Forced-flow pipelines

Ductile sewer pipes are standardised in DIN EN 598 for gravity-flow sewers and forced-flow pipelines pressurised up to 6 bar (600 kPa) in the nominal diameters DN 100 to DN 2000 [20]. They are used for combined, sanitary or storm water pipe-... 

Pipeline transport involves the appHcation of force to the material being moved, either through the use of pumps to transport Hquids, compressors to move gases, or flowing water to move soHds. In some appHcations, vacuum may create the pressure differential. 

In Fig. 15-9 two potentiostatically controlled protection rectifiers and an additional diode are included to drain peak currents. At pipeline crossings with an external rail network (e.g., in regions outside the urban area), the forced stray current drainage should be installed as close as possible to the rails that display negative potentials for the longest operation time. The currents absorbed from the positive rails continue to flow also in the region outside the rail crossings. Here the use of potentiostatically controlled rectifiers is recommended these should be connected not only to the rails but also to impressed current anodes. 

The procedure for performing a dimensional analysis will be illustrated by means of an example concerning the flow of a liquid through a circular pipe. In this example we will determine an appropriate set of dimensionless groups that can be used to represent the relationship between the flow rate of an incompressible fluid in a pipeline, the properties of the fluid, the dimensions of the pipeline, and the driving force for moving the fluid, as illustrated in Fig. 2-1. The procedure is as follows. 

Example 2-3 Scale-Up of Pipe Flow. We would like to know the total pressure driving force (AP) required to pump oil (/z = 30 cP, p = 0.85 g/cm3) through a horizontal pipeline with a diameter (D) of 48 in. and a length (L) of 700 mi, at a flow rate (Q) of 1 million barrels per day. The pipe is to be of commercial steel, which has an equivalent roughness (e) of 0.0018 in. To get this information, we want to design a laboratory experiment in which the laboratory model (m) and the full-scale field pipeline (f) are operating under dynamically similar conditions so that measurements of AP in the model can be scaled up directly to find AP in the field. The necessary conditions for dynamic similarity for this system are... 

You want to find the force exerted on an undersea pipeline by a 10 mph current flowing normal to the axis of the pipe. The pipe is 30 in. in diameter the density of seawater is 64 lbm/ft3 and its viscosity is 1.5 cP. To determine this, you test a ll in. diameter model of the pipe in a wind tunnel at 60° F. What velocity should you use in the wind tunnel to scale the measured force to the conditions in the sea What is the ratio of the force on the pipeline in the sea to that on the model measured in the wind tunnel ... 

We have seen how to determine the driving force (e.g., pumping requirement) for a given pipe size and specified flow as well as how to determine the proper pipe size for a given driving force (e.g., pump head) and specified flow. However, when we install a pipeline or piping system we are usually free to select both the best pipe and the best pump. The term best in this case refers to that combination of pipe and pump that will minimize the total system cost. 

Solution. Slack flow will not occur until the driving force (due to gravity) on the downstream side of the hill (from 2 to 3 in Fig. 7-5) exceeds the friction loss in this part of the pipeline that is, when Eq. (7-63) is no longer satisfied with A = itD1 /4 and Db = D. 

This would be evidenced by an increase on the pressure gauge. In most cases the swab or pig will progress past the interuption and regain its normal progression. However, if it did not, and the pressure continued to rise without fluctuation, the hydraulic pressure should be allowed to drop and then the pipeline re-pressurized in an attempt to force the pig past the obstacle. In the worst case, where the pig or swab became lodged, it would be necessary to reverse the flow by applying hydraulic pressure on the egress end of the pipeline. 

Swing Check Valves These valves (Fig. 10-159) are normally designed for use in horizontal lines or in vertical lines with normally upward flow. Since their seating force is primarily due to pipeline pressure, they may not seal as tightly at low pressures as at higher pressures. When suitable, nonmetallic seats may be used to minimize this problem. 

When fluid flows past objects or through orifices or similar restrictions, vortices may periodically be shed downstream. Objects such as smokestacks, chemical-processing columns, suspended pipelines, and electrical transmission lines can be subjected to damaging vibrations and forces due to the vortices, especially if the shedding frequency is close to a natural vibration frequency of the object. The shedding can... 

Inclined pipelines require the highest gas velocity to convey the same amount of solid materials when compared to both vertical and horizontal conveying. In this case, gas flow has to overcome the forces associated with horizontal conveying and the tendency of materials to slide back down the incline. In practice, a slope of less than 15° or more than 80° from the horizontal need not be considered an incline [Williams, 1983]. 

As an illustration, suppose the surface of water in a reservoir is 500 ft above the level of the site of a power plant and that there is available a flow of 200 ft3/s. In this case, H = z = 500 ft and P = 62.4 x 200 x 500 = 6,240,000 ft lb/s, or 11,340 hp, which is the total power available. If in the pipeline the friction loss is hf = 25 ft, then the power lost by friction is Whf and is seen to be 567 hp. Again, suppose a nozzle discharges 50 lb of water per second in a jet with a velocity of 120 ft/s H = V2/2g = 224 ft. Then the available power in the jet is 50 x 224/550 = 20.3 hp. The expression power equals force applied times velocity of the point of application of the force cannot be used in the preceding case, because it has no physical significance, as there is no force applied to anything, nor is there any point of application. In the case of a jet, the force it might exert would depend upon what happened when it struck an object, and the power produced would depend upon the velocity of the object. But the available power of the jet is a definite quantity, no matter what it acts upon or whether it ever acts upon anything. 

The generalization of such problems by introducing easily peneuable layers within the tube or duct, i.e. layers with disUibuted force (1.7), is oriented to a number of applications and brings also a light to main mechanisms associated with such flows. The applications include the water purification by porous inserts into pipelines, flows in vibrators, in journals and bearings with fibrous insets or brushes, in heat exchangers,... 

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