Entrance Pressure Research Articles

Effects of Vertical Glottal Duct Length on Intraglottal Pressures and Phonation Threshold Pressure in the Uniform Glottis

According to Titze's 1988 derivations for phonation threshold pressure (PTP), there are a number of important variables that PTP depends upon. A primary one is the vertical glottal duct length T: PTP decreases if T is increased. Changing the length of T, however, may have a significant effect on other variables that PTP depends upon. This study examined the effects of lengthening the vertical uniform glottal duct on the transglottal and intraglottal pressures, and the derived transglottal pressure coefficients, for five glottal diameters (0.01, 0.02, 0.04, 0.08, and 0.16 cm) and three transglottal pressures (500, 1000, and 1500 Pa) for the uniform glottis by using the computational fluid dynamics code Fluent (for laminar, incompressible, two-dimensional flow). The results suggest the following: A longer vertical glottal duct length increases the intraglottal and transglottal pressures, and more so for smaller glottal diameters, and increases the transglottal pressure coefficient. In addition, unlike the transglottal pressure coefficient, the glottal entrance pressure coefficient is highly dependent on the vertical glottal duct length only for lower flows and Reynolds numbers, but is relatively independent of duct length, glottal diameter, and transglottal pressure above a flow value of approximately 50 cm3/s, suggesting that the entrance pressure coefficient is a relatively local phenomenon. These results suggest that the vertical glottal duct length and its effects need to be taken into consideration for vocal fold modeling, aeroacoustics purposes, and the estimation of PTP.

Argon gas flow through glass nanopipette

We have observed the flow of argon gas through a glass nanopipette in vacuum. A glass nanopipette with an inner diameter of 100 nm and a shank length of 3 mm was set between vacuum chambers, and argon gas was introduced from the top of the nanopipette to the bottom. The exit pressure was monitored with an increase in entrance pressure in the range of 50–170 kPa. Knudsen flow was observed at an entrance pressure lower than 100 kPa, and Poiseuille flow was observed at an entrance pressure higher than 120 kPa. The proposed pressure-dependent gas flow method provides a means of evaluating the glass nanopipette before using it for various applications including nanodeposition to surfaces and femtoinjection to living cells.

Startup flow of elasto-viscoplastic thixotropic materials in pipes

Waxy crude oils transportation is one of the main challenges in offshore oil industry, specially after long shutdown periods when the flow has to be restarted. From the reservoir to the platform, the high-temperature crude oil undergoes a sudden temperature drop. As a consequence of cooling, the paraffin molecules precipitate forming a gel-like structure that can obstruct the tube completely. Under these conditions, the pressure required to startup the flow can be higher than usual operating pressure. Hence, the correct prediction of the minimum pressure required is of great importance. The aim of this work is to investigate the startup flow of yield stress materials being displaced by a Newtonian fluid in pipes. To this end, a flow-loop was developed and rheological tests were performed. Aqueous solutions of Carbopol® were used as a model fluid to mimic the waxy crude oil viscoplastic behavior. A polyester resin pipe with a threaded inner wall was used in order to avoid wall slip. The test section was validated with Hagen-Poiseuille law and with a Herschel-Bulkley analytical result. Applying different entrance pressures rates, the minimum pressure required to restart the flow was identified. An elasto-viscoplastic thixotropic behavior was observed through a delayed start up and the avalanche effect. Moreover, an increase in dimensionless entrance pressure rate results in a decrease in delay and clearance times. It is seen that the higher the viscosity of incoming fluid the lower the displacement velocity. A Herschel-Bulkley relationship between the dimensionless entrance pressure rate and the dimensionless shear stress required to start the flow is observed.

