田中 学

In this study, a moving boundary deformation model based on four-dimensional computed tomography angiography (4D-CTA) with high temporal resolution is constructed, and blood flow dynamics of cerebral aneurysms are investigated by numerical simulation. A realistic moving boundary deformation model of a cerebral aneurysm was constructed based on 4D-CTA in each phase. Four hemodynamic factors (wall shear stress [WSS], wall shear stress divergence [WSSD], oscillatory shear index [OSI], and residual residence time [RRT]) were obtained from numerical simulations, and these factors were evaluated in basilar artery aneurysms. Comparison of the rigid body condition and the moving boundary condition investigating the relationship between wall displacement and hemodynamic factors clarified that the spatial-averaged WSS and maximum WSSD considering only the aneurysmal dome has a large difference between conditions during the peak systole, and there were also significant differences in OSI and RRT.

The study of lung mechanics is important to futureproof resilience against potential novel threats to lung health. Medical imaging provides insight to lung function. High-resolution, high-speed synchrotron radiation micro-CT imaging at SPring-8 (Japan) and in situ mechanics were used to characterize healthy and diseased airways. Synchrotron radiation was important to maximize speed and spatial resolution to map the lung architecture clearly. Links between global lung mechanical measurements (pressure-volume) and regional tissue strains were made. Tissue strains were computed from a sequence of tomograms during a respiratory cycle, demonstrating clear differences for the surfactant-free lungs compared to the controls. Poorly ventilated areas were identified within three-dimensional strain maps computed via digital volume correlation. Occluded pathways at low pressures were seen to be opened at higher pressures, augmenting the deformation pathways. The results will aid correlations between microscale and macroscale measurements and the potential impact on patient management guidelines for mechanical ventilation.

The global spread of COVID-19 in 2020 had a significant impact on the population. Healthcare workers who have unpreventable contact with infected individuals are at high risk of infection. We therefore proposed “infection control methods in high-risk environments” and demonstrated that appropriate placement of suction devices in otorhinolaryngology examination rooms is effective for aerosol control [Takada M, Fukushima T, Ozawa S, Matsubara S, Suzuki T, Fukumoto I, Hanazawa T, Nagashima T, Uruma R, Otsuka M, Tanaka G: Sci Rep. 12(1), 18230, 2022]. As a further study of the previous research, this study analyzed the specific environmental factors that contribute to reducing the risk of infection by optimizing the manner in which suction devices are set up. The models of a patient and doctor were placed in an examination room. A steady flow of 2.5 m/s was applied to the patient’s mouth as exhalation. Aerosol diffusion was analyzed using computational fluid dynamics. The optimization parameters were the position and angle of suction inlet, and suction speed. The objective evaluation was the “maximum number of particles aspirated from the suction inlet”. A total of 150 designs were tested, and the search for the optimal positions was performed in the examination room. The optimization results showed that the maximum particle removal rate was 98.6%. There were six cases in which the particle removal rate was at least 98%. These positions were within the range of x = 0.120 to 0.159 m in the horizontal direction from the patient’s mouth to the suction inlet. The suction inlet was placed laterally in front of the patient, along the trajectory of the particles emitted from the patient’s mouth. Particle removal rates of over 98% at various suction speeds indicates that the position and direction of the suction inlet are more important than the suction speed. The adjustment of suction devices based on the results of this study would help reduce the risk of infection in healthcare settings.

Obstructive sleep apnea syndrome (OSAS) is a disorder that causes sleep apnea and hypopnea, which in turn causes various disorders in daily life. Because of the difficulty in measuring airflow dynamics, computational fluid dynamics (CFD) simulations are performed to evaluate upper airway airflow in OSAS in detail. However, the relationship between the severity of OSAS, as measured by the apnea hypopnea index (AHI), and airflow dynamics is unclear. In this study, CFD simulations of human snoring during sleep were performed to determine the correlation between AHI and pressure drops in the nasal cavity and throat, as well as between AHI and minimum cross-sectional area of the throat. For the simulation, 3D models of snoring in the open-mouth state, which is a common form of snoring, were reconstructed based on computed tomography images acquired from four patients with mild OSAS and six with severe OSAS. Each relationship was evaluated using Spearman’s rank correlation coefficient. The correlation coefficient between AHI and pressure drop in the nasal cavity was 0.745, with a significant correlation. There was no significant correlation between AHI and pressure drop in the throat or between AHI and minimum cross-sectional area of the throat. These results suggest that the pressure drop in the nasal cavity affects the severity of OSAS.

