Principles Of Fluid Mechanics Research Articles

General route to design polymer molecular weight distributions through flow chemistry

The properties of a polymer are known to be intrinsically related to its molecular weight distribution (MWD); however, previous methodologies of MWD control do not use a design and result in arbitrary shaped MWDs. Here we report a precise design to synthesis protocol for producing a targeted MWD design with a simple to use, and chemistry agnostic computer-controlled tubular flow reactor. To support the development of this protocol, we constructed general reactor design rules by combining fluid mechanical principles, polymerization kinetics, and experiments. The ring opening polymerization of lactide, the anionic polymerization of styrene, and the ring opening metathesis polymerization are used as model polymerizations to develop the reactor design rules and synthesize MWD profiles. The derivation of a mathematical model enables the quantitative prediction of the experimental results, and this model provides a tool to explore the limits of any MWD design protocol.

From thermomass energy to dark energy: Re-exploration to the origin of dark energy

Dark energy constitutes 68% of the matter of our universe, which has been successfully used in the standard cosmological model to explain the phenomenon of cosmic acceleration. However, the scholars still have different opinions in the origin of dark energy, making it one of the most important unsolved problems in the modern cosmology. There are several candidates to explain the origin of dark energy, such as vacuum energy, scalar field theory, light pressure, etc. However, all these models are still in debate and we are far from a commonly agreed theory to understand the true nature of dark energy. In this report, we intend to re-explore some fundamental properties and the origin of dark energy from the perspective of thermomass theory in the framework of energy conservation principle. Thermomass theory is a newly developed theory in the field of heat transfer, including some new physical quantities, such as thermomass, thermomass velocity, thermomass energy, etc. Thermomass is the relativistic mass of heat and thermomass energy is the relativistic energy. Based on the thermomass theory, the heat transfer can be understood as the direct flow of thermomass under a certain temperature gradient. Then the principle of fluid mechanics can be used to solve the heat transfer problems and a general heat conduction law has been established. Some non-Fourier heat transfer phenomena under the extreme conditions, such as ultrafast laser heating, ultrahigh heat flux at nanoscales, can be well explained by using the general heat conduction law. Meanwhile, a simplified expression of thermomass energy was defined as entransy. Guided by a minimum entransy dissipation principle, the structure of a complicated heat exchanger network can be optimized to increase the energy efficiency. Both the general heat conduction law and entransy model have been experimentally validated. The thermomass theory have been widely accepted and applied in the field of thermal science. But a question still remains: The thermomass energy dissipates during the heat transfer process, where does it go? Actually, we find an answer that the dissipated thermomass energy is closely related with the dark energy. Under the normal temperature and pressure conditions, the order of magnitude of thermomass and its energy is much smaller than that of the static mass and its energy. In the beginning of the Big Bang, the temperature exceeds 1015°C and the thermomass energy equals to or even is larger than the energy of static mass. According to the energy conservation principle, the energy at high level, i.e., electrical energy, optical energy, mechanical energy, etc., will dissipate into the energy at low level, i.e., heat. But in the heat transfer process, heat (thermomass) is conserved, while the thermomass energy will dissipate into a lower level, “invisible” energy. This kind of energy has four features: Filling the whole space, ultra-low energy density, negative pressure and gradually accumulated with time. All these features are in consistence with the performance of dark energy. Hence, we hypothesize that the dark energy comes from the dissipated thermomass energy, which is the motivating force of the cosmic acceleration and forms the main body of our universe.

