Principles Of Fluid Dynamics Research Articles

Heat transfer enhancement and field synergy analysis of vacuum collector tube with inserted rotor

Aiming at the large heat loss inside the traditional trough-type vacuum solar heat collecting tube, a new type of spiral three-blade rotor structure was designed and inserted into the inner tube side of the heat collecting tube. Based on the principle of fluid dynamics and field synergy, a mathematical model of the three governing equations of the fluid in the tube was established. Numerical simulations of the heat transfer and flow in the flow field in the two types of collector tubes with or without interpolated rotors were performed. Performance comparisons were made in terms of velocity field, pressure field, temperature field, and field synergy coupling ability. The results of the comprehensive evaluation index of heat transfer performance were finally given. The research shows that the PEC value continues to become larger with the increase in the inlet flow rate, from an initial value of 1.63 to a final value of 2.69. The heat transfer performance enhancement advantage of the new type vacuum heat collector tube is obviously greater than the disadvantage of flow resistance, and the comprehensive performance is better.

The BCPAP Score: Five Questions to Assess the Effectiveness of a Bubble CPAP Circuit.

Respiratory illnesses are a leading cause of infant mortality worldwide. Bubble CPAP is a simple and effective treatment for infants in respiratory distress. Across resource-limited settings, various bubble CPAP setups have been used with widely varying results. Based on fundamental fluid dynamics principles and clinical experience, the BCPAP score has been developed to gauge effectiveness of bubble CPAP delivery in different settings. Five questions addressing Bubbles, Circuit, Prongs, Airway and Pressure allow clinicians to rapidly determine whether they are delivering effective bubble CPAP. This article describes how to calculate a BCPAP score and explains the rationale behind the BCPAP score.

“Fossa navicularis” and “septum glandis”: A “flow-control chamber” for the male urethra?

A clear understanding of the normal anatomy of the glanular urethra is essential for anatomical reconstruction of the male urethra. In hypospadias surgery, tubularization of the neourethra over a catheter or stent has been the standard method for decades. However, the male urethra is not a tubular structure with uniform configuration and diameter by forming a fossa (navicularis) in the glans penis. We recently investigated the structural anatomy of the glanular urethra using magnetic resonance imaging (MRI). We have shown that the male urethra does not have a uniform tubular structure and not covered by the corpus spongiosum to the end. The glanular urethra that forms the “fossa navicularis” has a wider caliber than the proximal urethra. Its vertical elliptical shape resembles a laterally compressed slit-like passage. The fossa navicularis is covered by a thin layer of fibrous tissue (“septum glandis”) which is an extension of tunica albuginea of the corpus cavernosum and the corpus spongiosum. Our hypothesis is based on the results of MRI of the glanular urethra and the basic principles of fluid dynamics. We analyzed the flow dynamics of urine on this particular component of the urethra in terms of shape and structural properties. Because of its wider caliber than the proximal urethra, the glanular urethra (fossa navicularis) should cause an increase in pressure and a decrease in velocity of the urine flow. The navicular shape of the fossa and its elliptical external opening (the meatus) should allow urine to be expelled at higher flow rates and at opposite angles at the upper and lower corners which make the wave-like shape of the urine. It can be said that the changes in the volumetric form, pressure and velocity, as well as the wave-like shape of the urine flow are caused by the “fossa navicularis” covered by the “septum glandis”. We propose that the “fossa navicularis” and “septum glandis” play a role as ‘flow control chamber” in controlling the flow of the urine exiting the urethra, which must be taken into account for successful functional reconstruction of hypospadias.

CT-Derived Fractional Flow Reserve (FFRCT): From Gatekeeping to Roadmapping.

Coronary computed tomography angiography (CCTA) has emerged as the preferred modality in the diagnosis of coronary artery disease, but it is limited by modest specificity. By applying principles of computational fluid dynamics, flow fraction reserve, a measure of lesion-specific ischemia that is used to guide revascularization, can be noninvasively derived from CCTA, the so-called computed tomography-derived flow fractional reserve (FFRCT). The accuracy of FFRCT in discriminating ischemia has been extensively validated, and it has been shown to improve the specificity of CCTA. Compared to other stress myocardial perfusion imaging, FFRCT has superior or comparable accuracy. Clinical studies have provided strong evidence that FFRCT has significant prognostic implications and informs clinical decisions for revascularization, serving as a gatekeeper to invasive coronary angiography. In addition, FFRCT-based tools can be used to simulate the physiological consequences of different revascularization strategies, thus providing the roadmap to achieve complete revascularization. Although challenges remain, ongoing research and randomized controlled trials are expected to address current limitations and better define its role in clinical practice.