Healthcare providers are vulnerable to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) because of their close proximity to patients with coronavirus disease 2019. SARS-CoV-2 is mainly transmitted via direct and indirect contact with respiratory droplets, and its airborne transmission has also been identified. However, evidence for environmental factors is scarce, and evidence-based measures to minimize the risk of infection in clinical settings are insufficient. Using computational fluid dynamics, we simulated exhalation of large and small aerosol particles by patients in an otolaryngology examination room, where medical procedures require the removal of a face mask. The effects of coughing were analyzed, as well as those of humidity as a controllable environmental factor and of a suction device as an effective control method. Our results show that a suction device can minimize aerosol exposure of healthcare workers by efficiently removing both large (11.6-98.2%) and small (39.3-99.9%) aerosol particles. However, for coughing patients, the removal efficiency varies inversely with the particle size, and the humidity notably affects the aerosol behavior, indicating the need for countermeasures against smaller aerosols. Overall, these results highlight the potential and limitation of using a suction device to protect against SARS-CoV-2 and future respiratory infections.

The mechanisms underlying the growth and rupture of aneurysms are poorly understood. Although the wall shear stress (WSS) in elastic aneurysm models is examined using fluid-structure interaction (FSI) simulations, it has not been sufficiently validated using experimental modalities, such as particle image velocimetry (PIV) or phase contrast magnetic resonance imaging (PC-MRI). In this study, we investigated pulsatile flow in an elastic, image-based, patient-specific cerebral aneurysm model using PIV. The phantom model was carefully fabricated using a specialized technique by silicone elastomer. We explored the hemodynamics of the WSS and the kinetic energy cascade (KEC) in the elastic model compared with a rigid model, at the apex of the bifurcation of the middle cerebral artery (MCA) in vitro. The effects of elasticity on the WSS, WSS gradient (WSSG), and tensile strength of the aneurysm wall were also investigated, in addition to the effect of wall elasticity on the KEC compared to a rigid wall. Although the WSSG around the stagnation point had a large positive value, there was no difference between the two models. In particular, wall elasticity suppressed the WSS magnitude around the stagnation point and attenuated the KEC (i.e., the flow fluctuation). Future studies examining KEC frequency and WSS characteristics in a phantom model should consider assessing elasticity.

Pulsating flow within an elastic cerebral aneurysm model was visualized by particle image velocimetry (PIV) to clarify the effect of wall deformation on wall shear stress (WSS). In the experiment, we used a full-scale patient-specific cerebral aneurysm phantom model with a thin transparent silicone wall fabricated by soaking a plaster mold. The experiment was performed in two planes, one in the middle plane and the other perpendicular to it. The results showed that in the middle plane, the wall deformation reduced the maximum WSS in systole by about 20% and the averaged WSS by about 20% in comparison with the less-deformation model. On the other hand, for planes perpendicular to the aforementioned planes, the averaged WSS increased by about 10% in comparison with the less-deformation model. In addition, it was observed that the local WSS changed in intensity according to the plane and phase, because of movement of the separation point of the wall jet. This finding suggests that the wall deformation of cerebral aneurysm affects the magnitude of WSS.

