Analysis Of Convective Heat Transfer Research Articles

Analysis of forced convective heat transfer through nanofluids around a square cylinder using Eulerian-Eulerian mixture modelling

Numerical analysis of laminar forced convective heat transfer of Al2O3-H2O nanofluids around a square bluff body is presented. An Eulerian-Eulerian approach-based mixture model, considering the sli...

Study of laminar convective heat transfer through a sinusoidal corrugated channel with a zero degree phase shift using different nanofluids

The study shows numerical analysis of convective heat transfer of a corrugated channel for laminar flow in the fully developed region. Aluminum-oxide (Al2O3) and Copper-oxide (CuO) water nanofluid is used to investigated the relation of heat transfer characteristics with corrugated geometry and nanofluid. Second-order single-phase mass, momentum, and energy equation is solved using Computational Fluid Dynamics software ANSYS 16. A 3 m long corrugated channel having a wavelength of 0.5 m is used as the physical model. The nanofluid flows at a uniform speed with a temperature of 300 K. 500 W/m2 constant heat flux is applied at the lower corrugated channel. Difference between the two channel walls is 0.5 m. The sinusoidal corrugated channel has a phase shift (φ) of 0° which ensures symmetrical corrugated area. The investigation is done for fully developed flow with an added 2.5 m of plane channel geometry at the entrance of the corrugated section which ensure fully developed flow. Different volume fractions (1%–5%) was considered here with base fluid water to increase thermal properties in a Reynolds number range of 50–100 to ensure laminar flow through the corrugated section. Pumping power, Nusselt Number and Friction factor is calculated and all the results are compared with pure water. The results reveal that CuO-water has a higher heat transfer rate and Nusselt Number which is 12.2208% more than pure water. The required pumping power is 71.78343% higher for Al2O3 water nanofluid. The study shows how the difference in thermo-fluid properties of the nanofluids affect the overall heat transfer performance when used in a sinusoidal corrugated geometry.

Experimental and numerical investigation on convective heat transfer in actively heated bundle-pipe

The present work investigates heat transfer through natural convection using a series of experiments and computational modeling using Computational Fluid Dynamics (CFD) simulations in a one-meter bundle pipe with three internal pipes. The exact complex geometry is modeled where the flow channel is reduced through a spiral groove attached to a rod inside the internal tubes which was challenging compared to the flow in circular pipes in previous studies. To support the computational modeling investigations, convective heat transfer analysis is also studied through experiments with water as the production and heating fluids. Further, simulations are carried out with water-crude oil and aqueous ethylene glycol-water as the heating mediums and production fluids, respectively. Based on the heat transfer rates estimated from experimental data and CFD simulation results for the respective tubes, a modification to an existing Nusselt number is proposed for the range of temperature and flow rates used in the experiments. The proposed model, Nui = Pri m Rai n , was validated against experimental data and a good agreement with R2 values of more than 0.94 was achieved.

Analysis of Volume Fraction and Convective Heat Transfer on MHD Casson Nanofluid over a Vertical Plate

The numerous industrial and engineering applications of Casson nanofluid is due to the superiority of its thermophysical properties. Tomatoes paste, engine oil, soup etc., are examples of Casson fluid and when nanometer-sized particles are suspended in such Casson fluid, it becomes Casson nanofluid. This paper considers a natural convective magnetohydrodynamics flow of Cu-engine oil nanofluid across a convectively heated vertical plate. The effects of self-heating of the fluid (measured by the Eckert number), internal conductive resistance to external convective resistance (measured by the Biot number), magnetic field strength, volume fraction of the nanoparticles on the temperature and velocity of mass and heat transfer of Casson nanofluid is analysed. An appropriate model governing the flow of Casson nanofluid is formulated as a system of nonlinear partial differential equations. The natural convection boundary condition is included. To solve the problem, an appropriate similarity transformation is used to reformulate the system as a system of nonlinear ordinary differential equations. The shooting technique is used to convert the boundary problem to initial value problems before Runge-Kutta method, with the Gills constants, is used to solve the reformulated problem. The results are depicted as graphs. Flow velocity is found to increase as the base fluid becomes more Casson and as nanoparticle volume fraction increases. It is also found that increasing Eckert number, Biot number and magnetic field strength causes an increase in the flow temperature.

