Page 202 - Air and gas Drilling Field Guide 3rd Edition

8.2 Minimum Volumetric Flow Rate and Compressor Selection 193

where t st is atmospheric temperature ( F) and T st is absolute atmospheric temper-
ature ( R). Using Equation (5-11), the specific weight of the air at standard condi-

tions is
ð2; 116:0Þð1:0Þ
g ¼
st
ð53:36Þð519:67Þ
3
g ¼ 0:0763 lb=ft ;
st
3
where g st is the specific weight of the gas (lb/ft ), R e is the gas constant for API
standard conditions air (53.36 lb-ft/lb- R), and S g is the specific gravity of the par-

ticular gas used (for API standard conditions air S g ¼ 1.0).
Specific Weight of Air at 4000 ft Above Sea Level
At 4000 ft above sea level the average atmospheric pressure is
p at ¼ 12:685 psia
P at ¼ p at 144
2
P at ¼ 1826:6lb=ft abs;
where p at is atmospheric pressure (psia) and P at is atmospheric pressure (lb/ft 2
abs).
At 4000 ft above sea level the average atmospheric temperature is
o
t at ¼ 44:74 F
T at ¼ t at þ 459:67
o
T at ¼ 504:41 R;
where t at is atmospheric temperature ( F) and T at is absolute atmospheric temper-

ature ( R).

Using Equation (5-11), the specific weight of the air at standard conditions is
ð1826:6Þð1:0Þ
g ¼
at
ð53:36Þð504:41Þ
3
g ¼ 0:0679 lb=ft ;
at
3
where g at is the specific weight of the gas (lb/ft ), R e is the gas constant for API

standard conditions air (53.36 lb-ft/lb- R), and S g is the specific gravity of the
particular gas used (for API standard conditions air S g ¼ 1.0).
Minimum Volumetric Flow Rate at 4000 ft
From Figure G-13 the minimum volumetric flow rate is
q minst ¼ 1588:8 scfm

q minst
Q minst ¼
60
3
Q minst ¼ 26:48 standard ft =sec: