Free convection in an inclined cavity filled with a nanofluid and with sinusoidal temperature on the walls

2019 ◽  
Vol 29 (12) ◽  
pp. 4549-4568 ◽  
Author(s):  
Dalia Sabina Cimpean ◽  
Ioan Pop
Keyword(s):  
Boundary Conditions ◽  
Inclination Angle ◽  
Amplitude Ratio ◽  
Numerical Study ◽  
Brownian Diffusion ◽  
Two Phase ◽  
Content Type ◽  
Energy Devices ◽  
Inclined Cavity ◽  
Sinusoidal Temperature

Purpose This paper aims to develop a numerical study of the steady natural convection in an inclined square porous cavity filled by a nanofluid with sinusoidal temperature distribution on the side walls and adiabatic conditions on the upper and lower walls. Design/methodology/approach Governing equations transformed in terms of the dimensionless variables using the Darcy–Boussinesq approximation have been solved numerically using a central finite-difference scheme. The Gaus-Siedel iteration technique was used for the system of discretized equations. The two-phase nanofluid model including the Brownian diffusion and thermophoresis effects has been considered for simulation of nanofluid transport inside the cavity. Findings The numerical results of streamlines, isotherms and isoconcentrations are investigated and the effect of different important parameters, such as inclination angle of the cavity, amplitude ratio of the sinusoidal temperature or phase deviation, is discussed. The results obtained for no inclination of the cavity are compared and successfully validated with previous reported results of the literature. The important findings of the study are focused on the changes made by the inclination angle and the periodic thermal boundary conditions, on the heat and fluid flow. Originality/value The originality of the present study is given by the mathematical model presented for an inclined cavity, the numerical solution with new results for inclined cavity and the applications for design of solar energy devices such as solar collectors in which the boundary conditions vary with time because of changes in weather conditions.

Entropy generation of a nanofluid in a porous cavity with sinusoidal temperature at the walls and a heat source bellow

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Dalia Sabina Cimpean ◽  
Ioan Pop
Keyword(s):  
Heat Source ◽  
Entropy Generation ◽  
Amplitude Ratio ◽  
Brownian Diffusion ◽  
Two Phase ◽  
Content Type ◽  
Energy Devices ◽  
Porous Cavity ◽  
Phase Deviation ◽  
Sinusoidal Temperature

Purpose This paper aims to focus on the analysis of the entropy generation in an inclined square cavity filled with a porous media saturated by a nanofluid with sinusoidal temperature distribution on the side walls, adiabatic conditions on the upper wall and a heat source at the lower wall. Design/methodology/approach The two-phase nanofluid model including the Brownian diffusion and thermophoresis effects has been used for simulation of nanofluid transport inside the porous cavity. The governing equations and the entropy generation owing to fluid friction, heat and mass transfer are transformed in terms of the dimensionless variables, and the results are obtained by using the finite difference method of the second-order accuracy. Findings The numerical results of the model are investigated, and the effect of different important parameters, such as inclination angle of the cavity, amplitude ratio of the sinusoidal temperature or phase deviation, is discussed. The results for no inclination of the cavity is compared and successfully validated with previous reported results of the literature. The important findings of the study are focused mainly on the existence of the irreversibility phenomena which are affected by the conditions of the model and the values of the studied parameters. Originality/value The originality of this work is given by the presented mathematical model, the numerical solution with new results for entropy generation in an inclined porous cavity filled by a nanofluid and the applications for design of electronic or energy devices.

Numerical study of cavitating flow over hydrofoil in the presence of air

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Włodzimierz Wróblewski ◽  
Krzysztof Bochon ◽  
Mirosław Majkut ◽  
Krzysztof Rusin ◽  
Emad Hasani Malekshah
Keyword(s):  
Numerical Study ◽  
Cavitating Flow ◽  
Cavitation Model ◽  
Two Phase ◽  
Content Type ◽  
Flow Simulations ◽  
Cavity Structure ◽  
Dynamic Forces ◽  
High Dynamic ◽  
The Impact

Purpose The presence of air in the water flow over the hydrofoil is investigated. The examined hydrofoil is ClarkY 11.7% with an angle of attack of 8 deg. The flow simulations are performed with the assumption of different models. The Singhal cavitation model and the models which resolve the non-condensable gas including 2phases and 3phases are implemented in the numerical model. The calculations are performed with the uRANS model with assumption of the constant temperature of the mixture. The two-phase flow is simulated with a mixture model. The dynamics and structures of cavities are compared with literature data and experimental results. Design/methodology/approach The cavitation regime can be observed in some working conditions of turbomachines. The phase transition, which appears on the blades, is the source of high dynamic forces, noise and also can lead to the intensive erosion of the blade surfaces. The need to control this process and to prevent or reduce the undesirable effects can be fulfilled by the application of non-condensable gases to the liquid. Findings The results show that the Singhal cavitation model predicts the cavity structure and related characteristics differently with 2phases and 3phases models at low cavitation number where the cavitating flow is highly dynamic. On the other hand, the impact of dissolved air on the cloud structure and dynamic characteristic of cavitating flow is gently observable. Originality/value The originality of this paper is the evaluation of different numerical cavitation models for the prediction of dynamic characteristics of cavitating flow in the presence of air.