CFD Analysis of Swirl Effect in a Diesel Engine Using OpenFOAM

The combustion process is a basic activity performed by internal combustion engines in charge of release chemical energy from a fuel-air mixture and transforms them into mechanical energy to produce work. Principles of fluid mechanics and thermal sciences are applied in the analysis of the complex flows developed during internal combustion processes with the aim of maximizing work, improving energy efficiency, minimizing fuel consumption, and reducing pollutants caused by the heat released in combustion chambers. Computational Fluid Dynamics help analyzing the turbulent flow phenomena presents in inlet flow, compression, combustion, and exhaust flow processes and defining optimization models that describe and improve swirl and tumble flows in combustion chambers of internal combustion engines. The purpose of developing a numerical simulation is to characterize turbulent flows developed in the admission and cylinders of a diesel engine to study the complex and sudden changes in flow parameters in order to describe a combustion process. Therefore, this paper presents a description of the flow behavior in an engine combustion chamber through a virtual environment. RANS k - e turbulence model is computed with OpenFOAM CFD code in order to solve the system of partial differential equations that define the turbulent mixture flow and swirl effects of the flow over the engine combustion chamber. The results of this research have shown a good agreement between numerical and experimental methods; an error rate of 5 % has been reached by using the KEpsilon turbulence model.

Research on Lateral Force of Pile Based on Liquefaction Site Effect

This paper presents a theoretical investigation on the lateral force of pile in liquefaction site. Regarded liquefied soil as fluid, the vector method can be used to analyze the liquefaction velocity field and solve the analytical solution of the dynamic field by making use of the principle of fluid mechanics. In addition, by solving the velocity field with vector symbol operation method, the analytical expression of the lateral force in the liquefied flow field is obtained, and the sensitivity of the parameters in the analytical expression is analyzed. The results show that the stress field of the pile contains both the pressure resistance caused by surface pressure and the friction resistance caused by shear stress, when the liquefied soil flows laterally. The lateral forces on the pile are mainly composed of inertial forces and damping forces and are related to density, fluid viscosity, pile radius, and vibration frequency. With the increase of density, fluid viscosity, and pile radius, the added mass and added damping increase gradually. In a certain range, added mass and added damping are sensitive to vibration frequency.

Effect of solid particles on the lost circulation of drilling fluid: A numerical simulation

Lost circulation usually happens when drill through fractured formation. A clear understanding of the circulation loss mechanism is key to successful drilling operations. More attention has been paid to fracture development and lost circulation materials (LCMs) composition. Much work still needs to be done on how the solid particles affect the overall fluid loss process in rough-walled fractures. The control equations for liquid-solid multiphase flow in a 2D rough-walled stationary fracture were established based on fundamental principles of fluid mechanics. Among these equations, the drilling fluid was treated as a Bingham type non-Newtonian fluid, and the influence of solid particles on fluid flow was analyzed in detail. The finite difference method was adopted to the numerical solution of the equations, and the impact of such working parameters as fracture dimensions, bottomhole pressure differential, physical properties of both fluid and particle on the fluid loss were analyzed. The following conclusions can be drawn from the paper: (1) the presence of solid particles can lower the leakoff rate and accumulative leakoff rate to various degrees; (2) the larger the fracture dimension, the lower the leakoff rate and accumulative leakoff rate; (3) the larger the pressure differential, the higher the leakoff rate and accumulative leakoff rate; (4) the leakoff rate and accumulative leakoff rate will decrease with the increase of particle diameter and its volume concentration; (5) particle sphericity and yield stress have little influence on the leakoff rate and accumulative leakoff rate. (6) The higher the plastic viscosity of drilling fluid, the lower the leakoff rate and accumulative leakoff rate. The limitations of this study, suggested improvement and future direction of current work are also highlighted.

Quantification of blood flow patterns in the cerebral arterial circulation of individual (human) subjects.

There is a growing research interest in quantifying blood flow distribution for the entire cerebral circulation to sharpen diagnosis and improve treatment options for cerebrovascular disease of individual patients. We present a methodology to reconstruct subject-specific cerebral blood flow patterns in accordance with physiological and fluid mechanical principles and optimally informed by in vivo neuroimage data of cerebrovascular anatomy and arterial blood flow rates. We propose an inverse problem to infer blood flow distribution across the visible portion of the arterial network that best matches subject-specific anatomy and a given set of volumetric flow measurements. The optimization technique also mitigates the effect of uncertainties by reconciling incomplete flow data and by dissipating unavoidable acquisition errors associated with medical imaging data.

Identifying the Critical Factors Governing Translaminar Pressure Differential Through a Compartmental Model.

