Comparison of Single and Two-Phase Models for the Study of Mixed Convection Flows With Nanofluids

2010 ◽  
Author(s):  
Mahmood Akbari ◽  
Amin Behzadmehr ◽  
Nicolas Galanis
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mixed Convection ◽  
Single Phase ◽  
Volume Fraction ◽  
Solid Particles ◽  
Two Phase ◽  
Prediction Ability ◽  
Numerical Predictions ◽  
Phase Models

The single phase and three different two phase models (Volume of fluid, Mixture and Eulerian) are used to analyse laminar mixed convection flow of Al2O3-water nanofluids in a horizontal tube, in order to evaluate their prediction ability. The flow is considered steady and developing. The fluid’s physical properties are temperature dependent whereas those of the solid particles are constant. A uniform heat flux is applied at the fluid-solid interface. Two different Reynolds numbers and three different volume fractions have been considered. The governing three-dimensional partial differential equations are elliptical in all directions and coupled. Predicted convective heat transfer coefficients, velocity, and temperature profiles, as well as secondary flow’s velocity vectors and temperature contours are compared at different axial positions. To validate the comparisons and verify the accuracy of the results, the numerical predictions are compared with corresponding experimental data. There are essentially no differences between the predictions of the two-phase models; however their results are significantly different from those of the single-phase approach. Two-phase model results are closer to the experimental data, but they show an unrealistic increase in heat transfer for small changes of the particle volume fraction. Hydrodynamically, the two-phase and single-phase approaches perform almost the same but their thermal predictions are quite different.

Comparisons of single-phase and two-phase models for numerical predictions of Al2O3/water nanofluids convective heat transfer

2020 ◽  
Vol 31 (7) ◽  
pp. 3050-3061
Author(s):  
Zhaoping Ying ◽  
Boshu He ◽  
Di He ◽  
Yucheng Kuang ◽  
Jie Ren ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Single Phase ◽  
Two Phase ◽  
Numerical Predictions ◽  
Phase Models

COMPARATIVE NUMERICAL STUDY OF SINGLE-PHASE AND TWO-PHASE MODELS FOR BIO-NANOFLUID TRANSPORT PHENOMENA

2014 ◽  
Vol 14 (01) ◽  
pp. 1450011 ◽  
Author(s):  
O. ANWAR BÉG ◽  
M. M. RASHIDI ◽  
M. AKBARI ◽  
A. HOSSEINI
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Cfd Simulation ◽  
Numerical Study ◽  
Solid Particles ◽  
Two Phase ◽  
Constant Wall Temperature ◽  
Phase Models

A computational fluid dynamics (CFD) simulation of laminar convection of Al 2 O 3–water bio-nanofluids in a circular tube under constant wall temperature conditions was conducted, employing a single-phase model and three different two-phase models (volume of fluid (VOF), mixture and Eulerian). The steady-state, three-dimensional flow conservation equations were discretised using the finite volume method (FVM). Several parameters such as temperature, flow field, skin friction and heat transfer coefficient were computed. The computations showed that CFD predictions with the three different two-phase models are essentially the same. The CFD simulations also demonstrated that single-phase and two-phase models yield the same results for fluid flow but different results for thermal fields. The two-phase models, however, achieved better correlation with experimental measurements. The simulations further showed that heat transfer coefficient distinctly increases with increasing nanofluid particle concentration. The physical properties of the base fluid were considered to be temperature-dependent, while those of the solid particles were constant. Grid independence tests were also included. The simulations have applications in novel biomedical flow processing systems.

scholarly journals Role of Rotating Cylinder toward Mixed Convection inside a Wavy Heated Cavity via Two-Phase Nanofluid Concept

Nanomaterials ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 1138 ◽  
Author(s):  
Ammar I. Alsabery ◽  
Mohammad Ghalambaz ◽  
Taher Armaghani ◽  
Ali Chamkha ◽  
Ishak Hashim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Rotating Cylinder ◽  
Alumina Nanoparticles ◽  
Optimum Number ◽  
Two Phase ◽  
Rotation Direction

The mixed convection two-phase flow and heat transfer of nanofluids were addressed within a wavy wall enclosure containing a solid rotating cylinder. The annulus area between the cylinder and the enclosure was filled with water-alumina nanofluid. Buongiorno’s model was applied to assess the local distribution of nanoparticles in the host fluid. The governing equations for the mass conservation of nanofluid, nanoparticles, and energy conservation in the nanofluid and the rotating cylinder were carried out and converted to a non-dimensional pattern. The finite element technique was utilized for solving the equations numerically. The influence of the undulations, Richardson number, the volume fraction of nanoparticles, rotation direction, and the size of the rotating cylinder were examined on the streamlines, heat transfer rate, and the distribution of nanoparticles. The Brownian motion and thermophoresis forces induced a notable distribution of nanoparticles in the enclosure. The best heat transfer rate was observed for 3% volume fraction of alumina nanoparticles. The optimum number of undulations for the best heat transfer rate depends on the rotation direction of the cylinder. In the case of counterclockwise rotation of the cylinder, a single undulation leads to the best heat transfer rate for nanoparticles volume fraction about 3%. The increase of undulations number traps more nanoparticles near the wavy surface.

