Effect of vessel number on computational fluid dynamics in vascular networks / 中国组织工程研究

BACKGROUND:Mechanical factors can affect the angiogenic ability of vascular endothelial cells.How the vessel number affects the hydrodynamic properties of microvessels remains to be clarified. OBJECTIVE:To investigate the influence of vessel number on the hydrodynamics of vascular networks based on computational fluid dynamics. METHODS:Three three-dimensional models of vascular network with different vessel numbers were constructed using the Geometry module of ANSYS 19.0 software,and then the vascular network was meshed to tetrahedral elements in Mesh module.The vascular network was assumed to rigid wall without slip,and the blood was assumed to laminar,viscous,and incompressible Newtonian fluid.Blood density,velocity,and a series of blood viscosity coefficients were also established.The Navier-Stokes equation was used for calculation.Hydrodynamic properties of different parts of vascular network with different vessel numbers were analyzed and compared. RESULTS AND CONCLUSION:The streamline,velocity,and mass flow all had the same trend in the vascular network,that is,the outlet and inlet were higher and the middle junction of vascular network was lower.The more the number of vessels,the thinner the blood flow lines in each part of the vascular network.Also,the velocity,mass flow,and wall shear decreased with the increase of the number of blood vessels.Therefore,the changes in vessel number could influence the hydrodynamic environment in the vascular network.Computational fluid dynamics indicates that the changes in vessel numbers can influence the hydrodynamic properties of blood,and provides a new idea for treating bone hypoperfusion-induced diseases(fracture nonunion,bone defect,osteoporosis,etc.)through tonifying kidney and activating blood circulation based on the coupling between angiogenesis and osteogenesis.

Advances in Vascular Biomechanics and Mechanobiology / 医用生物力学

Vascular biomechanics mainly explores how vascular cells perceive mechanical stimuli,how mechanics affects the development of diseases,and the exploitation of various mathematical models to analyze the effects of mechanical factors on diseases.In recent years,researches in the field of vascular biomechanics are developing rapidly,and various research teams have analyzed the mechanical and biological processes of blood vessels from different directions,in order to gain a deeper understanding of the regulatory mechanisms of vascular biomechanical factors affecting the progression of various vascular diseases,and provide a theoretical basis based on the mechanobiology for the prevention and treatment of cardiovascular and cerebrovascular diseases.This article summarizes and discusses the recent research hotspots and emerging trends in the field of vascular mechanobiology based on domestic and foreign expert teams and combined with the work of this research team,thus providing a systematic framework for grasping hotspots and exploring new research directions in the field of vascular mechanobiology.

Application and progress of index of microcirculatory resistance / 中国介入心脏病学杂志

With the deepening of the research on coronary artery related diseases,people gradually realize that coronary microcirculation disorders have an important impact on the occurrence,development,curative effect and prognosis of cardiovascular diseases,and coronary microcirculation diseases have received more and more attention in ischemic heart disease.Since coronary microvessels cannot be directly observed through imaging,there are currently some indicators to evaluate coronary microcirculation function in clinical practice,among which the index of microcirculatory resistance(IMR)is widely used for the evaluation of coronary microcirculation function.Computational fluid dynamics derived IMR is accurate,easy to perform,and has a broad application prospect.This article provides a comprehensive review of the establishment,development,clinical applications,and progress of IMR.

Hemodynamic study of personalized Stanford type B aortic dissection based on computational fluid dynamics / 中国胸心血管外科临床杂志

@#Objective To establish a personalized Stanford type B aortic dissection numerical simulation model, and using computational fluid dynamics (CFD) numerical simulation to obtain the hemodynamic behavior and law of the type B aortic dissection at different stages of development. Methods Based on the theory of three-dimensional model reconstruction, we used CT images of a patient with type B aortic dissection in the Xiamen Cardiovascular Hospital of Xiamen University, relevant medical image processing software to reconstruct a personalized aortic three-dimensional model, and CFD to reconstruct the model which was simulated in fluid mechanics. Results The three-dimensional reconstruction model could intuitively observe the changing trend of the false cavity at different stages of the dissection development. Through fluid mechanics simulation, the blood flow rate, pressure, wall shear stress, vascular wall Von Mises stress and other parameters at different stages of the dissection development were obtained. Conclusion The hemodynamic behavior and law of relevant parameters in the development stage of aortic dissection are analyzed. The combination of the values of relevant parameters and clinical medical detection and diagnosis can well predict the development of the disease, and finally provide more theories and methods for the scientific diagnosis of aortic dissection.

