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Article

R. Bennacer, K. Sefiane, M. El‐Ganaoui and C. Buffone

A computational model is developed to describe convection in volatile liquids evaporating in capillary tubes. Experimental work has demonstrated the existence of such…

Abstract

A computational model is developed to describe convection in volatile liquids evaporating in capillary tubes. Experimental work has demonstrated the existence of such convective structures. The correlation between this convection and the phase change process has been experimentally established. Temperature distribution on the liquid‐vapour interface is considered in order to characterise the minimum of radial temperature gradient required to initiate and orientate Marangoni convection. Direct numerical simulation using finite volume approximation is used to investigate the heat and mass transfer in the liquid phase. The case of a capillary tube filled with a volatile liquid is investigated for various Marangoni numbers, to characterise heat and mass transfers under conditions close to realistic operating parameters. The simulation shows that a minimum irregularity in evaporative flux along the liquid‐vapour interface is necessary to trigger thermocapillary convection. The enhancement of heat and mass transfer by Marangoni convection is also investigated.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 14 no. 7
Type: Research Article
ISSN: 0961-5539

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Article

Souad Morsli, Mustapha Boussoufi, Amina Sabeur, Mohammed El Ganaoui and Rachid Bennacer

The use of natural ventilation by large openings to maintain thermal comfort conditions in the premises is a concept that is perfectly integrated into the traditional…

Abstract

Purpose

The use of natural ventilation by large openings to maintain thermal comfort conditions in the premises is a concept that is perfectly integrated into the traditional architecture of countries in the Mediterranean region or in tropical climates. In a temperate climate where the architecture is not usually designed to respond to the use of natural ventilation is seasonal and is done at the initiative of the occupants by making changes in the design of their doors. The European interest in natural ventilation, as a passive building air-conditioning technology, is increasing and has been the subject of a research program commissioned by the European Community. In this work, the authors consider a part of a housing compound as a refreshing floor. This floor is maintained at a constant cold temperature, the one vertical wall at hot temperature and other surfaces are adiabatic. Various scenarios are considered for this work. Mixed convection for different boundary conditions and different configurations is carried out. In addition, an airflow is injected through a window and extracted on the opposite window. Classical conclusion and transitional value on Richardson number have been completed by the new thermal configuration with nonsymmetric thermal conditions. The complex 3D flow structure is more obvious when one of the two flows (ventilation or natural convection) dominates. However, the induced heat transfer is less sensitive to the added ventilation. In this study, the authors consider a part of a housing compound as a refreshing floor. This floor is maintained at a constant cold temperature, the one vertical wall at hot temperature and other surfaces are adiabatic.

Design/methodology/approach

This is a qualitative preliminary study of a 2D–3D flow. The authors examine the competition between the natural convective flow and the added airflow on the flow structure and indoor air quality. The numerical model shows a good agreement with that obtained by researchers analytically and experimentally. To deal with turbulence, the RNG k-ε model has been adopted in this study.

Findings

The transfer is more sensitive between the 2D and 3D cases for the present analyzed case.

Originality/value

The study of ventilation efficiency has shown the competition between the big and small structures and the induced discomfort.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 1
Type: Research Article
ISSN: 0961-5539

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Article

Youssef Azizi, Brahim Benhamou, Nicolas Galanis and Mohammed El‐Ganaoui

The objective of the present study is to investigate numerically the effects of thermal and buoyancy forces on both upward flow (UF) and downward flow (DF) of air in a…

Abstract

Purpose

The objective of the present study is to investigate numerically the effects of thermal and buoyancy forces on both upward flow (UF) and downward flow (DF) of air in a vertical parallel‐plates channel. The plates are wetted by a thin liquid water film and maintained at a constant temperature lower than that of the air entering the channel.

Design/methodology/approach

The solution of the elliptical PDE modeling the flow field is based on the finite volume method.

Findings

Results show that buoyancy forces have an important effect on heat and mass transfers. Cases with evaporation and condensation have been investigated for both UF and DF. It has been established that the heat transfer associated with these phase changes (i.e. latent heat transfer) may be more or less important compared with sensible heat transfer. The importance of these transfers depends on the temperature and humidity conditions. On the other hand, flow reversal has been predicted for an UF with a relatively high temperature difference between the incoming air and the walls.