Assessment and Simulation of Gaseous Dispersion by Computational Fluid Dynamics (CFD): A Case Study of Shiraz Oil Refining Company

Air pollution is simply defined as the presence of any substances such as solids, liquids and gases in the atmosphere, in the adequate amount and time that endangers the life of humans and other living creatures, or damages monuments or properties. In recent years, rapid development of industries including oil and gas industries has led to emit a considerable amount of various gaseous pollutants into the atmosphere. Therefore, developing a reliable model to predict distribution of gaseous pollutants in urban and industrial zones has become an interesting subject among environmental experts. In this study, the distribution of gaseous pollutants emitted from twenty-three stacks of different units located in Shiraz oil refining company is simulated based on the principles of Computational Fluid Dynamics (CFD). To obtain a pattern of pollutants dispersion around the Shiraz refinery, pollutants such as CO, HC, SO2 and NO are considered. To validate the proposed model, concentration of some pollutants is measured at several points of inside and outside of the refinery area and compared with the corresponding values predicted by the proposed model. Results show that there is a good agreement between the measured data and those obtained from the CFD simulation within 6.3% accuracy. Additionally, the concentrations of SO2 and HC in outside of refinery are sometimes more than their standard concentrations.

Vertical-axis ocean current turbine design research based on separate design concept

Through reasonable structure design, this work made the blades that make up the impeller of turbine automatically opened and closed under the force of ocean current, realizing the capture of ocean current energy in different directions, which greatly improved the power generation efficiency of the turbine. The design of this turbine breaks the traditional integral single-blade design idea, divides the traditional integral blade that constitutes the large impeller into a series of sub-blades and solves the contradiction of the opposite torque caused by the water flow in the left and right blades during the rotation of the impeller. The control system composed of the fan-shaped angle control grooves and the gravity-tilted rotors realized the automatic opening and closing of the blades under the force of ocean current. The blades were designed into fish-shape based on the principle of fluid dynamics to reduce the water flow resistance. The physical model test and numerical simulation of the power generation efficiency of the device were carried out to verify the feasibility of the design model. And the results showed that the energy utilization efficiency of the new vertical-axis ocean current turbine was higher than that of the traditional single-blade turbine.

Fluid dynamics of thoracic cavity venous flow in multiple sclerosis

This paper hypothesizes, based on fluid dynamics principles, that in multiple sclerosis (MS) non-laminar, vortex blood flow occurs in the superior vena cava (SVC) and brachiocephalic veins (BVs), particularly at junctions with their tributary veins. The physics-based analysis demonstrates that the morphology and physical attributes of the major thoracic veins, and their tributary confluent veins, together with the attributes of the flowing blood, predict transition from laminar to non-laminar flow, primarily vortex flow, at select vein curvatures and junctions.Non-laminar, vortex flow results in the development of immobile stenotic valves and intraluminal flow obstructions, particularly in the internal jugular veins (IJVs) and in the azygos vein (AV) at their confluences with the SVC or BVs.Clinical trials’ observations of vascular flow show that regions of low and reversing flow are associated with endothelial malformation. The physics-based analysis predicts the growth of intraluminal flaps and septa at segments of vein curvature and flow confluences. The analysis demonstrates positive correlations between predicted and clinically observed elongation of valve leaflets and between the predicted and observed prevalence of immobile valves at various venous flow confluences. The analysis predicts the formation of sclerotic plaques at venous junctions and curvatures, in locations that are analogous to plaques in atherosclerosis.The analysis predicts that increasing venous compliance increases the laminarity of venous flow and reduces the prevalence and severity of vein malformations and plaques, a potentially significant clinical result.An over-arching observation is that the correlations between predicted phenomena and clinically observed phenomena are sufficiently positive that the physics-based approach represents a new means for understanding the relationships between venous flow in MS and clinically observed venous malformations.

Fluid dynamics of cerebrospinal venous flow in multiple sclerosis

Stenotic immobile valves and other malformations obstruct normal cerebrospinal venous outflow, resulting in reflux flow which combines with the normal outflow to produce standing pressure waves in the internal jugular and other cerebrospinal veins. It is hypothesized that, if the cerebrospinal venous structure between the obstruction and the deep cerebral veins is sufficiently non-compliant, the standing wave will result in bidirectional flow in the fine cerebral veins. Bidirectional flow in the fine veins, over extended periods of time, will cause disorder in the veins’ endothelial morphology, and ultimately, result in the disruption of the blood-brain barrier as observed in multiple sclerosis.This physics-based analysis demonstrates a positive correlation between clinically observed MS attributes with the predicted flow patterns and venous malformations that are based on fluid dynamics principles that include venous compliance influences.The physics-based approach used in this analysis provides new insights into MS pathologies based on predicted pressure and flow patterns.