Research progress on cardiovascular hemodynamic assessment based on computational fluid dynamics / 中国胸心血管外科临床杂志

@#Hemodynamics plays a vital role in the development and progression of cardiovascular diseases, and is closely associated with changes in morphology and function. Reliable detection of hemodynamic changes is essential to improve treatment strategies and enhance patient prognosis. The combination of computational fluid dynamics with cardiovascular imaging technology has extended the accessibility of hemodynamics. This review provides a comprehensive summary of recent developments in the application of computational fluid dynamics for cardiovascular hemodynamic assessment and a succinct discussion for potential future development.

Hemodynamic analysis of postoperative reintervention for Stanford type A aortic dissection / 中华胸心血管外科杂志

Objective:A residual false lumen progress risk prediction model was constructed based on computational fluid dynamics and biomechanical parameters were calculated to assess the factors affecting the long-term reintervention after the first operation.Methods:Patients with Stanford type A aortic dissection admitted to Fuwai hospital were retrospectively collected and divided into control group and thoracoabdominal aortic replacement group according to long-term prognosis or history of reintervention. The fluid parameters of the descending aorta were calculated based on the early CTA imaging data after first operation. The differences of parameters between the two groups were compared to explore the risk factors.Results:A total of 24 patients were included from January 2015 to May 2021. The average age was(47.88±9.84) years old, 21(87.5%) male, and 3 female. The balance position of luminal pressure difference in the descending aorta was closer to the opening of the left subclavicular artery[(22.00±3.91)cm vs.(36.00±1.77)cm, P<0.001], and the false lumen pressure was greater than the true lumen pressure in the thoracoabdominal aortic replacement group. Conclusion:The computational fluid dynamics method can simplify and visualize the complex human blood flow and postoperative structure based on the mathematical model. The lumen pressure balance point moving to the proximal are the risk factors for poor remodeling of the descending aorta and reintervention.

Virus aerosol transmission, dispersion, and infection probability simulation: A case study in subway carriages / 环境与职业医学

Background Subways are typical congregate settings and may facilitate aerosol transmission of viruses. However, quantified transmission probability estimates are lacking. Purpose To model spread and diffusion of respiratory aerosols in subways by simulation and calculation of infection probabilities. Methods The internal environment of carriages of Shanghai Metro Line 10 was used to establish a study scene. The movement of tiny particles was simulated using the turbulent model. Trend analysis of infection probabilities and viral quantum doses was conducted in a closed subway carriage scene by a quantum emission-infection probability model. Results Under a typical twelve-vent air conditioning configuration, respiratory droplet aerosols within a subway carriage dispersed rapidly throughout various regions due to airflow, with limited short-term diffusion to other carriages. Concurrently, owing to the uncertainty of airflow patterns, the airflow might circulate and converge within carriages, causing delayed outward dispersion or hindered dispersion of droplet aerosols upon entry into these zones. Passengers boarding the carriage could exacerbate the formation of these zones. When the air conditioning system functioned adequately (air exchange rate=23.21 h−1), the probability of a virus carrier transmitting the virus to other passengers within the same carriage via aerosol transmission was approximately 3.8%. However, in the event of air conditioning system failure (air exchange rate=0.5 h−1), this probability escalated dramatically to 30%. Furthermore, a super-spreader (with virus spreading exceeding 90% of the average) elevated the infection probability to 14.9%. Additionally, due to the complexity of turbulence within the carriage, if local diffusion occurred in 1/2 zones of a carriage, the anticipated infection probability would increase to 8.9%, or during the morning or evening rush hours leading to elevated aerosol concentrations, the infection probability would rise to 4.7%. The subway transmission probability for common coronaviruses diminished to as low as 0.9%. Conclusion Combined computational fluid dynamics and infection probability analysis reveals that in the prevalent twelve-vent air conditioning configurations, despite being a major transportation hub with substantial spatial-temporal overlap, the internal space of subway carriages exhibits a certain level of resistance to virus aerosol transmission owing to built-in ventilation capabilities. However, turbulence and passenger positioning may lead to localized hovering of droplet aerosols, thereby increase the risk of virus transmission. Furthermore, super-spreaders, poor operational status of built-in air conditioning system, and high passenger volume at morning or evening peak hours exert profound effects on virus transmission and infection probability.