Originality/value

Contrary to most studies in channel heat and mass transfer with phase change, the mathematical model considers the full elliptical Navier‐Stokes equations. This allows one to compute situations of flow reversal.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 17 no. 3
Type: Research Article
ISSN: 0961-5539

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Article

Diego Celentano, Marcela Cruchaga, Jorge Romero and Mohammed El Ganaoui

The purpose of this paper is to present a 2D numerical simulation of natural convection and phase‐change of succinonitrile in a horizontal Bridgman apparatus. Three…

Abstract

Purpose

The purpose of this paper is to present a 2D numerical simulation of natural convection and phase‐change of succinonitrile in a horizontal Bridgman apparatus. Three different heat transfer mechanisms are specifically studied: no growth, solidification and melting.

Design/methodology/approach

The analysis is carried out with a preexisting thermally coupled fixed‐mesh finite element formulation for generalized phase‐change problems.

Findings

In the three cases analyzed, the predicted steady‐state liquid‐solid interfaces are found to be highly curved due to the development of a primary shallow cell driven by the imposed furnace temperature gradient. In the no growth case, the heating and cooling jackets remain fixed and, therefore, a stagnant liquid‐solid interface is obtained. On the other hand, the phase transformation in the solidification and melting cases is, respectively, controlled by the forward and backward movement of the jackets. In these last two growth conditions, the permanent regime is characterized by a moving liquid‐solid interface that continuously shifts with the same velocity of the jackets. The numerical results satisfactorily approach the experimental measurements available in the literature.

Originality/value

The numerical simulation of the no growth, solidification and melting cases in a horizontal Bridgman apparatus using a finite element based formulation is the main contribution of this work. This investigation does not only provide consistent results with those previously computed via different numerical techniques for the no growth and solidification conditions but also reports on original numerical predictions for the melting problem. Moreover, all the obtained solid‐liquid interfaces are validated with experimental measurements existing in the literature.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 21 no. 4
Type: Research Article
ISSN: 0961-5539

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Article

Zohir Younsi, Lounes Koufi and Hassane Naji

A comprehensive investigation on the outlet air position effects on the thermal comfort and air quality has been achieved. In addition, airflow and temperature…

Abstract

Purpose

A comprehensive investigation on the outlet air position effects on the thermal comfort and air quality has been achieved. In addition, airflow and temperature distributions in ventilated cavities filled with an air-CO2 mixture with mixed convection are predicted. The airflow enters from the cavity through an opening in the lower side of the left vertical wall and exits through the opening in one wall of the cavity. This paper aims to investigate the outlet location effect, four different placement configurations of output ports are considered. Three of them are placed on the upper side and the fourth on top of the opposite side of the inlet opening. A uniform heat and CO2 contaminant source are applied on the left vertical wall, while the remaining walls are impermeable and adiabatic to heat and solute. The cooling efficiency inside the enclosure and the average fluid temperature are computed for different Reynolds and Rayleigh numbers to find the most suitable fluid outlet position that ensures indoor comfortable conditions while effectively removing heat and the contaminant. This is demonstrated by three relevant indices, namely, the effectiveness for heat removal, the contaminant removal and the index of indoor air quality.

Design/methodology/approach

The simulations were performed via the finite-volume scSTREAM CFD solver V11. Three different values of CO2 amount are considered, namely, 103, 2 × 103 and 3 × 103 ppm, the Reynolds number being in the range 100 ≤ Re ≤ 800.

Findings

Based on the findings obtained, it is the configuration whose air outlet is placed near the heat source and the contaminant, which provides a better air distribution and a ventilation efficiency compared to the others ventilation strategies.

