Process Variables: Pressure "Pressure" is the ratio of a normal force to the area on which the force acts. Units are thus or . Hydrostatic Pressure Think of a column of fluid of height hand cross sectional area A. The fluid has a density rho. The pressure Pat the base of the column is by definition the force exerted on the base divided by the area A; that force is the weight of the column plus any force acting on the top. This is the formula for the pressure due to a column of fluid, or "hydrostatic pressure". EXAMPLE:What is the hydrostatic pressure exerted by the water in a 6.00 ft diameter cylindrical tank which contains 90.0 gal? If we look at the hydrostatic pressure formula, we see that we need the pressure at the top of the column, the density of the fluid, and the height of the column. The density we look up: 62.4 lbm/ft3for water We aren't given the height of the column, but we do have dimensions on the tank. Since the volume is the product of the area and the height, we should be able to back out the desired number. Assume: tank has constant cross-section Page 1 of 5RMP Lecture Notes8/18/2009http://www.cbu.edu/~rprice/lectures/pressure.html
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