<title>Abstract</title> Thermoacoustic engines use waste heat available at a higher temperature to produce mechanical energy in the form of waves. The purpose of this study is to visualize the fluid behavior downstream of the stack of a thermoacoustic engine by applying numerical analysis and to explore the effect of vortex shedding on the temperature field. The self-sustained oscillation is reproduced by two-dimensional numerical analysis using the compressible solver of OpenFOAM, and the vorticity field and temperature field were visualized. The vortex downstream of the stack changed from symmetric to asymmetric near the peak of the flow velocity. Changes in the vortex structure by the unsteady flow caused irregular and non-uniform temperature field. It is found that the vortex significantly affects the heat transfer between the heat exchanger and the fluid.

<title>Abstract</title> We visualized the flow patterns in an alveolated duct model with breathing-like expanding and contracting wall motions using particle image velocimetry, and then, we investigated the effect of acinar deformation on the flow patterns. We reconstructed a compliant, scaled-up model of an alveolated duct from synchrotron microcomputed tomography images of a mammalian lung. The alveolated duct did not include any bifurcation, and its entire surface was covered with alveoli. We embedded the alveolated duct in a sealed container that was filled with fluid. We oscillated the fluid in the duct and container simultaneously and independently to control the flow and duct volume. We examined the flow patterns in alveoli, with the Reynolds number (Re) at 0.03 or 0.22 and the acinar volume change at 0%, 20%, or 80%. At the same Re, the heterogeneous deformation induced different inspiration and expiration flow patterns, and the recirculating regions in alveoli changed during respiratory cycle. During a larger acinar deformation at Re = 0.03, the flow patterns tended to change from recirculating flow to radial flow during inspiration and vice versa during expiration. Additionally, the alveolar geometric characteristics, particularly the angle between the alveolar duct and mouth, affected these differences in flow patterns. At Re = 0.22, recirculating flow patterns tended to form during inspiration and expiration, regardless of the magnitude of the acinar deformation. Our in vitro experiments suggest that the alveolated flows with nonself-similar and heterogeneous wall motions may promote particle mixing and deposition.

<title>Abstract</title><sec> <title>Background</title> The novel coronavirus disease 2019 (COVID-19) undermines the benefits of cancer screening. To date, no study has identified specific infection control methods. We aimed to provide practical methods for COVID-19 risk reduction during breast cancer screening mammography (MMG) by examining an overview of potential contamination routes of aerosols and possible risks for patients and health care providers. </sec><sec> <title>Methods</title> Computational fluid dynamics (CFD) simulations were conducted for airflow and aerosol dispersion in a 3D virtual model of a mobile MMG laboratory room. This model was constructed based on the actual mobile screening MMG bus ‘Cosmos’ in the Chiba Foundation for Health Promotion &amp; Disease Prevention. Examiner and patient geometries were obtained by scanning an actual human using a 3D Scanner. Contamination of the room was evaluated by counting the numbers of suspended and deposited aerosols. </sec><sec> <title>Results</title> We applied the CFD simulation model to the exhalation of small or large aerosols from a patient and examiner in the MMG laboratory. Only 14.5% and 54.5% of large and small aerosols, respectively, were discharged out of the room with two doors open. In contrast, the proportion of large and small aerosols discharged out of the room increased to 96.6% and 97.9%, respectively, with the addition of forced gentle wind by the blower fan. This simulation was verified by a mist aerosol experiment conducted in the mobile MMG laboratory. </sec><sec> <title>Conclusion</title> Adding forced ventilation to a MMG laboratory with two doors open may enable risk reduction dramatically. This could be applied to other clinical situations. </sec>

The nasal airway is an extremely complex structure, therefore grid generation for numerical prediction of airflow in the nasal cavity is time-consuming. This paper describes the development of a voxel-based model with a Cartesian structured grid, which is characterized by robust and automatic grid generation, and the simulation of the airflow and air-conditioning in an individual human nasal airway. Computed tomography images of a healthy adult nose were used to reconstruct a virtual three-dimensional model of the nasal airway. Simulations of quiet restful inspiratory flow were then performed using a Neumann boundary condition for the energy equation to adequately resolve the flow and heat transfer. General agreements of airflow patterns, which were a high-speed jet posterior to the nasal valve and recirculating flow that occupied the anterior part of the upper cavity, and temperature distributions of the airflow and septum wall were confirmed by comparing in-vivo measurements with numerical simulation results.