PurposeThe effective management of glaucoma is hindered by an incomplete understanding of its pathologic mechanism. While important, intraocular pressure (IOP) alone is inadequate in explaining glaucoma. Non-IOP–mediated risk factors such as cerebrospinal fluid (CSF) pressure have been reported to contribute to glaucomatous optic neuropathy. Due to the difficulty associated with experimental measurement of the salient variables, such as the retrobulbar CSF pressure, porosity of the subarachnoid space (SAS), and especially those concerned with the perioptic SAS, there remains a limited understanding of the CSF behavior contributing to the translaminar pressure gradient (TLPG), hypothesized to be a critical factor in the development of glaucoma.MethodAn integrated compartmental model describing the intracranial and orbital CSF dynamics, coupled with intraocular dynamics, is developed based on first principles of fluid mechanics. A sensitivity analysis is performed to identify anatomic characteristics that significantly affect the retrobulbar subarachnoid space (RSAS) pressure and, consequently, the TLPG.ResultsOf the 28 parameters considered, the RSAS pressure is most sensitive to CSF flow resistance in the optic nerve SAS and the potential lymphatic outflow from the optic nerve SAS into the orbital space. A parametric study demonstrates that a combination of resistance in the range of 1.600 × 1012 − 1.930 × 1012 Pa s/m3 (200.0 − 241.3 mm Hg min/mL) with 5% to 10% lymphatic CSF outflow yields RSAS pressures that are consistent with the limited number of studies in the literature.ConclusionsThe results suggest that a small percentage of lymphatic CSF outflow through the optic nerve SAS is likely. In addition, flow resistance in the orbital CSF space, hypothesized to be a function of patient-specific optic nerve SAS architecture and optic canal geometry, is a critical parameter in regulating the RSAS pressure and TLPG.

Travelling wave solutions in dilatant non-Newtonian thin films with second-order viscosity

Given any positive speed, we prove the existence of a travelling wave solution for a viscous incompressible thin dilatant liquid film coated with an insoluble surfactant. Relying on first principles of fluid mechanics, lubrication theory leads to a coupled system of second-order partial differential equations for the film's height and the surfactant's concentration where a second-order approximation of the viscosity function is used. The travelling wave solution is -regular and generates a heteroclinic orbit which connects two distinct equilibrium points of the associated plane dynamical system.

Simulation Study on Influence of Natural Gas Pipeline Pressure on Jet Fire

In order to study the influences of natural gas pipeline pressure on jet fire with FDS(fire dynamics simulation) software, based on principle of fluid mechanics and Thornton flame model, characteristics and hazard scope of the jet fire were comparatively studied for different pipe pressure. The results show that characteristics and hazard scope of the jet fire are largely affected by different pressure. When the pipe pressure is 0.2MPa and 0.4MPa, the size of both leak holes are same, during a same period, the latter flow is greater than the former. When the pipe pressure is greater than 0.8MPa, the leakage hole size is 100mm, and the maximum temperature, diameter and the high temperature affected area of the flame are increased.

Some fluid mechanical constraints on crystallization and recharge within sills.

The injection of hot magma into a sill can lead to heating and melting of the walls and roof of the reservoir while the injected magma cools and crystallizes. If the crystals are relatively dense, they will try to sediment from the injected magma to form a cumulate layer. In this cumulate layer, the crystals form a porous framework which traps the melt as it is built up. As the melt within the sill continually cools and precipitates dense crystals, there will be a gradual reduction in the density of the remaining silicate liquid. As a result, the melt which is progressively trapped in the pore space of the cumulate layer will become stably stratified in density. Using an idealized model of the fluid mechanical and thermodynamical principles, we explore some of the controls on the thickness and density stratification of cumulate layers following replenishment of a sill-like magma chamber. We show the balance between jamming of the crystal laden melt to form a homogeneous layer and the formation of a stratified cumulate zone depends on the cooling time scale compared to the sedimentation time scale. A key finding is that the composition and stratification in a packed crystal-melt suspension and the associated cumulate layer formed by cooling an intrusion of hot melt injected into the crust may have considerable variability, depending on the properties of the overlying roof melt and the size and hence fall speed of crystals which form in the melt. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