Теоретические основы гидрологии почв в трудах А.А. Роде и современные подходы к описанию движения и равновесия влаги в почвах

Classical Russian soil hydrology created by works of A.A. Rode, his colleagues and associates is based on the concept of water forms in the soil and soil hydrological constants. At the present state of development the soil hydrology uses all conceptual approaches designed by A.A. Rode and his colleagues which allow us to characterize the soil hydrology as an actively developing science, which has its own historical path, principles, application limits, benefits and possible long-term development path, which uses the developed and experimentally confirmed by A.A. Rode concept of “capillary-suspended” and “capillary-backed” water and, accordingly, the field and the capillary soil water capacities. The current stage of soil hydrology is characterized by the active application of quantitative approaches. At the present, in hydrology the soil water retention curve takes the central place, which stand out as the break point corresponding to the capillary water capacity and values of “air entrance pressure”. The examples describe the nonlinear characteristics the water retention curves with clearly dedicated air inlet pressure for heavy soddy-podzolic soil, gray forest soil and chernozem. Shaped hydrological characteristics of A. A. Rode such as “capillary-suspended” and “capillary-backed” soil water are still actively used in actual educational process.

Entrance pressure instability of LLDPE and its composites

The relationship between entrance pressure fluctuation and perturbation of the extrudates was elaborated experimentally.

Effect of extensional viscosity on cocontinuity of immiscible polymer blends

Cocontinuous blends were prepared from polyethylene (PE) and polylactic acid (PLA). The extensional and shear rheological properties of PE and PLA were independently tuned by varying long chain branching architecture. Shear rheological properties of the blend components were characterized by capillary and oscillatory rheometry. Extensional rheological properties were characterized by orifice entrance pressure drop and sheet wind-up. It was found that branching significantly increased zero-shear viscosity and extensional viscosity, but did not alter the shear viscosity at the shear rates typically observed in mixing flows. Adding a branched polymer to the blend allowed the other blend component to percolate into a continuous network with less material. Blending with two branched materials significantly broadened the range of cocontinuous compositions from 39–59 vol. % with a linear/linear blend to 25–76 vol. % for a branched/branched blend. This was attributed to the ability of a strain hardening matrix to promote elongation, and hence percolation, of the minor phase. Domain size was minimized when a slight amount of strain hardening was introduced, as this allowed formation of narrow features while stabilizing them against fiber breakup. All blends showed a rate of morphological coarsening during annealing inversely proportional to zero-shear rate viscosity, suggesting that quiescent coarsening flows are dictated by low-rate shear flow properties and not extensional properties. We find that our results and coarsening rates in the literature show the same linear dependence on the ratio of interfacial tension to log volume average zero-shear viscosity with a coefficient of ∼0.03, indicating a simple universal relation.

An Efficiency improved diffuser with extended sidewall for application in valveless micropump

A diffuser/nozzle pair serves as a flow rectifying element in a valveless micropump, which is one key component in microfluidics devices. This paper proposes a diffuser/nozzle element with extended sidewall, ‘lip’, at the diffuser’s large opening end. This novel structure is based on the fluid mechanism concept that an extended sidewall introduces extra entrance pressure loss, which is preferred in the nozzle direction. A clear improvement in efficiency is observed in both the numerical and experimental results.

The Influence of Inlet Pressure Control on Separation Performance of Multi-Product Cyclones

This paper is devoted and intended to solve the problems in determining the precise separation efficiency and accurate prediction for the solid yield of multi-product cyclones based on existing experimental data. The influence of inlet pressure control on separation performance of multi-product cyclones is investigated. Hydrocyclone separation performance is influenced by many factors such as the liquid level of agitating vessel and the entrance pressure. The liquid level can also be controlled through the entrance pressure control. The mathematical model of multi-product cyclone system is a high-order complex model and it is difficult to determine the specific expressions. The paper adopts a special optimal fuzzy PI_PID control strategy performed by Programmable Logic Controller system to enable inlet pressure control. By the force of contrast with experiment and analysis for many performance indexes, the effectiveness and applicability of the control approach are demonstrated. The research provides a method for control of high-order complex system of hydrocyclone separation.