A simulating method for dripping process of Ginkgo biloba leaf dripping pills based on computational fluid dynamics technology / 药学学报

A simulating method for dripping process of Ginkgo biloba leaf dripping pills based on computational fluid dynamics was constructed. Ginkgo biloba leaf dripping pills was explored as the experimental subject to simulate the dripping process based on FLOW-3D software. The dripping process was simulated through the derivation of the governing equations, the selection of the models, and simulation parameters. Firstly, the droplet morphologies and drop speeds under different liquid viscosity were simulated. It was found that with the increase of the liquid viscosity, the drop speed decreased and the difficulty of droplet preparation gradually increased. The simulation results were consistent with the experiment results. Secondly, the droplet morphologies at different drop speeds were investigated and verified by experiments. It was found that the simulation results had a good correlation with the experiment results. The results shown that the viscosity of the liquid was the critical material attribute, and the drop speed was the critical process parameter, according to the droplet morphology. The establishment of the simulation method can deepen the understanding of the dripping process and provide a reference for the selection of raw materials and process parameters.

Effect of nasal swell body on nasal airflow and Artemisia pollen deposition / 临床耳鼻咽喉头颈外科杂志

Objective:The nasal swell body（NSB） consists of the nasal septal cartilage, nasal bone, and swollen soft tissue, all of which are visible during endoscopic and imaging examinations. Although the function of the NSB remains uncertain, there is evidence to suggest that it plays a vital role in regulating nasal airflow and filtering inhaled air. Based on anatomical and histological evidence, it is hypothesized that the NSB is indispensable in these processes. This study aims to investigate the impact of NSB on nasal aerodynamics and the deposition of allergen particles under physiological conditions. Methods:The three-dimensional （3D） nasal models were reconstructed from computed tomography （CT） scans of the paranasal sinus and nasal cavity in 30 healthy adult volunteers from Northwest China, providing basis for the construction of models without NSB following virtual NSB-removal surgery. To analyze the distribution of airflow in the nasal cavity, nasal resistance, heating and humidification efficiency, and pollen particle deposition rate at various anatomical sites, we employed the computed fluid dynamics（CFD） method for numerical simulation and quantitative analysis. In addition, we created fully transparent segmented nasal cavity models through 3D printing, which were used to conduct bionic experiments to measure nasal resistance and allergen particle deposition. Results:①The average width and length of the NSB in healthy adults in Northwest China were （12.85±1.74） mm and （28.30±1.92） mm, respectively. ②After NSB removal, there was no significant change in total nasal resistance, and cross-sectional airflow velocity remained essentially unaltered except for a decrease in topical airflow velocity in the NSB plane. ③There was no discernible difference in the nasal heating and humidification function following the removal of the NSB; ④After NSB removal, the deposition fraction（DF） of Artemisia pollen in the nasal septum decreased, and the DFs post-and pre-NSB removal were（22.79±6.61）% vs （30.70±12.27）%, respectively; the DF in the lower airway increased, and the DFs post-and pre-NSB removal were（24.12±6.59）% vs （17.00±5.57）%, respectively. Conclusion:This study is the first to explore the effects of NSB on nasal airflow, heating and humidification, and allergen particle deposition in a healthy population. After NSB removal from the healthy nasal cavities: ①nasal airflow distribution was mildly altered while nasal resistance showed no significantly changed; ②nasal heating and humidification were not significantly changed; ③the nasal septum's ability to filter out Artemisia pollen was diminished, which could lead to increased deposition of Artemisia pollen in the lower airway.

