Transition of Mixtures of Polymers in a Dilute Aqueous Solution

1970 ◽  
Vol 92 (3) ◽  
pp. 411-418 ◽  
Author(s):  
W. D. White ◽  
D. M. McEligot
Keyword(s):  
Molecular Weight ◽  
Reynolds Number ◽  
Pressure Ratio ◽  
Polymer Concentration ◽  
Transition Process ◽  
Reynolds Numbers ◽  
Turbulent Regime ◽  
Calibration Data ◽  
Molecular Weight Polymer ◽  
Dilute Aqueous Solution

Data are presented for the flow of deionized water solutions of linear, unbranched polymers—Separan AP-30, Polyox WSR-35 and Polyox WSR-301, and mixtures of the latter two in a 0.0235 in. tube. The Reynolds numbers vary from about 1200 to about 12,000. Measurements were made at 4 deg C and near room temperature. Occurrence of transition is confirmed by oscillograph traces and pressure ratio calculations in addition to the usual “break” on a friction factor-Reynolds number graph. From the calibration data, it appears that for small tubes there is a critical parameter, such as molecular weight or polymer length, below which transition occurs as for water, but above which the transition Reynolds number depends on polymer concentration. The low and high polymers were mixed to vary molecular weight distribution of samples. It was found that the higher molecular weight polymer dominates the transition process, but in the turbulent regime the effects are roughly additive.

Effect of viscoelasticity on the soft-wall transition and turbulence in a microchannel

2017 ◽  
Vol 812 ◽  
pp. 1076-1118 ◽  
Author(s):  
S. S. Srinivas ◽  
V. Kumaran
Keyword(s):  
Molecular Weight ◽  
Reynolds Number ◽  
Reynolds Stress ◽  
Mass Fraction ◽  
Rectangular Cross Section ◽  
Pure Water ◽  
Polymer Concentration ◽  
Wall Turbulence ◽  
Solution Viscosity ◽  
Soft Wall

The modification of soft-wall turbulence in a microchannel due to small amounts of polymer dissolved in water is experimentally studied. The microchannels are of rectangular cross-section with height ${\sim}$160 $\unicode[STIX]{x03BC}\text{m}$, width ${\sim}$1.5 mm and length ${\sim}$3 cm, with three walls made of hard polydimethylsiloxane (PDMS) gel, and one wall made of soft PDMS gel with an elasticity modulus of ${\sim}$18 kPa. Solutions of polyacrylamide of molecular weight $5\times 10^{6}$ and mass fraction up to 50 ppm, and of molecular weight $4\times 10^{4}$ and mass fraction up to 1500 ppm, are used in the experiments. In all cases, the solutions are in the dilute limit below the critical overlap concentration, and the solution viscosity does not exceed that of water by more than 10 %. Two distinct types of flow modifications are observed below and above a threshold mass fraction for the polymer, $w_{t}$, which is ${\sim}$1 ppm and 500 ppm for the solutions of polyacrylamide with molecular weights $5\times 10^{6}$ and $4\times 10^{4}$, respectively. At or below $w_{t}$, there is no change in the transition Reynolds number, but there is significant turbulence attenuation, by up to a factor of 2 in the root-mean-square velocities and a factor of 4 in the Reynolds stress. When the polymer concentration increases beyond $w_{t}$, there is a decrease in the transition Reynolds number and in the intensity of the turbulent fluctuations. The lowest transition Reynolds number is ${\sim}$35 for the solution of polyacrylamide with molecular weight $5\times 10^{6}$ and mass fraction 50 ppm (in contrast to 260–290 for pure water). The fluctuating velocities in the streamwise and cross-stream directions are lower by a factor of 5, and the Reynolds stress is lower by a factor of 10, in comparison to pure water.

Experimental Investigation of Pressure Drop Characteristics of Viscous Fluid Flow Through Small Diameter Orifices

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Lalit Kumar Bohra ◽  
Leo M. Mincks ◽  
Srinivas Garimella
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Viscous Fluid ◽  
Euler Number ◽  
Small Diameter ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Operating Conditions ◽  
Turbulent Regime ◽  
Pressure Drops

Abstract An experimental study on the flow of a highly viscous fluid through small diameter orifices was conducted. Pressure drops were measured for each of nine orifices, including orifices of nominal diameter 0.5, 1, and 3 mm and three different orifice thicknesses, over wide ranges of flow rates and temperatures. The fluid under consideration exhibits steep dependence of the properties (changes of several orders of magnitude) as a function of temperature and pressure and is also non-Newtonian at the lower temperatures. At small values of Reynolds number, an increase in aspect ratio (length/diameter ratio of the orifice) causes an increase in Euler number. It was also found that at extremely low Reynolds numbers, the Euler number was very strongly influenced by the Reynolds number, while the dependence becomes weaker as the Reynolds number increases toward the turbulent regime, and the Euler number tends to assume a constant value determined by the aspect ratio and the diameter ratio. A two-region (based on Reynolds number) model was developed to predict Euler number as a function of diameter ratio, aspect ratio, viscosity ratio, and generalized Reynolds number. It is shown that for such a highly viscous fluid with some non-Newtonian behavior, accounting for the shear rate through the generalized Reynolds number results in a considerable improvement in the predictive capabilities of the model. Over the laminar, transition, and turbulent regions, the model predicts 86% of the data within ±25% for the geometry and operating conditions investigated in this study.