Study on the effects and properties of PVDF/FEP blend porous membrane

Polyvinylideneflouride (PVDF)/poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) blend flat-sheet membranes were fabricated by the immerged phase-inversion method. Micro–nanometer scale FEP particles were introduced into PVDF/N,N-dimethylacetamide (DMAc) casting solution. Effects of FEP content on the rheology behavior of casting solution and performances of PVDF/FEP blend membranes were investigated respectively. Results shown that: (1) With FEP content increasing, the viscosity of casting solution decreased while the value of non-Newtonian index n increased. When FEP content was 60wt.%, the value of n reached as high as 0.903 which demonstrated that the casting solution exhibited good Newtonian flowing property; (2) with FEP content increasing, the porosity and permeability of blend membranes increased obviously while the liquid entrance pressure (LEP) decreased. Blend membranes' cross-section morphologies shown that the increase in FEP content aided the formation of a larger and deeper finger-like pore structure; and (3) with FEP content increasing, mechanical strength of blend membranes decreased while the water contact angle increased at first then decreased.

An annular rotating-die technique in extrusion process: effect of mandrel rotating speed on entrance pressure drop and flow properties of molten HDPE

An annular rotating-die system proposed in this work was specifically designed and constructed so the mandrel could rotate in stationary barrel during extrusion. Effect of mandrel rotating speeds on flow properties and entrance pressure drop of melt HDPE with and without mandrel rotation was monitored in real-time in a single screw extruder. Experimental results showed that the entrance pressure drop decreased steadily with the increase of mandrel rotating speed from 0 to 70 rpm by an average of 45 %. Flow properties of melt HDPE were in accordance with pseudoplastic non-Newtonian behavior. In general, it was found that, at the same wall shear rate, wall shear stress detected in annular rotating-die (mandrel rotation) was lower than that found from normal annular die. The wall shear stress tended to decrease with the increasing mandrel rotating speed from 0 to 70 rpm by an average of 43 %. Possible explanations for the reduction in die entrance pressure drop and flow properties magnitudes for melt HDPE due to mandrel rotating effect were given in connection with the flow pattern of melt HDPE in the annular rotating-die.

Effects of entrance convergence angle and fiber content on the rheological properties of Pithecellobium clypearia fiber/high-density polyethylene composites

The entrance converging flow method was used to investigate the influences of entrance convergence angle and fiber content on the rheological behavior of Pithecellobium clypearia fiber (PCF)/high-density polyethylene (HDPE) composites. Shear and extensional rheological parameters were also measured. It is found that the extensional action exerted on the materials reaches a maximum at a die angle of 120° at certain plunger rates. Wall slippage occurs easily for PCF/HDPE composites with higher fiber content with a die entry angle of 120°, causing a substantial decrease in the entrance pressure drop of the orifice die. Both shear and extensional non-Newtonian indices of HDPE and PCF/HDPE composites were less than 1, consistent with shear- and tension-thinning rheological behavior. Within the fiber content range used in this study, the shear viscosity increased slightly with fiber content, while the extensional viscosity decreased initially and then increased with increasing fiber content.

Numerical Simulation of the Hydrodynamic Cavitation of the Impinging Streams Mixer

The impinging streams mixer is a new type micromixer. The cavitation phenomenon occurring in the mixers with T-shaped impinging streams (TS), conical impinging streams (CIS), vortex streams(VS) were investigated, respectively. The distribution of flow field in the mixer was simulated and calculated by commercial software Fluent 6.2.1. The results showed that under the same working conditions, a more obvious hydrodynamic cavitation may occur in the CIS type impinging stream than that in the CIS type or the VS type, and the vortex flow lead to an extension of the material residence time in the mixer. The distribution of turbulent kinetic energy and gas holdup were obtained by numerical simulating hydrodynamic cavitation under different entrance pressure conditions. It is showed that when the outlet pressure keeps a constant value, hydrodynamic cavitation can be enhanced by increasing the entrance pressure. The above research can be contributed to the producing of biodiesel and the solving of the key technical problem of oil and alcohol heterogeneous mixing.