Numerical Study on Near-Wall Natural Convection Over a Microscale Heating Wire

2012 ◽  
Author(s):  
Leping Zhou ◽  
Yunfang Zhang ◽  
Lijun Yang ◽  
Xiaoze Du ◽  
Minami Yoda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Heat Transfer Process ◽  
Brownian Diffusion ◽  
Wall Region ◽  
Two Phase ◽  
Heating Wire ◽  
Transfer Problems ◽  
Near Wall

The study of the natural convection over a very small heat sources is important in the analysis of heat transfer problems in the electronics industry. However, the characteristics of the spatial distribution of the velocity in the near wall region, which is crucial to the mechanisms of heat transfer process in natural convection around a microscale object, is not well understood. In this investigation, the microscale natural convection in the near wall region of a platinum micro heat source was investigated numerically, using FLUENT, a commercially available computational fluid dynamics (CFD) software, and compared with corresponding experimental results. The influence of the nanoparticles on the natural convection was observed using the single-phase or two-phase models available in FLUENT. The temperature and velocity fields were obtained, with which the Brownian diffusion coefficient was deduced. The results indicate that the temperature gradient induced Brownian diffusion and thermophoresis in the near wall region plays an important role in the microscale natural convection in the water/nanoparticle mixture investigated and are in good agreement with the results from a corresponding experimental investigation.

Natural convection in a partially heated wavy cavity filled with a nanofluid using Buongiorno’s nanofluid model

2017 ◽  
Vol 27 (4) ◽  
pp. 924-940 ◽  
Author(s):  
Ioan Pop ◽  
Mikhail Sheremet ◽  
Dalia Sabina Cimpean
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Rectangular Domain ◽  
Two Phase ◽  
Bottom Part ◽  
Content Type ◽  
Industrial Sectors ◽  
Nuclear Systems ◽  
Wavy Cavity

Purpose The main purpose of this numerical study is to provide a solution for natural convection in a partially heated, wavy cavity filled with a nanofluid using Buongiorno’s nanofluid model. Design/methodology/approach The domain of interest is a two-dimensional cavity bounded by an isothermal left wavy wall, adiabatic horizontal flat walls and right flat wall with a partial isothermal zone. To study the behaviour of the nanofluid, a two-phase Buongiorno mathematical model with the effects of the Brownian motion and thermophoresis is used. The governing dimensionless partial differential equations with corresponding boundary conditions were numerically solved by the finite difference method of the second-order accuracy using the algebraic transformation of the physical wavy cavity in a computational rectangular domain. The study has been conducted using the following values of the governing parameters: Ra = 104-106, Le = 10, Pr = 6.26, Nr = 0.1, Nb = 0.1, Nt = 0.1, A = 1, κ = 1-3, b = 0.2, hhs/L = 0.25, h1/L = 0.0-0.75 and τ = 0-0.25. Findings It is found that an increase in the undulation number leads to a weak intensification of convective flow and a reduction of Nū because of more essential cooling of the wavy troughs where the temperature gradient decreases. Variations of the heater location show a modification of the fluid flow and heat transfer. The upper position of the heater reflects the minimum heat transfer rate, while the position between the bottom part and the middle section (h1/L = 0.25) characterizes an enhancement of heat transfer. Originality/value The originality of this work is to analyse the natural convection in a partially heated wavy cavity filled by a nanofluid using Buongiorno’s nanofluid model. The results will benefit scientists and engineers to become familiar with the flow behaviour of such nanofluids, and the way to predict the properties of this flow for possibility of using nanofluids in advanced nuclear systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.

