Book - School of Science and Technology

Steam systems - principles 253whereZ 1 ˆ initial pressure factor ˆ P 1:9291Z 2 ˆ final pressure factor ˆ P 1:9292P ˆ steam pressure, absolute (kPa)M ˆ mass of steam flowing (kg/s)L ˆ length of pipe run (m)d ˆ diameter of pipe (mm)Solutions may be presented in tabular or graphical form as in Figure 9.14 where thedifference between the pressure factors Z 1 and Z 2 is plotted on the base scale against themass flow of steam on the vertical scale. It should be noted that, to avoid decimal placesand use whole numbers, mass flow in the figure is plotted in terms of g/s and the pressurefactors listed in Table 9.6 are actually 100 Z. The values within the figure and table,nevertheless, have been adjusted to be compatible. An example best illustrates the methodof use:Flow of saturated stream g/s10 45210005210052105Absolute pressure, bar, forvelocity of 50 m/sPipe sizes-mm2 3 4 5 6 7 8 9 10 150 125 1008065504032252015Pipe sizes-mm210.1 2 5 1.0 2 5 10 2 5 100 2 5(Z1– Z2) x 100 per m run1000Figure 9.14 Sizing chart for flow of saturated steam in steel pipes (BS 1387: heavy)