FEP Hollow Fiber Membrane and Its Membrane Distillation Process

The influence of draw ratio on the structure and properties of poly(tetrafluoroethylene-cohexafluoropropylene)(FEP) hollow fiber membrane which was fabricated by melt-spinning stretching(MS) method was investigated in this article.The primary FEP hollow fiber membrane structure was compact while the porous structure occurs after stretching.Furthermore,the increase of membrane draw ratios induced the obvious increase of membrane porosity and the N2flux while the decrease of the liquid entrance pressure(LEP).Meanwhile,the FEP hollow fiber membrane was applied to the vacuum membrane distillation(VMD) process to compared with M-S PP hollow fiber membrane which was the commercial product.The results show that the hydrophobic properties,LEP and mechanical strength of FEP hollow fiber membrane was better than PP hollow fiber membrane.The strong and stable of hydrophobic properties enabled the FEP membrane unpenetrated,which kept the desalination rate maintain up to 99%.The larger inner diameter(about 0.74 mm) of FEP hollow fiber membrane induced the use of internal pressure VMD type which brought about the higher VMD flux when the feed temperature increased.

Analysis of Y Type Branch Pipe Exhaust Ventilation Flow Characteristics

In order to study the internal gas flow of Y type branch pipes in the exhaust ventilation conditions, the branch pipe is simulated by using FLUENT software. Combined with experimental results, comparatively analyze exhaust ventilation pressure, velocity and vortex flow of the branch pipe. The results show that simulation and experimental data consistent overall trend, the difference is less than 8%, the main entrance pressure of the branch pipeline decreases with the width of the leakage increasing, leakage width of 0 mm, 1 mm, 2 mm cases, there is vortex tube, and valve and the main ventilation pipe case gas exchange occurs when no leakage, this study provides a theoretical and practical basis for further analysis of branch pipe exhaust ventilation.

Early Numerical Studies on the Peristaltic Flow through the Pharynx

AbstractThe flow through the pharynx from the GPJ to the UES has been numerically investigated with a non‐Newtonian fluid obeying the power law with similar rheological indices to a contrast medium used in videofluroscopy. Flow fields revealed the occurrence of reflux regions in the beginning, being this effect stronger at low entrance pressure, which could be related to abnormal swallowing. As a consequence, the bolus travels preferably along the walls. It has been also observed that the bolus head travels faster than the bolus tail, which indicates that the bolus is elongated. Results from this work can be further used for a rheological characterization of oral nutritional supplements for patients suffering from swallowing disorders.Practical ApplicationsThe flow through the pharynx has been numerically investigated with a non‐Newtonian fluid to get insight about causes leading to abnormal swallowing. Reflux has been observed in the beginning as result of a central stream and two symmetric loops generated along the walls, being this effect at low peristaltic pressure. Velocity fields revealed that the bolus head travels faster than the bolus tail, which is a result of the geometry and conservation of mass. Under these conditions, extensional stresses are generated by the flexion of the pharynx walls. Shear rate fields allowed establishing the shear rate range at which the bolus is subjected along the pharynx, which is useful for the rheological characterization of supplements for patients suffering from swallowing disorders.

Effect of Heterogeneity of Porous Media on Gas Permeation and Entrapment

Capillary trapping prevents the migration of CO2 in reservoirs due to buoyancy. The residual gas saturation is strongly influenced by the gas saturation after gas injection. In this study, we have investigated the effect of stratified structure of heterogeneous porous media on gas permeation and entrapment. Experiments were carried out at a laboratory condition for a nitrogen-water system with the packed beds of glass beads with various diameters which modeled stratified porous media. In the case of parallel structure, the injected gas selectively percolated into permeable layers. The gas permeation can hardly occur for the less permeable layers because of the capillary entrance pressure. In the case of serial structure, the interface of porous structure hindered the migration of gas across it, because of the capillary entrance pressure. When the gas percolated in the permeable layers, capillary fingering was developed in the layers. However, when the tip of finger reached the interface, fingers grew in tangential directions until the pressure built up to overcome the capillary entrance pressure. As a result, high gas saturation was achieved in the permeable layers of both upward and downward gas injections.