Hemodynamic changes in different types of intracranial aneurysms after treatment with flow diverter / 中华神经医学杂志

Objective:To analyze the hemodynamic changes of different types of unruptured intracranial aneurysms before and after flow diverter (FD) treatment with computational fluid dynamics (CFD), and lay research foundation for precision treatment and prognosis evaluation for unruptured intracranial aneurysms.Methods:Four patients with different types of unruptured intracranial aneurysms, admitted to Department of Neurosurgery, First Affiliated Hospital of Air Force Medical University from January 2022 to March 2022, were chosen. Digital subtraction angiography (DSA) data of the patients before and immediately after surgery were collected. Morphological and hemodynamic parameters of the aneurysms were calculated by 3D reconstruction, finite element simulation, and CFD methods: ostium ratio (OsR), neck ratio (NR), area ratio (ArR), volume ratio (VoR), wall shear stress (WSS), normalized wall shell stress (NWSS), blood inflow, relative inflow, aneurysm average velocity, parent artery average velocity, normalized velocity, residual flow volume (RFV), and inflow concentration index (ICI); differences of these indexes before and after treatment were compared.Results:The OsR of 6 aneurysms was 0.225, 0.267, 0.265, 0.389, 1.000, 1.000, respectively; NR was 1.220, 0.274, 1.090, 1.587, 2.809, and 4.019, respectively; ArR was 0.608 and 0.224, 0.623, 3.462, 1.225 and 1.784, respectively; and VoR was 0.386, 0.052, 0.212, 3.462, 0.422 and 1.882, respectively. The parameters of WSS, NWSS, blood inflow, relative inflow, aneurysm average velocity, parent artery average velocity, normalized velocity, RFV, and ICI decreased obviously after FD implantation.Conclusion:On the basis of 3D reconstruction combined with FD/coil virtual implantation, CFD-based hemodynamic analysis can obtain accurate parameters of different types of intracranial aneurysms before and after FD treatment.

Simulation analysis on the distribution characteristics and movement rules of particulate matter in a convenience store / 中国职业医学

Objective: The spatial distribution model of particulate matter based on time change in a specific place was established to analyze the spatial and temporal distribution characteristics and movement of particulate matter. Methods: A convenience store was selected as the research subject. The micro-climate and particle number concentration (PNC) of the site were detected, and numerical simulation was carried out by computational fluid dynamics (CFD) simulation method. Based on the discrete phase model, the temporal and spatial distribution characteristics and movement rules of simulated particles were analyzed. Results: The wind speed at the entrance of the convenience store was low and almost unchanged during the detection, while the wind speeds outside and inside outlets were high and changed sharply. The PNC of particle size of 0.02-1.00 μm was higher than that of particle size >1.00 μm (all P<0.05). The PNC with particle size of 0.02-1.00 μm from high to low were checkout counter, entrance, outer outlet and inner outlet (all P<0.05). The PNC of the checkout counter and entrance varies greatly, while the PNC of the outer outlet and inner outlet was relatively steady. The CFD simulation results showed that particles exhaled by individuals near the entrance of the checkout counter of the convenience store could be expelled outdoors more quickly with the influence of airflow. However, particles exhaled by individuals in the middle of the shelves remained suspended indoors for a longer period of time compared to those near the checkout counter. Particles emitted from the air conditioning outlet diffuse throughout the entire store and reach a steady state in 300 seconds. Conclusion: The particulate matter in the convenience store was mainly small particle with the size less than 1.00 μm. The residence time, downward trend and number of suspended particulates of human exhaled particles were related to air flow. The particulates escaped from the air conditioner could quickly spread to almost the entire convenience store.

