Convective Heat Transfer Rate Research Articles

Unsteady nonlinear mixed convective flow of nanofluid over a wedge: Buongiorno model

The article deals with 2D unsteady nanofluid flow past a vertical wedge along with nonlinear mixed convection. Brownian diffusion and thermophoresis effects are considered to model nanofluid flow. Convenient transformations are assumed to change the coupled nonlinear governing PDEs into ODEs. To analyze the problem, the solutions of transformed equations are numerically achieved via ‘bvp4c’, a MATLAB approach. Graphical presentation is adopted to see the impact of various influential parameters. Results reveal that nonlinear temperature and concentration convection parameters exhibit the same impact for velocity, temperature and concentration profile, though nonlinear convection parameter for temperature is more impactful than concentration. Velocity overshoot is observed for assisting flow situations. In nonlinear mixed convection flow, skin-friction coefficient, heat and mass transfer rates prominently change for favorable and adverse pressure gradient conditions.

Parametric analysis of artificial rib roughness for the enhancement of thermohydraulic performance of solar air heater: A review

Solar air heaters (SAHs) convert incident solar radiation to thermal energy on an absorber plate. Smooth absorber plates have a low convective heat transfer rate in traditional ducts. Artificial rib roughness is applied to the bottom sides of the absorber plate in order to improve heat transfer in SAHs. However, when the rib roughness is employed over the absorber plate of the airflow side, it also increases the pressure loss due to friction. The purpose of this work is to provide researchers with a scientific perspective on the geometry, structure of ribs, flow directions, and laminar zone in order to maximize heat transfer and reduce friction. This review article discusses different roughness parameters, various artificial roughness geometries, and thermohydraulic performance. Nusselt number and friction factor correlations have also been incorporated in this review article which is developed by various scientists based on their respective experimental results for various roughness parameters. The paper also provides a thorough analysis of current research, summarises prior developments, and speculates on potential future routes for developing new heat transfer systems. Furthermore, this review paper will assist researchers and academics in developing a sound understanding of the effects of roughness on the absorber plate.

Design assessment of a horizontal shell and tube latent heat storage system: Alternative to fin designs

In the present study, the charging and discharging performances of a horizontal shell and tube latent heat storage (LHS) system are analysed. The effective heat capacity approach is adopted to develop a numerical model using sodium nitrate as the phase change material (PCM) and air as the heat transfer fluid (HTF). The study proposes design alternatives to conventional shell and tube LHS systems by varying the PCM volume distribution and the surface area of heat transfer along the length. A novel design methodology is proposed, wherein, the outer shell of the LHS system is optimized into a cone and the cross-section of the HTF tube is varied. Based on the optimal shell dimensions, seven different designs having cylindrical/converging conical/diverging conical shells and cylindrical/converging/diverging cross-sections of the inner HTF tube are developed for a fixed PCM volume and heat transfer surface area. The LHS system with converging shell and converging cross-section HTF tube is found to have optimal performance with 37% and 47.3% reduction in charging and discharging times over the conventional cylindrical shell and tube system. The system is also compared with a fin and non-finned cylindrical shell and tube system at different inlet charging and discharging temperatures. The melting and solidification contours and melt fraction plots show a more uniform rate of natural convection and conduction heat transfer along the length of the proposed optimal design which is projected as an alternative to longitudinal fin design due to similar charging/discharging performances.

Mathematical modeling of porous combustion under various working conditions

Porous burner offers attractive advantages including high combustion performance and power ranges, and approximately zero pollutant emission. In this paper, the thermal behavior of premixed flame of a CH4/air mixture in a porous burner was examined using an unsteady In-house CFD code with an appropriate single reaction mechanism. In this regard, to solve the transient term, an implicit scheme was used, and displacement terms were solved using the upwind methodology. Additionally, the discretized central difference was employed to solve diffusion terms. At first, the results were compared with available published data, and then the influences of various working parameters, including solid matrix conductivity and volumetric heat transfer coefficient, were investigated on the flame structure. Thermal performance of the burner is studied by varying relevant parameters within a practical range. The predicted gas temperature profile near the reaction zone is much broader than that in an adiabatic premixed flame. The effect of volumetric heat transfer coefficient on the temperature profile is investigated. The local gas temperature decreases in the reaction zone and the solid temperature increases in the preheat zone with an increase in convective heat transfer. Also, the corresponding local convective heat transfer rates for different values of volumetric heat transfer coefficient are calculated and compared. Simulation results also indicate that increasing the effective thermal conductivity of the solid will decrease the solid phase temperature downstream of the flame location. Due to high temperature gradients in the solid matrix, its effective thermal conductivity has a significant impact on the conductive heat transfer rates.

