Heat Transfer In Laminar Flow Research Articles

Heat transfer analysis of nanofluid flow with entropy generation in a corrugated heat exchanger channel partially filled with porous medium

AbstractHeat exchanger research is mainly exploited to develop and optimize new engineering systems with high thermal efficiency. Passive methods based on nanofluids, fins, wavy walls, and the porous medium are the most attractive ways to achieve this goal. This investigation focuses on heat transfer and entropy production in a nanofluid laminar flow inside a plate corrugated channel (PCC). The channel geometry comprises three sections, partially filled with a porous layer located at the intermediate corrugate channel section. The physical modeling is based on the laminar, two‐dimensional Darcy–Brinkman–Forchheimer formulation for nanofluid flow and the local thermal equilibrium model for the heat equation, including the viscous dissipation term. Numerical solutions were obtained using ANSYS Fluent software based on the finite volume technique and the appropriate meshed geometries. The numerical results are validated with theoretical, numerical, and experimental studies. The simulations are performed for CuO–water nanofluid and AISI 304 porous medium. The coupled effects of porous layer thickness (δ), Reynolds number (Re), and nanoparticle fraction (φ) on velocity, streamlines, isotherm contours, Nusselt number (Nu), and entropy generation (S) are analyzed and illustrated. The simulation results demonstrate that heat transfer enhancement in clear PCC can be achieved using a porous layer insert. For the porous thickness range of [0.1–0.6], the corresponding range of average Nusselt number increase is [35.7%–176.9%], and the average entropy generation is [105.4%–771.9%]. The effect of the Reynolds number is more important in a porous duct than in a clear one. For δ = 0.4 and φ = 5%, the increase of Re in the range of [200–500] induces an increase in average Nusselt number in the range of [80.9%–108.4%] and average entropy in [222.9%–309.1%] comparatively to clear PCC. The effect of φ is practically the same for porous and clear channels. For φ = 5%, the increase on average Nu is about 9%, and entropy generation is 5%. Accordingly, important improvements in heat transfer in PCC can be achieved through the combined effect of flow Reynolds number and porous layer thickness.

Laminar flow and convective heat transfer of ferrofluid in a tube under oscillating magnetic fields: Effect of magnetic phase shift

In this study, laminar flow and forced convective heat transfer of water-based ferrofluids flowing through a uniformly heated pipe are experimentally investigated under the presence of phase-shifted oscillating magnetic fields. To investigate the effect of phase shift on heat transfer, electromagnets are positioned along the tube, and oscillating magnetic fields are applied with various phase shift angles between opposing magnetic poles. Experiments are conducted for different Reynolds numbers (400 to 1000), magnetic field frequencies (0 Hz, 1 Hz, and 5 Hz), phase shift angles (0°, 90°, and 180°), and nanoparticle volume fractions (0.5 % and 1 %). For each parameter set, local and average Nusselt numbers, as well as pressure drop values, are determined, and the effect of applied magnetic fields on the heat transfer rate is extensively discussed. Results showed that, applying an external magnetic field resulted in significant enhancements in the forced convective heat transfer of ferrofluid. Under an oscillating magnetic field with 0° phase shift, maximum of 40 % and 20.6 % enhancements were observed in local and average Nusselt numbers respectively under the investigated parameters. Furthermore, applying oscillating magnetic fields with a phase shift between opposing poles caused significant fluctuations in the fluid, led to remarkable improvements in convective heat transfer rates. For 90° and 180° phase shifts, enhancements in local and average Nusselt numbers were observed to increase up to 73 % and 36 %, respectively.

