Parallel piping systems

Flow Along Smooth Surfaces. When the flow is entirely parallel to a smooth surface, eg, in a pipe far from the entrance, only the shear stresses contribute to the drag the normal stresses are directed perpendicular to the flow (see Piping systems). The shear stress is usually expressed in terms of a dimensionless friction factor ... 

Check valves are required in the piping system at any point where backflow of gas after a shutdown has the ability to restart the compressor, running it backwards or, for that matter, even in the normal direction. Reverse rotation is totally bad, as many components of the various compressor types are not designed for reverse rotation, and there is some possibility, generally remote, that the compressor could reach a destructive over speed. Forward rotation is bad primarily because the intent was to stop the compressor, and it is now operating out of control. This is a problem, particularly if the shutdown was caused by a compressor failure indication, and the need to stop was to prevent further damage. In this mode, it is unlikely that the compressor can attain an overspeed condition. An application with a high potential for backflow is the parallel operation of two or more compressors. 

Broschka et al. (1983) report results of experimental tests on parallel plate flame arresters in piping systems. Tests were conducted on 3-inch and 6-inch diameter parallel plate flame arresters installed in 3-inch and 6-inch diameter piping sections using butane-air mixtures to generate a flame. The ignition source was varied from 3 to 43 feet from the flame arrester. The flame speed varied between 0 to 20 ft/s, and when the flame speed was 20 ft/s, the flame passed through the arrester (flame arrester failure). 

Components of a piping system that are connected in series produce additive pressure drops, while components that are connected in parallel must produce the same pressure drop. 

American Gas Association method, 121 Complex pipe systems, 122 Low pressure air, steam, 131 Panhandle formula, 120, 121 Panhandle-A formula, 121 Parallel system, 122 Series system, 122 Transmission factors, 120 Weymouth formula, 120 Flowsheet symbols, 17... 

Two-phase flow in parallel pipes, fed from a common manifold, displays interesting phenomena, as two phases may split unevenly when entering the parallel piping. Ozawa et al. (1979, 1989) performed experimental smdies on two-phase flow systems in parallel pipes of 3.1 mm diameter. They simulated the flow in boiling channels by injection of air and water into the pipes. 

Piping systems often involve interconnected segments in various combinations of series and/or parallel arrangements. The principles required to analyze such systems are the same as those have used for other systems, e.g., the conservation of mass (continuity) and energy (Bernoulli) equations. For each pipe junction or node in the network, continuity tells us that the sum of all the flow rates into the node must equal the sum of all the flow rates out of the node. Also, the total driving force (pressure drop plus gravity head loss, plus pump head) between any two nodes is related to the flow rate and friction loss by the Bernoulli equation applied between the two nodes. 

ISO 6721-8 1997 Plastics - Determination of dynamic mechanical properties - Part 8 Longitudinal and shear vibration - Wave-propagation method ISO 6721-10 1999 Plastics - Determination of dynamic mechanical properties - Part 10 Complex shear viscosity using a parallel-plate oscillatory rheometer ISO 9311-2 2002 Adhesives for thermoplastic piping systems - Part 2 Determination of shear strength... 

Figure 6.23a shows a typical piping system with apump operating against a static discharge head. Indicate the total static head (Fig. 6.23b) by a dashed line—in this installation Hts = 110 ft. Since static head is a physical dimension, it does not vary with flow rate and is a constant for all flow rates. Draw the dashed line parallel to the abscissa (Fig. 6.23b). 

The pumps, located in the buildings, are connected to each SG via independent piping system (two systems are available working in parallel). These piping systems are designed and installed in a manner to provide full reliability of feed water supply to the SGs. They are completely separated from the units feed water systems, originally designed. 

On the other hand, in bipolar cells, only the terminal cells are connected by intercell conductors, and there are typically many unit cells electrically in series between the terminal cells (Fig. 5.2). The two basic types of bipolar cells are the flat plate cell and the finger type cell. A group of bipolar cells that have a common piping system for the fluids, via manifolds, is referred to as an electrolyzer or sometimes a series or a stack. Within a single bipolar electrolyzer, there are sometimes more than one set of terminal cells. Bipolar electrolyzers can be connected via an external bus within a DC circuit in series or in parallel, but usually not both. Furthermore, in the case of mercury-cell plant conversions to membrane cells, the electrolyzers are connected electrically in parallel as shown in Fig. 5.3. 

For a parallel-flow double-pipe system we have... 

These measurements can be made on actual operating units on line but they may also be done using model heat exchanger units or instrumented pipe loops run in parallel to system flow. Figure 10.12 shows such an instrumented pipe loop test unit with five parallel, instrumented pipe runs. Water flow from the target system is diverted through this unit, so that conditions are representative of the actual operating system [18]. 

Twin oil coolers (Figure 15-3) should be provided and piped in parallel using a single multiport transflow valve to direct the oil flow to the coolers. The water should be on the tube side and the oil on the shell side. The oil-side pressure should be greater than the water-side pressure. This ratio is no assurance that water will not enter the system in the event of a tube leak, but it does reduce the risk. The oil system should be equipped with twin full-flow oil filters located downstream from the oil coolers. Since the filters are located downstream from the oil coolers, only one multiport transflow valve is required to direct the oil flow to the cooler-filter combinations. Do not pipe the filters and coolers with separate inlet and outlet block valves. 

A differential pressure switch set to alarm when the pressure drop reaches a predetermined point protects against the loss of oil flow. In addition to the differential pressure switch, a two-way, three-port valve with a pressure gauge is piped in parallel with the differential pressure switch for accurate indication of inlet and outlet oil filter pressure. When a single transflow valve is used with a cooler-filter installation, the differential pressure switch and pressure gauge assembly should span the cooler-filter system. 

A multiple pipe line system consisting of two or more parallel lines of different diameters and different lengths. 

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