Physical–numerical parameters in laminar simulations of natural convection on three-dimensional square plates

PurposeThe purpose of this study is to analyze the influence of the main physical–numerical parameters in the computational evaluation of natural convection heat transfer rates in isothermal flat square plates in the laminar regime. Moreover by experimentally validate the results of the numerical models and define the best parameter settings for the problem situation studied.Design/methodology/approachThe present work is an extension of the study by Verderio Junior et al. (2021), differing in the modeling, results analysis and conclusions for the laminar flow regime with . The analysis of the influence and precision of the physical–numerical parameters: boundary conditions, degree of mesh refinement, refinement layers and κ – ω SST and κ – ε turbulence models, occurred from the results from 48 numerical models, which were simulated using the OpenFOAM® software. Comparing the experimental mean Nusselt number with the numerical values obtained in the simulations and the analysis of the relative errors were used in the evaluation of the advantages, restrictions and selection of the most adequate parameters to the studied problem situation.FindingsThe numerical results of the simulations were validated, with excellent precision, from the experimental reference by Kitamura et al. (2015). The application of the κ – ω SST and κ – ε turbulence models and the boundary conditions (with and without wall functions) were also physically validated. The use of the κ – ω SST and κ – ε turbulence models, in terms of cost-benefit and precision, proved to be inefficient in the problem situation studied. Simulations without turbulence models proved to be the best option for the physical model for the studies developed. The use of refinement layers, especially in applications with wall functions and turbulence models, proved unfeasible.Practical implicationsUse of the physical–numerical parameters studied and validated, and application of the modeling and analysis methodology developed in projects and optimizations of natural convection thermal systems in a laminar flow regime. Just like, reduce costs and the dependence on the construction of experimental apparatus to obtain experimental results and in the numerical-experimental validation process.Social implicationsExclusive use of free and open-source computational tools as an alternative to feasible research in the computational fluid dynamics area in conditions of budget constraints and lack of higher value-added infrastructure, with applicability in the academic and industrial areas.Originality/valueThe results and discussions presented are original and new for the applied study of laminar natural convection in isothermal flat plate, with analysis and validation of the main physical and numerical influence parameters.

Fluid flow characteristics and convective heat transfer improvement on a gas turbine blade

AbstractThe flow field features and heat transfer enhancement are investigated on a gas turbine blade by applying the jet impingement cooling method. The distribution of the flow field and the Nusselt number (Nu) was determined on the targeted surface in the cooling channel. The injection holes of different shapes, such as circular, square, and rectangular were considered. The Reynolds numbers (Re) of the airflow in the range of 2000–5000 and aspect ratios of 0.5–2 were particularly focused. The flow vortices and recirculation in the cooling channel and their influence on the heat transfer enhancement were analyzed in detail under different airflow and geometric conditions. Decreasing the ratio of the distance between jet‐to‐target plate to the diameter of the jet orifice (H/d) increased the heat transfer rate and produced high‐intensity vortices and recirculation zones. It was noticed that the formation and generation of vortices and recirculation have important effects on the convective heat transfer rate at the impingement surface. Local Nusselt number, formation of complex vortices, and airflow recirculation in the cooling channel decreased with the increase in the distance between the jet hole and the targeted surface. It was found that with the increase in the Reynolds number of the jet, heat transfer between cold airflow and the targeted surface increased. Moreover, it was observed that the cooling performance of the round and square jet holes was better than the rectangular holes.

