Fluid_Flow_Rules_of_Thumb_for_Chemical

Fluid Flow

5

Sources

where:

u = velocity, ft/sec L = length, ft f = Fanning friction factor = Moody' s / 4 D = diameter, ft Re = Reynold' s Number

1. Branan, C. R., Rules of Thumb for Chemical Engi- neers, But terworth-Heineman, 2002, p. 4. 2. Simpson, L.L., "Sizing Piping for Process Plants", Chemical Engineering, June 17, 1968, p. 197.

Partially Full Horizontal Pipes

Example

The equations in the previous section are, of course, intended for use with full pipes. Durand provides a rapid way to estimate whether a horizontal pipe carrying liquid is full. The criteria are If Q/d 25 _> 10.2 the pipe is full. If Q/d 25 < 10.2 do a partially full flow analysis as follows. Let x = In (Q/d 25) and find the height of liquid in the pipe by:

Given:

Horizontal pipe d = 4 in ID Q = 100 gpm

Find:

Is the pipe full? If not, what is the liquid height? Also, what is the pipe's equivalent diameter?

H/D - 0.446 + 0.272x + 0.0397x 2 - 0.0153x 3 - 0.003575x 4

Find the "equivalent diameter" by:

Calculations:

De /D - - 0 . 01130+ 3.040 ( H / D ) - 3.461 (H/D) 2 + 4.108 (H/D) 3 - 2.638 (H/D) 4

Q/ d 25 - 1 0 0 / 3 2 - 3.125 Not full since Q/ d 25 < 10.2

[This is an empirical way to avoid getting De from De = 4 (cross-sectional flow area/wetted perimeter)] Note that for 1.0 > H/D > 0.5, De/D > 1.0. My calcu- lations and all references confirm this. De is substituted for D in subsequent flow analysis.

x = ln(3.125) = 1.1394 H/D = 0.779 H = 0.779 (4)= 3.12 in

De /D = 1 . 2 2 7 D e = 1 . 227 ( 4 ) = 4.91 in

Nomenclature

Source

D = pipe diameter, ft De = equivalent diameter, ft H - height of liquid in the pipe, ft Q = flow rate, gpm

Durand, A. A. and M. Marquez-Lucero, "Determining Sealing Flow Rates in Horizontal Run Pipes", Chem- ical Engineering, March 1998, p. 129.

d = pipe diameter, in q = flow rate, ft/sec u = velocity, ft/sec