Pressure losses in a pipe

Pressure loss in a piping system (not including the tanks, heat exchangers, distillation columns, etc.) is usually expressed in units oi feet of flowing fluid, or the equivalent converted to pounds per square inch. Some published pressure loss data is expressed as per 100 equivalent feet of the size pipe being used or estimated. 

Note that all the factors required for Eqs. (6.30) and (6.31) have been established in previous steps of this section. Thus, for any 90° standard ell using these two equations, we have the pressure loss established for two-phase flow acceleration. Simply multiply the calculated APen value by the number of 90° ells in the pipe segment. Remember that if a 15% pressure loss in a pipe segment results, a new pipe segment is required. 

Rapid eycling can occur when the pressure at the valve inlet decreases at the start of relief valve flow beeause of excessive pressure loss in the piping to the valve. Under these conditions, the valve will cycle at a rapid rate which is referred to as chattering. The valve responds to the pressure at its inlet. If the pressure decreases during flow... 

The table shows the length of pipe with equivalent pressure loss in a given size and type of fitting. ... 

Pressure drop in the transmission pipes is a combination of pressure losses in the pipes and pipe fittings7. Pipe fittings include bends, isolation valves, control valves, orifice plates, expansions, reductions, and so on. If the fluid is assumed to be incompressible and the change in kinetic energy from inlet to outlet is neglected, then ... 

The X value calculated is valid only over a range in which the pressure loss in the pipe does not exceed 15% of inlet value. This is a considerable handicap if the case involves a large pressure loss. Here the objective is to divide the pipe run into several segments. Each segment will have a different pressure inlet and probably a different temperature due to the gas-flashing cooling effect. This makes the solution longer, but consider the fact that this is a two-phase flow, not subject to easy or short solution in any case. 

From Eq. (63), the mechanical energy equation in head form, it is seen that, in the absence of a pump head, losses in a pipe system consist of pressure head changes, potential head changes, and velocity head changes. When fittings or changes in pipe geometry are encountered, additional losses occur. 

This section illustrates the use of material presented earlier to determine the pressure drop in a pipe system, mating of a pump to the pipe system and the head loss over a control valve. 

Use a suitable pressure-loss chart to determine the pressure loss in 510 ft of 4-in flanged steel pipe containing two 90° elbows and four 45° bends. The schedule 40 piping conveys 13,000 lb/h (1.64 kg/s) of 40-psig 350° F superheated steam. List other methods of determining the pressure loss in steam piping. 

Most piping designers use a chart to determine the pressure loss in steam piping because a chart saves time and reduces the effort involved. Further, the accuracy obtained is sufficient for all usual design practice. 

Pressure drop or head loss in a piping system is caused by fluid rising in elevation, friction, shaftwork (e.g., from a turbine) and turbulence due to sudden changes in direction or cross-sectional area. Figure 3-2... 

To extend the prediction of vs to flow regimes where Rec 0.1 it is necessary to use empirical correlations between Rec and a friction factor, similar to the approach used for calculating frictional pressure losses in turbulent pipe flow. The cutting friction factor/ is defined by... 

Ward Smith, A. J., The Flow and Pressure Losses in Smooth Pipe Bends of Constant Cross Section , J. Roy. Aeronautical Soc. 67 437—447 (1963). 

The first entry deals with the pressure drop due to frictional losses in a pipe. The key relationship is the... 

The pressure losses in a horizontally straight pipe and a horizontally bent pipe both increased with the increase of the air velocities, and the amount of the pressure loss increased with the increase of the rate of the snowball transportation under the positive and negative pressure condition. The pressure loss in a horizontally bent pipe was 1.3 8.5 times as large as in a horizontally straight pipe imder the positive pressure, and twice under the negative pressure. 

On the other hand, in the case of the negative pressure condition, the pressure loss in a vertically bent pipe decreased with the increase of the air velocities. 

T. Kobayashi and M. Kumagai, Experiments of Snow Removal Based on the Use of a Blower(l)—Pressure Loss in a Horizontal Straight Pipe—, Report of the National Research Center for Disaster Prevention, No.44 (1989), pp.105-121. 

By analogy with flow of water alone it is possible to introduce a coefficient of local resistance also for capsules flow and to define total pressure losses in a bend as the sum of friction losses in the straight pipe, he, and local losses in the bend... 

We now have to thank Stanton and PanneU, and also Moody for their studies of flow using numerous fluids in pipes of various diameters and surface roughness and for the evolution of a very useful chart (see Fig. 48.6). This chart enables us to calculate the frictional pressure loss in a variety of circular cross-section pipes. The chart plots Re)molds numbers (Re), in terms of two more dimensionless groups a friction factor < ), which represents the resistance to flow per unit area of pipe surface with respect to fluid density and velocity and a roughness factor e/ID, which represents the length or height of surface prelections relative to pipe diameter. 

The concept of the specific resistance used in equation 4 is based on the assumptions that flow is one-dimensional, growth of cake is unrestricted, only soHd and Hquid phases are present, the feed is sufficiently dilute such that the soHds are freely suspended, the filtrate is free of soHds, pressure losses in feed and filtrate piping are negligible, and flow is laminar. Laminar flow is a vaHd assumption in most cake formation operations of practical interest. 

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