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Building and Environment. 44(1):125-136.
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13th International Conference on Biomedical Engineering (ICBME2008);
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Computers in Biology and Medicine. 38(6):713-726.
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13th International Conference on Biomedical Engineering (ICBME2008);
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13th International Conference on Biomedical Engineering (ICBME2008);
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Journal of Biomedical Science and Engineering. 3(1):52-58.
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Journal of Aerosol Science. 42(2):100-113.
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Aerosol Science and Technology. 46(2):165-177.
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International Conference on Audio, Language and Image Processing 2008 (ICALIP2008, Paper 581);
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Fifth International Conference on CFD in the Process Industries;
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Journal of Computational Multiphase Flows. 1(1):57-82.
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ABSTRACT: Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in the computer code CFX4.4 is further developed to accommodate the wall nucleation at the heated wall and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Additional comparison using empirical relationships for the active nucelation site density and local bubble diameter is also investigated. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress to circumvent the deficiency through the consideration of additional momentum equations or developing an algebraic slip model to account for bubble separation.
Applied Mathematical Modelling.
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ABSTRACT: Turbulent particle-laden gas flow in an in-line tube bank is studied, computationally and experimentally. An Eulerian model with generalised Eulerian boundary conditions for the particulate phase is employed. In the momentum balance equations, the particulate phase momentum exchanges with solid walls are included. The turbulent effects of the gas phase are taken into account using a renormalization group (RNG) based k−ε turbulence model while the particulate turbulent diffusivity is related to the turbulent viscosity of the gas phase. The experiment is performed in an in-line tube bank located in a horizontal wind tunnel, using laser-Doppler Anemometry (LDA). The comparison of numerical predictions with experimental data is made for the mean axial and transverse velocity profiles of both phases, the turbulent intensity of the gas phase, and the distribution of particle concentration in the tube bank. Very good agreement with experimental data is obtained for computed values of the mean velocity of both gas and particulate phases, and the particulate concentration distribution. Interesting information is also presented which shows the different flow behaviour demonstrated by the gas and particulate phases, in particular for larger particles.
Chemical Engineering Science.
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ABSTRACT: Improved wall heat flux partitioning accounting sliding bubbles and a mechanistic model that incorporates the fundamental consideration of bubble frequency during low-pressure subcooled flow boiling is presented. A model considering the forces acting on departing bubbles at the heated surface is employed. Coupled with a three-dimensional two-fluid and population balance equations based on the modified MUSIG (MUltiple-SIze-Group) model, the behavior of an upward forced convective subcooled boiling flows in a vertical annular channel is simulated. Comparison of model predictions against local and axial measurements (heat fluxes ranged from 152.9 to 705.0 kW/m2) is made for the void fraction, Sauter mean bubble diameter and interfacial area concentration covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved between the predicted and measured profiles. Reasonable agreement with recent experimental measurements is also attained for the predicted growth and waiting times of bubble frequency at particular local wall superheat and subcooling temperatures.
International Journal of Heat and Mass Transfer.
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ABSTRACT: This paper presents a numerical study of a dilute gas–particle flow in a 90° bend by employing a Lagrangian particle-tracking model combined with a particle–wall collision model and a stochastic wall roughness model. The major objective of this study was to investigate the effects of wall roughness on the particle flow properties. The numerical simulation revealed that wall roughness significantly reduced the ‘particle free zone’ and smoothed the particle number density profiles by altering the particle rebounding behaviours. It was also found that wall roughness reduced the particle mean velocities and also increased the particle fluctuating velocities in both streamwise and transverse directions.
International Journal of Heat and Mass Transfer.
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ABSTRACT: This paper presents a numerical study of dilute gas-particle flows in an in-line tube bank. The physical characteristics of the particle–wall collisions and their contributions to particle phase flow field were investigated employing a Lagrangian particle-tracking model, which includes an algebraic particle–wall collision model and a stochastic wall roughness model. Particles with corresponding diameters of 1 μm, 15 μm and 93 μm were simulated under the gas flow condition of 11.2 m/s. The predicted mean velocities and fluctuations for both gas and 93 μm particles were validated against experimental data. The numerical predictions revealed that the wall roughness has a considerable effect by altering the rebounding behaviours of the large particles, and consequently affecting the particles motion downstream and shifting particle collision frequency distribution on the tubes. Also, the results demonstrated that the velocity fluctuations for large particles are predominantly determined by the particle–wall collisions.
Computers & Chemical Engineering.
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ABSTRACT: Detailed data of air flow patterns can assist in the understanding of the physiological and pathological aspects of nasal breathing as well as the prediction of gas-particle flows. A computational model of a human nasal cavity was constructed from CT scans and air flow rates of 7.5L/min and 40L/min were simulated. The study obtained air flow patterns and its features such as pressure drop and airflow distribution and profiles for the left and right nasal cavities. The results were compared with each other while some results were compared with experimental and numerical data that were available. The flow patterns in the nasal valve and turbinate were studied in particular detail, since the airflow profiles in these regions have not been well investigated. Maximum velocities were found at the narrowest cross-sections at the nasal valve region. The airflow distribution showed airflow remaining close to the nasal septum wall and little flow reached the outer meatus regions. The role of the turbinates with respect to the airflow distribution and the possible health implications on the differences in the left and right cavities was briefly discussed.
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ABSTRACT: The air conditioning capability of the nose is dependent on the nasal mucosal temperature and the airflow dynamics caused by the airway geometry. A computational model of a human nasal cavity obtained through CT scans was produced and CFD techniques were applied to study the effects of morphological differences in the left and right nasal cavity on the airflow and heat transfer of inhaled air. A laminar steady flow of 10L/min was applied and two inhalation conditions were investigated: normal conditions, 25°C, 35% relative humidity and cold dry air conditions, 12°C, 13% relative humidity. It was found that the frontal regions of the nasal cavity exhibited greater secondary cross flows compared to the middle and back regions. The left cavity in the front region had a smaller cross-sectional area compared to the right which allowed greater heating as the heat source from the wall was closer to the bulk flow regions. Additionally it was found that the residence time of the inhaled air was important for the heating ability in laminar flows.
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ABSTRACT: In this paper, modelling gas–liquid bubbly flows is achieved by the introduction of a population balance equation combined with the three-dimensional two-fluid model. For gas–liquid bubbly flows without heat and mass transfer, an average bubble number density transport equation has been incorporated in the commercial code CFX5.7 to better describe the temporal and spatial evolution of the geometrical structure of the gas bubbles. The coalescence and breakage effects of the gas bubbles are modelled according to the coalescence by the random collisions driven by turbulence and wake entrainment while for bubble breakage by the impact of turbulent eddies. Local radial distributions of the void fraction, interfacial area concentration, bubble Sauter mean diameter, and gas and liquid velocities, are compared against experimental data in a vertical pipe flow. Satisfactory agreements for the local distributions are achieved between the predictions and measurements. For gas–liquid bubbly flows with heat and mass transfer, boiling flows at subcooled conditions are considered. Based on the formulation of the MUSIG (multiple-size-group) boiling model and a model considering the forces acting on departing bubbles at the heated surface implemented in the computer code CFX4.4, comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter, interfacial area concentration, and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Good agreement is achieved with the local radial void fraction, bubble Sauter mean diameter, interfacial area concentration and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress through the consideration of additional momentum equations or developing an algebraic slip model to account for the effects of bubble separation.
Applied Mathematical Modelling.