Flow of non-Newtonian fluids over a confined baffle

1991 ◽  
Vol 226 ◽  
pp. 475-496 ◽  
Author(s):  
F. T. Pinho ◽  
J. H. Whitelaw
Keyword(s):  
Reynolds Number ◽  
Polymer Concentration ◽  
Local Strain ◽  
Reynolds Numbers ◽  
Newtonian Fluids ◽  
Momentum Balance ◽  
Recirculation Region ◽  
Reynolds Stresses ◽  
Recirculation Bubble ◽  
Number Range

Measurements of wall pressure, and mean and r.m.s. velocities of the confined flow about a disk of 50 % area blockage have been carried out for two Newtonian fluids and four concentrations of a shear-thinning weakly elastic polymer in aqueous solution encompassing a Reynolds-number range from 220 to 138000. The flows of Newtonian and non-Newtonian fluids were found to be increasingly dependent on Reynolds numbers below 50000, with a decrease in the length of the recirculation region and dampening of the normal Reynolds stresses. At Reynolds numbers less than 25000, the recirculation bubble lengthened and all turbulence components were suppressed with increased polymer concentration so that, at a Reynolds number of 8000, the maximum values of turbulent kinetic energy were 35 and 45% lower than that for water, with 0.2% and 0.4% solutions of the polymer. Non-Newtonian effects were found to be important in regions of low local strain rates in low-Reynolds-number flows, especially inside the recirculation bubble and close to the shear layer, and are represented by both an increase in viscous diffusion and a decrease in turbulent diffusion to, respectively, 6% and 18% of the largest term of the momentum balance with a 0.4 % polymer solution at a Reynolds number of 7700. The asymmetry and unsteadiness of the flow at Reynolds numbers between 400 and 6000 is shown to be an aerodynamic effect which increases in range and amplitude with the more concentrated polymer solutions.

Effect of Extending Oil on Viscoelastic Behavior of Elastomers

1983 ◽  
Vol 56 (4) ◽  
pp. 784-807 ◽  
Author(s):  
N. Nakajima ◽  
E. R. Harrell
Keyword(s):  
Molecular Weight ◽  
Viscoelastic Properties ◽  
Polymer Concentration ◽  
Viscoelastic Behavior ◽  
Chain Structure ◽  
Frequency Range ◽  
Molecular Weight Polymer ◽  
Wide Range ◽  
Two Samples ◽  
Superposition Principles

Abstract For a number of years, oil-extended elastomers have been in commercial use. The obvious advantage is to dilute elastomers with less expensive oil. In addition, oil improves the processability of the elastomer. This enables the use of a higher-molecular-weight polymer, which, in turn, yields mechanical properties comparable or superior to those of a lower-molecular-weight polymer without oil extension. The viscoelastic properties of the oil-elastomer mixtures at a wide range of concentration and temperature offer information useful for understanding elastomer processability. The viscoelastic properties of such systems are also most sensitive manifestations of the polymer chain structure and, therefore, they represent fundamental characteristics of a given elastomer sample. In this work, two samples of ethylene-propylene copolymer differing in chain structure were selected. The oil-elastomer mixtures were prepared for polymer concentration in the range of 2.5–100%. The viscoelastic properties have been measured in the temperature range of 30–150°C. The frequency range was 10−1–102 rad/s and in some cases −2–102 rad/ s. The superposition principles have been examined with these data for both the temperature and concentration dependence.

scholarly journals Compressible starting jet: pinch-off and vortex ring–trailing jet interaction

2017 ◽  
Vol 817 ◽  
pp. 560-589 ◽  
Author(s):  
Juan José Peña Fernández ◽  
Jörn Sesterhenn
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Vortex Ring ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Chamber Pressure ◽  
Vortex Interaction ◽  
Dominant Feature ◽  
Chamber Temperature ◽  
Starting Jet

The dominant feature of the compressible starting jet is the interaction between the emerging vortex ring and the trailing jet. There are two types of interaction: the shock–shear layer–vortex interaction and the shear layer–vortex interaction. The former is clearly not present in the incompressible case, since there are no shocks. The shear layer–vortex interaction has been reported in the literature in the incompressible case and it was found that compressibility reduces the critical Reynolds number for the interaction. Four governing parameters describe the compressible starting jet: the non-dimensional mass supply, the Reynolds number, the reservoir to unbounded chamber temperature ratio and the reservoir to unbounded chamber pressure ratio. The latter parameter does not exist in the incompressible case. For large Reynolds numbers, the vortex pinch-off takes place in a multiple way. We studied the compressible starting jet numerically and found that the interaction strongly links the vortex ring and the trailing jet. The shear layer–vortex interaction leads to a rapid breakdown of the head vortex ring when the flow impacted by the Kelvin–Helmholtz instabilities is ingested into the head vortex ring. The shock–shear layer–vortex interaction is similar to the noise generation mechanism of broadband shock noise in a continuously blowing jet and results in similar sound pressure amplitudes in the far field.