Numerical and experimental analysis of the sinusoidal heat flux source of heat transfer in laminar flow in a tube for single phase flow

Numerical and experimental analysis of the sinusoidal heat flux source of heat transfer in laminar flow in a tube for single phase flow

Enhancing Natural Convection Heat Transfer Through Dome-Shaped Nanofluid Enclosures: Two-Phase Simulation Analysis

This study utilizes numerical analysis to investigate laminar flow and natural convective heat transfer of nanofluids (NFs) within dome-shaped enclosures (DSEs). The horizontal walls of the enclosure are adiabatic, while the vertical walls on the right and left are maintained at isothermal conditions with low and high temperatures, respectively. The study focuses on examining the impact of DSEs on flow patterns and natural convection (N.C.) under varying parameters, including Rayleigh numbers (Ra), Lewis numbers (Le), enclosure inclination angles, dome angles, and buoyancy ratio number (Nr). The Prandtl number (Pr) and nanoparticle volume fraction are consistently maintained at 10 and 0.05, respectively. The governing equations have been resolved by applying the Eulerian–Eulerian two-phase model. The study reveals that the DSE significantly influences flow dynamics, leading to smoother circulation patterns that intensify convection currents. This movement of hot fluid toward cooler regions within the enclosure enhances natural convective heat transfer. Across all enclosure inclination angles, the average Nusselt number (Nu) increases with higher Ra, while the Le remains constant at 4. Significantly, due to its robust convective currents, the average Nu in the DSE with a 45° dome angle surpasses those of corresponding square and rectangular enclosures.

Enhancing heat transfer in buoyancy-driven laminar flow: a numerical investigation of heated concentric cylinders with porous fins

Enhancing heat transfer in buoyancy-driven laminar flow: a numerical investigation of heated concentric cylinders with porous fins

Laminar flow and convective heat transfer characteristics of plain and wavy wall cross confined circular cylinder

An attempt is made to identify the convective heat transfer characteristics of the plain wall (Pw) and wavy wall (Ww) cross confined circular cylinder in the laminar flow regime (20 ≤ Re ≤ 100). The study has been extended to identify the wake heat transfer characteristics for various confinements (L = 0.5D, 1D, 1.5D and 2D), such that the weaker and stronger heat transfer region in the downstream of cross-confined cylinder has been investigated. CFD solver Ansys Fluent (Version 18.0) is used for assessing the field variables, the results are analyzed using streamline plots, λ 2-criterion vortex identification method, Nusselt number and field synergy method. The wall confinement is highly significant on heat transfer, the maximum Nusselt number is observed at high confinement (L = 0.5D) for all the Reynolds number studied. The changes in Nusselt number with respect to confinements is more significant at high confinements (L = 0.5D and L = 1D), become less significant at low confinements (L = 1.5D, 2D). It is found around 73% and 50% rise in Nusselt number for the confinement height, L = 0.5D as compared to L = 1D at Reynolds number 20 and100, respectively. Besides, in order to identify the heat stagnation region in the wake, contour of zero temperature gradient along the flow direction is observed. From the contour, it is identified that more heat stagnation region in the wake of Pw confined cylinder as compared to Ww confinement which is due to the three-dimensional behavior of flow in the wake.

Enhancing heat transfer in laminar channel flow by tuning the mass distribution of a flexible reed

Recent studies have leveraged wall-mounted flexible reeds to augment heat transfer efficiency in channel flows. In this study, we demonstrate that tuning the reed's mass distribution can substantially elevate this heat transfer enhancement. Numerical simulations incorporating the fluid–structure–thermal interaction are performed to investigate the impact of mass distribution on the reed dynamics and the associated heat transfer augmentation. The results indicate that the mass distribution of the reed significantly affects its motion mode, which, in turn, critically modulates the heat transfer characteristics. The maximum thermal efficiency factor is obtained when the reed's mass is concentrated at its distal end. Furthermore, the enhancement effect of tuning reed's mass distribution on heat transfer efficiency is closely related to the bending stiffness γ. Within the range of bending stiffness considered in this study (0.02–0.14), the effect of tuning the reed's mass distribution on the thermal efficiency factor exhibits a trend of increase–decrease–increase as the bending stiffness increases. At high bending stiffness, simply tuning the reed's mass distribution can increase the channel heat flux and reduce energy loss, thereby achieving the goal of enhancing the thermal efficiency factor. At γ = 0.14, allocating the reed's mass at its distal end resulted in a notable enhancement, with a thermal efficiency factor surge of 11.1%.

