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Article

M.K.M. Ho, G.H. Yeoh and J.Y. Tu

This study aims to examine both the population balance approach based on the MUltiple SIze Group (MUSIG) model and the average bubble number density transport equation…

Abstract

Purpose

This study aims to examine both the population balance approach based on the MUltiple SIze Group (MUSIG) model and the average bubble number density transport equation (ABND) model for 3D, low pressure, gas‐liquid, subcooled boiling, vertical flows. The purpose is to assess the ability of both models to predict the radial profile of void fraction, bubble Sauter mean diameter and interfacial area concentration which characterise subcooled boiling.

Design/methodology/approach

Improvement in the ABND model to simulate gas‐liquid bubbly flows with heat transfer was achieved by combining the condensation expression with the gaseous mass transport equation within the CFD commercial code CFX4.4.

Findings

Overall, both the ABND model and the MUSIG model provided good results in terms of the above‐mentioned criteria when compared against experimental measurements. However, the ABND model was found to have limitations in predicting high‐subcooled boiling flows due to the lack of bubble size resolution to adequately capture the effect of condensation over a range of bubbles sizes.

Originality/value

It is shown that the ABND model provides an economic alternative to the MUSIG model in terms of complexity and computational time, as long as one is aware of the limitations in simulating high‐subcooling flow regimes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 18 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

G.H. Yeoh, R.K.K. Yuen, E.W.M. Lee and S.C.P. Chueng

This paper presents a comparison of numerical predictions employing a Computational Fluid Dynamics fire model against a series of turbulent buoyant fire experiments…

Abstract

This paper presents a comparison of numerical predictions employing a Computational Fluid Dynamics fire model against a series of turbulent buoyant fire experiments recently carried out in a two‐room compartment structure by Nielsen and Fleischmann at the University of Canterbuty, New Zealand. The model incorporates turbulence, combustion, soot generation and radiation due to a fire. An evaluation of the various approaches—volumetric heat source approach or a more sophisticated handling the fire through a combustion model—is carried out. The effect of radiation due to combustion products and soot is also investigated. The model considering combustion with radiation contribution by both the combustion products and soot provides the best agreement between the predicted results and measured data. The presence of soot is seen to significantly augment the global radiation process within the two‐compartment enclosure.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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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

Paul Stark and Udo Fritsching

The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a…

Abstract

Purpose

The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a single submerged water jet. At wall temperatures above the liquid boiling point, the vapor formation process and the interaction of the vapor phase with the developing jet-flow field are included.

Design/methodology/approach

The time-dependent flow and temperature distribution during all occurring boiling phases as well as the local and temporal distribution of the heat transfer coefficient on a flat plate can be simulated.

Findings

The influence of the liquid jet flow rate (10,800=Re_d=32,400) and the nozzle distance to the plate (4=H/d=20) on the transient cooling process are analyzed. This includes the time-dependant positions of the transition regions between the boiling phases on the plate as well as the temperatures at these transition regions. Additionally, the local heat transfer rates are a direct result of the unsteady cooling simulation.

Originality/value

A single model approach is developed and utilized to simulate the unsteady cooling process of a flat plate with an impinging water jet including all occurring boiling phases.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Muhannad R. Alasiri and Mustafa Mahamid

Standard fire resistance curves such as ASTM E119 have been used for so long in structural fire practice. The issue with use of these curves that they do not represent…

Abstract

Purpose

Standard fire resistance curves such as ASTM E119 have been used for so long in structural fire practice. The issue with use of these curves that they do not represent real fire scenarios. As a result, the alternatives have been to either conduct experiments or find other tools to represent a real fire scenario. Therefore, the purpose of this paper is to understand the temperature effects resulted from a designed fire on steel beams and whether the standard fire curves represent a designed fire scenario.

Design/methodology/approach

Computational fluid dynamics (CFD) models were developed to simulate a designed fire scenario and to understand the structural responses on the beams under elevated temperatures. Consequently, the results obtained from the CFD models were compared with the results of three-dimensional (3D) non-linear finite element (FE) models developed by other researchers. The developed FE models were executed using a standard fire curve (ASTM E119). A parametric study including two case studies was conducted.

Findings

Results obtained from performing this study showed the importance of considering fire parameters such as fuel type and flame height during the thermal analysis compared to the standard fire curves, and this might lead to a non-conservative design as compared to the designed fire scenario. The studied cases showed that the steel beams experienced more degradation in their fire resistance at higher load levels under designed fires. Additionally, the models used the standard fire curves underestimated the temperatures at the early stages.

Originality/value

This paper shows results obtained by performing a comparison study of models used ASTM E119 curve and a designed fire scenario. The value of this study is to show the variability of using different fire scenarios; thus, more studies are required to see how temperature history curves can be used to represent real fire scenarios.

