Horizontal pipes

In situ measurement of the concentration of radioactive tracers in the different phases requires that the phases are separated and arranged according to density difference over the measurement cross section in a horizontal pipe. In general, the measurements are performed with two spectral gamma radiation detectors placed on top and bottom of the pipe respectively. 

Fig. 11. Flow regimes for air—water in a 2.5-cm horizontal pipe where is superficial Hquid velocity and is superficial gas velocity.

In inclined or vertical pipes, the flow regimes are similar to those described for horizontal pipes when both gas- and Hquid-flow rates are high. At lower flow rates, the effects of gravity are important and the regimes of flow are quite different. For Hquid velocities near 30 cm/s and gas velocities near... 

Fig. 1. Pressure required for propagation of decomposition flame through commercially pure acetylene free of solvent and water vapor in long horizontal pipes. Gas initially at room temperature ignition by thermal nonshock sources. Curve shows approximate least pressure for propagation (0), detonation,...

The predetonation distance (the distance the decomposition flame travels before it becomes a detonation) depends primarily on the pressure and pipe diameter when acetylene in a long pipe is ignited by a thermal, nonshock source. Figure 2 shows reported experimental data for quiescent, room temperature acetylene in closed, horizontal pipes substantially longer than the predetonation distance (44,46,52,56,58,64,66,67). The predetonation distance may be much less if the gas is in turbulent flow or if the ignition source is a high explosive charge. 

Fig. 2. Predetonation distances (in m) observed in acetylene at various pressures in horizontal pipes of various diameters. Gas quiescent, at room temperature, ignition by thermal nonshock sources (44,46,52,56,58,64,66,67). To convert kPa to atm, divide by 101.3.

The proper installation of both orifice plates and Venturi-type flow tubes requires a length of straight pipe upstream and downstream of the sensor, ie, a meter mn. The pressure taps and connections for the differential pressure transmitter should be located so as to prevent the accumulation of vapor when measuring a Hquid and the accumulation of Hquid when measuring a vapor. For example, for a Hquid flow measurement in a horizontal pipe, the taps are located in the horizontal plane so that the differential pressure transmitter is either close-coupled or connected through downward sloping connections to allow any trapped vapor to escape. For a vapor measurement in a horizontal pipe, the taps should be located on the top of the pipe and have upward sloping connections to allow trapped Hquid to drain. 

Figure 1 shows the particulate loading of a pipe containing gas and particulates where the nonuniformity induced by a disturbance, ie, a 90° bend, is obvious (2). A profile of concentration gradients in a long, straight, horizontal pipe containing suspended soHds is shown in Figure 2. Segregation occurs as a result of particle mass. Certain impurities, eg, metal-rich particulates, however, occur near the bottom of the pipe others, eg, oily flocculates, occur near the top (3). Moreover, the distribution may be affected by Hquid-velocity disturbances and pipe roughness.

FIG. 6-24 Gas/liqi lid flow patterns in horizontal pipes. From Alves, Chem. Eng. Progr., 50, 449 56 [1.9.54].)... 

FIG. 6-26 Parameters for pressure drop in liqiiid/gas flow through horizontal pipes. (Based on Lockhatt and Maitinelli, Chem. Engr. Prog., 45, 39 [1.94.9],)... 

Sample Withdrawal from Process A number of considerations are involved in the design of sample-withdrawal devices that wih provide representative samples. For example, in a horizontal pipe that conveys process fluid, a sample point on the bottom of the pipe wih collect a maximum amount of rust, scale, or other solid materials being carried along by the process fluid. In a gas stream, such a location will also collect a maximum amount of liquid contaminants. A sample point on the top side of a pipe will, for liquid streams, collec t a... 

HEM for Two-Phase Pipe Discharge With a pipe present, the backpressure experienced by the orifice is no longer qg, but rather an intermediate pressure ratio qi. Thus qi replaces T o iri ihe orifice solution for mass flux G. ri Eq. (26-95). Correspondingly, the momentum balance is integrated between qi and T o lo give the pipe flow solution for G,p. The solutions for orifice and pipe now must be solved simultaneously to make G. ri = G,p and to find qi and T o- This can be done explicitly for the simple case of incompressible single-phase (hquid) inclined or horizontal pipe flow The solution is implicit for compressible regimes. 

HEM for Horizontal Pipe Discharge For horizontal pipe flow, Fi = q = 0, and ... 

The general compressible flow solution simplifies for horizontal pipe flow to ... 

Equipment in which water flow is slow or intermittent is subject to deposition and associated corrosion. Hence, service water-system components that operate intermittently frequently suffer attack. Deposits accumulate in narrow orifices, screens, long horizontal pipe runs, sumps, or at regions of constricted flow. 

Figure 13.4 A large plug of dezincified metal beneath a deposit. Plugs often form on the bottom of horizontal pipes, beneath deposits.

The Lapple charts for compressible fluid flow are a good example for this operation. Assumptions of the gas obeying the ideal gas law, a horizontal pipe, and constant friction factor over the pipe length were used. Compressible flow analysis is normally used where pressure drop produces a change in density of more than 10%. 

Figure 24. Example of flow pattern map for air water system in horizontal pipes.

Water can be trapped behind heat exchanger baffles and then suddenly vaporized by circulation of hot oil. It can also be trapped in dead-ends and U-bends in pipework (see Section 9.1.1). Such U-bends can form when one end of a horizontal pipe is raised by thermal expansion. The trays in a distillation column were damaged during startup when hot gas met water, from previous steaming, dripping down the column [3J. Section 17.12 describes an incident somewhat similar to a foamover. 

Flow of Water from Open-End Horizontal Pipe... 

Reading from top at 150 psig, no superheat, down ver-dcally to intersect the horizontal steam flow of 1432 Ibs/min, follow diagonal line to the horizontal pipe size... 

Pipe in whatever plane shall be adequately supported. Reference should be made to the relevant parts of BS 3974, Part 1. In some instances, short vertical lengths in otherwise horizontal pipe mns may be self-supporting. 

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