Fluid Dynamics (CFD) model was created to simulate the STHeX behavior, and its accuracy was confirmed by comparing it to the Bell-Delaware method results. The two sets of calculations exhibited good agreement, validating the CFD model. The velocity component of the fluid flow was analyzed both qualitatively and quantitatively. The flow patterns of eddies on the STHeX were carefully examined and their correlation with thermal performance was investigated. This study demonstrates that the swirl flow baffle geometry leads to a more turbulent flow pattern, resulting in an increase in the overall heat transfer coefficient. The findings indicate that the swirl flow baffle enhances heat transfer performance and reduces pressure drop in comparison to a conventional STHeX.

Secondary flow characteristics and their relationship with thermal performance inside the absorber under non-uniform heat flux

Under the focusing characteristics of parabolic trough solar collectors, enhancing secondary flow intensity and shifting the secondary flow vortex center towards the bottom of the absorber can extend the lifespan of the absorber and improve thermal performance. This study combines the Monte Carlo Ray Tracing method (MCRT) and the Finite Volume Method (FVM) to investigate the fluid flow and heat transfer characteristics inside the absorber under non-uniform thermal boundary conditions. The effects of inlet flow rate (Vin), inlet temperature (Tin), and protrusion structures on the secondary flow vortex position are examined. Through numerical analysis, secondary flow intensity (Se), heat transfer coefficient (h), Nusselt number (Nu), and friction factor (f) are calculated. The results show that increasing the Tin significantly enhances secondary flow intensity, thereby improving heat transfer within the absorber. Specifically, when Tin increases from 400.15 to 600.15 K, Se increases by a factor of 7.87, while h increases by 98.96%. Increasing the Vin shifts the secondary flow vortex downward, enhancing heat transfer at the bottom of the absorber. For example, when Vin increases from 100 to 200 L min−1, Se remains largely unchanged, while h increases by 44.68%. Compared to semi-cylindrical protrusions, tetrahedral protrusions are more effective at suppressing the upward shift of the secondary flow vortex, reducing velocity losses caused by fluid-wall interaction, and achieving better heat transfer enhancement. Under conditions of Tin = 500.15 K and Vin = 100 L min−1, the Nu increases by 14.6% for tetrahedral protrusions and 7.3% for semi-cylindrical protrusions, while the f increases by 12.3% and 10.9%, respectively, compared to the smooth absorber.

Thickness Profile Measurements of Acoustic Induced Maneuvering of Thin Film Evaporation

The transient and steady-state effects on the thickness profile of an extended meniscus in presence of an surface acoustic wave are reported experimentally in the nanoscale range using spectral reflectance. The fluid flow and heat transfer in the evaporating thin film region are interpreted through the changes in the thickness profile. The measurement of the steady-state thickness profile exhibits thinning of the adsorbed layer along with stretching of the evaporating thin film region in the presence of acoustic energy at different amplitudes (73.50–86.87 µm). The derived pressure difference increases for a thinner adsorbed layer, suggesting a rise in the flow driven toward the evaporating thin film region. The associated average heat flux enhances (109%) for the stretched evaporating thin film. The transmission of acoustic energy into kinetic energy in the liquid results in instability near the interline region. Subsequently, the generation of sessile droplets along the extended meniscus is observed. Further, the changes in the sessile droplets (generation diameter, mean diameter, rate of generation and heat flux) near the extended meniscus for different frequencies are analyzed. The results corroborate enhanced cooling upon application of an acoustic wave.

Preliminary Assessment of the Operational Performance of the Pb-16Li Heat Extraction System

A dual-coolant heat extraction system has been designed, developed, and operated for extraction of the heat load from molten Pb-16Li in a thermo-fluid lead lithium magnetohydrodynamic experiment. The system uses the heat transfer oil Therminol 55 as a primary coolant that extracts heat from lead lithium in a Pb-16Li/thermic fluid (TF) heat exchanger (HX). The extracted heat load is further rejected to cooling water by a TF/water HX, in which demineralized water extracts the heat load from the hot heat transfer oil. In this system, the heat transfer oil is circulated in the loop at a nominal flow rate of ~35 liters per minute (lpm) and in the temperature range of 250℃ to 270°C, while the water loop is operated at a nominal flow rate of ~30 lpm at room temperature. In the present study, the performance of the heat extraction system is tested to extract a heat load of ~24 kW continuously for the duration of ~100 h. During the experiment, the overall heat transfer coefficient, heat duty, and effectiveness of the HXs are validated with theoretical estimations. The present study discusses design and operation details of the system, along with the performance characteristics of the major components of the system.