The mortality and morbidity rate due to the severe effect of intracranial aneurysm (IA) is increasing, which has driven research trend on aneurysm rupture risk. By understanding the nature and causes of the aneurysm rupture, preventive measures could be taken in avoiding rupture besides recommending proper treatments such as endovascular coiling. However, the presence of flow recirculation causes the aneurysm wall to degenerate and weakened. The weakened wall is due to the haemodynamic factors such as velocity, wall shear stress (WSS), time average WSS (TAWSS), OSI and RRT, which were analysed in this study. In the present study, the flow model simulated a human patient-specific aneurysm at the apex of the bifurcation in the middle cerebral artery (MCA) in the transient state. Experimental results of full-scale models were collected on a median, side plane to study the flow behaviour and validation to the numerical simulation settings, which resulted in good agreement with only 8% difference. The simulation results obtained showed several interesting findings. The jet flow into the aneurysm led to complex vortex formation due to impinging flow behaviour within the aneurysm dome. Additionally, the area that recorded low velocity was at 30% of low TAWSS with only 1% of OSI that was more than 0.3, while the OSI critical value and 0.27% area exceeded RRT threshold, which caused the large oscillating blood flow direction and activated the atherosclerosis progression. These results suggest that the jet flow into the dome may cause further damage to the wall of the MCA aneurysm, which will help in providing an insight towards completing a guidance system assessment of rupture risk for medical practitioners in future work.

This paper describes the simulation of airflow in human nasal airways using voxel-based modeling characterized by robust, automatic, and objective grid generation. Computed tomography scans of a healthy adult nose are used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulations of restful inspiratory flow are then performed using various mesh sizes to determine the level of granularity required to adequately resolve the airflow. For meshes with close voxel spacings, the model successfully reconstructs the nasal structure and predicts the overall pressure drop through the nasal cavity.

To establish a new simplified approach to quantify the impact of surgical intervention on nasal airflow, we used voxel-based computational fluid dynamics simulations to analyze nasal airflow under unsteady flow conditions mimicking a sniff, which involves brief inhalation accompanied by rapid acceleration. The time-transient distribution of the flow rate in the coronal cross-section was investigated to validate the results of this voxel method against those of conventional boundary-fitted method. Despite a simple approach using coarse voxel grids, the voxel method accurately reproduced rapid changes in flow distribution during a sniff. We also found that correctly modeling rapid changes in the characteristic flow structure in a nasal cavity (including a jet posterior to the nasal valve and a recirculating flow in the upper anterior region of the cavity) is important for reproducing the unsteady flow distribution during a sniff. Thus, the voxel-based simulations can be used to assess the dynamics of unsteady nasal airflows.

For laminar flow in the side branch of a T-junction, periodic fluid vibrations occur with the Strouhal number independent of characteristic flow conditions. As the mechanics is unknown, an experiment was performed to establish the underlying cause in high-shearrate flow. The fluid vibration appears along both the shearing separation layer and the boundary between two vortices immediately downstream of the side branch, where the shear rates are several orders larger than those further downstream. This vibration is caused by flow instability induced in two types of high-shear-rate flow confirming that is a universal phenomenon associated with the geometry of the T-junction.

The effect of a simple bare metal stent on repression of wall shear stress inside a model cerebral aneurysm was experimentally investigated by two-dimensional particle image velocimetry in vitro. The flow model simulated a cerebral aneurysm induced at the apex of bifurcation between the anterior cerebral artery and the anterior communicating artery. Wall shear stress was investigated using both stented and non-stented models to assess the simple stent characteristics. The flow behavior inside the stented aneurysm sac was unusual and wall shear stress was much smaller inside the aneurysm sac. Stent placement effectively repressed the temporal and spatial variations and the magnitude of wall shear stress. Hence, there is an effective possibility that would retard the progress of cerebral aneurysms by even simple stent.