Thermal insulation design of subsea vertical X-mas tree

Temperature drop is commonly observed in subsea vertical X-mas trees during shutdown. The presence of a huge temperature difference between internal crude oil and external seawater can cause severe equipment degradation of the oil flow channel (e.g., hydrate precipitation), which can block the oil flow channel and interrupt the production process. The most vulnerable parts of a subsea vertical X-mas tree tend to be components with high convective heat transfer rates, such as production modules and short joints. We proposed an innovative approach for the insulation design of underwater equipment under a shutdown condition. First, we obtained a heat transfer analysis of the tree under working conditions through computational fluid dynamics to ascertain the initial temperature condition for an unsteady-state analysis. Second, we investigated the unsteady heat transfer characteristics of the tree with an insulation layer in the shutdown state and derived the relationships between insulation duration and thickness by data analysis. We used data analysis to identify the relationship between insulation duration and thickness. Finally, we derived the empirical formula of insulation thickness for underwater equipment given the effect of environmental factors on the heat preservation effect. We performed the experiment with an oil pipeline, and the results showed that the internal oil of the equipment did not hydrate within 8 h under the shutdown condition with insulation layers.

STUDY AND VALIDATION OF MESHES IN TURBULENT ISOTHERMAL PROBLEMS OF NATURAL CONVECTION IN FLAT PLATES

The study of natural convection on flat plates is of great interest in the areas of Engineering, both for the simplicity of geometry and the wide variety of applications. In the study and definition of a numerical model, an ideal mesh configuration is the one that best represents physically, with minimal numerical influence and with the lowest computational cost, the problem addressed. The influence of two mesh configurations (non-uniform staggered and entirely uniform), at different refinement levels, was studied to evaluate natural convection heat transfer rates in flat plates of AR = 5; in isothermal conditions, in turbulent regime with the κ−ω SST RANS model and using free and open-source software OpenFOAM®. The physical-numerical methodology applied, and the numerical results obtained were validated from experimental results in the literature. The non-uniform staggered mesh configuration proved to be more adequate in precision, and computational cost to the problem situation studied. The entirely uniform mesh proved to be infeasible due to the high number of elements and computational cost demanded.

Influence of fully submerged permanent magnets in the evaluation of heat transfer and performance analysis of single slope glass solar still

In this experimental study, permanent magnets with three different sizes (M-1: 32 mm inner diameter, 70 mm outer diameter and 15 mm thick, M-2: 25 mm inner diameter, 60 mm outer diameter and 10 mm thick, M-3: 22 mm inner diameter, 45 mm outer diameter and 9 mm thick) are fully submerged in the single-slope glass solar still. The performance of magnetic solar stills (MSS) with three different sizes at 2 cm depth water to ensure that magnets are fully submerged is compared with conventional solar still (CSS) at the location 17.3850°N, 78.4867°E. Tiwari model is adapted to calculate the heat transfer coefficients (HTC), internal and exergy efficiencies. MSS with M-1, M-2 and M-3 significantly enhanced the convective, radiative, and evaporative heat transfer rate for the 2 cm depth of water. This is due to the desired magnetic treatment of water, which reduces the surface tension and increases the hydrogen bonds. The MSS's total internal HTC, instantaneous efficiencies led CSS by 25.52%, 28.8%, respectively, with M-1. Having various magnetic fields due to different magnets sizes increases MSS's exergetic efficiency by 33.61% with M-1, 33.76% with M-2, and 42.25% with M-3. Cumulative yield output for MSS with M-1, M-2, and M-3 is 21.66%, 17.64%, 15.78% higher than CSS. The use of permanent magnets of different sizes in the MSS is a viable, economical and straight forward technique to enhance productivity.