COASTAL ENGINEERING, COASTAL RESEARCH, UNIVERSITIES AND CLIMATE CHANGE

Coastal Engineering was new in 1950/1960 and at first, it was all about solving urgent coastal problems. There were no recipes, no formulas, no models; nor was there much experience at that time. Inventiveness and ingenuity were the key design ingredients. Coastal Engineering is a broad subject that is concerned with the interaction between the water and the shore. This involves fluid motion, such as waves and currents and its interaction with a shore that can be anything from sandy beaches to marshlands to highly engineered shorelines, such as found in centers with dense populations. It involves complex hydraulics and fluid mechanics principles on the one hand and complex design criteria on the other hand. It also involves detailed knowledge of the environmental systems where the projects are located. Thus, one obvious need for Coastal Engineering analysis and design is individuals with broad knowledge, interests and background. Such individuals need access to and communication with colleagues in related technical and scientific areas. As a result, much of the early coastal engineering was done at universities.

The transient behaviours of free surface in a fully penetrated weld pool in gas tungsten arc welding

In order to study the phenomenon of the weld pool free surface evolution from partial to full penetration in gas tungsten arc welding (GTAW), the measurement method based on the lattice laser reflection on the weld pool surface was designed. Lattice lasers information and the concavity-convexity in the weld pool free surface were analyzed. Based on the volume of fluid method and the basic principle of fluid mechanics, temperature field and the flow field model which considered the free surface in a fully penetrated weld pool in GTAW were established. Fluid flow including the factor of buoyancy force, electromagnetic force and surface tension gradient was numerically analyzed for a fully penetrated weld pool in stationary GTAW. The result shows that: thermal expansion of metals is the main reason for the convex surface of weld pool at partial penetration. When fully penetrated, the concave surface of the lower surface is greater than that of the upper surface.

The experimental study of shunt-decompression arterialized vein flap

BackgroundArterialized vein flap is a kind of unphysiological flap. Unphysiological reconstruction of blood circulation leads to higher load than that supported by physiological flap and is the culprit of flap swelling, blood stasis, skin blistering, and necrosis after flap grafting. To resolve the multiple disadvantages of traditional flap grafting, by introducing the principles of fluid mechanics, shunt-decompression surgery is prepared to decline the circulation preload and improve the prognosis of arterialized vein flap grafting.MethodsBy introducing the principles of fluid mechanics, we established the model of shunt-decompression arterialized vein flap, which satisfied the common properties of general fluid that the interface pressure between object and fluid is reduced when the velocity of fluid is increased and vice versa—the effect of Bernoulli. Under this rule, we anastomose the arterialized vein to the branch of main artery of recipient region or make end-to-side anastomosis, which can maintain the blood flow of main artery, decrease the perfusion of flap, and preserve the decompressive effect of main artery to branches. From March, 2016 to September, 2016, we performed animal experiments on ten male bama mini pigs with average weight of 28 ± 2.35 kg. Superior epigastric artery of pig was used for feeding artery to arterialize the superficial epigastric veins. The total area of flap is 8 cm × 6 cm. End-to-side anastomosis and end-to-end anastomosis were established in experimental group and control group, respectively. Doppler speckle perfusion imaging apparatus was used to monitor the alterations of flap perfusion, blood flow of flap, tissue swelling and survival of flaps.ResultsThe average flap perfusion (PU) at 1 week after surgery is 83.62 ± 3.14 in experimental group and 98.14 ± 6.54 in control group, respectively (P < 0.05), indicating the significant reduction of flap blood perfusion in experimental group as compared with control group. As to the survival of flaps, 7 flaps completely survived, 3 showed partial necrosis, and no one was found as complete necrosis in experimental group, while only 3 flaps survived, and 4 flaps and 3 flaps showed partial necrosis and complete necrosis in control group, respectively (P < 0.05).ConclusionBased on the physiological features of arterialized vein flap and its problems in clinical application, we improved the anastomosis strategy of flap grafting and obtained excellent experimental outcomes, which provides an insight for the clinical application of arterialized vein flaps.

