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CE 230-Engineering Fluid Mechanics. Lecture # 7& 8 Pressure Variation in Static Fluids & its Applications. Pressure variation in a static fluid. Pressure difference between two points in a static fluid is the weight of unit fluid column between them. dp/dz = - γ z +ve up
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CE 230-Engineering Fluid Mechanics Lecture # 7& 8 Pressure Variation in Static Fluids & its Applications
Pressure difference between two points in a static fluid is the weight of unit fluid column between them • dp/dz = -γ z +ve up This equation is valid as long as we are in the same fluid. • Two possibilities • Constant γ • Variable γ
Manometry • Use of pressure change with elevation to determine pressure at a point • Use of pressure change with elevation to determine the difference in pressure between two points
Problem 3.31 If the air is under atm. P. the water position is 1.Find P if l=40 cm. Dia ratio=8, density = 800 kg/m3
Determine the weight of the man if the piston weighs 50 lb and area in contact with water is 1.5 ft2 3 ft
Problem 3.42determine the difference in pressure between points A and B.
What if γ is variable? (Compressible fluid) • For air say γ = pg/RT in troposphere T=T0-α(z-z0) • Integrate basic equation to get pressure variation
Figure 3.5 (p. 39)Temperature variation with altitude for the U.S. standard atmosphere in July (2).