Laminar Flow Heat Transfer Studies in a Twisted Square Duct for Constant Wall Temperature

Abstract: Three dimensional analysis of steady fully developed laminar flow inside twisted duct of square cross section flow area is studied for Reynolds number range of 100 – 2000 using a commercially available software. Twist ratio used are 2.5, 5, 10 and 20. Heat transfer results are generated for a uniform wall temperature case for Prandtl number range of 0.7 to 20. Maximum values for the product of friction factor and Reynolds number is observed for a twist ratio of 2.5 and Reynold number of 2000. Maximum Nusselt number is observed for the same values along with Prandtl number of 20. Correlations for friction factor and Nusselt number are developed involving swirl parameter. Local distribution of friction factor ratio and Nusselt number across a cross-section is presented. Heat transfer enhancement for Reynold number of 2000 and Prandtl number of 0.7 for twist ratio of 2.5, 5, 10, and 20 are 33 %, 18 %, 10 % and 7 % respectively. The results are significant because it will contribute to development of compact heat exchanger.

New insight into the heat transfer and pressure drop correlations for laminar and turbulent flow in a circular tube with a twisted-tape insert: A discriminated dimensional analysis

Discriminated dimensional analysis combined with the scale analysis has been implemented to obtain new correlations describing the dimensionless pressure drop as Hagen number and Nusselt number for laminar and turbulent swirl flow in a circular tube with a classical twisted-tape insert. The new insight into the phenomenon revealed that the swirl parameter Swh, as a criterion of similarity, governs the process in the entire region of swirl fluid flow in a circular tube with a classical twisted-tape insert. The validity of the analysis has been demonstrated by an excellent agreement between a large experimental data set for isothermal pressure drop and Nusselt number from many different sources with the predictions of the Hgh+−Swh and Nuh+−Swh correlations.

Heat transfer of laminar non-Newtonian fluid flow through pipes boosted by inlet swirl

Heat transfer of laminar non-Newtonian fluid flow through pipes boosted by inlet swirl

Numerical investigation for convective heat transfer of nanofluid laminar flow inside a circular pipe by applying various models

Numerical investigation for convective heat transfer of nanofluid laminar flow inside a circular pipe by applying various models

Numerical investigation of convective heat transfer of single wall carbon nanotube nanofluid laminar flow inside a circular tube

Numerical investigation of convective heat transfer of single wall carbon nanotube nanofluid laminar flow inside a circular tube

Numerical investigations on the effect of bubble injection on heat transfer of natural convection in laminar flows

AbstractIt was found that the injection of bubbles into liquid can effectively improve heat transfer efficiency, so it is important for industrial applications to investigate the effect of bubble injection on heat transfer. The effect of bubble injection on natural convective heat transfer in steady laminar flows in a vertical channel is investigated using the volume of fluid (VOF) method, and the effects of bubble diameter, Eötvös number (Eo), bubble arrangement, and bubble distance from a hot wall on the heat transfer between the hot wall and liquid are studied, respectively. The results show that bubble injection can effectively improve the heat transfer between the hot wall and liquid; an increase in bubble diameter and Eo can improve the enhancement effect of heat transfer and can expand the enhancement area of heat transfer; the closer to the hot wall a bubble is, the better the enhancement of heat transfer is; and the spacing and arrangement of bubbles also have important effects on the heat transfer between the hot wall and liquid. The comparison shows that the enhancement of heat transfer is the best for the vertical arrangement of double bubbles, which increases the local heat transfer coefficient by 3.2 times. The enhancement of heat transfer generated by bubble injection is related to the degree of disturbance of the local liquid phase caused by bubble injection. The more strongly the local liquid is disturbed, the thinner the local temperature boundary layer becomes, and the better the enhancement of heat transfer is.

