Page 614 - Air and Gas Drilling Manual

11-52 Air and Gas Drilling Manual
.
d
d
o
D o o 070 inches
12
.
D o 0 0583 ft
100

Figure 11-14: Power versus drill bit speed for a Rift Pneumatics, Model 650, 6 1/2 inch
outside diameter, downhole pneumatic turbine motor operating by a 2.635 lb/sec weight
rate of flow. The motor is fitted with gear box with a 112.5 to 1 reduction ratio. (courtesy
of Rift Pneumatics Incorporated).
The total cross-sectional area of flow through the drill bit open orifices, A o, is

A o 3 (. 2
0 0583)
4
.
A 0 00802 ft 2
o
Using Equation 4-11 the specific weight of the air flow at the bottom of the annulus,
, is
a5