Numerical analysis of forced convection heat transfer in a rectangular micro-channel totally filled with Ag/ water nano fluid in slip flow regime using the lattice Boltzmann method

Numerical simulation reported on heat transfer and fluid flow in a two-dimensional rectangular micro channel totally filled with Ag/water. The first –order slip/jump boundary conditions were uniformly imposed to the up and bottom walls. The governing conservation equations are translated in dimensionless form using the thermal Single Relaxation Time (T-SRT) modified Lattice Boltzmann Method (LBM) with double distribution functions (DDFs). The viscous dissipations effects are adopted into the energy equation. Effects of nanoparticle volume fraction φ, slip coefficient, B, on the flow of Nano fluid and heat transfer were studied. The results were interpreter in terms of slip velocity; temperature jump and Nusselt number. Based on the results found, it can be concluded that decreasing the values of slip coefficient enhances the convective heat transfer coefficient and consequently the Nusselt number (Nu) but increases the slip velocity at the wall and temperature jump values.

Heat Transfer Characteristics of Latent Heat Thermal Energy Storage for Floating Concentrate Solar Power Systems

The heat transfer characteristics of the latent heat thermal energy storage (LHTES) for floating concentrated solar power (CSP) systems were investigated experimentally and numerically. The understanding of natural convection heat transfer between the heat transfer fluid (HTF) and a tube bundle in the heat exchanger is important for the thermal design of the LHTES. As a primitive study, the analytical model of natural convection heat transfer was developed between the HTF and the tube bundle in the heat exchanger of LHTES. In this study, D-mannitol was used as the HTF for the LHTES. To simplify the tube bundle of the heat exchanger, a heated cylinder was installed in the liquid D-mannitol. In the experiment, the average temperature of the cylinder and the heat flux were measured, and the heat transfer coefficient under the natural convection was obtained. Meanwhile, the numerical analysis of natural convection heat transfer was conducted using the commercial computational fluid dynamics (CFD), PHOENICS. The temperature and velocity profiles around the heated cylinder were obtained in the numerical simulation. The heat transfer coefficient was compared with the author’s experimental data. The numerical result was in good agreement with the measured heat transfer coefficient.

Evaluation of radiative and convective heat transfer analysis for the human body in high temperature sauna

Evaluation of radiative and convective heat transfer analysis for the human body in high temperature sauna

Thermal convection and entropy generation of ferrofluid in an enclosure containing a solid body

PurposeThis study/paper aims to deal with thermal convection and entropy production of a ferrofluid in an enclosure having an isothermally warmed solid body placed inside. It should be noted that this research deals with a development of passive cooling system for the electronic devices.Design/methodology/approachThe domain of interest is a square chamber of size L including a rectangular solid block of sizes l1 and l2. Thermal convection of ferrofluid (water–Fe3O4 nanosuspension) is analyzed within this enclosure. The solid body is considered to be isothermal with temperature Th and also its area is L2/9. The vertical borders are cold with temperature Tc and the horizontal boundaries are adiabatic. The flow driven by temperature gradient in the cavity is two-dimensional. The governing equations, formulated in dimensionless primitive variables with corresponding initial and boundary conditions, are worked out by using the finite volume technique with the semi-implicit method for pressure-linked equations algorithm on a uniformly staggered mesh. The influence of nanoparticles volume fraction, aspect ratio of the solid block and an irreversibility ratio on energy transport and flow patterns are examined for the Rayleigh number Ra = 107.FindingsThe results show that the nanoparticles concentration augments the thermal transmission and the entropy production increases also, while the augmentation of temperature difference results in a diminution of entropy production. Finally, lower aspect ratio has the significant impact on heat transfer, isotherms, streamlines and entropy.Originality/valueAn efficient numerical technique has been developed to solve this problem. The originality of this work is to analyze convective energy transport and entropy generation in a chamber with internal block. To the best of the authors’ knowledge, the effects of irreversibility ratio are scrutinized for the first time. The results would benefit scientists and engineers to become familiar with the analysis of convective heat transfer and entropy production in enclosures with internal isothermal blocks, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