Nonhomogeneous Model for the Mixed Convection and Entropy Generation of a Nanofluid in a Lid-Driven Inclined Enclosure With Discrete Heat Source

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
S. Dutta ◽  
S. Bhattacharyya ◽  
I. Pop
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Entropy Generation ◽  
Inclination Angle ◽  
Volume Fraction ◽  
Numerical Study ◽  
Homogeneous Model ◽  
Staggered Grid ◽  
Brownian Diffusion ◽  
Bejan Number

Abstract A numerical study on the mixed convection of Al2O3–water nanofluid in a lid-driven inclined square enclosure partially heated from below is performed based on Buongiorno's two phase model. The velocity of the nanoparticles relative to the base fluid is considered due to thermophoresis and Brownian diffusion. The thermophysical properties of the nanofluid are assumed to be dependent on temperature as well as the nanoparticle volume fraction. A control volume method over a staggered grid arrangement is used to discretize the governing equations. The discretized equations of two-dimensional continuity, momentum, energy, and volume fraction are solved through a pressure-correction-based semi-implicit method for pressure linked equations (SIMPLE) algorithm. The effects of relevant parameters such as nanoparticle diameter (25 nm ≤ dp ≤ 90 nm), Richardson number (0.1≤Ri≤5), nanoparticle bulk volume fraction (0 ≤φb≤ 0.05) on the mixed convection of the nanofluid is studied by considering the inclination angle of the enclosure to vary between 0 deg and 60 deg. The entropy generation as well as the Bejan number is evaluated to illustrate the thermodynamic optimization of the mixed convection. Both the heat transfer and entropy generation are higher in the nanofluid compared to the clear fluid and the rate of increment in entropy generation remains lower than the rate by which the heat transfer is augmented in the nanofluid. We find that due to the presence of the Brownian diffusion and thermophoresis in the nonhomogeneous model, a higher heat transfer is yielded as compared to the homogeneous model. The discrepancy between the homogeneous and nonhomogeneous models is significant when the mixed convection is dominated by the shear force. When the mixed convection is dominated by the thermal buoyancy, an increase in positive inclination angle of the enclosure creates a significant increment in the heat transfer.

Three-dimensional modelling of natural convection and entropy generation in a vertical cylinder under heterogeneous heat flux using nanofluids

2019 ◽  
Vol 30 (1) ◽  
pp. 119-142 ◽  
Author(s):  
Iman Rashidi ◽  
Lioua Kolsi ◽  
Goodarz Ahmadi ◽  
Omid Mahian ◽  
Somchai Wongwises ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Consumption ◽  
Boundary Conditions ◽  
Entropy Generation ◽  
Three Dimensional ◽  
Thermal Storage ◽  
Content Type ◽  
Energy Devices ◽  
Simulation Results

Purpose This study aims to investigate a three-dimensional computational modelling of free convection of Al2O3 water-based nanofluid in a cylindrical cavity under heterogeneous heat fluxes that can be used as a thermal storage tank. Design/methodology/approach Effects of different heat flux boundary conditions on heat transfer and entropy generation were examined and the optimal configuration was identified. The simulation results for nanoparticle (NP) volume fractions up to 4 per cent, and Rayleigh numbers of 104, 105 and 106 were presented. Findings The results showed that for low Ra (104) the heat transfer and entropy generation patterns were symmetric, whereas with increasing the Rayleigh number these patterns became asymmetric and more complex. Therefore, despite the symmetric boundary conditions imposed on the periphery of the enclosure (uniform in Ɵ), it was necessary to simulate the problem as three-dimensional instead of two-dimensional. The simulation results showed that by selecting the optimal values of heat flux distribution and NP volume fraction for these systems the energy consumption can be reduced, and consequently, the energy efficiency can be ameliorated. Originality/value The results of the present study can be used for the design of energy devices such as thermal storage tanks, as both first and second laws of thermodynamics have been considered. Using the optimal design will reduce energy consumption.

Study of electrokinetic effects for heat transfer in microchannel with sinusoidal thermal boundary conditions

2019 ◽  
Vol 29 (10) ◽  
pp. 3872-3892
Author(s):  
Muhammad Raees Ul Haq ◽  
Hang Xu ◽  
Liang Zhao
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Temperature Variation ◽  
Heat Transfer Rate ◽  
Electric Double Layer ◽  
Transfer Rate ◽  
Content Type ◽  
Classical Energy ◽  
Regularity Results ◽  
Sinusoidal Temperature