A microfluidic device with spatiotemporal wall shear stress and ATP signals to investigate the intracellular calcium dynamics in vascular endothelial cells.

Intracellular calcium dynamics plays an important role in the regulation of vascular endothelial cellular functions. In order to probe the intracellular calcium dynamic response under synergistic effect of wall shear stress (WSS) and adenosine triphosphate (ATP) signals, a novel microfluidic device, which provides the adherent vascular endothelial cells (VECs) on the bottom of microchannel with WSS signal alone, ATP signal alone, and different combinations of WSS and ATP signals, is proposed based upon the principles of fluid mechanics and mass transfer. The spatiotemporal profiles of extracellular ATP signals from numerical simulation and experiment studies validate the implementation of our design. The intracellular calcium dynamics of VECs in response to either WSS signal or ATP signal alone, and different combinations of WSS and ATP signals have been investigated. It is found that the synergistic effect of the WSS and ATP signals plays a more significant role in the signal transduction of VECs rather than that from either WSS signal or ATP signal alone. In particular, under the combined stimuli of WSS and ATP signals with different amplitudes and frequencies, the amplitudes and frequencies of the intracellular Ca2+ dynamic signals are observed to be closely related to the amplitudes and frequencies of WSS or ATP signals.

A Simplified Irrigation Pump Testing Method for Developing Countries: A Case Study in Bangladesh.

Much of South Asia experiences a monomodal rainfall pattern with a distinct dry season following the annual monsoon. Enabling irrigation during the dry season has therefore been crucial in assuring improved productivity and double‐cropping. This is particularly the case in southern Bangladesh, where recent government initiatives have called for an expansion of surface water irrigation to reduce pressure on groundwater tables in intensively cultivated areas in the north of the country, where dry season boro rice is grown. This paper describes a method based on first principles of fluid mechanics to characterize the performance of surface water irrigation pumps used by small‐scale farmers in South Asia and Bangladesh. This method is unique, as it incorporates an optimized protocol suitable for resource‐limited conditions found in many developing countries and provides a comprehensive yet simple‐to‐use pump selection method for surface water irrigation pump customers. Using pump impellers as a case study, the method also characterizes the effect of pump geometric variations resulting from the variable production and assembly practices found in different manufacturing workshops. This method was validated with a case study in Bangladesh supported by both full‐scale field testing and numerical simulation results. © 2018 The Authors. Irrigation and Drainage published by John Wiley & Sons Ltd on behalf of International Commission for Irrigation and Drainage

Sperm head morphology is associated with sperm swimming speed: A comparative study of songbirds using electron microscopy

Sperm exhibit extraordinary levels of morphological diversification across the animal kingdom. In songbirds, sperm have a helically shaped head incorporating a distinct acrosomal membrane or "helical keel," the form and extent of which varies across species. The functional significance of this helical shape, however, remains unknown. Using scanning electron microscopy, we quantified inter- and intraspecific variation in sperm head morphology across 36 songbird species (Passeriformes: Passerida). Using phylogenetic comparative methods, we investigated the relationship between sperm head morphology and both sperm swimming speed and the frequency of extra-pair young (EPY). We found that species whose sperm had a relatively more pronounced helical form (i.e., long acrosome, short nucleus, wide helical membrane, and a more pronounced waveform along the sperm head "core") had faster-swimming sperm. We found no evidence of a relationship between interspecific variation in sperm head morphology and EPY, although we did find that among- and within-male variation in sperm head traits were negatively correlated with EPY. Applying principles of fluid mechanics, we discuss how the helical form of the sperm head may influence swimming speed, and suggest that further studies considering aspects of sperm morphology beyond sperm length are needed to improve our understanding of sperm structure-function relationships.

