Effect fluid viscosity

The above derivation for LMTD involves two important assumptions (1) the fluid specific heats do not vary with temperature, and (2) the convection heat-transfer coefficients are constant throughout the heat exchanger. The second assumption is usually the more serious one because of entrance effects, fluid viscosity, and thermal-conductivity changes, etc. Numerical methods must normally be employed to correct for these effects. Section 10-8 describes one way of performing a variable-properties analysis. 

Several prelreatmcnt techniques have been practiced in conjunction with the use of organic polymeric membranes. The choice of a particular technique to apply depends to a great extent on the chemical nature of the feed, membrane resistance toward the feed stream and the product requirements. The characteristics of the feed such as the panicle size or molecular weight distribution, effective fluid viscosity and pH (and therefore the... 

These relationships are valid for isolated bubbles moving under laminar flow conditions. In the case of turbulent flow, the effect of turbulent eddies impinging on the bubble surface is to increase the drag forces. This is typically accounted for by introducing an effective fluid viscosity (rather than the molecular viscosity of the continuous phase, yUf) defined as pi.eff = Pi + C pts, where ef is the turbulence-dissipation rate in the fluid phase and Cl is a constant that is usually taken equal to 0.02. This effective viscosity, which is used for the calculation of the bubble/particle Reynolds number (Bakker van den Akker, 1994), accounts for the turbulent reduction of slip due to the increased momentum transport around the bubble, which is in turn related to the ratio of bubble size and turbulence length scale. However, the reader is reminded that the mesoscale model does not include macroscale turbulence and, hence, using an effective viscosity that is based on the macroscale turbulence is not appropriate. 

Foam Mobility. The objective of foam is to control acid mobility in high permeability zones. The mobility of a given fluid (M) in a reservoir zone or layer is simply the ratio of the permeability of this zone to the effective fluid viscosity, which is given by Darcy s law as ... 

Particle settling velocity decreases with the increasing of effective fluid viscosity. However, the lifting efficiency of the particle increases. 

Commonly used heat-transfer surfaces are internal coils and external jackets. Coils are particularly suitable for low viscosity Hquids in combination with turbine impellers, but are unsuitable with process Hquids that foul. Jackets are more effective when using close-clearance impellers for high viscosity fluids. For jacketed vessels, wall baffles should be used with turbines if the fluid viscosity is less than 5 Pa-s (50 P). For vessels equipped with cods, wall baffles should be used if the clear space between turns is at least twice the outside diameter of the cod tubing and the fluid viscosity is less than 1 Pa-s (10... 

Supercritical Mixtures Dehenedetti-Reid showed that conven-tionaf correlations based on the Stokes-Einstein relation (for hquid phase) tend to overpredict diffusivities in the supercritical state. Nevertheless, they observed that the Stokes-Einstein group D g l/T was constant. Thus, although no general correlation ap es, only one data point is necessaiy to examine variations of fluid viscosity and/or temperature effects. They explored certain combinations of aromatic solids in SFg and COg. 

D = diameter of cylinder or effective width of objecl V = free-stream velocity p = fluid density [L = fluid viscosity... 

Effect of Fluid Viscosity and Inertia The dynamic effect of viscosity on a rotating liquid slurry as found in a sedimenting centrifuge is confined in veiy thin fluid layers, known as Ekman layers. These layers are adjacent to rotating surfaces which are perpendicular to the axis of rotation, such as bowl heads, flanges, and conveyor blades, etc. The thickness of the Ekman layer 6 is of the order... 

Although it is entirely possible for erosion-corrosion to occur in the absence of entrained particulate, it is common to find erosion-corrosion accelerated by a dilute dispersion of fine particulate matter (sand, silt, gas bubbles) entrained in the fluid. The character of the particulate, and even the fluid itself, substantially influences the effect. Eight major characteristics are influential particle shape, particle size, particle density, particle hardness, particle size distribution, angle of impact, impact velocity, and fluid viscosity. 

Effects of viscosity on Process Fluid Heat Transfer Film Coefficient... 