Heat transfer and thermal efficiency enhancement using twisted tapes in sinusoidal wavy tubes with nanofluids: a numerical study

PurposeThe purpose of the study is to propose a novel implementation of twisted tape in sinusoidal wavy-walled tubes to enhance the rate of heat transfer without compromising thermal efficiency. The study numerically investigates the fluid flow characteristics and analyzes the effect of different geometrical configurations, including wall wave amplitude, tape twist angles and nanoparticle volume fractions, on heat transfer improvement and performance factor.Design/methodology/approachThis problem is numerically investigated using computational fluid dynamics, and the method is the finite volume method. A two-phase mixture model is used for nanofluid modeling.FindingsThe study investigated the effect of wall waviness, twisted tape, and nanoparticles on forced convective heat transfer and friction factor behavior in laminar pipe flow in three different Reynolds number regimes. The results showed that implementing twisted tape in wavy tubes significantly increased the rate of heat transfer and the performance factor, with the best twist ratio between 90 and 180°. Adding nanoparticles also enhanced heat transfer and performance factor, but to a lesser extent than wavy wall-twisted tape combinations. The study suggests selecting a proper combination of wavy wall and twisted tape at each Reynolds number to achieve an optimum solution.Originality/valueTo the best of the authors’ knowledge, the implementation of the selected passive methods in sinusoidal wavy tubes has not been studied before, and no previous studies have taken into account such a mix of heat transfer improvement techniques.

Numerical simulation of laminar flow and free convection heat transfer from an isothermal vertical flat plate

Numerical simulation of laminar flow and free convection heat transfer from an isothermal vertical flat plate

Second Law Analysis for Free Convection in an L-Shaped Cavity Filled with Nanofluid

The paper aims to analyze the effects of various Prandtl number and different nanoparticles for heat transfer and entropy generation of free convection laminar fluid flow in an L-shaped cavity filled by nanofluid. To investigate the second law characteristics of free convective flow and heat transfer from an L- shaped geometry filled by water and nanofluids (Cu-water, Ag-water, Al2O3-water), the effects of Prandtl number and various nanoparticles on the average Nusselt number, total entropy generation and Bejan number has been numerically analyzed. Isotherms, stream function and entropy generation caused by heat transfer are also presented for various Prandtl numbers and various nanoparticles. The governing equations are solved using penalty finite element method with Galerkins weighted residual technique. The results reveal that Ag-water nanofluid with highest Prandtl number gives the highest amount of irreversibility as well as rate of heat transfer. Cu-water and Ag-water nanofluid produces more irreversibilities than Al2O3-water nanofluid and base fluid. Also the results show that the Nusselt number and Bejan number increase with the increase of Prandtl number. Therefore, Prandtl number may be an important parameter for desired heat transfer increment with decreasing entropy generation in the given geometry.

Improved asymptotic expansion method for laminar fluid flow and heat transfer in conical gaps with disks rotating

PurposeThe purpose of this paper was to study laminar fluid flow and convective heat transfer in a conical gap at small conicity angles up to 4° for the case of disk rotation with a fixed cone.Design/methodology/approachIn this paper, the improved asymptotic expansion method developed by the author was applied to the self-similar Navier–Stokes equations. The characteristic Reynolds number ranged from 0.001 to 2.0, and the Prandtl numbers ranged from 0.71 to 10.FindingsCompared to previous approaches, the improved asymptotic expansion method has an accuracy like the self-similar solution in a significantly wider range of Reynolds and Prandtl numbers. Including radial thermal conductivity in the energy equation at small conicity angle leads to insignificant deviations of the Nusselt number (maximum 1.23%).Practical implicationsThis problem has applications in rheometry to experimentally determine viscosity of liquids, as well as in bioengineering and medicine, where cone-and-disk devices serve as an incubator for nurturing endothelial cells.Social implicationsThe study can help design more effective devices to nurture endothelial cells, which regulate exchanges between the bloodstream and the surrounding tissues.Originality/valueTo the best of the authors’ knowledge, for the first time, novel approximate analytical solutions were obtained for the radial, tangential and axial velocity components, flow swirl angle on the disk, tangential stresses on both surfaces, as well as static pressure, which varies not only with the Reynolds number but also across the gap. These solutions are in excellent agreement with the self-similar solution.