Originality/value

The studies on heat and mass transfers by natural and forced convection in ventilated cavities remain a fruitful research topic. Thereby, such a study deals with different ventilation strategies through cavities containing an air-CO2 mixture subjected to a mixed regime. In particular, the air inlet velocity and contaminant sources’ effects on thermal comfort and air quality have been investigated.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 11
Type: Research Article
ISSN: 0961-5539

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Article

Noureddine Abouricha, Mustapha El Alami and Khalid Souhar

The purpose of this paper is to model the convective flows in a room equipped by a glass door and a heated floor of length l = 0.8 × H and submitted to a sinusoidal…

Abstract

Purpose

The purpose of this paper is to model the convective flows in a room equipped by a glass door and a heated floor of length l = 0.8 × H and submitted to a sinusoidal temperature profile and mono alternative temperature profile.

Design/methodology/approach

The paper opts for a numerical study of convective flows in a large scale cavity using the Lattice Boltzmann Method (LBM) by considering a two dimensions (2D) square cavity of side H and filled by air (Pr = 0.71). All the vertical walls, the ceiling and the rest of the floor are thermally insulated, the hot portion of length l = 0.8×H is heated with two imposed temperature profiles of amplitude values 0.2 ≤  a  ≤ 0.6 and for two different periods ζ = ζ0 and ζ = 0.4×ζ0. One of the vertical walls has a cold portion θc = 0 that represents the glass door.

Findings

A systematic study of the flow structure and heat transfer is carried out considering principal control parameters: amplitude “a” and period ζ for Rayleigh number Ra = 108. Effects of these parameters on results are presented in terms of isotherms, streamlines, profiles of velocities, temperature in the cavity, global and local Nusselt number. It has been found that an increase in amplitude or period increases the amplitude of the temperature in the core of cavity. The Nusselt number increases when the amplitude “a” of the imposed temperature increases, but this later is not affected by variation of the period.

Originality/value

The authors used LBM to simulate the convective flows in a cavity at high Ra, heated from below by tow imposed temperature profiles. Indeed, they simulate a local equipped by a solar water heater (SWH). The floor is subjected to a periodic heating: Sinusoidal heating (Case 1) for which the temperature varies sinusoidally (SWH without a supplement), and mono alternation heating (Case 2), the temperature evolves like a redressed signal (SWH with a supplement). The considered method has been successfully validated and compared with the previous work. The study has been conducted using several control parameters such as the signal amplitude and period in the case of turbulent convection. This allowed us to obtain a considerable set of results that can be used for engineering.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 5
Type: Research Article
ISSN: 0961-5539

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Article

Tarik Kousksou, Mustapha Mahdaoui, Arid Ahmed and Jean Batina

– The purpose of this paper is to conduct a numerical study to analyze the melting process along a vertical wavy surface with uniform surface temperature.

Abstract

Purpose

The purpose of this paper is to conduct a numerical study to analyze the melting process along a vertical wavy surface with uniform surface temperature.

Design/methodology/approach

The cavity horizontal walls are insulated while the left hot wavy wall and the right cold wall are maintained at temperatures, TH=38.3°C and TC=28.3°C, respectively. The enclosure was filled by solid Gallium initially at temperature TC. A numerical code is developed using an unstructured finite-volume method and an enthalpy porosity technique to solve for natural convection coupled to solid-liquid phase change. The validity of the numerical code used is ascertained by comparing the results with previously published results.

Findings

The effect of number of wavy surface undulation and amplitude of the wavy surface on the flow structure and heat transfer characteristics is investigated in detail. The numerical results show that the enhanced total heat transfer rate seems to depend on the amplitude of the wavy surface.

Originality/value

Flow and heat transfer from irregular surfaces are often encountered in many engineering applications to enhance heat transfer such as micro-electronic devices, flat plate solar collectors and flat-plate condensers in refrigerators, etc. Roughened surfaces could be used in latent storage systems where the wall heat flux is known. One of the reasons why a roughened surface is more efficient in heat transfer is its capability to promote fluid motion near the surface; in this way a complex wavy surface is expected to promote a larger heat transfer rate than a flat plate. This complex geometry will promote a correspondingly complicated motion in the fluid near the surface; this motion is described by the nonlinear boundary-layer equations.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Hong-Yan Liu, Ji-Huan He and Zheng-Biao Li

Academic and industrial researches on nanoscale flows and heat transfers are an area of increasing global interest, where fascinating phenomena are always observed, e.g…

Abstract

Purpose

Academic and industrial researches on nanoscale flows and heat transfers are an area of increasing global interest, where fascinating phenomena are always observed, e.g. admirable water or air permeation and remarkable thermal conductivity. The purpose of this paper is to reveal the phenomena by the fractional calculus.