Thermal Performance Evaluation of an Induced Draft Evaporative Cooling System through Adaptive Neuro-Fuzzy Interference System (ANFIS) Model and Mathematical Model

The shift from fossil fuel to more renewable electricity generation will require the broader implementation of Demand Side Response (DSR) into the grid. Utility processes in industry are suited for this, having a large thermal time constant or buffer, and large electricity consumption. A widespread utility system in industry is an induced draft evaporative cooling tower. Considering the safety aspect, such a process needs to maintain cooling water temperature within predefined safe boundaries. Therefore, in this paper, two modelling methods for the prediction of the basin temperature of an induced draft evaporative cooling tower are proposed. Both a white box and a black box methodology are presented, based on the physical principles of fluid dynamics and adaptive neuro-fuzzy interference system (ANFIS) modelling, respectively. By analysing the accuracy of both models with a focus to cooling tower fan state changes, i.e., DSR purposes, it is shown that the white box model performs best. Fostering the idea of using such a system for DSR purposes, the concept of design for flexibility is also touched upon, discussing the thermal mass. Pre-cooling, where the temperature of the cooling water basin is lowered before a fan switch off period, was simulated with the white box model. It was shown that beneficial pre-cooling (to lower the temperature peak) is limited in time.

A Novel Method for Estimating the Vertical Velocity of Air with a Descending Radiosonde System

Knowledge of vertical air motion in the atmosphere is important for both meteorological and climate studies due to its impact on clouds, precipitation and the vertical transport of air masses, heat, momentum, and composition. The vertical velocity (VV) of air is among the most difficult and uncertain quantities to measure due to its generally small magnitude and high temporal and spatial variability. In this study, a descending radiosonde system is developed to derive VV at the low and middle troposphere in north China during the summer months. The VV is estimated from the difference between the observed radiosonde descent speed and the calculated radiosonde descent speed in still air based on the fluid dynamic principle. The results showed that the estimated VV generally ranged from −1 m/s to 1 m/s, accounting for 80.2% of data points. In convective conditions, a wider distribution of the VV was observed, which was skewed to large values relative to those in nonconvective conditions. The average VV throughout the entire profile was close to 0 m/s under nonconvective conditions. In contrast, distinctive vertical air motions below 5 km above the ground were recorded under convective activities. Vigorous air motions with an absolute VV >2 m/s were occasionally observed and were often associated with the occurrence of cloud layers. Moreover, the detailed structure of the instant air motion near the cloud boundaries (i.e., top and base), with an absolute VV >10 m/s in convective weather systems, was clearly revealed by this technique. The uncertainty estimation indicated that this method has the potential to capture and describe events with vertical air motions >0.69 m/s, which is useful for a convective weather study. Further studies are required to carefully assess the accuracy and precision of this novel VV estimation technique.

Development of a globally optimised model of the cerebral arteries

The cerebral arteries are difficult to reproduce from first principles, featuring interwoven territories, and intricate layers of grey and white matter with differing metabolic demand. The aim of this study was to identify the ideal configuration of arteries required to sustain an entire brain hemisphere based on minimisation of the energy required to supply the tissue. The 3D distribution of grey and white matter within a healthy human brain was first segmented from magnetic resonance images. A novel simulated annealing algorithm was then applied to determine the optimal configuration of arteries required to supply brain tissue. The model was validated through comparison of this ideal, entirely optimised, brain vasculature with the structure and properties of real arteries. This analysis established that the human cerebral vasculature is highly optimised; closely resembling the most energy efficient arrangement of vessels. In addition to local adherence to fluid dynamical optimisation principles, the optimised vasculature reproduced expected brain perfusion territories, featuring well-defined boundaries between anterior, middle and posterior regions. This validated brain vascular model and algorithm can be used for patient-specific modelling of stroke and cerebral haemodynamics, identification of sub-optimal conditions associated with vascular disease, and optimising vascular structures for tissue engineering applications and artificial organ design.