BACKGROUND: Many numerical studies have been published with respect to about flow structures around cerebral aneurysm assuming to be rigid. Furthermore, there is little experimental research concerning aneurysm with elastic wall. Wall shear stress in elastic wall comparing with rigid wall should be clarified in experimental approach and verified in CFD. OBJECTIVE: We have experimentally realized elastic aneurysm model accompanying with wall deformation. Wall shear stress was examined for both rigid and elastic aneurysm models in pulsatile flow. METHODS: Effect of elasticity on wall shear stress inside aneurysm induced at the apex of anterior cerebral artery was experimentally examined by particle image velocimetry in vitro. In order to adjust the wall deformation, the pressure adjustment chamber was specially equipped outside the aneurysm wall. RESULTS: Effect of elasticity on wall shear stress was noticed on the comparison with that of rigidity. Wall elasticity reduced the peak magnitude, the spatial and temporal averaged wall shear stress comparing with those of wall rigidity experimentally. These reductions were endorsed by fluid-structure interaction simulation. CONCLUSION: Elastic wall comparing with rigid wall would reduce the peak magnitude, the spatial and temporal averaged wall shear stress acting on vascular wall.

Nasal air flow and temperature were analyzed using a voxel model constructed directly from medical images. The nasal cavities of a healthy male were reconstructed using CT slices in the axial direction at an image resolution of 0.488 mm/pixel and a slice interval of 0.40 mm. The rough surfaces in the image, which were caused by the resolution, were smoothed using a bilinear interpolation algorithm. A voxel-based simulation of inspiratory flow was then performed with a voxel pitch of 0.20 mm. With an interpolation image resolution of 0.163 mm//pixel, the voxel model successfully simulated an overall pressure drop and airflow temperature to the same extent as the conventional boundary-fitted model.

Abstract: The location and concentration of particle deposition of pollen by filtration in the human nasal cavity were visualized in a transparent silicone nasal airway model using laser-induced fluorescence (LIF) to clarify the relationship between flow and particle deposition. The model was created from a water-soluble plaster mold fabricated by a 3D printer based on X-ray computed tomography images. The working fluid was air and the tracer particles as a substitute for cedar pollen were lycopodium powder doped with fluorescent dye (Rhodamine 6G). After particle deposition, the nasal airway model was filled with an aqueous solution of glycerin that had the same refractive index as silicone. Then, LIF was applied to illuminate the deposited particles with a YAG laser sheet. Results revealed that particle deposition in the right and left cavities was highly heterogeneous and was related to the complex flow structure in the nasal cavities.

The objective of this study is to visualize the chaotic mixing patterns induced by oscillatory flow in a curved tube. The velocity field during oscillatory flow in a curved tube with inner diameter of 10 mm and tube length of 314 mm was numerically simulated using the commercial software Fluent. The working fluid was water and the flow was assumed to be 3D, laminar, unsteady, and incompressible. To clarify the effect of the curvature, the ratio of the tube radius to the curvature radius a/b was varied from 0.0125 to 0.075, and oscillatory flow frequency f was varied from 0.5 to 2.0 Hz. To visualize the fluid mixing patterns, trajectories were also calculated for the minute particles that follow convective movement. To examine the chaotic features of flow, the largest Lyapunov exponent was then evaluated. The visualized tracer patterns revealed the characteristic fluid mixing patterns with repeated stretching and folding in the radial and longitudinal cross-sections, and the length of a stretched tracer line increased with increasing a/b and with decreasing f. The average value of the largest Lyapunov exponent was positive under all flow conditions and was changed in response to the tracer line length. These results indicate that the flow mixing pattern induced by oscillatory flow in a curved tube is chaotic.

