Fluid_Flow_Rules_of_Thumb_for_Chemical

4

Rulesof Thumb for Chemical Engineers

Calculations:

on purpose, uZ/2g head is converted to PV or vice versa. We purposely change uZ/2g to PV gradually in the fol- lowing situations" 1. Entering phase separator drums to cut down on turbulence and promote separation 2. Entering vacuum condensers to cut down on pressure drop We build up PV and convert it in a controlled manner to uZ/2g in a form of tank blender. These examples are dis- cussed under appropriate sections.

Use AH - u2/2g. Flow is sonic, so use AP - 100 - 50 - 50 psi (2" 1 pressure drop). Hole d i ame t e r - 1/8 i n - 0.125 in Hole area - n • (0.1252)/4 - 0.0123 in2 = 0.0000852 ft2 Densi ty of me t h a n e - (161b/76ft 3) x (100/76) x [(460 + 76)/(460 + 60)] - 0.285 lb/ft 3 (See "Approximate Physical Properties" in Section 25, "Properties," for the rule-of-76.) AH - 50 lb/in 2 x 144 in2/ft2 x f t 3 / 0 . 2 8 5 lb - 25,263 ft u2 - 25 , 263 ( 64 . 4 ) - 1,626,900 u - 1275 ft/sec F l ow - 1275 ft/sec x 0.0000852 ft2 x 0.285 lb/ft 3 x 3600 sec/hr - 111 lb/hr

Example

Given:

Methane (Mw = 16) Line @ 100 psia and 60~ Hole in the line of 1/8 in diameter Hole discharges to atmosphere (15 psia) Assume Z - compr es s i b i l i t y- 1.0

Source

Branan, C.R. The Process Engineer's Pocket Handbook, Vol. 1, Gulf Publishing Co., Houston, Texas, p. 1. 1976.

Find:

Flow through the hole in lb/hr

Full Plant Piping

exchanger tubeside pressure drop calculations), a con- stant of 23,000 should be used instead of 20,000. The equation applies to:

A handy relationship for turbulent flow in full com- mercial steel pipes is:

AP F - W 18~ . . L~

Liquids Compressible fluids at: Non-critical flow AP less than 10% of inlet pressure

where:

APF - Frictional pressure loss, psi/lO0 equivalent ft of pipe W = Flow rate, lb/hr

It was derived from the Fanning equation:

~t = Viscosity, cp 9 - Density, lb/ft 3 d - Internal pipe diameter, in.

APE - - (2f U2 L 9) / (32.2 D)

and the approximate relationship: 2

This relationship holds for a Reynolds number range of 2,100 to 1 0 6. For smooth tubes (assumed for heat

f - 0.054/Re ~