There are several similar relationships for centrifugal pumps that can be used if the effects of viscosity of the pumped fluid can be neglected. These relate the operating performance of any centrifugal pump for one set of operating conditions to those of another set of operating conditions, say conditions, and conditions 2. 

Reynold s number It is a dimensionless number that is significant in the design of any system in which the effect of viscosity is important in controlling the velocities or the flow pattern of a fluid. It is equal to the density of a fluid, times its velocity, times a characteristic length, divided by the fluid viscosity. This value or ratio is used to determine whether the flow of a fluid through a channel or passage, such as in a mold, is laminar (streamlined) or turbulent. 

An experimental study of the laminar-turbulent transition in water flow in long circular micro-tubes, with diameter and length in the range of 16.6-32.2 pm and 1-30 mm, respectively, was carried out by Rands et al. (2006). The measurements allowed to estimate the effect of heat released by energy dissipation on fluid viscosity under conditions of laminar and turbulent flow in long micro-tubes. 

An enzyme, acid, or oxidative "breaker" is added to effect a controlled depolymerization and thus a programmed loss of fluid viscosity. This depolymerization is timed to occur when the sandladen fluid is opposite the productive formation. The sand then drops out of suspension and is packed against the formation. The sand creates a high permeability fluid pathway from the formation... 

Transport Properties. Because the feed is primarily air and because substantial amounts of N2 and 02 are present in the effluent stream, we will assume that the fluid viscosity is that of air for purposes of pressure drop calculations. For the temperature range of interest, the fluid viscosity may be taken as equal to 320 micropoise. The pressure range of interest does not extend to levels where variations of viscosity with pressure need be considered. The effective diffusivities of naphthalene and phthalic anhydride in the catalyst pellet may be evaluated using the techniques developed in Section 12.2. 

Since the absolute thickness of the effective hydrodynamic boundary layer is very small, below a particular size range minimum, no hydrodynamic effects are perceived experimentally with varying agitation. This, however, does not mean, that there are no such influences Further, the mechanisms of mass transfer and dissolution may change for very small particles depending on a number of factors, such as the fluid viscosity, the Sherwood number (the ratio of mass diffusivity to molecular diffusivity), and the power input per unit mass of fluid. 

In between these two extremes, the effective hydrodynamic boundary layer depends on the combined effects of particle size and hydrodynamics. Talking about borderline particle sizes is meaningful only if all other relevant data, such as the fluid viscosity,... 

The above results seem to be contradictory and irreconcilable. This is not so because the effect of viscosity is associated with those of flow rate, surface tension, and orifice diameter. Since the effect of viscosity is negligible when the flow rate tends to zero, even a large difference in the viscosities of the two fluids under consideration does not, at small flow rates, show the influence of viscosity. This is precisely the case in the investigations of Datta et al. (D4). What was mistakenly interpreted as the influence of viscosity, was probably, in reality, the influence of the reduced surface tension though the viscosity had been increased a hundredfold, the surface tension was simultaneously reduced by about 5 dynes per centimeter. At the extremely small flow rates (<0.1 cm3/sec) employed, the effect of viscosity was presumably negligible. 

The above discussion dealt with only that particular situation where the continuous phase approximated to an inviscid fluid. However, the equations thus derived can be easily modified to include the effects of viscosity of the of the continuous phase. Under constant pressure conditions also, viscosity of the continuous phase tends to increase the bubble volume by increasing the drag during both the expansion and detachment stages. 

A further problem in plotting the data is that the fluid viscosity has very little effect on the dispersion (El). Therefore, the Reynolds number might not be appropriate as a plotting variable (C5). However, no other dimensionless group has yet been proposed, and so the Reynolds number was retained in Fig. 8. 

In practice all real fluids have nonzero viscosity so that the concept of an inviscid fluid is an idealization. However, the development of hydrodynamics proceeded for centuries neglecting the effects of viscosity. Moreover, many features (but by no means all) of certain high Reynolds number flows can be treated in a satisfactory manner ignoring viscous effects. 

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