Purpose The purpose of this study is to obtain the numerical as well as regularity results for the nonlinear elliptic set of equations arising in the study of fluid flow in microchannel induced by the pressure in the presence of interfacial electrokinetic effects. Design/methodology/approach For the numerical study, the authors implemented traditional FDM approach, and for the regularity results they used the classical energy estimates. The interfacial electrokinetic effects result in an additional source term in classical momentum equation, hence affecting the characteristics of the flow and heat transfer. The sinusoidal temperature variation is assumed on side walls. Findings The results were obtained for various combinations of physical parameters appearing in the governing equations. This study concludes that in the presence of electric double layer, the average heat transfer rate reduces along with larger values of Reynolds number. It is observed that the heat transfer increases with the increase in amplitude ratio and phase deviation. The flow behavior and heat transfer rate inside the microchannel are also strongly affected by the presence of κ (kappa). Originality/value To the best of the authors’ knowledge, the problem of heat transfer through microchannel in combination with sinusoidal temperature variation at boundary with electric double layer effects has not been considered previously. Hence, this paper focuses on the influence of the sinusoidal boundary temperature distributions on both sidewalls of a rectangular microchannel through parallel plates with electrokinetic effects on the pressure-driven laminar flow. In addition, a detailed mathematical analysis is also to be carried out to verify the regularity of this model with the proposed boundary conditions. The study used the classical energy method to get the regularity results.

Two-phase investigation of water-Al2O3 nanofluid in a micro concentric annulus under non-uniform heat flux boundary conditions

2019 ◽  
Vol 30 (4) ◽  
pp. 1795-1814 ◽  
Author(s):  
Davood Toghraie ◽  
Ramin Mashayekhi ◽  
Hossein Arasteh ◽  
Salman Sheykhi ◽  
Mohammadreza Niknejadi ◽  
...  
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Boundary Conditions ◽  
Surface Area ◽  
Uniform Heat Flux ◽  
Two Phase ◽  
Content Type ◽  
Concentric Annulus ◽  
Uniform Heat ◽  
Flux Boundary Conditions

Purpose This is a 3D numerical study of convective heat transfer through a micro concentric annulus governing non-uniform heat flux boundary conditions employing water-Al2O3 nanofluid. The nanofluid is modeled using two-phase mixture model, as it has a good agreement to experimental results. Design/methodology/approach Half of the inner pipe surface area of the annulus section of a double pipe heat exchanger is exposed to a constant heat flux which two models are considered to divide the exposing surface area to smaller ones considering the fact that in all cases half of the inner pipe surface area has to be exposed to the heat flux: in model (A), the exposing surface area is divided radially to two parts (A1), four parts (A2) and eight parts (A3) by covering the whole length of the annulus and in model (B) the exposing surface area is divided axially to two parts (B1), four parts (B2) and eight parts (B3) by covering half of the annulus radially. Findings The results reveal that model (B) leads to higher Nusselt numbers compared to model (A); however, at Reynolds number 10, model (A3) exceeds model (B3). The average Nusselt number is increased up to 142 and 83 per cent at models (A3) with Reynolds number 10 and model (B3) with Reynolds number 1000, respectively. Originality/value This paper is a two-phase investigation of water-Al2O3 nanofluid in a micro concentric annulus under non-uniform heat flux boundary conditions.

A comparative analysis on the single-phase and two-phase mixture models for calculation of ferrofluid convective heat transfer in the presence of a magnetic field: a numerical study

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hamed Jafari ◽  
Mohammad Goharkhah ◽  
Alireza Mahdavi Nejad
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Single Phase ◽  
Numerical Study ◽  
Phase Method ◽  
Two Phase ◽  
Content Type ◽  
Phase Models

Purpose This paper aims to analyze the accuracy of the single and two-phase numerical methods for calculation of ferrofluid convective heat transfer in the presence of a magnetic field. The findings of current study are compared with previous single-phase numerical results and experimental data. Accordingly, the effect of various parameters including nanoparticles concentration, Reynolds number and magnetic field strength on the performance of the single and two-phase models are evaluated. Design/methodology/approach A two-phase mixture numerical study is carried out to investigate the influence of four U-shaped electromagnets on the hydrodynamic and thermal characteristics of Fe3O4/Water ferrofluid flowing inside a heated channel. Findings It is observed that the applied external magnetic field signifies the convective heat transfer from the channel surface, despite local reduction at a few locations. The maximum heat transfer enhancement is predicted as 23% and 25% using single and two-phase models, respectively. The difference between the results of the two models is mainly attributed to the slip velocity effect which is accounted for in the two-phase model. The magnetic field gradient leads to a significant increase in the slip velocity which in turn causes a slight difference in velocity and temperature profiles obtained by the single and two-phase models in the magnetic field region. According to percentage error calculation, the two-phase method is generally more accurate than the single-phase method. However, the percentage error of both models improves by decreasing either magnetic field intensity or Reynolds number. Originality/value For the first time in the literature, to the best of the authors’ knowledge, the current work analyzes the accuracy of the single and two phase numerical methods for calculation of ferrofluid convective heat transfer in the presence of a magnetic field.

Sign in / Sign up

Export Citation Format

Share Document