Physical–numerical parameters in turbulent simulations of natural convection on three-dimensional square plates

PurposeThis paper aims to study, experimentally validate and select the main physical and numerical parameters of influence in computational numerical simulations to evaluate mean heat flux by natural convection on square flat plates.Design/methodology/approachSeveral numerical models were built to study the influence of physical and numerical parameters about the predictions of the natural convection heat transfer rates on the surface of a flat plate with aspect ratio = 1, in isothermal conditions, turbulent regime and using the free and open-source software OpenFOAM®. The studied parameters were: boundary conditions (using or not using wall functions in properties ε, κ, νt and ω), degree of mesh refinement, refinement layers and turbulence models [κ – ε and κ – ω Shear Stress Transport (SST)]. From the comparison of the values of the mean Nusselt number, obtained from numerical simulations and literature experimental results, the authors evaluated the precision of the studied parameters, validating and selecting the most appropriate to the analyzed problem situation.FindingsThe validation and agreement of the numerical results could be proven with excellent precision from experimental references of the technical scientific literature. More refined meshes with refinement layers were not suitable for the studies developed. The κ – ε and κ – ω SST turbulence models, in meshes without refinement layers, proved to be equivalent. Whether or not to use wall functions in turbulent boundary conditions proved to be irrelevant as to the accuracy of results for the problem situation studied.Practical implicationsUse of the physical and numerical parameters is studied and validated for various applications in natural convection heat transfer of technology and industry areas.Social implicationsUse of free and open-source software as a research tool in the Computational Fluid Dynamics (CFD) area, especially in conditions without large financial resources or state-of-the-art infrastructure.Originality/valueTo the best of the authors’ knowledge, this work is yet not available in existing literature.

Numerical Analysis on Convective Heat Transfer Enhancement by Using Ferrofluid

Ferrofluidconsist of nanoparticles of magnetic material. They to external magnetic field and become highly magnetic in the presence of same. Due to this property of ferrofluid, it is being used in many applications like energy harvesting, heat exchanger, electronic cooling, seal, lubrication and damping. Thermophysical properties of ferrofluid can be controlled by varying externally applied magnetic field. Addition of ferrofluid into base liquid, under the action of externally applied magnetic field, increases heat transfer rate. This paper focuses on enhancement in convective heat transfer due to addition of ferrous material in base liquid under the effect of externally applied magnetic field. As intensity of externally applied magnetic field will increase, convective heat transfer rate also increases.

Heat Transfer by Natural Convection in a Square Enclosure Containing PCM Suspensions

Research on using phase change material (PCM) suspension to improve the heat transfer and energy storage capabilities of thermal systems is booming; however, there are limited studies on the application of PCM suspension in transient natural convection. In this paper, the implicit finite difference method was used to numerically investigate the transient and steady-state natural convection heat transfer in a square enclosure containing a PCM suspension. The following parameters were included in the simulation: aspect ratio of the physical model = 1, ratio of the buoyancies caused by temperature and concentration gradients = 1, Raleigh number (RaT) = 103–105, Stefan number (Ste) = 0.005–0.1, subcooling factor (Sb) = 0–1.0, and initial mass fraction (or concentration) of PCM particles (ci) = 0–0.1. The results showed that the use of a PCM suspension can effectively enhance heat transfer by natural convection. For example, when RaT = 103, Ste = 0.01, ci = 0.1, and Sb = 1, the steady-state natural convection heat transfer rate inside the square enclosure can be improved by 70% compared with that of pure water. With increasing Sb, the Nusselt number can change nonlinearly, resulting in a local optimal value.

Experimental and numerical investigation of thermal performance in solar air heater with conical surface

The absorber plate surface modifications of a solar air heater (SAH) increase the convective heat transfer rate of the inlet air. Forced convection heat transfer of air in a SAH with a staggered arrangement of conical obstacles has been carried out experimentally and numerically at mass flow rates (0.04, 0.08, and 0.1 kg/s) under ambient conditions for the aim of to enhance the thermal efficiency and to create proper volume for heat storage material in terms of the effectiveness of the SAH. The thermal efficiency for the absorber with conical obstacles was 14.0, 14.6, and 11.8% higher than the flat absorber plate for the mass flow rates, respectively. The results show that the number of Nusselt obtained in conical surface experiments was highest for all cases tested regardless of Reynolds number. The experimental results are compared with the numerical results obtained by the CFD method. The model results indicate good agreement with the experimental results. Also, the results show that the heat transfer in front of the conical elements is high, and the back is low; in the smooth absorber, a linear velocity distribution is seen along the channel; however, in the conical surface absorber, the velocity distribution due to turbulence is very variable.