scholarly journals New Perspective for Heat Transfer Evaluation During Film Condensation Inside Tubes

2021 ◽  
Vol 39 (2) ◽  
pp. 390-402
Author(s):  
Yanán Camaraza-Medina
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Single Phase ◽  
Film Condensation ◽  
Mean Deviation ◽  
Two Phase ◽  
Wide Range ◽  
The Mean ◽  
Vertical Tubes

This paper presents the main results of the research developed by the author in his postdoctoral investigations on heat transfer calculations during film condensation inside tubes. The elements studied are combined in an analysis expression that provides a reasonable fit with the available experimental data, which includes a total of 22 fluids, including water, refrigerants and a wide range of organic substances, which condense inside horizontal, inclined and vertical tubes. These experimental data were obtained from the reports of 33 sources. Available data covers tube diameters from 2 to 50 mm, mass flow rates from 3 to 850 kg/(m2s), reduced pressures ranging from 0.0008 to 0.91, values for single-phase from 1 to , Reynolds number for two-phase from 900 to 594390, Reynolds number for single-phase from 65 to 84950 and vapor quality from 0.01 to 0.99. The mean deviation found for the analyzed data for horizontal tubes was 13.4%, while for the inclined and vertical tubes data the mean deviation was 14.9%. In all cases, the agreement of the proposed model is good enough to be considered satisfactory for practical design.

Two-phase model for mixed convection and flow enhancement of a nanofluid in an inclined channel patterned with heated slip stripes

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Subhasree Dutta ◽  
Somnath Bhattacharyya ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Temperature Jump ◽  
Volume Fraction ◽  
Volume Flow Rate ◽  
Homogeneous Model ◽  
Jump Condition ◽  
Two Phase ◽  
Content Type ◽  
The Impact

Purpose The purpose of this study is to analyze the heat transfer and flow enhancement of an Al2O3-water nanofluid filling an inclined channel whose lower wall is embedded with periodically placed discrete hydrophobic heat sources. Formation of a thin depletion layer of low viscosity over each hydrophobic heated patch leads to the velocity slip and temperature jump condition at the interface of the hydrophobic patch. Design/methodology/approach The mixed convection of the nanofluid is analysed based on the two-phase non-homogeneous model. The governing equations are solved numerically through a control volume approach. A periodic boundary condition is adopted along the longitudinal direction of the modulated channel. A velocity slip and temperature jump condition are imposed along with the hydrophobic heated stripes. The paper has validated the present non-homogeneous model with existing experimental and numerical results for particular cases. The impact of temperature jump condition and slip velocity on the flow and thermal field of the nanofluid in mixed convection is analysed for a wide range of governing parameters, namely, Reynolds number (50 ≤ Re ≤ 150), Grashof number ( 103≤Gr≤5×104), nanoparticle bulk volume fraction ( 0.01≤φb≤0.05), nanoparticle diameter ( 30≤dp≤60) and the angle of inclination ( −60°≤σ≤60°). Findings The presence of the thin depletion layer above the heated stripes reduces the heat transfer and augments the volume flow rate. Consideration of the nanofluid as a coolant enhances the rate of heat transfer, as well as the entropy generation and friction factor compared to the clear fluid. However, the rate of increment in heat transfer suppresses by a significant margin of the loss due to enhanced entropy generation and friction factor. Heat transfer performance of the channel diminishes as the channel inclination angle with the horizontal is increased. The paper has also compared the non-homogeneous model with the corresponding homogeneous model. In the non-homogeneous formulation, the nanoparticle distribution is directly affected by the slip conditions by virtue of the no-normal flux of nanoparticles on the slip planes. For this, the slip stripes augment the impact of nanoparticle volume fraction compared to the no-slip case. Originality/value This paper finds that the periodically arranged hydrophobic heat sources on the lower wall of the channel create a significant augmentation in the volume flow rate, which may be crucial to augment the transport process in mini- or micro-channels. This type of configuration has not been addressed in the existing literature.

