What Is Viscosity

A further complication of determination of the viscosity of a macromol-ecular solution is that the viscosity depends on the concentration of macromolecules. Newton developed a formula for predicting the viscosity of a solution of macromolecules and solvent q, knowing the solvent viscosity r, shape factor for the macromolecule v, and the volume fraction of macromolecules 9. Newton s law of viscosity is given in Equation (4.2) and provides a relationship among viscosity, shape factor, and volume fraction of polymer. 

Using this formula it is possible to predict the viscosity of a macromolecu-lar solution knowing the shape factor of a macromolecule and its volume fraction. However, to do this we must hrst determine the shape factor. This equation also tells us that macromolecules with large shape factors have high viscosities and show increased strain-rate dependence of the viscous component of the stress in tissues. Therefore, we need to be able to evaluate the shape factor for different macromolecules. 

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C What is viscosity What causes viscosity in liquids and in gases Is dynamic viscosity typically higher for a liquid or for a gas ... 

What is viscosity What is the relationship between intermolecular forces and viscosity ... 

What is viscosity Significance at a microscopic level 227 Tab. 8.1. Main fluorescence techniques for the determination of fluidity (from Valeur, 1993)... 

What is viscosity How does it depend on intermolecular forces ... 

Before we are in a position to discuss the viscosity of polymer melts, we must first give a quantitative definition of what is meant by viscosity and then say something about how this property is measured. This will not be our only exposure to experimental viscosity in this volume—other methods for determining bulk viscosity will be taken up in the next chapter and the viscosity of solutions will be discussed in Chap. 9—so the discussion of viscometry will only be introductory. Throughout we shall be concerned with constant temperature experiments conducted under nonturbulent flow conditions. 

In connection with a discussion of the Eyring theory, we remarked that Newtonian viscosity is proportional to the relaxation time [Eqs. (2.29) and (2.31)]. What is needed, therefore, is an examination of the nature of the proportionality between the two. At least the molecular weight dependence of that proportionality must be examined to reach a conclusion as to the prediction of the reptation model of the molecular weight dependence of viscosity. 

In discussing Fig. 4.1 we noted that the apparent location of Tg is dependent on the time allowed for the specific volume measurements. Volume contractions occur for a long time below Tg The lower the temperature, the longer it takes to reach an equilibrium volume. It is the equilibrium volume which should be used in the representation summarized by Fig. 4.15. In actual practice, what is often done is to allow a convenient and standardized time between changing the temperature and reading the volume. Instead of directly tackling the rate of collapse of free volume, we shall approach this subject empirically, using a property which we have previously described in terms of free volume, namely, viscosity. 

What Kenics Mixer model of 3-in. Schedule 40 is required to process a Newtonian fluid with a viscosity of 150,000 cP, a density of 60 Ib/ft, and a flowrate of 650 Ib/hr What is the pressure drop (AP) and theoretical horsepower ... 

Determine which 2-in. Schedule 40 mixer model is required to process water-like fluids at a flowrate of 10 gpm. What is the required theoretical horsepower (Data viscosity = 1 cP Density = 62.4 Ib /ft assume = 0.00015 ft)... 

The conductivity and viscosity of an ionic liquid is often combined into what is termed Walden s rule [Equation (3.6-4)] [54],... 

Yet, some authors reported an increase, instead of reduction of viscosity after finishing treatment of filler [266, 267]. Plueddeman in [268] noted that increase or decrease of melt viscosity with finishing agents depends on what is the resultant reaction of the filler, agent and matrix - neutral, acid or basic. The viscosity may be optimized by using the right formulation. For example, agents with basic... 

Helium is an interesting example of the application of the Third Law. At low temperatures, normal liquid helium converts to a superfluid with zero viscosity. This superfluid persists to 0 Kelvin without solidifying. Figure 4.12 shows how the entropy of He changes with temperature. The conversion from normal to superfluid occurs at what is known as the A transition temperature. Figure 4.12 indicates that at 0 Kelvin, superfluid He with zero viscosity has zero entropy, a condition that is hard to imagine.v... 

