Machinery's Handbook, 31st Edition
Pressure 2751 Table 2. Mass Density and Specific Weight of Water at Selected Temperatures Temperature Mass Density Specific Weight °F °C slug/ft 3 kg/m 3 lbf/ft 3 N/m 3 32 0 1.94 999.835 62.42 9810 50 10 1.94 999.835 62.41 9800 60 15.6 1.938 998.804 62.37 9800 70 21.1 1.936 997.773 62.31 9790 80 26.7 1.934 996.743 62.23 9780 100 37.8 1.927 993.135 62.02 9740 120 48.9 1.918 988.497 61.74 9700 140 60 1.908 983.343 61.37 9640 160 71.1 1.896 977.158 60.98 9580 180 82.2 1.883 970.458 60.55 9510 200 93.3 1.869 963.243 60.12 9440 212 100 1.86 958.605 59.83 9400 Table 3. Properties of Common Fluids at Atmospheric Pressure Fluid Temperature Density Specific Weight Specific Gravity °F °C slug/ft 3 kg/m 3 lbf/ft 3 N/m 3 Air 68 20 2.33 × 10 –3 1.205 0.075 11.8 1 Nitrogen 68 20 2.26 × 10 –3 1.165 … … 0.9669 Water 68 20 1.936 998.2 62.4 9.81 x 10 3 1 Seawater 68 20 1.987 1024 63.9 10.03 x 10 3 1.025 Pressure.— Pressure, p , is defined as the average force per unit area, A , exerted by a fluid. p The pressure at a point in a static fluid is the same in all directions, and the same at all points in that fluid. The pressure exerted by a fluid on a solid surface is always perpendic ular to that surface. Pressure measured relative to atmospheric pressure is called gauge pressure. Pressure measured relative to a perfect vacuum is called absolute pressure. The relation ship between absolute pressure and gauge pressure is given in the following equation: P a P g P atm = + where P a = 14.696 psi (US); and, P a = 101.325 kPa (SI) . F A = -- The change in pressure in a non-moving liquid due to a change in elevation is dependent on the specific weight of the fluid and can be calculated using the following equations. Ele vation is always taken to be positive in the upward direction relative to the reference plane. The pressure caused by elevation is independent of the shape and size of the container and its free surface. p = g h where g is specific weight (lbf/ft 3 or N/m 3 ), h is elevation (ft or m), and p is pressure (lbf/ft 2 or N/m 2 ) p = γ h 144 ----- where g is specific weight (lbf/ft 3 ), h is elevation (ft), and p is pressure (psi)
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