Conjugate forced convection transient flow and heat transfer analysis in a hexagonal, partitioned, air filled cavity with dynamic modulator

Background– Forced convection heat transfer in a cavity is of great importance due to its strong relevance to the practical aspects. Most of the studies focus on this topic from a steady perspective. But adding a flow modulator enhances a system's thermodynamic performance and makes such a system more realistic and widens the field of application. Such studies are unsteady and often quite expensive. As a result, only a few literatures are available with very idealistic geometric configuration and boundary conditions. Methodology– Two-dimensional unsteady continuity, momentum and energy equations are used for the mathematical modeling of the problem incorporating the Boussinesq approximation. A free triangular discretization scheme is adopted to solve the moving mesh problem by formulating the Arbitrary Lagrangian Euler (ALE) finite element approach. Parameters– Numerical studies are carried out for a fixed Prandtl number (Pr = 0.71) and fixed geometry of the rotating blade while varying the other parameters i.e. Rayleigh number, Reynolds number and Biot number. This dynamic boundary problem encompasses a wide range of parameters i.e. (100 ≤ Re ≤ 103), (103 ≤Bi ≤ 104) and (104 ≤ Ra ≤ 107) to evaluate the thermodynamic behavior of the thermo-fluid system. External flow condition is taken into consideration in terms of Biot number. Effects of these parameters are visualized through streamlines, heatlines, spatially average Nusselt number evaluated on the heated surface and system effectiveness. Objective– Present computational study focuses on the transient analysis of the conjugate forced convection flow and heat transfer characteristics in a hexagonal, air filled cavity. This cavity is equipped with a floor heater of constant heat flux under the rotational influence of an adiabatic flow modulator. And the blade is placed in the central position of the cavity which is rotating in the clockwise direction. Also, the whole computational domain is composed of four different domains, one convective domain and three solid domains. The solid domains are made of brick and glass as per their practical aspects. Findings– A Fast Fourier Transform (FFT) analysis is presented to comprehend the thermo-oscillating system response. FFT plots indicate that for all of the cases the fundamental frequency of the system response conforms to the blade frequency. Moreover, present numerical results show that the heat transfer effectiveness has an inverse relationship with the Biot and Rayleigh numbers while improves significantly with the increase of Reynolds number and reaches a critical state for Recr = 650. Higher Reynolds number also attenuates the degree of power spectrum. Conclusion– To attain a higher heat transfer effectiveness the thermo – fluid system should be operated at low Rayleigh number with higher Reynolds number.

OVERLAPPING MULTI-DOMAIN SPECTRAL METHOD FOR NON-DARCIAN MIXED CONVECTION CHEMICALLY REACTING FLOW OF MICROPOLAR FLUID OVER A FLAT PLATE IN A POROUS MEDIA

An efficient overlapping multi-domain spectral method is presented and used in the analysis of a two-dimensional steady laminar MHD mixed convection flow, heat and mass transfer over a vertical flat plate embedded in a porous medium. The effect of chemical reaction, thermal radiation, heat source/sink and other parameters influencing the flow has been analyzed by imposing magnetic force transverse to the plate in a non-Darcy porous medium with constant wall temperature and concentration conditions. The flow equations are expressed in dimensionless form and solved using overlapping multidomain bivariate spectral local linearization method (OMD-BSLLM). An analysis of the convergence and accuracy of the OMD-BSLLM is given using error norms and residual errors. Comparisons with previously published work for special cases of the problem are performed and excellent concurrence is found; hence reliable results are being presented. The influence of certain parameters on the fluid properties and flow characteristics is analyzed. The skin friction, heat and mass transfer coefficients are presented for the concentrated flow and the turbulent boundary layer flow. The flow characteristics are found to be smaller for turbulent boundary layer flows than concentrated particle flows. This type of flow has an application in catalytic and chromatographic reactions, packed absorption and distillation towers.