Gas Phase Distribution Effects on Heat Transfer in Upward Vertical Bubbly Channel Flows

2016 ◽  
Author(s):  
Haden Hinkle ◽  
Deify Law
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Bubble Size ◽  
Single Phase ◽  
Volume Fraction ◽  
Phase Distribution ◽  
Vertical Channel ◽  
Channel Flows ◽  
Two Phase ◽  
Ansys Fluent

Two-phase (non-boiling) flows have been shown to increase heat transfer in channel flows as compared with single-phase flows. The present work explores the effects of gas phase distribution such as volume fraction and bubble size on the heat transfer in upward vertical channel flows. A two-dimensional (2D) channel flow of 10 cm wide by 100 cm high is studied numerically. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. The bubble size is characterized by the Eötvös number. The volume fraction and the Eötvö number are varied parametrically to investigate their effects on Nusselt number of the two-phase flows. All simulations are compared with a single-phase flow condition.

A Study on Uncertainties in Estimations of Thermal Conductivity of Alumina Nanofluids

2015 ◽  
Vol 809-810 ◽  
pp. 525-530 ◽  
Author(s):  
Madalina Georgiana Moldoveanu ◽  
Alina Adriana Minea
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Performance ◽  
Unsolved Problem ◽  
Volume Fraction ◽  
Solid Particles ◽  
Two Phase ◽  
Polymeric Particles ◽  
Semi Empirical ◽  
Thermal Conductivities

An innovative way of improving the thermal conductivities of fluids is to suspend small solid particles in the fluids. Various types of powders such as metallic, non-metallic and polymeric particles can be added into fluids to form slurries. The thermal conductivities of fluids with suspended particles are expected to be higher than that of common fluids. Application of nanoparticles provides an effective way of improving heat transfer characteristics of fluids. By suspending nanophase particles in heating or cooling fluids, the heat transfer performance of the fluid can be significantly improved. Moreover, the thermal conductivity of nanofluid is strongly dependent on the nanoparticle volume fraction. So far it has been an unsolved problem to develop a sophisticated theory to predict thermal conductivity of nanofluids, although there are some semi empirical correlations to calculate the apparent conductivity of two-phase mixture. In this article few correlations were considered and differences were noted between different theories. In conclusion, a lot of uncertainties in determining thermal conductivity were noticed.

scholarly journals MHD Mixed Convection in a Lid-Driven Cavity with a Bottom Trapezoidal Body: Two-Phase Nanofluid Model

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2943 ◽  
Author(s):  
Muhammad Sadiq ◽  
Ammar Alsabery ◽  
Ishak Hashim
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Solid Body ◽  
Richardson Number ◽  
Hartmann Number ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Building Design ◽  
Current Work ◽  
Two Phase

The current work examines the effects of a bottom trapezoidal solid body and a magnetic field on mixed convection in a lid-driven square cavity. The Al 2 O 3 -water nanofluid used is assumed to obey Buongiorno’s two-phase model. An isothermal heater is placed on the bottom base of the trapezoid solid body, while the cavity’s vertical walls are kept cold at temperature T c . The top moving wall and the remaining portions of the cavity’s bottom wall are thermally insulated. The Galerkin weighted residual finite element method is employed to solve the dimensionless governing equations. The parameters of interest are the Richardson number ( 0 . 01 ≤ R i ≤ 100 ), Hartmann number ( 0 ≤ H a ≤ 50 ) , nanoparticle volume fraction ( 0 ≤ ϕ ≤ 0 . 04 ), and the length of the bottom base of the trapezoidal solid body. The obtained results show that increasing the Richardson number or decreasing the Hartmann number tends to increase the heat transfer rate. In addition, both the thermophoresis and Brownian motion greatly improve the convection heat transfer. It is believed that the current work is a good contribution to many engineering applications such as building design, thermal management of solar energy systems, electronics and heat exchange.

Numerical Analysis of Mixed Convection of Nanofluids Inside a Vertical Channel

2016 ◽  
Vol 13 (03) ◽  
pp. 1650012 ◽  
Author(s):  
M. B. Akgül ◽  
M. Pakdemirli
Keyword(s):  
Mixed Convection ◽  
Single Phase ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Vertical Channel ◽  
Eulerian Model ◽  
Two Phase ◽  
Thermal Fields ◽  
Laminar Mixed Convection ◽  
Effective Particle

Laminar mixed convection of an Al[Formula: see text]O[Formula: see text]/water nanofluid inside a vertical channel is investigated numerically. Single-phase and two-phase Eulerian models are employed to analyze flow and thermal fields of the nanofluid in conjunction with the suitable expressions for the particle viscosity and effective particle thermal conductivity. The results of two-phase Eulerian model are compared with the single-phase model and with the published experimental data. Effects of the solid volume fraction, Reynolds number and Grashof number on the heat transfer performance of the nanofluid are investigated and discussed in detail.

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