Details

Journal of Structural Fire Engineering, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 2040-2317

Keywords

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Article

P.H. Oosthuizen and J.T. Paul

A numerical study of the flow in and heat transfer across a verticalcavity containing pure water when the aspect ratio of the cavity is low, i.e.1 or less, has been…

Abstract

A numerical study of the flow in and heat transfer across a vertical cavity containing pure water when the aspect ratio of the cavity is low, i.e. 1 or less, has been undertaken. One vertical wall of the cavity is kept at a temperature that is below the freezing point of water while the opposite wall is kept at a temperature that is above this freezing temperature. Ice therefore forms in part of the cavity, the conditions being such that there can be significant natural convection in the water. The upper surface of the cavity is open i.e. the water has a free surface, heat transfer from this surface being assumed negligible. The lower surface of the cavity is assumed to be adiabatic. Only the steady state has been considered here. It has been assumed that the flow is laminar and two‐dimensional and that liquid and solid properties are constant except for the water density change with temperature which gives rise to the buoyancy forces. The governing equations have been written in dimensionless form and these equations have been solved using a finite element‐based procedure in which the position of the solid‐liquid interface is obtained using an iterative approach. Solutions have been obtained for modified Rayleigh numbers of between 103 and 108 for various degrees of under‐cooling and for cavity aspect ratios of between 0.25 and 1. The density inversion that occurs with water has been shown to have a large effect on the steady state freezing of water in a cavity. The aspect ratio of the cavity has also been shown to have a significant influence on the results when the aspect ratio is less than 0.5.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 6 no. 5
Type: Research Article
ISSN: 0961-5539

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Article

Katarzyna Stęchły, Gabriel Wecel and Derek B. Ingham

The main goal of this work was the CFD analysis of air and oxy-coal combustion, in order to develop a validated with experimental measurements model of the combustion…

Abstract

Purpose

The main goal of this work was the CFD analysis of air and oxy-coal combustion, in order to develop a validated with experimental measurements model of the combustion chamber. Moreover, the purpose of this paper is to provide information about limitations of the sub-models implemented in commercial CFD code ANSYS Fluent version 13.0 for the oxy-coal combustion simulations. The influence of implementation of the weighted sum of gray gas model (WSGGM) with coefficients updated to oxy-coal combustion environment has been investigated.

Design/methodology/approach

The sub-models validated with experimental measurements model for the air combustion has been used to predict the oxy-coal combustion case and subsequently the numerical solutions have been compared with the experimental data, which enclose the surface incident radiation (SIR) and the flue gas temperature. To improve the numerical prediction of the oxy-coal combustion process the own routine for calculating properties of the oxy-combustion product has been implemented.

Findings

The results of numerical simulation of combustion in the air environment fitted within the experimental measurements accuracy. However, the air combustion sub-models implemented for the oxy-coal combustion simulations does not predict the SIR within the experimental data accuracy. The implementation of own routine, which uses the coefficients calculated for oxy-coal combustion environment shows improvement in numerical prediction of oxy-coal combustion.

Originality/value

The radiative properties of gases in the combustion chamber during oxy-coal combustion calculated using the WSGGM implemented in ANSYS Fluent 13.0 do not predict the SIR within experimental measurement accuracy, however, implementation of WSGGM with updated coefficients provide a reasonable improvement in numerical prediction of SIR in the oxy-coal combustion.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Content available

Abstract

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 18 no. 2
Type: Research Article
ISSN: 0961-5539

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Article

Yanqiu Chen, Xiaodong Zhou, Taolin Zhang, Yuqi Hu and Lizhong Yang

– The purpose of this paper is to study the behavior of smoke flow in a typical high-rise residential building fire in six common smoke control systems.

Abstract

Purpose

The purpose of this paper is to study the behavior of smoke flow in a typical high-rise residential building fire in six common smoke control systems.

Design/methodology/approach

The pressure, temperature and CO2 concentration were used to trace the motion of turbulent smoke flow through CFD.

Findings

It is found that the hot smoke could rise up and spread into the indoor space on the upper floors through the staircase. When the pressure in the evacuation staircase is higher, it would be more difficult for the smoke to enter the staircase and transport vertically. On the other hand, the smoke would soon transport to the indoor space on the upper floors horizontally. During this process, the smoke shows a more disorder horizontal transport under the sole effect of thermal buoyancy than the co-existence of thermal buoyancy and the air inlet.

Research limitations/implications

Because of the chosen research approach, the research results may need to be tested by further experiments.

Practical implications

The paper includes implications for the design of smoke control systems and evacuation in a building fire.

Originality/value

This paper fulfils an identified need to study the behavior of smoke in a fire and optimize the design of smoke control systems.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Md Delwar Hossain, Md Kamrul Hassan, Anthony Chun Yin Yuen, Yaping He, Swapan Saha and Waseem Hittini

The purpose of this study is to review and summarise the existing available literature on lightweight cladding systems to provide detailed information on fire behaviour…

Abstract

Purpose

The purpose of this study is to review and summarise the existing available literature on lightweight cladding systems to provide detailed information on fire behaviour (ignitibility, heat release rate and smoke toxicity) and various test method protocols. Additionally, the paper discusses the challenges and provides updated knowledge and recommendation on selective-fire mechanisms such as rapid-fire spread, air cavity and fire re-entry behaviours due to dripping and melting of lightweight composite claddings.

Design/methodology/approach

A comprehensive literature review on fire behaviour, fire hazard and testing methods of lightweight composite claddings has been conducted in this research. In summarising all possible fire hazards, particular attention is given to the potential impact of toxicity of lightweight cladding fires. In addition, various criteria for fire performance evaluation of lightweight composite claddings are also highlighted. These evaluations are generally categorised as small-, intermediate- and large-scale test methods.

Findings

The major challenges of lightweight claddings are rapid fire spread, smoke production and toxicity and inconsistency in fire testing.

Originality/value

The review highlights the current challenges in cladding fire, smoke toxicity, testing system and regulation to provide some research recommendations to address the identified challenges.

Details

Journal of Structural Fire Engineering, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 2040-2317

Keywords

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