scholarly journals The Effect of Reynolds Number on the Performance of Partial Admission and Re-Entry Axial Turbines

1965 ◽  
Author(s):  
Robert G. Adams
Keyword(s):  
Reynolds Number ◽  
Power Systems ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Test Program ◽  
Optimum Pressure ◽  
Auxiliary Power ◽  
Partial Admission ◽  
Open Cycle ◽  
Axial Turbines

In turbines designed for open-cycle auxiliary power systems for orbital and reentry vehicles, turbine blade Reynolds numbers of less than 1000 are not uncommon. An investigation of the effect of Reynolds number in this range on the performance of partial admission and reentry axial turbines, which are the predominant types of turbine used in this class of power system, was recently conducted. This paper describes the test program carried out, the results of the investigation, and examines the implications of the results on the design of turbines for this application. In general, it was found that the drop in efficiency with reduced Reynolds number was not so rapid with the types of turbine studied as with the full-admission turbine. The optimum pressure-ratio split was also found to be significantly affected by the Reynolds numbers encountered in the turbine stages.

scholarly journals FABRICATION OF BIODEGRADABLE POLYESTER MICROSPHERES BY ELECTROSPRAYING METHODS FOR DRUG CARRIER APPLICATION

2018 ◽  
Vol 54 (5A) ◽  
pp. 99
Author(s):  
Nguyen Vu Viet Linh
Keyword(s):  
Molecular Weight ◽  
Encapsulation Efficiency ◽  
Drug Carrier ◽  
Polymer Concentration ◽  
Loading Capacity ◽  
High Molecular Weight Polymer ◽  
Molecular Weight Polymer ◽  
Micro Particles ◽  
Morphology And Structure ◽  
Chain Entanglements

This research investigated the effects of polymer concentration, molecular weight polymer and type of polymer on the morphology of electrosprayed microparticles by Scanning Electron Microscopy. Electrospraying process has been studied to produce nano- and micro- particles for drug carrier application because of high loading capacity and high encapsulation efficiency. Controlling morphology and structure of electrosprayed particles can decide the release of drug from these particles. Particles were hollow and wrinkled semi-spheres as using low polymer concentration while wrinkled spheres as using higher polymer concentration. The electrosprayed particles obtained spherical morphology when the polymer concentration is high enough to generate significant chain entanglements. The results also indicated that high molecular weight polymer could produce spherical microspheres, even with low polymer concentration. The electrospraying process fabricated the microspheres from biodegradable PLA and PCL for drug carrier application. 

A Study on Reynolds Number Effects in Turbomachines

1964 ◽  
Vol 86 (3) ◽  
pp. 227-235 ◽  
Author(s):  
O. E. Balje´
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Fair Agreement ◽  
Low Reynolds Numbers ◽  
Reynolds Number Effects ◽  
Comprehensive Test ◽  
Specific Speed ◽  
Low Reynolds

Typical space power units have a tendency to encounter low Reynolds numbers in the last turbine stages. Comprehensive test data on the effect of low Reynolds numbers on the efficiency of turbomachines are lacking. An attempt is made to assess this influence, using conventional aerodynamic arguments. By distinguishing between viscous and nonviscous losses some tentative values have been calculated which are in fair agreement with the few available test data. These considerations indicate that the stage pressure ratio and the specific speed affect the Reynolds number influence significantly.

Effect of Plenum Length and Diameter on Turbulent Heat Transfer in a Downstream Tube and on Plenum-Related Pressure Losses

1981 ◽  
Vol 103 (3) ◽  
pp. 415-422 ◽  
Author(s):  
S. C. Lau ◽  
E. M. Sparrow ◽  
J. W. Ramsey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient

A systematic experimental study was carried out to determine how the heat transfer characteristics of a turbulent tube flow are affected by the length and diameter of a cylindrical plenum chamber which delivers fluid to the tube. The net pressure loss due to the presence of the plenum was also measured. The experimental arrangement was such that the fluid experiences a consecutive expansion and contraction in the plenum before entering the electrically heated test section. Air was the working fluid, and the Reynolds number was varied over the range from 5,000 to 60,000. It was found that at axial stations in the upstream portion of the tube, there are substantially higher heat transfer coefficients in the presence of longer plenums. Thus, a longer plenum functions as an enhancement device. On the other hand, the plenum diameter appears to have only a minor influence in the range investigated (i.e., plenum diameters equal to three and six times the tube diameter). The fully developed Nusselt numbers are independent of the plenum length and diameter. With longer plenums in place, the thermal entrance length showed increased sensitivity to Reynolds number in the fully turbulent regime. The pressure loss coefficient, which compares the plenum-related pressure loss with the velocity head in the tube, increases more or less linearly with the plenum length. With regard to experimental technique, it was demonstrated that guard heating/cooling of the electrical bus adjacent to the tube inlet is necessary for accurate heat transfer results at low Reynolds numbers but, although desirable, is less necessary at higher Reynolds numbers.

Sign in / Sign up

Export Citation Format

Share Document