Positive Pressure and Negative Pressure Irrigation Dynamics with Different Needle Designs Using Computational Fluid Dynamics

@#This study aimed to investigate the irrigation dynamics of the positive pressure side-vented (SV) needle, EndoVac (micropores) needle and modified apical negative pressure (mANP) open-ended needle using computational fluid dynamics (CFD). A simulation of a prepared root canal (conical frustum) of 15 mm length with an apical diameter of 0.40 mm following Protaper F4 apical preparation was created using three-dimensional (3D) CAD software. The 3D simulated needle of SV 30G needle, EndoVac with micropores needle and mANP, 30G flat open-ended needle were also created. The irrigation dynamics were evaluated through transient CFD simulations. In addition, the irrigation dynamics of mANP at 0.2 mm, 0.5 mm, and 1.0 mm short from the working length were also assessed. The EndoVac and mANP showed negative apical static pressure and streamline patterns able to reach the apical region, thus indicating negligible extrusion. Meanwhile, SV showed positive apical static pressure and almost nonexistent streamlines beyond the needle tip. The SV showed the highest wall shear stress (WSS) magnitude of 1030Pa whereas Endovac (161 Pa) and mANP1 (258 Pa). However, SV revealed lower average WSS (10 Pa) compared to mANP1 (13 Pa) and mANP2 (11 Pa). This is due to SV developed a localised maximum WSS opposite the open vent area only therefore, uneven distribution of WSS. The EndoVac system developed a localised maximum WSS in the pair of micropores furthest away from the apical. CFD analysis of the EndoVac, mANP and SV showed different technique approach, needle design and needle depths insertion affect the irrigation dynamics pattern and magnitude.

Computational Study of Fenestration and Parallel Grafts Used in Aortic Arch Lesion / 医用生物力学

Objective To explore hemodynamics of the aortic arch and supraarch vessels after thoracic endovascular aortic repair with fenestration and parallel grafts techniques, and compare the differences of these techniques. Methods Four patients with aortic arch lesions whose supraarch vessels were reconstructed by different surgical techniques (fenestration, chimney and periscope) were studied, and three-dimensional (3D) geometric models were established based on postoperative image data. The physiological flow obtained from two dimensional (2D) phase contrast magnetic resonance imaging were imposed on the ascending aorta inlet and the supraarch vessels outlets. The pressure waveform of 3-element Windkessel model was imposed on the descending aorta outlet. Through computational fluid dynamics ( CFD ) simulations, the hemodynamic parameters were obtained, including the pressure of supraarch vessels, the velocity vector of the stent inlet, and the relative residence time. Results The pressure change of the periscope stent was the largest, followed by the fenestration stent, and the pressure change of the chimney stent was the smallest. The velocity of the fenestration and periscope stent inlet was uneven, which might form vortex. The velocity of the chimney stent inlet was even. The high relative residence time concentrated in distal end of the fenestration stent outer wall, the ‘gutter’ part, and the place where the chimney and periscope stent adhered to the vessel wall. Conclusions The pressure difference between the inner and outer walls of the fenestration and periscope stent was high, so it was recommended to use the balloon-expandable stent. The pressure difference between the inner and outer walls of the chimney stent was low, so it was recommended to use the self-expanding stent. The predicted location of thrombosis was consistent with the clinical follow-up data, so it may be used for surgical planning and risk assessment of interventional treatment of aortic arch lesions.

Hemodynamic Effects of Banding Width on Pulmonary Artery / 医用生物力学

Objective To investigate the effects of banding width on hemodynamic characteristics of pulmonary artery (PA) by constructing pulmonary artery banding (PAB) models with different widths. Methods Based on clinical practice, with the same banding position and degree, computer-aided design (CAD) was utilized to reconstruct three-dimensional PAB models with different banding widths (2, 3, 4, 5 mm). Hemodynamic characteristics of the models with different banding widths, including pressure, streamlines, energy loss, energy efficiency and blood flow distribution ratio, were compared and analyzed through computational fluid dynamics (CFD). Results The pressure of PA decreased significantly, while the change of banding width had no significant effects on the pressure drop level at banding position. With the increase of banding width, the energy loss decreased, and the energy efficiency showed an upward trend. The blood flow of the left PA raised, and the ratio of blood flow distribution between the left PA and right PA increased, with the maximum reaching up to 2.28 : 1. Conclusions The increase of banding width can reduce the energy loss of PA and improve the energy efficiency of blood flow, but it will lead to the imbalance of blood flow distributions between the left and right lungs. Both the balance of blood flow distribution and the energy loss should be considered in choice for banding width of PAB. The virtual design of PAB surgery based on CAD and CFD will assist individualized banding width selection in future.