Analysis of Laminar Convective Heat Transfer Over Structured Non-Wetting Surfaces

Structured non-wetting surfaces provide alternating no-slip and partial slip boundary conditions to the fluid flow which, in turn, affects the convective heat transfer performance over the surfaces. In this paper, an analytical model is developed for the interfacial Nusselt number, the overall Nusselt number and a thermal hydraulic performance factor for fluid flow in a cylinder patterned with structured non-wetting surfaces, for the two cases of uniform wall heat flux and uniform wall temperature. In addition, by considering the stability of the Cassie state of wettability and its transition to the Wenzel state for flow over superhydrophobic surfaces, the present model overcomes certain limitations of the previously reported studies in the literature. Based on the analytical formulations and the stability constraints, the present paper provides optimum design maps for tailoring structured non-wetting surfaces for maximizing convective heat transfer and the combined thermal-hydraulic performance in applications. Use of the design maps on example cases is also discussed. It is shown that the use of structured non-wetting surfaces is most effective for low Reynolds numbers and/or small cylinder radius.

Numerical simulation and analysis of natural convective flow and heat transfer of nanofluid under electric field

To study the effect of electric field on the natural convective heat transfer enhancement mechanism of nanofluid, numerical study was carried out by the lattice Boltzmann method (LBM). The physical model and boundary conditions were established based on experiments. The velocity and temperature distributions with various conditions were compared. The electric field forces on nanoparticle were also discussed. Simulation results reveal that electrophoretic force plays the most important role in the motion of the nanoparticle. The simulation values are in good agreement with the experimental results. Moreover, the electric field forces reform the velocity field and temperature field generated by natural convection. The local thermal conductivities of nanofluid are improved by the local electric field. Besides, to reveal the interaction between natural convection and EHD effect, a dimensionless number called electric convection number and fitting equations are proposed and analyzed. In addition, movements of nanoparticle and basefluid under electric field are inverse, which is beneficial to the stability of nanoparticle in the basefluid.

Analysis of convective heat transfer over a square cylinder with rounded corners under steady flow regime at low Reynolds number

This work deals with the numerical simulation of square cylinder with different rounded corners and numerical analysis of convective heat transfer is studied, here emphasis is being laid on both type of flow regime i.e. unsteady flow regime and steady flow regime i.e. between 40 ⩽ Re.⩽ 160 and Pr is kept as 0.7 and thus the finding suggests that the heat transfer increases significantly with rounded corners in square cylinder.

Numerical simulation of heat transfer in a large room with a working gas infrared emitter

The article presents a new approach to determining the main characteristics of the thermal regime in the buildings and structures heated by the gas infrared emitters, based on the analysis of convective heat transfer in the air and thermal conductivity in the enclosing structures. The authors have considered a mathematical model of turbulent heat transfer in the framework of the standard k-e model under radiant heating conditions. The simulation was carried out for a large room with an approximation to the real operating conditions of an industrial facility. The options for heating an empty room and the room with an object were considered.

Thermophysical properties of Maxwell Nanofluids via fractional derivatives with regular kernel

The researchers have diverted their mind to improve the thermophysical properties of convective heat transfer analysis. The studies on nanofluids have been reported because these systems display an anomalous enhancement of convective heat transfer. In this paper, we made a comparative analysis of Maxwell nanofluid with nanoparticles suspended in ethylene glycol through modern approaches of fractional differentiations. The governing equations of Maxwell nanofluid for velocity and temperature are fractionalized in terms of Atangana–Baleanu and Caputo–Fabrizio operators and then solved analytically by invoking Laplace transform to generate series solutions. The general solutions of temperature and velocity field are established in terms of Mittag–Leffler and Fox-H functions, respectively. Modern approaches of fractional differentiations have been analyzed for memory effects on the Maxwell nanofluid for improving the thermophysical properties. The impacts of rheological parameters are underlined for the volume fraction of nanoparticles, relaxation time and single- and multi-walled carbon nanotubes suspended in ethylene glycol. A graphical illustration is depicted to disclose the physical aspects of the problem based on the functionality of modern approaches of fractional differentiations. Our results suggest that thermal conductivity of Maxwell nanofluid increases when nanoparticle’s volume fraction increases.

