Jian Wen

Numerical simulations for detailed airflow dynamics in a human nasal cavity

Nasal physiology is dependent on the physical structure of the nose. Individual aspects of the nasal cavity such as the geometry and flow rate collectively affect nasal function such as the filtration of foreign particles by bringing inspired air into contact with mucous-coated walls, humidifying and warming the air before it enters the lungs and the sense of smell. To better understand the physiology of the nose, this study makes use of CFD methods and post-processing techniques to present flow patterns between the left and right nasal cavities and compared the results with experimental and numerical data that are available in literature. The CFD simulation adopted a laminar steady flow for flow rates of 7.5 L/min and 15 L/min. General agreement of gross flow features were found that included high velocities in the constrictive nasal valve area region, high flow close to the septum walls, and vortex formations posterior to the nasal valve and olfactory regions. The differences in the left and right cavities were explored and the effects it had on the flow field were discussed especially in the nasal valve and middle turbinate regions. Geometrical differences were also compared with available models.

Comparison of micron- and nanoparticle deposition patterns in a realistic human nasal cavity

Knowledge regarding particle deposition processes in the nasal cavity is important in aerosol therapy and inhalation toxicology applications. This paper presents a comparative study of the deposition of micron and submicron particles under different steady laminar flow rates using a Lagrangian approach. A computational model of a nasal cavity geometry was developed from CT scans and the simulation of the fluid and particle flow within the airway was performed using the commercial software GAMBIT and FLUENT. The air flow patterns in the nasal cavities and the detailed local deposition patterns of micron and submicron particles were presented and discussed. It was found that the majority of micron particles are deposited near the nasal valve region and some micron particles are deposited on the septum wall in the turbinate region. The deposition patterns of micron particles in the left cavity are different compared with that in the right one especially in the turbinate regions. In contrast, the deposition for nanoparticles shows a moderately even distribution of particles throughout the airway. Furthermore the particles releasing position obviously influences the local deposition patterns. The influence of the particle releasing position is mainly shown near the nasal valve region for micron particle deposition, while for submicron particles deposition, both the nasal valve and turbinate region are influenced. The results of the paper are valuable in aerosol therapy and inhalation toxicology.

From CT Scans to CFD Modelling – Fluid and Heat Transfer in a Realistic Human Nasal Cavity

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 the process described. CFD techniques were applied to study the effects of morphological differences in the left and right nasal cavities on the airflow and heat transfer of inhaled air. A laminar steady flow of 15 L/min was applied and two inhalation conditions were investigated: normal air 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 role of the turbinates to condition the air may not be solely reliant on the surface area contact but may in fact be influenced by the nature of the flow that the turbinates cause.

Improvements on Flow Distribution and Heat Transfer Performance of Plate-fin Heat Exchangers by Qusai-S Type Header Configuration

ABSTRACT In order to reduce flow maldistribution and enhance the heat transfer performance, an improved quasi-S-type header configuration of plate-fin heat exchangers is proposed. Based on the analysis of the fluid flow distribution, the results indicate that the outlet velocity of the conventional header is uneven. However, the qusai-S-type header not only effectively reduces the geometric mutation, but also extends the hydraulic path, which guides fluid to the two sides and thereby reduces the maldistribution. The qusai-S-type header was designed on the basis of the cubic curve (denoted as configuration B), Bézier curve (configuration C), or two semi-circular segments uniting with one-line segment (configuration D). Compared with the conventional header (configuration A), the maldistribution parameters for configuration B, C, and D decrease by 75.2–93.9%, 80–94.8%, and 78.4–94.3%, respectively. Yet, the power consumptions of them increase by 26.3%, 22.3%, and 42.3%, respectively. Besides, the effectiveness of the conventional plate-fin heat exchanger declines about 15.1% due to improper header configuration, while the decrease of effectiveness can be controlled within 2.0% using the improved header configurations. Therefore, the improved header configurations can effectively enhance the flow uniformity and the heat exchanger effectiveness, but with a low power consumption penalty.

PIV Investigations of Flow Patterns in the Entrance Configuration of Plate-fin Heat Exchanger

Abstract Flow characteristics in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The flow field was measured using the two-frame cross-correlation technique. Streamline and velocity contour graphs at different cross-sections were obtained in the experiment. The experimental results indicate that flow maldistribution in the conventional header is very serious, while the improved header configuration with punched baffle can effectively improve the uniformity. The flow maldistribution parameter in plate-fin heat exchanger has been reduced from 1.21 to 0.21, and the ratio of the maximum velocity to the minimum is reduced from 23.2 to 1.8 by installing the punched baffle. The results suggest room for the optimum design of plate-fin heat exchanger.

Numerical prediction for subcooled boiling flow of liquid nitrogen in a vertical tube with MUSIG model

Multiple size group (MUSIG) model combined with a three-dimensional two-fluid model were employed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribution patterns of void fraction in the wall-heated tube were analyzed. It was found that the average void fraction increases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and subcooled temperature. The local void fraction exhibited a U-shape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient against experimental measurements, which demonstrated the accuracy of the numerical model.

The effects of injection modes on instantaneous particle deposition in a realistic human nasal cavity

To understand the instantaneous particle deposition in nasal cavity, effects of two injection models on particle deposition characteristic were discussed in this paper. Based on a realistic human nasal cavity geometry obtained from CT scans, a comparison of deposition pattern in the nasal cavity between single injection and continuous injection was investigated through the Lagrangian approach. The instantaneous airflow field was simulated with the tidal volume of 159 and 318 mL by two sine wave curves at inlet. For the case of single injection, particles have finished deposition in the first half of inhalation, and a negative correlation between the tidal volumes and deposition can be observed when the particle diameter was larger than 10 µm. Moreover, particles were mainly deposited in the turbinate area that was beneficial for aerosol therapy. The inertial parameter was not suitable to predict the particle deposition in the case of single injection. With respect to continuous injection, a reduction in total deposition caused by the deceleration process of inhalation can be observed after 1.5 s. The deposition was closely associated with the time-varying flow field, and particles were mainly deposited in the anterior region and turbinate area. Besides, the particle deposition increased with the inertial parameter for continuous injection. The results indicated that the injection modes had an influence on both the total deposition and local deposition pattern in the nasal cavity. Copyright

Inhalation of Toxic and Therapeutic Particles in a Human Nasal Cavity

The reconstruction of the nasal cavity from computed tomography (CT) scans to a computational model was performed in order to (i) analyse the air flow field and (ii) particle dynamics. The scans were converted into MegaWave2 in preparation for processing. The solid modeling program, CATIA combined with the meshing program GAMBIT was then used to establish a model ready for computational fluid dynamics (CFD) analysis. A steady state laminar flow at 7.5 L/min was used to capture the flow field. Complex flow patterns including vortices were found in the nasal valve region. This flow feature enhances the deposition patterns in the anterior region of the cavity. Fibrous particles and low density particles were introduced into the air flow stream with their trajectories and deposition location recorded. Low-density drug particles lightens the particle inertial properties however the particle inertia is more sensitive to the particle size rather than the density. The toxicity of fibres has been linked to its length where fibre deposition in the lungs can be carcinogenic. It was found that asbestos had very low deposition, ap10% and was independent of fibre length, leading to deep lung deposition. In comparison, the carbon fibre was more sensitive to changes in the length and exhibited increases in deposition as the fibre length increased.