Impact of cylinder corner modification on fluid dynamics and heat transfer: Corner cut size and cut angle

The impact of corner modifications on fluid dynamics and heat transfer characteristics of a square cylinder is numerically investigated at a Reynolds number Re = 150 (based on cylinder width W), with corner cut size C* (= C/W) = 0–0.5 and cut angle α = 0°–45°, where C is the corner cut size. The corner cut modification gradually modifies the baseline square cylinder (C* = 0, α = 0°) to a number of octagonal and hexagonal shapes and finally to a diamond cylinder (C* = 0.5, α = 45°) through a total of 64 distinct shapes. The focus is given on the dependence on C* and α of time-averaged and fluctuating flow fields around the cylinders, Strouhal numbers, fluid forces, and time-mean Nusselt numbers. Results of fluid forces and Nusselt number are also compared to those of circular cylinders at the same Reynolds number. Time-average and fluctuating fluid forces are reduced for several modified shapes compared to the baseline case, with some modifications yielding forces even smaller than those observed for the circular cylinder. Heat transfer improves for all modified shapes relative to the baseline square cylinder yet remains lower than that of the circular cylinder. The time-averaged flow fields reveal three distinct wake patterns depending on C* and α. The study identifies several shapes with improved fluid dynamic characteristics that can be applied in mechanical, civil, and environmental engineering applications.

Unified Solution of Conjugate Fluid and Solid Heat Transfer--Part II. High-Order Conjugate Heat Transfer

Unified Solution of Conjugate Fluid and Solid Heat Transfer--Part II. High-Order Conjugate Heat Transfer

Fluid motion and heat transfer in an ASTM-E659 apparatus

Fluid motion and heat transfer in an ASTM-E659 apparatus

FLUID FLOW AND THERMAL ANALYSIS OF BLOOD FLOW IN AN AUTOMATICALLY GENERATED 2D VASCULAR NETWORK FEATURING THE POROUS MEDIA-BASED OUTFLOW BOUNDARY CONDITIONS

Blood flow and thermal analyses in biological tissues are utterly important to better understand the transport phenomena in human tissues with reference to cardiovascular diseases, drug delivery, and thermal ablation. In the existing literature, there is room for new computationally lighter numerical analyses, including both fluid flow and heat transfer. This paper presents an analysis of blood thermo-fluid dynamics within an automatically generated two-dimensional (2D) vascular network, employing the constrained constructive optimization algorithm for structure generation, the porous media assumption for outflow boundary conditions, and heat transfer coefficient analysis for terminal vessels. Through comparisons with theoretical results, the model demonstrates mathematical robustness. Results of the simulations show that blood velocity decreases with increasing number of bifurcations, offering quantitative insights into its decay in magnitude and on its impact on heat transfer. Blood temperature rises in vessels with low velocity, hindering its cooling effects in the surrounding tissues. The study highlights the influence of bifurcation levels on heat transfer coefficient reduction, suggesting longer pathways and time periods to reach high temperature within the blood vessels, due to the cooling effect of pulsating blood flow in larger vessels. The quantitative analysis of the heat transfer coefficient and Nusselt number provides insights into heat transfer between blood and the surrounding tissue, offering also valuable information for numerical bioheat models in thermal therapy simulations.

MATHEMATICAL RANDOM GENERATION OF METAL FOAM AND NUMERICAL 3D SIMULATIONS OF HEAT TRANSFER IN A HYBRID SOLAR COLLECTOR

This study explores numerically the heat transfer of a hybrid solar collector. The collector is a Cartesian channel partially filled with randomly generated metal foam (MF). The channel is subjected to solar irradiation, and through it the air flows from the side due to natural convection or ventilation. To generate the MF, random Gaussian correlations are used. This technique allows spatial control of density, permeability, and porosity, whose values are also theoretically accessible. To solve the equations of fluid dynamics and heat transfer, a finite volume multigrid scheme is used. An energy equation is framed on the two-temperature model, and a momentum equation is that of the clear fluid case, since the pores' volumes are largely greater than the ver in the porous media. The velocity as well as temperature fields are discussed for different pertinent parameters, and mathematic correlations are given between the Nusselt, porosity, Richardson, and Reynolds numbers. It is found that heat transfer is improved with increasing metal foam blocks and with decreasing porosities for different Reynolds numbers, however it decreases with Richardson number. It is also found that the two-temperature model is more realistic than models with averaged properties, and gives a wide range of perspectives thanks to the possibility of carrying out numerical and experimental investigations on the same MF model: randomly generated and printable in 3D.