A comparative study on convective heat transfer in indoor applications

Analytical solutions may not always be applicable in the calculation of the turbulent flow convective heat transfer rate, unlike the radiative and the conductive ones. Therefore, experimental correlations on convective heat transfer coefficient have been developed in enclosures. Convective heat transfer in a cavity is classified as natural, forced, and mixed convection on the basis of the driving forces (buoyant or mechanical). In recent years, there has been an increasing interest in the mixed convection, particularly in cooled ceiling – displacement ventilation indoor applications. It seems this interest is tending to increase while contamination of viruses and energy saving are growing as health and environmental concerns worldwide. Hence, the reasons behind the interest in mixed convection applications have been investigated along the paper.This comparative study seeks to explain the progress of convective heat transfer at indoor applications by reviewing mostly experimental correlation studies in time. The mixed convection has not been widely studied experimentally in indoor applications in comparison to natural and forced convection. Therefore, this study is devoted to indicate this gap in the literature on this issue and it includes all convection types with a wide and up-to-date review, descriptions, explanations, and comparisons, as well. Moreover, almost all empirical correlations on the topic are given in tables in detail. It can be concluded that general correlations for mixed convection applications is needed. Correlations related to radiant floor cooling applications are nearly non-existent. Additionally, more experimental studies are required for various split air conditioner cases. These gaps in the literature are unveiled and comparison of applications with various convection types have been made as a first comparative study in the literature.

Enhancement of channel-flow convection heat transfer using piezoelectric fans

This paper presents the experimental and numerical studies on the convection heat transfer enhancement of air channel flow using a piezoelectric fan. Significant improvements in channel convection heat transfer are observed experimentally by operating the piezoelectric fan at 90.3 Hz under various channel flow velocities. The peak-to-peak displacement of the piezoelectric fan increases up to 11.8 mm, which covers 53% of the channel width. The piezoelectric fan is tested at three different relative locations from a heated surface in the channel. As a result, the piezoelectric fan, aligned at the front-end of the heated surface, achieves a maximum heat transfer enhancement of 102% at the channel Reynolds number of 603. The numerical study is performed using ANSYS Fluent to investigate complex flow fields created by the piezoelectric fan and their impact on the thermal responses of the heated surface in the channel. The Q-criterion analysis is used to identify vortical structures generated from the piezoelectric fan and understand their transport characteristics. It is found that the formation, propagation, and impinging dynamics of vortical structures are the significant factors that affect the convective heat transfer rate of the heated surface in the channel.

Numerical Investigation of Electrohydrodynamic Forced Convection Heat Transfer from a Circular Cylinder

In this study, the heat transfer by forced convection over a circular cylinder was studied numerically in the presence of an electric field and the effects of the installation angle of discharge electrode, wire–cylinder spacing and electrohydrodynamic (EHD) number were also investigated. The results showed that the location of discharge electrodes has a considerable effect on changing the flow pattern, velocity profile, and scheme of thermal boundary layer. It was found that the corona wind can increase the local and average Nusselt numbers. However, in some cases, the EHD actuator had a negative effect on the convective heat transfer rate due to the interaction between the corona wind and the main flow. In addition, EHD enhancement is more effective at high EHD numbers and low wire–cylinder spacing values. Based on the results, a maximum enhancement of 42.1% was observed in the average Nusselt number using the EHD technique. Finally, the EHD efficiency was calculated as an outstanding result to assess the performance of the EHD actuator. The results revealed that although the EHD is more effective at higher electric field strengths in terms of thermal enhancement, it is not cost-effective because of the high power consumption.