Principles of aerosol jet printing

Aerosol jet printing (AJP) has emerged as a promising method for microscale digital additive manufacturing using functional nanomaterial inks. While compelling capabilities have been demonstrated in the research community in recent years, the development and refinement of inks and process parameters largely follows empirical observations, with an extensive phase space over which to optimize. While this has led to general qualitative guidelines and ink- and machine-specific correlations, a more fundamental understanding based on principles of aerosol physics and fluid mechanics is lacking. This contrasts with more mature printing technologies, for which foundational physical principles have been rigorously examined. Presented here is a broad framework for describing the AJP process. Simple analytical models are employed to ensure generality and accessibility of the results, while experimental validation using a silver nanoparticle ink supports the physical relevance of the approach. This basic understanding enables a description of process limitations grounded in fundamental principles, as well as guidelines for improved printer design, ink formulation, and print parameter optimization.

Brine heat recovery unit for Multi Effect Desalination (MED) system based on Scheffler Concentrator using shell and coil heat exchanger

Three stage standalone solar thermal Multi Effect Desalination (MED) pilot plant for remote and arid rural regions of Sultanate of Oman using fixed focus type Scheffler concentrator producing 100 litres per day has been set up at author’s institute. Preliminary tests carried out on this plant yielded lower outputs of 60-65 litres per day. Heat loss through high temperature brine discharged at 85°C was observed as one of the reasons for lower yield. Literature reviewed and analysis shown that desalination outputs can be increased with increased feed water inlet temperature. To recover this heat and preheat the feed water supplied, brine heat recovery unit using counter flow type shell and coil heat exchanger has been proposed in this paper. Helically coiled heat exchanger has been selected for its compactness, higher heat transfer area per unit volume, higher inside heat transfer coefficient and lower fouling rates due to induced turbulence. The operating parameters of this heat exchanger will handle hot brine at 80-85°C and 1 bar pressure. In the present work, heat load, number of turns, coil length and pressure drop calculations are done for estimating the theoretical values based on heat transfer & fluid mechanics principles using numerical correlations from the literature reviewed. The steady state analysis has shown that that coil pitch, inside tube diameter, mass flow rate through the coil and shell affects the heat transfer rates. Practical dimensional constraints have been taken into consideration while finalising the dimensions of the heat exchanger. Overall effectiveness of 84.6% has been calculated for the proposed heat exchanger.

Understanding fluid homoeostasis in infants and children: part 2.

Part two of this article focuses on the care and management of infants and children who are seriously ill and who have lost so much fluid that they have entered a state of shock. The pathophysiology of shock is reviewed and the types and stages of shock are considered. The challenges of identifying shock are explored and the management of fluid resuscitation with colloids rather than crystalloids is analysed. An overview of the complex management of a young person in shock is provided using a case history format. The article offers the opportunity to extend readers' knowledge of some of the special tests that may be required to support the diagnosis of shock and provides an overview of the expected results.

The Effect of Droplet Sizes on Overspray in Aerosol‐Jet Printing

One of the most important concerns of aerosol‐jet based printing (AJP) is the substantial amount of overspray (OS) that can accompany printed traces. In this study, the authors develop a full, three‐dimensional (3‐D) computational fluid dynamics (CFD) model of the aerosol carrier gas flow (CGF), that is, confined by an annular sheath gas flow (ShGF) during the AJP process. The authors then use this model to pinpoint the fundamental fluid mechanics principles that control the OS in a standard AJP process as a function of the droplet size distribution and the ShGF rate. In their model, the authors consider the trajectories of various sized, monodisperse droplets in an ink‐stream in order to unravel the manner in which the OS is dictated by the intricate interplay between drop size and both gas flow (CGF and ShGF) rates. Their results explain several experimental results, namely 1) that there is an abundance of smaller sized drops in the OS region at low ShGF rates; 2) that the OS first reduces and then increases as the ShGF rate increases; and 3) that there is no longer a prevalence of smaller particles in the OS region at larger ShGF rates. The authors also discuss the hitherto unaddressed issues related to how 1) the large impact velocity of the ink droplets at the substrate surface (and the resultant Weber number) and 2) the misalignment between the CGF and the cylindrical axis of the ShGF annulus appear to affect OS. The authors anticipate that their analysis will provide an important understanding in the optimization of operating parameters for AJP with respect to OS that can result in an overall improvement in printing resolution.