Heat transfer enhancement in laminar water flow through a square channel by streamwise ultrasound irradiation

This research focuses on the heat transfer of laminar water flow in a square channel under 28–120 kHz and 60–120 W ultrasonic waves, irradiated along the streamwise direction. The experiment was conducted at Reynolds numbers of 400–2000, and the uniform surface heat flux of the pipe was set as 3.1–12.9 kW/m2. In this study, ultrasound-induced streaming was investigated using a particle image velocimetry (PIV) technique, and cavitation bubbles were detected using a digital camera. From the results, the maximum heat transfer enhancement was 155% with 28 kHz and 120 W ultrasound at q = 12.9 kW/m2, Re = 400, and x/Dh = 2.58. The Nu ratio, which represents the capability of ultrasound-induced heat transfer enhancement, was also determined. A maximum Nu ratio of 2.017 was achieved with 28 kHz and 120 W ultrasound at q = 7.2 kW/m2 and Re = 400 or St = 28.16 × 104. With a relatively low Re, the poorest heat transfer was observed at St values ranging from 40 × 104 to 120 × 104. This study provides a predictive formula for the Nu ratio, with deviations ranging from 6.89 to 13.2%. Furthermore, the PIV analysis suggested that acoustic streaming of Eckart type appears under the ultrasound irradiation and its velocity enhancement effect becomes maximal under the conditions for the maximum Nu ratio. It is also confirmed that the ultrasound irradiation can enhance the nucleation of bubbles at the pipe wall; ultrasound-induced dynamics of these nucleated bubbles are expected to further disturb near-wall liquid motion and contribute to heat transfer enhancement.

Entropy Generation-Based Analysis of Laminar Magneto-Convection in Different Cross-Section Channel Filled with Ferrofluid and Subjected to Partial and Full Magnetic Fields

Heat transfer and entropy generation of laminar flow of a ferrofluid in different cross-section channel subjected to partial and full magnetic field are investigated in this study. A constant heat flux condition was applied on the external surface. The conservation equations (mass, momentum, and energy) are solved numerically via the finite volume method with a second-order precision. The effects of fully or partially applying a magnetic field with different directions and intensities on thermodynamic features, heat transfer, and entropy generation have been investigated. Analyses were carried out in four different cross-section channels, namely triangular, rectangular, circular, and elliptical. Results indicate that the circular cross-section channel provides higher heat transfer rates and lower entropy generation than non-circular cross-section channels.

Comparative studies of fluid mixing and heat transfer behaviors in a millimeter scale T-type mixer with triangular baffles

In chemical processes, fluid mixing and heat transfer efficiency are very important. To guarantee high mixing efficiency and heat transfer performance during chemical processes, we designed and embedded triangular baffle structure in millimeter-sized T-type mixers. Through Computational Fluid Dynamics (CFD) simulation and visualization experiments, the influence of triangular baffle on the heat transfer performance of mixing was studied. The results show that visualization experiment verifies the reliability of the model. Compared with T-mixer, the mixing index (M) of the T-mixer with double triangular baffle (DTB) has increased by 88.2% and the Nusselt number (Nu) has increased by 32.9%–65.2%, which shows that DTB has a good effect of enhancing mass and heat transfer. The Performance Evaluation Criterion (PEC) of DTB is within 1.22–2.43, which is 3.1%–24.5% higher than single triangular baffle (STB), indicating that DTB has good hydrothermal performance. The PEC is larger at medium to low Reynolds number (Re < 200). In addition, compared with the mixers reported in the literature, the M and Nu of T-type mixer with DTB have increased by 4.5% and 14.2%, respectively. It indicates the superiority of the structure in enhancing mass and heat transfer. The present study can be used to enhance mass and heat transfer in laminar flow.