Numerical simulation of mixed convection flow and heat transfer in the lid-driven triangular cavity with different obstacle configurations

There are several industrial applications, particularly lid-driven walls, for mixed convection heat transfer characteristics across various cavities. In order to increase the effectiveness of cooling, electrical, electronic and nuclear devices and to monitor the fluid flow and heat exchange of solar thermal installations and thermal storage, such a problem requires further investigation. The main goal of this profound study is to examine the convective heat transfer nature of thermal convection on Newtonian MHD fluid in a lid-driven triangular cavity subjected to heating by a thick triangular wall, including the effects of varying Richardson number, Reynolds number, Hartmann number, and cold circular obstacle. Graphical illustration shows that the upper wall having temperature Th is moving from left to right, whereas inclined sidewalls are adiabatic. Further, a cold circular obstacle containing temperature T∗∗ is placed near the left and right wall of the triangular cavity with T∗∗ < Th. The governing flow equations are tackled by the Galerkin Finite Element Method (GFEM) to prepare the desired results. Velocity contours, isotherms and heat transfer rates demonstrate flow kinematics and heat transport processes. The high estimate of the Reynolds number has been found to provide a decent rate of convective heat transfer to a good liquid progression. For a higher number of Grashof, which achieves the maximum convection intensity, it is checked that natural convection dominates within the convection system. The Richardson number is a rising function of the Nusselt number, while the opposite trend is observed due to the rise in the Hartmann number.

Double‐diffusive natural convective stream due to moving vertical plate with nonlinear thermal radiation and Newton's boundary constraint

AbstractThis article investigates the heat and mass transmission of the double‐diffusive convective stream over a moving vertical plate with nonlinear thermal radiation and newton boundary conditions. The governing partial differential equations of the stream, heat, and concentration profiles were transformed into a system of nonlinear ordinary differential equation by utilizing resemblance transformation. This system was then resolved numerically by applying the fourth order Runge‐Kutta method with most efficient shooting technique. The effect of convection, buoyancy ratio, nonlinear thermal radiation, Prandtl number, Rayleigh number and Schmidt number are graphically scrutinized. The numerical results are obtained for velocity, temperature, and concentration profiles. It is found that when the velocity profile increases, heat and mass transfer rate decreases with an increase in the parametric value of buoyancy ratio parameter. It is found that the effect of nonlinear thermal radiation stabilizes the thermal boundary layer growth. The skin friction coefficient decreases with an increase in Prandtl number. However, the Nusselt number increases with an increase in the local convective heat transfer rate. The present results are very much promising, and further, there is a very good agreement of results when compared with earlier published results for some limiting conditions.

The effect of magnetic field on the performance improvement of a conventional solar still: a numerical study.

Due to growing demand for potable water, the improvement of fresh water production systems such as conventional solar stills is a crucial issue. Conventional solar stills are one of the simplest methods of the production of fresh water from saline water; however, they are fairly low-performance devices. Since oxygen is a paramagnetic gas, the humid airflow in a conventional solar still can be controlled by an externally imposed magnetic field. Therefore, this paper presents the effect of magnetic field on the performance improvement of a conventional solar still as a novel technique. The governing equations of the problem are discretized by the finite volume method. The impacts of the applied magnetic field arising from a multilayer solenoid on the streamlines patterns, temperature and mass fraction contours, the production rate of water ([Formula: see text]), and the average heat transfer rate (Nu) are presented at five specified times (cases). The influences of important factors such as intensity (0≤NI≤100000) and location of the magnetic field (Xc=0.15, 0.49, and 0.83) on the heat and mass transfer rates are explored. It is found that the production rate of water and heat transfer rate are increasing functions of magnetic field intensity. For the applied magnetic field with NI = 105and Xc = 0.83m, water productivity and convective heat transfer rate can be increased by about 43%, 38%, 41%, 40%, and 48% for cases 1, 2, 3, 4, and 5, respectively.

Viscous dissipation and joule heating effects on forced convection power law fluid flow through annular duct

Here we numerically analyse the effects of viscous dissipation and Joule heating on forced convection heat transfer rate of electrically conducting magnetohydrodynamic, ( MHD) power law fluid flow through annular duct. Mathematical model is formulated for constant properties power law fluid with steady, incompressible and laminar fully developed flow assumptions. Heat transfer results are determined by taking constant heat flux with peripheral wall temperature “known as H1 thermal boundary condition” at the solid walls of the channel. It has been observed that the effect of viscous dissipation reduces due to enhance damping magnetic field effect by increasing the value of Hartman number, Ha, especially in the case of shear thickening fluids.