The present paper deals with the longitudinal heat transportation by an oscillatory flow in a curved tube heat transportation pipe. The velocity and temperature fields during oscillatory water flow in a curved tube with inner diameter of 10 mm were numerically simulated using the commercial software FLUENT. To clarify the effect of the curvature on heat transportation, the ratio of the tube radius to the curvature radius was varied from 0.0125 to 0.075, and oscillatory flow frequency was varied from 0.1 to 2.0 Hz. The effective thermal diffusivity exhibited a peak at a curvature ratio around 0.05-0.07 and reached a value 12 times higher than that of a straight tube. It was also found that the dispersion of fluid particles due to secondary flow caused the enhancement of heat transportation. (C) 2013 Elsevier Ltd. All rights reserved.

The present paper deals with experimental and numerical study on the longitudinal heat transportation by an oscillatory water flow in a curved heat transportation tube. The heat transportation experiments were conducted for the curved tube with an inner diameter of 10 mm, and a tube length of 314 mm. The experimental apparatus mainly consisted of a test tube, hot water bath (323 K), cold water bath (293 K), and an apparatus generating the oscillatory flow. The ratio of the tube radius to the curvature radius was varied from 0.0125 to 0.075, and oscillatory flow frequency was varied from 0.5 to 2.0 Hz. As a result, the effective thermal diffusivity exhibited a peak at a curvature ratio around 0.05-0.07 and reached a value about 5 times higher than that of a straight tube. To discuss the heat transportation augmentation mechanism, the flow and temperature fields were investigated by numerical analyses. The analyses revealed that dispersive motion of fluid particles due to secondary flows plays a major role in enhancing heat transportation via curved tubes.

The duration of supercooling for erythritol, a promising phase change material with a melting point of 118°C, was investigated in a glass tube using three small specimen volumes of 0.025, 0.40, and 16.0 cm3 in glass tube diameters of 1.02, 10.0, and 27.3 mm, respectively. The supercooling duration was measured by the temperature increase of the specimen due to the release of latent heat under a constant degree of supercooling from 38 to 98°C. The supercooling duration was largely dependent on the supercooling degree and specimen sizes, and increased from approximately 0.1 to 20 000 min with a decrease in the supercooling degree and specimen size. The effects of the supercooling degree and specimen size on the supercooling duration are discussed in terms of the Johnson-Mehl-Avrami equation and three nucleation theories based on the observed solidification position; homogeneous nucleation, heterogeneous nucleation from the wall, and heterogeneous nucleation from insoluble particles.

This study describes a new approach to provide detailed quantification of the impact of surgical intervention on bilateral nasal airflow using voxel-based simulation. Computed tomography and magnetic resonance imaging scans were used to reconstruct 3D realistic models of both the pre- and post-operative nasal airways. Voxel-based simulation of quiet restful inspiratory flow was then performed using meshes of varying refinement to determine the level of mesh refinement required to adequately resolve the flow and heat transfer. For meshes with voxel pitches of 0.10 mm, the voxel model successfully simulated the overall pressure drop and airflow temperatures.

This work describes a new approach to simulate the airflow and air-conditioning in the individual human nasal airways using voxel-based modeling with Cartesian structured grid. Computed tomography imaging scans of a healthy adult nose were used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulation of quiet restful inspiratory flow was then performed using meshes of varying refinement to determine the level of mesh refinement required to adequately resolve the flow and heat transfer. For meshes with a voxel pitch of 0.20 mm or less, the voxel model successfully reconstruct the realistic nasal structure and simulate the overall pressure drop and airflow temperature. The resultant streamlines and vorticity distributions reveal the characteristic flow structure in the nasal cavities, with high speed jet posterior to the nasal valve, recirculating flow that occupies the anterior part of the upper cavity, and low speed flow in the olfactory region. It was also found that the impinging jet plays an important role in the air-conditioning performance in the nasal cavities.