Application of Biomechanical Stress from Coronary Computed Tomography Angiography in Coronary Plaque Assessment and Prediction of Adverse Cardiovascular Events / 医用生物力学

Long-term exposure to risk factors will lead to coronary atherosclerosis, which will lead to the formation and progression of coronary plaque. Early identification of high-risk plaque characteristics will help prevent plaque rupture or erosion, thus avoiding the occurrence of acute cardiovascular events. Biomechanical stress plays an important role in progression and rupture of atherosclerotic plaques. In recent years, non-invasive coronary computed tomography angiography (CCTA) computational fluid dynamics (CFD) modeling has made it possible to acquire the corresponding biomechanical stress parameters. These coronary biomechanical stress parameters, especially wall shear stress (WSS), will aid in the development of a more accurate clinical model for predicting plaque progression and major adverse cardiovascular events ( MACE ). In this review, the biomechanical stress and the role of WSS from CCTA in atherosclerosis were introduced, and the researches on the relationship between biomechanical stress from CCTA and coronary artery diseases were discussed.

Current research status and application prospect of numerical simulation in traditional Chinese medicine drying / 中国中药杂志

With the rapid development of computer technology, numerical simulation has gradually become an important method to study drying process and improve drying equipment. Using computer to simulate the drying process of traditional Chinese medicine(TCM) is characterized by intuitiveness, scientificity, and low cost, which serves as an auxiliary means for technical innovation in TCM drying. This paper summarizes the theories of different drying methods and the research status of numerical simulation in drying, introduces the modeling methods and software of numerical simulation, and expounds the significance of numerical simulation modeling in shortening the research and development cycle, improving drying equipment, and optimizing drying parameters. However, the current numerical simulation method for drying process has problems, such as low accuracy, lack of quantitative indicators for the control of simulation results on the process, and insufficient in-depth research on the mechanism of drug quality changes. Furthermore, this paper put forward the application prospect of numerical simulation in TCM drying, providing reference for the further study of numerical simulation in this field.

Numerical Simulation of Thrombus Formation after Artery Bypass Grafting with Distal-End Side-to-Side Anastomosis / 医用生物力学

Objective To study the difference in thrombus formation at distal end of the graft with two different treatments.Methods For coronary artery bypass grafting with distal-end side-to-side anastomosis (DESSA), two models with or without distal end trimming of the graft were established. Using the blood substance transport and diffusion model considering biochemical reactions, combined with hemodynamics parameters of shear rate, fluid residence time, and platelet distribution, the possibility of thrombus formation was evaluated. Numerical simulation method was used to investigate thrombus growth in coronary artery bypass grafting with DESSA.ResultsFor the model without distal end trimming of the graft, the thrombus was first formed on inner wall at distal end of the graft, and then grew inward until the thrombus occupied most of the graft region at distal end, which indicated that thrombus formation was in a stable state, and the volume of the thrombus didn’t change, the final volume of the thrombus was 15.05 mm3. For the model with distal end trimming of the graft, the final volume of the thrombus was 7.35 mm3, which was 51.2% smaller than that of the model without distal end trimming of the graft. Thrombus was formed on inner wall of the graft above the anastomosis for the model with distal end trimming of the graft, and the wall thickness was about 0.16 mm, which was 10.65% of the graft radius (1.50 mm). In the above two procedures, multiple vortices (blood flow velocity less than 10 mm/s) were formed in distal region of the graft, which further promoted thrombus formation at distal end of the graft. The area of thrombus formation obtained from numerical simulation was consistent with clinical investigation.Conclusions For clinical coronary artery bypass grafting with DESSA, the volume of the generated thrombus can be reduced for the model with distal end trimming of the graft. However, the effect of thrombus formation on inner wall of the graft above the anastomosis on coronary artery bypass grafting needs further study.