Characterizing drip patterns in bloodstain pattern analysis: An investigation of the influence of droplet impact velocity and number of droplets on static pattern features

This work characterizes fundamental features of static drip patterns simulated for forensic bloodstain pattern analysis. The purpose of this study was to determine if and how two independent variables, impact velocity and droplet number, influence the parent stain size, shape and satellite spatter distribution of drip patterns created with whole ovine blood. To do this, 500 drip patterns were created in a controlled environment at five varying impact velocities and ten different droplet numbers on a hard paper surface. Digital images of the dried patterns were processed and analyzed using Fiji (ImageJ). The data collected from each pattern support the hypotheses that drip patterns contain predictable and reproducible elements based on impact velocity and droplet number. Basic fluid dynamic principles demonstrate that the size of the parent stains, as well as the number and distribution of satellite stains increase with increasing Weber number. A decrease in the circularity of the parent stains was also noted. This study provides fundamental qualitative and quantitative data on observable elements of drip patterns that can be used practically by bloodstain pattern analysts for pattern identification and classification.

Study on Wind Induced Interference Effect of T Shaped Light Camping Housing Group

In order to study the wind induced interference effect of T shaped flat light camping house under regular arrangement, based on the theory of atmospheric boundary layer and the basic principle of computational fluid dynamics, the FLUENT software was used to keep the transverse distance Sx=2H unchanged by using the wind direction angle and the longitudinal distance as variable parameters. A total of 15 numerical values are simulated and the T shape is flat under the regular arrangement. The surface wind pressure distribution of the light camping house group is studied. The average wind pressure coefficient of the selected target house is compared with the single house data, and the interference factor is introduced to describe the interference effect of the group housing, and the area and the conditions of the target housing enlarging effect and shielding effect are obtained. The study shows that 0 degrees is the most unfavorable wind angle, and the most interference factor is 3.45, and the interference factor less influenced by the longitudinal distance, and most of the areas are sheltered effect. It can be seen that the wind induced interference effect of the camping house under the regular arrangement should not be ignored, and enough attention should be paid to the design.

Porous PolyHIPE microspheres for protein delivery from an injectable bone graft

Delivery of osteoinductive factors such as bone morphogenetic protein 2 (BMP-2) has emerged as a prominent strategy to improve regeneration in bone grafting procedures. However, it remains challenging to identify a carrier that provides the requisite loading efficiency and release kinetics without compromising the mechanical properties of the bone graft. Previously, we reported on porous, polymerized high internal phase emulsion (polyHIPE) microspheres fabricated using controlled fluidics. Uniquely, this solvent-free method provides advantages over current microsphere fabrication strategies including in-line loading of growth factors to improve loading efficiency. In the current study, we utilized this platform to fabricate protein-loaded microspheres and investigated the effect of particle size (∼400 vs ∼800 μm) and pore size (∼15 vs 30 μm) on release profiles. Although there was no significant effect of these variables on the substantial burst release profile of the microspheres, the incorporation of the protein-loaded microspheres within the injectable polyHIPE resulted in a sustained release of protein from the bulk scaffold over a two-week period with minimal burst release. Bioactivity retention of encapsulated BMP-2 was confirmed first using a genetically-modified osteoblast reporter cell line. A functional assay with human mesenchymal stem cells established that the BMP-2 release from microspheres induced osteogenic differentiation. Finally, microsphere incorporation had minimal effect on the cure and compressive properties of an injectable polyHIPE bone graft. Overall, this work demonstrates that these microsphere-polyHIPE composites have strong potential to enhance bone regeneration through controlled release of BMP-2 and other growth factors. Statement of significanceThis manuscript describes a method for solvent-free fabrication of porous microspheres from high internal phase emulsions using a controlled fluids setup. The principles of emulsion templating and fluid dynamics provide exceptional control of particle size and pore architecture. In addition to the advantage of solvent-free fabrication, this method provides in-line loading of protein directly into the pores of the microspheres with high loading efficiencies. The incorporation of the protein-loaded microspheres within an injectable polyHIPE scaffold resulted in a sustained release of protein over a two-week period with minimal burst release. Retention of BMP-2 bioactivity and incorporation of microspheres with minimal effect on scaffold compressive properties highlights the potential of these new bone grafts.

Pulsatile Flushing: A Review of the Literature.

Flushing is an essential strategy in maintaining patency of a central vascular access device. However, there is no standard practice regarding flushing techniques. Pulsatile flushing has been discussed in the past based on the principles of fluid dynamics. Recently, in vitro studies regarding pulsatile flushing have shed light on the usefulness of this technique. A critique of the current literature regarding pulsatile flushing compared with standard continuous flushing is presented here.

