Friction in pipes

Viscosity (See Sec. 5 for further information.) In flowing liquids the existence of internal friction or the internal resistance to relative motion of the fluid particles must be considered. This resistance is caUed viscosity. The viscosity of liquids usuaUv decreases with rising temperature. Viscous liquids tend to increase tlie power required by a pump, to reduce pump efficiency, head, and capacity, and to increase Friction in pipe lines. 

Friction in piping, entrance and exit head losses... 

Cf Friction frictional forces Fluid friction in pipes,... 

The velocities at the entrance and exit of the system can be calculated from the respective diameters of the tanks or pipes and the volumetric flow rate of the food. The energy loss term E/ consists of losses due to friction in pipe and that due to friction in valves and fittings ... 

Fig. 8 Friction in pipes related to Reynolds number. (From Ref.. )...

We have so far discussed friction in pipe flow. Actually, the supplest case of turbulent friction is that of flow over a flat plate with negligible pressure gradient. This case applies to many important technological problems, such as drag on ships, airplanes, turbines, compressors, and propellers. An approximate analytical approach, which is beyond the scope of this text, leads to... 

RELATIONS BETWEEN SKIN-FRICTION PARAMETERS. The four common quantities used to measure skin friction in pipes, hj-, Ap, x , and f, are related by the equations... 

Friction in pipes. For straight horizontal pipes resistance to flow arises because of viscous shear or friction at the wall. Dimensional analysis leads to the conclusion that for smooth pipes the pressure drop (scaled to make it dimensionless) is a function only of the Reynolds number. The dimensionless group containing the pressure drop is known as the friction factor ... 

Chilton and Colburn (Ref. 4) have published a method for predicting such pressure drop for solid packings, based on the Fanning equation for friction in pipes. They modify the friction equation to... 

There are also many empirical formulas used for calculatiag the friction head loss in piping systems. These must be used carefuUy because many are based on the properties of specific fluids and are not appHcable over a broad range of fluids, temperatures, and pressures. For example, the Ha2en and Wdhams formula widely used for water flow ... 

The viscous or frictional loss term in the mechanical energy balance for most cases is obtained experimentally. For many common fittings found in piping systems, such as expansions, contrac tions, elbows and valves, data are available to estimate the losses. Substitution into the energy balance then allows calculation of pressure drop. A common error is to assume that pressure drop and frictional losses are equivalent. Equation (6-16) shows that in addition to fric tional losses, other factors such as shaft work and velocity or elevation change influence pressure drop. 

Successive reflections of the pressure wave between the pipe inlet and the closed valve result in alternating pressure increases and decreases, which are gradually attenuated by fluid friction and imperfect elasticity of the pipe. Periods of reduced pressure occur while the reflected pressure wave is travehng from inlet to valve. Degassing of the liquid may occur, as may vaporization if the pressure drops below the vapor pressure of the liquid. Gas and vapor bubbles decrease the wave velocity. Vaporization may lead to what is often called liquid column separation subsequent collapse of the vapor pocket can result in pipe rupture. 

Friction Head This is the pressure required to overcome the resistance to flow in pipe and fittings. It is dealt with in detail in Sec. 5. 

Increase in piping friction to the discharge vessel due to the following ... 

The treatment of vent flow calculations in most typical relief wstem configurations involves two classes of computation models flow in low-fric tion geometries such as nozzles and frictional flow in pipes and fittings. 

For determining the frictional head, refer to friction loss in pipes, bends, elbows and reducers and valves as provided in Tables A.I and A.2 ... 

Table A. I provides, for a particular rate of discharge in GPM. the friction loss in pipes for every 100 feet of straight pipe length, reasonably smooth and free from incrustation.

Table A.2 Friction in fittings in equivalent of pipe length (ft)...

Within low-pressure operating ranges, the slight pressure loss due to friction in vapor pipes may mean an appreciable loss of total available temperature difference. 

Lj = Faetor for friction in fittings, equivalent length in pipe diameter per unit length of pipe (1/ft)... 

The total piping system pressure drop for a particular pipe installation is the sum of the friction drop in pipe valves and fittings, plus other pressure losses (drops) through control valves, plus drop through equipment in the system, plus static drop due to elevation or pressure level. For example, see Figure 2-2. 

Friction Head Loss (Resistance) in Pipe, Fittings, and Connections... 

Flow is <2000, therefore, flow of viscous or laminar system consists of friction factor, fp, for 4-in. pipe = 0.017 (Table 2-2). 

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