Reconstruction and Flow Field Analysis of Human Airway Based on Reverse Engineering / 医用生物力学

Objective In view of the situation that tracheal atrophy causes the overall airway size to become smaller in the elderly, effects of the airway wall surface on reconstruction of a narrow airway and the airflow field under different respiratory conditions were investigated. Methods A three-dimensional (3D) model of human airway was established by using Mimics, and flow field in the airway was simulated by computational fluid dynamics (CFD) method. The inner wall pressure and the distribution of airflow were analyzed and compared under different breathing states. Results Under different respiratory states, the pressure of endotracheal wall was relatively uniform in the endotracheal wall, but decreased significantly in air inlet of the bronchial stenosis segment, and reached negative pressure near the narrowest area. The airflow velocity decreased from the center of the pipe to the boundary layer, and the velocity reached the maximum at the narrow area. Vortex was generated when airflow passed through the narrow area, and the larger the inlet flow velocity was, the larger the positive pressure and negative pressure were, the more obvious the pressure drop at the narrow area was, and the more obvious the vortex phenomenon was. Conclusions The constriction of the airway stenosis area caused by negative pressure will lead to the patient’s dyspnea, and the eddy current will cause the airway wall to be affected by the aerodynamic shear stress and may damage the airway wall mucosa. Therefore, understanding of the pressure distribution and velocity distribution in the narrow airway can provide references for clinical diagnosis and treatment of such diseased airways.

Computational fluid dynamics analysis of influence of different pipe structures on gas mixing uniformity / 中国辐射卫生

Objective Tostudy the influence of pipe structures on the mixing uniformity of airborne effluents from nuclear power plant chimneys. Methods We used the computational fluid dynamics (CFD) method to simulate the velocity distribution and gas mixing in long straight pipes (I type) with square section and circular section, 90° single-bend pipes (L type) with square section and circular section, and 90° double-bend pipes (S type and U type) with square section and circular section. Results For the long straight pipe, due to the lack of flow disturbance caused by structural changes, the mixing effect was not good; when the pipe section was circular, it might take mixing distance 20 times the hydraulic diameter to achieve the uniformity index required by the relevant standard; for the square pipe, the distance might be longer. In the single bend pipe with square section, the velocity uniformity was improved more greatly after the bend, and the tracer gas met the mixing uniformity at a shorter distance (11 times the hydraulic diameter), as compared with the single bend pipe with circular section. For the S-type double-bend pipe, the tracer gas appeared uniformly mixed after a distance 6 times the hydraulic diameter in the square pipe, and 7 times the hydraulic diameter in the circular pipe. For the U-type double-bend pipe, the gas in the square pipe also achieved uniform mixing ata shorter distance downstream, and the airflow showed greater disturbance when passing through the bend. Conclusion The CFD method can make an accurate prediction for the change patterns of gas mixing uniformity in pipes with different structures, and can partially replace physical experiments to study the factors affecting the mixing uniformity of airborne effluents from the chimney of nuclear power plants.

Rational design of a 500 m3 fermenter for erythromycin production by Saccharopolyspora erythraea / 生物工程学报

Erythromycin is a macrolide antibiotic produced by Saccharopolyspora erythraea. Its yield is greatly affected by the fermentation conditions and the bioreactor configurations. In this study, a novel scale-up method for erythromycin fermentation was developed based on computational fluid dynamics (CFD) and time constant analysis. Firstly, the dissolved oxygen (DO) was determined as a key parameter according to the physiological properties of S. erythraea cultivated in a 50 L bioreactor. It was found that the time constant of oxygen supply (tmt) in a 500 m3 bioreactor should be less than 6.25 s in order to satisfy the organism's oxygen uptake rate (OUR). Subsequently, a 500 m3 bioreactor was designed using the time constant method combined with empirical correlations. The impeller combination with one BDT8 impeller at bottom and two MSX4 impellers at upper part was determined, and then validated by numerical simulation. The results indicated that the tmt of the bioreactor (< 6.25 s) and the fluid properties, including gas hold-up, shear stress and fluid vector, met the requirements of erythromycin fermentation. Finally, the industrial production of erythromycin in the 500 m3 showed the design method was applicable in large scale fermentation.