Design/methodology/approach

This paper begins with the continuum assumption in conventional theories, and then the fractional Gauss’ divergence theorems are used to derive fractional differential equations in fractal media. Fractional derivatives are introduced heuristically by the variational iteration method, and fractal derivatives are explained geometrically. Some effective analytical approaches to fractional differential equations, e.g. the variational iteration method, the homotopy perturbation method and the fractional complex transform, are outlined and the main solution processes are given.

Findings

Heat conduction in silk cocoon and ground water flow are modeled by the local fractional calculus, the solutions can explain well experimental observations.

Originality/value

Particular attention is paid throughout the paper to giving an intuitive grasp for fractional calculus. Most cited references are within last five years, catching the most frontier of the research. Some ideas on this review paper are first appeared.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Y. Guo, R. Bennacer, S. Shen, D.E. Ameziani and M. Bouzidi

The purpose of this paper is to apply the lattice Boltzmann method (LBM) to simulate mixed flow, which combines natural convection for temperature difference and forced…

Abstract

Purpose

The purpose of this paper is to apply the lattice Boltzmann method (LBM) to simulate mixed flow, which combines natural convection for temperature difference and forced convection for lid driven, in a two‐dimensional rectangular cavity over a wide range of aspect ratios (A), Rayleigh numbers (Ra) and Reynolds numbers (Re).

Design/methodology/approach

The LBM is applied to simulate the mixed flow. A multi‐relaxation technique was used successfully. A scale order analysis helped the understanding and predicting the overall heat transfer.

Findings

In the considered lid driven cavity, the Richardson number emerges as a measure of relative importance of natural and forced convection modes on the heat transfer. An expression of the overall heat transfer depending on the cavity slender (A) is deduced. The validity of the obtained expression was checked in mixed convection under the condition of low Richardson number (Ri) and the limitation condition was deduced.

Practical implications

This paper has implications for cooling system optimization and LBM technique development.

Originality/value

This paper presents a new cooling configuration, avoiding critical situation where the opposing effect induce weak heat transfer; and a stable and fast LBM approach allowing complex geometry treatment.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 20 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Mohamed Amine Moussaoui, Mohamed Jami, Ahmed Mezrhab and Hassan Naji

The purpose of this paper is to investigate the laminar flow and heat transfer characteristics in a two‐dimensional horizontal channel with two square blocks placed…

Abstract

Purpose

The purpose of this paper is to investigate the laminar flow and heat transfer characteristics in a two‐dimensional horizontal channel with two square blocks placed side‐by‐side using a numerical scheme based on a coupling between the lattice Boltzmann method and the finite difference method.

Design/methodology/approach

The multiple‐relaxation‐time (MRT) lattice Boltzmann equation model coupled with the finite difference method are used to predict numerically the velocity and the temperature fields.

Findings

A complex structure of the fluid flow was observed for various dimensionless block separation distance (G). An unsteady flow was found when the two blocks are placed side by side (G = 0). For G < 1.5, the presence of each block develops the street of Van Karman which generates complex binary vortex street. In the opposite case (G > 1.5), the effect of this parameter (G) on the fluid is reduced, whereas, the distance between the blocks and the nearest walls have a great influence on the fluid flow and the heat transfer. When the obstacles are posed on the walls (G = 3), an important heat exchange between the blocks and the nearest walls is noted.

Originality/value

This study offers more knowledge on natural convection in an obstructed channel. Furthermore, this work shows the effectiveness of the MRT lattice Boltzmann equation model for this kind of geometry.

Details

Engineering Computations, vol. 27 no. 1
Type: Research Article
ISSN: 0264-4401

Keywords

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