Nanoparticle transport phenomena in confined flows.

Nanoparticles submerged in confined flow fields occur in several technological applications involving heat and mass transfer in nanoscale systems. Describing the transport with nanoparticles in confined flows poses additional challenges due to the coupling between the thermal effects and fluid forces. Here, we focus on the relevant literature related to Brownian motion, hydrodynamic interactions and transport associated with nanoparticles in confined flows. We review the literature on the several techniques that are based on the principles of non-equilibrium statistical mechanics and computational fluid dynamics in order to simultaneously preserve the fluctuation-dissipation relationship and the prevailing hydrodynamic correlations. Through a review of select examples, we discuss the treatments of the temporal dynamics from the colloidal scales to the molecular scales pertaining to nanoscale fluid dynamics and heat transfer. As evident from this review, there, indeed has been little progress made in regard to the accurate modeling of heat transport in nanofluids flowing in confined geometries such as tubes. Therefore the associated mechanisms with such processes remain unexplained. This review has revealed that the information available in open literature on the transport properties of nanofluids is often contradictory and confusing. It has been very difficult to draw definitive conclusions. The quality of work reported on this topic is non-uniform. A significant portion of this review pertains to the treatment of the fluid dynamic aspects of the nanoparticle transport problem. By simultaneously treating the energy transport in ways discussed in this review as related to momentum transport, the ultimate goal of understanding nanoscale heat transport in confined flows may be achieved.

A New Prediction Method for Flashing Parameters in Heavy Oil Production by Steam Flooding

Flashing is a new problem in heavy oil production technology with steam flooding. It can cause pump air locks, pump and pump tubing damage, reduced production, and other problems. A difficulty in predicting flashing parameters involves accurate calculation of the bottomhole temperature and pressure. Based on the principles of heat transfer and fluid dynamics, we have proposed the following models: a model for the wellbore temperature distribution, a model for the stress distribution, a model for calculating the partial loss of pressure when the fluid flows through a fixed valve, and also a model for calculating the parameters for steam flooding of heavy oil, taking into account corrections for the influence of the parameters of the oil — water mixture on the steam critical temperature vs. pressure curve. Taking into account the nature of the fluid, the moisture content, the temperature and other wellbore parameters, the model permits real-time monitoring of flashing in the pump. Experiments were conducted on Jin 45-22-K281 wells. We performed a comparative analysis of the calculated and experimentally measured values. We have shown that the model for calculating flashing parameters is sufficiently accurate for the bottomhole fluid conditions. Analysis of the factors influencing the flashing effect may be useful for providing a theoretical basis for steam flooding parameters.

A study on the working mechanism of internal pressure of super-large cooling towers based on two-way coupling between wind and rain

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world\'s tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

Statistical properties of an enstrophy conserving finite element discretisation for the stochastic quasi-geostrophic equation

ABSTRACTA framework of variational principles for stochastic fluid dynamics was presented by Holm, and these stochastic equations were also derived by Cotter, Gottwald and Holm. We present a conforming finite element discretisation for the stochastic quasi-geostrophic equation that was derived from this framework. The discretisation preserves the first two moments of potential vorticity, i.e. the mean potential vorticity and the enstrophy. Following the work of Dubinkina and Frank, who investigated the statistical mechanics of discretisations of the deterministic quasi-geostrophic equation, we investigate the statistical mechanics of our discretisation of the stochastic quasi-geostrophic equation. We compare the statistical properties of our discretisation with the Gibbs distribution under assumption of these conserved quantities, finding that there is an agreement between the statistics under a wide range of set-ups.

Assessing the impact of design factors on the performance of two miniature microbial fuel cells

Every day, wastewater treatment requires large amounts of electricity. Microbial Fuel Cells (MFCs) can convert wastewater treatment plants from net power consumers into energy neutral/positive systems by generating electricity from wastewaters. We investigate here the design factors that have major impacts on the performance of two miniature MFCs, and, consequently, of the resulting stack of MFCs. A versatile mathematical model is provided, which simulates the complex MFC system by integrating fluid dynamic principles with mass transport phenomena and (bio)electrochemical reactions. The model is used to support an in-depth study of the two MFCs, which differ for electrode spacing, anodic volume and fluid pattern within the anodic chamber, and to associate any difference in performance to design factors. Finally, system scale-up is demonstrated by generating stacks of the two MFCs. Thanks to the versatility of the model developed, this study becomes a guide for the effective development of future miniature MFCs.