Analysis of mixed convective heat transfer from a sphere with an aligned magnetic field

Numerical computations are performed to examine the flow and heat transfer characteristics for mixed convective flow past a sphere in an assisting flow arrangement with an aligned magnetic field. The flow is considered as laminar, steady and incompressible and the working fluids as Newtonian. A spherical geometry higher order compact scheme (SGHOCS) is employed to solve the set of non-linear governing transport equations. The results are enumerated in terms of streamlines, isotherms, drag coefficient together with local and average Nusselt number on the surface of the sphere by varying the following parameters: Reynolds number 1 ≤ Re ≤ 200; Prandtl number 0.72 and 7; Richardson number 0 ≤ Ri ≤ 1.5; interaction magnetic parameter 0 ≤ N ≤ 10. For lower values of Ri, although the flow separation phenomena in the downstream region suppresses for weaker strength of the magnetic field (N ≤ 0.5), it again increases on further increase in N. For higher values of Ri, with an increase of N, the flow separation phenomena completely suppresses. The drag coefficient (CD) increases with N for any values of Re, Ri and Pr and for N ≥ 1, CD=KN+B where K and B are constants that depends on Ri and Pr and K = 0.32 for Ri = 0 which is consistent with the results in the literature. On the basis of variation of Nu on the sphere surface, three different regions are identified and moreover a strong interplay between N and Ri in dictating the characteristic of heat transfer is found for all values of Re. In the mixed convection domain the average Nusselt number (Nu¯) first decreases with N and then tends to a constant value for higher values of Reynolds number, in contrast with the forced convection case, when Nu¯ decreases with N and then tends to increase almost linearly with N. Based on the numerical results for the considered range of parameters, correlations are developed for CD and Nu¯, which are relatively in good agreement with reported results in the literature for special cases of both forced and mixed convective flows past a sphere in the absence of a magnetic field.

Numerical Analysis of Unsteady Natural Convection Flow and Heat Transfer in the Existence of Lorentz Force in Suddenly Expanded Cavity Using Open FOAM

The present study reveals the significance of the magnetic field or Lorentz force on the unsteady natural convection flow and heat transfer in the suddenly expanded cavity. The Lorentz force based magnetohydrodynamics (MHD) solver using electric potential formulation coupled with the energy equation by the means of Boussinesq approximation is developed in the open-source CFD tool OpenFOAM. The unsteady flow is generated by the buoyancy force keeping the Rayleigh number (Ra) at 109, at the fixed Prandtl number (Pr) of 0.71. The effects of the magnetic field on the flow and heat transfer are explained for various orientations of magnetic field (Bx, B45, and By) in terms of Hartmann number (Ha=0, 50, 100, 300 and 500). The increase in the magnetic field increases the strength of the Lorentz force, which regulates the flow pattern and suppresses down the unsteady nature of flow and heat transfer into the steady-state. It is perceived that the average Nusselt number decreases as the intensity of Bx and B45 magnetic field increases. However, for By magnetic field the average Nusselt number increases up to Ha of 100 as compared to the non-MHD case (Ha=0). The distribution of Lorentz force in the domain plays a significant role in the governing of the fluid flow and heat transfer.