Mass transport phenomena in airways, including dispersion, may be influenced by the complicated three-dimensional (3D) branching geometry, which undergoes expansion and contraction during the respiratory cycle. In this study, we investigated the effects of this expansion and contraction on gas dispersion in multi-branching airways using computational fluid dynamics. A 3D multi-branching airway model was constructed based on mammalian computed tomography images, with diameters ranging from 1.25 mm in the parent tube to 0.35 mm in the daughter tube. We examined the dispersion of oxygen in the airway when subject to oscillatory flow while the airway expanded and contracted sinusoidally with time. After several respiratory cycles, the oxygen fraction was higher in the airway-motion model than in the rigid model, and it increased as the volume expansion factor increased. Furthermore, the oxygen fraction increased as the breathing frequency was increased for the airway model undergoing wall motion. Transport simulation of passive tracer particles showed that, although the particles were dispersed around the initial position in the rigid model, many particles were anchored around the carina and dispersed widely in the airway-motion model. These results indicate that steady streaming and unsteady flow behavior due to airway branches and expanding and contracting motion may enhance gas dispersion in multi-branching airways. (C) 2013 Elsevier Ltd. All rights reserved.

We visualized pulmonary acini in the core regions of the mouse lung in situ using synchrotron refraction-enhanced computed tomography (CT) and evaluated their kinematics during quasi-static inflation. This CT system (with a cube voxel of 2.8 mu m) allows excellent visualization of not just the conducting airways, but also the alveolar ducts and sacs, and tracking of the acinar shape and its deformation during inflation. The kinematics of individual alveoli and alveolar clusters with a group of terminal alveoli is influenced not only by the connecting alveolar duct and alveoli, but also by the neighboring structures. Acinar volume was not a linear function of lung volume. The alveolar duct diameter changed dramatically during inflation at low pressures and remained relatively constant above an airway pressure of similar to 8 cmH(2)O during inflation. The ratio of acinar surface area to acinar volume indicates that acinar distension during low-pressure inflation differed from that during inflation over a higher pressure range; in particular, acinar deformation was accordion-like during low-pressure inflation. These results indicated that the alveoli and duct expand differently as total acinar volume increases and that the alveolar duct may expand predominantly during low-pressure inflation. Our findings suggest that acinar deformation in the core regions of the lung is complex and heterogeneous.

Computational fluid dynamics (CFD) simulation was carried out for an oscillatory flow in an expanding and contracting model of small airways, and the effects of airway geometry and rhythmic breathing motion on the kinematic irreversibility of oscillatory flow were revealed. A 3D realistic model of multi-branching small airways was reconstructed from X-ray CT images of a mouse, which were obtained by the high-resolution synchrotron radiation CT system of SPring-8. Airway diameters range from 360 μm in the primary branch to 55 μm in the distal branch. The airway model was expanded and contracted in a sinusoidal volume change with time such that the geometry remains self-similar throughout a period. The Fluent software package was used for calculation of the fluid particle trajectory in the airway model. The dispersion of the fluid particle was evaluated in terms of the variance of the marked minute particles in the axial direction. The results show that the axial dispersion is enhanced by the expanding and contracting motion of the airways. It was also found that the augmentation of steady streaming is responsible for enhanced dispersion of fluid particles. © 2011 Elsevier Ltd. All rights reserved.

To reveal the natuit of turbulence in a lung, the measuitments of turbulence in the oscillatory flow in realistic model human centml airways were made by particle image velocimetry (Ply). The transparent silicon model of multi-branching airways was fabricated from X-ray CT images by rapid prototyping. The multi-branching airways comprise trachea, right and lefi bronchi and airway diameters range from 14 to 2 mm. Experiments were performed for the Reynolds number from 1200 to 2200 and for the Womersley number from 1.9 to 2.3 in the trachea. The spatial and temporal variations of turbulent intensity were strongly dependent on the airway geometry and the phase of oscillatory flow. The expiratory flow generates strong tuthulence which explosively occurs in the entire cross section especially in the right bronchi, whereas the inspiratory flow generates itlatively weak turbulence near the airway wall. © 2011 The Japan Society of Mechanical Engineers.