All gases and most liquids of simple molecular structure exhibit what is termed Newtonian behaviour, and their viscosities are independent of the way in which they are flowing. Temperature may, however, exert a strong influence on viscosity which, for highly viscous liquids, will show a rapid decrease as the temperature is increased. Gases, show the reverse tendency, however, with viscosity rising with increasing temperature, and also with increase of pressure. 

Water flows in a 50 mm pipe, 100 m long, whose roughness e is equal to 0.013 mm. If the pressure drop across this length of pipe is not to exceed 50 kN/m2, what is the maximum allowable water velocity The density and viscosity of water may be taken as 1000 kg/m3 and 1.0 mN s/m2 respectively. 

A cylindrical tank, 5 m in diameter, discharges water through a horizontal mild steel pipe, 100 nj long and 225 mm in diameter, connected to the base. What is the time taken for the water level in the tank to drop from 3 m to 0.3 m above the bottom The viscosity of water may be taken as 1 mN s/m2. 

A solution of sodium hydroxide of density 1650 kg/m3 and viscosity 50 mN s/m2 is agitated by a propeller mixer of 0.5 m diameter in a tank of 2.28 m diameter, and the liquid depth is 2.28 m. The propeller is situated 0,5 m above the bottom of the tank. What is the power which the propeller must impart to the liquid for a rotational speed of 2 Hz ... 

A centrifugal pump is required to circulate a liquid of density 800 kg/m2 and viscosity 0.5 x 10 3 Ns/m" from the reboiler of a distillation column through a vaporisor at the rate of 0.004 m3/s, and to introduce the superheated vapour above the vapour space in the reboiler which contains a 0.07 m depth of liquid. If smooth-bore 25 mm diameter pipe is to be used, the pressure of vapour in the reboiler is 1 kN/m2 and the Net Positive Suction Head required by the pump is 2 m of liquid, what is the minimum height required between the liquid level in the reboiler and the pump ... 

Calculate the thickness of the boundary layer at a distance of 150 mm from the leading edge of a surface over which oil, of viscosity 0.05 N s/m2 and density 1000 kg/m3 flows with a velocity of 0.3 m/s. What is the displacement thickness of the boundary layer ... 

What is a non-Newtonian fluid Describe the principal types of behaviour exhibited by these fluids. The viscosity of a non-Newtonian fluid changes with the rate of shear according to the approximate relationship ... 

Oil of viscosity 10 mN s/m2 and density 950 kg/m3 is pumped 8 km from an oil refinery to a distribution depot through a 75 inm diameter pipeline and is then despatched to customers at a rale of 500 tonne/day. Allowance must be made for periods of maintenance which may interrupt the supply from the refinery for up to 72 hours. If the maximum permissible pressure drop over the pipeline is 3450 kN/m2, what is the shortest time in which the storage tanks can be completely recharged after a 72 hour shutdown Take the roughness of the pipe surface as 0.05 mm. 

Crude oil is pumped from a terminal to a refinery through a foot diameter pipeline. As a result of frictional heating, the temperature of the oil is 20 deg K higher at the refinery end than at the terminal end of the pipe and the viscosity has fallen to one half its original value. What is the ratio of the pressure gradient in the pipeline at the refinery end to that at the terminal end ... 

Oil of density 950 kg/m3 and viscosity 10-2 Ns/m2 is to be pumped 10 km through a pipeline and the pressure drop must not exceed 2 x lt N/m2. What is the minimum diameter of pipe which will be suitable, if a flowrate of 50 tonne/h is to be maintained Assume the pipe wall to be smooth. Use either the pipe friction chart or the Blasius equation (R/pu1 = 0.0396/ -1/4). 

Water, of viscosity 1 mN s/m2 flowing through the pipe at the same mean velocity gives rise to a pressure drop of I04 N/m2 compared with 105 N/m2 for the non-Newtonian fluid. What is the consistency ("k vaiuei of the non-Newtonian fluid ... 

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