Efficiency analysis of thermosyphon solar flat plate collector with low mass concentrations of ND–Co3O4 hybrid nanofluids: an experimental study

In the present study, the thermal efficiency, convective heat transfer and friction factor analysis are investigated for a flat plate solar collector with thermosyphon (natural circulation) system using water and nanodiamond–cobalt oxide hybrid nanofluids as the working fluids. The nanodiamond–cobalt oxide hybrid nanoparticles were synthesized using in situ growth and chemical co-precipitation method and characterized using X-ray diffraction, transmission electron microscope and vibrating sample magnetometer. The investigations were performed at different volume flow rates 0.56–1.35 L min−1 and various mass concentrations of 0.05–0.15%. The thermal conductivity and viscosity of nanofluids were measured experimentally at various mass concentrations and temperatures. Due to the augmented thermo-physical properties of hybrid nanofluids, the collector reached higher coefficient of heat transfer as well as improved thermal efficiency than the water data. Maximum thermal conductivity and viscosity enhancements are found to be 15.71% and 45.83% at particle loadings of 0.15% mass concentration and at a temperature of 60 °C. Results show the Nusselt number enhancement of 0.15% mass concentration of hybrid nanofluid is 21.23% with maximum friction factor penalty of 1.13 times against water data. The collector thermal efficiency is found to 59% for the case of 0.15% mass concentration of hybrid nanofluid, where the thermal efficiency of water is 48%. The empirical correlations were developed for Nusselt number and friction factor for collector with hybrid nanofluids within the deviation of ± 3%.

An improved high-order ISPH method for simulation of free-surface flows and convection heat transfer

The present work introduces a modified Incompressible Smoothed Particle Hydrodynamics (ISPH) model for simulation of free-surface flows and convection heat transfer. First, two new gradient and Laplacian models are proposed based on the Taylor series expansion and then used for discretization of the diffusion terms, Pressure Poisson's equation (PPE), and divergence of velocity. To maintain overall high-order accuracy, an explicit third-order TVD Runge-Kutta scheme is employed for discretization of the transient terms in Navier-Stokes and energy equations. Moreover, a new Hybrid Particle Shifting Technique (HPST) is developed by combining the classical PST and a collision model. A new kernel function is developed by combination of the Gaussian and polynomial functions and is then applied to the simulation of classical 1D Sod shock tube. Furthermore, a novel Hybrid Free-surface Detection (HFD) technique is proposed for accurate imposition of Dirichlet pressure boundary condition at the free surface area. The validity and applicability of proposed numerical schemes are verified against the several challenging benchmark cases including: dam-break flows with/without an obstacles, stretching water drop, rotating square patch of fluid, Rayleigh-Taylor instability, energy and exergy analysis of natural convection heat transfer in differentially heated cavity. The results show that, the newly constructed kernel function can successfully guarantee the stability and convergence of the numerical solution. Furthermore, it is found that, the proposed Hybrid Particle Shifting Technique (HPST) can efficiently resolve the unphysical discontinuity and suppress spurious pressure fluctuations.

A Comparative Numerical Study on Conjugate Natural Convection From Vertical Hollow Cylinder With Finite Thickness Placed on Ground and in Air

Abstract The present work reports a comparative analysis of natural convection heat transfer from a thick hollow vertical cylinder either placed on the ground or suspended in the air. The numerical simulations have been performed by varying the cylinder length to its outer diameter (L/Do) in the range of 0.2–20, the thickness ratio (Di/Do) in a range of 0.5–0.9, and Rayleigh number (Ra) from 104 to 108. The flow and heat transfer characteristics have been delineated precisely with the presentation of the thermal plume and flow field in the vicinity of the cylinder. The variation of average Nusselt number (Nu), local Nu, and contribution to total heat loss from different surfaces with the pertinent parameters have been elucidated graphically. The average Nu is always more for the cylinder in the air compared with the case when it is on the ground. However, the difference between the Nu for these two cases diminishes, as the L/Do increases. It has also been found that the contribution to total heat loss from the inner surface of the hollow cylinder suspended in air increases with L/Do, attains a peak, and decreases sharply. Cooling time curves for the cylinder placed in air or on the ground have been described precisely. Finally, a correlation for the average Nusselt number as a function of all the pertinent parameters has been proposed that can be useful for industrial and academic purposes.