The freezing behavior of liposomes such as internal freezing, contraction by dehydration and disruption of membrane after thawing was examined by microscopic observation. Liposome suspensions were prepared by gentle hydration method using phosphatidylcholine (egg) and distilled water. The observed liposomes ranged in diameter from 5 to 150μm. The sample of liposome suspensions was cooled from -1℃ to -50℃ at cooling rates of 1,2 and 5℃/min and heated to 0℃ at heating rate of 10℃/min. As a result, two different patterns for freezing were observed: internal freezing and contraction without internal freezing. When the internal freezing was observed, the membrane was unexceptionally disrupted after thawing. When the internal freezing was not observed, two different cases were observed after thawing: disruptive and contractive conditions. These different freezing patterns were primarily dependent on the liposome size. In addition, the cooling rate became a key factor determining the freezing patterns in small liposomes.

Computational fluid dynamics (CFD) simulation was carried out for an oscillatory flow in a 3-D realistic model of the human central airways, and the effect of airway geometry on the oscillatory flow structure was revealed. The computational model of multi-branching airways was prepared from X-ray CT images. Airway diameter ranges from approx. 2 to 14 mm. The flow in the airway model was simulated using CFD software: Fluent. The resultant flow showed differences compared with that observed in a simplified planar multi-branching model. The inspiratory flow patterns were relatively similar to the patterns observed in a simplified airway model, but the expiratory flow patterns strongly depended on the realistic airway geometry and showed more complicated secondary flow structures. Secondary flow velocities were higher in the realistic airway model than in the simplified airway model in both the inspiratory and expiratory flows. Performing Lagrangian fluid particle tracking, we discussed the convective dispersion due to asymmetric inspiratory and expiratory velocity profiles.

This paper deals with heat transportation by oscillatory flow in grooved ducts. The heat transportation rate, work rate, heat transportation efficiency and variances of fluid particles and heat were analyzed with the computer code FLUENT. The frequency and amplitude of the oscillatory flow was 0.05Hz and 45mm. The internal diameters of the contraction section and the expansion section were 6 and 12mm respectively and the length of the contraction section was fixed to be 10mm with the length of groove varying from 0 to 40mm. We found: (1) Heat transportation rate reached about 4.5 times as large as that of smooth round pipe at the groove length of around 10-15mm. (2) Heat transportation efficiency increased to about 6.4 times that of smooth pipe at the groove length of 20mm. (3) The dispersion of fluid particles caused the augmentation of the heat transportation of grooved ducts with 40mm≧groove length≧5mm. (4) The grooved ducts with the groove length of 10-15mm had the maximum value of the variance of fluid particles which accounted for their high heat transportation rates.

Numerical simulations were carried out for heat transfer during oscillatory flow in a circular straight tube with a solid tube in its center. The solid tube was inserted to enhance axial heat transfer by increasing lateral heat transfer effect for high frequency. The results show that the axial heat transfer increases with an increase in the inserted tube diameter. The results also show that the inserted tube materials do not have any substantial effect on the axial heat transfer. The efficiency based on the ratio of heat transfer to the work done becomes larger compared with that in a bundle of circular capillary tubes.

Present paper deals with experiments of direct-contact freezing of Hexadecane particles injected from multi-nozzle into stagnant pure water, ethylene glycol 30 wt% water solution and ethylene glycol 50 wt% water solution. The experimental parameters were varied in the ranges of n=0.001〜0.51, Re=34〜257 and Pγ=8.8〜42. Main results obtained are summarized in the followings; (1) an empirical equation for drag coefficient of solidified Hexadecane particles was proposed, (2) the relationship between particle density and variations of rising velocity was investigated, (3) the relationship between particle density and Nusselt number of particle swarm was clarified, (4) It was found that one dimensional heat conduction model can be applied to predict the solidification mass fraction of single particle and particle swarm including uniform size particles, and (5) It can be applied to predict the solidification mass fraction of particle swarm including various size particles formed by destruction of laminar and turbulent jet as well.