Predictions of flow behaviors and entrance pressure drop characteristics of a rubber compound in a capillary die using various rheological models

Rubber compounds have highly viscoelastic properties. The viscoelastic behaviors that have been exhibited during die extrusion include die swell and vortices in regions of sudden contraction. In this study, the application of rheological models to the capillary die extrusion process is investigated. Experiments and simulations were conducted using a fluidity tester and finite element analysis, respectively. The velocity distributions, velocity profiles, pressure drops, and vortices at the capillary die entrance were analyzed through computer simulations for various viscoelastic models [i.e., Phan‐Thien and Tanner (PTT), Giesekus, POMPOM, simplified viscoelastic, and generalized Newtonian models]. Different models exhibited different pressure drops and different velocity profiles in the capillary die. Only the full viscoelastic models (PTT, Giesekus, and POMPOM) predicted the vortex at the corner of the reservoir that is the capillary die entrance. However, the simplified viscoelastic and generalized Newtonian models did not predict the vortex. All the viscoelastic models studied in this article predicted the die swells in various ways, and these were compared with the experimental results. The PTT and simplified viscoelastic models exhibited good agreement with the experimental results of the die swells. POLYM. ENG. SCI., 54:2441–2448, 2014. © 2013 Society of Plastics Engineers

Size Design of Capillary and Barrel of Multi-Function and All-Electric Rheometer

Multi-function and all-electric rheometer (MAR) was designed by the authors to study the nonlinear viscoelasticity of polymer melts at high shear rate. It is important to design suitable size of capillary and barrel because it is the calculation basis for some other important parts and determines the shear rate range of MAR. Considering the shear rate range, the entrance pressure correction and the wall slip correction, the length and diameter of capillary and barrel of MAR were designed through particular analysis and precise calculation.

On the Pressure Dependency of the Bagley Correction

Abstract The effect of pressure on the viscosity of polymer melts is an often forgotten parameter due to the inherent difficulty to measure this quantity. Different experimental approaches have already been undertaken in literature in the past. A popular methodology to measure the pressure dependence of the viscosity is to use a capillary rheometer equipped with a counter pressure chamber in which the exit pressure can be controlled. In order to process the data, one of the key elements is the Bagley correction that is required to determine the correct entrance pressure at a specific shear rate. In all analysis approaches presented in literature on data at controlled exit pressure, the Bagley correction was always determined at atmospheric exit pressure, disgarding possible effects of an enhanced exit pressure. In this paper, a new analytical approach is presented that for the first time allows for a direct assessment of the entrance pressures obtained when capillary measurements are performed with controlled counter pressures. It is demonstrated, using polycarbonate, that the entrance pressure correction needed to obtain correct viscosity values under pressure is significantly different than the one needed to correct measurements performed at atmospheric exit pressure.

The Frequency-Domain Analysis of the Rheological Data Acquired with Multi-Function and All-Electric Rheometer

The key parts of multi-function and all-electric rheometer (MAR) designed by the authors were introduced. The data processing method based on frequency-domain analysis were established. Intrinsic vibration displacement is defined to eliminate the effect of steady velocity displacement and extract the useful information of vibration displacement. The actual frequency, amplitude and phase of the superimposed vibration displacement and the entrance pressure were obtained by the frequency-domain analysis of the intrinsic vibration displacement and the entrance pressure. The control precision of the superimposed vibration displacement frequency and amplitude of MAR proved to be high. The direct current component of entrance pressure can be seen as the mean entrance pressure which stands for the flow resistance. The study of mean entrance pressure is useful in discovering the energy consumption mechanism of the polymer processing introduced vibration energy. Loss angle can be calculate according to the phase of entrance pressure and superimposed vibration displacement. The higher order harmonic of the entrance pressure can be used to characterize the nonlinear viscoelasticity of polymer melts. The factors which depend on the shear rate and influence the viscoelasitic properties can be studied by test the loss angle based on MAR.